Strong, A. Brent Fundamentals of Composites Manufacturing - Materials, Methods, And Applications

Fundamentals ofComposites Manufacturing Materials, Methods, and Applications Second Edition A. Brent Strong Society of Manufacturing Engineers Dearborn, Michigan Copyright © 2008 Society of Manufacturing Engineers 987654321 All rights reserved, including those of translation. This book, or parts thereof, may not be reproduced by any means, including photocopying, scanning, digitizing, recording, or micro- filming, or by any information storage and retrieval system, without permission in writing of the copyright owners. No liability is assumed by the publisher with respect to use of informa- tion contained herein. While every precaution has been taken in the preparation of this book, the publisher assumes no responsibility for errors or omissions. Publication of any data in this book does not constitute a recommendation or endorsement of any patent, proprietary right, or product that may be involved. Library of Congress Catalog Card Number: 2007935302 International Standard Book Number (ISBN): 0-87263-854-5 ISBN 13: 978-087263854-9 Additional copies may be obtained by contacting: Society of Manufacturing Engineers Customer Service One SME Drive, P.O. Box 930 Dearborn, Michigan 48121 1-800-733-4763 www.sme.org/store SME staff who participated in producing this book: Rosemary Csizmadia, Senior Production Editor Steve Bollinger, Manager, Book & Video Publications Frank Bania, Cover Design Frances Kania, Administrative Coordinator Printed in the United States of America Preface THE PURPOSE OF THIS BOOK designers will gain an understanding of the People entering the composites field need causes of material performance and be able a way to learn the basics. Whether they are to choose from a wider set of acceptable ma- learning about composites in a college course terials than might otherwise be possible. or in the workplace, they need a simple text that gives enough detail to help with THE IMPORTANCE OF COMPOSITES understanding. They also need a reference MANUFACTURING book that presents material in an easily Improving manufacturing technology understandable format. The first edition of is the greatest challenge today in the field this book has filled that need but is now over of composites. When composites are cho- a decade old. This second edition describes sen for an application principally because advances that have been developed in the re- of their properties, it is natural that the cent past, expands upon the explanations of manufacturing methods would be chosen the first edition to give further understand- to optimize those properties, even to the ing, and adds key information that will serve point where good manufacturing methods as a reference for refreshing and expanding might be adversely affected. This practice your knowledge of composites. has been evident in the aerospace industry where many composite parts have been THE IMPORTANCE OF MATERIALS IN made by processes that require high labor COMPOSITES and costly techniques. Up to recent years, The field of composites is about materials even large airplanes have been primarily and the way they are made into products. (In hand-made. the aerospace world, this is called materials In some applications, the practice of prop- and processing or M&P.) Therefore, the first erty optimization will continue in spite of the focus of this text is on materials. This is re- problems that might arise in manufactur- flected in several major chapters devoted to ing. However, those in charge of manufac- understanding the basic materials that are turing have the challenge of improving the put together to create composite structures. manufacturing process so that the quality Too often the materials side is viewed by of the performance of the part can be main- composite engineers as merely a way to get tained. Competitive pressures may also data that will allow design calculations to be play a part to encourage reduction of costs made. This text tries to simply and clearly through manufacturing improvements. present the details of why composite materi- These manufacturing improvements must als behave the way they do. Thus composites be done while still maintaining or improving Fundamentals of Composites Manufacturing: Materials, Methods, and Applications xi xii Preface part properties. Applications involving most finishing. From metals came ideas in cast- advanced composites fit into this category. ing, forming, and mold making. Some of For other composite parts a different situ- the reinforcement products are, of course, ation occurs with respect to manufacturing. from the textile industry but other concepts In these the choice of composites is based include textile fiber handling, cloth pattern on both material performance and manu- cutting, and lay-up. A broad spectrum of en- facturing efficiencies. Parts made by these gineering disciplines has contributed—from criteria are generally engineering composite bridge building to laser cutting. Insight products. In these parts the need to im- and innovation are key elements to prog- prove manufacturing is critically important ress and success in the field of composites because of the inevitable pressures of the manufacturing. marketplace for reduced costs and improved throughputs. FEATURES OF THE BOOK Regardless of the situation, good initial choices about the type of manufacturing For classroom use or individual reading, process used and then subsequent improve- the book contains many features to make ments to it are critically important. Too often learning easier. the initial choice of manufacturing method 1. Each chapter begins with an overview is made based on previous experience or on of the key points to be addressed. The available equipment. A rigorous method for order of the chapter follows the order of evaluating the choice of manufacturing pro- the overview so that you can see what cess is rarely used. Then, after the method is is in the chapter and easily find it. chosen, there is great reluctance to change 2. Each chapter contains a case study dis- it significantly. This is especially true in cussing a specific application of one or situations where the part and the manu- more principles taught in the chapter. facturing process have been approved by a governmental agency or a major assembler 3. A summary is given in each chapter like an airplane company. These products so that the key learning points can be are locked into technologies that are diffi- reviewed. cult to modify. However, as experience with 4. For assistance to college professors, long-term performance of composite parts each chapter has a laboratory experi- grows and the data bases of composite prop- ment dealing with the concepts of that erties and designs increases, the reluctance chapter. to change manufacturing processes will 5. A set of questions is given in each decrease. Experience diminishes risk. chapter so that individuals can assess The composites industry will continue learning and professors can use them struggling to cope with the requirements for in preparing questions for exams. superb mechanical properties and the need for economical manufacturing methods. The 6. A bibliography details additional read- manufacturing side is changing rapidly and ing for each chapter. a premium is being placed on the innovative 7. A glossary of important terms is found individual. at the back of book to assist in under- Manufacturing technologies have been standing or remembering terms given borrowed from many other industries. From in the book. Each of the terms defined in plastics came the concepts used in resin the glossary is marked in bold print the curing, composites molding, extrusion, and first time it is used in the text. Fundamentals of Composites Manufacturing: Materials, Methods, and Applications Preface xiii 8. Improving upon the first edition, figures have been enhanced and added to expand the breadth and depth of coverage. 9. Providing a valuable additional re- source, the Composites Manufacturing video series produced by the Society of Manufacturing Engineers (SME 2005) complements this text. The series offers excellent visual representations of the materials and manufacturing methods addressed in the text. The videos are excellent as supplements to lectures and in laboratories. To learn more about this series, visit SME’s website, www. sme.org/cmvs, or call 800-733-4763. Fundamentals of Composites Manufacturing: Materials, Methods, and Applications Contents Preface......................................................... xi Polymerization of Unsaturated Polyesters .............................................48 1 Introduction to Composites Effects of Various Diacid, Glycol, and Chapter Overview......................................1 Specialized Monomers ..........................51 Concept of Composites ..............................1 Crosslinking Mechanisms .........................57 Roles of the Matrix and Reinforcement in Cure Control Additives .............................65 Composites ...........................................2 Molding Compounds ...............................66 History of Composites ................................4 Property Optimization ..............................70 Composite Types—Advanced and Case Study 3-1 ........................................76 Engineering ............................................7 Case Study 3-2 ........................................78 Markets ...................................................10 Summary ................................................79 Composites Industry Structure ...................13 Laboratory Experiment 3-1 .......................80 Case Study 1-1 ........................................15 Questions................................................82 Summary ................................................16 4 Epoxies Laboratory Experiment .............................17 Questions................................................17 Chapter Overview....................................85 Overview of Epoxy and Its Uses ................85 2 Matrices and their Properties Structure of the Polymer............................85 Chapter Overview......................................1 Crosslinking and Processing Parameters ....91 Polymers, Plastics and Resins Physical and Mechanical Properties of Defined ................................................19 Cured Epoxy Composites ....................104 Polymerization, Naming, Characteristics, Special Composite Applications ..............109 and Molecular Weight ...........................21 Case Study 4-1 ......................................111 Thermoplastics and Thermosets ................27 Summary ..............................................112 Aromatic and Aliphatic Materials ..............31 Laboratory Experiment 4-1 .....................112 Wet-out of Fibers .....................................41 Questions..............................................113 Additives: Fillers, Pigments, Viscosity 5 Specialty and High-performance Control Agents, Surface Agents .............42 Thermosets Case Study ..............................................43 Summary ................................................44 Chapter Overview..................................115 Laboratory Experiment 2-1 .......................45 Introduction ...........................................115 Laboratory Experiment 2-2 .......................45 Vinyl Esters ............................................115 Questions................................................46 Phenolics ...............................................122 Carbon Matrix .......................................130 3 Unsaturated Polyesters Polyimides and Related Polymers.............136 Chapter Overview....................................47 Cyanate Esters ......................................140 Overview of Polyester Resins and Polyurethanes .......................................142 Their Uses ............................................47 Silicones ................................................146 Fundamentals of Composites Manufacturing: Materials, Methods, and Applications vii viii Contents Dicyclopentadiene (DCPD) .....................151 9 Reinforcement Forms Case Study 5-1 ......................................154 Chapter Overview..................................245 Summary ..............................................154 Introduction ...........................................245 Laboratory Experiment 5-1 .....................155 Filaments, Strands, Tows, Rovings, Questions..............................................156 and Yarns ...........................................245 6 Thermoplastic Composites Woven and Knitted Fabrics (Cloth) ..........247 Non-woven Fabrics (Mat) .......................252 Chapter Overview..................................159 Prepregs ................................................253 Review of Thermoset and Thermoplastic Braided, Stitched, and Composites ........................................159 Three-dimensional Laminates ..............255 Engineering Thermoplastic Composites ...164 Preforms ...............................................258 High-performance Thermoplastic Hybrids .................................................260 Composites ........................................168 Whiskers ...............................................261 Case Study 6-1 ......................................174 Case Study 9-1 ......................................261 Summary ..............................................175 Summary ..............................................262 Laboratory Experiment 6-1 .....................176 Laboratory Experiment 9-1 .....................262 Questions..............................................176 Questions..............................................263 7 Ceramic and Metal Matrix 10 Quality and Testing Composites Chapter Overview..................................265 Chapter Overview..................................179 History of Composite Materials Testing ....265 Non-polymeric Matrix Composites ..........179 Quality Control Principles .......................266 Properties and Uses of Ceramic Matrix Component Material Testing ..................272 Composites ........................................182 Mechanical Testing.................................275 Manufacturing of Ceramic Matrix Thermal and Environmental Testing ........287 Composites ........................................186 Flammability Testing...............................292 Properties and Uses of Metal Matrix Non-destructive Testing and Inspection ....298 Composites ........................................188 Case Study 10-1 ....................................303 Manufacturing of Metal Matrix Summary ..............................................303 Composites ........................................191 Laboratory Experiment 10-1 ...................304 Case Study 7-1 ......................................193 Questions..............................................305 Summary ..............................................193 Laboratory Experiment 7-1 .....................194 11 Composite Design Questions..............................................194 Chapter Overview..................................307 Introduction ...........................................307 8 Reinforcements Methodology of Composite Structure Chapter Overview..................................197 Design ...............................................308 General Fiber Characteristics .................197 Basic Stress Types ...................................311 Glass Fibers ..........................................203 Laminate Theory ....................................313 Carbon/Graphite Fibers .........................207 Rule of Mixtures .....................................315 Aramid and Other Organic Fibers ..........218 Modeling and Finite Element Analysis .....317 Boron, Silicon Carbide, and Other Lay-up Notation .....................................321 Specialty Fibers ...................................226 Symmetry and Balanced Laminates .........323 Natural Fibers .......................................228 Cracking in Composites .........................325 Fiber-matrix Interactions .........................230 Vibration and Damping .........................327 Case Study 8-1 ......................................240 Smart Structures.....................................329 Summary ..............................................241 Fatigue..................................................329 Laboratory Experiment 8-1 .....................242 Composites versus Metals ......................333 Questions..............................................242 Residual Stresses ....................................339 Fundamentals of Composites Manufacturing: Materials, Methods, and Applications Contents ix Case Study 11-1 ....................................341 15 Compression Molding Summary ..............................................345 Chapter Overview..................................407 Laboratory Experiment 11-1 ...................346 Process Overview ...................................407 Questions..............................................347 Equipment .............................................408 12 Sandwich Structures, Joints, and Bulk Molding Compound (BMC)/Sheet Post-processing Operations Molding Compound (SMC) Molding ....408 Preform Compression Molding ...............412 Chapter Overview..................................349 Prepreg Compression Molding ...............413 Sandwich Structures—Concept Part Complexity, Properties, and Other and Design ........................................349 Performance Considerations ................413 Core Material ........................................353 Case Study 15-1 ....................................414 Other Z-direction Stiffeners.....................357 Summary ..............................................415 Joints ....................................................359 Laboratory Experiment 15-1 ...................415 Post-processing Operations ....................366 Questions..............................................416 Case Study 12-1 ....................................370 16 Resin Infusion Technologies Case Study 12-2 ....................................370 Case Study 12-3 ....................................372 Chapter Overview..................................417 Summary ..............................................373 Process Overview ...................................417 Laboratory Experiment 12-1 ...................373 Resin Infusion Technologies ....................420 Questions..............................................373 Equipment and Process Parameters .........424 Preform Technology for Infusion ..............425 13 Open Molding of Engineering Resin Characteristics ..............................427 Composites Core and Flow Media Materials ..............429 Part Design for Resin Infusion .................431 Chapter Overview..................................375 Centrifugal Casting ................................432 Process Overview ...................................375 Case Study 16-1 ....................................432 Gel Coat Considerations ........................375 Summary ..............................................432 Lay-up Molding .....................................378 Laboratory Experiment 16-1 ...................434 Spray-up Molding ..................................381 Questions..............................................435 Tooling (Molds) ......................................383 Quality Control and Safety .....................386 17 Filament Winding and Fiber Case Study 13-1 ....................................386 Placement Summary ..............................................386 Chapter Overview..................................437 Laboratory Experiment 13-1 ...................387 Process Overview ...................................437 Questions..............................................387 Filament Winding ..................................437 14 Open Molding of Advanced Variations in Filament Winding ...............448 Composites Fiber Placement .....................................449 Case Study 17-1 ....................................450 Chapter Overview..................................389 Summary ..............................................450 Process Overview ...................................389 Laboratory Experiment 17-1 ...................451 Prepreg Lay-up ......................................390 Questions..............................................451 Vacuum Bagging ...................................395 Curing ..................................................398 18 Pultrusion Roll Wrapping .......................................400 Chapter Overview..................................453 Tooling (Molds) ......................................401 Process Overview ...................................453 Case Study 14-1 ....................................402 Reinforcement Preforming ......................454 Summary ..............................................402 Resin Impregnation ................................455 Laboratory Experiment 14-1 ...................405 Die Forming and Curing ........................457 Questions..............................................406 Pulling...................................................457 Fundamentals of Composites Manufacturing: Materials, Methods, and Applications x Contents Cutting and Trimming ............................458 Planning................................................529 Shapes and Applications ........................458 Corporate Creativity...............................531 Case Study 18-1 ....................................459 The Ethical Process .................................534 Summary ..............................................460 Managing Technology ............................535 Laboratory Experiment 18-1 ...................460 Case Study 22-1 ....................................538 Questions..............................................461 Summary ..............................................538 19 Thermoplastic Composites Processing Laboratory Experiment 22-1 ...................539 Questions..............................................540 Chapter Overview..................................463 Wet-out of Thermoplastic Composite 23 Composites Applications Materials ............................................464 Chapter Overview..................................543 Processing Short-fiber Thermoplastic Introduction ...........................................543 Composites ........................................467 Traditional Composites Markets ..............543 Thermoplastic Composites Molding Learning Lessons—Space Structures ........553 by Traditional Thermoset Processes ......470 The Ultimate Composite Structure— Thermoplastic Composites Molding ISOTRUSS® .........................................559 by Unique Processes ...........................474 Critical Market—Armor ..........................561 Case Study 19-1 ....................................478 Breakthrough Markets—Commercial Summary ..............................................478 and Corporate Airplanes.....................564 Laboratory Experiment 19-1 ...................479 Future-today Markets—Unmanned Questions..............................................480 Vehicles ..............................................567 20 Damage Prevention and Repair Case Study 23-1 ....................................573 Summary ..............................................577 Chapter Overview..................................481 Laboratory Experiment 23-1 ...................577 Damage and Its Effects ..........................481 Questions..............................................577 Damage Prevention ...............................483 Damage Assessment ..............................487 Glossary ...................................................579 Smart Structures.....................................491 Index .........................................................599 Repair ...................................................495 Case Study 20-1 ....................................501 Summary ..............................................502 Laboratory Experiment 20-1 ...................503 Questions..............................................504 21 Factory Issues Chapter Overview..................................505 Problem of Emissions and How to Deal with Them ..................................505 Government Regulation .........................509 Material Storage ....................................513 Contamination in the Plant .....................514 Disposal, Waste, and Recycling...............516 Factory Simulation .................................516 Case Study 21-1 ....................................521 Summary ..............................................522 Laboratory Experiment 21-1 ...................523 Questions..............................................523 22 The Business of Composites Chapter Overview..................................525 Economics of Composites Manufacturing Processes .....................525 Fundamentals of Composites Manufacturing: Materials, Methods, and Applications 1: Introduction to Composites 1 1 Introduction to Composites CHAPTER OVERVIEW of a binder or matrix that surrounds and This chapter examines the following: holds in place reinforcements. The binders or matrices (these terms are • The concept of composites considered equivalent) of most importance • Roles of the matrix and reinforcement in the marketplace are polymeric, and are, in composites therefore, the ones of most interest in this • A history of composites book. Some attention also will be given to both metal and ceramic matrix composites. • Composite types—engineering and ad- Generally, for all of these matrix materials, vanced the reinforcements considered are fibers. • Markets Some discussion will, however, be devoted • Composites industry structure to particle filled composites and nano fillers in their various forms. Some writers have suggested an alternate THE CONCEPT OF COMPOSITES definition of composites: Mixtures of two or In the broad sense, the term composite more solid materials that are mechanically materials refers to all solid materials com- separable, at least in theory, and possessing posed of more than one component wherein complementary properties. This definition those components are in separate phases. emphasizes the improvements in proper- This definition includes a wide assortment ties possible when composites are made. of materials, such as: fiber reinforced plas- The more narrow definition of composites tics, regular and steel reinforced concrete, suggested previously fits within this alter- particle filled plastics, rubber reinforced nate definition and, as will become clear, plastics, wood laminates, ceramic mixtures, the complementary nature of matrix and and even some alloys. The breadth of the reinforcement is the reason composites are materials encompassed within this defini- so important commercially. However, not all tion precludes their examination at anything properties and characteristics are advanta- except a cursory level within the pages of a geous when composites are made. For each single book. Therefore, this book will focus application the advantages and disadvan- on one major branch of composite materi- tages should be weighed. als—those that are fiber reinforced—a much Some of the advantages and disadvantages narrower definition. So, when the terms of composites are listed in Table 1-1. As the “composites” or “composite materials” are properties and characteristics of composites used, the definition envisioned is: Composite are explored throughout this book, these materials are those solid materials composed advantages and disadvantages will become Fundamentals of Composites Manufacturing: Materials, Methods, and Applications 1 2 1: Introduction to Composites more obvious. Some important properties orientations of the reinforcements, manu- of composites and metals are compared in facturing method, processing conditions, Figure 1-1. Note the low weight, low thermal and combinations made with other materials expansion, high stiffness, high strength, and all give additional variety in the properties high fatigue resistance of composites versus available. (The reader who is not familiar steel and aluminum. These graphs lump all with composites might benefit from viewing composites into one group, and all types of the series of videos from the Society of Manu- steel and aluminum into two others, but the facturing Engineers, which complement data correctly reflect the general trends. this textbook. The particular video entitled Of great value is that the separate char- “Composite Materials” would be especially acteristics of the matrix and reinforcements useful for an introduction to composites [So- contribute synergistically to the overall prop- ciety of Manufacturing Engineers 2005].) erties of the composite. Moreover, because so many different matrix and reinforcement ROLES OF THE MATRIX AND materials can be chosen, a wide range of REINFORCEMENT IN COMPOSITES properties is possible. Within a particular The matrix is the continuous phase of the choice of matrix and reinforcement, the composite. Its principal role is to give shape Table 1-1. Advantages and disadvantages of composites. Advantages Disadvantages • Lightweight • Cost of materials • High specific stiffness • Lack of well-proven design rules • Metal and composite designs are seldom • High specific strength directly interchangeable • Tailored properties (anisotropic) • Long development time • Manufacturing difficulties (manual, slow, • Easily moldable to complex (net) shapes environmentally problematic, poor reliability) • Part consolidation leading to lower overall • Fasteners system cost • Low ductility (joints inefficient, stress risers • Easily bondable more critical than in metals) • Good fatigue resistance • Solvent/moisture attack • Good damping • Temperature limits • Crash worthiness • Damage susceptibility • Internal energy storage and release • Hidden damage • Low thermal expansion • EMI shielding sometimes required • Low electrical conductivity • Stealth (low radar visibility) • Thermal transport (carbon fiber only) Fundamentals of Composites Manufacturing: Materials, Methods, and Applications 1: Introduction to Composites 3 Figure 1-1. Property comparison of metals and composites. Fundamentals of Composites Manufacturing: Materials, Methods, and Applications 4 1: Introduction to Composites to the structure. Therefore, matrix materi- characteristic of composites allows the part als that can be easily shaped and then hold designer to specify certain percentages of the that shape are especially useful. The most fibers to be in certain exact orientations for common materials with this characteristic a particular application. If the forces on the are polymers. Therefore, well over 90% of part would come from all directions, then modern composites have polymeric materials the designer would specify randomization or (sometimes referred to as plastics or resins) multi-directionality of the fibers. The com- as their matrix. posite part manufacturer has the obligation As the continuous phase, the matrix to control fiber orientation so the directional surrounds and covers the reinforcements. and percentage specifications of fiber can be Hence, the matrix is the component of the satisfied. This manufacturing task has led composite exposed directly to the environ- to several manufacturing methods that are ment. Another role of the matrix is, there- unique for composites. These and other more fore, to protect the reinforcements from traditional manufacturing methods, which the environment. The degree of protection can be modified to accommodate composites, desired is one of the key considerations in will be examined later in this book. choosing the type of polymeric matrix for the All of the properties of composites arise, composite. For example, polymeric matrices to some extent, from the interaction or give good protection against moderately presence of both the matrix and the rein- hostile conditions but may be inadequate forcement. However, as just discussed, some when high temperatures or some aggressive properties are dominated by either the ma- solvents are present. These extreme condi- trix or the reinforcement. Even when one tions may require a ceramic or metal matrix component of the composite dominates, both composite. components generally must work in concert The matrix is the component of the com- to obtain optimal performance. For example, posite that first encounters whatever forces if the matrix does not bond well to the fibers, might be imposed. Generally, the matrix is or the fibers are not strong, little improve- not as strong as the fibers and is not expected ment in strength is obtained over just the to withstand these imposed forces. However, strength of the matrix. Some properties the matrix must transfer the imposed loads such as toughness, electrical properties, and onto the fibers. The effectiveness of load damping arise from a strong combination or transfer is one of the most important keys interaction of the matrix and the reinforce- to the proper performance of the compos- ment. These combination properties will ite. Almost all of the common commercial be discussed with a particular emphasis on polymeric, metallic, and ceramic matrix the nature of the interactions required for materials adequately transfer the loads onto enhanced performance and the expected the fibers. results from such interactions. The roles of The principal role of the reinforcement is matrix and reinforcement are summarized to provide strength, stiffness, and other me- in Table 1-2. chanical properties to the composite. Gener- ally, the mechanical properties are highest in HISTORY OF COMPOSITES the direction of orientation of the fibers. For Early in history it was found that combi- example, if all the fibers in a composite are nations of materials could produce properties oriented in the long direction of the part (like superior to those of the separate compo- strands in a rope), the composite is stron- nents. For example, mud bricks reinforced gest when pulled in the long direction. This with straw were used by ancient Israelites Fundamentals of Composites Manufacturing: Materials, Methods, and Applications Nature uses the to resolve a bottleneck in the making of metal same principle in celery and. less obviously. If the parts proved to be Fiberglass had been made. and other mechanical properties to the composite • Protects the reinforcements from the • Dominate other properties such as the environment coefficient of thermal expansion. then metal dies could be made in 1930. Fundamentals of Composites Manufacturing: Materials. They were trying steel reinforced concrete. conductivity. two tips) to which cattle tendons were panies seemed to be creating new aircraft bonded on the tension side and strips of designs and innovative concepts in manufac- cattle horns on the compression side. when an engineer became intrigued for full production runs. Methods. resin (the only resin available at the time). and many of these new assembly was steamed and bent into the innovations required new materials. and Applications . soon followed. The initial product made of this finely drawn What a success! molten glass was insulation (glass wool). Each in trees where the pith surrounds a fibrous changed aircraft design needed new molds. strength. Roles of the matrix and reinforcement in a composite. Many of the tools (molds. molds for its sheet forming process.1: Introduction to Composites 5 Table 1-2. engineers reasoned that maybe if the plastic Corning Fiberglas® Company began to sell molds were reinforced with fiberglass they fiberglass to interested parties around the would be strong enough to allow at least a United States and those customers found that few parts to be made so the new designs could the fiberglass could serve as a reinforcement. Douglas engineers tried using cast The history of modern composites (of the plastic molds. and wood. such as toughness in Egypt. The in 1937 when salesmen from the Owens. and One company. to form the core of a bow (center grip. Mongols made composite bows The fiberglass salesmen soon realized that by bonding together (using glue made from the aircraft industry was. be quickly verified. This is what and metal molds were expensive and had long gives the celery. two Many of the small and vigorous aircraft com- arms. Dies were made us- by a fiber that was formed during the process ing the new fiberglass material and phenolic of applying lettering to a glass milk bottle. a animal hoofs and bones) five pieces of wood likely customer for this new type of material. but they could not withstand type discussed in this book) probably began the forces of the metal-forming process. and thermal transport • Transfers loads to the reinforcements • Contributes to properties that depend upon both the matrix and the reinforcements. engineers believed the material would help Bridges and walls are constructed today of solve a production problem. This turing almost daily. proper shape. bought then cooled slowly (for up to a year) to create one of the first rolls of fiberglass because its some of the most powerful bows ever made. (reinforcing) cellulose material. lead times. almost by accident acceptable. wrapped with silk thread. Douglas Aircraft. Matrix Reinforcements • Gives shape to the composite part • Give strength. stiffness. in particular. but Other applications in tooling for aircraft structural products soon followed. They eventually (although not immediately) and thousands of other applications. Some were already fixed. therefore. Higher performance possible replacements for aircraft metals. which included the development The fast pace of composites development of filament winding and spray-up. among the last parts that utilized the expertise they had devel- on an aircraft to be designed were the ducts. radomes (domes meet these criteria. be strong. For instance. other components. This car was reasonably suc- mandrels (internal molds). composite automobile body had been made The composites were hand laid-up on plaster and tested. This often resulted in directly to commercial application. after the resin Corvette® in 1953. asbestos-phenolic Not long afterward. A major effort was with benzoyl peroxide being patented in initiated to develop the design rules and 1927 and many other peroxides following manufacturing methods for composites as not too long afterward. resins also became available about this time Several critical parts (including wing sets with the invention of epoxies in 1938. Metals did not easily engine nacelles (covers). the United relative ease of curing when compared to States government became concerned phenolics. and Applications . Then. Almost everyone agreed that the pent-up ficult-to-access locations. developed and. and II. methods. phenolic ship bearings. Some of this development work was Since all the other systems within the aircraft supported by the materials suppliers. Literally thousands of and molded in matched metal dies. such as ducts that twisted and turned around the fiberglass reinforced polyester boats. in the identify new markets and new products frantic days of the war. sandwich accelerated even more during World War structures. Even- such ducts were made in numerous manufac. unsaturated polyester switch gears. became the preferred resin because of their At about this time (1942). halt. The for the AT-6 trainer) were made to prove materials and the applications seemed to be out the design concepts and manufacturing converging at the same time. many companies who had been active posites for structural and semi-structural in making war materials were faced with parts of the airplanes themselves was being an acute problem. tually the dominant molding method for Fundamentals of Composites Manufacturing: Materials. composites more When the war effort came to a sudden widely used in tooling. and preferred material for many of these aircraft non-aircraft applications such as cotton- manufacturing applications. thin. so fiberglass reinforced to protect aircraft radar antennas). Peroxide curing systems. Not only were even more aircraft being prepreg materials. needed that the supplies of metals for aircraft for the polyesters. usually in the most dif. were already available might not be available. the ducts were required war-oriented applications were converted to go around them. which was made using cured. the plaster mandrels were broken out fiberglass preforms impregnated with resin of the composite parts. Methods. cotton-acetate bayonet scabbards. which were made cessful and led to the development of the in the required shape. oped. often Other early WWII applications included with compound curves. fire-resistant composites. By 1947 a completely shapes. linings. but the use of com. a struc- phenolic production tooling became the tural wing box for the PT-19 airplane. Composites seemed to be the answer. cotton-asbestos-phenolic brake resins became available (patented in 1936). and highly shaped.6 1: Introduction to Composites jigs and fixtures) for forming and holding turing plants clustered around the aircraft aircraft sections and assemblies needed to manufacturing/assembly facilities. Metal ducts just demand for automobiles was a logical appli- could not be easily made in these convoluted cation for composites. They needed to quickly explored and adopted. a patent was issued for producing the Polymeric composites can be divided into first carbon (graphite) fiber. storage containers. It is and furniture. and other cially advanced composite materials such mechanical properties. wholly composite pipes. bicycles. acquired filament wind- ing technology from W. composites add lightness and strength to a plained in a later chapter. composites are as number six on that list and cited espe. however. M. Kellogg Company COMPOSITE TYPES—ADVANCED and began making small rocket motors. In this aircraft. high-performance Recent material and process improve. first fully filament wound aircraft fuselage. medical devices. golf of sheet molding compound (SMC) or bulk clubs. In addition to structures. as ites seem to have found their place in the well as an increasing number of other parts world. very new. armor aerospace applications (like rocket motor (structural and personal). bows and arrows). the National Academy ness-to-weight ratios) obtained from these of Engineering issued its list of the top 10 materials. Methods. but are also used ment. and Applications . characterized by long. appliance parts. and other products. automobiles. bridges. non-corrosive earthquake performance. Ad- performing fibers and resins have led to vanced composites are typically used for tremendous advances in aerospace. the wrapping of concrete struc- aircraft. In 1978. stiffness. when the Egyptians and Israelites used picked up speed in the 1960s and 1970s gave straw to reinforce mud bricks. The advanced composites are generally the Beech Starship. space kets for composite materials. tennis rackets. and other construction edifices. They are finding increased use.C. that require the superb properties (primar- especially in products where performance ily high strength-to-weight and high stiff- is critical. The academy said molding compound (BMC)—both to be ex. engineering achievements of its lifetime The stealth bomber is probably the most (the 25 years prior to 1989). used for their strength. the crowning jewel ary exists. In 1989. some of the as graphite-epoxy materials used to make stealth properties of the bomber depend Fundamentals of Composites Manufacturing: Materials. advanced composites and engi- used in many of the rocket motors and in neering composites. Some of the products made during the Some composite product applications are post-war era now represent the major mar. wide range of everyday objects. just as it was in 1500 began in the 1950s (during the Cold War) and B. these include boats. including stealth aircraft. which then was two groups. clubs. and many other for high-performance sporting goods (golf high-performance applications. interesting that construction is still a major The push for aerospace dominance that market for composites. a new impetus to further composite develop- ment. It ranked sophisticated of all products made with the development of advanced composites composites. cases and airplane parts). Other important fibers were also de. Compos. and so one type of com- of this period was the development of the posite transitions gradually into the other. In fact. reinforcements and by resins with superior ments and the development of higher thermal and mechanical properties. sports equip. These differ principally aircraft. Inc. Hercules. in the type and length of the fiber reinforce- veloped during this period. tures with composites for improvement of tub and shower assemblies. No sharp division bound- Kevlar®) in 1971. In AND ENGINEERING 1961.1: Introduction to Composites 7 automobile parts was compression molding lighter and stronger aircraft. including boron ment and in the performance characteristics fibers in 1965 and aramid fibers (DuPont’s of the resins used. strength and good durability at moderately terial and then cured to give a hard. and other parts made prove performance of the columns during from conventional thermoset resins. The value of stealth technology. canoes. Man 11 (1) A summary of the differences and similari- Small bird 0. The processes for manufactur- overwrap. Table 1-6 provides a comparison Fundamentals of Composites Manufacturing: Materials. A comparison of the processing and F-117A Stealth 1. or proximately the same RCS as a train boxcar thermoplastic resins with short fibers (called (108 ft2 [10 m2]). or some other mechanical property. Such conventional processes include B-17 Flying Fortress 861 (80) injection molding. structures illustrate the capability of engi- Highway overpass columns are wrapped neering composite materials to give good with carbon fiber and epoxy composite ma. The RCS is the area both shorter in length and lower in mechani- seen on radar.1) fabrication methodologies of advanced Fighter and engineering composites is given in B-2 Stealth Bomber 0. and Applications . The fiber reinforced thermoplastics are normally molded by the same processes Airborne Object RCS. tubs. while the B-2 has about the fiber reinforced thermoplastics). The smaller the area. This overwrap on the column ing FRP products are generally less precise in maintaining exact fiber orientations and resin/fiber content than the advanced fiber Table 1-3. which buckle and collapse in an earthquake.076.4 (100) logues. an injection molded nylon gear Small fighters 22-32 (2-3) might be cracking because of high torque Small single-engine requirements. decreases the tendency of the concrete to als. such as shape. The products made from fiber reinforced ther- B-47 bomber 431 (40) moplastics are generally the same as their B-52 bomber 108 (10) non-reinforced counterparts.01) Table 1-5. Generally. ft2 (m2) as their non-reinforced thermoplastic ana- Jumbo jet 1. fuel storage tanks.01 m2]). These cross-sections (RCS) of various airborne ob. same wingspan as the B-52 but has the RCS Products made from thermoset resins of a small bird (0. When comparing with low-cost thermoset resins or fiberglass the various RCSs. with fiberglass (FRP) include train cars. Radar cross-sections (RCSs) of processes. spas. extrusion. typical airborne objects. includes many other factors.00001) and advanced composites is given in Table 1-4. stiff- ness.01) ties in materials technologies of engineering Insect 0. Large fighter 54-65 (5-6) For example. note that the B-52 has ap. and so on. The second major group of composite ma- can be illustrated by comparing the radar terials is engineering composites.0001 (. shower stalls. materials are characterized by fibers that are jects as shown in Table 1-3. but have the B-1B bomber 11 (1) reinforcement added to gain strength. they are either made difficult the object is to see.1 (. Wrapping concrete highway columns boat hulls. for protection against corrosion and to im.1 (.8 1: Introduction to Composites upon the unique nature of composite materi. which plane could result in three times more strength.1 ft2 [. (called fiber reinforced plastics or FRP). Methods. strong low prices. the more cal properties. These earthquakes is a relatively new application.1 (. This problem might be solved 11 (1) by using a fiberglass reinforced nylon. Comparisons of materials technologies. fluids conditions water. Exotic fuels. and Applications . and processing Extreme conditions: 180–700° F chemicals (82–371° C) environmental conditions. waste materials. sea water.1: Introduction to Composites 9 Table 1-4. solvents. much more possible Cryogenic conditions Balsa and foam core materials Extensive use of honeycomb core Core materials consistent with materials near-ambient use conditions Aluminum Core material Core use technology built upon Nomex™ (aramid) usage marine and boat market Carbon fiber Extensive design and manufacturing technology base Fundamentals of Composites Manufacturing: Materials. Methods. Property FRP Composites Advanced Composites Predominantly E-glass products High-strength S-glass (R.and T- C-glass for corrosion glass versions) Corrosion versions of E.and Carbon and graphite C-glass Aramid (like Kevlar™) Reinforcement Limited “natural” fiber usage Boron fiber Often referred to as: Quartz (fused silica) FRP = fiber reinforced plastics Polyethylene (like Spectra™) GRP = glass reinforced plastics Advanced polymeric fibers GFRP = glass fiber reinforced Ceramic fibers plastics Continuous fiber roving and Continuous fiber roving and tow chopped fibers dominate materials dominate Woven roving products Prepreg materials (unidirectional Typical fiber Tightweave glass fabrics tapes and fabrics) form(s) (numerous) Higher fiber volumes (55–65%) Glass veil materials Complex structural textile products Commercial mat and stitched/ bonded materials Polyester and vinyl ester leading Epoxies generally baseline candidates Bismaleimides (BMI) and cyanate Wide variety of polyester esters for higher temperatures formulations Polyimides Resin matrix Phenolics for fire applications Numerous high-performance Limited epoxy use in certain areas thermoplastics Entirely thermosets—except for Toughened resin system interest some glass fiber thermoplastics and use for damage tolerance Ambient temperature range (25– Broader temperature exposure 140° F [4–60° C] typical) range Exposure to UV and weather Space environments Application conditions Aerospace service conditions temperature and Exposure to fuels. and we enjoy recreation this text. with composite tennis racquets. we fly in cal differences between engineering and planes with composite parts. tape lay-up. golf clubs. our homes have advanced composites. Comparisons of composites processing and fabrication methodologies. MARKETS The breadth of the composites market can Composite materials are part of our lives be seen in the data compiled by the Ameri- every day. steel. Property FRP Composites Advanced Composites Production quantities often quite Production quantities often much large: 100s to 1000s or more smaller: typically less than a few Production Pipe—usually miles/kilometers hundred quantities Tank systems—usually on the Complex parts often less than a order of several hundred dozen Generally simple and requires Processes more complex and only moderate labor skills tightly controlled with paperwork Filament winding. VARTM. thermoforming Seemann Composites resin Considerably more quality control infusion molding process and in-process inspections [SCRIMP®]) Autoclave processing of many parts Steel and aluminum molds and Invar. such as in of composites throughout the remainder of washers and dryers. “chop and hand lay-up and vacuum spray. resin film processes vacuum-assisted resin infusion [RFI]. heated oil. and boats. fiber placement. some SCRIMP™). and Applications . Precise temperature-time-pressure- Cure methods and electric heaters used in vacuum cycles for many parts some tooling applications Heated tooling during most process steps of the market applications and philosophi. resin Manufacturing transfer molding [RTM]. pultrusion. contact molding. heated platens. infusion (RTM. Methods. systems with composite panels. These tables will serve composite showers and numerous compos- as references for understanding the nature ite parts used in hidden places. Filament winding. transfer molding [VARTM]. and aluminum tooling tooling Tight dimensional controls Fiberglass tooling common Extensive tooling design efforts Tooling materials Tool surfaces often gel coated Highly polished tool surfaces and methods Simple tooling fabricated for Composite tooling using carbon- prototyping as well as some fiber laminates production Higher temperature tooling Overall tool cost significantly lower requirements Often ambient cure Controlled oven or autoclave Oven cure on some parts curing typically Steam.” resin infusion (resin bagging.10 1: Introduction to Composites Table 1-5. We ride in cars and light rail can Composites Manufacturing Association Fundamentals of Composites Manufacturing: Materials. Market applications and philosophical differences of composites.0–5. Defense (DOD). pressure. American Society of Department of Transportation Mechanical Engineers (ASME). Federal (SAE). National Underwriters Laboratories (UL). B-basis used using nominal properties with backup testing to verify Designers often talk in terms of performance Design factors “fiber and resin weight” percent Designers use “fiber volume” and when preparing manufacturing “resin weight” percent when specifications preparing specifications Designs specify numerous environmental factors (damage. etc.0 Built to endure more robust handling Operates at extremes of performance Safety factor Safety factors dependent upon capability (SF) certification standards Safety factors dependent upon rigid customer or industry standards Generally use vendor data or data Generally an extensive data base is derived from limited testing developed from numerous tests S-basis or B-basis design approach A-basis often used. Methods. Property FRP Composites Advanced Composites Generally ambient (25–140° F Typically high performance over [4–60° C]) conditions broad temperature ranges: Some extremes as a result of fluids –65 to 165° F [–54 to 74° C] for and chemicals being processed many defense-related products Application Cryogenic and space applications temperature incur lower temperatures High-temperature operating conditions in 300–700° F [149– 371° C] range for aerospace parts Economic Low cost—materials less expensive More performance than cost driven considerations FRP products are lower-cost items Materials considerably higher cost Typically use SF = 2. National Institute of British Standards (BS) Standards and Technology (NIST) Fundamentals of Composites Manufacturing: Materials. and Applications . following American Society for Testing and customer and governing agency Testing and Materials (ASTM). temperature. Institute (ANSI).0 Typically use SF = 1. American National Standards Aviation Authority (FAA).25–3. Aeronautics and Space Society of Automotive Engineers Administration (NASA).1: Introduction to Composites 11 Table 1-6. (DOT).) Materials testing often limited to Materials and structural component quality control upon material testing often extensive receipt Significant testing at various Testing often uses material supplier environmental or load limits data and past experience Less reliance on vendor-supplied data Certification to industry standards: Certification rigid. American requirements: Department of certification Petroleum Institute (API). Carbon fiber usage is expected to importance in the origin of composites. corrosion-resistant (12%). Methods. composites shipments. As the (20%). and appliance/business ume growth and price decline. marine volume of carbon fiber has increased. the aerospace products are fewer in fiberglass. which is presented in Figure 1-2. similar to data worldwide.S. Of expand into markets traditionally held by course. carbon fiber have grown geometrically since which compose this category. electrical/electronic equipment (10%). Both trends. The largest mar. are expected equipment (5%) are also large markets. vol- consumer (7%). The growth of the carbon fiber market is ket for composites is transportation (32%). Construction its introduction in the early 1970s. is than other products. possibly a key to understanding the com- thus suggesting the large amount of compos. such as automotive.12 1: Introduction to Composites (ACMA). its (10%). U. posites market in the future. which is for the United States. price has steadily declined. The to continue at least until the price of carbon aircraft/aerospace market represents only fibers reaches a minimum based on raw ma- 1%. number but much higher in profit (per item) This data. which is surprisingly small in light of its terial cost. and Applications . Fundamentals of Composites Manufacturing: Materials. Should this Figure 1-2. Shipments of ites in automobiles and other land vehicles. and low in cost. Although. Structure of the composites industry. Fundamentals of Composites Manufacturing: Materials. higher production COMPOSITES INDUSTRY STRUCTURE capabilities. lower costs. A diagram of the structure of the com- ity they tend to emphasize one or the other posite industry is given in Figure 1-3. of course. in real. all markets would like to have. the aerospace manufacturers of fibers and resin supply industry desires products that are high in the raw materials to the remainder of the performance and. The of these factors. These manufacturers are general- high in cost and low in production rate. the automotive market seeks com. and higher performance. and Applications . the aerospace products. si- multaneously. Clearly. the Figure 1-3. For example. Methods. as a result. they are also industry. The tub/shower Trends in the major composites markets market also optimizes on cost.1: Introduction to Composites 13 happen. are not necessarily the same. to make the fibers and resins. some major restructuring could posite parts that are high in production rate occur within the raw material manufactur. In ly large companies utilizing complex plants contrast. These automotive products ers and/or within the pricing structure for will generally be lower in performance than fiberglass. therefore. they can This is especially true with fiber reinforced be made using unidirectional fibers held thermoplastics. This system process. the independent prepregger/compounder dating and molding process are discussed does the molding. especially the resin manufactur- or knitted fabric. This combining of raw materials use of prepregs to only high-value applica- can be done just prior to or during the tions such as aerospace and sporting goods molding process. braided. the higher cost generally limits the ite part. Or. often by The second type of combination system someone other than the molder. These ing compounds than could be conveniently companies allow the fabricator/molder to buy made by the fabricator/molder. separate step before molding. Just Not shown are distribution companies that as with the prepreggers.” Prepregs are made with composites. with the resin. For instance. the prepregs must be kept refriger. the raw materials go directly from is associated with engineering composites the manufacturer to the fabricator/molder. more than one step in the overall composites The prepregs. and careful wetting of the fibers. In most of these cases. prepregs are associated with advanced impregnated fibers. the raw material using cloth or some other woven. performance of molding general types of combinations are made. For advanced composites. When using the most common molding compounds and prepregs. thus preserving the idea Fundamentals of Composites Manufacturing: Materials. Then the composite their overall ease of fabrication. compounds is lower than with prepregs. in a sheet form. Neverthe- material is molded to create the compos. Each class of company can be involved in tations. Hence. the combina. The molding in smaller lots and offer improved delivery compounds can be either in sheet form or service over the raw material suppliers. in a bulk material. and Applications . a sepa- air. and composite material. often sold as a log. Mold- Several different types of intermediate ing compounds usually contain chopped companies might be involved in combining fiberglass (rather the continuous fibers of the resin and the fibers prior to molding. and then heats the prepreg material to rate division of the raw material supplier or mold and cure. Some raw material suppliers in a parallel array and then coated with are also involved in making sheet and bulk the resin. the elimination of the must be combined together to make the problems associated with wet resin. Therefore. Molding compounds are. however. compresses them to remove the parts. The fabricator/mold- fibers or resins. alternately. they resin-fiber content. later in this book in the chapter on open pany seeking to begin the manufacture of molding (long fibers). which is an abbreviation of “pre. suppliers. are often involved in compounding. the compounders might provide service for the manufacturers are often able to make more precise mold- by warehousing the raw materials. can be made business. which is impregnated ers. Methods. precise resin and fiber contents and orien. When for composites is compounding or manu- done just prior to or as part of the molding facture of molding compound. cost by pointing to their carefully controlled After the raw materials are made. it can be done as a products. or fiberglass reinforced plastic (FRP). Or. Two prepregs). less. The details of this consoli. the number of ers who use prepregs justify the additional resin and fiber manufacturers is small. associ- tion of resin with reinforcement is called a ated with engineering composites whereas prepreg. Some independent prepreg- fabricator/molder lays the prepreg sheets in gers and compounders also mold composite the mold. resins. A few of the raw material suppliers mold ated so they do not cure prematurely.14 1: Introduction to Composites capital investment would be high for a com. The parts directly. The concept was to build the car/plane so CASE STUDY 1-1 the wings could be attached to the car when- Flying Car ever the car was to be used as the cabin of the Developments in the field of composites airplane. thus of those developments was especially innova. Hence. is still alive. The concept. the car would be used after WWII were critical to establishing the as a standard automobile. The wings would materials’ position in the world today. Otherwise. turn in the wing assembly. Prototypes were made and successfully day be a major factor in modern technology. but What a boon these car/planes would be to- also would like to combine that flying with day in Los Angeles and other cities with mas- family vacations. automobile with an all-composite body (for On the other hand. bly at one airport. permitting the driver to rent a wing assem- tive but had only a brief period of success. would like to continue with their flying. while no longer com. However. and drive away. although never That development was the auto/plane. fly to the vacation site. One be available for rent at various airports. (Courtesy Brandt Goldsworthy) Fundamentals of Composites Manufacturing: Materials.1: Introduction to Composites 15 that the company is not competing directly weight savings) that would allow a special against its customers. mercial. demonstrated. is still being pursued and may some. fully commercialized. the concept. maybe the problems Figure 1-4. Convair reasoned tracted or folded into a storage compartment that the many returning wartime pilots inside the car. wing assembly to be attached. The car/plane is shown in Figure 1-4. and Applications . Methods. Flying car. Modern The development of the auto/plane was versions tend to have the wings permanently led by Convair Aircraft Company in the attached to the car but capable of being re- years following WWII. Convair made an sive freeway problems and long commutes. chiefly in aerospace. In fact. Typical engineering composite ap- polymer matrices. now seems to be dominated by consumer centration. dangerous than the roads! The matrices for advanced composites have higher thermal and protective capabilities SUMMARY than those used in engineering composites. The growth of the mechanical properties. and especially if they have high and industrial products. (fibers and resins only) or molding com- At low fiber concentrations and when the pounds (fibers. ernmental policy. are chiefly in aerospace and high-value concentration. combine synergistically.16 1: Introduction to Composites would simply be moved from the surface to properties of the composite structure. The proper. These the air above the city. Applications for engineering composites or metal). and in others they supply them to a maker of posites (fiber reinforced thermoplastics) can the intermediates. It has Fiber reinforced thermoplastics and FRPs are been strongly influenced in the past by gov- engineering composites. In some fibers are short. is called fiberglass reinforced plastic (FRP). construction products. and the many other products they are separately. the properties of the com. In general. tubs ties are better in the combined state than and showers. resins. The principal roles of the matrix materials at the time of molding or matrix are to give shape to the part. and type) and the type of products where performance is a premium. and Applications . These The matrix also contributes to properties intermediate materials are called prepregs such as toughness. When supply their materials directly to the molder the matrix is a thermoplastic. these com. the materials plications would include automotive parts. ties of composites vary widely depending The applications of advanced composites on the nature of the reinforcement (length. the combination that have been collectively identified as fi- is often better than just the simple addition berglass reinforced plastics. Methods. matrix material (polymer/plastic. the proper. but some advanced thermoplas- materials are called composites. The composite market is growing. molders and fabricators of the composite ness to the composite. The composites market is multi-tiered in The principal roles of the reinforcements structure. The most common composites are more cost sensitive and in much higher are made with fiber reinforcements and volume. The heart of the business is the are to give mechanical strength and stiff. been combined by another company. The reinforcements parts. and filler). instances the raw material manufacturers posite are dominated by the matrix. When reinforcements are added to binding Usually the advanced composite matrices are matrix materials. These molders/fabricators can ei- also dominate a few other properties such as ther combine the reinforcements and the thermal expansion. tic matrices are also available. they dominate the composites business is strong and may be- Fundamentals of Composites Manufacturing: Materials. reinforcements and matrix have already and transfer loads to the reinforcements. When the fibers are somewhat rial suppliers and the intermediate material longer and encapsulated by a low-cost manufacturers also can serve as molders and thermoset matrix. Some raw material sup- be viewed as specialty grades of traditional pliers also make the intermediate materials thermoplastics with improved mechanical as part of their product line. ceramic. that is. the composite material fabricators. of the properties of each element. The raw mate- properties. protect use intermediate materials in which the the reinforcements from the environment. but If the fibers are longer and higher in con. appliance parts. making the skies more composites are called advanced composites. the resulting combination thermosets. which are the typical reinforcement levels. 2005. Distinguish between a prepreg and a molding compound. Upper Saddle LABORATORY EXPERIMENT River. Strong. Methods. Property Differences Between Reinforced and Non-reinforced Materials Objective: Discover the differences in the properties of composites and non-reinforced products by examining their properties as obtained from a typical database. 5. and Applications . Inc. “Composite Materials” DVD from the Fundamentals of Composites Manufacturing: Materials. 2006.. 212-512-2000) or an electronic database (such as Prospector available through IDES. www. 3. QUESTIONS 1. 3rd Edition. Brent.1: Introduction to Composites 17 come even stronger as the price of some raw Composites Manufacturing video series.sme.org/cmvs. materials (especially carbon fibers) drops Dearborn. and higher volumes. Distinguish between engineering com- posites and advanced composites. Compare the various properties of typical thermoplastic and thermoset resins at two levels of reinforcement. The McGraw-Hill Companies. Inc. A. Identify three advantages of compos- ites over metals for structural applica- tions. Plastics: Materials and Processing. either written or electronic. 800-788-4668) fill out Table 1-7. 4. 6. neat = 0% and 30%. Indicate two major forces that led to the development of composites during WWII. NJ: Prentice-Hall. What are two factors that contribute to the stealth of an airplane? BIBLIOGRAPHY Society of Manufacturing Engineers (SME). MI: Society of Manufacturing with improved manufacturing technologies Engineers. Procedure: Using either a written data- base (such as that found in Modern Plastics Encyclopedia. What is the purpose of the resin in parts with long fibers at high fiber concentra- tions? 2. and Applications .18 1: Introduction to Composites Table 1-7. Property Resin Type Neat Resin Reinforced (30%) Nylon Tensile strength Tensile modulus Flexural strength Flexural modulus Izod impact Heat distortion temperature Polycarbonate Tensile strength Tensile modulus Flexural strength Flexural modulus Izod impact Heat distortion temperature Unsaturated Polyester Tensile strength Tensile modulus Flexural strength Flexural modulus Izod impact Heat distortion temperature Epoxy Tensile strength Tensile modulus Flexural strength Flexural modulus Izod impact Heat distortion temperature Fundamentals of Composites Manufacturing: Materials. Property differences between reinforced and non-reinfroced materials. Methods. chain-like structure where each unit is like tics. and Applications 19 . mers. and then attempt product. This chapter will discuss the or pile. Some peo. Then. and molecular weight a link in the chain. pigments. PLASTICS AND RESINS polymers are rarely if ever found isolated in DEFINED nature. and plastic—inter. characteris. Figure • Wet-out of fibers 2-1 illustrates the relationship between a group of monomers and a polymer molecule. the single long • Matrix-dominated properties chain is called a polymer molecule. the name The terms plastics and resins are often applied to these short polymers is oligo- used to refer to polymer matrices.) monomer units are joined together. metal. The normal situation is. single POLYMERS. posed of several thousand monomer units. The monomers are made of atoms that have a specific and consistent • Thermoplastics and thermosets grouping. that can be made into a polymer is called mal considerations a monomer. Therefore. of many similar chains clustered in a group lic. When only a few pleting the chapters on matrices. plastics and resins defined molecular units are joined together into a • Polymerization. matrices. naming. terms—polymer. The polymers are found as mixtures Matrix materials can be polymeric. even when oligomers Fundamentals of Composites Manufacturing: Materials. only a few monomer units. surface agents molecule is simple and a convenient method to represent polymers. viscosity Although the concept of a single polymer control agents. resin. (The following few chapters will Some single polymer chains can be com- discuss specific types of polymeric matrices. or ceramic. even those polymers with only a few units changeably. concepts: The term polymer means “many units” and refers to the way in which individual • Polymers. A single molecular unit • Solidification. in actuality. and other ther. These mixtures of polymers are some- general nature and properties of polymeric what analogous to a plate of spaghetti. generally.1: Introduction to Composites 19 2 Matrices and their Properties CHAPTER OVERVIEW to adhere to those differences even though a This chapter examines the following more relaxed usage is often accepted. thus com. Methods. while others make distinctions. When the monomers are linked • Aromatic and aliphatic materials together into a polymer chain. however. melting. will later be joined together to form long This text will define the terms and explain the chains when they are molded into a finished differences seen by some. that ple in the composites industry use all these polymers have long chains and. • Additives: fillers. one chapter will be devoted to ceramic while other polymer molecules may have and metallic matrix composites. process. meaning to form or polymers in anticipation of their eventual mold. Whereas the terms “polymer” terials that are not yet in their final form and “resin” can refer to both naturally oc- and shape. although they also can be solid used only to refer to synthetics. the matrix in The term plastics refers to polymeric high-performance composites is not re- materials after they have been finally ferred to as a plastic. Methods. they are sometimes called pre. tree sap was used to hold other materials used with fiberglass. the Greek plastikos. The cost resins are often called fiberglass rein- term “resin” originated from the Greek forced plastics (FRP). plastic is liquids. The matrix for these shaped. with low-cost composites. a resin is changed into a linkage into much longer chains. are present. plastic through some forming or molding The term resin refers to polymeric ma. Because materials together and was also shaped into of this association of the term “plastic” amulets and other decorative pieces. (The word “plastics” comes from high-performance composites is called a Fundamentals of Composites Manufacturing: Materials. plastics word meaning tree sap. might refer to any of the common matrix anciently. This reflects that. Monomers uniting to form a polymer.20 2: Matrices and Their Properties Figure 2-1.) Hence. In this sense. Composite materials that will be subsequently heated materials made from fiberglass and low- to melting and then formed or shaped. and Applications . Most of the common resins are curring and synthetic materials. ization and chain-growth polymerization) The unpaired electron on the newly and condensation polymerization (also bonded monomer is like the electron in the called step-wise polymerization). and Applications . a terminating agent either is course. thus creating an- chemicals. This same 1 of Figure 2-2. and the polymer can grow to be very long. it is highly representations of addition and condensa. as has gins with the activation of some molecule. process of an activated chain reacting with The unpaired electron in the free-radical a new monomer can continue many times has a strong driving force to pair with an. electrons is another monomer which. although it When the new monomer is added. This activation is shown in Step other active site on the chain. the activated reactive species such as a free-radical. That is. which was the second electron in the weak CHARACTERISTICS. (See the “Composite Materials. The Free-radicals are molecular species that addition of a new monomer has the effect of have an unpaired electron. 2005 for a good review of the the free-radical. the monomer has an unpaired electron. Society of Manufacturing available. reactive and seeks to bond with another tion polymerization are presented in Figures electron from yet another weak bond. Figure 2-2). other electron and form a bond. which can form a highly carbon double bond. Methods. Only certain types of monomers The process of linking the small units have the kind of weak bonds that can be (monomers) into long chains (polymers) is easily attacked by a free-radical and are thus called polymerization. nearby molecule. Addition Polymerization the most abundant source of easily removed The addition polymerization reaction be. Simplified original free-radical. The 2-2 and 2-3. Usually. of Eventually. contain a carbon-carbon double bond. Therefore. simply by heating the peroxide. AND bond. It is said. usually contains a carbon- usually a peroxide. Figure 2-2). a new could also occur through the action of certain free electron is created. Normally. After the bond is formed nature of matrix materials. The activation lengthening the chain by one monomer unit step forming the free-radical usually occurs (Step 3. therefore. perhaps thousands of monomer units (Step the free-radical will pull an electron from a 4. as shown in Step 2 of Figure 2-2. POLYMERIZATION.2: Matrices and Their Properties 21 “resin. been pointed out. The monomer will then bond with Engineers. Polymerization can appropriate as starting materials for the proceed by several different mechanisms. of the appropriate monomers are those that erization (also called free-radical polymer. polymerization reaction. NAMING. The most common The two most common are addition polym.) between the free-radical and the monomer. activated monomer can react with any eas- ily removed electron in its vicinity. The nearby molecule is.” is in high concentration and thus readily video program. that the monomer MOLECULAR WEIGHT has been activated. one of the monomers that has been introduced into the mixture or simply occurs chosen because it has a bond from which through contamination or reactions with Fundamentals of Composites Manufacturing: Materials.” sometimes even after it has been an electron can be easily extracted and it shaped. monomer reacts with a new monomer. This chain growth is usually weak bond in a nearby molecule (usually promoted by performing the polymerization a monomer molecule) and pair that electron reaction with high monomer concentrations with its own unpaired electron to create a and high heat and/or with the use of a cata- new bond between the free-radical and the lyst that facilitates chain growth. but not so and further reaction stops (Step 5. which activated chain.22 2: Matrices and Their Properties Figure 2-2. the activation is quenched each grow into separate chains. Fundamentals of Composites Manufacturing: Materials. When is usually just high enough to initiate the the terminating agent is encountered by the chain reaction on several monomers. termination from some natural or bination with unreacted peroxide. minor constituents of the mixture. the monomers in the chain growth steps. when most of the monomer is termination does not occur because of com. erization reaction to ensure that premature Eventually. Therefore. and Applications . a powerful terminating agent. as shown at the bottom of Figure 2-2. Care must be taken during the polym. Figure high that the peroxide will compete with 2-2). Addition polymerization. The general representation of the poly- the initial concentration of the peroxide mer. which is introduced termination agent occurs. used up. Methods. C. The total number of units bonded reactive group. Figure 2-3). These end tion polymerization. of another to form a of the actual number of monomers in each linkage element. identical monomers on ei. is the nature of the basic sation polymerization. however. two different monomer groups are usually of minor importance in types. must be present. of course. What is present in all monomers that react by conden- shown. and Applications . Each the properties of the molecule and so are must have certain characteristics. mers (M1 and M2) into a linked molecule. which are left out of the general formula. Therefore. polymer will have both ends of the second ther side. Methods. is Condensation Polymerization also formed (Step 1. In condensa- terminator on the other end. The parentheses and horizontal end groups. L. The first characteristic monomer that has combined to form the is that each monomer must have two active polymer. M1 and M2. X. does not show either the original link with although. one monomer will have both meant to indicate that the monomer is ends that are one reactive group and the other bonded to other. The second characteristic of together is represented by n. Y. or the link with the result in long polymer chains. Usually. a number that condensation monomers is that the active end is usually an average number because poly.2: Matrices and Their Properties 23 Figure 2-3. of one monomer must react with mers tend to have a statistical distribution the active end group. A condensation by-product or condensate. the linked Fundamentals of Composites Manufacturing: Materials. Condensation polymerization. as shown in Figure 2-3 (the Xs extensions through the parentheses are and Ys). both reaction sequences the peroxide on one end. The reactions that occur in condensation Note that the linked molecule resulting polymerization are quite different from those from this reaction (Step 1) has two active occurring during addition polymerization ends—an X and a Y. which joins the two mono- molecule. group. This is especially true This is because of the low concentration of if the temperature is relatively cool since initiating free-radical used (hence only a few the movement of the linked chain can be chains are initiated) and the highly reactive slow and encounters between the active nature and rapidity of the chain-growth ends and monomers would be rare. fore. respectively. Examples of this type are with the longer linked chain and the new epoxy and silicone. react with type 2 monomers. condensation polymerization conducted at elevated temperatures and in usually results in fewer and shorter mol- high monomer concentrations to improve ecules. The most com- shown in Step 2.24 2: Matrices and Their Properties molecule can react with additional mono. are made from ethylene and propylene mono- The resulting product is referred to as a mers. long chains was originally a problem with Fundamentals of Composites Manufacturing: Materials. respectively. There. contain the epoxy group and the silicone a new linkage element is formed that joins a group. the polymerization reaction is usually In contrast. as the the characteristics of the polymers made polymer gets longer and the concentration by the two methods are quite different. greatly diminished. Polymers created by the longer linked molecule as shown in Step 3. lymerization often result in the formation of mer and making an effective encounter is relatively few but very long-chain polymers. each competing to quench the reaction by the addition of for new monomers to add. The reaction that occurs of the molecules. The mixture can be polymerizations because any two monomers cooled to stop the reaction when the desired can react to begin new chains. In practice. condensation polymerization reaction are Figure 2-3. which Another condensate by-product is formed. and Applications . new monomer to the previous molecule and a condensate is created. because these molecules monomer is analogous to the others. of the linked chains. X. Figure 2-3) again results mon method for naming polymers made by in a combined state product in which a new addition polymerization is to simply combine linkage element forms and the new monomer “poly” with the name of the monomer. especially those not be a problem as both monomer 1 and not formed by these two principal methods. That is. The sequence of steps shown in Figure Polymer Characteristics 2-3 can continue as long as sufficient mono. Examples 2-3 is that the longer linked chain has both of this type are polyesters and polyamides. as is added to the previous linked molecule. with polyethylene and polypropylene. Names for polymers are largely dependent The reaction of the linked molecule with upon the type of the polymerization reaction another monomer (of type M1 in the case used to make the polymer. Many chains begin in condensation reaction efficiencies. Therefore. steps (causing the chains to grow very long). Polymer Naming Systems mers of either type M1 or M2. usually named by combining “poly” with The only new feature in the reaction the name of the linkage element formed sequence to be noted in Step 3 of Figure when the monomers join together. Methods. A few polymers. thus creating chain length is reached. it can only which contain the ester and amide linkages. the probability of chain-reaction steps typical of addition po- the linked chain encountering a new mono. It is also possible a large number of chains. Achieving very end-termination molecules. monomer 2 are usually present in high are named for some unique characteristic concentrations. The of monomer gets smaller. ends the same. Since the addition and condensation reac- mers are present to react with the ends tions proceed by such different mechanisms. This should respectively. until it freezes. The tempera- more dominant in increasing mechanical ture at which the molecules lock in place and properties than molecular weight. Therefore.) Most the material becomes a solid is called the of these properties will be discussed in the freezing point. It refers to the container. When the molecules Thermal Considerations are arranged in orderly arrays. For instance. This broadness of reinforcement) that they are considered in the melting/freezing point is especially true this chapter. Although comes so slow that the forces of attraction somewhat difficult to quantify in terms of between the molecules overcome many of the the actual number of monomer units present molecular motions (especially translation) in any one particular chain. However. the melting/freezing point traditional liquids such as water) and its as. with all other fac. chapters on mechanical properties. This cooling removes heat en- The length of the chain is usually char. restricted in their lateral or translational lecular weight. ergy from the liquid. Liquids can be be used for both the amorphous and crys- poured and will change shape to match the talline types of polymers. tors being constant. Such polymers are said Solidification. freedom while the molecules in the solid For simplicity. just to guish them from the primary bonds linking name a few of the most important properties. hardness. is sharper. which is a measure of the number motion (especially translational motion) be- of monomer units in the chain. which slows the motions acterized by a quantity called molecular of the molecules. abrasion resistance. if the molecules are highly entangled and randomly arranged. higher molecular weight the attractions that cause the molecules to usually results in higher strength. the term melting point will are more fixed in position. The most common method of changing However. Melting. stiffness. tractions or secondary bonds to distin- melt viscosity. Molecules attract each other but these at- tistically. the molecules are properties are improved by increasing mo. After (A rough rule of thumb is that mechanical becoming locked in place. However. but their atoms can still vibrate presence of the reinforcement may be even and rotate to a limited extent. the atoms in the chains themselves. and melting point. the molecular and the molecules lock into set positions. sharply defined fundamental and highly dependent upon temperature that can be called the melting the nature of the matrix (rather than the point or freezing point. The amorphous “melting point” is sociated solid is the ability of the molecules the temperature at which the material can in the liquid to move about with relative be treated like a liquid in molding processes. become a solid are usually called either at- toughness. Fundamentals of Composites Manufacturing: Materials. Eventually the molecular weight. there is no single. Methods. the movements. and Applications . in composites. liquid-like. molecules together as a molecule. The effects of molecular weight on tractions do not have the same strength as the properties of polymers are evident and the primary bonds that hold the atoms of the important.2: Matrices and Their Properties 25 condensation polymerization reactions. because a mass of two of the properties—thermal behavior polymer molecules varies so greatly in (especially melting) and toughness—are so length. In strict definition. which are The major difference between any liquid called crystalline regions (to be covered in (including liquid polymer resins but also more detail later). and Other to be amorphous. whereas solids resist changes in temperature at which the material becomes shape and do not need a container. the major producers seem to have from a liquid to a solid is by cooling the liquid solved this problem today. weight can be treated and understood sta. 26 2: Matrices and Their Properties If the frozen solid material were to be primary bonds between the monomer units. heated again, the molecules would again When this happens, the polymer breaks apart gain energy, first in greater vibrations and and degrades. Rarely, however, does the poly- rotations, and then with increased lateral mer revert to monomers under these condi- and translational movements. With con- tions. Because this breaking apart occurs at tinued heating the molecules would break such high temperatures, the polymer is more loose from their intermolecular attractions likely to oxidize and degrade. The oxidation and become free to move about. This is the results in some off-gases and the formation melting point. Normally, the temperature at of char, a charcoal-like material that is a which the molecules lock in and break loose non-meltable solid residue. A similar reaction is the same. Thus, the freezing point and occurs when coal or wood is heated exces- melting point are the same temperature. sively without catching fire to form charcoal. Remember, the melting/freezing points are When polymers degrade, they no longer actually regions of temperatures and the possess many of the desirable properties of numbers reported are merely representative the original polymer. Hence, care should be of the regions. taken to not allow polymers to reach their The melting point of a polymeric material decomposition temperature. The decompo- is strongly dependent upon its molecular sition temperature is not highly dependent weight. As the molecular weight increases, on molecular weight because the strengths the melting point also increases. This de- of the bonds broken upon decomposition pendence can be understood by realizing are the same whether the molecule is large that as the molecular weight increases and or small. The decomposition temperatures the polymer chains get longer, they will for small and large molecules are shown in entangle or intertwine to a greater extent Figure 2-4. with neighboring polymer molecules, thus Other thermal transitions and properties restricting the translational movements of can be important in polymer matrices. The all the molecules. Hence, more heat will be most important of these other properties is required to break loose these longer molecules the glass transition temperature, often since they must overcome both the natural abbreviated as Tg. This thermal transition intermolecular attractions and the greater occurs in the solid phase and marks a change entanglement. This higher amount of energy from a rigid solid to one that is more pliable. required to reach this disentangled and free The motions of the atoms in a rigid, solid movement state is seen as a higher melting material below the Tg are generally simple point. Therefore, the solid region of a high- vibrations in rigidly fixed positions. Above molecular-weight polymer extends to a higher Tg but still below the melting point, the vi- temperature than does the solid region of a brations and rotations are more expansive low-molecular-weight polymer. Simply put, and the atoms may move laterally for short as the molecular weight increases, so does distances. However, they are still locked the melting point. This relationship can be into relatively fixed positions because of seen in Figure 2-4. continued entanglements. Hence, between The decomposition point is another the Tg and the melting point, the material important thermal transition in polymers. becomes somewhat pliable, although still At the decomposition temperature, sufficient a solid. In some materials the change in heat has been put into the polymer so that physical state can be quite apparent. The the motions of the atoms (vibrations and state above the glass transition is referred translations) are great enough to break the to in these materials as the “leathery state.” Fundamentals of Composites Manufacturing: Materials, Methods, and Applications 2: Matrices and Their Properties 27 Figure 2-4. Temperature transitions for small and large polymers. Crystalline materials do not exhibit a strong for a polymer. This property is determined Tg transition because they are locked into using a test apparatus that heats a sample position by the crystalline structure, which of the composite material (5 × 0.50 × 0.25 is not broken apart until the melting point. in. [12.7 × 1.3 × 0.64 cm]) in a heated bath However, even highly crystalline polymers of mineral oil or some other liquid that is typically have some amorphous regions, and thermally stable at the temperatures to be these regions exhibit a Tg transition. used and will transfer heat readily to the A property closely related to the glass sample. A weight (designated by the test transition temperature is the heat distor- procedure and dependent upon the type of tion temperature (HDT), which is defined plastic material being tested) is then placed by the deflection temperature under load on the sample. The entire apparatus is then test (ASTM D648). (Note: ASTM is the ac- heated, usually with stirring to ensure good ronym for the American Society for Testing heat uniformity in the liquid. The tempera- and Materials—a society that supervises ture at which the sample deflects (bends) a the establishment and dissemination of specified distance under these conditions testing standards for materials.) While not is the HDT. a thermal transition in the same sense as the melting point or the glass transition THERMOPLASTICS AND THERMOSETS temperature, the HDT is a convenient As has been evident from the discussion measure of the maximum use temperature of the thermal properties of polymers and Fundamentals of Composites Manufacturing: Materials, Methods, and Applications 28 2: Matrices and Their Properties the preliminary suggestions about the me- Thermosets are resins that are usually chanical properties (to be discussed in more liquids (or easily melted solids) at room detail later in this textbook), the interactions temperature. They are placed into a mold between molecules, such as entanglements and then solidified into the desired shape by and intermolecular attractions, have major a process other than freezing. The molded effects on key polymer properties. Another material is set in its shape by a heating type of interaction between molecules has process in which bonds are formed between such a strong effect on the properties of the molecules. These bonds or crosslinks polymers that all polymers can be classified change the basic nature of the material. according to whether or not this interaction After the polymer material has been heated is present. The interaction is the formation and the crosslink bonds formed, which is of actual bonds between the molecules. called curing, the thermoset material can These bonds between molecules are called no longer be melted. Hence, thermosets crosslinks. Polymers in which crosslinks will not melt upon heating in contrast to are not present are called thermoplastics thermoplastics, which are capable of being and polymers in which the crosslinks are remelted. Therefore, thermosets become present are called thermosets. Following is a fixed (set) with heat. discussion of some properties of thermoplas- A typical example of a thermoset reaction tics and thermosets and their differences, is the baking (curing) of a cake, where the especially their performance under differ- thermoset polymer is the gluten in wheat ent thermal conditions. The crosslinks are flour. The flour is dissolved in water with bonds between the polymer molecules. They other additives to make a batter. The liquid have approximately the same strength as batter is then placed into a cake pan (mold) the bonds between the atoms of the polymer and baked (cured). After curing, the cake molecule itself. cannot be remelted. If it is heated again, the Thermoplastics are resins that are sol- cake burns or chars (degrades). ids at room temperature. They are melted Several molding processes, such as hand or softened by heating, placed into a mold or lay-up, spray-up, compression molding, fila- other shaping device when in the molten ment winding, resin transfer molding, and stage, and then cooled to give the desired pultrusion, are based on thermoset behav- shape. Several molding processes, such as ior. Some of the most common thermosets extrusion, injection molding, blow mold- include: unsaturated polyester, vinyl ester, ing, and thermoforming, are based on this epoxy, polyimide, phenolic, and cyano-ac- type of resin behavior. Some of the com- rylate. Many of these thermoset resins are mon thermoplastics include: polyethylene, especially important in composites. polypropylene, nylon, polycarbonate, poly- The vastly differing behaviors of thermo- ethylene terephthalate (PET), polyvinyl plastics and thermosets arise from a basic chloride (PVC), acrylic, and acetal. Even difference in the chemical structure of the after molding, thermoplastics can be melted thermoset and thermoplastic resins. That by reheating, so the thermal environment significant difference arises because thermo- of thermoplastic resins is a consideration set resins have sites along the polymer chain in its use. If the temperature is too high, that can be activated to become reactive. the product could undesirably soften, dis- These sites react in such a way that chemical tort, and lose other key properties. Hence, bonds are formed between adjacent polymer thermoplastics become plastic (moldable) molecules. Because these sites exist on all with heat. the thermoset molecules, the potential exists Fundamentals of Composites Manufacturing: Materials, Methods, and Applications 2: Matrices and Their Properties 29 for the entire group of polymer molecules low- and high-molecular-weight polymers. to become joined together, which is often, However, in the case of crosslinking, the mo- although not always, the result. The process lecular weight can become extremely high, of crosslink formation is called curing. increasing the melting point so much that it When crosslinks form, they restrict the will actually occur above the decomposition movement of polymer molecules and the at- point, as depicted in Figure 2-5. Therefore, oms within the molecules to an even greater the molecular weight increase is so large that degree than either intermolecular attrac- a thermoset material will decompose before tions or entanglement. However, below the it melts. In other words, the thermoset is not glass transition temperature of the polymer, meltable and will decompose if heated to a the molecules are locked in and the move- high temperature. ments of the atoms within them are so re- Another method of comparing thermo- stricted that the additional restrictions from plastics and thermosets is to observe the the crosslinks are sometimes not apparent. viscosity profiles of the two materials as they As the temperature is raised, the crosslinks are molded. Profiles of this type are shown in restrict the movement of the atoms such that Figure 2-6 for a typical thermoplastic and a when the temperature is reached that would typical thermoset. Note that the axes of the have been the Tg in a non-crosslinked poly- graph are viscosity versus time or tempera- mer (assuming the polymers are identical ture. This double label on the x-coordinate except for the crosslinks), the restrictions are merely reflects that the time and tempera- so great that the normal flexibility achieved ture are usually increased together, so the at Tg cannot be obtained. In other words, Tg independent variable could be either one. is increased by the presence of crosslinks. As The initial viscosity of the thermoplastic more crosslinks form, the molecules become is above the liquid-solid line, indicating that ever more restricted and the heat energy re- at room temperature the thermoplastic quired for movement continues to increase. is a solid (high viscosity). Heating of the Therefore, Tg will continue to increase as thermoplastic causes motion in the mol- the amount of crosslinking increases. The ecules and eventually results in melting, examination of Tg has become a convenient shown as the point where the thermoplastic method for following the extent of crosslink- curve drops below the liquid-solid line. The ing in some polymers. viscosity of the thermoplastic continues to The behavior differences between thermo- drop as the temperature is increased as plastics and thermosets also can be under- indicated in the thermoplastic curve. At stood in terms of molecular weight. When a any point along the curve, the temperature crosslink forms, thus linking two polymer could be reversed and the material would molecules, the molecular weight of the move upward along the same curve. That is, combined molecule becomes approximately the thermoplastic can be repeatedly heated twice as much as it was when the two were and cooled, melted and solidified, without separate. The molecular weight continues changing the basic nature of the material. to increase as more molecules are linked This is suggested by the double-direction together. It is evident that with only a mod- arrow associated with the thermoplastic erate number of crosslinks, many polymer curve. chains can be joined together, resulting in The initial viscosity of the thermoset is a high molecular weight. The effect of this usually just below the liquid-solid line. How- higher molecular weight is to increase the ever, it may be an easily melted solid (just melting point, as shown in Figure 2-4 for above the line). For both thermoplastics and Fundamentals of Composites Manufacturing: Materials, Methods, and Applications 30 2: Matrices and Their Properties Figure 2-5. Changes in the melting point when curing a thermoset resin. thermosets, the initial effect of increasing representing the thinning due to tempera- temperature is to lower viscosity. But the ture slopes sharply downward. This curve sharper drop in the thermoset line is be- dictates the nature of the first part of the cause of the lower initial molecular weight thermoset curve. With continued heating, of thermosets, which means that thermal the molecules start to react and crosslinks effects are more pronounced. In contrast to begin to form. These take some time to de- the behavior of thermoplastics, the viscosity velop, thus giving the initial drop in viscosity of the thermoset resin reaches a minimum from purely thermal thinning. The crosslink- and then rapidly increases to a position ing line shows how the viscosity increases substantially above the liquid-solid line. The as the crosslinks develop (see Region B). behavior of the thermoset line is actually a Eventually the crosslinking curve crosses the combination of two separate phenomena liquid-solid line. At this point, the material that add together to give the thermoset ef- is a cured solid. The summation of the tem- fect. These two effects are represented as two perature thinning curve and the crosslinking additional lines (given only for explanation curve results in the initial drop and then purposes) in Figure 2-6. the sharp rise in viscosity of the thermoset As the temperature is initially raised, curve. The thermoset material is irreversibly the molecules begin to move and melting/ changed from a liquid to a solid as indicated thinning occurs. This period is identified by the single-direction arrow associated with in Figure 2-6 as Region A and the curve the thermoset curve. This is in contrast to Fundamentals of Composites Manufacturing: Materials, Methods, and Applications 2: Matrices and Their Properties 31 Figure 2-6. Viscosity curves for a typical thermoplastic and a typical thermoset. the double-ended arrow associated with the be explained. That difference is the extent thermoplastic line. to which a polymer contains the aromatic The degree of crosslinking is sometimes group. The aromatic group and various rep- called the crosslink density. With most resentations of that group in polymers are polymers, the theoretical number of cross- pictured in Figure 2-7. The name “aromatic” links can be calculated. This then can be is used because most of the molecules con- related to some thermal or mechanical prop- taining this group have a strong odor. Years erty of the polymer that is easily measured, ago they were called aromatic because they such as HDT or Tg. This allows other samples were easily identified by their smell. How- from production to be measured as a quality ever, not all chemicals with strong smells are control standard to see if they have achieved aromatic in the structural sense. the desired crosslink density. The aromatic group is formed from six carbon atoms and attached hydrogen at- oms, one per carbon. When not attached AROMATIC AND ALIPHATIC to another part of a molecule, the aromatic MATERIALS group is the benzene molecule. When at- Before considering other matrix-dominat- tached to another part of the molecule, ed properties, a basic difference in polymers the hydrogen at the attachment point is that affects many of the properties should removed. Three representations are given Fundamentals of Composites Manufacturing: Materials, Methods, and Applications 32 2: Matrices and Their Properties Figure 2-7. Aromatic molecules. Fundamentals of Composites Manufacturing: Materials, Methods, and Applications 2: Matrices and Their Properties 33 in Figure 2-7a and all three are equivalent. reinforcement together. However, in some The later two representations are merely properties, the reinforcement will largely de- shorthand versions of the first. termine the property with little contribution Because of its physical nature, the aro- from the matrix, while in others, the matrix matic group imparts special properties. It will dominate. Therefore, it makes sense is a rather large group of atoms, very stable to discuss the matrix-dominated properties and resistant to most of the chemical pro- in this chapter on matrices and to discuss cesses that a polymer might encounter in the reinforcement-dominated proper- use. Because of its size and shape (flat and ties in the chapter where reinforcements stiff), the aromatic group imparts stiffness are discussed in detail. Those situations and strength to the molecules in which it when the property is strongly affected by resides. More aromatic groups usually mean both materials or when the interaction of more stiffness and strength. the materials is critical to the composite’s The aromatic group can be attached to the performance will be discussed in chapters polymer in several ways. One attachment on composite properties and fiber-matrix method, shown in Figure 2-7b, is dangling interfaces. from the polymer backbone. This is called Even though composite properties are the the pendant attachment. Another method primary focus of this book, an understand- of incorporating the group into a polymer ing of the properties of the non-reinforced is shown in Figure 2-7c where the aromatic matrix can be useful in predicting matrix- group is part of the backbone. A third meth- dominated composite properties. It is also od is when the aromatic molecules form a useful in choosing which matrix material network. The stiffness and strength of the should be chosen for a particular application. polymer are increased in all methods of at- Therefore, the properties for a wide variety tachment. However, the attachment as part of representative matrix materials (non-re- of the backbone has a greater effect than the inforced) are given in Table 2-1. The details pendant, and the network of aromatic rings of each of the matrix materials presented has more effect than either the backbone or will be discussed in the next few chapters the pendant. of this book. Some polymers have no aromatic groups The discussion in the previous chapter of at all. These polymers are said to be aliphat- the role of the matrix as a component of a ic. “Aliphatic” simply means the absence of composite indicated that the matrix must aromatic. As the number of aromatic groups protect the reinforcement from the environ- increases in the polymer, it is said to have ment. Some of the environmental conditions greater aromatic content. At some point, the that might affect composite properties in- aromatic content will become important in clude the following: heat, solvents, staining determining the properties of the polymer. agents, gases, fire, electricity, and light. At that point, the polymer is usually referred Another key property that has a strong to as simply aromatic in nature. relationship to the matrix is toughness, Other polymer properties affected by the although this property is different from aromatic content are discussed in the fol- the others because it is also strongly de- lowing sections. pendent upon the reinforcement. Each of the environmental conditions or threats is Matrix-dominated Properties listed in Table 2-2 and will be addressed in Most composite properties are dependent the following sections. If the matrix is the upon the combination of the matrix and dominant factor in each of these properties, Fundamentals of Composites Manufacturing: Materials, Methods, and Applications 34 Table 2–1. Properties of various matrix materials (non–reinforced). Property Polyesters Epoxies Polyimides Phenolics Thermoplastics Ceramics Metals Maximum use 175–285 200–350 400–600 300–400 340–450 1,500–4,000 1,000–2,000 temperature, (79–141) (93–177) (204–316) (149–204) (171–232) (815–2,204) (538–1,093) ° F (° C) Fundamentals of Composites Manufacturing: Materials, Methods, and Applications Flexural 8–23 45–55 15–25 7–14 14–18 6–10 — strength, (55–159) (310–379) (103–172) (48–96) (96–124) (41–69) ksi (MPa) Flexural .5–.6 2.0–2.4 .5–.8 1.0–1.2 .4–.5 — — modulus, (0.3–0.4) (1.4–1.7) (0.3–0.6) (0.7–0.8) (0.3–0.4) Msi (GPa) Density (g/cc) 1.1–1.2 1.2–1.25 1.3–1.4 1.3–1.4 1.1–1.2 1.8–2.5 2.0–6.0 Tensile 3–13 5–15 6–13 5–9 5–20 4–20 7–70 strength, (21–89) (34–103) (41–89) (34–62) (34–138) (28–138) (48–482) ksi (MPa) Tensile .3–.6 .6–.7 .5–.6 .8–1.7 .3–.7 .5–17 7–70 modulus, (0.2–0.4) (0.4–0.5) (0.3–0.4) (0.6–1.2) (0.2–0.5) (0.3–12) (5–50) Msi (GPa) Izod impact, .2–.4 .2–.3 1.0–1.5 .2–.6 .4–1.3 <1 1.5–2.2 ft–lb/in. (kJ/m) (3.2–6.4) (3.2–4.8) (16.0–24.0) (3.0–9.6) (6.4–21.0) (<16.0) (24.0–35.8) Moisture 0.15–0.60 0.1–0.7 1.1–1.2 — 0.01–0.3 — — absorption, % Elongation, % 1.4–4.0 — 1.1 0.5–0.8 — — — 2: Matrices and Their Properties Coefficient — 6–7 3–5 3–5 3–5 0.5–0.6 0.6–1.2 of thermal expansion (× 10–5) 2: Matrices and Their Properties 35 then the specific nature of the matrix itself is Thermal Properties likely to be a primary determining factor in The most important matrix-dominated how the material responds to the various en- properties are clearly those associated with vironmental conditions. A general discussion thermal conditions. The matrix might melt about the natures of the polymers and how (if a thermoplastic) or char (if a thermoset) they might affect properties are useful and when the temperature of the composite ma- will be provided in this chapter. The specific terial is raised excessively. details will be discussed when each particular As previously discussed, when interac- polymer is introduced in later chapters. tions between molecules are full bonds or Table 2-2. Environmental agents that can strongly affect the matrix. Environmental Agent Possible Effects on the Matrix Heat Thermoplastics are melted with the melting point being dependent upon the specific nature of the polymer, including the molecular weight and the amount of secondary bonding. Thermosets are softened but not melted. Excessively high temperatures can result in degradation (decomposition) of thermosets and thermoplastics. Solvents The degree of interaction of the polymer with the solvent is dependent on the chemical reactivity of the polymer and how similar it is to the solvent. In general, highly polar molecules react strongly with highly polar solvents. Staining agents Polar staining agents will have stronger interactions with polar matrix materials and the resulting stains will be more strongly embedded. Gases Oxidation can readily degrade some polymers and the effect increases with the reactivity of the bonds along the backbone. This effect is enhanced if the permeation of the gas into the polymer is high. Permeation is increased when the chemical nature of the gas is similar to the chemical nature of the polymer. Permeation is also increased when the atoms in the polymer are further apart. Thus, crosslinking reduces permeation as does crystallinity. Fire Fire-retardant properties depend upon many polymer factors. The most common ways to improve fire-retardant properties are to increase aromatic content, add fillers, and add halogens. Electricity Almost all polymeric materials have high electrical resistance, high dielectric strength, and low conductivity. Changes in polymer type result in minor changes in these properties, but all are significantly different from those of metallic materials. Light Ultraviolet (UV) radiation can degrade polymers. Aromatics are somewhat more sensitive to UV light than aliphatics. Fundamentals of Composites Manufacturing: Materials, Methods, and Applications 36 2: Matrices and Their Properties crosslinks, for example, in thermosets, the aromatic group to move freely as it must in melting point is raised above the decompo- a liquid. Hence, the melting point is higher. sition temperature and no melting occurs. Decomposition points are lowered slightly Within the realm of thermoplastics, several types of interactions less permanent than crosslinks can also occur. In general, any interaction or association between molecules will increase the melting point of the poly- mer. One such interaction is entanglement or intertwining, which is typical of polymers and increases as the molecular weight of the polymer increases. Other intermolecular interactions, such as secondary bonding, the most common type being hydrogen bonding, will also raise the melting point. Secondary bonds are broken by heating and are not, therefore, of the same strength as crosslinks. Some polymers pack closely together in the solid state and form structures that are analogous to crystals in ceramic and metal materials. These regions of close packing are therefore called crystalline regions. The crystalline regions are held together by secondary bonds, or crystalline bonds, which increase the melting point in these regions. Most polymers having crystalline regions are thermoplastics; this is because the crosslinks in thermosets tend to interfere with the packing of the polymers. Molecular motion in a crystalline region is highly restricted. Therefore, the type of molecular motion needed for a glass transition is missing within the crystalline region. The crystalline part of a group of molecules would not have a Tg, but other regions in the same molecular mass where no crystallinity exists could have a Tg. Such mixed polymers are called semi- crystalline. The regions of non-crystallinity are called amorphous regions. Figure 2-8 shows representations of the crystalline and amorphous regions. The presence of aromatic content increas- es the melting point of most polymers. This is simply understood because more thermal energy is required to get the large, stiff, Figure 2-8. Representations of crystallinity in polymers. Fundamentals of Composites Manufacturing: Materials, Methods, and Applications 2: Matrices and Their Properties 37 by aromatic content because the bond where etrate further, thus increasing the interac- the aromatic group is attached to the poly- tion between polymer and solvent. Stronger mer is slightly less stable than most of the interactions could result in swelling, even at other polymeric bonds. room temperatures, and the loss of some key properties. Even stronger interactions could Resistance to Solvents and Water result in the polymer actually dissolving, in Resistance to chemicals depends upon the which case it would cease being a matrix for chemical nature of the matrix. In general, the composite. The polymer could also react the more the chemical nature of the polymer with the solvent to form bonds, thus chang- resembles the environmental chemical that ing the basic nature of the polymer; this is interacting with it, the more the effect of usually results in significant deterioration the environmental chemical. The chemical of key properties of the composite. natures of materials are often complex and, Water is a strongly polar molecule. therefore, difficult to describe in brief. How- Therefore, polar matrix materials, such as ever, one aspect is so important that it can unsaturated polyesters, are more susceptible sometimes be the only aspect of the chemi- to water attack than non-polar molecules, cal nature that needs to be considered. That such as polypropylene. aspect is chemical polarity. The rule of similarities between polymer Chemical polarity, or simply polarity, is and solvent also applies to aromatic poly- a measure of how evenly the electrons are mers. Therefore, highly aromatic polymers distributed throughout the molecule. In are readily attacked by highly aromatic some molecules the electrons are naturally solvents. Other factors can also come into drawn to particular atoms within the mol- effect, but the rule of similarities is good as ecule. Molecules with an oxygen or nitrogen a first indication of whether a material will atom will often be polar because electrons be attacked by a particular solvent. are often drawn to the site of these atoms. Some thermoplastics, especially those When some site within the molecule is rich associated with high-performance applica- in electrons, some other site must be scarce tions, are especially solvent resistant. This since the total number of electrons in the resistance arises because these materials molecule is a constant. The electron-rich have compact polymeric packing; that is, sites are negative and the electron-poor sites the polymeric molecules are tightly packed are positive. When this polarity exists, two with many intermolecular interactions, but polar molecules will have strong attractions not crosslinks as these molecules are still because the negative site on one molecule thermoplastics. Further, the molecules are will be attracted to the positive site on the often highly aromatic and have great stabil- other molecule. Therefore, a polar solvent ity. Therefore, there is little capability for molecule can react strongly with a polar solvents to attack, except in the case of the polymer molecule because the positive site most aggressive aromatic solvents and then on one molecule will be attracted to the neg- only under hot conditions. ative site on the other. The stronger the at- The use of composites for their chemical traction, the more the polymer’s properties resistance is widely applied and a rapidly are changed by the solvent. If the attraction growing market. Some industries, such as is slight, the interaction might only be seen pulp and paper manufacturing, oil and gas over long times or at elevated temperatures. transport and refining, chemical processing, Raising the temperature swells the polymer and waste-water treatment are major users and allows the solvent molecules to pen- of composite pipes, fittings, and tanks. These Fundamentals of Composites Manufacturing: Materials, Methods, and Applications 38 2: Matrices and Their Properties industries rely on the corrosion resistance the space between the atoms in the polymer of composites as well as their strength and increases or as the size of the permeating relatively low cost. The choice of matrix resin gas decreases. This occurs simply because is largely dependent on the type of chemical the gas molecules can work their way environment expected in the application. through the polymer more easily when the Most of the chemical-resistant resins are spaces are bigger. Therefore, crosslinking, categorized as “moderate” as to the degree which pulls the molecules tighter together, of chemical attack they can withstand. Many will decrease permeability. Crystallinity also resins can adequately meet the required decreases permeability. standards. About one-third of the total tank and pipe market requires premium resins Fire Resistance where chemical attack is strong; thus special The resistance of a polymer to fire de- resins with specific resistances are required. pends on several factors. Some types of Specifications for use in these applications polymers burn more readily than others do. often require that special tests be passed by Most aliphatic polymers burn readily while the intended composite material. aromatic polymers burn with greater dif- Staining agents have interactions with ficulty. Highly aromatic molecules tend to polymers that are much like solvents. Polar burn slowly, if at all, and form chars when staining agents are more likely to interact they burn. Those chars resist further burn- with polar matrices. When they interact, the ing. Therefore, if the non-flammability of permanence of the stain is stronger. a material is a desired property, that prop- erty can be enhanced by adding aromatic Permeability and Resistance to Gases content. If the polymer desired is aliphatic, The most important interactions with and even for some aromatics, some other gases are those that cause chemical changes method of imparting the flame-retardant in the polymer from the chemical attack by property is needed for many applications. the gas. In this regard, the effect of gases is The most common method of enhancing fire much like the effect of solvents. retardation is to include in the composite The most important reactive gas is oxygen. mixture compounds containing the halogen When oxygen reacts with the polymer, deg- atoms—fluorine, chlorine, bromine, and radation usually occurs and the polymer iodine. The halogens unite with hydrogen experiences a significant reduction in useful during the burning process to create a dense properties. Some specialty chemicals, such as gas that smothers the flame. The problem Irganox®, are highly effective in preventing with suppressing a flame by using halogens or retarding polymer oxidation. These types is that the gas created is hazardous and opti- of antioxidants are usually added at small cally dark and dense. Nevertheless, halogen concentrations (typically 1–2%). materials can be beneficial in reducing flame Another interaction between matrix ma- spread and are used extensively. terials and gases is permeability, that is, Halogens can be added to resins in several the ability of a gas to pass into or through a ways. These are understood by considering material. This tendency is increased when the various methods of adding halogens to the gas and the polymer have similar chemi- a polyester resin mixture. One method is cal natures. The increase in permeability is by bonding halogen atoms to one or more probably from a swelling that occurs from of the components of the polyester resin. solvent-like effects between the gas and the Any of the components of the polyester mix- polymer. Permeability is also increased as ture—diacid, glycol, or solvent—can be the Fundamentals of Composites Manufacturing: Materials, Methods, and Applications of certain fillers. and Applications . The UV minum oxide. Composite airplane skins can be made containing phosphorous. The electrical properties of a polymer are The nature of the atoms has some effect on most often important in the electronics in. ments with the incident light or because of Fundamentals of Composites Manufacturing: Materials. boards or other components or sealants. UV light can Electrical Properties degrade polymers. of airplanes where conductivity to prevent such as magnesium chloride or calcium damage from lightning strikes is neces- bromide. most composites are not minerals can be added to increase dielectric because of the interaction of the reinforce- properties. will sub. important example of this is on the surface ters. thus they are ments. Hence. are improved by the addition is Tinuvin®. UV frequencies are near the natural molecules are released and can help to sup. One more extensively in the chapter on polyes. are used commercially. ATH. which Other properties that pertain to light are is used as a flame-retardant filler. the tendency of the electrons to become ex- dustry where composites are used as circuit cited by the UV light and degrade. the interactions between this UV light further advantage that it does not contribute and the electrons are strong. including metal-coated reinforce- in suppressing flammability. alu. Generally. or including a wire mesh within the frequently added to resin mixes along with composite laminate. ATH range of frequencies is just higher than vis- is a molecule in which three water molecules ible light and is a major component of sun- are loosely bound. Some minor electrical property resin to be used because of cost reasons or for changes result from the chemical nature of its particular physical properties. bonds along the polymer backbone. all are significantly mer has poor UV resistance and the applica- better in electrical resistance than metals tion will subject the resin to UV light. When heated. chemicals can be added to the resin mixture fications regardless of the type of polymer. A typical UV inhibitor resistance. (This is discussed tive nature of composites is a problem. especially those sary. Methods. all will work For some applications. Other powdered or translucent. enhance the ef. whereas many plastics are clear material to surface arcs. For instance. some and have been used without significant modi. The most important interaction of light The most common of these fillers is alumina with the polymer matrix is from the ultra- trihydrate (ATH). such as arc called UV inhibitors. frequencies of the electrons in the chemical press a flame by cooling and smothering it. to enhance UV stability. have high electrical resistance and dielectric Some applications may require a particular strength. conductive by adding metallic powders as fectiveness of halogen-containing materials fillers. violet (UV) component of light. There- ATH is relatively inexpensive and has the fore. These chemicals are Some electrical properties. often resulting to the toxicity of the smoke given off. also called alumina. and hydrated alumina.) Halogens also can be added as fillers. Another method to reduce flammability is to use some non-halogenated fillers that have UV Resistance and Optical Properties other beneficial properties that fight fires. Some materials.2: Matrices and Their Properties 39 source of halogenated atoms. the nonconduc- in reducing flammability. All of these methods the halogens. in excitation of the electrons and a resultant breaking of the bond. relatively unimportant in composites. However. If the poly- the polymers. aromatic polymers are more easily degraded Almost all polymers are nonconductive and by UV light than are aliphatic polymers. these water light. For stantially raise the resistance of a composite example. or otherwise moves in response to interactions so that elongations can proceed the impact. pendant groups. ever. and thus prevent a localized posite mix. form. Hence. is to decrease the amount of interpolymer vibrates. The most im. for some applications. matrix and reinforcements spread the en- However. widely among the atoms of the molecules. One problem is that strength and quickly diffuse the energy of the impact. the use requirements of accumulation.40 2: Matrices and Their Properties the frequent inclusion of fillers in the com. is one of some rubber or elastomeric material into the the factors that affects toughness. These materials are called other property. such ary bonds to neighboring molecules and few as from a falling or striking object. without breaking the elastomers or rubber materials are of this matrix material or the fiber reinforcement. proving the toughness of the composite. combination of both matrix and reinforce. In thermosets. cific location. that has a flexible backbone. might be compromised. But the polymer resin. Therefore. type and they obviously have high elongation depends upon the ability of the matrix to or stretch. Methods. tion in several ways. the energy. This latter property is re. material is often two phases and becomes The matrix can diffuse energy by convert. Polymers of this portant type of toughness is impact tough. the ability to quickly diffuse tougheners or toughening agents. The abil. it also de- the more likely the material is to diffuse creases the thermal stability of the material. In traditional resins. Toughness is a measure of the ability of One method is simply to use a polymer the material to absorb energy. It is related to stiffness or cost. that is. it also can be achieved by adding ergy. rotates. Usually. Elon- energy. How. Opacity is usually accomplished with filler The best situation is to have both the or a finely woven reinforcement material. Another way to improve elongation is to mix as has been already pointed out. and Applications . changes in the strength and therefore strongly dependent toughness of the matrix are the key to im- upon the nature of the reinforcement. reinforcement types. aramid fibers are the choice when toughness is a premium. lated to the strength of the composite which. ness is elongation. stiffness are often decreased significantly and the ability of the matrix and fibers to and so other critical polymer properties. toughness is dependent on the material to stretch when a force is applied. such withstand the accumulation of energy at a as the ability to pass loads onto the reinforce- particular point. This is Yet another method to improve elongation done when the matrix stretches. ments. which may be sufficient to the polymer are that the material be opaque break the matrix or the fibers at some spe- and that the reinforcements not be seen. the ability of the Therefore. other fibers have Toughness is a key property for many to be used because of such requirements as composite applications. the ity to absorb energy. is of most importance here because gation is usually improved but the resulting it is highly dependent upon the matrix. Polymers can be improved in their elonga- ment properties. How- Toughness ever. highly susceptible to attack by chemicals ing the impact energy to some other energy and UV light. As will be discussed in the chapter on pigments to the polymer matrix. Fundamentals of Composites Manufacturing: Materials. the more efficient the more freely. toughness is also strongly related to A key matrix property that affects tough- the ability of the matrix to absorb energy. type are usually aliphatic with few second- ness or the ability to absorb an impact. preferably heat and motion. this usually movement and the spreading of the movement means reducing the number of crosslinks. While this may improve toughness. control of resin viscosity achieved only with great difficulty. mer so it has a naturally high elongation which gives good wet-out. a critical function of the intermingling thermoplastic fibers with the matrix is simply to wet and bond to the fibers reinforcement fibers. is an important parameter to achieving suc. are currently used commercially. wet-out so they naturally have higher elongation of the fibers with thermoplastics can be dif- than do thermosets. and their job. This Because thermosets have a low molecular is especially important in thermoplastics weight before curing. it cannot penetrate the fiber bundles. There. Therefore. stage where the temperature of the material is higher and the thermoplastic is a liquid. pressing a wetted. so too does the viscosity. put into a mold. that thermoplastics do not undergo any and some key mechanical properties. (Remember ted and then the material is cured. At high molecular weights thick. However. environmental problems associated with the ness standards.2: Matrices and Their Properties 41 its solvent and gas permeation resistance. but the health and otherwise aromatic molecule to meet tough. or aromatic contents. This is a major limitation in the use of thermoplastic composites find use when of thermoplastics and one that is addressed toughness is an important property. including dusting the composite unless the fibers have been well fibers with thermoplastic powder. Dry fibers do not receive the transfer thermoplastic sheet onto the fibers as they of loads that must occur for the fibers to do are arranged in their layered structure. Some thermoset materials have during cure. for many applications. Therefore. the excellent properties that can be achieved cess in composite preparation. they are melted. WET-OUT OF FIBERS Several methods of introducing the thermo- The matrix cannot perform its duties in the plastic have been tried. thermoplastics have no crosslinks then cooled to solidify. It is also possible to Another method of wetting the fibers with mix highly elastomeric substances (rubbers) thermoplastics is to apply it as a solid and into the polymer matrix to achieve improved then achieve fiber wetting during the molding toughness. increases. the best method to increase toughness in a Some thermoplastic (and even some ther- polymer is to modify the nature of the poly. fore. have advantages and disadvantages and all nects all parts of the composite. but also requires without compromising (much) the other that the solvent be extracted either before or properties. this means the resin is too also increases. chemical reaction when they are molded. thermoplastic resin increases. rather. If the vis. the viscosity of some which are like groups of filaments in a string thermoplastics is so high that wet-out is or yarn. As the mo- The viscosity of the resin is the single lecular weight and aromatic content of the most important factor in wet-out.) As a result. some limitations exist in this method. with high-performance thermoplastic resins One problem immediately encountered is gives incentives to companies to resolve the that as the molecular weight of the polymer wet-out problem. Therefore. the majority ficult. in detail in the chapter on thermoplastic The most sophisticated and probably composites manufacturing processes. they are ideal for use because they do not change their molecular with composites because the fibers are wet- weight as they are processed. This type of molecule seems presence and recovery of the solvent often to have the balance of properties required make this method unpractical. All of these methods and form a continuous phase that intercon. Methods. and Of course. Not only does this require ad- incorporated aliphatic segments within an ditional processing steps. This fact Fundamentals of Composites Manufacturing: Materials. moset) resins are applied from a solvent. and Applications . the viscosity cosity is too high. benefits such as fire retardation. not. inhibitors. but is most often done in Nevertheless. Therefore. the term “resin system” includes lar viscosity for some molding operation. common. electrical property enhancers. of the resin and filler will be less costly in terms of total weight or total volume than VISCOSITY CONTROL AGENTS. such as as the resin and fibers. additives are most obvious effect of the filler is to thicken not considered to be essential components the resin mixture. such as a manufacturer of mold- can be a major component of the mixture. Fillers can also impart some special cussed later. occasionally. and tougheners. impart some other beneficial property. This can be done by the property. ing reasonably low concentrations of fillers Some are general and find wide use. basic composite materials (resin system and Fillers are usually mixed into the liquid reinforcements) to improve some specific or molten resin. thus no particular length-to-width ratio and are assisting the molder in knowing when wet. but are. Note that in this when the material needs to have a particu- sense. The tively high concentrations. care must always be most common fillers are common minerals. and Applications . Methods. fillers. Fillers usually have often changes when they are wetted. solvent. and cure system. ticles. PIGMENTS. the resin. care should be taken in adding Some additives have already been dis. therefore. or Fundamentals of Composites Manufacturing: Materials. Cost reduction is usu- SURFACE AGENTS ally the most important reason to use fillers Additives are the materials added to the in composite materials. instead. ing compounds. thermoset formulations by the molder. The general types are considered in ments. One method to specific matrix-dominated properties. even when present in rela. color. thermoset material. the higher viscosity usually re- are all essential to the basic formation of a duces the ease with which fibers are wetted. although some increased stiffness or this section and those for a specific resin reduced strength and reduced elongation is type are considered when that resin is dis. Fortunately. ensure that the filler/resin mixture will still ditives include flame-retardant materials. Ad. others are used only with one particular especially in the presence of fiber reinforce- resin. fillers to ensure that the resulting mixture cussed in this chapter as they related to will still wet-out the fibers. Fillers usually cost much less than the resin and therefore any combination ADDITIVES: FILLERS. while to the resin mixture is generally not large. pounder. which have been the color or sheen of the reinforcement fibers purified and ground. such as limestone and talc.42 2: Matrices and Their Properties alone may have led to the overwhelming use Fillers of thermosets with long fiber composites. although one. UV limits. the pure resin itself. taken to achieve good wet-out. Fillers are solid materials ground to (The short fiber composites can be wetted fine powders and added to the resin mix more easily and therefore thermoplastics are to reduce overall cost and. Many other The effect on mechanical properties of add- additives are used with matrix systems. at least not to the same extent this thicker mixture is desirable. par- ting has occurred. fibers. For some applications of the mix. to often used. which However. wet the fibers is to control the viscosity of such as halogen-containing resins or special the mixture so it stays within acceptable fillers.) Even with the ease of fiber wet. The ting using thermosets. Most additives are present in only resin manufacturer or by a special com- small concentrations. erally. ther the polymer. Hence. Fundamentals of Composites Manufacturing: Materials. been well formulated as can be seen from its An equally troubling problem is when a superior performance against the normally certain amount of filler is needed and the vis. These secondary bonds will are presented in Table 2-3. might be added to thicken the mixture. Using viscosity Pigments and Dyes reducers also allows higher filler levels to be The color of a composite is affected by the used for purposes such as cost or flammabil- way light is absorbed or diffracted by ei. excellent thermoplastic. In these cases. and Applications . able that reduce the tendency of materials to als can be ground. Often. additives are avail- also known as dyes. but sometimes they cannot be used or. Alternately. Additives that cause specific light Surface Agents to be absorbed are called colorants. if the viscosity of the surface to be coated and facilitates wet- is too low. Dyes and pigments are available ing the charge or the energy on the surface in a wide range of colors and shades. this problem can be solved Viscosity control is important for the by adding a surfactant to the resin mixture. thus colorants can be organic. For instance. clearly illustrates the effect of the resin in This is accomplished because there is some reducing the amount of impact. decompose with heat and are therefore not the standard epoxy has more extensive dam- important in the final product. The Some resins have a tendency to foam. Surfaces that might have side of the mold or drip off the fibers. Methods. fibers. inorganic powders called foam.2: Matrices and Their Properties 43 dimensional control (called low profile and cosity of the mixture is too thick. even with fillers the material is still too thin. complicating their application especially containing molecules. Gen. but during age than either the toughened epoxy or the processing they add considerable viscosity thermoplastic. or additives in the material. of the resin or filler particles in the mixture. based on carbon. a thixotrope can be Toughened Resins used to significantly increase the viscosity of Some resins have been modified to become the mixture with the addition of only a small tougher. Such thinning is especially important for fiber wet-out and spraying. Pigments are also more stable at Another problem associated with the high temperatures. (vibrant). discussed in the section on molding com. dyes are more subtle in color than Silicones are materials that can serve as pigments but pigments are more intense anti-foaming agents of this type. The results secondary bonding induced between the of a standard impact on three composites polymer chains. In this case. Fillers this problem include molds and fibers. in which case they are with spraying. The toughened epoxy has to the resin mixture. alter- CASE STUDY nately. These additives usually work by chang- pigments. the materi. surface energy and charge is the tendency of some surfaces to not be wetted by the resin Viscosity Control Agents mixture. proper molding of resin mixtures to make The surfactant changes the charge or energy composite parts. ity control. which can give a significant damage that occurs with a particular type increase in viscosity either by itself or with of impact. the material might run down the ting by the resin. pounds in the polyester chapter). The results of this type of modifica- amount. additives can be used to thin the material. As can be seen. A common material of this type is tion can be seen by comparing the extent of fumed silica. A comparison of three materials the addition of special thixotrope enhancers. The melting point or freezing the resistance of the composite to solvents. When crosslinking ness. Matrix materials dominate some proper. Hence. and cooled to solidify. temperature. and when there is primary to improve its elongation will improve tough- bonding or crosslinking. Fundamentals of Composites Manufacturing: Materials. These changes may include adding occurs. The matrix dominates transitions.3 (37) 0. They are molded plastic is obviously different.2 (5. A They are melted. crosslinks is called curing.44 2: Matrices and Their Properties Table 2-3. those without them are called thermoplas- This is an indication that their chemical tics. Resin Type Standard Epoxy Toughened Epoxy Thermoplastic Damage area. all the terms. Comparison of three matrix materials after a standard impact. test is a measure of the amount of solvent Matrix materials are often classified by interaction with polar solvents. Therefore. The thermo.3 (37) 1. As the intermolecular both the matrix and the reinforcement. with various other additives and the fibers. modifying the polymer so cally increased. toughness is im- tanglement or intertwining. The most common interaction is en. point is dependent on the nature of the stains. the standard and toughened epoxies with crosslinks are called thermosets and have the same amount of moisture pickup. having much by mixing the resin. rubber material. Other matrix-dominated properties are ties of composites. the melting point in.5 (10) 2 (13) Weight gain with water. This will usually raise the it has segments that have high elongation. (g) 1. mixed with additives and plastic is the material after it has its final reinforcements. The linked materials cannot be melted—they weight gain of water under a standard soak decompose first. This ability to diffuse energy is when the molecular weight is greater. matrix and on the amount of interactions Toughness is a property dependent upon between molecules. The most important of mostly associated with agents in the environ- those properties is associated with thermal ment of the composite. Thermoplastics can polymer. decomposition temperature. and then placed into a mold shape. the molecular weight is dramati. Those seen. be melted again because no crosslinks are ably by many people. Methods. When a matrix can effectively diffuse the creases. However.5 (22) 1. when closely associated with elongation of the secondary bonding or intermolecular attrac. oz. are used interchange. yet been molded to its final. Then the mixture is placed into a SUMMARY mold where it is heated so that the cross- The matrix can be called a resin and may links form.2 (cm2) 3. the crosslinks are formed. The process of forming the even be called a plastic.7) The chemical nature of the materials is melting point so high that it is above the assessed with the results of the solvent in. resin. useful form. Thermoplastics a resin is a polymeric material that has not are usually solids at room temperature. usually a liquid at room lower water absorption. plastic. in. cross- teraction test also shown in Table 2-3. fire. polymer. formed. The thermosets cannot be melted after nature is still about the same. interactions increase. As can be whether they have crosslinks or not. which is higher proved. gases. Strictly speaking. and Applications . energy from an impact. and light (UV). and matrix. changes in the polymer tions are present. It can be contained in a battery 4. viscos. and Applications . about 12 × 12 in. However. perature. Therefore. fiber are the same in all the samples. Cure the thermal-cure epoxy in of a standard viscosity. or some other modification made that perature because of the higher number will give good fiber wetting. Place a sample on the test apparatus and then pour the melted resin onto a and heat to the point of deflection as pile of fiberglass mat. The supports. 2. Some of polyester will typically be lower than the more common additives are fillers.5 × 30. wet the fibers completely. Obtain some thermoplastic resin. Obtain several sheets. Methods. LABORATORY EXPERIMENT 2-1 Determining the Heat Distortion LABORATORY EXPERIMENT 2-2 Temperature Fiber Wet-out Objective: Determine the heat distortion temperature (HDT) of a composite. Note that the HDT into the fibers so they are fully wetted. If the nificantly different HDTs. Note the time and effort required to wet 2. Make several piles comprised of polyester. Note the time and effort required. ing up sheets of fiberglass cloth with a (30. and two samples with a thermal. Pour the resin at two different temperatures. Cut the samples into the specified the fibers. and deflection gage are is. in using two different types of resins—a ing the maximum use temperature for a thermoset and a thermoplastic—to make composite. sively. a solvent than the same epoxy cured at a low tem- added. Make several composite samples by lay. 1.5 cm) of a standard fiberglass room-temperature-cure unsaturated mat. the epoxy because of the nature of poly- ments. a room-temperature-cure two layers each of the mat. laboratory container. Work the resin specified in the test. apparatus can be made quite inexpen. a high treatment materials. The higher matrix viscosity is too high for good fiber cured epoxy should have a higher HDT wetting. This will be D648). Procedure: Procedure: 1. dimensions (see American Society for 3. including the elimination of crosslinks (that pressure rod. Heat the pellets to melting 3. Discuss the problems and advantages of jar or some other heat-resistant glass each of the resin wet-out experiments. pig. amount of crosslinking could alter the order somewhat. the heat can be raised. readily obtained from laboratory supply The matrix cannot do its job if it does not houses. and surface esters versus epoxies. using a thermoplastic). Obtain some unsaturated polyester res- cure epoxy. ASTM preferably polyethylene. of crosslinks formed at the higher tem- Several additives can improve the perfor. composites. Make onto one of the piles of mat and work it sure the percent weight of resin and into the fibers so they are fully wetted. epoxy.2: Matrices and Their Properties 45 and reducing the intermolecular interactions. The HDT of the unsaturated mance or cost of the resin mixture. 4. viscosity control agents. which Objective: Determine the differences is a simple and effective method of assess. Testing and Materials standard. Fundamentals of Composites Manufacturing: Materials. in pellets. The materials should all have sig- ity control of the resin is important. 5. Explain why polymer. MI: Society of Manufacturing 9. Explain why a crosslinked material the polymers? What happens when cannot be remelted at high tempera- these materials are heated above ture. Explain the differences between the at room temperature. 3rd Edition. 1995. What is aromatic content and what Engineers. 1. such similarity between solvent and poly- as Teflon®. Methods. “Composites. and thermoplastics (solids) in terms of molecular weight. focus- ing on the molecular properties of 2. likely cause of this condition. room temperature? 3. Indicate what is meant by a polar flammability of a polymer and how material. OH: ASM International.” Mate- fewer but longer polymer chains than rials Park. Strong. Engineered Mate- tion reaction be expected to create rials Handbook. Arlington. Association. Discuss the concept of chemical 13. What is molecular weight? Discuss ing. Dearborn. Explain the room-temperature condi. Inc. Brent. “Composite Materials” DVD from the the following properties: toughness. besides molecular weight. A. www. Composites Manufacturing video series. What can be done to improve wet-out of fibers if the viscosity of the resin is too high? BIBLIOGRAPHY 7. VA: Composites Fabricators why it must be determined as a sta. Upper Saddle tion of uncured thermosets (liquids) River. plastic. Why would the addition polymeriza. tistical average. What happens to thermosets and thermoplastics when they are cooled below room temperature? What happens to ther- mosets and thermoplastics when they are heated above room temperature (under curing conditions)? Fundamentals of Composites Manufacturing: Materials. are its effects on flammability and Strong. Plastics: Materials 11. 8.sme. and strength. can only be melted with mer and how that similarity might great difficulty because they begin to affect the solvent sensitivity of the degrade when heated.org/cmvs. Some thermoplastic materials. Give two factors that determine the 14. and Applications . What is the terms resin. this is so. and polymer. Discuss how crosslinking might affect 2005. gas permeability. Fundamentals of strength? Polymer Resins for Composite Manufactur- 10. 2006. ASM International. Brent. What is an example of another property. Some thermoset materials are solids 1. Explain how toughness can be im- which can raise the melting point of proved in composites. Vol. and Processing. those might be useful or not in actual products. 4. the condensation reaction? Society of Manufacturing Engineers (SME). NJ: Prentice-Hall.46 2: Matrices and Their Properties QUESTIONS 12. 1987. polymers? 6. A. 15. thermoset polyes.1: Introduction to Composites 47 3 Unsaturated Polyesters CHAPTER OVERVIEW base in developing technologies and design This chapter examines the following parameters. how- • Polymerization of unsaturated polyes. In general. not to the total market volume of unsaturated the least of which is low cost. by far. and Applications 47 . Other resins may continue to take ters (TPs) are. and golf carts. of choice. alter. and the resins of first choice for many composite specialized monomers products. But these markets are not detrimental spread application is due to many factors. the advantages seem to outweigh the ters disadvantages and polyesters continue to be • Effects of various diacids. glycols. ever. a wide range of of composites. ease of molding. However. was built. and a wide experience plastics (FRP) or more simply just fiberglass Fundamentals of Composites Manufacturing: Materials. poly. brittleness. the resin on which the composites industry nately and equivalently. and uses air pollution difficulties. such as fiberglass reinforced property possibilities. It is just this possibility of OVERVIEW OF POLYESTER RESINS widely varying properties that originally led AND THEIR USES to the adoption of unsaturated polyesters as Unsaturated polyesters (UP) or. some specific property or combination of prop- They are used in applications such as boats. polyester thermosets concepts: have several drawbacks or disadvantages in properties and manufacturing such as • Overview of polyester resins and their relatively poor durability. most of which is less than vinyl esters and about 33–50% less based on polyester thermosets as the resins than epoxies. Several companies make polyester resins • Crosslinking mechanisms and therefore have vested interests in their • Crosslinking agents continued marketplace dominance. Polyester thermosets have become so ester thermosets have advantages in ease prevalent that references to broad categories of cure. This wide. Methods. Unsaturated polyesters because of the overall growth of polyesters are commonly priced about 25% the composites industry. the most commonly portions of the composite market because of used thermosetting resins for composites. tion. These • Cure control additives companies are active in improving polyesters • Molding compounds by creating new permutations of the basic building blocks used to make them and by • Property optimization inventing new building blocks from which they can be made. In addition to their cost advantage. erties that uniquely fit a particular applica- corrugated sheets. and wa. and Applications . Methods. oil and gas. The output product of construction make polyester thermosets from the polymerization reaction is unsatu- the major resin of the construction and rated polyester resin and it is usually sold home-building market. The first Most boats. ter transport and treatment.” the type of polyester used for curing—clearly separate in your mind. POLYMERIZATION OF UNSATURATED tics. from various chemicals (monomers) using tions for unsaturated polyester (UP) or ther. some automobiles use ther. that is. Another major point of clarification is Essentially every brand of automobile and appropriate before discussing the details nearly every automobile model use polyester of polyesters. are one of the major resin types for tanks The second process important in un- and pipes used to contain non-corrosive saturated polyesters is crosslinking or chemicals in industries such as paper and curing. They do not form crosslinks.). the term No list of uses of polyester thermosets can “polyester” will refer to the thermoset resin possibly be complete. the actual making of the unsaturated hull and often for the deck and. polyesters used for soda bottles or for fibers. some appreciation for the scope of its market. and many other items inherent limitations. The polyesters used for Therefore. many of the masts and other fittings. composites and thermoset resins.48 3: Unsaturated Polyesters (which seems confusing since this name does soda bottles and fabric are thermoplastics. available and in discovering some of their spas. these applications is different from those used in typical composites. especially small pleasure craft. An understanding of the molding and their total operations. An overview of polymeriza- major appliances use polyester thermosets tion will be given because it will assist in for pump housings. This process is done at the time pulp. Polyester thermosets in bulk (tank cars. not address the existence of a matrix). To avoid confusion. ties of the part and the molding economics Note that no mention has been made of strongly depend on how curing takes place. as explained in Chapter Two Fundamentals of Composites Manufacturing: Materials. It can be safely said curing process is necessary because this step that polyester thermosets are practically also determines many of the final proper- everywhere. Tub and shower units. and vari. Because this book focuses on polyester. The differences are those of thermosets versus thermoplas. for sailing polyester resin. sheet molding compounds (SMCs) automati. The polyesters that dominate the com. The polymerization step ships. that use polyester as the principal material for the is. Virtually every when the unsaturated resin is mixed with major manufacturing industry in the world the reinforcement and molded to make a uses polyester thermosets in some part of part. building panels. POLYESTERS posite market have a reactive unsaturated Polyester resins are made (polymerized) site and are thermosets. is usually done in large chemical plants by Most clothes washers. Two different chemical pro- thermoset parts. understanding the types of polyester resins ous other components. the condensation polymerization reaction. of molding of the composite parts. but a short list can give unless specifically stated otherwise. then using thermoset polyesters. etc. moset polyester (TP). chemical processing. hence the abbrevia. barrels. driers. and many other resin producers. motor shrouds. of these processes is polymerization. cesses are important in first making and mosets for almost their entire body structure. so they are not cally imply that the resin is a thermosetting thermosets. and usually polyethylene terephthalate (PET). it is important to keep Although these materials are made from these two processes—polymerization and “polyesters. ” but it Figure 3-1. each The polymerization reactions for making a of the monomers must have two active typical polyester are depicted in Figure 3-1.” Occasionally. will be referred to as simply “acids. the diacid ester groups. These reactive with polyesters.” “Glycol” is the name given to molecules materials. types must react with each other to form The reactive groups on glycols are the OH a linking entity that ties them together. side of a central group labeled as a generic As was discussed in the chapter on matrix “G. the name of polymers formed by with two alcohol groups. composed of the atoms COOH and some- ated in the reaction. This is exactly the case times called carboxylic acids. the two monomers that combine reactive group).3: Unsaturated Polyesters 49 on matrix materials. ends (called difunctional where the prefix As shown at the beginning of the reaction “di” means two and “functional” means sequence. Further. where the links formed as acid groups are shown on either side of the a result of the polymerization reaction are generic diacids. And. Methods. They are located on either condensation by-product is also formed. at least two types of Polymerization Mechanism monomers must be present. “A. Fundamentals of Composites Manufacturing: Materials. and Applications . The reactive groups the condensation method is often “poly” in the diacids (meaning two acid groups) are plus the name of the new linking entity cre. Polymerization of a typical polyester. A (alcohol) groups. the two monomer to make polyesters are glycols and diacids. that favor the formation of long chains Both ends can react with new monomers to and can run the polymerization reactions further elongate the molecule. Indeed. They are react with each other provided the alcohol joined by an ester linkage. by adding a quenching agent that will react ously. the result. the concentrations of the diacid and glycol The term alkyd (pronounced al’-kid). that is. de. A. the ester linkage is quite polar and so some tive ends. reaction also could be stopped by simply Typically. the term “alkyd” refers lowering the temperature of the reaction. polymers. however. the condensate by-product. Many of these properties are pres- together in an alternate arrangement. Polymer Properties and Control mer and the acid end reacts with a new glycol The properties of polymers are dependent monomer. end of one chain encounters the acid end ter the new molecule has been formed. non-polymer ester compounds. Also. alcohol ends react with peratures. tions with more new monomers. One is obviously the sults in the formation of a new ester linkage presence of the ester group. monomers become so low that continued rived from a contraction of alcohol and acid. These reac- must have two reactive groups. For example. and Applications . such as water. a new polymer chain can begin called an ester linkage. Or. the H on the glycol and the OH mers with the active ends of the growing on the diacid join together and form water. and two glycol groups. The resulting molecule still has two ac. to those polyester resins used for paints and since these types of reactions are carried quick-drying molding compounds. Chemists operating polymer- new molecule still retains two active ends—an ization reactions have found conditions alcohol end (OH) and an acid end (COOH). Methods. growth is not possible. Simultane. such sensitivity the ensuing reactions will follow the same is seen in polyesters. This process is shown as Step 1 in Figure 3-1. even in commercial that is a combination of the original glycol polymerization operations. are known in organic chemistry to have a When Step 2 has been completed. Each of would be expected. “di. both chemical and ing molecule has three ester linkages joining physical. The initial linkage whenever a diacid encounters a glycol. The polymerization is another name for unsaturated polyesters. set of typical properties. upon several factors. thus permitting additional reac. atoms about this link is characteristic of At any time during the polymerization the organic group called esters and so it is reaction. two ent in the polymerized products as well as acid groups. the reactions can be ended H2O. These chains can and the original diacid monomers. tions can continue in the same pattern until acid” is the more appropriate term. that of another. Ester groups and the elimination of a water by-product. G. note that af. of the active ends with new monomers. Polyester resins typically absorb diacid monomers and acid ends react with significant water at about 200° F (93° C) and glycol monomers to form ester linkages and lose significant strength when that absorp- Fundamentals of Composites Manufacturing: Materials. to optimize the length of chain (molecular Step 2 in Figure 3-1 shows the reactions weight) as desired. ease of beginning a chain often leads to many Note that Step 1 has resulted in a molecule chains being formed. sensitivity to polar solvents. out at high temperatures to facilitate the When a glycol comes into contact with effectiveness of the encounters of the mono- a diacid. Each of the reactions in Step 2 re. hence. The alcohol end reacts with a new diacid mono. the O on the glycol bonds with the C with the end of the chain but will not have in the acid group. The arrangement of the an active site for further reactions.50 3: Unsaturated Polyesters should be clearly understood that each acid water by-products in each case. especially at high tem- pattern. ASTM D1639. how long of these carbon-carbon double bonds in the the polymer chains have become. such as chemical resistance and molecules. EFFECTS OF VARIOUS DIACID. polyester molecule. Therefore. tional chemistry techniques such as titration. some of the low-melting solid resins. As the mo.Of content could be present because the reac. the diacid lecular weight of the polymer increases. Residual acid explaining the polymerization reaction. The name unsatu- of the extent to which the polymerization rated polyester emphasizes the presence reaction has proceeded. the name given is in polyester thermosets. Methods. meaning carbon-carbon taken when the polymer solution is hotter double bonds in aliphatic compounds. The viscosity measure.3: Unsaturated Polyesters 51 tion occurs. to occur.000. (See the American erties of the polyester is the choice of the Society for Testing and Materials standard. as is than the conditions used in defining a stan. The acid number is a measure of the Typical molecular weights for these materi- amount of acid monomer that has not yet als are 800–10. residual acid content is reduced in the choice of diacid or glycol is determin- by conducting the polymerization reaction ing which of these monomers will contain in an excess of glycol and ensuring that the the unsaturation required for crosslinking acid number is below a certain value. Water absorption at low tem. ceeded. (The specific mechanism of this Processing viscosity is another critical crosslinking will be discussed in a following parameter monitored during the polymeriza. AND SPECIALIZED Titration of the acid by a base can be done quickly and automatically. the is the monomer that contains the carbon- viscosity increases. course. for details of the test. Under standard conditions. carbon unsaturation. organic molecules that contain the carbon- The processing viscosity is also a measure carbon double bond. section. therefore. but are more difficult to process. that is. This was done for simplicity in stability of molecular weight. The amount of acid not reacted (acid number) can be determined using conven. Higher-performance res- been reacted and.) Unsaturation is a term applied to tion reaction along with the acid number. One of the most important considerations Generally.) Figure 3-1 has represented these monomers in High amounts of residual acid groups have a generic form (with the letters A and G). thus giving a rapid MONOMERS and reliable measurement of the state of the A factor that strongly affects the prop- polymerization reaction. the case in most of the common diacids used dard viscosity. GLYCOL. These peratures. The term olefinic ment during the polymerization reaction is unsaturation.000 A list of the most commonly used un- centipoise (thick liquids) and even higher for saturated diacids is given in Figure 3-2.” that can be found in the literature. Normally. this does not represent any real sys- tion was not carried out to completion or tem since specific monomers must be chosen because the amount of diacid monomer was when the polymerization is done. permeation chromatography (GPC). The Fundamentals of Composites Manufacturing: Materials. liquid un- saturated polyester resins range in viscosity Diacid Monomers from 50 centipoise (thin liquids) to 4. is usually not a problem. a measure of ins tend to have higher molecular weights. greater than needed to react with the glycol. is another name properly a “processing viscosity. and Applications . as would be encountered with a viscosities are typically determined by gel motor boat. not been shown to be detrimental to several key giving the actual formulas of the monomer properties. specific types of glycol and diacid monomers. how far the polymerization reaction has pro. rated polyesters. (Fumaric is form shown in Figure 3-2. maleic anhydride pronounced foo-mahr’-ic).”) Although not strictly a diacid in the opposite sides of the molecule. is double bond (unsaturation site) is critical converted into the trans-isomer under the for the crosslinking of polyesters. has the same atoms. but in this fumaric or maleic acids. chapter. the presence of the carbon-carbon which is not as stable as the trans-isomer. and Applications . Unsaturated diacid monomers typically used in making polyester thermosets. The second molecule. (Maleic used in commercial production of unsatu- is pronounced mah-lay’-ic. maleic anhydride is case the acid groups are on the same side the most common of the unsaturated diacids of the carbon-carbon double bond.) This arrange. H2O removed. pound can be thought of as maleic acid with bons. The third unsaturated acid group (COOH) and a hydrogen atom molecule is maleic anhydride. fumaric acid. Because the cost to make maleic atomic arrangement. An erization occurs. (Anhydride means “without the acid groups are arranged so they are on water. In the first molecule. anhydride is substantially less than either maleic acid. ment is called the cis-isomer where “cis” As will be shown in a later section of this means “on the same side. Every Fundamentals of Composites Manufacturing: Materials. This com- are attached to each of the unsaturated car. This arrangement readily converts to maleic acid and then to is called the trans-isomer where the term fumaric acid under the conditions of polym- “trans” means “across” and “isomer” means erization. Methods. carbon-carbon double bond (unsaturation) conditions normally present when polym- is in the center of each of the molecules.52 3: Unsaturated Polyesters Figure 3-2.” The cis-isomer. that is. diacids will now be examined. sometimes the concentrations and conditions of the referred to as a general-purpose polyester crosslinking reactant to achieve the level thermoset. “iso resins”—two of the most common saturated diacids.3: Unsaturated Polyesters 53 carbon-carbon double bond is a potential and achieved polymers with a wide range site for crosslinking. This is most easily to an aromatic ring on adjacent carbons done by mixing the two types of diac. Replace some of the unsaturation sites The proper name of the monomer from with saturated sites. improved strength. It converts to the second method.) The orthophthalic anhydride. materials. The various resin manufacturers have Isophthalic acid (pronounced eye-so- tried a multitude of different saturated diacids thal’-ick) is the second most common of the Fundamentals of Composites Manufacturing: Materials. ortho has low cost and good technology is used to optimize the prop. Simply conduct the crosslinking reac.) Because polymer structure to be tightly tied together of the widely varying properties that can and impart brittleness to the final part. acid where the two acid groups are attached carbon double bond. Methods. Ortho is. improved stiffness. both methods of limiting linking reaction is discussed.) Two be achieved from the choice of saturated methods are commonly used to accomplish diacids. (More about this A molecule related to orthophthalic acid is will be discussed later in this chapter. therefore. of crosslinking desired. so its properties are the same as the ortho trolled by the manufacturer of the polyester diacid. Those properties include of the various types of diacid monomers. the various polyesters are often this limited crosslinking. Compared to the other common satu- the technology of polymerization. This rated diacids. 3-2. are present in this and the other Because of differences in the reactivities aromatic diacids. use some which ortho resin is made is orthophthalic diacid monomers in the polymerization acid (pronounced or-tho-thal’-ick). will become more meaningful as the cross- Commercially. polyester resins tion so that only some of the sites are are often referred to as “ortho resins” or reacted. Unsaturated crosslinking are used. lower the order of addition and the conditions flammability. (The typical formed at a tremendous number of locations mixture of diacids used to make a cross- on each molecule. nate with the glycols along the backbone of A list of the most common saturated the polyester molecule. named according to the type of saturated 1. and lower resistance to UV under which they are added is part of light. Experience has shown linkable polyester would be one from the that the best properties are obtained if some unsaturated diacids illustrated in Figure of these potential sites are not crosslinked. polymerizing with both diacid under polymerization conditions and saturated and unsaturated diacids. of properties. Since the polymeriza. The first method. discussed in the chapter on matrix double bonds and those that do not. polyesters containing ortho are the most limiting the number of sites that reacts. styrene compatibility. and one or more from the saturated (Too many crosslinks can cause the entire diacids illustrated in Figure 3-3. is con. common of all the types commercially is controlled by the molder who can vary available. around the ring. It is a di- reaction that do not contain the carbon. The properties of aromatic ids—those containing carbon-carbon materials. For example. and Applications . 2. crosslinks could be diacids is given in Figure 3-3. This latter property erties of the polyester molecules. The effects of these various tion reaction results in having acids alter. diacid used. resin. Fundamentals of Composites Manufacturing: Materials.54 3: Unsaturated Polyesters Figure 3-3. Saturated diacid monomers typically used in making polyester thermosets. Methods. and Applications . However. Both com- in the structures of the monomers can re. Adipic has other carbon. The major differences between (Halogens are F. therefore. the presence of halogens helps to smother water. Glycol Monomers called the gel coat. the longer Fundamentals of Composites Manufacturing: Materials. It may be surprising that ortho than the aromatic diacids. common application for iso polymer is as the outer coating for a composite part. Several gly- usually not at elevated temperatures. has the added advantage of imparting chemi- cause it is more costly to make. flame-retardant monomers. small changes the conditions of polymerization. There are many and iso have different properties since they other non-aromatic (that is. properties. This layer. cols can be chosen as monomers in making Terephthalic acid (pronounced tair-a. But in iso. ring with attachment on two carbons sepa. toughness. The most cal resistance. which Tetrabromophthalic anhydride affects the manner in which the polymers (pronounced tet-rah-brom-oh-thal’-ick) and can pack together. Since these intermolecular interac. It aromatic ring. the attachment expensive. Br. usually measured by an increased flexibility and toughness are imparted to the heat distortion temperature (HDT). and tere. iso. Therefore.” a are also used in applications where moderate name that reflects the presence of two alco- chemical or water resistance is needed. and resistance to heat. It also has improved weathering but has some important differences from (better resistance to UV light and oxygen) ortho resins. it has two acid groups attached to an very different from ortho. Iso resins Glycols are occasionally called “diols. good properties. Tere is the third possible ar. polyester molecule.3: Unsaturated Polyesters 55 polyester thermosets (behind ortho). and I atoms. must be the first line of The polymerization reaction for making defense against the environment. Polymers con. the attachments is not aromatic and. The most commonly used glycol monomer in rangement of two acid groups on an aromatic unsaturated polyesters is ethylene glycol. a better job at that than does ortho. or otherwise chlorendic acid (pronounced clor-en’-dick) interact. Almost any halogen-containing iso strength over ortho strength is as much compound is flame retardant. pounds contain halogens and are therefore sult in substantial changes in the polymer’s effective in improving flame resistance. and chemicals. ortho or iso. additional resistance. If the number of carbons taining the tere group have higher thermal in the glycol chain is increased. points change the shape of the polymer. toughness and weatherability properties when the diacid monomers are incorporated besides adipic. Some commercial thal’-ick) or tere is less common than either glycol monomers are listed in Figure 3-4. Chlorendic acid Iso costs about 10% more than ortho be. much more elongation and is therefore Iso resin has the properties of aromatics tougher. are two compounds that are diacids under tions affect many properties. so the choices as 34% in non-reinforced materials and 10% listed here are just two of many possible in composites. intertwine.) As iso and ortho are that iso has improved discussed in the chapter on matrix materi- strength. but they are usually more into the polyester polymers. The improvement of the flame. but hol (OH) groups on the molecule. Like Adipic acid (pronounced ah-dip’-ick) is ortho. Methods. als. and Applications . Cl. chiefly because of its low cost and generally rated by two other carbons. and iso does polyesters is between diacids and glycols. aliphatic) differ only in the points of attachment of the compounds that can be used for their acid groups on the aromatic ring. is less rigid are to carbons separated on the ring by one (more flexible) and less strong. unsaturated polyesters. carbon atom content of propylene glycol hardness (a measure of the hardness of the contributes to its frequent use to impart material) drops from about 50 to about 25. Neopentyl matic characteristics. the molecule becomes more and so both strength and toughness can be flexible and tougher. improved over the other glycols already dis- Highly aliphatic glycols with up to nine cussed. Cost is. For example. also also adds weathering and chemical/water shown in Figure 3-4. However. than the simpler glycols. the Barcol nor glycols will react during the polyester Fundamentals of Composites Manufacturing: Materials. the resulting polymer becomes significantly Specialized Monomer Additives softer. is increased. and Applications .56 3: Unsaturated Polyesters Figure 3-4. greater toughness. somewhat higher atoms in the chain are used commercially. Even longer and more A common glycol used to impart some flexible chains are seen with diethylene aromatic content. with all of the normal aro- glycol and neopentyl glycol. however. Glycol monomers used in making polyester thermosets. compound also has some aliphatic content. This particular aromatic resistance. ic and illustrate that as aliphatic character the non-aromatic carbon groups on the ends. as the glycol chain is lengthened. is bisphenol A. These monomers are all aliphat. Methods. as the glycol chain is Some monomers that are neither diacids increased from 2 to 6 carbons. polymerization occurs. shown in Figure 3-5. the resulting material The resulting polymer is a polyester and. Methods. Another advantage is resin uniformity. isophthalic polyester of the material must be done before or during and bisphenol A fumaric acid polyester. followed to consistently result in good parts. recipe and single molding procedure can be The mechanical properties of polyes. equipment cialty monomers used to achieve enhanced conditions. Crosslinking or provements not possible with the standard curing has a major impact on the econom- diacids or glycols. Also. it is unsaturated. The fibers also must be positioned is the first chemical process used in making properly before curing has finished. to achieving good properties in the molded ene (DCPD). It desirable (usually) mechanical. with some training and ids. developed may no longer exist. can. hardness. polyester thermosets and it is conducted by The unsaturated polyesters are able to large resin companies. the glycol monomers (usually reaction. Pure DCPD resin has many interesting careful monitoring of the reaction variables. the principles of crosslinking can is. at least until the marketplace responds. When this happens. bonds are formed between the poly- only one type). At the most basic level. properties that may lead to its widespread the process can be kept within reasonable use in some of the markets now serviced by control parameters. DCPD can be polymerized by itself. becomes solid with dramatic increases in because one of the monomers has a carbon. be understood and. undergo crosslinking reac. right conditions. Some under which the original procedure was work has also indicated that the surface uni. which takes ments along the polymer chain that contain Fundamentals of Composites Manufacturing: Materials. ter resins made with DCPD as one of the Sadly.) and the circumstances mechanical and physical properties. During the crosslinking than one). other thermoset resins. without the presence of glycols or diac. and Applications . polymerization ity fluid. the curing reaction is a complicated monomers exhibit improvements in flexural process affected by many different variables. crosslinking is When the diacid monomers (usually more easily understood. Inevitably molding also typically achieved when DCPD is incor. as they are stored.3: Unsaturated Polyesters 57 polymerization process to give property im. reinforcing fibers must be introduced before curing so that they can be wetted by CROSSLINKING MECHANISMS the liquid resin while it is still a low-viscos- As previously indicated. stiffness. suppliers. modulus and flexural strength over conven. The resulting solid tions and become thermoset. and chemical properties. and other carbon double bond. some of which cannot be fully controlled by tional polyesters. so any molding unsaturated polyesters. Two typical material cannot be remelted. also improved when DCPD is present. acids and glycols by a unique ring-opening Some molders may believe that a simple mechanism. weather. conditions of ingredients the cost improvement over many of the spe. The second chemical form crosslinks because they have some seg- process is crosslinking or curing. porated into the resin. conditions will change (humidity. strength. One of the most interest. This chemical will react with parts. and any other specialized mer molecules. ics of the molding of parts and is critical ing of these materials is dicyclopentadi. place at the time of molding. are the period when the crosslinks are forming. Sometimes formity (lack of dimples or shrink marks) is poor parts are made without realizing it. physical. thus linking them together monomers are mixed together under the to form enormous interconnected networks. Improvement in HDT is any simple procedure. therefore. that However. etc. organic peroxides will split simple conditions—that makes polyester apart to form two segments.5 to double bonds to react and crosslinking to 2%) of material that initiates the curing occur. A generic poly- carbon double bonds were already present in ester polymer is shown in Figure 3-6a with some of the monomers that reacted to form the carbon-carbon double bonds specifically the polyester polymer and were not affected identified. other parts of the by the polymerization reaction as explained chemical chain. but these curing involves a series of chemical steps. steps is given in Figure 3-6. Methods. has an unpaired electron. affected by the polymerization reaction. Specific unsaturated polyester molecules. The carbon. each of which thermosets useful as matrix materials.58 3: Unsaturated Polyesters Figure 3-5. a carbon-carbon double bond. Crosslinks also Crosslinking Steps can be formed by mechanisms that do not The creation of the crosslinks during use carbon-carbon double bonds. For simplicity. a The curing or crosslinking reaction begins separate reaction is used after polymeriza. do not apply to the polyester thermosets and A simplified depiction of the crosslinking are discussed in later chapters. and Applications . are repre- previously. The most common initiator is an a time completely independent of the po. when the unsaturated polyester is mixed tion is completed to cause the carbon-carbon with a small amount (usually about 1. It is this capability—to crosslink at reaction. When heated or chemi- lymerization reaction and under relatively cally triggered. A chemical entity Fundamentals of Composites Manufacturing: Materials. Since these double bonds are not sented generically with the circles. organic peroxide. glycols and acids. Unsaturated polyester crosslinking reactions. Fundamentals of Composites Manufacturing: Materials. Methods. and Applications .3: Unsaturated Polyesters 59 Figure 3-6. the double bond disappears. of the carbons in the carbon-carbon double tiator on the carbon-carbon double bond. These segments containing electron on the initiator attracts one of the unpaired electrons are reactive and seek two electrons in double bond. is shown in Figure 3-6a. Methods. thus forming loosely held electrons with which they can a new bond between the initiator and one form a stable bond.60 3: Unsaturated Polyesters Figure 3-6. When one of the electrons has been in which one of the bonds has loosely held taken from the carbon-carbon double bond. the unpaired free-radical. electrons. with only a single Fundamentals of Composites Manufacturing: Materials. and Applications . containing an unpaired electron is called a As shown in Figure 3-6b. Continued. bond. The attack of this ini. This long applied the term “catalysts” to these could cause several styrene molecules to join peroxide initiators. These small molecules can move nants.3: Unsaturated Polyesters 61 carbon-carbon bond remaining. they are This is one of the reasons it is so critical to called reactive diluents. a new bond is formed between the free-radical located on the carbon atom. therefore. trons in the double bond. are both solvents and reactive agents. is another styrene molecule. with more poly- tion sites and allow bonding between them. However. the crosslinking reactions could be on one of these small molecules is shown in terminated prematurely and the desired Figure 3-6d. of a polymer. When a styrene electron. migrates to the second carbon where on the polymer. Some of these other solvents to give additional movement to the reactants can include oxygen. mers. the free-radical on These materials are referred to as initiators a styrene will encounter an unsaturation or peroxides throughout this text. molecules and. Because the free-radical can react with The process is finally terminated when any material having an unsaturation site. direct reactions between cal persists. The most probable or efficiency of a reaction but are not con. however. This chain-reaction mechanism often Hence. reactant. Because these small molecules number of crosslinks might not be formed. The new free-radical residing on the the two polymer molecules become linked backbone carbon is also reactive and together through the styrene bridge. if these other potential will. Methods. A common free-radical attack tions. eventually. The free-radical on the styrene to the polymer. will aggressively seek to bond with some The presence of several styrene molecules other electron that might be loosely held. In between polymers is formed. It now resides on the second polymers are difficult because the polymers polymer as shown in Figure 3-6f. and other peroxide (free-radical) about freely between the polymer chains and segments. by strict definition. Hence. Figure 3-6c shows the bond and the new occurs. and a new free- Note that initiators are consumed in the radical is formed on the styrene as shown in reactions they initiate by becoming bonded Figure 3-6e. control the concentration of initiator and The most common reactive diluent is any other material that might react with styrene—an aromatic ring attached to a free-radicals. in the bridge is depicted in Figure 3-6f. the free-radical could react the styrene is not shown as a single molecule with a carbon-carbon double bond site on but as a group. common usage has centration. where Theoretically. react with the free-radical site reactants are present in large concentra- on the polymer. Eventually. the free-radical reacts with something small molecules containing these sites are other than a carbon-carbon bond in styrene added to the polymer mix as co-reactants and or another polymer. attack is made on the elec- it becomes a new free-radical (unpaired elec. Fundamentals of Composites Manufacturing: Materials. site on another polymer. a rearrangement tron). The are relatively large molecules that do not free-radical might react with more styrene move around easily to line up the unsatura. polymers are linked together. the free-radi- practice. is erroneous. When this happens. and Applications . simply because of mobility and con- sumed therein. They are not. can then react with any unsaturation site true catalysts. polymer and the styrene. The other carbon-carbon double bond. contami- polymers. although that name in in a small chain pendant from the backbone this case. which was originally in the double molecule approaches the unpaired electron bond. therefore. which improve the speed that it might encounter. Even when the crosslink a neighboring unsaturated polymer. this direct linkage between polymers continues until most or all of the polyester occurs only rarely. curing reaction. obviously the temperature at which the cur- ecules or co-reactants. is so viscous that ef- ous because of their tendency to decompose. 2. in many cases.5 to 2% of the areas are thick and others thin. The small molecules. which. considered in setting the conditions of the mers used in creating the polyester polymer. also known as acetyl crosslinking reaction as a bridge between acetone peroxide (AAP). the types of linking agents generally have a second major chemicals that affect the activation reaction. Co-reactants. thick sections may retain exothermic heat Hence. and should be confuse the bridge molecules with the mono. Because the exotherm of several of these bridging molecules will adds heat to the system. the peroxides should if not thinned by a solvent. Therefore. The inclusion of Fundamentals of Composites Manufacturing: Materials. called an exotherm (meaning heat is molecules are called crosslinking agents. given off by the reaction). heating could occur and the part could be Several different organic peroxides are warped. Therefore. This liberated linking two sides of a chasm. function in the polyester curing process. the co-reactant dibenzoyl peroxide (BPO). and incomplete crosslinking. of these is methyl ethyl ketone peroxide Therefore. All peroxides are danger. tion should be given for the exotherm or While this explanation has focused on the reaction may proceed too quickly. These bridge heat.62 3: Unsaturated Polyesters Crosslinking Agents. Most room-tempera- ture cures involve MEKP and some chemi. consideration should be given to (MEKP). wet-out of the fibers. thus facilitating their linkage. (LPO). several ignition and fire.3-pentanedione or crosslinking agent is important to the peroxide (2. If some small quantities. Co-reactants and Crosslinking Agents as cal accelerator (as will be described later in Solvents and Diluents this chapter). and generally be stored in refrigerators and in Co-monomers small quantities. only a few initiator molecules not dissipated well through them. The just one polyester chain and the molecules dangers of reacting too quickly can include it bonds with. in actual practice. thermally activated. differential total resin weight.3 PDO). sometimes with explosive force under certain and other processing steps would be difficult conditions. The characteristics ing reaction is run. To not under some circumstances. link During the curing process. the initiators are only needed in and cause excessive heat build-up. different polymers throughout the mix. It is relatively stable and has the this possibility when designing equipment capability of being chemically as well as for mixing and molding thermosets. heat is liber- the polymers together much like bridges ated as new bonds are formed. usually 1. If an exothermic reaction begins used commercially as part of the cure system to overheat. Methods. Polymers are good heat insulators so heat is Therefore. degradation and loss of initiator (peroxide) molecules will react properties. with several carbon-carbon double bonds to Another consideration is the dimensional begin these crosslinking reactions on many thickness of the material that is reacted. are needed to get the reactions started. The first consideration is this text will refer to them as bridge mol. Each one differs from the others in In addition to serving as a bridge. Other common peroxides are As described previously. such as styrene. and Applications . The most common be dispersed into a thinner configuration. and the type of resins with which it is most They are solvents or diluents for the resin commonly used. the cross- the temperature of activation. or co-monomers. it is critical that the material for polyester thermosets. some compensa- be discussed later in this chapter. can be a problem co-reactants. and lauroyl peroxide the polymers. ficient curing reactions. “reactive diluent. grees. itself has shrinkage of about 3%. crosslinking agent will be used up in forming adjusted for the amount of co-reactant pres- the crosslinks and no residual free solvent ent. which curing takes place. they are also co-reactants. Methods. ally beneficial properties are the basis for its widespread acceptance and use as the Curing most common crosslinking agent. both are important for polyester as that could significantly erode the physical thermoset applications. changes in properties attributable to styrene tures. This is because they add type of behavior is exhibited by all of the mass to the system and that mass must be crosslinking agents. it of solvation and bridging (co-reaction). the shrink- those solvents that also serve as bridges. therefore. thus allowing them These alternate curing reactions will not be to align more readily to achieve effective covered in this textbook as they are much linkages. ture has. low water of the finished product. these are absorption. Styrene. This double na. although at different heated to achieve the same reactivity level concentration levels and to different de- as would be present with just resin. One also adds susceptibility to UV light. Even with greater content but then decreases as those crosslinking agents that allow room. Because of the particular co-reactant. most of the room temperature and elevated tempera. Those that contain the allyl group. This same slow the reaction. systems. strength initially increases elevated temperatures for curing. However. The first chemicals brittleness. The crosslinking agent can affect other which is aromatic. But when This problem has been solved by choosing a crosslinking agent is present. and thermal stability to the generally less important than its functions crosslinked polyester product. A potential problem with the inclusion of Each of the crosslinking agents has a a solvent in the curing mixture is that no characteristic exotherm and a characteristic solvent should be present in the final product shrinkage. the amount of styrene continues to increase temperature curing will. most or all of the range from a low of 7% to as much as 27%. certain effect is the change in the temperature at chemicals. led to the alternate term already introduced. which are listed later in the table. In general. Styrene. generally relative to the amount of resin. The polyester resin and mechanical properties of the composite. require For example. It also lowers the overall viscosity less important than the peroxide-based cure of the resin so that fiber wet-out is easier. the concentra- Some of the crosslinking agents are much tion level of the crosslinking agent should less effective with peroxide-initiated curing be optimized carefully for each particular reactions and tend to be used in other reac. therefore. and Applications . adds the typical aromatic characteristics of the curing reactions and properties of stiffness. linking agent. has shrinkage of about 17%. Careful research has indicated listed in Table 3-1 are generally capable of that as the amount of styrene increases crosslinking polyester thermosets at both relative to the amount of resin.3: Unsaturated Polyesters 63 the solvent greatly improves the mobility tion methods such as with ionic catalysts. go through a maximum for that property. The additional the common crosslinking agents are both shrinkage from the crosslinking agent can solvents and co-reactants. however. under some conditions.” A list Common Crosslinking Agents of common crosslinking agents is given in The low cost of styrene and its gener- Table 3-1. However. grade of resin. the most commonly used cross- will be left in the polymer. of the resin molecules. age increases by an amount characteristic that is. Fundamentals of Composites Manufacturing: Materials. and. strength. Methods. high flash point. Crosslinking agents (solvents/co-reactants) used with polyester thermosets. and stiffness. Crosslinking Agent Characteristics Styrene Low cost. thus improving the smoke rating discussed in Case Study 3-1. The emission of some composite resins. The ably the most common crosslinking agent United States government has established other than styrene. lower smoke density. low elongation. low smoke. molding compounds (pastes) Diallyl isophthalate Very low volatility. mostly for molding compounds Trimethylol propane UV and electron beam cures triacrylate Triallyl cyanurate (TAC) High HDT. low shrinkage Para-methyl styrene Low volatility.64 3: Unsaturated Polyesters Table 3-1. A strategy to problem with styrene and some of its other achieve improved overall flammability deficiencies has led to the adoption of several characteristics has been to use halogens to alternate crosslinking agents with polyester suppress the flame and MMA to obtain a thermosets. Some of the current tage that it gives off little smoke when it strategies to reduce styrene emissions are burns. low odor (MMA) Butyl acrylate and Good weather resistance butyl methacrylate Alpha methyl styrene Cooler cure. as is shown in Table 3-1. high strength. poor physical properties Vinyl toluene Low volatility. as a superior material for weather and UV try has adopted even more restrictive but light resistance. high flash point Diallyl phthalate (DAP) Very low volatility. thus improving upon Fundamentals of Composites Manufacturing: Materials. MMA is well known exposure limits for styrene and the indus. MMA also has the advan- voluntary standards. and Applications . reduced exotherm. molding compounds (pastes) (DAIP) Octyl acrylamide Solid co-reactant. multi-site crosslinking Triallyl isocyanurate High HDT Diallyl maleate High HDT Diallyl Fire retardant tetrabromophthalate A potentially serious problem with styrene Methyl methacrylate (MMA) is prob- is its effect as a hazardous material. good general properties and heat distortion temperature (HDT) Methyl methacrylate Good weather resistance. Some progressed so far that the material is hard. Two of avoid that heating. higher levels of create heat (exotherm). the molder may want to shorten the shipped in metal containers or dark glass time to cure or to cure at a lower tempera. Therefore. radical chain-reaction mechanism. and crosslinking agent—many dif. of all the potential sources of free-radicals. and Applications . the level of inhibitor should be the mixture can be sufficient to initiate the known so that the correct amount of perox- crosslinking reaction. cure reaction. Contaminants are also with proper choices of cure control additives. which increases initiator should be added to overcome the the reaction rate. to heat it. In some cases. Hence. in many polyester resins and styrene or other initiator.3: Unsaturated Polyesters 65 general-purpose resins in both flame and Both belong to the general chemical category smoke ratings. of the resin. All of these objectives can be achieved ing to the resin. inhibitor effect and carry out the crosslink- ture crosslinking and extend the shelf life ing reaction properly. reactive diluents. which is the time after the materials of inhibitor because they are more likely to have all been mixed and before the cure has become hot during transit or storage. the cre. resins should be stored in these additives is to slow the cure rate so cool locations. which will shorten the shelf life of the resin. manufacturer. some chemical methods Fundamentals of Composites Manufacturing: Materials. Some molders desire to Several types of inhibitors exist. such as those already been discussed—polyester polymer. they of inhibitor are present. such as when the mold is the most common chemicals widely used as large and would require an enormous oven inhibitors are hydroquinone and catechol. For example. that shelf life (storage time) will be longer. If cool storage is not available. Free-radicals also can the reinforcement or the time for placing the be created simply by the action of UV light materials into the mold is long. materials are often added that deactivate (or react with) free-radicals. thus Promoters preventing their reaction with the polyester Most organic peroxides are activated to resin. bottles to prevent UV light from penetrat- ture. Therefore. Methods. are especially susceptible ferent materials are routinely mixed with to decomposition by heat and they often thermoset resins to control the rate of the decompose to form a free-radical. Free-radicals can be created by several CURE CONTROL ADDITIVES mechanisms other than by decomposition In addition to the major components of of organic peroxides. Because Additives that accomplish all of these func. some the polyester thermoset mixture that have carbon-carbon double bonds. tions are discussed in this section. These materials are called inhibitors free-radicals by heating the material as it because they inhibit crosslinking. called free-radical scavengers. capable of creating free-radicals. resin manufacturers offer summer and Extending the pot life is usually desired in winter resins because of the differing levels cases where the process time for mixing of inhibitor added. resins are usually hand. When formulating the resin mixture ation of just small amounts of free-radicals in for curing. cures in the mold. Therefore. inhibitors are usually added. most resin mixtures contain a small amount Inhibitors of inhibitor when shipped from the resin Because polyesters crosslink by a free. On the other on the resin. to avoid prema. This is especially true ide initiator can be added. the purpose of whenever possible. When high levels because as the crosslinks are formed. Resins made A molder may also want to extend the pot in the summer often have enhanced levels life. the Co+3 is quite the actual molding operation. initiator and all other components of the cur- One safety caution is extremely important ing system. potassium. These materials are especial- ly useful in promoting the decomposition of Molding compounds are made so that dibenzoyl peroxide (BPO) to form free-radi. • Some time delay is required between magnesium. cure. Fundamentals of Composites Manufacturing: Materials. To ensure the entire mixture is packaged for shipment that this never happens. The inclusion of the initiator or the accelerator should be independently in the mix limits the conditions of storage. Because of the repeating better than the molder. The mixture could explode. Methods. the compounder mixes the and tertiary amine promotion systems. which the efficiency of the cobalt compound. to decomposition from these amines than To achieve this ready-to-use status.66 3: Unsaturated Polyesters have been developed to react with the or. perhaps prematurely. such as calcium. especially MEKP. However. either the peroxide and storage. Even at low tempera- is present. In practice. compounder than the molder in some such as dimethyl analine (DMA) and diethyl cases. to create to making these molding compounds. In the process. curing will slowly proceed. Hence. This step is often done by a manu- cobalt octoate. age of molding compounds is usually done linking may begin even when no promoter at low temperatures. These chemical materials pounds are made by mixing the resin or resin are called promoters or accelerators. based on the weight of the resin. tures. Therefore. usually less than 0. and copper. There are a few advantages to making a changes from a purple or pink to a green. MOLDING COMPOUNDS ganic peroxides and cause them to split apart Unsaturated polyester molding com- into free-radicals. solution with fillers and/or reinforcements The most common promoters are cobalt in a step that is separate from the molding compounds. Promoters resin. molding compound in a step separated from ish brown color. solvent. cross. such as the accelerator. without needing cals. with the in using promoters/accelerators. and other desired materials should never be mixed directly with perox. analine (DEA). other metal ions. It can then • The compounder’s expertise in the ma- react with another MEKP molecules to make terial and its properties are sometimes more free-radicals. stor- since as soon as the peroxide is added. Sometimes • Economies of scale may apply. • Specialized equipment can be used to little cobalt is needed. can be better accommodated by the Other promoters are the tertiary amines. the molding compound will added first. (such as fillers and reinforcements). all the from cobalt compounds. Then ides. On the other hand. Such a free-radicals. Some peroxides are more susceptible any additional mixing or preparation steps. Therefore. and Applications . the promoter is usually free-radicals. nature of the cobalt reactions with MEKP.5% mix the materials. added into the resin/solvent mixture and If the molding compound gets hot enough thoroughly stirred before the other material to cause the peroxides to activate and form is added. they are ready for molding. often by the resin manufacturer. unstable under normal curing conditions and it reverts to the Co+2 form. will further improve compounding and molding. the cobalt loses manufacturer is often called a compound- an electron (going from Co+2 to Co+3) and er. The cobalt compound reacts facturer whose operation is solely dedicated with peroxides. such as cobalt naphthenate or operation. ingredients necessary for curing must be some resins have been found to cure most mixed into the molding compound when it efficiently with a combination of the cobalt is made. Methods. parts in hot water depends strongly on the When solvated. ing is required. pigments. These thalate (DAIP). Both of these are listed in include alkyds. However. and good dimensional constituents. been used for many years. bobbins. and ground mold. lu. The alkyds are prepared by sively for electrical parts. cooled. the allyl group. and the ments are usually short fibers or mineral method of adding reinforcement. When polymerized into a linear. Each fibers so that the paste-like consistency can is discussed briefly in this section. diallylphthalate (DAP) and diallyl isoph- ing compounds are commonly used. or differ in the types of unsaturated polyesters DAIP molding compounds. and possibly short fibers. Allyl- The mixing is usually done in a heated roller ics are also used for potting. and possibly even the minor moisture sensitivity. This powder is usually molding compound. blending the resin with the initiator and switches. Even with the best of each type drying rate. alkyds are used for paints. lylphthalate [DAP] and diallyl isophthalate uncrosslinked polymer and then combined [DAIP]). the process of mill that gives some curing to the polymer. crushed. polyester thermosets are likely to absorb significant moisture in hot Allylics water and lose mechanical and chemical The allylics (pronounced al-lil’-icks) are a properties. if any. and insulators. be maintained. applications in which a high degree of shap- ter molding compounds based on general. just as they would be for any stability. These these materials are called allylic. the dency to absorb water. pouring the liquid or paste resin into Fundamentals of Composites Manufacturing: Materials. (Compression molding is with molding compound are dependent upon discussed in detail later in this text. Compounds The most common of these monomers are Several types of polyester thermoset mold. the semi-solid material is removed be potted into a container that serves as a from the rollers. allylics (principally dial. These then with cellulose pulp. and sheet molding compound (SMC). DAP. mineral filler. This is done by placing the article to reached. compression molded. The reinforce- used. thus restricting their long-term stability of polyester thermoset application to low-water environments. a particular organic chem- istry group containing the carbon-carbon Polyester Thermoset Molding double bond in a particular arrangement. selection of all the constituents in the mold. For example. with a filler and possibly a reinforcement. molding (discussed in a later chapter). the reinforce. chiefly connectors.3: Unsaturated Polyesters 67 a time limit on storage is also applied to the into molding powder. but have found the hot-water performance can be affected limited use because of their relatively slow adversely.) Alkyd the resin type. Table 3-1. If any constituent is changed. the solvent. low ment. parts are made by compression or transfer bricants. the alkyds have some ten- other composite product. the types of active diluents. and Applications . of constituent. Allylics are also used exten- purpose resins. often requiring only The properties of the molded parts made low pressures. The paints have high durability and have ing compound. parts have high electrical resistance. Thus performance in this type group of unsaturated polyesters based upon of environment requires careful attention resins formed from a monomer containing to all constituents. encasing an article or assembly in a resinous When the proper degree of polymerization is mass. Allylic pastes are used as body putty for Alkyds repairing automobiles and for many other Alkyds (pronounced al’-kids) are polyes. the filler. bulk molding compound (BMC). the pre-initiated applies to these mixtures. In making SMC. including in SMC because the mixing system is less body panels. the longer semi-structural members. handling and removed for storage at a cool bile industry has adopted this method for temperature. wetting the fibers. because SMC ducts. The resultant ment fibers are chopped to the desired length materials are stored at low temperatures to (typically 1–3 in. Sheet Molding Compound Larger parts can be made with sheet Bulk Molding Compound molding compound (SMC). and unrolled and of a mold and then the material moves to cut to the desired lengths. The compo- Bulk molding compound (BMC) or. fibers do not impede movement as can occur One problem inherent in the use of BMC with BMC. Even with careful part to be molded.25 in. filler. and Applications . but the method of mixing the components is made by combining the unsaturated is quite different. Rather. The polyethylene sheets adjustment of the resin viscosity and using are removed from the SMC sandwich as the the proper amounts of resin. although these concentrations can vary placed on top of the chopped fibers. is the limited amount of material movement When SMC is to be used. The mixing of the resin/filler mixture is doctored onto a mov- components is done at room temperature to ing sheet of polyethylene film as shown in avoid premature curing and with as little Figure 3-7. (.68 3: Unsaturated Polyesters the mold so that the desired portion of the the mold will tend to cause separation of the part is covered with resin. to the molding station. Therefore. The term premix also blending process. The entire mixture automated and rapid molding of parts with is then rolled to an appropriate size for easy moderately high complexity. and then curing components. A second poly- tions of BMC components are: resin and sty. and enclosed by the polyethylene be metered. sandwich is formed with the reinforcements BMC materials are sticky and have a in the middle. and various has less movement in the mold. usually a large com- the charge of BMC is placed in the center pression molding machine. dough molding compound (DMC). Generally. The reinforce- about 2 in. which allows them to mixture. material is placed into the mold. ethylene sheet that has also been doctored rene = 25%. These lengths are fill the mold as the closing mold presses typically about the same size in area as the against the material. onto the resin/filler layer.6 cm) thick. sition of SMC is about the same as BMC. This sandwich is passed between rollers Therefore. Methods. into an open mold. (40 cm) mold remains as part of the assembly. shot by shot. reinforcement = with a layer of resin/filler mixture is then 30%. film. Potting in their longest dimension. Typical concentra. Sufficient forcement. The layer of resin/filler mixture agitation as possible so that long fibers (up to is about . grills. the roll is taken that is possible within the mold. Also. Fiber length can be longer manufacture of numerous parts. The automo. surrounded by the resin/filler dough-like consistency. trim. movement over long distances in layers of SMC sheet are placed in the mold Fundamentals of Composites Manufacturing: Materials. and ponents are not mixed together in a batch reinforcement fibers. ternately. the molding are limited to about 16 in. and rein. air-conditioning likely to break the fibers. the com- polyester resin with an initiator. [3–7 cm]) and sprinkled prolong their shelf life. This permits largely ture. filler. Thus a widely depending upon the application. al. the principal molding method is that push the fibers into the resin/filler mix- compression molding. electrical components. After the casting is completed. [5 cm]) can be used. is used extensively in the electrical industry to encapsulate wire ends. parts made by BMC the resin. filler = 45%. A special addi- layers of SMC together. into the mold. to obtain the thickness desired. It is called the low-profile or low- of a part made from SMC is the body of the shrink system. the mold is closed. Sheet molding compound (SMC) machine. smaller strips of body panels in automobiles has required SMC can be laid into the mold. there must be enough and dimples that are unacceptable in the movement of the resin to bind the various automotive panel market.3: Unsaturated Polyesters 69 Figure 3-7. and Applications . Methods. Because the SMC is placed shrinkage of polyester materials as they so that it covers the surface of the mold. defect-free surface. the addition of about 2–5% low-profile Fundamentals of Composites Manufacturing: Materials. Large parts can be tive system has been developed to solve this made by this process. When all the development of a molding system that of the material has been properly placed will result in a smooth. If additional Molding Systems thickness is needed in some locations but is The use of BMC and SMC for exterior not wanted in other places. A well-known example problem. crosslink (often 7–10%) normally results in little movement of material occurs within fiber show-through and small sink marks the mold. The system is based upon Corvette® (General Motors). The inherent part is cured. However. and the often called a Class A surface. of course. Reactive chemistries. also have been used to Curing provide ripening of polyesters in place of the The curing of a polyester resin is a com- metallic ion systems. It is possible to add a and additional fillers containing divalent thinner to the mixture that will reduce the metal ions. the resin runs down. The mechanisms for plex process and is critically important to thickening and low-profile expansion have achieving good composite part properties. One group set to a particular temperature (usually about of popular thixotropes works by increasing 180° F [82° C]). the material is carefully stirred. therefore. mation of cure characteristics. minutes the material will suddenly thicken. Control of viscosity might be needed in This is the onset of gelation—that point just the opposite way—the mixture may when the crosslinking reaction is dominating be so viscous that fibers and fillers might the viscosity and a permanent deformation Fundamentals of Composites Manufacturing: Materials. For example. such as Ca+2 and Mg+2. pressure PROPERTY OPTIMIZATION transducers. that is easy to add to the resin before the ary bonds between the polymer and the met. The cure can be affected by most of the a matter of some ongoing research. Methods. of the effects of the most common variables ated resin system. Some components are relatively minor in Therefore. Thus the The characteristics of the cure of an ac- use of thermoset polyesters in automobiles tual part are not always easy to measure has increased steadily for many years. The resin might be so thin that performed by placing a measured amount of on a vertical surface. couple. this of the low-profile additives because of the section is intended to give an overall view normal curing that takes place with an initi. A stopwatch is started and the hydrogen bonding in the mixture and. consists of salts of organic acids in a solution which results from the formation of second. and Applications . The ad. because it is difficult to put the appropriate monitoring devices (thermocouples. gives control and specific parameters to the and to suggest ways in which these variables thickening and.70 3: Unsaturated Polyesters additive consisting of thermoplastic resins not be fully wetted. Such a material can allow greater filler results in thickening of the resin/fiber/filler and fiber loading levels. But the low-profile system in the system. Such mal bath or on a hot plate that has been a material is called a thixotrope. al ions.) in the right area without Viscosity disrupting the cure or final properties. components. might be altered to achieve optimal part pansion upon curing that compensates for properties. fillers and fibers are mixed in. The cup is then placed into a ther- ing a material that thickens the resin. This process is called ripening. not been clearly defined and are. This can be prevented by add. normal polyester cure shrinkage. some laboratory tests have been volume but can be important in optimizing developed that give a reasonable approxi- the performance of the part. building viscosity. produces the ex. and conditions. etc. viscosity and allow wetting of the solid mate- dition of these materials to polyester resins rials. After a few consequently. the polyester resin mixture in a small cup thereby leaving resin-poor areas near the top that has been instrumented with a thermo- of the surface. They are in the mix. Therefore. The most viscosity control can be important to achieve common laboratory tests are cure time and uniform distribution of all the components exotherm peak measurements. such as the reaction of urethanes. A popular thinner mixture. components of the polyester system and by The thickening of BMC and SMC occurs innumerable variables in the conditions un- to some extent even without the presence der which curing takes place. But this is breaking apart too quickly. the peak exotherm exotherm conditions can give a reasonable temperature also increases.3: Unsaturated Polyesters 71 of the resin is observed. This is caused understanding of the conditions that exist by the heat retention of the polymer mate- during the cure of a real part. will decrease the gel time since there are therm temperature is not too short. often of a different thickness. and Applications . Increasing the initiator (MEKP) concen- perature exotherm indicates a hot mixture. erally cure in a faster time. the part will gen. Fundamentals of Composites Manufacturing: Materials. as The combination of the gelation and the thickness increases. when heat is retained. Further. This is the gelation also that the gel/exotherm test is done us- (or gel) point and the time to this point is ing a set amount of material. In general. the called the gel time. A high-tem. These relationships are real part to be molded is not only larger but shown in Figure 3-8. which more free-radicals present and they initi- would indicate that the peroxide initiator ate more crosslinking reactions. Remember effect gradually levels off since the higher Figure 3-8. Gel time and exotherm measurements. rial and the accompanying higher reactivity if the gel time is short. For instance. tration along with a constant concentra- and generally that the cure will proceed to tion of accelerator (cobalt naphthenate) completion provided the time to peak exo. Methods. the peak exotherm temperature also will be Following are the variables that make the higher. If the initiator concentra. Hence. They are generally in controlling the cure of an unsaturated added to the resin mixture by the resin Figure 3-9. These are chemicals that Several of the most important factors absorb free-radicals. Not only will the Then the variables can be divided into three cure reaction be much faster when the groups—those that make the cure reaction concentration of initiator is increased. pears on a teeter-totter arranged according tion and the amount of accelerator (cobalt to whether it generally makes the curing naphthenate) both increased. Remem. the decrease reaction go slower or faster. the reaction is both faster curing reaction go slower. faster. Fundamentals of Composites Manufacturing: Materials. • Inhibitors. The action of in gel time would be even greater. but go slower. or either way. Methods. however.72 3: Unsaturated Polyesters concentration of initiator will not all become polyester thermoset part are summarized active without also increasing the amount in Figure 3-9. and Applications . Additives to the polyester mix and their general initial effects on curing rate. initiator concentration. Each of the properties ap- of accelerator. that the extent of crosslinking the gel/exotherm test results in light of the will eventually decrease with increasing actual conditions that exist in the real part. these factors will help to modify or interpret ber. and hotter since the number of free-radicals available is greater. 3: Unsaturated Polyesters 73 manufacturer to stop or interrupt any crosslinking reactions. cycle. Some ap. however. wax or a film. calcium sulfate. sufficient Since oxygen is almost always present. the styrene makes reactions. Because free-radicals • Oxygen. The mold is com- powdered inorganic materials such as posed of a massive amount of material calcium carbonate. radicals. Therefore. The action of agents. However. to check the crosslinking occur more quickly and each flame-retardant type for specific efficiently. • Styrene or other crosslinking • Flame retardants. Because the mold is often at room Fundamentals of Composites Manufacturing: Materials. Therefore. That is. the oxygen can be proximation of the amount of inhibitor excluded from the reaction area by us- remaining in the resin can be gained ing some surface-coating material like from gel/exotherm tests. such as interactions amount of ozone (O3) molecules present between the molecules with heat and as well. styrene metals. They add mass to the system and ab. additional styrene will slow is based primarily on their additional the reaction. Therefore. mostly of O2 molecules but has a small ent mechanisms. mass and assumes they have little direct fect of styrene is as the crosslinking chemical interaction in the crosslinking agent. the curing re- while the resin is stored. which might serve as accelera- is a solvent for the system. planned curing is to be done. Styrene is placed on the teeter. them as favoring slowing the reaction Therefore. tors. their principal effect is added totter on the slower side (see Figure mass and the subsequent absorption of 3-8) because of its initial effect. and Applications . speed up the reaction. the simple designation of which must be heated in the reaction. Methods. effects. the possibility of having chance inhibitors in their ability to absorb free- creations of free-radicals is quite high. and that acts as a heat sink. peroxide initiator must be added first the amount of peroxide initiator used to react with any remaining inhibitor is normally adjusted to overcome its and then react with the resin. This effect would generally reactivity. Therefore. while others might serve as free- increasing the amount of styrene will radical absorbers and therefore inhibit. These materials are usually • Mold heat capacity. these materials can be complicated. Alternately. When in these instances it is called a quench. • Filler. It is best. The used. dilute the total system and add mass. perhaps the talc. thus reducing crosslinking chain reaction that might the exotherm and slowing the overall be started by the chance creation of reaction. Two different effects are oc. Normal oxygen gas is made up can be created through several differ. heat that occurs. although it is • Reinforcements. Sometimes oxygen is of resin could be prematurely crosslinked actually used to stop the reaction and unless protected with inhibitors. free-radicals. These ozone molecules are like light. the second ef. if oxygen is present Should these chance reactions occur or added to the system. Some flame retardants contain first is the dilution effect. de- curring simultaneously with styrene pending on the type of flame retardant and the other crosslinking agents. In this role. most important mass in the entire sys- sorb some of the heat generated by the tem. the entire batch action is slowed. The fibers are usu- usually seen later in the overall curing ally inert to the crosslinking reactions. introduced into the system by shining Consideration should be given to final a special light on the polymer. The peroxides are useful • UV light (sunlight). If the part is to be cured without resin systems. the classification of the started and. then a combination of a perox. such as naphthanates. the the break-up of the peroxide molecules. which is a threshold bar- resin system and thus the curing reac. they compounds. UV light is intentionally ide and an accelerator system is needed. in some used. To pre- free-radicals that initiate the crosslink. mold will accelerate the curing mecha. such as color. It is this possibility Here are the variables that make the cur- that leads to the addition of inhibitors ing reaction go faster. These most any chemical reaction for several materials are added to the system to im- different. rier for effective reactions to occur. Methods.) The heating of the without the organic metal accelerators. Yet tion is retarded. some peroxide and colliding likelihood is increased. Molecules must collide to react. they will collide harder and. This UV part characteristics. then a heat-activated peroxide is inhibitors are added. Also. cold state that direct formation of free-radicals at occurs during most molding. This Some accelerator systems are further means that when the molecules collide. the only a small amount is needed to greatly viscosity of the mix is reduced by heat. the rate of the mold as slowing the reaction is simply a curing reaction. improve the efficiency of the perox- ing so the molecules move more freely ide. However. improved by adding aniline compounds. (Not all collisions oxides. Therefore. most common accelerators are organic and when molecules are heated. to prevent crosslinking from occurring • Initiators. Heat also can cause reflection of the normal. resins are ing reaction.74 3: Unsaturated Polyesters temperature. of movement of the molecules. The sons. • Heat. therefore. ally peroxides. Usually they will collide is increased. Hence. which are sometimes have a higher chance of creating an called co-accelerators. With accelerators. When heated. If a part is to be cured with usually stored in opaque containers and heat. therefore. the carbon-carbon double bonds in the polyester molecules. heat is absorbed out of the of activation. rea. molecules increases the overall energy Because of the sensitivities of peroxides in the system. systems do not need to be heated and Higher heat also increases the energy room temperature cures can be done. These materials are gener. prove the efficiency of the initiator. such as DMA. great care should be the molecules to overcome the energy taken to control the accelerator system Fundamentals of Composites Manufacturing: Materials. With some per- effective collision. Heat will increase the rate of al. however. heat. as light can cause crosslinking to occur these can be affected by the peroxide without the use of peroxides or external chosen. dental fillings. thus increasing the number of chains nism. the co-accelerators are effective result in bonding. and Applications . although interrelated. prematurely. thus making it easier for to the accelerators. the chance cobalt or some other metal. vent this from happening. In some cases. • Accelerators (promoters). of move more. This type of materials because they break apart energy will create free-radicals at the easily with heat or chemicals to form carbon-carbon double bonds. such as those used in heating. another effect of heating is to increase the mold is heated. Therefore. and Applications . During the cure. each with its coating or film can be added only to that own reactivity. These materials are more slowly with others. Some resins are especially sensi- ness variations. small amounts of wax. thus chains can increase system viscosity quenching the reaction. tive to certain initiators and therefore proceed rapidly when they are used but • Wax or films. The heating also can cause the resin retains heat and therefore any residual peroxide to break apart increases the overall temperature and and initiate some additional chains. thus slowing the reaction tective layer that excludes the oxygen. This behavior can be a Following are the variables that can major problem when parts have sig. a wax or more types of polymers. but the amount • Resin grade/type. therefore. ficiency of molecular collisions. The resin is the most of crosslinking that occurs could be complicated component in the entire higher in those thicker areas. Figure 3-9). Hence. On the other hand. Water adds to the total mass in the wax rises to the top and forms a pro. although it can retard other object because bonding agents do rates in others. active when water is present. only will the reaction rate be higher in the thicker areas. is to monitor and record humidity and Fundamentals of Composites Manufacturing: Materials. will cure quickly and result in heat in the thicker regions can cause high-temperature exotherms and high greater thermal shrinkage and result in crosslink densities. Others. crosslinks. est inhibition effect is usually on the Resins might even be mixtures of two surface exposed to the oxygen. The best practice of the molecules and provide greater ef. about resin reactivity as it might occur Some polyester resin systems contain in the particular system used. therefore. such as hardness or gloss. Water can • Post-cures. Not or slower. the higher tion. When parts are thick. resulting in the formation of more • Part thickness. the system. Methods. The length of added to exclude oxygen and prevent the chain of the resin before crosslink- its inhibition effect. • Water. so variable could cause embrittlement in the thick in its effects that it cannot be classified areas and internal stresses in the part on either side of the teeter-totter (see because of the increase in part shrink. slowly. by absorbing heat. This layer of wax can be a problem if the water can increase reactivity in some resultant part is to be bonded to some peroxide systems. proceed more be carefully designed to minimize thick. Since the great. done to generate additional movement difficult to predict.3: Unsaturated Polyesters 75 concentrations and the order of addi. This mixture and is. Some resins are less re- not adhere well to most waxes. the manufac- surface to prevent a decrease in surface turer of the resin should be consulted properties. Furthermore. parts should that are less reactive. with less cracking or part deformations like sink unsaturation or with unsaturation sites marks and dimples. The action of water is. make the curing reaction go either faster nificant differences in thickness. Some resins. which can occur ing can affect the reaction rate. This is tems. especially age that occurs with higher degrees of those with a high degree of unsatura- crosslinking. and therefore slow the reaction rate. Adding heat after the part also affect the action of accelerator sys- is formed is called post-curing. thereby tion of the peroxide and accelerators. reaction rate. Long when it reacts with free-radicals. at the heart of polyester molding and must some metals will interfere with the be carefully controlled to make good quality basic crosslinking reactions. little effect on the system. Because the nature Other additives might be added for long- of the contaminant is not specified. Some contaminants are might similarly be added. The best situation is to understand. materials) and dyes (organic colorants) are frequently added to polyester mixtures. The most common UV-protecting filler tion and act to control and limit its is carbon black. the production of poor ponents. and Applications . proceeds quickly because too much peroxide However. may have a more predictable and protective capabilities and could be added by repeatable effect. Therefore. It works well and is relatively low cost. all else being equal. thus retarding the system. there. However. Some fillers may have UV fore. and control the effects of the various since some contain metals. potentially. All of the other variables air-quality limits for styrene. monitor. Cures that are too slow and too fast can be • Pigments. Usually these significant parts of the environment in materials are added in small percentages some manufacturing plants and. if the cure tems. incomplete crosslinking would and a potentially harmful vapor if breathed likely result and that would lead to poor in excess. such as iron components in the mixture and the variables oxides. Methods. thus increasing the cost to achieve experimentation should be observed before the same production volumes as could be changing to a new colorant. Antioxidant protective chemicals quality parts. it also has a high vapor pressure was used.76 3: Unsaturated Polyesters water content in the system and then that may increase reaction rate could like- attempt to correlate its effect on the wise cause problems with the part. ers. However. some colorants to reduce the amount of crosslinking. Pigments (solid inorganic presence. term. add mass. Usually pigments have problems. (less than 10%). the part could CASE STUDY 3-1 be too brittle. Additives • Contaminants. cured-product improvement. If the cure proceeds too quickly because too much heat is generated. ultraviolet (UV) light degradation are added known invites variation in the process to the resin before mixing with other com- and. In general. It is good to be aware themselves or in combination with other fill- of the possibility for such contamina. if the reaction proceeds too These are often in low concentrations (less slowly. overall system. attained with faster cures. the U. Long may affect the cure system (they can act cures will also increase the number of molds as accelerators) and therefore caution and needed. These limits Fundamentals of Composites Manufacturing: Materials. Often the nature of the effect is not known. and other physical properties and poor solvent and governments have established maximum water resistance. the fact that the effect is un. the cure is likely to be lower than than 10%) and generally have little effect on desired because contamination has had time other properties. Pigments parts over the long run. Also. the crosslinking might Reduced Emissions Resins proceed so quickly that all of the styrene is Styrene is the most widely used co-reac- not used and the resulting part could have tant or reactive diluent for polyester sys- residual styrene content. The cure reaction is effect.S. however. specialty chemicals that protect against However. they can have an accelerating that control the rate. Further. In contrast to that. has also reduced the Some resin manufacturers have found amount of styrene available for crosslinking. different polymers could be formed. because mixtures of multiple types of diacids This starving means that the number of and glycols are often used in making poly- styrene molecules in each of the crosslinks ester resins that have different reactivities. such as neopentyl glycol. or at been successfully reduced. flow more easily. the shorter polymer An example of such a change would occur chains allow the carbon-carbon double under the following two scenarios. are The first method to reduce the viscosity of known to be more soluble in styrene than the the base resin was. alternate components might give additional therefore. preferential positioning of the second diacid So. Hence. they molecular chains. cracking. to reduce the mo. However. Therefore. and Applications . These effects are much more existing resin systems so that less styrene important in gel coats than in laminating. the resin companies higher crosslink density. would be needed. Some of the acids viscosity for fiber wet-out could be reduced. control requirements. acids and glycols. the distribution of the acids formed overall. the result could be a density approximately cancel each other out. that is. the resin properties can amount of styrene needed to achieve a good be significantly changed. which was dictated by viscosity result of the decrease in styrene. This strategy was not only Strategy 2: Develop new polymer systems. Fundamentals of Composites Manufacturing: Materials. the diacids and glycols. Methods. to shorten the other common components. This re. distortion temperature. is reduced. it also gave quick Polyesters are made from the reactions of di- results. chalking. ultraviolet light ferent paths to attempt to reduce the amount resistance. However. Therefore.3: Unsaturated Polyesters 77 have been gradually reduced so that comply. But the Strategy 1: Modify existing polymer sys. diacids are mixed together and then added sults in a higher number of crosslinks being to the glycols. brittleness is about where it would be in at the ends of the polymer. Therefore. the new The amount of styrene needed in these resins might have both reduced styrene con- lower-molecular-weight resin systems has tent and improved physical properties. Shorter chains emission resins. also may be affected. Hence. if one of the di- brittleness from the reduction in styrene acids is added to the glycols and then the content and from the increase in crosslink second is added later. that new resin systems requiring lower sty- Therefore. At the same time. therefore. This means the benefits such as increased toughness or heat viscosity is lower. If two bonds to occur more frequently. That reduced level least no major reduction in properties as a of styrene. these have less intermolecular entanglement and. These changes occur a “starved” situation during crosslinking. extent of these effects must be evaluated tems. such as blister resistance. Other properties. the nature of the crosslinking rene concentrations can be made by varying has also changed. and surface of styrene emissions. The initial effort by almost all of the on a case-by-case basis with each resin and resin manufacturers was to modify their application. two very the unmodified resin system. the effects on could be random. The lower amount of the sequence of the addition of the diacid styrene available for crosslinking results in and glycol components. and molders have embarked on several dif. and glycols. prudent commercially. Generally heat distortion temperature ing with them is becoming more difficult for and solvent resistance will be increased by FRP molders. smoothness. are used in higher concentrations in reduced- lecular weight of the resin. Resin producers have found The resin manufacturers realized that if that by varying the types and quantities of the viscosity of the base resin were lower. Hence. thus allowing fore. definite trigger point for commencement of ity used with the monomer. Some new molecular concepts have been Another approach is to simply combine shown to improve or. has the unique property of a sharp melting pletely new monomers that are not like point that can be chosen to fit the needs of styrene at all.78 3: Unsaturated Polyesters Another major area of focus is the blend. esters include: polyurethanes. and vinyl esters. Short chains such ations. the unique advantages that they offer. This material also has a high vapor polymer types. However. the final polyester resin. so it too is considered a hazardous monomers. sometimes known as ing of unsaturated polyesters with other acrylic. are being the potential for poor bonding wherever the investigated as styrene alternatives. Therefore. it may be or as blends after full polymerization has more compatible with some polymer systems been done. An- other example is t-butyl styrene. allow lower concentrations the interesting blends with unsaturated poly. the the crosslinking reaction. and Applications . These films contain have a higher molecular weight and. mixture. cost eral. epoxies. some alternate monomers. is a unique of the fiberglass is still excellent since only heat-activated polymer material that has a enough is added to achieve the same viscos. but the proper. These innova- and then use these dimers and trimers as tive cure systems may not apply to all situ- the reactive diluents. referred to as mixtures. Such layers. problem with this method has always been which have lower vapor pressures. this concept is really using diluent for unsaturated polyesters and vinyl an old technology for a new purpose. there. It has sion between materials on both sides of the an additional methyl group on the benzene film is thus promoted. called the Intelimer® system. such as lower smoke generation. However. a lower vapor pressure. This adhesion problem has approach is to choose monomers that are been alleviated somewhat by creating adhe- similar to styrene in chemical reactivity but sion-promoting films. Intelimer Some have been looking at using com. Performance of these materials is almost A recent development by Landec Corpora- the same in the cured product. Some of and. methacrylate (MMA). Strategy 4: Form a surface layer to sup- ties of the blend can be substantially better. lower air-pollution potential. In gen. These blends can be done as pressure. This polymer is cost of producing the dimers and trimers is not a polyester and has nothing to do with significant. to be used to achieve acceptable viscosities. these blended polymers are higher in is a drawback. but should at least be considered for as these are sometimes called oligomers. carbon-carbon double bonds. Again. One wax is present. at least. Adhe- vinyl toluene is similar to styrene. but has a lower vapor pressure and. MMA also can give some improved properties phenolics. The prime example is methyl a particular system. The major CASE STUDY 3-2 drawback to using alternate monomers is New Curing Options their higher cost. ring. The esters. crosslinking to occur through the film. For instance. However. press the emission of styrene. and wet-out tion. therefore. present new two or three styrene molecules together options for curing polyesters. Methods. cost than the basic polyester. therefore. melamines. air pollutant (HAP). have been used for many years Strategy 3: Use other monomers. Fundamentals of Composites Manufacturing: Materials. Styrene is to exclude oxygen so that cures can be im- not the only monomer that acts as a reactive proved. often referred to as copolymers. thus allowing for the use of less resin or for often formed by adding wax to the resin entering new markets. and ester linkage formation. Several other diacids are also curing and lower residual styrene content since all of the resin is at temperature when the curing begins. by the polymer and do not interact with the These are summarized in Tables 3-2 and cure system. the ability to make many types of products with differing properties. polyesters and their attributes. tert-butyl perbenzoate (initiator). when encapsulated. unsaturated diacids are used commercially. First. One improvement is the enhanced viscosity control in the thermally activated systems Diacids/ because only viscosity is dependent on the Attributes Anhydrides temperature until the trigger temperature is reached. Common diacids used in final product are comparable. tertiary amine (co-accelera. if not better. The new mol- the special polymer. This market chemical resistance dominance is chiefly because of their low Terephthalic Thermal stability price. Another therefore. are protected as monomers in thermoset polyesters. and Applications . the shelf life of the resin is extended Experience has shown that the best poly- because some of the critical materials. which allow polymer is chosen to be at the lower range of further reactions with additional monomers. Physical properties of the Table 3-2. The melting point of the ecule still has two reactive ends. site) Orthophthalic Low cost. styrene SUMMARY compatibility Polyester thermosets (PT) or unsaturated polyesters (UP) are the most common of all Isophthalic Strength. When these resistance monomers react. water/ the resins used in composites. When the melting point of 3-3. potential crosslink sites. like ester properties are achieved when some the initiator. can be encapsulated. thus creating additional ester links and lon- ter. and ease Adipic Toughness. The advantage is more rapid release of the critical most common of these saturated acids are component. the temperatures used in curing the polyes. weatherability The polymerization process begins with the Halogenated Flammability reaction of a glycol with a diacid. they form an ester group Fundamentals of Composites Manufacturing: Materials. one of the key that links the two monomers together. Methods. Some of the monomers must contain the encapsulating polymer is reached. Usually. the a carbon-carbon double bond or unsatura- component is released and it immediately tion point for the crosslinking reaction to begins to interact with the other components occur. which can result in more uniform ortho and iso. of the diacids are not unsaturated and not. es. reaction conditions will support additional tor). containing this feature and several different This type of system has several advantag. These reactions can continue as components are available: organic cobalt (an long as the monomer concentrations and the accelerator). These Various diacids and glycols can be used materials. Systems with the following encapsulated ger chains. thus improving the ability to wet Maleic/fumaric Unsaturation (crosslink the fibers in a repeatable manner. ing premature activation less likely. dibutyl tin dilaurate (accelerator).3: Unsaturated Polyesters 79 In the Intelimer system. thus mak. of molding with these resins. the diacid is the monomer of the cure system. Water components of the cure is encapsulated in is also formed as a by-product. Some additives to control the curing LABORATORY EXPERIMENT 3-1 mechanism are important in polyester mixes. others use general-purpose polyester resins. and Applications . new bond and another free-radical. is The cure system is affected by many vari- activated by heat. tor. fillers. Attributes of glycols commonly Table 3-4. colorants. with any other unsaturation site to create a cure temperature. contain low-profile additives to improve the The curing or crosslinking reaction in surface of the molded composite part. Normally contaminants. water. HDT. Some are Various glycols can be used to modify and based on allylic materials. All the molding various glycols are toughness and resistance compounds have high filler contents. each imparting its own Various molding compounds are sold as particular advantages. Eventually all of the building blocks of monomers and additives. inhibitors are used to extend Curing Agents the shelf life or pot life of polyesters. usually an organic peroxide. Glycols Attributes Resin Purpose Ethylene Low cost Dicyclopentadiene Lower cost. polymers in the mixture are linked together Table 3-5 shows some generic recipes to il- in a great mass. bridges of two or three styrene molecules Polyester resins are made from a series of link polymers together. accelera- bon-carbon double bond unsaturation sites. which can combine with car. thickness of the part. (flexural strength. ready-to-use molding materials. Objective: Determine the effects of perox- erators are other important additives that ide concentration and accelerator concentra- make the curing reaction proceed faster or tion on gel time and various physical properties at lower temperatures. Methods. or chemicals to form ables. strength used commercially.80 3: Unsaturated Polyesters Table 3-3. low-profile systems are especially important eral mechanism as addition polymerization. in making automotive body panels. and improve the properties of the polyesters. The most com- mon of these are summarized in Table 3-4. initiator. (DCPD) improved stiffness Propylene Styrene compatibility Styrene butadiene Toughness Diethylene Toughness rubber (SBR) Neopentyl Weathering. An initiator. toughness. chemical resistance toughness Bisphenol A Water/chemical resistance. storage The activated polymer can then combine time after activation. Accel. Some to environmental factors. Fundamentals of Composites Manufacturing: Materials. time.). and others. added for various purposes. Purpose of some polymeric used in polyester resins. etc. types of resin. These unsaturated polyesters uses the same gen. lustrate how various components might be Additional polymeric materials might be added to achieve particular properties. inhibitor. additives used in polyester resins. including the following: mix ratios and free-radicals. Effects of Concentration Changes in For example. such as DAP. The most common properties added with the such as BMC and SMC. water/ Thermoplastics Surface quality. and solvent/crosslinking agent. Generic recipes for unsaturated polyesters. Components Purpose or Characteristic Unsaturated Saturated Reactive Specialty Glycol Acid Acid Diluent Monomer Low cost Maleic anhydride Orthophthalic Ethylene Styrene None Fundamentals of Composites Manufacturing: Materials. Methods. 3: Unsaturated Polyesters Table 3-5. low cost Weathering Maleic Adipic Propylene Methyl None methacrylate 81 . and Applications Flexible (low cost) Maleic Orthophthalic Diethylene Styrene None Gel coat Maleic Isophthalic Propylene glycol Styrene None and neopentyl High-temperature Fumaric Bisphenol-A Ethylene Styrene None performance Flame retardant Maleic Tetrabromophthalic Ethylene Styrene None anhydride High flexural Maleic anhydride Orthophthalic Propylene Styrene DCPD properties. phone 800-817-7376. Give 6. and 2. Suggested concentrations are polyesters. 10. What is the meaning of “unsaturated” Corporation. What is a low-profile additive used material becomes so thick that it takes for? a permanent set. Why is styrene especially useful as a and Processing. Suggested concentra.0%. Upper Saddle diluent or solvent for polyesters? River.008%. Obtain some general-purpose polyester peak exotherm measured? resin and place it in six cups.” Brochure published by Landec 1. Start a stopwatch and continuously stir to? each cup and note the time when the 14. 13. parting unsaturation to the polymer? 2005. www. 3603 Haven Ave. Some companies heat SMC material measure the rise in temperature. Describe the difference between “sum- concentration. 15. A. MI: Society of Manufacturing 3. Why are exotherms greater when parts should have the same weight of resin being cured are thicker? and the total volume should not be 8. Methods. 0. Each cup 7. 12.82 3: Unsaturated Polyesters Procedure: 6. No date. “Composite Materials” DVD from the 2. with respect to polyesters and what is the CA 94025. What does the name “polyester” refer 4. Mix in three different concentrations of and after curing? MEKP (initiator). 4. (accelerator) so that each of the MEKP concentrations has both accelerator con. Society of Manufacturing Engineers (SME). Plastics: Materials 5. mer” and “winter” polyester resins. ter and a thermoplastic polyester. What is an inhibitor or stabilizer? Engineers. and temperature versus MEKP concentra- tion (with lines for both accelerator BIBLIOGRAPHY concentrations). participate in polyester curing? Dearborn. 1. tions are 0. time versus MEKP concentration (with lines for both accelerator levels). add two different 11. component usually responsible for im.. Landec Corporation. before 2. Brent. What factor causes iso and ortho resins 5.5%. two cups with each 9. Plot the results on coordinates of gel a reason why this may be done. After the peroxides are thoroughly tiator and a catalyst? mixed into the resins. 3rd Edition.sme. just prior to putting it in the mold. Fundamentals of Composites Manufacturing: Materials. What is an accelerator or promoter? Strong. NJ: Prentice-Hall. What is the difference between an ini- 3. What is an exotherm and how is the 1. (2 cm) high in differences between a thermoset polyes- the cup. Menlo Park. Put a thermocouple into each cup at the to behave differently? same time as the watch is started and 16. What are the most important chemical more than about 1 in. Give three methods to terminate a concentrations of cobalt naphthenate polyester curing reaction. 2006. What is a peroxide and how does it Composites Manufacturing video series. Describe the distinguishing charac- centrations and mix well with the other teristics of aromatic and aliphatic materials.0%. Inc. and Applications .004% and 0. “Intelimer® Catalysts Have a Pre-set ‘Switch’ Tem- QUESTIONS perature.org/cmvs. 3: Unsaturated Polyesters 83 Strong. Fundamentals of Polymer Resins for Composite Manufactur- ing. Brent. Fundamentals of Composites Manufacturing: Materials. Methods. 1995. Arlington. VA: Composites Fabricators Association. and Applications . A. not just those made with epoxy as the matrix. detail in the chapters on reinforcements and tion with many other types of composite applications. kets for advanced composite materials are Another major application for nonreinforced emerging as the price of the carbon/graphite epoxy resins is as adhesives. materials. is higher than poly- pregs. cars. sporting goods. Many other ther- • Crosslinking and processing param. appliances. although not among the highest of • Special composite applications (pre. epoxy resins are often used in conjunc. that most often use high-performance com- metal pipes and tanks.1: Introduction to Composites 85 4 Epoxies CHAPTER OVERVIEW is for electrical circuit boards. In contrast to led to their widespread use as the principal the polyester thermosets. thermoset materials. The most important of these is for fibers as the reinforcement). STRUCTURE OF THE POLYMER The largest market for reinforced epoxy The epoxy resins are characterized by resins in laminate sheets. Epoxies (pronounced ee-pox’-ees) are the The relatively good thermal stability of second most widely used family of thermo. which is about the presence of the three-member ring ep- 25% of the total of all epoxies produced. fibers decreases. In this applica. The markets coatings (paint) on products such as ships. ites (chiefly those using carbon or graphite plications. epoxies have a low • Overview of epoxy and its uses tendency to emit gases even when subjected • Structure of the polymer to an electrical discharge. moset resins emit gases from unreacted eters crosslinking agent/solvent or from unreact- ed monomer. oxy group. about 50% of all resin in most high-performance compos- epoxy resins are used for nonreinforced ap. and industrial machines. However. Also. their excellent adhesive properties. posites are aerospace. many other mar- that need an especially durable coating. setting resins for composite applications and their good mechanical properties have (after polyester thermosets). tooling) ester thermosets and most other low-cost thermosets that might compete with them OVERVIEW OF EPOXY AND ITS USES in the electrical circuit board market. epoxies. Methods. sometimes called the oxirane Fundamentals of Composites Manufacturing: Materials. Epoxies are This chapter examines the following especially useful for these boards because concepts: of their inherent low conductivity and high dielectric strength. and Applications 85 . This is discussed in more tion. and numerous devices medical devices. Another advantage of epoxies • Physical and mechanical properties of in this application is their thermal stability cured epoxy composites which. The mo- lecular synthesis depicted in Figure 4-3 is the most common. there is a major difference between the frequency of occurrence of the epoxy rings along the epoxy polymer backbone and the occurrence of the car- bon-carbon double bonds in unsaturated polyesters. Methods. In some epoxy molecules. actual glycidyl groups.” This is a standard representa. to tion in organic chemistry and is meant to see a more complete picture. the epoxy rings some organic group. (To be general in the representation. analogous in this sense to the carbon-carbon double bond sites in unsaturated polyes- ters. These reactions are done by the manufac- turer of the epoxy resin and are not part of the curing or molding operation. the epoxy rings or glycidyl groups are only attached to the ends of the polymer or the ends of branch chains as illustrated in Figure 4-2. However. The starting materials are bisphenol A and epichlorohydrin. which is then attached to As indicated previously. Then. the R is a complex group and could even be a polymer). small organic group. while in others jointly discussed. understanding of epoxy resins. If the epoxy ring is attached Epoxy Ring to another carbon. The two parts of the molecule are the organic group is simply represented considered separately to obtain a simplified with an “R. a highly reactive monomer. group.86 4: Epoxies group. which is represented as the R 4-1a. epoxy ring and the bridge carbon is called As such. which is where crosslinking occurs The epoxy polymer can be thought of as in epoxies and which gives epoxy polymers being composed of two parts—the epoxy many of their characteristic properties. The reaction bonds the epoxy rings. Epoxy and glycidyl groups. the nature of indicate that many organic groups could be epoxies is considered when both the epoxy chosen. Fundamentals of Composites Manufacturing: Materials. to add the epoxy ring to the ends of a polymer chain or to create a polymer containing the epoxy rings. the R is a ring and the remainder of the polymer are simple. sides of the aromatic segment. that is. Whereas the carbon-carbon double bonds occur frequently along the polymer backbone and possibly as often as every 10-20 atoms in normal commercial polymers. these rings have been called “ac- the glycidyl group as illustrated in Figure tive sites” in previous chapters and are 4-1b. or with the bridge carbon) and the rest of other organic group as illustrated in Figure the polymer. and Applications . the combination of the are the sites where crosslinking occurs. Several methods are used to synthesize the epoxy polymer. This ring (either as just the three-member ring epoxy group can be attached directly to an. to both Figure 4-1. The hydroxyl group is attached to the polymer segment groups add to some properties. in this case. such as ad- with an oxygen molecule in a linkage known hesivity. This situation would result in the reactions in large plants and the output prod. Other than serving as the linkage point for ies indicates the various components as they the molecule used to cure the epoxy.” These types of epoxy resins are remainder of the molecule. in actual practice. epoxy molecules name of the epoxy is “diglycidyl ether of bi. Because the number of is molded and the output is finished parts repeat units in this segment can change. Therefore. molecule can be gained by examining a few ing in DGEBPA.” Each glycidyl by some (amine) curing agents. of the final cured polymer. This from the epoxy ring is the addition of hydroxyl molecule has two glycidyl groups on each (OH) groups to the molecule. The most common name system for epox. An understand- often abbreviated by using various critical ing of the non-epoxy ring parts of the epoxy initials (as highlighted in the name). The epoxy resin contribution to the properties of the polymer shown in Figure 4-3 is a good example. Generalized representation of an epoxy polymer. result. the bisphenol resins. the main exist in the final epoxy resin. n can be large or small. the As previously indicated.” Then the polymer segment is named and. The crosslink in Figure 4-3. consist of two parts—the epoxy rings and sphenol A. same linkage of the epoxy rings as shown ucts are uncured epoxy resins. shown in Figure 4-3. but the segment between the reactions are done at the time the epoxy part rings would be longer. Referring again to The reactions used to synthesize the epoxy Figure 4-3. that made from the cured epoxy resin. specific epoxy molecules. which are end and so the name begins with “diglycidyl” formed as part of the epoxy curing process where the “di” means “two. and Applications . OH groups on the ends (where n is typically The synthesis reactions are done by chemical 2-12). in organic chemistry as “ether. is. are separate A reactant would be a short-chain polymer from the reactions used to crosslink the epoxy having a few bisphenol A units between two resins discussed in the following paragraphs. The Non-epoxy Ring Portion it is the bisphenol A polymer. Methods. the properties of Fundamentals of Composites Manufacturing: Materials.4: Epoxies 87 Figure 4-2. and Applications . The properties of the uncrosslinked more crosslinks than the standard DGEBPA. State) has three aromatic rings in the center. epoxy polymer (DGEBPA) as a function of n are given in Table 4-1. therefore.88 4: Epoxies Figure 4-3. This molecule has three ends to which 2 105 (40) Semi-solid epoxy rings can be attached. The molecule depicted in Figure 4-4 Polymer (HDT). This material. DGEBPA. number of units in the polymer section. called 12 300 (150) Solid Fundamentals of Composites Manufacturing: Materials. n Several other common epoxies are rep. Properties of uncrosslinked distortion temperature increases and the DGEBPA epoxy resin as a function of the viscosity increases. 9 265 (130) Solid Figure 4-5 illustrates a tetra-functional (four-ended) polymer. n ° F (° C) with a glycidyl group extending from the ring. the heat Table 4-1. each units. A common epoxy synthesis reaction. The as the molecular weight increases (as n gets four crosslinking sites provide substantially larger). As expected. the products based on these polymers change TGMDA in the United States and TGDDM in accordingly. is popular when a part requir- that the epoxy polymer’s properties change ing high thermal tolerance is needed. The amount of 4 160 (70) Solid crosslinking is. higher than with the standard two-ended epoxy. when the number of repeat units increases. thus increasing the molecular weight. This is another way of saying Great Britain. of Temperature (Physical ins. Methods. Heat resented to give an understanding of the Number Distortion Viscosity breadth of variety capable with epoxy res. Hence.4: Epoxies 89 Figure 4-4. Tetra-functional epoxy. This has several pendant chains on the backbone. which results in a tighter structure and re. It has high thermal stability and excellent mechani. Methods. other than those that can be obtained just The molecule depicted in Figure 4-6 is by increasing the degree of crosslinking. It is also an excellent Fundamentals of Composites Manufacturing: Materials. there are no aromatic double bonds. that in this epoxy can be quite high with resulting is. Figure 4-5. Some types of epoxies require properties quires more heat to cause movement. sometimes with no repeat units at ends of the backbone can be capped with an all. made from a polymer called a novolac that One of these is a cycloaliphatic epoxy. and Applications . Tri-functional epoxy. non-aromatic molecule is generally a short Each of these pendant chains and the two polymer. the number of crosslinks epoxy where the “S” means saturated. Figure 4-7 illustrates a cycloaliphatic epoxy ring. good weathering properties. mon to most aliphatics. which are com- cal properties. linking). thus contributing to high stability in thermal stability as measured by HDT in the epoxy molecule and increasing the (see Table 4-2). or can be obtained with the more traditional for some other reason. an imide-based polymer can be including those illustrated in the preceding used as the basis of the epoxy polymer. aliphatic nitrogen. The imide group is stiff and aromatic (cyclical). When an epoxy resin with high thermal solvent for other epoxies when a solvent is properties is desired (that is. Aromatic 290–350 (145–175) (cyclical) Epoxy resins containing halogen atoms. and in Figure 4-9. Methods. Resin Type ° F (° C) Aliphatic 230–300 (110–150) (straight chain) Aliphatic 255–270 (125–132) (cyclical) Aromatic 265–290 (130–145) (straight chain) Figure 4-6. Here the bromine atoms are attached to the aromatic rings. Cycloaliphatic epoxy. Therefore. polymers that do not have the epoxy group cyclical polymers typically have higher ther. even though the flame spread is low. the higher the thermal properties significantly. These structures vary stable. these bromines will dissociate from the ring and combine with hydrogen atoms to form HBr. can be classed into four convenient imide group is a five-member ring containing groups: aliphatic (straight chain). attached will be discussed in the chapter on mal stability than linear polymers. higher than needed to improve wet-out of the fibers. aromatic (straight chain). The figures. Also. specialty resins. (Imide aromatic content. It should be noted that this gas is choking and irritating to the eyes and Figure 4-7. As expected. In a fire. Comparison of the heat distortion temperatures (HDTs) of various types of cured epoxy resins. can be used for applications where low flame spread is required. and Applications . chiefly Cl and Br. and carbons as depicted (cyclical).90 4: Epoxies Table 4-2. oxygen. mucous membranes. the smoke can be hazardous or toxic. A typical halogenated polymer is shown in Figure 4-8. methods of increasing the amount of cross- The most common types of epoxy polymers. Novolac-based epoxy resin (epoxydized phenolic resin). Epoxy HDT. a heavy gas that smothers the fire. the higher the HDT.) Fundamentals of Composites Manufacturing: Materials. which shows comparisons of epoxy and generally has better stability than merely unsaturated polyester crosslinking param- the mix of rubber and epoxy and avoids some eters. This is called the chain more flexible. This epoxy is to join a sheet of the epoxy with a toughness is achieved by making the polymer sheet of rubber material. the information pre- rubber polymers is to add thermoplastic sented in this section is summarized in Table polymers to the epoxy. other method of adding flexibility to an epoxy is to mix together the epoxy resin with some rubber polymers. while not often used.4: Epoxies 91 Figure 4-8. the aromatic duplex method and. An imide-based epoxy. character has been reduced in favor of higher does have some advantages in ease of fabri- amounts of linear aliphatic segments. The molecule shown in Figure 4-10 gives another method of adding toughness to an high toughness to epoxy functionality. To do this. Still section of the text are the same as the major Fundamentals of Composites Manufacturing: Materials. cation and mixing. An. Methods. A modification to adding context of familiarity. The headings of each subsection in this of the negatives of rubber tougheners. A flame-retardant epoxy. while not CROSSLINKING AND PROCESSING ideal in terms of weathering and mechanical PARAMETERS strength. has improved toughness over the To put the crosslinking of epoxies into a epoxy resin itself. This mixture. This combination 4-3. Figure 4-9. and Applications . thus allowing for easy by a reactive group on the end of another comparisons between text and table. This item-by-item examination of both ends allows the hardener to react with crosslinking and processing parameters also two epoxy groups on two different molecules. will then bond to polyesters where the active group. The ring-opening reaction is illustrated in Figure 4-12. The placement of the epoxy ring is. quite different from unsaturated which is slightly positive. polyesters. The ta. of course. of the chain. and Applications . there is much greater choice in The epoxy ring opening reaction is quite the nature of the backbone for epoxies than different from the free-radical crosslink- for polyesters in which the crosslinking site ing reaction used to crosslink unsaturated is integral to each repeat unit. at the end of side chains. as with the novolac ally the more accessible of the two epoxy- epoxy. the oxygen that was part of the epoxy ring. the nitrogen on the hardener linking occurs in epoxy resins. entries in the table. This site is (which has a slight negative charge and is usually at the ends of the polymer chain or. The ni- a second attachment is attempted. is usu- of the epoxy polymer. the bond with the carbon. the ring is still at the end of a side ring carbons. If and thus breaks open the epoxy ring. A flexibilized epoxy. the epoxy ring. the ring trogen loses a hydrogen molecule as it forms will open. A typical ble also serves as a convenient review of the hardener is shown in Figure 4-11. The hydrogen. called the hardener. Fundamentals of Composites Manufacturing: Materials. Because the epoxy group is on the end usually reacts with the nitrogen. No such group is formed during the is based upon the opening of the epoxy ring unsaturated polyester crosslinking reaction. Methods. carbon double bond. which present in each of the repeating groups is the terminal carbon of the chain. It is therefore the atom that chain. The epoxy reaction creates an OH group that is important to some of the Type of Crosslinking Reaction properties of the epoxy resin. occurs along the back. It is slightly positive carbon in the epoxy ring. When the end of the amine Active Site on Polymer hardener comes into close proximity with The epoxy group is the site where cross. resins discussed later in the text. in therefore called a nucleophile) seeks the some instances. Even when the epoxy group is The end carbon of the epoxy ring.92 4: Epoxies Figure 4-10. will be useful for comparing and contrasting linking the two molecules together. never in the middle of the chain because the The nitrogen forms a bond with the carbon epoxy ring only has one attachment point. molecule. The new carbon-nitrogen bond is the critical bone of the polymer in each of the polymer bond for crosslinking. It has crosslinking parameters of the unsaturated amine groups (NH2) on both of its ends. a carbon. such as adhe- The crosslinking reaction in epoxy resins sivity. The polyesters discussed in a previous chapter in presence of active groups like the amines on this text. repeat units. Processing Parameter Epoxy Unsaturated Polyester Active site on polymer Epoxy ring C C Unsaturation C C O Type of crosslinking reaction Ring opening Addition/free radical By-products of the cure None None reaction Reactive agent to begin cure Hardeners (usually a Initiators (usually a peroxide) bi-functional short polymer) Amount of hardener or Usually 1:1 with polymer 1–2% of polymer initiator Toxicity of uncured reactants Some are skin irritants and Few problems although possible carcinogens styrene emissions can be a problem Use of solvents/diluents Less frequent Usually styrene (active in the reaction) Volatiles from the system Low Relatively high Fiber wet-out/viscosity Generally high viscosities Low viscosities and easy and wet-out more difficult wet-out Cure temperatures Mostly elevated. promoters. some at Mostly at room temperature room temperature or slightly elevated Accelerators.4: Epoxies 93 Table 4-3. Comparisons of epoxy and unsaturated polyester crosslinking parameters. and Not common Frequent catalysts Cure rates Generally moderate to long Generally short to moderate Pot life Adjustable from minutes to Generally short hours Use of inhibitors Rare (none) Frequent Use of fillers Occasionally Often in high concentrations Degree of cure Post-curing not uncommon Rarely needs post-curing Shrinkage Low High Fundamentals of Composites Manufacturing: Materials. Methods. and Applications . However. Several other thermoset curing reactions Reactive Agent to Begin Cure do produce by-products. Epoxies and thermoset esters.94 4: Epoxies Figure 4-11. and Applications . so this can be an The comparison of reactive agents in important consideration. With poly- to cure the polymer. be taken for the elimination of by-products. This by-product must be removed By-products of the Cure Reaction by the resin manufacturer to obtain the In one aspect the epoxy and thermoset desired resin properties. Table 4-3 illustrates the greater variety of The reactions used to synthesize the poly. choices available for crosslinking epoxies mer should not be confused with the reactions versus unsaturated polyesters. little if polyester curing reactions are the same— any residue of the by-product remains in neither curing reaction results in a by-prod. by-product formation as part of polymerizations. The structure of the cured epoxy is illus. uct such as that created by condensation Therefore. polyester resins are synthesized by conden- trated in Figure 4-13. the resins shipped from the manufacturer. sation reactions in which a by-product is formed. This greatly simplifies the polymer synthesis can be largely ignored by curing reactions because no care needs to the molder. A typical epoxy molecule and amine hardeners. Methods. only peroxides are commonly used Fundamentals of Composites Manufacturing: Materials. Fundamentals of Composites Manufacturing: Materials. Epoxy curing reaction with amine hardeners. Figure 4-13. and Applications . Reaction showing a cured epoxy.4: Epoxies 95 Figure 4-12. Methods. once the epoxy ring is ring. and can be slow or fast to epoxy adhesives. This means the major epoxy resin. Some catalytic ring open. However. as with parts A and B of household groups or many. if necessary. temperature. The critical com. often heated. thus causing the active site on active sites on the epoxy and on the hardener. trations of epoxy groups in the resin and ies are sometimes given as: combine Parts A reactive sites on the hardener are important and B and mix thoroughly and. and rings then have OH groups that can further other molecules that with a simple reaction react with other polymers. to create a hydroxyl (OH) group on one of For epoxies. several types of reactive the carbons that previously was part of the groups will open the epoxy ring and start epoxy ring. The most common reactive groups opened. in more sophis- react. Thus.96 4: Epoxies as reactive agents. In every case. analines. and Applications . in determining the amount of crosslinking heat to complete the curing. Methods. later in this chapter. However. directions for curing epox. Molecules that have reactive groups used to cure epoxies are called hardeners or Amount of Hardener or Initiator curing agents. and the concentration of reactants in the Most hardeners react with epoxy rings crosslinking reaction. many different molecules within each thought of as an initiator.). Each eral. the hardener and homopolymerization type can affect the curing characteristics and reactions will both occur to cause crosslink- final part properties. the physical and mechanical Many factors influence the choice of properties of the crosslinked polymer. these the crosslinking sequence. The hardener. These newly opened phenols. acids. therefore. A list of the most common mine the activation of the peroxide—the hardeners and their advantages is given temperature at which the cure takes place in Table 4-4. as will be discussed ing of the epoxy. Under certain conditions. So. is called homopolymerization. the reaction is ticated systems and especially where prop- started merely by mixing the epoxy with the erties need to be optimized. This reaction as an anhydride). When these ing materials are also available. hydroxyl groups can react with other epoxy ponent of a reactive group (hardener) is that rings in a crosslinking reaction. Hence. To facilitate the movement of to be carefully considered when deciding how the hardener and the epoxy. There are. can have only two reactive tions. the epoxy molecule can react with for this purpose are amines. the mixtures are much of each component to mix together. however. and then only a few of to be the following: compatibility with the those are available. properties. and resultant in polyester systems are those that deter. amides. the hardener might be course. a chain- can form one of these reactive groups (such reaction system is established. of conditions occur. The two epoxy sites. some hardeners can have epoxy and hardener are often referred to as multiple active sites. The relative concen- Parts A and B. mercaptans (sulfides). processing characteristics parameters that affect the crosslinking agent (time. Heating also may be required to Just as some epoxy resins have more than activate the reaction of some hardeners. and. other epoxy molecules. un- it contains a group that will open the epoxy der these conditions. the number of hardener. the polymer to come into proximity with the as well as the molecular weight of both need epoxy ring. etc. The molecules containing In simple epoxy systems the resin and the reactive groups can be small molecules hardener are mixed in roughly equal propor- or polymers. in gen- of these major types that could be used. but the most important seem relative amounts of each material that will Fundamentals of Composites Manufacturing: Materials. achieved. More about the properties of that the number of crosslinks will be rela. and has a higher per unit of weight will be high. the for complete reaction at all sites is called the maximum amount of crosslinking is stoichiometric ratio. room. therefore. critical mix ratios. good electrical Long. weatherability give exactly the right number of active sites If the stoichiometric ratio is used. maximum use temperature. flexibility Elevated temperature cure Urea Adhesion. poor HDT Catalytic Long pot life. Hardeners Advantages Disadvantages Aliphatic Convenience. elevated cures Polysulfide Moisture insensitive. usually imposed. flexibility. the epoxy polymers will be discussed later tively few. hardness Solid. A small brittleness can occur with increasing cross- epoxy molar mass number means there are link density so some reasonable limits are only a few atoms between the active groups. the number of crosslinks formed sensitive to solvent attack. low heat toughness. amines temperature cure. number of active sites per molecule. Methods. Some epoxy resins and harden- The most convenient method for compar. Fundamentals of Composites Manufacturing: Materials. Skin irritant. low cost. Higher crosslink density Therefore. in this chapter. stability. called the crosslink density. create a large number of mer and the hardener is to consider the epoxy crosslinks per unit length of polymer. However. less is small. long amines resistance and elevated cures Polyamides Room-temperature cure. Generally. Advantages and disadvantages of important epoxy hardeners. chemical Solids at room temperature. This is the molecular weight number of crosslinks per unit length is of the epoxy (or of the hardener if consider. but it is often high epoxy molar mass numbers suggest less tough. a ing the hardener molar mass) divided by the high crosslink density is desired. low viscosity blushes Aromatic Moderate heat resistance. stiffer. and Applications . High cost. high viscosity. quick set Odor. ers have a large number of active sites ing the number of active groups in the poly. poor moisture Melamine Hardness. elevated cures. and. The molar mass. high HDT Long. low toxicity distortion temperature (HDT) Amidoamines Toughness Poor HDT Dicyandiamide Good HDT. elevated cures properties Anhydrides Heat and chemical resistance Long. color Elevated temperature cure Phenol HDT. Conversely. chemical resistance. when the epoxy mass number means the material is stronger.4: Epoxies 97 Table 4-4. a crosslinked than. If the same number of epoxy rings and tional hardener (four active sites) and a hardener active sites are mixed together bi-functional epoxy (two active sites) in less (stoichiometric mixture). physical properties at maximum. the crosslink more than two active sites per molecule. This gives When the concentration of the hardener’s a three-dimensional crosslinked matrix if active sites is much less than the number either the epoxy resin or the hardener has of the epoxy’s active sites. and Applications . rings. hardener. The physical properties of such When the concentration of curing agent a product are generally not as good as if it reactive sites exceeds the number of epoxy were highly crosslinked.98 4: Epoxies The various cases of mixing a tetra-func. Fundamentals of Composites Manufacturing: Materials. and more than the stoichio. the material forms a thermoplastic Figure 4-14. equal to. thermoset polymer is obtained with most metric ratio are illustrated in Figure 4-14. Schematic representing curing at various hardener/epoxy concentrations. Methods. density will be low and the polymer will be This is the case in Figure 4-14 where the a simple adduct between the epoxy and the hardener is tetra-functional. but the environmental problems associated The two curing systems. This has been possible because. the chance of opening the epoxy ring. such as with of ingesting the material is low. solvents can be reactions and solvent removal from the cured added to provide the capability to wet-out part is not necessary. the amount of hardener handling the uncured resins and hardeners. ver. The appropriate amount of hardener is Another problem is the potential toxicity determined. In practice. Solvents have been used with epoxy resins sus the epoxy case where the hardener and to obtain thinning and easier fiber wet-out. is typically density. of the polymer. Remember that polyester should be consulted before handling. vapor pressures associated with solvents ried out simultaneously or sequentially—one are not present in most epoxy resin curing by the traditional epoxy method on the ends systems. direct contact should be avoided. contaminants. may be Polyester thermosets offer a distinct appropriate for some of the most worrisome contrast in the amount of initiator needed of the resins and hardeners. such as styrene that brittleness that comes with high crosslink will react in the addition reactions. of vapors or liquids if ingested. most low vapor pressures in contrast to polyesters molders will use about 20% less hardener where styrene vapors are often concentrated. epoxy and poly. used is less than the stoichiometric amount. The material versus the amount of hardener used in an safety data sheet (MSDS) for the specific resin epoxy system. After curing. than resin on a molar mass basis to allow Thus. stances. possibly to reduce the thermosets. Protection is given by the simple practice mopolymerization (as discussed previously of wearing plastic or rubber gloves when in this chapter). These solvents are removed from the mer and high crosslink density. Since almost any type of polymer can in contrast to polyester thermosets. no such problem exists. and one by the additional However. A solvent. precautions. hardeners are known to cause skin irritation. if high-molecular-weight ep- mechanism in the middle used by polyester oxy resins are used. thermosets use peroxide initiators. the pre-cured epoxy resin will likely used because it is consumed in the curing be a solid. This dual-cure system the reinforcement or mix easily with a allows for both a high-molecular-weight poly. there is be used as the heart of an epoxy system. finished parts. High Some uncured epoxy resins and some excesses of hardener will result in nonpoly. In this filled by the hardener. Researchers der which the crosslinking reaction is run have suggested that some resins or harden- as homopolymerization usually requires ers are potential carcinogens. such as a respirator. Therefore. two crosslinking reactions can be car.4: Epoxies 99 resin and the physical properties again Toxicity of Uncured Reactants reduce and linear polymers result. possibly with chemical accelerators. Nevertheless. the likelihood of breathing the vapors for homopolymerization and other methods from epoxies is not high. the high case. with them have forced their elimination in ester. in part. filler. by the conditions un. Fundamentals of Composites Manufacturing: Materials. Methods. Likewise. higher cure temperatures than normal most of the epoxy resins and hardeners have hardening reactions. an no need for a solvent to be a bridge molecule innovative system uses an epoxy polymer that between epoxy chains as this linking role is contains carbon-carbon double bonds. Only a small Use of Solvents/Diluents amount (1–2%) of initiator is required. most cases. Therefore. resin are often 1:1 in concentration. In these cases. can be combined in some unique in. When the epoxy polymer is capable of ho. Fortunately. and Applications . meric products that have poor properties. Epoxy resins are generally more viscous Reactive solvents. This complication can be alleviated by and hardeners have low vapor pressures and using a latent hardener and then choosing a are. espe- tion) of the polymer. the viscosity drops. and hardeners. epoxies. some heating may be required just to higher-molecular-weight resin. intended application. A general be heated to melt the solid mass. This usually requires the use of solvent to reduce its viscosity. it is a The performance of the polymer is often bother in processing as the entire batch must related to the cure temperature. Most epoxies are cured at elevated tempera- For instance.100 4: Epoxies Volatiles from the System significantly shorten the pot life or working As already indicated. However. A method of reducing the viscosity of Cure Temperatures epoxy resins is to combine different epoxies. as used in polyesters. epox- wet-out. epoxy depends strongly on the nature of Addition of a low-viscosity resin also helps the resin and hardener and. thus increasing the likelihood viscosity resin also based on bisphenol A. should be taken to not become exposed to An epoxy resin also can be diluted with the vapors. and Applications . When this is a respirator. Some resins and. which can occur upon cially. rule is that the maximum use temperature The problem of fiber wet-out with ep. temperatures to reduce the cure time to a While this freezing does not produce changes reasonable level. The normal absence of solvents thinning but not so high that the hardener in epoxy systems also leads to low volatil. have been used successfully fiber wet-out is much more difficult with as reactive diluents. somewhat. the heating and wet- ity of the system. Methods. However. therefore. from different families are combined. If resins make them liquids at room temperature. Conversely. ing reaction. which usually increases with resin before it is applied to the fibers. a low-viscosity resin based on tures to facilitate the movement of the resins bisphenol A can be combined with a higher. of their colliding and resulting in a crosslink- This allows the molder to obtain moder. most epoxy resins time. the curing reaction also ies used at high temperatures need to be begins when the resin is heated. of solvent in the polyester system. which are. should not exceed the glass transition of oxies is sometimes solved by heating the the polymer. Therefore. on the prevent unwanted solidification (crystalliza. inherently low in emitted heating temperature high enough to cause volatiles. they The temperature selected for curing the should be checked carefully for compatibility. done. the solvent is removed prior to or dur- ing the cure and adequate provisions must Fiber Wet-out/Viscosity be made to control the solvent emissions. which may cured at even higher temperatures. especially because of the not commonly used with epoxies. are than polyesters. Since both epoxy and hardener ate-to-low viscosity and yet retain the ac. is activated. The Fundamentals of Composites Manufacturing: Materials. But some normal presence of styrene or some other low-molecular-weight epoxies. thus facilitating increasing crosslinking). although usually short ceptable physical properties typical of the ones. reactive. if solvents are out can be done quickly so the crosslinking used or if the resin or hardener is heated. When increasing the cure temperature (and heated. some hardeners do not react readily at prolonged storage when the freezing point room temperature and therefore need higher of a resin is at or below room temperature. reaction simply does not have sufficient time the volatility will increase and caution to proceed very far. Therefore. are often polymers. in the chemical nature of the polymer. course. polysulfides are much more reac- at room temperature but will react rapidly at tive with epoxies if a basic material. are used for composites. reactive than the original amine. and high-perfor. oxies are usually made from multifunctional Another type of accelerator is basic. For Some hardeners react slowly with epoxies example. such as for up to six months at ambient temperature. are faster than a com- fibers are spread and easily wetted. The high-temperature ep. Note that the DICY is Epoxy cures can be as short as a few min- often suspended in the epoxy resin as a small. use of accelerators and/or catalysts to reduce ing of the resin and the hardener. the common high-temperature promoters. Methods. to crosslink. ground to particles. the use of accelerators. would be the case for a room-temperature Therefore. even size solid.” A typical example of a latent ecule off the polysulfide and leaves a strongly hardener is dicyandiamide (DICY). and Applications . It was ecule to the oxygen of the epoxy ring. However. some epoxy-hard- Some epoxy resins will cure at room ener reactions can be facilitated through the temperature. type generally reacts with the hardener to They have high crosslink density. slightly more positive. and and an epoxy. as the hardener and result in incomplete cures. resins. is present. called high-temperature-vulcanization however. Cures in which DICY is the curing agent oc- cur when the epoxy mixture is heated to at Cure Rates least 250° F (121° C). which is the gel time. The terminal carbon ing agent with extensive cooking. acid can react with the amine-derivative high-performance coatings. are not used in epoxies. These are called Some acids act as accelerators by reacting room-temperature vulcanization (RTV) with the epoxy ring to make it easier to open.4: Epoxies 101 cure temperature for common epoxies used Accelerators. sometimes derivative hardeners. such as high temperatures. This and highly aromatic epoxies and hardeners. (Refer Applications for RTV epoxies are grouting. to Figure 4-13 for the reaction of a hardener household adhesives. is most often used with amine and amine- Elevated temperature epoxies. which.) This type of acid accelerator simple coatings. cobalt compounds. Promoters. DICY should be used only when the cure of a large part. For even Because most epoxies are cured at el- higher performance or for resins more difficult evated temperatures. when ground and mixed The types of accelerators or promoters into a liquid epoxy resin. This is because referred to as latent because their ability to the tertiary amine takes a hydrogen mol- react is “hidden. It is a solid negative sulfide behind.) slightly negatively charged hardener. make it a more effective attacking agent. Even through tightly packed fibers may filter out polyester cures that take several hours. which is less mance adhesives. (“Vulcanization” is an old name for The acid molecule donates a hydrogen mol- crosslinking still used occasionally. which derived from the crosslinking reaction of then makes the carbons in the epoxy ring natural rubber using sulfur as the crosslink. electrical potting. Vulcan is subsequently more easily attacked by the was the Roman god of fire. inhibit the reaction as the excess (HTV) products. utes but are usually several hours long. Too much acid will. and catalysts is less common than epoxies are cured at 350° F (177° C). This means when heated. and Catalysts in composites is 250° F (121° C). These curing reactions are that processes in which the resin is forced generally slower than polyester cures. parably sized epoxy part. even if the epoxy Fundamentals of Composites Manufacturing: Materials. curing agent. hence the name. hardener to form an amine salt. These hardeners are often a tertiary amine. with polyesters. initiated merely by the mix. often an aliphatic amine. provides stability used in polyester thermoset systems. and Applications . of course. Occasionally. The cure ies. mercial composite processes that sometimes Figure 4-15. and then a gradual curing times of epoxies and the need to heat cool down for another hour. the materials provides for long pot life in ing profile for an epoxy is shown in Figure most epoxy systems. have a shorter to about 355° F (179° C) and held for about pot life than high-temperature-cure epox- two hours to complete the cure. Those epoxies that cure at room curing.102 4: Epoxies were heated to cure and the polyester was Pot Life cured at room temperature. A typical cur. The pot life is the working time of the A typical epoxy cure would be a ramp resin during fiber wet-out and other pre-cure up to the cure temperature over about one operations. Fundamentals of Composites Manufacturing: Materials. The system is then further heated temperature will. a system 4-15. which can result in temperature for an hour. Typical curing profile for an epoxy. This allows the some urgency to complete the molding of the system to equilibrate and gives uniform material. which is the time that the resin about 250° F [121° C] or 350° F [177° C]) can be stored without reacting. Usually this is not a problem as even in rates and temperatures depend on both the the RTV systems the pot life is sufficient for resin and the hardener and are suggested most manufacturing processes. Methods. The resin/fiber system is heated to will be intentionally heated or use reactants about 130° F (54° C) where it is held at that are especially active. holding at the cure temperature (often shelf life. (This is a different time than hour. Typical com- by the resin manufacturer.) The long for one to five hours. lowered exo- they do not have to be discarded when some therm. the hardener crystals remelt self-lubricating properties. abrasion resistance. highly weight sensitive. Therefore. so long as a resins advertise that they do not need to minimum performance level is reached. meaning that the the manufacturer usually sets a maximum epoxy composite is used where mechani- shelf life after which the material is as. and patching repairs—all discussed later in this text. to improve the shelf life of such materials This arises from the generally high per- is to lower the temperature of the mixture formance requirements placed on epoxy during storage and thereby extend the parts. even at low temperatures. cal and physical properties are to be at sumed to have become too hard (cured) to maximum and weight a minimum. which means that they will (depending. weight is usually not a demonstrated up to one year of shelf life major consideration with polyesters. resin transfer molding. on the type of not have to be refrigerated and. improved solvent. improved arc hardener. Fundamentals of Composites Manufacturing: Materials. As the prepreg is dried by evaporat. even more. thus material is needed. These use. Inhibitors of the called prepregs. whenever resin and hardener Use of Fillers are mixed. In be stored at low temperatures. ing that may come from extreme and rapid One mechanism to provide this long cure changes in the temperature of the composite life is to use a hardener that is applied to part). thus reinitiating filament winding. They have contrast to epoxies. Prepregs and any other material for epoxies. and Applications . These Following are some of the most common are valuable new resins because of this advantages of using fillers with epoxies. These the performance requirement. increased density. and general need for heated of resin and hardener that are pre-coated curing make the use of inhibitors unneces- onto the reinforcements.4: Epoxies 103 use room-temperature-cure epoxies include and mix with the resin. Some epoxy life. Even when kept refrigerated. improved ability the prepreg in a solution with resin and to machine the composite part. are discussed later in this type used in polyester systems are unknown chapter. using fillers. sary in most epoxy systems. increased viscosity. These materials. Normal industry practice is to discard performance factors usually outweigh the the materials after they have reached this cost advantages that can be obtained from maximum shelf life. filler chosen): extended pot life. that consist of mixed resin and hardener will gradually cure. improved compressive inhibiting the reaction between resin and strength. This high performance is often shelf life. Some epoxy resins have been developed the cost of the product usually outweighs that have extremely long shelf life. the hardener crystallizes ductivity in applications where a conductive and becomes separate from the resin. curing will occur. resistance. When the prepreg is heated dur. With polyester thermosets. relatively stable pot under some circumstances. it should be anticipated that In contrast to thermoset polyesters. when kept at room temperature. the crosslinking reaction. and improved ing molding. increased electrical con- ing off the solvent. Use of Inhibitors The shelf life of epoxies can be a problem The long cure times. lack of peroxide initiators in the cur- products are made from materials consisting ing system. Methods. to some extent. characteristic. The best that can be done epoxy composites rarely contain fillers. reduced shrinkage. resistance to thermal shock (crack- maximum time limit has been exceeded. 104 4: Epoxies Degree of Cure dimensional tolerances are critical. The crosslink. property is also important when the mold gests that post-curing might be important as is made of a flexible material and shrinkage a method of getting more efficient use of the could change the shape of the mold itself. The creation of the OH group during the crosslinking reaction (see Figure 4-13) Shrinkage and the possible presence of OH groups in One advantage of epoxies over unsaturated the body of the polymer give epoxy resins the polyesters is the low shrinkage that occurs superior ability to adhere to many surfaces. Since these changes paratively rare. the cure is done at elevated temperatures. are only on the ends of the chains. in the properties of epoxy composites and linking as do epoxy polymers. even within a its energy when it is bonded to some other polymer type. whereas the cross. during the molding process. will generally result in lower surface. The presence of the OH group creates high ing reactions of polyesters tend to draw the surface energy—a characteristic of materials molecules together tightly. and then placing the COMPOSITES part into an oven where it is given an ex- tended additional curing time at an elevated As was discussed in the chapter on matrix temperature. Polyester parts also can be post-cured to in properties that are mainly dependent advance the crosslinking. Even within those improve the part’s physical and mechanical considerations. However. but this is com. Post-curing is done by removing the part from the mold after considerable PHYSICAL AND MECHANICAL curing has taken place so that the part is PROPERTIES OF CURED EPOXY dimensionally stable. some properties of composites are the cure. this section examines the trends require the same mobility to achieve cross. The post-curing advances materials. Fundamentals of Composites Manufacturing: Materials. Methods. on the reinforcement. compares those with the expected properties polyester polymers can react adequately of polyester thermosets. Low shrinkage improves molding of epoxies results in a strong tendency to capabilities. much like Adhesion an epoxy. comparison are given in Table 4-5. molds. The reason for this linking reactions of epoxies are far less tight. The higher the energy of the surface. that are good in adhesion. in cases where matrix materials (not polyesters or epoxies) the polyester does not have the required when they are discussed in later chapters. This The slow cure rate for epoxy resins sug. it creates a higher degree mainly dependent on the matrix and others of crosslinking in the part. the high surface energy shrinkage. the choice of matrix can properties. that is. The results of that at room temperature provided there is suf. the net with polyesters is due to the greater number result is a lowering of the energy of the of crosslinks and the relative frequency of entire system—a condition favored by nature the crosslink sites along the backbone. usually not major. and Applications . Therefore. in and described by the laws of thermodynam- comparison to epoxies where the crosslinks ics. which can ficient solvent present to form the bridges serve as a reference for comparisons of other between molecules. make some differences. This is done to on the reinforcement. the more likely it is to have a lowering of Lower crosslink density. especially for parts in which bond with other surfaces. Therefore. Polyester polymers do not are small. good adhesion is that if a high-energy surface The greater tightening of the molecular mass is bonded to some other surface. mobility at room temperature. The adhesion in the chapter on resin-fiber bonding. This strong bonding is methods that attempt to separate the fibers seen in many of the properties of composites from the resin that binds them. This property is measured by the reinforcements. These are used reinforcement is the principal element for in many applications. ceramics. even though the used extensively for adhesives. of course. composites. epoxy resins are not do its job. stiffness. Property Epoxy Unsaturated Polyester Adhesion Excellent Good Shear strength (fiber-matrix Excellent Good bond) Fatigue resistance Excellent Moderate Strength/stiffness Excellent Good Creep resistance Moderate to good Moderate Toughness Poor to good Poor Thermal stability Good Moderate Electrical resistance Excellent Moderate Water absorption resistance Moderate Poor to moderate Solvent resistance Good Poor to moderate UV resistance Poor to moderate Poor to moderate Flammability resistance Poor to moderate Poor to moderate Smoke Moderately dense Moderately dense Cost Moderate Low As previously mentioned. the epoxy material has a tendency the resin and the fiber is the composite’s to form strong bonds with the surface of shear strength. Therefore. Just as with other identified with the bond strength between surfaces. the reinforcement can. and Applications . This is one Fundamentals of Composites Manufacturing: Materials. ods for doing this will be discussed in detail tance. The between the matrix and the fibers is a key important consideration here is that epoxies aspect of these properties since if the matrix have excellent shear strengths. The meth- including strength. differences between the adhesive to other materials such as metals. capabilities of epoxies can make sufficient and plastics. and other mechanical of composites to other composites as well as properties.4: Epoxies 105 Table 4-5. also used difference that the mechanical properties as adhesives in systems that do not involve could be significant. and solvent resistance. Possibly the most important aspect of adhesion in epoxy composites is the bond Shear Strength (Fiber-matrix Bond) strength between the epoxy matrix and the The composite property most closely reinforcement fibers. creep resis. Comparisons of unsaturated polyester and epoxy properties. most other matrix materials. stiffness. especially in slips along the reinforcement and does not comparison with thermoset polyesters and transfer the load. Epoxies are. Methods. including the bonding strength. if epoxies are strongly crosslinked. the fiber-matrix polyesters and epoxies are moderately good. It is strongly controlled by the presence the resin and the fibers. Fatigue also depends on the ability of the when the fibers are not continuous in the matrix to withstand repeated flexing. then. As mentioned previ. possibly more for these overall structure. That stiffness is dependent posite products are chiefly dependent on on the aromatic nature of the resin and the the reinforcement. over time rial under long-term loads. However. the other factor is the stiffness of the polymer strength and stiffness properties of com. bond strength also affects strength and stiff. This failure is often the is usually a stretching or sliding of the mate- result of breakdown of the bonds between rial. Even though the than polyesters in this property. excellent resistance to this type of internal indicating poor elongation. If the matrix breaks or deflects under crease the molecular weight of the resin. Therefore. that will prevent it from transferring This can be done in thermosets most easily the load to the fibers. with the repeated movements of the com. polyesters are excellent Strength/Stiffness because of their high crosslink density. a slippage in the matrix can result in involves the ability of the matrix to elongate movement of the fibers or creep. The first of properties. responsibility of holding the fibers in place. Therefore. of fiber reinforcements that have almost no ously. In this regard. Fundamentals of Composites Manufacturing: Materials. good elongation while still maintaining many Normally. they ness. This strength and stiffness are high-performance composites. Creep Resistance posite part are below the normal strength Creep is the gradual movement of a mate- and stiffness of the materials. and Applications . More cross- epoxies is usually excellent. movements over long periods of time. backbone itself. Epoxies are usually better properties than any others. matrix stiffness under load is important in posite part and the overall strength of the these cases and epoxies are known to have matrix. Overall. as described previously. especially polyester brittleness becomes a problem. Even when the movements imposed on the com.106 4: Epoxies of the key reasons why epoxies are used in thermosets. the matrix Toughness strength and stiffness have some relevance The normal procedure to improve me- to the strength and stiffness of the compos. attributable to the high aromatic character of most epoxies and the basic internal adher- Fatigue Resistance ence of epoxy molecules to their neighbors. Although epoxies can be quite stiff. This movement the part might fail. Even considering the effects of the fi- ber and the fiber-matrix bond. Methods. the integrity of the fiber-matrix bond creep under normal environmental condi- is critical to the successful performance of tions. This part. two important factors affect of the most important strength and stiffness the amount of matrix creep. some types have motion. by increasing the crosslink density until the ally stronger and stiffer than most of the crosslinked structure becomes so rigid that competitive resins. can become slightly superior to polyesters. The As with unsaturated polyesters. But. fatigue resistance in these is the crosslink density. load. links hold the matrix in place better. because the matrix has the the composite. Fatigue resistance is a measure of how which is usually stronger and more stable a material performs with repeated forced than in polyesters. Epoxies are gener. chanical and physical properties is to in- ite. fibers are a critical factor. Therefore. These aliphatic segments act One factor is the extent of crosslinking. to achieve higher tougheners is the addition of a thermoplastic crosslinking. the thermal stability is the basic nature Fundamentals of Composites Manufacturing: Materials. generally. Methods. there. As with other flexible crosslinks act the same as a flexible thermosets. Less aromaticity or higher aliphatic an epoxy with a thermoplastic will be a ma- content generally means more flexibility jor factor in the future of epoxy resins. higher the thermal stability or allowable use These types of materials are called tough. An example of a toughened The second important factor affecting (or flexibilized) epoxy is given in Figure 4-10. rubber polymers is that chemical resistance mer chain segment between the epoxy end and strength are often negatively affected. The problem with adding part is dependent on the length of the poly. improved will combine the processing advantages of a toughness but decreased overall strength. and Applications . improved toughness. the ability. in the cured polymer these and longer curing times. damage tolerance of thermoplastics. brittleness. therefore. including higher temperatures crosslinks and. epoxy polymer. and maximum use temperature in of shaping. Long polymer segments are gener. the ibility and. like internal springs. Closely associated with the adding of rubber fore. the toughness of an epoxy by using a highly tional reactants and more aggressive curing flexible hardener. ened epoxies. groups. with short polymer segments and. toughness eventually reaches backbone. character in the epoxy and hardener mol. a maximum value after which the rigidity Another method to increase the tough- of the highly crosslinked structure leads to ness of epoxies is to add rubber polymers. toughness of the epoxy the polymer melt). With epoxies. (mixing of monomers) or alloyed (mixed into ing in the polymer. complex synthesis of the epoxy resin. But this factor is resin and forms a separate phase when the counteracted by the presence of more ends two polymers are mixed. ing the polymerization stage to form a fully The toughness of the epoxy part is also compatible polymer that has domains of ther- dependent upon the amount of aromatic moplastic surrounded by areas of thermosets. These can be copolymerized with the epoxy In addition to the amount of crosslink. Many experts believe that the combination of ecules. Obviously a compromise must polymer to an epoxy. A tactic for improving toughness without major sacrifices in other physical properties Thermal Stability is to include aliphatic segments along the Two important factors strongly affect the backbone of an otherwise highly aromatic thermal stability of epoxy composites. with the impact strength and the final part. This gives flexibility to the conditions. temperature. also possible to increase be achieved through the use of multifunc. The higher the density of the crosslinks. This in the molecules and. giving improved flex. thermoset. low viscosity for wet-out and ease stiffness. higher crosslinking can It is.4: Epoxies 107 optimizing toughness in composites often The major problem with toughened epoxies requires a compromise with some other is the higher cost associated with the more properties. of course. This problem is especially acute if the rub- ally tougher than short polymer segments ber material is incompatible with the epoxy of the same chemical type. Some can be added dur- simultaneously. Many thermoplastics be reached on the length of polymer chain can add toughness and their effectiveness is segment and crosslink density if toughness generally dependent on their compatibility and the other properties are to be maximized with the epoxy resin. therefore. they are highly susceptible to water absorp- However. Even non. therefore. Most compos- molecules along their backbones. forces is that water absorption resistance is Still another factor in thermal stability. resistance of epoxies as good. The electrical properties of epoxies are UV Resistance improved because of the lack of solvent The high aromatic content common to or monomer residues. thus removing this problem from epoxies distortion temperatures (HDTs) of various in general. countering that is the presence of have higher HDTs than equivalent amine- the OH groups formed when epoxy resins are cured polymers. most organic Epoxies seem to have the right compromise solvents) have little effect on epoxies. non-aromatic solvents (that is. Other resins. but not as stiff as aromatics. polyesters may have epoxies given in Table 4-2 show that aro. the nature of the hardening water and will. whereas non-polar and both a function of performance and of cost. Hence. The net result of these two opposing all affect the use temperature. They have better electrical majority of solvents are reasonably resisted. properties than the cheaper polyesters and leading to a characterization of the solvent are lower priced than the better performing. are vastly superior to epoxies. only moderate in epoxies. These OH groups have an affinity for of the polymer. have Water Absorption Resistance higher thermal properties than straight- The high aromatic content of most epoxy chain aliphatics. is the temperature at have a high number of doubly bonded oxygen which degradation occurs. which are stiff. Therefore.108 4: Epoxies of the polymer chain. high-performance resins. acid-cured. Epoxies are increases the ability of the water to penetrate. the aromatic content cured. absorb water mol- agent. considerable residual styrene content that matics have higher thermal properties than can be vaporized if the polyester is heated. This is attracted to epoxies. aliphatics. straight-chain aliphatic epoxies However. especially at high temperatures where to high temperatures and the degradation the natural swelling of the polymer further temperature can be important. some applications see excursions tion. Epoxies are generally superior to polyesters but are better than thermoset polyesters. long before this temperature is reached. with high-perfor- although not one that is related to most mance polymers being superior. Solvent Resistance Epoxy resins are resistant to solvents Electrical Resistance that are dissimilar from their basic nature. This results in exci- large enough that they do not volatilize eas. Table 4-2 also shows that resins helps them resist water absorption. in resisting water absorption. the heat ily. Epoxies are the preferred resin for com. and Applications . The bond electrical fields and cause the electrical between the aromatic group and the molecule properties to decline precipitously. tation of the bond electrons by UV light and Fundamentals of Composites Manufacturing: Materials. In contrast. Polar solvents. only moderately good in these applications. to which it is attached have about the same crosslinked epoxy and hardener polymers are energy level as UV light. discussed in the chapters on specialty and high-performance resins. which can become most high-performance epoxies is not good volatile when heated or subjected to strong for ultraviolet (UV) light resistance. and the overall crosslink density can ecules. These oxy- ites have lost their stiffness and strength gen molecules are highly polar. like water. will be slightly posites used in electrical applications. Polyesters normal applications. and that cyclical aliphatics. Methods. For instance. The in this regard. material is laid into the mold. prepreg material is tacky and so the release Epoxies and polyesters are similar in smoke paper is used to keep the layers from sticking generation. the amount of resin/hardener coated onto the When halogens are used to give non-burn. The resultant can become acrid and potentially dangerous. A form of epoxy combined with reinforce- dency of materials to burn. Used extensively materials tend to char rather than burn in the aerospace and sports equipment in- freely. Polyester resins are approximately half to The paper layer is removed as the prepreg one-third the cost of epoxies and. the amount of smoke is often high. ric or. Methods. The same high. wetted by the resin. cost is one of the a part. then laid into the mold or otherwise shaped. and the need aliphatic polymers. against a sheet of release paper to which the matics. a group of carefully arrayed fibers through a will further reduce the flammability of the resin bath resulting in the fibers being fully resin. which is seen as a reduction in both dustries. pulled ally added to the polymer during synthesis. Alternately Smoke and more commonly in commercial practice. a prepreg is a sheet made of fibers the ability of the material to be ignited or cloth onto which liquid epoxy resin mixed and the rate at which the material burns. the smoke a roller applicator system. Excess resin was removed by squeezing the fiber/resin sheet. Several layers tions where profits are low and volumes are are often placed on top of each other until Fundamentals of Composites Manufacturing: Materials. In both types of complished on a machine that pulled the fab- resins. SPECIAL COMPOSITE APPLICATIONS Flammability Resistance Prepregs High aromatic content reduces the ten. cial practice over the resin bath because ing is not vigorous (a smoldering effect). Cost When the material is to be molded into Without any question. fore. This method is preferred in commer- emitted in large amounts even though burn. In common practice. resin/hardener mixture has previously been The smoke is quite dark (sooty) and can be applied. the most important factors that restrict their ter weatherability. and Applications . the roll is allowed to return to room major impediments to widespread adoption temperature so it is tacky and pliable. paper can be carefully controlled by using ing characteristics to the resins. the cost differential is critical. The aromatic ment is called a prepreg. the use to composite applications where cost is UV resistance of both materials is enhanced not the major factor in the purchase of the through the use of chemical additives that resin. in applica. The sheet is rolled up and stored at low temperatures until use. light’s attack on the resin. to cure them with elevated temperatures are sistant to UV light and have significantly bet. It is of epoxies as replacements for polyesters. the coating process was ac- similar in this property. the dry fabric or arrayed fibers can be pressed Even though the burn rate is low for aro. These are much more re. if unidirectional fibers were used. thus preserving the life of the resin.4: Epoxies 109 subsequent rupture of the bond. These types of applications usually absorb UV light or absorb the products of UV require high-performance materials. the addition of halogen atoms. There- situation applies to aromatic polyesters. the cost of epoxy resins. with hardener has been coated. the greater Polyesters and epoxies can be made using difficulty in wetting the fibers. together. usu. In research Epoxies and highly aromatic polyesters are and development. the materials can be enclosed will release. the material is advantageous in keeping it in Most epoxy molds are made by forming place in the mold and in keeping the various them over a positive model of the part to be layers in place on top of one another. Metals have are frozen in place by the stiffeners. expansion situations.110 4: Epoxies the desired thickness is reached. pressure can be applied simultaneously. The flat nature of applications. or can be the original part itself. The ease of forming epoxies by The epoxy mold is usually backed by stiff- molding gives them an inherent advantage eners to give additional rigidity to the mold. composite. Invar®. The model is often made from epoxy filled gether. the surface becomes much Fundamentals of Composites Manufacturing: Materials. especially for molds that must These stiffeners can be metal. even wood and are arranged on the back of the metals have improved surface hardness the epoxy mold so that critical dimensions and durability over epoxies. onto the epoxy surface as a fine spray. the advantage for molds that will be used Some epoxy molds are stabilized by adding to make many parts or for molds where the large amounts of filler. and Applications . This coat- mal expansion coefficient the same as car. ing is usually nickel. which is splattered bon-epoxy composites has been developed. epoxy molds have proven to the prepreg material and the use of a pa. The higher-temperature adoption as a material for tooling (molds). point to the difference bility. molded. as the part being cured. the value of design of composite parts often stipulates matching the thermal expansion of the mold that the directions of the layers be different. Some These molds have improved dimensional sta- molders will. For these critical For additional stability of the surface. Curing is almost always done at the highest possible Tooling temperature to ensure that the epoxy will Many of the key performance characteris. Autoclaves are conveniently used to with glass beads so it will machine easily cure these prepreg parts because heat and and not be so heavy as to be cumbersome. or be made quickly and at low cost. the epoxy is laid onto the surface in a vacuum bag and cured. The thickness of methods are discussed further in the chapter the epoxy is determined by the desired stiff- on molding of advanced materials. This model can be made by machin- The laid-up material is then cured. After The metal. is very expensive and curing the metal. However. These molding of the model and then cured. casting. The tacky nature of requirements. Because the difficult to machine. cure gives a higher crosslink density in the In this application. often metal particles. However. a metal with a ther. be far less expensive and often durable or per layer to separate the layers in the roll precise enough to meet part performance facilitate this cutting. survive repeated moldings (even at lower tics of epoxies have led to their widespread temperatures). epoxies are competing epoxy and results in a more durable mold. epoxy molds can be metal coated. thus in thermal expansion properties between allowing the mold to be cut directly from a the metal molds and the composite part and dimensional representation of the part as will therefore prefer epoxy tooling because would be available from a computer-aided it has the same expansion characteristics design (CAD) program. over metals. dimensions are especially critical. however. with the part has given this metal a special the prepreg materials are often laid down niche where high volumes and precision at specific angles and may even be precut parts are both important. For many other to fit specific shapes. After treating the model so the mold epoxy Alternately. often ing. squeezing the layers to. with metals. ness of the surface of the mold. under pressure. Methods. They are often easy to machine. several techniques have been used for resin or prepreg material must be discarded monitoring the state of the cure. Many instances occur routinely where fore. the cost of the equipment required to cures of these materials. Methods. setting resins. It detects changes in the ability of the to be largely retained. Cure and Shelf-life Monitoring temperature. time as the method for determining when because of some unknown storage condition. time would also allow careful control of the The shelf-life period has traditionally crosslink density. Another were not directly associated with the part. Hence. and device/technique is especially convenient others changed as the part became cured. on the basis the end period was when the polymer was of viscosity. In addition. and Applications . The small amount of metal resin as the characteristic property to sense reduces the cost of the mold and allows the the changes in the cure state of the poly- thermal expansion properties of the epoxy mer. It was found that many fully monitored using CrossCheck include electrical properties. for measuring the rapid. problem is the possibility of using material These methods used oven temperature or that is within the stated shelf-life limits but. The CrossCheck some value and are still dominant in the device and technique have been success- industry. re. thus device has been used for measuring changes limiting the use of this technique. There. the useable cured part. thus reduc. in the mixing of components in various poly- An inexpensive and easy-to-use device meric formulations. etc. Charge transfer capability is directly linked to changes in the CASE STUDY 4-1 material state such as crosslinking. initial period was a time of stability and then ing the ability to distinguish. polymer to transfer charge. the (named CrossCheck™) has recently been resistivity of the base resin was measured developed that allows the cure state to be and then monitored as it changed as various Fundamentals of Composites Manufacturing: Materials. UV-cure epoxies and cyano-acrylates. viscosity. the make these measurements is quite high. This device uses the resistance of the durable epoxy. These were largely unsuccess. tance changes quickly. defined whether or not a resin can be used. of various electrical properties of the part as Other resins that have been success- indicators of cure. permittivity. they lack the precision of a method fully used to monitor shelf life and out-life that directly senses the state of the part as changes in several different types of thermo- it is being cured. Comparisons with ful because the viscosity became high long physical specimens have confirmed that the before the part was fully cured. room-temperature Sadly. because it is “out of date” and suspect on The first methods of monitoring the cure whether it is still acceptable for use. the cure was completed. mization of toughness and strength. While these have it has seriously degraded. The sistivity. The results of these studies Initial experimental attempts used the have shown a gradual change in resistance viscosity of the resin to sense the cure state followed by a period in which the resis- of the part. It is usually sold Reaching this optimum cure temperature/ as a hand-held instrument. repeatable measurement. ratio is high enough to provide a stable and ping the cure can be determined explicitly. thus permitting the opti. The experiments led to the use shelf life can be easily monitored. a nearly cured part from a fully getting harder (curing).4: Epoxies 111 more scratch resistant than even the most sensed. In these studies. The device uses multiple The long cure times for epoxy molding electronic techniques to reduce the inherent have suggested that molding cycles might noise to a point where the signal-to-noise be shortened if the optimal moment for stop. such as conductivity. dielectric strength. a bond is formed from the atom facturer) and place in separate cups. The processing of epoxy resins is some- check. to the carbon that was previously attached to 100 ml (3. used. Pour one of the hardener materials into epoxy and the hardener resins have at least one of the resin cups.) on the end of the hardener molecule. have wide applicability for monitoring what more difficult than polyesters. epoxies are creep resistance.112 4: Epoxies components (such as accelerators. ecule possessing active hydrogen is added Procedure: to the epoxy resin and thoroughly mixed to begin the crosslinking reaction.7 oz). Prepare various amounts of hardener hydrogen bonds to the epoxy oxygen. which were previously only detect. The cure rates are slow. Adhe- excellent balance between good properties sion of epoxy resins to the fibers is good as and moderate cost has led to this position. The superior to polyester thermosets. mon are listed in Table 4-4 along with the and surfactants) were added. Mix the materials two active groups. shrinkage is SUMMARY low for epoxies. (of a type suggested by the resin manu- taneously. each hardener ties thoroughly. advantages and disadvantages of each. pigments. adhesion and to the high aromatic content The epoxy resins are characterized by the of most epoxy resins. Usually. a wide selection of properties. ml (6. Epoxy resins are the second most widely The properties of epoxies are generally used matrix materials for composites. That 2. Methods. that forms a flat plate. Crosslinking occurs because both the 3. Devices and techniques. Pour equal 100 ml (3. However. The epoxy resin into four different metal or crosslinking reaction involves the opening glass cups. Wet-out of the fibers is more able with costly equipment. are now easily difficult with epoxies because the resins are detected with techniques and devices readily usually high viscosity and solvents are rarely available at modest costs.4 oz). Objective: Determine the differences in The epoxy ring is the point at which the properties from mixing resin and hardener crosslinking reaction takes place. The shelf-life changes and normal cures.4 oz. In is adhesion to other materials. a three-member problem with any composite material but ring with two carbon molecules and an a few means are available to toughen epox- oxygen molecule. The choice 4. such as Cross. 150 ml (5. A mol. Toughness can be a presence of the epoxy ring.8 oz). The epoxies are usually cured at elevated tem- changes. 1. Several of the most com. peratures. the epoxy polymers are highly aromatic so that LABORATORY EXPERIMENT 4-1 the advantages of strength and stiffness can Resin and Hardener Ratios be used in the composite part. and Applications . These acti. that was previously attached to the hydrogen Suggested amounts are: 50 ml (1. together at least two epoxy chains. in different proportions. Simul. (A convenient Fundamentals of Composites Manufacturing: Materials. as is and properties are at a premium. Hence.1 oz). (Pint canning bottles will of the epoxy ring by the active hydrogen work fine. This ring can be added to ies without sacrificing other key properties the chain end of a variety of resins to give too much. due in part to the excellent the foremost resin. and 200 the oxygen. Pour the contents of the cup into a mold of hardeners is wide. Strength fields where advanced composites are used and stiffness are superior for epoxies.) portions of vating molecules are called hardeners. thus leading to long cure cycles. TX: Shell the mixtures. (It is recommended that at least three 2040 Willard Dow Center. 2. VA: Composites Fabricators the resin of choice in making composite Association. No date. Fundamentals of would this typically be done? Polymer Resins for Composite Manufactur- 5. Company. MI. the importance 3766. 48674. Arlington. www. MI: Society of Manufacturing 3. Strong.” brochure. specimens be cut for each mixture. Carbon Fibers and QUESTIONS their Composites. the mixture to monitor the tempera. Heat the mixture to the cure tempera. Form 296-346-1289. What is a hardener and how does it dif- 2005.” brochure. Indicate three reasons why epoxies are ing. Describe the differences in crosslink Engineers. FL: Taylor 1. 10. metal frame. Chemical Company [now called Resolution]. 2040 Willard Dow Center. Plastics: Materials and Processing. 2006. A. 1995. Box 2463. After cool down. Test the tensile properties (strength.sme. Fundamentals of Composites Manufacturing: Materials.4: Epoxies 113 mold is made from two pieces of plate 6. of the properties in composites even though no fibers are present in these “Formulating with Dow Epoxy Resin. MI. Discuss two methods that might be em- ture.) 48674. 8. & Francis. ins versus thermoset polyesters. TX 77252. MI: Dow Chemical ences. Describe the physical property changes River. A. MI: Dow Chemical Company. Brent. Boca Raton. ployed to make an epoxy resin tougher.O.org/cmvs. “Dow Liquid Epoxy Resins. Report the properties and discuss P. 6. 800-832- the following: trends. 2005. Midland. Form 296-00224-0199 WC+M. 8. curing? Dearborn. Why is cure sensing more important in 7. Upper Saddle 4. remove the cured plate epoxies than in polyesters? from the mold. 3rd Edition. Contrast the environmental differences 5. 9. Describe the naming system for epoxy glass covered with film and a simple resins. Houston.) 7. density that would be expected in epox- ies and in polyesters. Mid- land.” bro- samples. NJ: Prentice-Hall. Houston. parts for airplane structures such as wing and tail components. No 9. “Composite Materials” DVD from the fer from an initiator used in polyester Composites Manufacturing video series. in epoxies that come from increasing the aliphatic content of the resin. Insert a thermocouple into the edge of between epoxy and polyester resins. Repeat steps 3 through 7 for each of the BIBLIOGRAPHY hardener/resin combinations. 11. Discuss three advantages of epoxy res. Morgan. When Strong. SC: 2445-96. “Epon® Epoxy Resins Turn Up FRP Per- stiffness. Brent. Midland. chure. and Applications . and the causes of differ. Cut tensile specimens out of each plate. Society of Manufacturing Engineers (SME). Peter. date. What are the advantages and disadvan- ture suggested by the resin manufac. tages of each of the methods? turer and hold for the suggested time. and elongation) for each of formance. Inc. Midland. Methods. although expensive than unsaturated polyesters but in some cases the properties will be com. ters) are a family of thermosetting resins their unique properties will be examined. including their manufactur- several specialty resins are used for applica. Vinyl esters are popular because • Polyimides and related polymers they have the combination of good chemical • Cyanate esters resistance and good price. In most cases. are not as expensive as epoxies. will be discussed. special ters and epoxies are not quite appropriate. and Applications 115 . silicones. The vinyl pared to metals and other composite and esters have superior toughness and corrosion non-composite resins. manufacturing procedures. these properties will be com. of these resins. and dicyclopentadiene (DCPD). and silicones. Phenolics also have good thermal • Dicyclopentadiene (DCPD) stability as do carbon matrix composites. Methods. are identified. One important property that has wide application is chemical re- • Carbon matrix sistance. fit between. The molecular fea. Flammability • Polyurethanes is another key property that is especially important and the key resin in this case is • Silicones phenolics. In some cases. some particular property • Introduction will be especially important in these materi- • Vinyl esters als and it will determine the major applica- • Phenolics tions for the resin. both unsaturated polyesters and pared to polyesters and epoxies. polyimides. Excellent tough- INTRODUCTION ness is a characteristic of cyanate esters. resins. Vinyl ester resins are slightly more convenient reference materials. Vinyl esters (pronounced vine’-ell ess’- As the specialty resins are discussed. ing characteristics and curing mechanisms. their contributions are important because of the criticality of some products that can VINYL ESTERS only be made with these resins. resistance (to organic solvents and water) in tures of these resins that give rise to their comparison to polyesters. which are epoxies. that have many similarities to. Although the composites market is domi. but are generally Fundamentals of Composites Manufacturing: Materials. All nated by unsaturated polyesters and epoxies. and seem to In general. tions in which the properties of the polyes.1: Introduction to Composites 115 5 Specialty and High-performance Thermosets CHAPTER OVERVIEW special or outstanding properties also will This chapter examines the following: be discussed. which might be Even though specialty resins only represent used in molding products made from these about 20% of the total composites market. air-pollution control applications ecules in which a carbon-carbon double bond such as scrubbing towers. and reason. This usually done by a large chemical company. Those carbon-carbon double important. The combination of excellent processing which contain a carbon-carbon double bond characteristics. or unsaturation. the epoxy backbone with vinyl ester groups. double bond. by reacting an epoxy resin with acrylic acid. These polymers are made emissions during polyester manufacturing. ily understood from their diagrammatic The vinyl esters cure much like unsaturated structure shown in Figure 5-1.116 5: Specialty and High-performance Thermosets not as good in these properties as the epoxies. equipment hous. easier to cure ester molecule is seen to be a combination of than the epoxies. and Applications . good properties. Representation of a typical vinyl ester polymer. therefore. in its back- Figure 5-1. of vinyl esters. Another im. Some of these applications are called “vinyl” groups and so the name include: pipes and tanks for the chemical vinyl ester was created to identify those mol- industry. as shown in Figure 5-2. Fundamentals of Composites Manufacturing: Materials. unsaturated polyesters. the same general methods used to crosslink portant advantage of vinyl esters over tradi. seen as residing between Because acrylic acid has a carbon-carbon epoxies and thermoset polyesters. are eas. was linked to the rest of the molecule by an ings where moderate impact performance is ester linkage. and/or toughness of unsaturated polyesters Occasionally. tional thermoset polyesters is the generally The synthesis of vinyl ester polymers is lower styrene content that can be used. carbon-carbon double bonds are not adequate. The able cost suggest that vinyl esters be used name vinyl ester arises because the chemi- in applications where cost is an important cal group that connects the carbon-carbon factor but where the chemical resistance groups to the main polymer chain is an ester. on each end replacing the epoxy rings. The acrylic acid opens Structure and Synthesis the epoxy ring and forms new bonds with the The reasons for the intermediate nature oxygen and carbon at the epoxy ring site. and marine applications where bonds are sites that can be crosslinked using corrosion resistance is critical. Methods. alleviates some of the problems of styrene not by the molder. The vinyl polyesters and are. unsaturated polyester with a peroxide initia- able for subsequent crosslinking reactions. the ester linkages at each end of the structures of some common vinyl esters are molecule make the resin more susceptible shown. and Applications . These should be compared with the to water and other solvent attack than the similar epoxy molecules in Figures 4-3 and analogue epoxy. can be seen in Figure 5-3 where the chemical First. into a vinyl to the end of the chain. The synthesis path of aromatic and strong backbone associated vinyl esters from epoxies and acrylic acid is with epoxies is retained in the vinyl ester. In essence. that unsaturation becomes attached crosslinked by using a hardener. The ester is changed the polymer from an epoxy. The reason is simple. Thus. the vinyl ester group becomes the end The beneficial nature of the often highly group of each chain. the synthesis reaction has polyester. Methods. Fundamentals of Composites Manufacturing: Materials. bone. sometimes emphasized by calling vinyl esters But the properties of the crosslinked vinyl “acrylic-modified epoxies. so multiple sites are avail. tor and styrene. but not as susceptible as a 4-6.” The similarity of ester are somewhat different from those of vinyl ester backbones and epoxy backbones epoxies because of two important reasons.5: Specialty and High-performance Thermosets 117 Figure 5-2. which is a point that is susceptible to attack by water. Synthesis of a vinyl ester from an epoxy. The reaction of the ester that has carbon-carbon unsaturation acrylic acid occurs with all of the epoxy rings at the ends and can be crosslinked like an in the molecule. Epoxies do not. use styrene as their bridge molecule polymers. shown in Figure 5-4. each containing a free radical. begin with a that the crosslinking of vinyl esters is done peroxide initiator that splits into two parts. The esters occur intermediate between epoxies and polyesters in every repeating unit of the polyester but as was stated earlier. This is shown as Step 1 in Figure but. Epoxy-based vinyl esters. Note that a when converting an epoxy to a vinyl ester. cal reactions as was discussed in the chap- sociated with the hardener would be changed ter on unsaturated polyesters. of double bonds on the ends of the vinyl ester course. Those free esters with styrene as the bridge molecule(s) radicals then react with the carbon-carbon between polymer chains. typical of properties associated with the polyester the chain-reaction nature of the free-radi- groups and the properties in the epoxy as. rather. and Applications . only near the ends of the chains of the vinyl esters. Methods.118 5: Specialty and High-performance Thermosets Figure 5-3. but still polyester thermoset. vinyl esters are fewer than the polyester. in the same manner as in unsaturated poly. and solvents and the vinyl ester have more bone but also some characteristics of the of these ester sites than the epoxy. of course. Therefore. the 5-4. Crosslinking Reactions The second important reason for the dif. use a hardener. The crosslinking reactions of vinyl es- ferences between epoxies and vinyl esters is ters. Fundamentals of Composites Manufacturing: Materials. Hence. new free radical is formed on the end of the These two factors result in molecules that polymer chain where the vinyl ester group have some characteristics of the epoxy back. is located. This reaction is. Crosslinking reactions for a vinyl ester. and Applications . Methods. Fundamentals of Composites Manufacturing: Materials.5: Specialty and High-performance Thermosets 119 Figure 5-4. The peroxide initiators. the carbon-carbon reducing the amount of water the vinyl ester double bonds are more reactive (accessible) is likely to absorb. the shrinkage is analine as the curing system. because there are fewer reac. reduces the polar character of the vinyl ester Because vinyl ester unsaturation is at the compared to the polyester. the lower number of double-bond container. lead to a high degree of crosslinking. tion is carried out in a styrene solution. accelerators. a without the need of a reactive solvent such thin glass cloth material. the free radical on the polymer end with a Also. Furthermore. thus reducing general chemical ingredients can vary from those used in typical activity. consistently to give fast gel times with nearly Corrosion resistance of vinyl ester parts complete reaction of every double bond. For instance. Just as with unsaturated commonly used accelerators in vinyl esters polyesters. the most styrene molecule. the optimal concentra- • Operate at the lowest possible tempera- tions and. bone has some additional benefit in chemical thus resulting in all of the molecules being resistance. and the conditions The polyester sites on the polymer are under which the reaction proceeds. vinyl ester resins cure rapidly and compared in Figure 5-5. thermosets often can be used in crosslinking • Remove corrosive fumes. thus significantly end of the polymer chain. The typical polymer. This sometimes can be further improved by some high reactivity of the vinyl ester groups allows or all of the following methods: some vinyl ester systems to be crosslinked • Use one or two layers of glass veil. Because vinyl esters have crosslinking bridge as shown by the oval in fewer polyester sites than traditional ther- Step 4. Unreacted carbon-carbon double bonds mon peroxide for polyesters. However. and • Dilute the corrosive liquid that is attack- other additives typically used in polyester ing the polymer as much as possible. a vinyl ester resin and a polyester resin are As a result. in some cases. the vinyl ester crosslinking reac. the most common along the backbone of the polyester are Fundamentals of Composites Manufacturing: Materials. • Use benzoyl peroxide and dimethyl tive groups in vinyl esters. polyester systems. This step also shows the attachment moset polyesters. vinyl esters. instead of cobalt accelerators. The attack is followed in Step 3 by a bonding Properties between the styrene and the polymer. Also. even when styrene near the exposed side of the vinyl ester is used. reactive sites and the greater mobility (reac- • Post-cure the part to enhance the tivity) of the end groups (versus mid-molecule amount of crosslinking and therefore polyester-type groups) allows a significant make the structure tighter. one the most vulnerable locations for chemical or several styrene molecules can form the (corrosion) attack. and Applications . The reduction in polyester groups joined into a large crosslinked network. while methyl ethyl ketone peroxide (MEKP) is the most com. The non-reacted ends of the vinyl high aromatic content of the vinyl ester back- esters will likely join to different molecules. they are inherently less of the first polymer to a second vinyl ester susceptible to chemical attack.120 5: Specialty and High-performance Thermosets Step 2 in Figure 5-4 shows the attack of for vinyl esters is benzoyl peroxide (BPO). A plot of weight gain for than the carbon-carbon bonds in polyesters. the optimal choice of ture. Methods. and place it as styrene. are the aromatic amines (analines). reduction in the amount of solvent (reactive diluent). which will lower than that of most polyester resins. Corrosion Resistance Depending on the relative concentrations of polymer and styrene. factors responsible for the higher strengths obtained with laminates made of vinyl es- Adhesive Strength ters when compared with traditional poly- The hydroxyl groups that are pendant esters. The effects of these agents in Figure 5-2) have a generally beneficial are most likely to be seen in long-term effect on the internal bonding of compos- thermal aging performance and resistance ite laminates. This is one of the entire chain is not cleaved.5: Specialty and High-performance Thermosets 121 Figure 5-5. The hydroxyl groups also provide from the polymer chains of the vinyl ester sites where adhesives can bond to vinyl Fundamentals of Composites Manufacturing: Materials. just esters have carbon-carbon double bonds as the hydroxyl groups do in epoxy resins. they play a role in to aggressive environments. molecules (which are made when the ep- especially from agents such as oxygen and oxy is converted to a vinyl ester as shown oxidizing acids. highly susceptible sites for chemical attack. vinyl ester resins from water absorption. and Applications . which results in (compared with polyesters) and the severity excellent glass fiber wetting and good adhe- of the problem should attack occur since the sion to the glass fibers. This reduces These hydroxyl (OH) groups react with the the number that are likely to be unreacted surface of the glass fibers. Methods. That is. vinyl bonding the resin to the reinforcement. only on the ends of the chains. However. Weight gain of polyester vs. The cost of phenolic resins is typically or alumina trihydrate fillers. The most common methods are haloge. and talc are used. substantially less than in polyesters. and low can have higher molecular weight. Since the color of phe- nolics varies from brown to amber and the Toughness shade is difficult to control. There. which are • excellent flammability performance. vinyl esters. 10–15% higher than polyester thermosets. sawdust. most important thermosets. important in applications where toughness As with the polyesters. and is required. Fundamentals of Composites Manufacturing: Materials. Hence. the vinyl esters spread. and Applications . than polyesters. sheet molding compounds (SMCs) and bulk junction boxes. because their properties are unique and valu- nation of the resins and adding halogenated able. The epoxy backbone in vinyl esters is does not contain a pigment. Because phenolic resins have However. They are still among the the same way as with polyesters and epox. automotive molded parts. vinyl esters do not respond well high crosslink densities. they have high to the divalent thickeners used in polyester shrinkage and are quite brittle. inexpensive fillers such affect molding properties. Phenolics have been used for many years Molding as general.122 5: Specialty and High-performance Thermosets esters. Almost all SMC and BMC molding compounds. most applica- The presence of the crosslinkable sites tions where the phenolic will be seen use a (carbon-carbon double bonds) only on the pigment to make the color uniform. discussed in detail after the section on syn- Because the vinyl esters are usually cross. which smoke toxicity. in general. often crosslinked without solvents. especially the combination of low flame even compared with epoxies. molding compounds (BMCs) and will compete consumer appliance parts. therefore. gation associated with terminal crosslinking. non-reinforced thermoset plastics Highly filled vinyl esters can be used as in applications such as electrical switches. vinyl esters will tend to be less brittle pans are black. Phenolics (pronounced fen-ahl’-icks) were the first thermoset materials synthe- Flame Retardant sized (under the name of Bakelite® by Leo Vinyl esters are made flame retardant in Bakeland in 1907). and even especially for specialty resin applications. The improved toughness of vinyl epoxies. thesis and crosslinking reactions. • low heat transfer. Methods. They are. the major properties of phenolics are: the molecular weight of the vinyl ester can be greater than in normal epoxies. ture of the polymer. thus giving them greater adhesive PHENOLICS strength. ground nut shells. handles for pots with similar polyester molding compounds. In the vast majority of this change in materials does not generally phenolic products. leads to increased toughness. adhesives for plywood. the properties of phenolics are best esters over polyesters comes from the higher understood in light of the molecular struc- strength of the backbone and the higher elon. and tougher than polyesters. undoubtedly ies. phenolics handles for cooking fore. In brief. Other have fillers added to reduce shrinkage and thickening agents have been developed and improve toughness. but phenolic glue in plywood. which is really not seen by the consumer. low smoke generation. as wood flour. linked in a solution with the reactive diluent. Carbon ends of the vinyl ester polymer means that black is the most common pigment. For instance. billiard balls. and pans. so most the crosslink density of vinyl esters will be phenolic parts seen by customers are black. all on the phenolic ring. especially low flammability. react with a formaldehyde molecule to link are so strong that their use as a matrix for phenolic rings together with a carbon bridge both fiberglass and carbon fiber composites (called methylene because the carbon has is increasing significantly. The increased demand for phenolics has • high electrical resistance. minor allowances for the unique nature of Even though the properties and cost of their curing process. Nevertheless.5: Specialty and High-performance Thermosets 123 • high thermal stability. Methods. epoxies. spurred work to simplify the molding of phe- nolic composites (discussed later). and traditional composite processes with only • good adhesion. vinyl esters. Phenolic polymerization and crosslinking. a the difficulty in processing phenolics when small organic compound often used as a sol- compared to the polyesters. and Applications . sites. Fundamentals of Composites Manufacturing: Materials. certain key advantag. phenolics are attractive and the market for non-reinforced phenolics is quite large. vinyl esters. Phenolic • excellent resistance to chlorinated sol- composites can now be made by a variety of vents. This lower usage results from an aromatic molecule. Phenol has three active epoxies. and vent or preservative. or tion polymerization reaction between phenol. and formaldehyde. two attached hydrogen molecules) as shown Figure 5-6. their Polymer Structure use in fiber-reinforced composites is much Phenolics are formed from the condensa- less common than polyesters. Each site can es of phenolics. When desired. The major difficulty with resoles the concept that the totally unreacted mate. resoles non-crosslinked polymer in the form of are called one-step resins. because the intermediate materials are more When used to coat reinforcement fibers. which When any crosslinking reaction is stopped requires a somewhat longer pot life. this water C-stage. three-dimensional water-soluble liquid. used as composite resins is the formation of rial. To obtain the good proper- the fully cured and crosslinked material is the ties required of most composites. In both reaction can be molded and cured into a rigid foam. an intermediate is formed and the These foams will readily absorb and hold reaction can be stopped at the intermediate water and are used widely by florists as em- stage. kali (strongly basic) solution. but the intermediate stage is still to reduce the cure time. thus resulting The uncured (B-staged) resole is a viscous. These catalysts become activated when have been B-staged. the water as a condensate or by-product of the intermediate material is the B-stage. When crosslinking is highly moldable. This permits the interme. The multiple reaction sites strictly needed. in a tightly crosslinked. Resoles can be used to coat fibers in composites and Crosslinking Reactions they give strength and body to paper when The crosslinking reaction can be carried subsequently cured. called a novolac. is an essentially accomplish this final crosslinking. The resulting material needs to be added to the resole to material.124 5: Specialty and High-performance Thermosets in Figure 5-6. In the second type of B-staging reaction. such as pultru- final parts. They also can be stirred out under two different conditions that vigorously to form a foamed material. which results The liquid nature of resole material per- when the concentration of the formaldehyde mits the making of sheet molding compound reactant is much greater than the concen. the consistency of whipping cream. coating and impregnation material. That can be done with One of the two reaction conditions for some difficulty and an extra processing step phenolic B-staging is with an excess of al. The name derives from heated. It is convenient to stop at this stage bedding forms for making floral displays. and curing reaction. can be used. which is a minimally crosslinked. called SMC also apply to phenolic SMC. convenient to handle and ship than are the the resole/fiber mixture is usually catalyzed monomers. sequences. Methods. and Applications . Although not a powder (after stripping out the water). needs to be extracted. is required. Most of the same can be carefully controlled to produce a storage restrictions common with polyester viscous liquid intermediate product. the process is accomplished by using a latent catalyst sys- called B-staging and the resin is said to tem. sion. Fundamentals of Composites Manufacturing: Materials. the reaction proceeds with sufficient diates to be made by a resin manufacturer rapidity that even composite processes re- who then ships them to the molders of the quiring a short reaction time. These conditions are opposite of about 300° F [150° C]). It is widely used as a structure. Since no additional those used to form resoles. a resole. an acid catalyst can reduce on the phenolic ring allow each ring to be the gel time of many resole systems. desired. which then ing reaction sequences. linear polymer of aromatic rings linked by the phenol is in excess compared to the carbon bridges. is the A-stage. usually monomers. Filament winding. is best at an intermediate stage. (SMC) in an analogous fashion to that of un- tration of the phenol reactant. the resole formaldehyde reactant and an acid solution can be crosslinked by simply reheating (to is used. This process saturated polyester resins. about proceed by two slightly different crosslink. joined to two or three others. Further. thus may not be truly comparable. Novolacs. Methods. (UV) light resistance of phenolics is poor. The most important difficulty in the pro. To reduce the amount of con. animal and vegetable fats. the novolac-phenolic resins are sold for con. of course. sim. de. and bases is also good. a common practice portant in many of the other resins. such as toluene. During to withstand strong acids or strong bases (al- crosslinking. the most common solvents are resistance of phenolics to weak acids and water. in the Fundamentals of Composites Manufacturing: Materials. public transportation. For instance. Much of the impetus for the below the boiling point of water. Because a second unique properties are an overriding feature material (hexa) must be added to novolacs. in properties. mineral version to other resins. simple alcohols. As with the drawbacks in using phenolics for com.5: Specialty and High-performance Thermosets 125 Novolacs will not crosslink with just the ad. but phenolics are not able simple aromatics. Phenolics have excellent resis- composites as previously discussed. the manufacturing conditions used is formed throughout the polymer mixture in making the phenolic. especially at about 320° F (160° C) for 1–24 hours. Then. This condensate However. used as the resin in polymers. and oils. when crosslinking reaction. the novolac-phenolic resins can be readily This capability is indicative of the highly converted into epoxy and vinyl ester resins crosslinked aromatic nature of the phenolic which are. chlorinated hydrocarbons. One of the limitations of phenolics is it cessing of phenolics is the creation of the has some generally lower mechanical prop- water by-product from the condensation erties. ethers. advances the amount of crosslinking and The most common of the curing agents for allows the water by-product to diffuse out novolacs is hexamethylene tetramine or. However. but require a curing agent. hexa. after increased use of phenolics is the enactment a considerable amount of the crosslinking of stricter specifications for flammability re- has been achieved. kaline solutions). phenolics for reinforced phenolics is flammability are often initially cured at temperatures performance. This dition of heat. To minimize the By far. both resoles and novolacs. esters. are rarely used Properties in making composites directly. Phenolics have good chemical resistance. they are often sold oils. as powders. other aromatic materials. the most important property formation of condensate bubbles. These conditions are less im- densate in the sample. the ultraviolet posite applications. they are called two-step resins. pending on the thickness of the part. ply. especially impact toughness. and Applications . ketones. Hexa is heat activated. When tance to alcohols. of the part. so molding The need for additional steps in process- of novolacs is usually done with pressure and ing phenolics has limited their use to mainly heat to compress the powder and activate those composite applications where their the crosslinking reaction. Hence. the part is post-cured quirements in many applications. such as ethanol. that dictates their use. including the oven and can result in small bubbles and voids post-cure aging. phenolics do not The need to evaporate the solvent is one of have good resistance to boiling water. make a major difference in the part. The as solutions. these solvents are evaporated. permitting the vaporized water to escape. and this occurs with compared to other high-volume thermosets. when compression molding phenolics in a direct property comparisons with other hot press is to open the mold slightly and materials can be confusing because the data quickly during the molding cycle. This process is called bumping the mold Flammability Performance or breathing the mold. benzene. of less then 35 and ure 5-6. the Federal Aviation Administra.500 100 HF <200 0 NO2 <100 0 HCl <500 0 HCN <150 0 SO2 <100 80 Fundamentals of Composites Manufacturing: Materials.0 minutes) <200 15 Ds (maximum) — 51 Smoke chamber gas analysis (parts per million) of the National Bureau of Standards CO <3. The low smoke generation of a tion agencies have likewise increased their phenolic over time versus a polyester and requirements. molecules are difficult to ignite and. Flammability specifications and test results for a typical phenolic resin. Other transporta. a resistance to burning. As dis- phenolics easily meet these requirements. and toxicity tests. is obvious. Typical Transportation Typical Phenolic Result Test Requirement Flame spread test (ASTM E 162). such as the tardant properties exhibited by phenolics flame spread index. burn slowly. increase the safe evacuation time for pas. Highly aromatic tions.126 5: Specialty and High-performance Thermosets 1980s. especially when cost is also considered. high aromatic This table also lists off-gases. which are content is beneficial in many ways.5 minutes) <100 1. Therefore. The desirable combination of flame-re- ining their flame characteristics. they Table 5-1. usually because of potential toxicity. into a three-dimensional structure. Is. they do not readily volatilize. This is because well under the specified limits.0 Ds (4. of less than 100 after 1. and smoke characteristics is extremely hard to achieve with any other as measured by smoke optical density tests resin. which are tightly interconnected (per ASTM E 662). Methods.0 Smoke density (ASTM E 662) Ds (1. Ds. and composites is often measured by exam. cussed in previous chapters. when As noted in the table. The flammability of plastics an epoxy is shown in Figure 5-8. The first impression of this structure a smoke density. These favorable flammability results can Typical requirements for transportation be understood by looking at the molecular applications are for a flame spread index structure of the phenolic resin shown in Fig- value (ASTM E 162). One is restricted in some transportation specifica. Here the superior performance of phenolics sengers in airplane fires. and Applications .5 is that it is highly aromatic with many ben- minutes and less than 200 after 4 minutes zene rings. Is <35 1. The results of tests on several typical tion tightened aircraft fire specifications to resins are shown graphically in Figure 5-7. As shown in Table 5-1. phenolic off-gases are finally ignited. the general advantage of weight savings with composites is augmented by the addition to its excellent non-flammability. This char is even more resistant to burning than the original phenolic. In (13 mm) within the char. as explained previously. This limited burning results in the formation of a char. An interesting and somewhat unique application for phenolic/carbon fiber com- posites is in the exit nozzles of rockets.300° C]). and floors of aircraft interiors. Applications Because of their favorable flammability properties. and Applications . not only is the phenolic slow to burn. it forms a product that further reduces burning. which are depicted in Figure 5-9.200° C). and other public transportation panels. In this application. Hence. highly aromatic compounds. Figure 5-7. Furthermore. it is formed slowly and is chiefly composed of relatively harmless hydrocar- bons. While the smoke from burning aromatics is quite dark. train interiors. When pheno. Furthermore. phenolic composites are the ma- terial of choice for walls. the temperature is Fundamentals of Composites Manufacturing: Materials. These halogens form dense and choking smoke that is avoided with phenolics. Phenolic flammability. especially those that are cross- linked. the smoke density results of phenolics are also favorable. characteristics and tends to contain the lic/carbon-fiber composites are exposed to heat within the char zone. ceilings.5: Specialty and High-performance Thermosets 127 do not easily create flammable vapors that facilitate ignition and propagate the spread of the flame. much like the char (charcoal) that forms when wood burns incompletely. tend to burn incompletely in limited oxygen environments as is almost always the case in real fires. as occur in the exhaust resistance is so effective that even though flow path of a rocket (as high as 6. advantage of superior thermal insulation the char has superior thermal insulation during firing of the rocket. Methods. Hence. This low flam- mability is natural with phenolics and so the addition of halogen materials is not necessary as required with many other resins. but when burned. it does not contain the halogen compounds that exist in other flame- retardant polymers.000° F temperatures on the inside surface of the [3. the phenolic resin degrades and char reach 4. just 0.000° F (2. The thermal high temperatures.5 inches turns into char. When used in this trains and subways. Rocket be porous and weak and quickly wear away nozzles are designed so that the thickness from the action of the hot and high-veloc. ficient to last for the entire length of the burn when reinforced with a high-temperature.128 5: Specialty and High-performance Thermosets Figure 5-8. As the char In 1979. which is several inches thick. BART. A non-reinforced char would consumed by this ablative process. Smoke chamber results from the National Bureau of Standards. is called an ablative material. transportation applications. Methods. thus continuing the thermal the temperature is elevated no more than resistance of the material until it is totally 10° F (5° C). also chars. (with a reasonable safety factor). stable reinforcement like carbon fibers. had a serious fire in Fundamentals of Composites Manufacturing: Materials. the phenolic composite the operation is in tunnels or underground. the Phenolics are specified in non-aerospace char erodes slowly. which then normal nozzle. such as public cess known as ablation. only 500° F (260° C). of the phenolic/carbon fiber material is suf- ity exit gases coming from the rocket. little by little in a pro. especially when some of type of application. But. and Applications . a new layer of composite greater San Francisco. the rapid transit system of layer erodes away. On the outer skin of a underneath the char is exposed. density gives excellent creep resistance to phenolic composites. These phenolic-fiberglass polyester material forms the basic composite gratings can withstand brief direct flame structure and then a phenolic is used to coat contact without major structural damage. several chains pendant from its backbone. and achieve the surface and then painted to the desired color. Some manufacturers have made products posites as grating materials for decking on combining polyesters and phenolics. For instance. development of some impact-resistant grades The novolacs are a type of phenolic that is further increases the penetration of phenolic relatively low in cost. and resistance to fuels and lubri- cants are the properties of most interest. Specifications in Europe. and Applications . have led to the use of phenolic composites in most European mass-transit applications. phenolics can be mounted directly. A novolac can have composites into the automotive market.5: Specialty and High-performance Thermosets 129 a train while it was in a tunnel. This is a three-step process compared to the Fundamentals of Composites Manufacturing: Materials. The high crosslink tive material. resulting in a death and several injuries. When other resins One other application for phenolics that may require molded-in metal inserts for has already been alluded to in the discus- mounting the composite part to an assem. which are even more stringent than in the United States. The phenolic is often a paste They have low thermal conductivity. The overall mix of properties available from phenolics has led to many applica- tions in addition to those directly related to low flammability. side walls. Methods. The offshore oil rigs. A non-transportation application that is therefore. phenolics have been used for interior sur- faces—ceilings. automotive manufacturers continue to use consider- able amounts of phenolic for under-hood applications where low flammability. and end walls—in all BART vehicles. Halogenated polyesters can meet the standards for exterior parts. good material that is smoothed onto the polyester resistance to chemicals. Figure 5-9. Since then. usu. strength of steel at much lower weights. Rocket exit nozzle with phenolic as the abla- cal attack by solvents. The recent tant types of epoxy and vinyl ester polymers. the surface. thus novolacs as reactants in making some impor- reducing manufacturing costs. The structures are highly aromatic and. high heat performance under load. growing rapidly is the use of phenolic com. ally displacing metals. sions of epoxies and vinyl esters is the use of bly. These desirable properties are the result of the aromatic nature of phenolics and the tight crosslinking that prevents movement of the molecules (high heat stability and dimensional stability) and reduces chemi. dimensional stability. but only with some difficulty. have good mechanical properties. if the resin is used and then. CARBON MATRIX • intermolecular interactions. in the chapter on reinforcements. and silicon with distillation. it is appropriate to discuss and silicones. through a series of bond strength is high. Other resins that show oxidation and these would impart thermal Fundamentals of Composites Manufacturing: Materials. stable materials since thermal stability is The requirement for high activation the principle property imparted by using a energy relates to the tendency (or lack carbon matrix. There is no “carbon” Strong bonds in the polymer. The characteristics of the car. Following are the main factors contributing mable surface. For instance. aromatic carbons and oxygen when the more volatile components of coal atoms. as will be discussed ecules usually indicates high bond strengths. especially resin that can be purchased from a resin along the backbone. rials as the basic materials used in making • high heat capacity. process does give the benefit of a non-flam. and Carbon matrix materials are much differ. will be discussed last. Clearly.130 5: Specialty and High-performance Thermosets normal two-step process of gel coating and good thermal stability. But there are also other bonds that have been found to have high bond energies such as sili- Thermal Stability Characteristics cone with oxygen and aromatic carbons with Before considering the details of carbon nitrogen. but the phenolic-polyester and silicones. some other in thermal degradation. the product left behind trogen atoms. In theory. are essential for thermal manufacturer and added to fibers to make stability since it is bond breakage that results a composite structure. thermal stability of can be pigmented are being developed to polymers: eliminate the painting step. almost any resin that cre. The excellent thermal insulation and • high activation energy. thus simplifying • high bond strength. Instead. carbon-carbon composites. These are important in polyimides matrix materials. carbon and fluorine. and the bond will be matrix. Pitch is also a precursor material oxygen. The bond ates a high-carbon-containing char can be strength is usually expressed in terms of the used to create the carbon matrix. The most bond energy. stable to higher temperatures. aromatic carbons with other aromatic tar or crude oil have been removed through carbons. thereof) for bonds to be broken through bon matrix materials will then be examined some chemical reaction. Some phenolic pastes that to the high-temperature. which is the energy required common resin used in this conversion process to completely separate the atoms and break is phenolic. Therefore. that resin is converted into a “carbon” the bond will be high. effects. considered in this text. the phenolic coating process. which are discussed later in the general characteristics of thermally this chapter. Another material occasionally the bond. • absence of easily degraded atomic struc- tures. the presence of aromatic mol- for making carbon fibers. Among the highest bond energies used as the basis for forming carbon matrix are those between aromatic carbons and ni- composites is pitch. surprising strength of phenolic/carbon fiber • stabilization by resonance or inductive composites has led to the use of these mate. some and related to the general characteristics types of bonds are especially susceptible to for thermal stability. and Applications . • backbone stiffness and steric hin- ent from all of the other matrix materials drances. Methods. such as the polyimides polyester lay-up. the energy to break steps. In essence. have high activation energies. therefore. The bonds around the aromatic mer softens sufficiently to lose mechanical ring resist most ordinary chemical attacks properties. those that retain their physical properties The thermal stability of a polymer is under the following thermal and time con- also achieved when there are interactions ditions: 500° F (260° C) for 1. high achieved in the bonds that participate in the heat absorption is required before the poly- conjugation. In aro. terferences are caused by the shape of the directed to the bond. This property is called chanical forces are present in the molecule electron conjugation and great stability is and hold the atoms in place. When these atoms volatilize.500° F crosslinks. consider each one independently. the backbone of a polymer also can be caused ternally without causing internal damage. stability are not completely independent. significant loss of properties However. they Thermally stable polymers usually possess break their bond with the polymer and often several simultaneously. One method of developing stiffness along Heat capacity is a measure of the ten.000° F (538° C) for 1 hour. Resistance to oxidation is the most bonds might be broken when heated exten- important type of chemical resistance in sively. and Applications . Therefore. single. the high number of total bonds means thermally stable polymers because of the that the breakage of only a few bonds has natural tendency for oxidation to occur at little effect on the overall properties of the high temperatures in the presence of air. (shape) interactions. This means the stiff polymer is and. A typical example stability and. the electrons of the double bonds to be spread When a polymer backbone is rigid. causing it to rupture atomic units and are. The energy is not. therefore called steric and degradation to take place. This is the case with graphite heat capacity is high. ride (PVC) where the chlorine atoms break from the carbon backbone and combine with Nominal Performance Criteria and Testing a neighboring hydrogen to form HCl. polymer. some bonds such as double bonds requires more energy (heat) than would be in aromatic rings alternate around the ring the case without the crosslinks or other in- (single. the backbone is to employ structures that dency of a material to absorb heat. The stiffness of vibrate so that the energy is dissipated in. or 1. Thermally stable the crosslinks must be broken for extensive polymers also would be characterized by high Fundamentals of Composites Manufacturing: Materials.000 hours.) and this causes termolecular attractions. Stability is achieved because (816° C) for 5 minutes. When are planar. polymers with high heat capacity along the backbone. ditions. degradation to occur. me- over several atoms.5: Specialty and High-performance Thermosets 131 weaknesses and have low activation ener. Some atomic structures are especially The properties that lead to thermal prone to volatilization under thermal con. etc. A polymer is designated as thermally matic molecules there are few of these easily stable when it meets certain nominal (ideal) volatilized atomic groups. the atoms have the ability to absorb energy by internal get in each other’s way. by interferences between the atomic units Thus. While some of the gies. Thus. therefore. Thus. therefore. or inductive effects. the atoms rotate and materials and polyimides. double. aromatics performance criteria. each prop- combine with a neighboring atom to produce erty represents a different aspect of thermal a stable gaseous molecule. However. These types of in- mechanisms. Methods. or bonds between the molecules such as 1. more likely to have sufficiently high me- This results in stabilization by resonance chanical properties at high temperature. Such materials are are noted for their non-volatilizing nature. it is instructive to is the thermal degradation of polyvinyl chlo. Methods. (Tg). Metal matrix composites are also plotted in tance to non-oxidative thermal breakdown Figure 5-10 and will be discussed in a subse- (thermolytic processes). in Figure 5-10. thermal tran- (carbon matrix materials reinforced by carbon sition measurements. oxidation at elevated temperatures. Polyimides. as well as the more direct of properties at temperatures below 500° F performance-related properties. Carbon-carbon composites detection of volatile off-gases. high temperatures and high exposure times. the heat distor- of course. The methods used to determine thermal The ability of various composite materials stability are listed in Table 5-2 and include to retain their properties when exposed to the the following: weight loss. have The characteristics of thermal stability higher temperature capability than the epox. carbon-reinforced phenolics). and loss of properties as indicated by ther- Other materials. and Applications . such as ablative composites mal mechanical analysis. The effects of time and temperature on the ability of various composites to retain properties. resistance to ies and will be discussed later in this chapter. the melting point (Tm). (260° C). and decomposition shows epoxy composites have good retention temperature (Td). such as that effects of time and temperature is presented measured by thermal gravimetric analysis. Figure 5-10 also tion temperature (HDT). they are ablating. which also appear. ties of polymers determined by these tests have good retention at high temperatures but include the glass transition temperature only at relatively short durations. in carbon matrix materials will be discussed Figure 5-10. Fundamentals of Composites Manufacturing: Materials. exposed to radiation and chemical agents.132 5: Specialty and High-performance Thermosets melting or degradation points. because. Some basic proper- (for example. resis. and stability when quent chapter. such as those mea- fibers) are shown to retain properties at both sured by differential scanning calorimetry. Carbon matrix composites have applica. and Td calorimeter (DSC) • Can also measure induction time to onset under isothermal conditions Heat distortion • Measures flexural rigidity during a programmed temperature rise temperature (HDT) • Useful in detecting use temperature Gas • Detects off-gases with time and temperature chromatography (GC) Mass spectroscopy • Analysis of off-gases with the other specialty resins used in high eroded away by the hot gases passing around thermal applications. applications. Whereas phenolic matrix com. or in various rocket valve bodies of performance. Most of the applications of carbon matrix posites are ablative. Methods. When critical dimensions need to be main- tions similar to many of the phenolic ap. simply with- Applications stand the temperatures of that environment. or when the nozzle itself the carbon matrix composites is in high. Tm. The most important use of for vector control. Test Comment Thermogravimetric • Monitors weight loss during a programmed temperature rise analysis (TGA) • Typical reported value is when 10% weight loss is experienced • Depends on the atmosphere used with inert values higher than air (oxygen) • Often is the first test used because it requires only a small sample and a short time Isothermal weight • Measures properties for long durations at a set temperature (usually loss the temperature of expected use) • Typically mechanical properties are also monitored • Can be a costly test because of the times involved and the large number of samples needed Thermal • Measures changes in mechanical properties (usually flexural or mechanical penetration) with a programmed temperature rise analysis (TMA) • Can be done quickly with only a small sample Differential • Detects thermal transitions during a programmed temperature rise scanning • Determines Tg. and Applications . cones and exit throats are two common carbon matrix materials are used.5: Specialty and High-performance Thermosets 133 Table 5-2. Thermal stability tests. the composite. such as in the throat leading to the plications but with much higher standards exit nozzle. carbon matrix composites have little ablation but. that is. the material is composites involve high thermal stability Fundamentals of Composites Manufacturing: Materials. Rocket nose the extra material required of an ablative. must be lighter weight and cannot carry temperature applications. rather. tained. Some specific parts carbon-carbon composites means that resins using carbon matrix composites include that cure or process at high temperatures flame barriers. This preform. for the environment. therefore. when Manufacturing Process oxygen is present. a function of the difficult and time-consum- tional losses of the composite are premium ing manufacturing process. Oxidation protection also has been The creation of the carbon matrix begins improved by adding oxidation inhibitors to with the combination of reinforcement and the matrix during the manufacturing process resin into an uncured preform. both materials replace brake linings reinforced the matrix and reinforcement should be with asbestos and are. flames will cause the carbon matrix com- posite to oxidize. posites. and then cured. makes this tooling ideal for carbon composites (CCC). As previously for parts. However. shaped to fit the mold contours. brake linings are usually made of carbon ma. much safer capable of withstanding high temperatures. the low coefficient of ther- ment. The thermal stability of the in gas turbine engines. and Applications .134 5: Specialty and High-performance Thermosets and dimensional stability. the designation of carbon matrix of the carbon matrix and the high abrasion composites as carbon-carbon composites is resistance of the composite. turbines. The brake lining application preform. carbon fibers. dictates that over the traditional metal material. Therefore. As a result. exhaust systems. the most common raw materials The use of carbon matrix composites in used to make this preform are phenolic resin brake linings for aircraft. indicated. can be molded in the carbon-carbon tooling combustors. which are more thermally These tools will not be as durable as metal stable than any other common reinforce. tooling. Both of the opposing a mold. Carbon matrix composites are also sions from expansion and contraction. An interesting application for carbon- forcement for carbon matrix composites is carbon composites is as a tooling material. which is close to the CTE for carbon tant composites are often called carbon. and carbon fibers. which is parts where the lighter weight and lower fric. and possibly burn. When carbon matrix materials are mal expansion (CTE) of carbon-carbon com- used with carbon reinforcements. used in traditional internal combustion en. this trix and carbon reinforced composites. direct exposure to high-value applications. which have the highest specific heat capacity The preform material is placed into of any known material. cepts of manufacturing of carbon matrix posite with a ceramic coating. Methods. the manufacture of other composite materi- Another application for the high-tempera. often silicon composites is diagramed in Figure 5-11. This cost. when in its and some luxury passenger cars has become uncured state. and self-lubricated with little worry about changes in dimen- bearings. carbon matrix composites be used only in In some applications. The major drawback to the use of carbon gines for pistons and other high-temperature matrix composites is cost. the resul. These curing step and then a final finishing step Fundamentals of Composites Manufacturing: Materials. trucks. is sometimes termed a green a major market. strict definition of more important is the high thermal energy the terminology would allow this name only absorption of carbon matrix composites. when the reinforcement is carbon fibers. racecars. Because of the frequent use of car- takes advantage of the high thermal stability bon fibers. For most composites. carbide. the most commonly used rein. especially when high numbers of items ture stability of carbon matrix composites is are not expected. als. ducting. However. That possibility can be A process that illustrates the major con- largely prevented by coating the carbon com. fibers themselves. Possibly even widespread. flexural. This other carbon-rich material. would complete the manufacturing process. This step. When the liquid is in the gaseous about 1. In through the evolution of the oxygen. called sis step. ditional resin. Methods. with pressure a porous structure that is held together by or vacuum. the composite. hydro. Each of the pores and the steps required are unique to this would be a point for crack initiation. for carbon matrix composites. carbon-carbon composites among the most To improve the mechanical properties of expensive of all composite materials. but the mechanical proper- molded material must be converted first. ties would be inferior. the steps are time reducing greatly the tensile. As will be seen. is vaporized and then. this process. done. caused to infiltrate the porous the strength of the residual matrix and the carbon matrix composite.832° F (1. such as acety- evolution of non-carbon atoms leaves behind lene. the pores are filled by adding The next step in the process is a pyroly. which can be either a gas or The temperature of this process is usually a liquid. and other atoms contained therein. the would be good. the thermal properties of the part However. Pyrolysis involves heating the part impregnation. thus material.5: Specialty and High-performance Thermosets 135 Figure 5-11. additional resin to the part.000° C). and consuming and expensive. can be done by infusing in the absence of air (oxygen) so that the the porous carbon matrix material with ad- resin chars but does not oxidize (burn). If no further step were nation is done in the liquid state. the impregnation process is called the resin becomes nearly all pure carbon chemical vapor deposition (CVD). Production flow chart for carbon-carbon composites. state. the impregnating resin or some gen. During pyrolysis. the porous Fundamentals of Composites Manufacturing: Materials. When the impreg- reinforcing fibers. and Applications . thus making compression properties. which would include sanding. These polymers. A set of performance heated in the presence of oxygen.000° F (1. However. partly idealistic and partly realistic. That is. the performance of the com- with pressure or vacuum. Such materials may also possess some that the carbon matrix will not burn when additional benefits. Hence. The composite material is then subjected The presence of the carbon fibers gives the to another impregnation step. This process can generally intended for high-temperature be speeded up with pressure. trimming. which is allowed to seep into Because carbon matrix composites are the pores of the composite. or other similar processes composite polymers. if required. which reflects the softening of the non-carbon atoms in the remainder of the material. would have several im- that allow the carbon matrix composite to fit portant performance properties including: into an assembly. often on the order importance. when a crack begins the pores of the bulk material. This greatly improves the toughness When impregnation is completed. high cost of carbon-carbon composites have The carbon matrix composite may then led to efforts to develop other polymers be coated. in which carbon-carbon composite good crack-stop- either gas or liquid resin is infused into ping capability. The entire process to make carbon/carbon • excellent thermal stability. that could offer high thermal stability and Finally. filled with new resin. reinforcement in carbon-carbon composites. The minimum costs of such a process are high. such as silicon have been identified for polymer candidates carbide.500° F (816° C).500° C). even applications.927° C). and 3.649° C). the within the carbon matrix. of a carbon-carbon composite at room tem- When impregnation has proceeded so that perature (70° F [21° C]) and then at three the pores of the carbon matrix composite are higher temperatures: 1. drilling might be called thermally stable structural attachment holes. Obviously the than the best epoxies. seems to be the mechanical prop- carbon matrix material. pyrolyzed. and Applications . in some properties at high temperatures is drogen. hy.532° F (2. due to the stability of both the resin and the create a few more pores in the newly im. the ma. other highly rigid materials. temperature. This step favorable economics. pregnated areas. is almost always a ceramic. thus creating some erty most negatively affected by the rise in porosity in the bulk material as well. Table 5-3 lists the performance of days or weeks.500° F (1. both of processes posites at various temperatures is of great take considerable time. Methods. It also drives off additional Modulus. the POLYIMIDES AND RELATED POLYMERS number of non-carbon atoms is few and so The extremely long processing times and the porosity is minimal and can be ignored. the new resin by driving off the oxygen. This is called carbonization and occurs at about 4. The coating goals. the composite is again 3.136 5: Specialty and High-performance Thermosets carbon matrix composite is covered with the Properties liquid resin. nates. This second pyrolysis carbonizes The excellent retention. performance would be greater than 90% Fundamentals of Composites Manufacturing: Materials. usually composites takes many weeks and may even defined as being substantially better take as long as six months. that have good thermal stabilities at less The applied coating is non-flammable so cost. and even increase. the crack grows process of impregnation and pyrolysis is until it hits a carbon fiber and then it termi- repeated several times. and other atoms and will. of the carbon-carbon composites relative to terial is subjected to a higher temperature. This step is not done for all parts. therefore. By this time. the part is finished. other desirable properties.0 × 103 — warp/longitudinal (179) (228) (276) direction.927) Tensile strength—warp/ 48. (276) (310) (345) psi (MPa) Modulus—warp/ 16. These polymers have proven to or superior to high-performance epoxies be valuable as composite matrix resins for and superior to phenolics. usually im. psi (GPa) (109) (109) (99) (83) Compressive strength— 26. defined as being Highly aromatic polymers with high inter- better than carbon-carbon and at least nal stiffness.0 × 103 35.0 × 103 50.4 × 106 12. set polyimides have had considerable com- Based upon previous experience with mercial success: end-capped polyimides and chemical structures. highly aromatic com.0 × 106 12. bismaleimide (BMI).0 × 103 30. discussed in the chapter on thermoplastic • acceptable processing ability that is composites.0 × 103 — transverse direction. many years in applications requiring ther- • excellent toughness that is equivalent mal stability.5 × 106 16. Mechanical properties of a typical unidirectional carbon-carbon composite at various temperatures. (179) (207) (241) psi (MPa) retention of properties with long-term from internal bonding as from crosslinking exposure to 600° F (316° C). (114) (114) (103) (86) psi (GPa) Modulus—fill/transverse 15. discussed separately in pounds.0 × 106 direction.0 × 103 62. Polyimides can be either thermoplastics • good mechanical properties.8 × 106 14.500 (1.0 × 103 — fill/transverse direction. Fundamentals of Composites Manufacturing: Materials.0 × 103 longitudinal direction. Methods. Two general types of thermo- equivalent to or better than phenolics. are ideal candidates for plying that the Tg is greater than 600° F polymers having high thermal stability and (316° C).500 (816) 3.0 × 103 45. such applications. Temperature. and Applications .5 × 106 15.0 × 103 33.5: Specialty and High-performance Thermosets 137 Table 5-3.0 × 103 54.5 × 106 longitudinal direction. The thermoplastics will be high-performance epoxies. psi (MPa) Compressive strength— 26. polyimides have been used for as good as a high-performance epoxy. especially those with high stiffness this section. ° F (° C) Property 70 (21) 1.8 × 106 15.000 (1.649) 3. equal to or thermosets. or high crystallinity.0 × 103 60.0 × 103 40. • good oxidative stability. (331) (372) (414) (427) psi (MPa) Tensile strength—fill/ 40. Several different monomers could be used in making polyimides. The cure time for PMR-15 and other poly- Figure 5-12. and Applications .138 5: Specialty and High-performance Thermosets Structure and Crosslinking Reactions The imide group can bond to other atomic The polyimides are characterized by the groups and. that react to form the polyimide chains When linked with an aromatic molecule. Those chosen for PMR-15. Therefore. The most be called an aromatic heterocycle. Another drawback is that a polymer. and have acceptable pro- cessing and properties. It conjugates the electrons from containing nitrogen and two carbonyl groups the aromatic ring with the electrons in the (carbons that are double-bonded to oxygen oxygen-carbon bonds of the imide group. therefore. This results in a final molecular (or formulated) weight of about 1. This group is illustrated in Figure aromatic-heterocyclic polymer chain is high- 5-12a. can be included as part presence of the imide group in the polymer of a polymer backbone. The backbone. other chemical ring groups. common of these polyimide types is called PMR-15. composed of only strong bonds. among many thermal stability. The imide group is a ring structure ly aromatic. It can be summarized as a reaction to form the imide ring (called imidization) and then a chain-lengthening step followed by an end-capping step. Rings having more than one stiff and generally planar with few backbone type of atom. the molecular weight is controlled by the relative concentrations of the three monomers. as and another that attaches to the ends of illustrated in Figure 5-12b. solvent is often used to impart some flexibil- Fundamentals of Composites Manufacturing: Materials. There- fore. Methods. relatively low cost. such as the imide ring. The heterocy- clic groups or molecules are often highly End-capped Polyimides stable and can be aromatic themselves or The end-capped polyimides are synthe- coordinate their electrons with an aromatic sized by combining three monomers—two molecule to achieve even more stability. as in Figure 5-12. Very molecules). In actual practice. are readily available. The length of the polymer chain is controlled by the end-capping step. which will be explained later in this section. The imide group and its inclusion in a imides is long. a general name that can be understood why this polymer has high can be applied to imide rings. PMR stands for polymerization of monomer’s reaction. it is contains both carbon and nitrogen atoms. which bonds around which rotation can occur.500. the most widely used end-capped thermoset polyimide. and the 15 is an ab- breviation for 1. it are called heterocyclic. the molecule can the chains to form end caps.500 formulated molecular weight. The PMR-15 synthesis is complicated. the number of polymer units formed is typically between two and four. The removal process requires that the poly. in the solid ing methods such as resin transfer molding Fundamentals of Composites Manufacturing: Materials. Polyimides also have been used much research continues on polyimides for ducts on engines and airplane engine made from different monomers in attempts blades. usually in but would also result in higher brittleness an autoclave. Experience eliminates the problems of solvent removal has shown that 1. Some high-speed yet not diminish its good properties. ronments. weight loss is relatively fast at 800° F (427° C). when needed. easier processing than other polyimides. The typical crosslinking window is the solvent must be removed or bubbles and 480–520° F (249–271° C). Then. at least in part. the high Some of the major uses of polyimides are crosslink density at a 1. imides be cured under vacuum. Therefore. While this iphatic content of the most common end-cap. and Applications . lar weight for the most common PMR resin is a compromise. developmental aircrafts require the thermal stability of polyimides for their skins. For short durations. temperatures even as high as 900° F (482° C) Although pressure is still required to get the can be tolerated. and semi-automated composite manufactur- ing would occur. Lower molecular surface blemishes might remain on the part. Thermal data indicates that an autoclave is not required. state. weights would give improved processing. many believe that reported a significant loss in polyimide prop- improvements can still be made. Higher molecular weights Bismaleimide (BMI) would give improved strength and stiff. for small parts to a few hours for thick parts). good design per and other groups within the polymer can practice would suggest that some consider- be points of vulnerability in highly thermo. Although the PMR-15 polymer has prop. Recently built fighter aircraft employ to eliminate the problems with PMR-15 and polyimides for firewalls.500 formulated molecular during molding. However. the use of dation occurs. and hot/wet properties than epoxies and perature at which the crosslinking occurs. That pre.5: Specialty and High-performance Thermosets 139 ity to the polymer during cure. and radomes. Some studies have it a commercial success. Therefore. These molders lay up the weight works for most applications. the preform can Thermal stability is clearly the most im- be placed in a mold (usually a compression portant reason to use polyimides. oxidative environments. When cured. although some surface oxi- end groups to crosslink properly. especially fins The selection of 1. and relatively erties that have been good enough to make slow at 600° F (316° C). they would have much slower These resins can be used in many automated crosslinking reactions since the crosslink. moderate at 700° F (371° C).500 molecular weight as bearings and seals in high thermal envi- leads to rigidity and brittleness. has not been fully characterized. Methods.500 formulated molecu. the molecular weight can be form can be placed in an oven at 165–400° F easily adjusted by varying the relative con- (74–204° C) for 1–2 hours to evaporate the centrations of the monomers. solvent. The high al. BMI resins have gained popularity as a ness but would result in a glass transition material that has better thermo-oxidative temperature that would be above the tem. They can mold) and heated to 600° F (316° C) for a typically be used at 550–600° F (288–316° C) relatively short period of time (a few minutes for continuous service. erties under hot/wet conditions. Further. ation be given to this possibility. including improved wet-out and lower voids. some molders have because of the higher crosslink density that developed an alternate molding method that would occur with shorter chains. This Properties and Applications is also true of some missiles. but prepreg so that a preform is made. when desired. and Applications . This property is substantially imide rings. For example. fuselage. among the common and high-performance Fundamentals of Composites Manufacturing: Materials. Much effort has been given to toughening and understructure are all made with BMI BMI and several routes are available. Methods. and engine and exhaust parts for co-react the BMI monomer or extended chain some Formula 1 racecars. (four carbon units containing a carbon-car. has become especially important in sev- Because of the low molecular weight of the eral high-performance aircraft because of monomer. Crosslinked BMI can achieve a Tg as high bon double bond) with imide rings. filament winding. as 572° F (300° C) with an oven treatment ing occurs at the double bond in the terminal of 6 hours. result in higher crosslinking and using prepregs. The major uses for the resin are in radomes. distortion temperatures. improved thermal properties. Other applications include the to extend the length of the monomer (called aft flap hinge fairing of the C-17. curing is often done at about Structure 482° F (250° C). BMI is the resin of choice for the majority of the Properties and Applications composite panels used in the F-22 Raptor fighter jet. as epoxies. The wings. Bismaleimide (BMI) structure. To obtain the best properties. empennage. cyanate esters have found special applica- tions because of their superior dielectric loss properties and low moisture absorption. skins covering phase-array antennae. These conditions are superior to epoxies. The cyanate esters have the lowest dielectric loss properties Figure 5-13. One is composites. usually at temperatures that have thermal and strength properties of about 250° F (121° C). return signals. Many electrical applications require low dielectric loss properties so that the signals are not absorbed by the resin. While not as good as BMI similar to those used for high-performance resins in thermal and strength properties. the resulting thermoset has high their high speed and need for high heat crosslink density and is brittle. Another toughening technique is to helicopter. Higher cure temperatures will. which causes weaker transmission. and overheating of the components within the electronic enclosure. and pultrusion. All CYANATE ESTERS of these methods result in thermoplastic BMI materials that can be crosslinked simply by Cyanate esters are another group of resins the addition of heat. monomer with additives based on inherently tough materials such as diallyl bisphenol A. the inner extending the chain) by the reaction of the core cowl for the Pratt and Whitney 4168 monomer with a diamine. The crosslinking reaction can be better than high-performance epoxies and carried out simply by heating the monomer. the tail boom of the Bell Model 412 diamine. Crosslink.140 5: Specialty and High-performance Thermosets (RTM). The name comes from that will allow the crosslinking to proceed at the combination of two (bis) maleic groups lower temperatures. advanced stealth composites. and space structures. usually methylene engine. well as in hand lay-up and vacuum bagging however. Several cure accelerators are Figure 5-13 illustrates the structure of a available for some of the BMI formulations typical BMI monomer. 5: Specialty and High-performance Thermosets 141 thermoset resins. esters are attributable to the symmetrical ylene (PE). The unique carbon-nitrogen therefore. and nitrogen atoms in its structure. or PTFE material. Methods. the electrical properties Figure 5-14. Fundamentals of Composites Manufacturing: Materials. and Applications . resulting in weak dipoles. have more favorable dielectric arrangement of the electronegative oxygen properties among the common plastics. Structure and Crosslinking Reactions there is little tendency for the electrons to The structure of cyanate esters is depicted be transmitted through the structure and. Cyanate ester structure. dielectric losses are low. When re- ring is highly stable and stiff. in Figure 5-14. Only two thermoplastics. When the dipoles are weak. The low dielectric properties of cyanate polytetrafluoroethylene (PTFE) and polyeth. much like inforced with ultra-high-strength PE fibers aromatic rings. a molecular rearrangement occurs that cre- polyurethanes are known for their tough. Furthermore. in contrast to condensation thermoplastics) can be added to the cyanate reactions. For instance. as illustrated in Figure 5-15. The urethane bond some improvement in toughness. they have great potential for hydrogen on the polyol forms a bond with applications in the automotive industry. and dielectric loss but at the expense of Tg. crosslinks vacuum. where toughness oxygen in the polyol forms a bond with is a prime advantage. the polyol monomer condensation reactions. Polyurethanes are compounds that have two isocyanate groups one of these important groups. such the nitrogen in the isocyanate. Some previous manufacturing possibilities of polyurethanes bonds in the polyol and in the isocyanate make it an attractive choice. thus giving a groups. For instance. The other monomer in the reaction to form a urethane is an isocyanate. characteristics of polyurethanes make their When a polyol reacts with an isocyanate. which is POLYURETHANES the double-bonded NCO combination of at- Several traditional thermoset resins not oms as shown in Figure 5-15. Moreover. The polyol monomer depicted in able in space applications. no condensate is formed when the ester monomers and prepolymers to give urethane bond is created. which means multiple alcohol is reduced. Therefore. Many such variations urethane is similar to a condensation reaction have been tried and some are commercially in that two monomers. and Applications . The types of chemical composite applications. for space applications. in volatile solvents. tures have been announced to bring together mer. each having at least available. little tendency this case OHs. as opposed to lymerization reaction. The linkages can be aliphatic or weight savings—another valuable property aromatic or mixed. a cyanate ester. In most of is formed from the reaction of a polyol with an the cases where a thermoplastic is added to isocyanate. Methods. If three or is seen for cyanate esters to out-gas in high more reactive groups are present. Therefore. Fundamentals of Composites Manufacturing: Materials. unite to form the poly- Polymers with high elongation (usually mer. the Tg of the cyanate ester A polyol. However. that the properties can be suited to a variety Specific properties can be improved by of applications. the rapid the carbon in the isocyanate. (OH) molecules. and without highly must have at least two reactive groups. ates a more stable molecular structure. Further. to polymerize. Several are called diisocyanates. Just as with a condensation po- rearrangement reactions. This monomer normally associated with composites are must also have at least two reactive groups being examined as possible new resins for to form a polymer. As a result. can form. adding methyl groups polyurethane resin technology and fiberglass to the rings will improve water absorption reinforcement technology. The ness. can have from two to many Cyanate esters are made by addition and OH groups. the as automobile body panels. the Figure 5-15 is shown with two OH groups density of cyanate esters is slightly lower and some generic linkages between these than similar epoxy molecules.142 5: Specialty and High-performance Thermosets of the composite can be even lower than for of technologies and formulations suggests the neat resin (non-reinforced). The wide choice break to allow these new bonds to form. two reactive groups. Replacing the methyl hydrogen with fluorine Structure and Crosslinking Reactions gives a further reduction in the dielectric loss The basic chemistry for formation of a poly- but also decreases Tg. use in composites quite logical. This property is especially favor. some joint ven- slightly varying the type of cyanate mono. Reactions by molecular arrangement have are common in commercial polyurethanes. two general arrangements be obtained by using a triisocyanate. the polyols nates are toluene diisocyanate (TDI) and also can have many different groups between methylenediphenyl isocyanate (MDI). It is this variation in the is darker in color and has lower oxidative types and arrangements of atoms between resistance and ultraviolet (UV) light stability the reactive groups that gives such variety than TDI. Just nate monomer. and can give some useful comparisons to one based on ether linkages and the other polyurethanes. The epoxy ring was opened on ester linkages between the polymer units. They chemistry. Excellent weather Although many types of linkage groups can resistance and improved UV resistance can be used in polyols. the groups of atoms between as the epoxy molecules could have many dif. coatings. of the molecule. Urethane linkage formation. The principal involved a molecular rearrangement.5: Specialty and High-performance Thermosets 143 Figure 5-15. been previously encountered with epoxies Both are relatively short-chain polymers. by the reaction of a hardener and the bond. The ether-based polyurethanes are generally ing between the epoxy and the hardener more flexible than the esters. are large aromatic groups. the isocyanates. Even greater UV stability and in- in the types of epoxies and polyurethanes creased toughness can be obtained by using that can be made. role of the polyol in polyurethane chemistry Ester-based polyurethanes have higher me- is like the role of the epoxy molecule in epoxy chanical properties than the ethers. The isocyanate role in polyure. are more often used in molded parts and thanes is like the hardener in epoxy chem. ferent chemical groups or arrangements of Typical examples of commercial diisocya- atoms between the epoxy rings. The type of polyurethane (PUR) istry. Methods. The use of ether-based urethanes is in foams. Fundamentals of Composites Manufacturing: Materials. an aliphatic diisocyanate. MDI the OH groups. much as polyols would have Usually the linkage groups in the isocya- OH groups on the ends of the branches. and Applications . Epoxy molecules generally have epoxy most likely to dominate composites has not groups on the ends of the various branches yet been fully demonstrated. the molds are simply opened and When it comes to thermal capability. Methods.2–20. The sag can be reduced Polyurethanes also can be molded by significantly by additional crosslinking. Polyester is formed inside the mold. its use in applications is its toughness. react rapidly with water. two liquid components are pumped through a Stiffness. often with much heat being evolved. the the part extracted. (15. Properties and Uses tion should be used in the storage and use of The major property of PUR that drives isocyanate materials. 360° F (163–182° C). lay-up. These chemicals cause respi. ing. even without external heat. all of which will be discussed later ratory distress and can be toxic. a comparison of elongation of the mixing and metering of these materi. This toughness comes from the high flexibility Molding and elongation of the structure. The closed mold injection sag values of a PUR reinforced with 20–30% process can be automated easily.144 5: Specialty and High-performance Thermosets Caution must be exercised in the handling open mold processes such as spray-up and of isocyanates. and can be large assuming that some care However. especially useful for In the closed mold injection processes.3 mm) at normal enclosed nature of the process has further automotive painting temperatures of 325– increased its desirability. a closely allied considered elastomers. Polyure- textbook. When the polyurethane is formed flexible. Therefore. transfer molding (RTM). to form the polyurethane. usually with only resins are generally stiffer than polyure- moderate pressures required. traditional thermoset processes such as but this results in more brittleness at room compression molding. In most cases. or structural reaction in. the thanes so the composites of polyesters are.3 closed mold injection processes later in this cm) at –20° F (–29° C) repeatedly. The polyurethane polymer stiffness does have some effect. is chiefly a function of the amount mold into which a reinforcement preform has of glass reinforcement in polyurethanes just already been placed (assuming there is a as it is in polyesters. general casting polyurethane with 55% fiber- als. (These processes as 90D. (1. stiffer than polyurethanes. Some spe- suited to this mixing of reactive liquids and cialty grades of reinforced PUR have elon- combining with a reinforcement are resin gations as high as 600% and are. although the matrix reinforcement). the cryogenic applications. cally have a maximum elongation of 5%.000 molding (RRIM). transfer molding. Therefore. which simplifies However. Manufacturing methods especially well PURs can be flexible or stiff. The totally fiberglass are 0. Polyurethanes can process called reinforced reaction injection have tensile strengths as high as 2. They will in this textbook. These properties lead to an ability of will be discussed in detail in the chapter on some PUR sheets to deflect 6–8 in.05 in. molds can be made of inexpensive materials on average. psi (14–48 MPa) and Shore hardness as high jection molding (SRIM). Property Polyol and the isocyanate monomers are comparisons between resins are hard to generally liquids when they are combined make because of the many grades available. and Applications . including some that are quite is filled. and temperature. polyurethanes have a wider range is exercised to ensure that the entire mold of stiffnesses. therefore.000–7. reinforced PUR ma- Fundamentals of Composites Manufacturing: Materials. Hence. (cured). therefore. extreme cau. generally measured by flexural mixing chamber or tube and then into a closed modulus. the reaction between glass reinforcement shows elongations from the polyol and the isocyanate is almost 5–55% whereas polyester SMC would typi- instantaneous.) thanes are. little part is to be bonded into an assembly or evidence to support these charges has been covered with another coating. The advantages of PUR is abrasion resistance. of weatherometer). as do which are so critical for exterior automotive many plastics. also much more durable (less ripping) and Fundamentals of Composites Manufacturing: Materials. The sives than polyesters. oxygen bonded for these horizontal applications. in reducing the flammability of PURs with ily molded to a class-A surface. applications of reinforced poly- reasons PURs are used so widely in athletic urethanes will continue to develop.5: Specialty and High-performance Thermosets 145 terials are not currently used for horizontal Another issue raised against PUR flam- automotive exterior panels because of exces. polyurethanes are not going to but can be regained to near original values replace polyesters except where the unique with washing and waxing. are flexibility. After 1. such as polyesters. some PUR materials have Taber wearability that unique processing methods. This adhesion monoxide. gloss is significantly lost. Therefore. Many of the mechanical properties of although some concerns have been raised PURs are competitive with polyesters and with PURs’ flammability characteristics. However. PURs can be eas. rather than is also an advantage when the reinforced harmless carbon dioxide. and good adhesion. SMC would be the plastic of choice of internal oxygen (that is. but as of yet. the surface they have not been carefully demonstrated. One is the possibility of formation an airtight bag. This advantage is one of the principle advantages. Although this gas may be present in and off-gases. which are not present in poly. volatile solvents or co-reactants. Methods. Reinforced in processing are shorter cure cycles. In general. 10–20% more than polyesters. Some shoes. and the lack of is far better than most other plastic materi. It is esters. a highly toxic vacuum during cure to remove trapped air gas. which is poisonous. mability characteristics is the low amount sive sag. They are other off-gases and combustion products. abrasion resis- Another property that is leading to sales tance. With these als. Paint adhesion is properties or processing advantages are somewhat less than SMC after 1. and Applications .000 hours in a QUV (a type stringent flammability requirements. Further. These polyurethane or closely smoke from PURs. The most important properties in the weatherometer. however. widely distributed and accepted. toughness. the levels detectable are related polymer bags are much easier to ap- small and generally lost amidst all of the ply than the traditional nylon bags. Some progress has been made parts. some much better. Therefore. some new applications for Some authorities have suggested that polyurethanes in composites have been polyurethanes have some problems with of high interest. which is required to apply a of hydrogen cyanide (HCN). other plastics resins. Paintability. will burn. polyurethanes as a bagging material. Polyurethane grades to be as replacements for other materials or suitable for use in composites cost about as totally new applications for composites. Two flammability issues have been sprayed onto the composite part to achieve raised. in the polymer molecule) compared to many Polyurethanes are generally better adhe. Recently. These applications use flammability. smoothness and paintability of PURs. has been a little more difficult to common reinforced PUR material can meet achieve. adhesion critics suggest that this lower oxygen content to the fiber reinforcements is better across a will lead to the formation of more carbon wide range of reinforcements. but The most serious limitation to the use of the majority of applications are more likely polyurethanes is cost. no however. will be as replacements for polyesters. other polymer systems. are not a problem. PUR materials.000 hours significant. Methods.000 repeat units. A also raises the possibility of entire bagging silane molecule is illustrated in Figure systems that are sprayed on rather than 5-16b. It is often found in nature combined with oxygen and is the principal component of sand (silicon dioxide).146 5: Specialty and High-performance Thermosets will therefore greatly increase the produc. the polymer backbone and various small organic groups bonded to the silicon SILICONES atom. resins. small organic groups. bit more hidden. other uses of silicones oils. Various forms of silicon-containing materials. such as mold rubbers. These short-chain silicones here so that its many uses can be appreciated and the best silicone for each use selected. but is not used directly in any plastics ap- plications. and siliconates. Purified silicon is used in computer chips and transistors. The symbol for elemental silicon is given in Figure 5-16a. The use of these bagging materials mers in making silicone polymers. the silicones can take several forms: There are. rubbers. out. but others may be a in the composites industry. hydrogen. Even those hidden uses are surprisingly important and can significantly Properties and Uses affect operations. They are: • Silicon is the element (atom) charac- terized in the chemistry periodic table and listed just under carbon. Oils. tivity of a molding operation that requires However. ing the length of the polymer chain to less posites. coatings. and resins have widespread use release and adhesives. Fundamentals of Composites Manufacturing: Materials. of course. adhering layers of material. and Applications . and other atoms for special purposes. These small molecules are sometimes used as Figure 5-16. it is useful to explore all the uses of than 1. The importance • Silicones are polymers (made from of this innovation will be seen when bagging silanes) characterized by a series of is discussed in the chapter on open molding alternating silicon-oxygen bonds along of advanced composites. Depending Silicone resins are widely known but not upon how the polymerization is carried necessarily as a resin matrix for composites. Structures and Crosslinking Reactions A clear understanding of the basics of silicones requires that three terms. Even though this chapter Silicone oils are polymers made by limit- is about resins as matrix materials for com. See Figure 5-16c. their principal use is as mono- bagging. • Silane is composed of small molecules of silicon combined with chlorine. in conjunction with composites. be clearly differentiated. especially as coupling agents. which are often confused. thus The dry materials are then further heated imparting high elongation and the elastic to cure the silicone rubber. etc. also perature-vulcanization (RTV) silicones. The groups of silicone elastomers other additives to achieve a wide variety of that require high temperature to cure are viscosities. the polymers matic) group.000. ety of organic solvents and dispersed in wa- Silicone elastomers probably are the most ter to provide a wide range of coatings. pigments. Methods. As with natural rubber. labeled with Xs in Figure 5-16c. When applied as coatings. with less heat stability and at a higher price. but is stiffer. However. The cross- silicon atom in the siloxane polymer (the Xs linking usually is done at elevated tempera- in Figure 5-16c) are methyl groups.000 repeat units. pre-cure and post-cure generally called high-temperature-vulcaniza- mechanical properties. The phenyl-substituted blending short-chain-length silicone oils polymer has higher heat stability. colors. chemically and physically inert. highly compress. Curing of silicone elastomers is usually the silicone elastomers are crosslinked (also done with peroxide initiators or curing agents called curing or vulcanizing) to improve (catalysts) but also can be done with sulfur (as heat stability and mechanical properties. oxidation resistance. ity fluids and used as sprays. however. nature of rubbers. better into fatty-like materials called thickeners. by being water repellent. Silicone viscosity changes a wide range of properties for special ap- little with temperature and shear rate. and improved tough- Silicon oils are also blended with low-viscos. such as lacquers. and Applications . This is the polymer formed the solvents evaporate and the silicones when all of the organic groups bonded to the crosslink to form a hard surface. good low-temperature flexibility. to name just a few compounds. temperature or solids in solvent solutions The most common silicone polymer is di. The organic tion (HTV) silicones. Some substituent other than methyl. The chains are linear.000 repeating units and can be as long to allow the liquid component to evaporate.5: Specialty and High-performance Thermosets 147 polymers are usually liquids (oils) at room prominent properties. ganic groups attached to the silicon atoms in which are used as coatings. like greases or pastes. it has the ability to form a film that prevents Silicone rubbers can be dissolved in a vari- things from sticking together. silicone solution. such as leather the siloxane polymer chain can improve the waterproofing agents. the proper- silicone greases or pastes can be made by ties are modified. Silicone oils are generally characterized This solvent improvement comes. The molded Fundamentals of Composites Manufacturing: Materials. silicone elastomers can crosslinking techniques somewhat unique to be compounded with fillers. methylsiloxane. These important segment of the silicone market. coatings are generally applied to a substrate These materials are polymer chains of over and then heated or simply allowed to stand 1. Those that can be cured groups attached to the silicon atom in the at room temperature are called room-tem- polymer. when the chain ap. methyl groups is replaced by a phenyl (aro- proaches 1. solvent resistance of the silicone material. If one or both of the temperature. ible. They also can The incorporation of fluorine into the or- be dispersed into water to form emulsions. which is the most common become thicker. and Other substitutions can be made to provide thermally stable. is done with natural rubber) or other special Like other rubbers. as 100. and silicones. and high Silicone resins can be used as molding chemical resistance. usually with fillers. and plications. good water repellency. can be selected to further change polymer Silicone resins can be liquids at room properties. It has tures with a peroxide initiator added to the excellent flexibility. ness. have long been used as matrix materials in which gives them more life than many other composite parts. If such such as aluminum. Releases are generally applied mer form of silicone. the cure times mixtures. of this technology is in the baking industry ger cure times. subsequently contaminated parts. substrates with silicone polymers to make plications. While this is con- [149° C]). higher cost. care must be taken to restrict the is high-temperature performance and high spray to the mold only. which provide the including wax-based products. reports that silicones were sucked into the rather. baking sheets. or layers of the composite part. They are also re- pal subject of this chapter. toluene. a short-glass. terproofing agents for masonry and wood. solvent resistance. Silicones as oils (liquids instead of sprays) are well adapted as mold releases. The disadvantages use of mold release. of their low surface tension. and the other two substituents composite material. which then sold in solutions and used principally as wa. Silicone resins sistant to oxidation and thermal degradation. modified silanes. and pigments. Silane coupling agents used release. contamination occurs. These are not polymers but. delamination of the Siliconates are silane molecules where composite or reduced properties can result. A commercial application over conventional organic resins include lon. However. and several proprietary low flammability. The coatings are sold as the silicone to get on or in the components unmodified resins and with various fillers. tool making and other applications where temperature stability.148 5: Specialty and High-performance Thermosets articles have excellent thermal stability and cohol. Usually one of the other is isolated from other areas of production substituents is a short organic group. They are usually ventilation system of a factory. The advantage of these coatings venient. fluorocarbons. and release from a flat surface is desired without low electrical conductivity. electrical properties are important. release paper. Those It also can be used as a release material for properties include fire and arc resistance. Several materials besides silicones for this purpose have two different types are frequently used as mold release agents of reactive end groups. Mold releases are vital to most composites Coupling agents are an important part manufacturing operations to protect the of ensuring a good bond between the matrix tool and part from damage by unwanted and the reinforcement. For example. fiber-reinforced silicone resin can be used as A technology related to mold release a molding compound to provide structural agents is the coating of paper and other and protective characteristics in electrical ap. polyvinyl al. Silicone/glass laminates are com. the mono- adhesion. There have been some are OH groups. mold releases in high-heat-cure cycles. are long (typically 30 minutes to 2 hours) and Silicone mold releases are often applied cure temperatures are high (typically 300° F in an aerosol spray form. is frequently used as a directly to the tool (mold) and then the coupling agent in bonding organic polymers composite part is built on top of the layer of to fiberglass. This type of paper is used monly used in circuit boards where their good extensively in making composite prepregs. and sensitivity to where cookies and other products are placed some solvents such as acetone. ability to chemically bond to both the or- Fundamentals of Composites Manufacturing: Materials. Silane. such so there is no possible contamination of the as methyl. Methods. and not to allow surface hardness. one of the substituents (Xs in Figure 5-16) It is also important to be sure that the spray is a metal oxide. and on silicone paper to achieve release from the carbon tetrachloride. They are Composite Applications easily spread as a thin film over molds because Matrixes for composites are the princi. and Applications . coatings. cycle. cone is one of its major advantages. of course. As with all adhesive more load onto the fibers and making the materials. Flexible tooling is. The improvement in bonding from good coupling agents are used to make sili- the coupling agents is especially effective cones good adhesives and sealants. The choice depends upon the (demonstrating excellent property retention complexity of the design to be reproduced. others are if pressure is required during the molding among the stickiest of materials. those same systems are improved from difficult conditions are present. their excellent release properties. non-organic surfaces is excellent. ing application for silicones in composites. These prim- matically reduces the tendency of the fibers ers are available from the manufacturers of to pull out of the resin. Methods. etc. a resin and a curing agent.5: Specialty and High-performance Thermosets 149 ganic polymer and the inorganic reinforce. systems. less dimensionally stable than hard tooling. In some es- photomicrographs show improved wetting pecially difficult situations. Hence. flexible tooling will deform and the being able to adhere to Teflon® under water. When a coupling agent is present. The same concepts that make silanes ments.000–78. facturer along with the sizing (a protective When the need arises to duplicate a compli- coating). Silicone adhesives tend to improved from 55. While be held to extremely tight tolerances. When adhesives. ibility required with the resin that will be Fundamentals of Composites Manufacturing: Materials. chemical stability (resistant tems. than from a hard mold. if using silicone adhesive and composite stronger. clay. added to the polymer mix. Silicone ture stability (over a range from –85 to 500° F rubbers are generally sold as two-part sys- [–65 to 260° C]). Adhesives and sealants are other useful Therefore. thus transferring the silicone adhesives. if the dimensions of the part must products in the composites industry.000–80. many solvents. and good electrical the extent of undercuts. In these cases. Flexible tooling (molds) is a rapidly grow- plied to the fiberglass by the fiberglass manu. The number of parts that can be made glass and mineral reinforcements (such as from a flexible mold is generally much fewer talc.000 psi (379–538 be somewhat more expensive than organic MPa) when coupling agents are used. oils. over 20 years of life).) are added. the dry flexural strength has been clean surfaces. such as epoxies. the coupling agent is a hard mold. good weatherability are available. part dimensions will change. for example. The type of coupling agent can be cated part. als can perform like silicones. apply them to carefully prepared. a primer should of the fibers by the resin. The resin is to bases. Many resin types atmospheric pollutants). Silane coupling agents are typically ap.000 psi (138–552 MPa). However. acids. However. This wetting dra. especially with undercuts and/or specified to ensure optimal compatibility high-detail replication. especially if the mold Coupling agents improve adhesion in seal. and Applications . and adhesives where the resin make a new mold from silicone is consider- must bond to a metallic or other non-organic ably less than would be required to make surface. In polyester/fiberglass primer. silicone tooling is with most of the common thermoset resins often the easiest and least expensive material used in composite fabrication and with many for creating the mold. the cost and effort to ants. few materi- 20. Properties that give silicone adhesives an The simplicity of making a mold using sili- advantage over other adhesives are tempera. and most chosen to fit the application. is heated. Also. flex- some types of silicones are most noted for ible tooling may not be appropriate. be used to enhance adhesion. of the thermoplastic resins to which fiber. when wet. when the composite is exposed to water or bonding between composite materials and solvents. and the compat- properties (low conductivity). or by placing of vacuum).6 the nylon sheet and sealant materials. Moreover. The benefits of ture or less time if heated.150 5: Specialty and High-performance Thermosets cast in the mold to make the final parts. working time required. pattern is then mounted securely to the bot. are almost eliminated with the thicker pouring into the mold. this has been accomplished by of the mold and then a silicone rubber tool creating a vacuum bag assembly over the part is placed on top of the composite. Recent developments in using the thermal Reusable vacuum bags have become an im. tion (RTV) silicone sealants. which could be made of silicone film. there is a contents usually requires applying a vacuum reduced need for autoclaves. The nylon bag and sealant materials the pattern. expansion of silicone elastomers in a con- portant application because of the high cost of trolled manner offer an economical alternative vacuum bagging using disposable materials. and more rugged silicone bags. lay-up and the vacuum bag to collect any patibility with the material of the master to resin that may flow out of the part during be cast against and the resin to be used to evacuation. The are not reused. and com. especially for during curing. (74 cm) for a few minutes. Because the bags are con- pumped around and over the pattern. several composite manufactur- tom of a rigid. then placed into an autoclave or oven and The mold is then made by first preparing cured. Sili- cm) clearance around and above the pattern. typically <1%. cone bags vastly reduce the time needed to The pattern and inside of the box are then create the vacuum assembly and are reusable coated with mold release. Several sheets of release material. It must be clean and dry. Achieving low void the case of advanced composites. they can be high-volume production processes. Methods. is called trapped rubber molding (TRM). require low void con. prepare the surface for proper casting. Recently. in tents. open box that has an area and ers have shown that silicone bags can replace depth sufficient to give at least .25 in. thereby reducing curing agent are mixed and then poured or long-term costs. from the autoclave is uniformly applied to This is done by placing a top on the box the part through the silicone bag. to achieve pressurization of composite parts Many composite applications. Automatic dispens. which such as clear versus colored agents. (0. the mold can be using reusable silicone vacuum bags become removed (stripped) from the pattern. The technique to the part during initial cure and then apply. bag. Best formable to the shape of the part. This assembly consists of a sheet part of the mold or simply a platen is then Fundamentals of Composites Manufacturing: Materials. The result is part definition advanced composites. The entire vacuum assembly is make the final parts. Should the ing and de-airing equipment is available for silicone bags become damaged. The of nylon film secured to the upper face of the curing agent is chosen to be compatible with mold using two-sided tape to create a vacuum the resin in light of other considerations. The resin and (from 30 to 100 cycles). The other to be cured. The composite lay-up is placed in one half Traditionally. pressure results are obtained if the mix is de-aired. and subjecting it to a vacuum of about 29 bag failures (breaks in the bag causing loss in. ing pressure during the latter stages of cure. more with a barrier coat to increase mold life and costly polyimide films. superior to non-pressurized parts and. which are common with nylon the resin mix into a vacuum system before bags. The even more pronounced at elevated tempera- silicone mold is then placed in a frame to give tures (up to 550° F [288° C]) where nylon it some dimensional stability and it is coated films must be replaced with the stiffer. repaired with room-temperature-vulcaniza- After curing for 24 hours at room tempera. and Applications . and absorbent help ensure thorough mixing of curing agent materials are placed between the composite and resin. a closed mold. With the continuing pressure to lower creates pressure on the composite part. ers are made by a liquid injection system into Several silicone materials are used as ad. sions and shrinkage. trapped rubber molding tool because of the following properties: it can be easily cast. was a cover for chlor-alkalai cells. ability to hide the fibers so the visual charac- the addition of the silicone powder can also teristics of the reinforced polyester are better. composites field. These cov- to achieve curing of the composite. sphere. and it exhibits long mold life. and esters. tant pipe. Concentrations potential. compelling advantages over the materials invented by United Technologies. silicone powders higher Tg and more rapid development of ac- can reduce the amount of flame retardant ceptable hardness. through the expansion of the silicone media Two important applications for DCPD that is heated. the use of non-polluting solvents. of only 1 to 5% can modify a plastic’s burn DCPD has been used in composites for characteristics. halogenated. In DCPD reacts with maleic acid and results in a highly filled resin systems. some resin manufacturers have (VOC) solvents. it is temperature Occasionally a new resin emerges in the stable. Other silicone additives improve dispersion which reduces the amount of harmful emis- properties and enhance resin compatibility. DCPD also improves the Some have been developed as crosslinking cure of the resin when in an oxygen atmo- agents for thermoplastic resins. usually with an independent have recently been commercialized. As the as. improve processing by reducing the amount The DCPD has low viscosity. molding is called the THERM-X™ process. Methods. thus assisting in making the surface A relatively new application is the use of tack-free even when exposed to air. Sili. the silicone expands and cone. silicones as low-volatile-organic-compound Recently. reducing the rates of heat many years as an additive to improve the release. Dicyclopentadiene process. and smoke and carbon monoxide performance of traditional unsaturated poly- evolution in halogen-free.5: Specialty and High-performance Thermosets 151 placed on top of the silicone rubber tool and and as solvents for high-performance coatings. These materials have proven announced the inclusion of DCPD as a to be invaluable in paint removal applications component in epoxy resins. The most important advantages of silicon rubber with a barrier. a tool and composite part are both (DCPD) seems to be on the brink of becoming placed inside a pressure vessel and then the newest star of the composite resin mar- completely surrounded by compressible ketplace. Some of the coatings are also made from sili- sembly is heated. In thermoplastic systems. of course. and Applications . the phosphorus flame-retardant systems. will continue to grow. such as alu. DCPD also improves the filler required. The pressure is provided polyesters. The first control from the heat supplied to the mold. cone is well suited for implementation as a such as silicones. thus allowing of energy required to extrude the material. clamped or held shut in a press. a reduction in the total amount of styrene. DCPD are improved toughness and chemical minum foil. An alternate system to trapped rubber because the new resin has some distinct. In these modified polyester resins. This occurs. The other is corrosion-resis- ditives in plastics for a variety of purposes. VOC levels. The DCPD Fundamentals of Composites Manufacturing: Materials. In this currently being used. Here the advantages of toughness One application that has excellent promise combined with corrosion resistance better is the use of a high-molecular-weight silicone than vinyl esters suggest strong market powder as a flame retardant. DICYCLOPENTADIENE (DCPD) it has high tear strength. between the silicone and the resistance over the traditional unsaturated part for protection. 152 5: Specialty and High-performance Thermosets is polymerized in the backbone and epoxy groups are still on the ends for crosslink- ing. The addition of DCPD significantly improves the Tg of the epoxy, raising it from 320° F (160° C) at 22% concentration to 356° F (180° C) at 28% concentration. Another modification to the formation of pure DCPD monomer is the copolymer between DCPD and butadiene. This gives a significant increase in toughness over what is already a tough polymer. Similar copolymers between DCPD and ethylene also have been commercialized. These copolymers, some- times called cyclic olefin copolymers (COCs), are thermoplastics and compete against tra- ditional thermoplastics such as polystyrene, polycarbonate, and acrylic. Structure and Crosslinking Reactions The structure of the dicyclopentadiene monomer can be depicted in several, equiva- lent representations. Because these can be confusing, the most common methods of showing the structure are given in Figure 5-17. Figure 5-17a is probably the most representative of the actual geometry of the molecule. Figure 5-17b is simply the same as Figure 5-17a, but without the atoms shown. Note that this representation assumes a carbon atom is at each node. Figure 5-17c is a planar representation of the molecule. Both Figure 5-17a and b emphasize the three-dimensional nature of the molecule and its similarity to norbornene, an impor- tant organic molecule. Note that the DCPD monomer is also similar to the nadic end-cap- per used in some polyimide resins. The polymerization of DCPD begins with Figure 5-17. Alternate representations of dicyclopenta- the opening of the six-member ring that diene (DCPD). contains the carbon-carbon double bond. This step results in a linear polymer in which the remaining bicyclic structure is tion (ROMP). A complex organometalhalide pendant from the polymer chain. The chain catalyst is employed in polymerization. In backbone includes the carbon-carbon double the past, the sensitivity of this catalyst to the bonds. This reaction mechanism has been presence of oxygen and other contaminants called ring-opening-metathesis polymeriza- was a major problem making the reaction Fundamentals of Composites Manufacturing: Materials, Methods, and Applications 5: Specialty and High-performance Thermosets 153 difficult to carry out. In the last few years thermal shock resistance in cultured marble a new catalyst system based on ruthenium applications. (Grubbs catalyst) has been developed that The advantages of DCPD when com- vastly reduces the complications associated pared to traditional unsaturated polyester with the polymerization. The reaction is and vinyl ester formulations are: improved highly exothermic so some control over the toughness (sometimes initially as high as temperature is required. However, the use 100 times better but falling to about 10 of the new catalyst along with a reaction times better over time), stiffness, corrosion modifier, triphenylphosphene (TPP), has resistance, reduction of styrene, and the made the polymerization quite routine. The ability to have a single-stage cure from a reaction rate is usually fast. low-viscosity resin. Although it is theoretically possible to stop the reaction at the linear thermoplas- Processing tic polymer stage, the practical matter is An important advantage of DCPD is the that the reactivity of the DCPD monomer ability to use the resin in liquid injection results in crosslinking reactions proceeding molding processes, such as structural re- at the same time the linear polymer is being action injection molding (RIM) and resin formed. The high reactivity results from the transfer molding (RTM), which are dis- many reactive sites on the DCPD monomer cussed in detail in a later chapter. Some where crosslinking can occur. Crosslinking significant advantages are obtained in using occurs at the double bond in the pendant bi- DCPD versus other more traditional resins. cyclic ring. Additional crosslinking can occur Because of the reactivity of the DCPD po- at the carbon-carbon double bond along the lymerization, the need for expensive RIM backbone. As a result, the polymeric struc- metering equipment is largely eliminated. ture is complex and has high crosslinking With DCPD, the only requirements are density. The interlocking structure combined a simple mixing vessel, a feeding motor with the aliphatic nature of the polymer pump, and some temperature control over results in extraordinary toughness. the mold. Impregnation of the fiber preform is rapid because of the low viscosity of the Properties and Uses resin. Reaction time is fast. The high reactivity of DCPD can be used Other typical composite manufacturing in combination with other monomers and methods such as filament winding, centrifugal polymers to obtain some unique properties. casting, pultrusion, and spray-up have been As already discussed, DCPD has been used as demonstrated to work at least as well with an additive in relatively minor amounts with DCPD as with polyesters and vinyl esters. both unsaturated polyesters and epoxies. DCPD also has some disadvantages ver- These products have been used to make au- sus traditional unsaturated polyesters and tomobile body filler, bath tubs/shower stalls, vinyl esters. For instance, its high toughness spas, sinks/vanities/counter tops, truck seems to decrease with time. This may be bodies/caps, boats, personal watercraft, due to oxidative attack on the carbon-carbon decorative building columns, and in electri- double bonds over time. Hence, oxidation cal applications. Many applications benefit stability is also lower than in some high- from the superior surface finish that DCPD performance vinyl esters and polyesters. At gives to traditional polyester parts as well as present, no appropriate coupling agents with its superior physical properties. Of special fiberglass have been developed, so bonding to note is the higher Tg that leads to improved the reinforcement is less than optimal. Fundamentals of Composites Manufacturing: Materials, Methods, and Applications 154 5: Specialty and High-performance Thermosets CASE STUDY 5-1 being wet down, the material is cured and the shin guard has the permanent shape Rapid-curing Fiberglass Shin Guards of the user’s shin. A student and an avid soccer player, “Several layers of fiberglass and plastic Spencer Larsen has reported the following materials comprise the reinforcement and breakthrough. His report is used in part. cushioning part of the shin guard. The inside “In recent years a development in sports layer is made of ethylene vinyl acetate that equipment has revolutionized the soccer has a knitted covering and several holes world. A material that was initially used for punched for ventilation. The inner layers making medical splints has now found its are several fiberglass layers of different way onto the playing field. Now its job is to weaves that provide thickness variation and prevent some of the injuries that it so often strength as needed for optimal performance. aided in fixing. The product is a rapid-curing The outer layer of the shin guard is a fabric fiberglass shin guard. It is made from a pro- capable of stretching to account for the shap- prietary, fiberglass reinforced polyurethane ing of the shin guard to the shin. and seems to have just the right blend of “The composite shin guards compete manufacturability and properties. against several other designs and materials. “The material comes as a prepreg in a The typical design of the fiberglass/PUR shin watertight bag. Several layers of fiberglass guard is better at dispersing impact forces cloth are impregnated with a dry mixture of than almost any other shin guard while be- isocyanate and polyol that becomes reactive ing lighter than most of the others and about when brought into contact with water. In average in thickness. Overall, it is clearly the addition to solvating the materials so that best choice.” they can react with each other, the water molecules react with isocyanate molecules, which are in excess concentration in the pre- SUMMARY preg and form intermediate reactive groups. The specialty and high-performance ther- These groups further react with additional mosets are used when environmental condi- isocyanate to form a polyurethane. tions are severe. One of the most adverse “The instructions for the curing of the environments for a composite material is shin guards tell the user to wet the mate- when it is used as a pipe or tank for holding rial by putting it under a running faucet or aggressive chemicals. For these applications, by dipping it into a container of water. The vinyl esters have proven to be both cost ef- greater concentration of water molecules fective and durable. In general, vinyl esters provides for a much quicker curing time, are the resin of choice for corrosive situations usually 10–20 minutes. Once the material or when most common solvents need to be has cured, further exposure to water does transported or stored. Of course, vinyl esters not affect the shin guards. They are even also have their limitations. Some extremely advertised as being machine-washable. aggressive liquids will attack vinyl esters. “Thanks to the combination of reactive Therefore, care should be taken to test the resin and fiberglass, the guard can be custom materials and/or consult a reliable chemical fit to the user’s shin. Before and immediately compatibility table before using vinyl esters after being exposed to moisture, the material or any polymer matrix in liquids that might is flexible and can be shaped to the shin and be detrimental to their performance. held in place by an elastic wrap (like an ACE® When the environment may include the bandage) or a tight sock. A few minutes after danger of a fire, the usual choice of matrix Fundamentals of Composites Manufacturing: Materials, Methods, and Applications 5: Specialty and High-performance Thermosets 155 is a phenolic. These highly aromatic ma- used for housings over antennae and for terials resist burning and have relatively radomes. little smoke. Moreover, the smoke emitted The polyurethanes are just now achieving is generally of a lower toxicity than most high volumes as matrix materials for com- other resins. Hence, critical transportation posites. They are tougher than most other environments, such as on airplanes, ships, matrix materials and have good processing trains, and buses, as well as high-density capabilities. Therefore, it is expected that public areas, require that phenolics be used more polyurethane matrix composites will be as the resin matrix of interior components. used in applications where moderate damage Phenolics are also used in applications where might be a problem. a char needs to be formed so that the heat will Silicones have been used in the compos- not be transported throughout the material. ite industry for many years. Mold releases, Such an application would be the exhaust vacuum bags, flexible molds, adhesives and, nozzle of a rocket. In this case, the phenolic of course, matrices have all been made from is reinforced by carbon fibers. As the char is silicones for many years. The matrix materi- formed, the carbon fibers and char are slowly als perform especially well in environments eroded away (called ablation) and the heat is of both low and high temperature, although retained in the char zone. not as high as with polyimides. For situations where ablation must be DCPD is a relatively new matrix material much slower than can be obtained with that has some nice properties. It is tough and phenolics, such as for aircraft brakes, and corrosion resistant. DCPD is a low-viscosity for high-temperature environments, the resin that cures quickly to give a nice surface material of choice is carbon-carbon compos- and excellent properties. ites. The matrix is actually a char, usually of phenolic, which is then filled with additional resin and charred again. This process is LABORATORY EXPERIMENT 5-1 repeated until the matrix is nearly without Solvent Resistance of Composite Resins voids. The resulting material is largely pure Objective: Determine the solvent resis- carbon. The reinforcement is also carbon. tance of specialty resins versus polyester Hence, carbon-carbon is the name of the thermosets. material. The major drawback to carbon- Procedure: carbon composites is high cost. 1. Obtain samples of composites made When a material must be found that has from traditional polyesters and from higher thermal stability than epoxies, easier several specialty resins. Some good processing than phenolics, and lower cost specialty resins would include vinyl than carbon-carbon, the most logical choice ester, phenolic, and cyanate ester, all is polyimides. These resins are highly aro- with fiberglass. matic and stiff—both characteristics typi- cal of high strength and thermal stability. 2. Cut the samples into tensile bars. The However, polyimides are quite difficult to shape can be found by looking at the process and are higher priced, at least in tensile test in the ASTM procedures. comparison to epoxies. Therefore, their use 3. Divide the polyester samples and the is usually restricted to only high-tempera- specialty resins into at least two groups ture environments. of at least two samples each. One of the Cyanate esters have especially good elec- sample groups of each type of resin is trical properties and are therefore often for the control and the other groups Fundamentals of Composites Manufacturing: Materials, Methods, and Applications 156 5: Specialty and High-performance Thermosets are for exposure at different times, if 2. What are three advantages and disad- possible. vantages of vinyl esters versus epoxies 4. Place the control samples in a place in composites? where they will not be subjected to 3. Discuss an important application for chemicals or light. phenolic composites. What are the mo- 5. Using goggles and protective clothing, lecular features that lead to its excellent carefully place the other samples in a performance in this application? pan containing sufficient amount of 4. Why do phenolics make a good starting a chemical to cover the samples. You material for carbon-carbon composites? might choose one of the following as a 5. What is meant by B-staging? What possible chemical: nitric acid, hot water, are the A and C stages? Explain how acetone, bleach, etc. resins other than phenolics might be 6. Leave the samples in the material for B-staged. a few days or, preferably, a few weeks. 6. Why do carbon-carbon composites take Make sure the test is clearly labeled so long to make? with a warning indicating the nature of 7. What is the difference between pyroly- the chemical. Also make sure the test is sis and oxidation? Why is pyrolysis used in some location where the pan will not in making carbon-carbon composites? get bumped and spilled. If noxious odors are emitted from the chemical, the test 8. What are two key criteria for a ther- should be run inside a chemical hood. mally stable composite? 7. Using goggles and protective clothing, 9. What molecular features suggest that carefully remove some or all of the polyimides will have good thermal sta- samples. If you have enough samples, bility? you might take out some of them at two 10. What are the unique properties of or more different times. Use gloves and PMR-15? How are they related to its tongs to remove them. Be careful not to molecular structure? spill or drip on your clothes. 11. Give two key properties of polyurethane 8. Carefully wash the samples. Use safety composites. In which applications are equipment as previously outlined. Dry these properties important? the samples with a cloth. 12. List four different uses for silicones in 9. Obtain the control samples and then the composites industry. test both the control samples and the 13. What causes the high reactivity of exposed samples using a tensile test ma- DCPD? chine. Note the tensile strength, modu- 14. Explain how a self-healing composite lus and, especially, the elongation. works. 10. Compare the elongation as a function of the exposure time for the polyester and specialty resins. BIBLIOGRAPHY Brown, E.N., Sottos, N.R., and White, S.R. QUESTIONS 2001. “Fracture Testing of a Self-healing 1. Indicate three advantages of vinyl esters Polymer Composite.” Submitted for publica- over traditional unsaturated polyesters tion in Experimental Mechanics: An Interna- in composites. tional Journal. Fundamentals of Composites Manufacturing: Materials, Methods, and Applications 5: Specialty and High-performance Thermosets 157 Cull, Ray A. 1980. “Characteristics of High-temperature Polymers.” Personal communication, quoted from Cassidy, P. E., Thermally Stable Polymers. New York: Marcel Dekker, Inc. Goodman, Sidney H. (ed.). 1998. Handbook of Thermoset Plastics, 2nd Edition. West- wood, NJ: Noyes Publications. Larsen, Spencer. 1989. “Composites in Medi- cal Applications.” Report for MFG555. McDowell, Enoch. No year. “A Closer Look at OSi® Fiberglass Technology.” Report for plastics materials and manufacturing class. Quoted (in part) by permission. Peters, S. T. 1998. Handbook of Composites, 2nd Edition. London: Chapman and Hall. Reardon, Joe, Manager, Applications En- gineering for HyComp, Inc. 2002. Private communication in January. Society of Manufacturing Engineers (SME). 2005. “Composite Materials” DVD from the Composites Manufacturing video series. Dearborn, MI: Society of Manufacturing Engineers, www.sme.org/cmvs. Strong, A. Brent. 1995. Fundamentals of Polymer Resins for Composite Manufactur- ing. Arlington, VA: Composites Fabricators Association. Strong, A. Brent. 1996. Composites Fabrica- tion, October, pp. 41–47. Strong, A. Brent. 2006. Plastics: Materials and Processing, 3rd Ed. Upper Saddle River, NJ: Prentice-Hall, Inc. White, S.R., Sottos, N.R., Geubelle, P.H., Moore, J.S., Kessler, M.R., Sriram, S.R., Brown, E.N., and Viswanathan, S. 2001. “Au- tonomic Healing of Polymer Composites.” Letters to Nature 409, 794–797. Woodson, Charles S. 1999, 2000, 2001. Cym- etech, LLC, personal communications. Fundamentals of Composites Manufacturing: Materials, Methods, and Applications 1: Introduction to Composites 159 6 Thermoplastic Composites CHAPTER OVERVIEW different for each of the polymer types, as de- This chapter examines the following scribed in previous chapters. The net result topics: of the crosslink formation in all thermosets is a dramatic solidification of the resin, an in- • Review of thermoset and thermoplastic crease in strength and stiffness, an increase composites in the glass transition temperature, and an • Engineering thermoplastic composites increase in the melting point. The melting • High-performance thermoplastic com- point is raised high enough that it is usually posites above the decomposition temperature of the polymer and the crosslinked polymer can no longer be melted. REVIEW OF THERMOSET AND Thermoset resins have distinct advan- THERMOPLASTIC COMPOSITES tages in composites. The uncured thermoset As discussed briefly in previous chapters, resin is mixed with the fibers before the all resins are either thermosets or ther- crosslinking reaction while it is still low moplastics. The pre-cured thermosets are in molecular weight and, therefore, low in relatively low-molecular-weight resins in viscosity. These low-viscosity resins (often which bonds are caused to form between the having viscosities similar to thin motor oil) molecular chains during molding—a process will easily wet the fibers. As will be seen, the called crosslinking or curing. Crosslink- higher molecular weight of the thermoplas- ing forms a polymer network of extremely tics makes fiber wet-out much more difficult. high molecular weight, which results in Another advantage is that the crosslinking significant changes in many properties. The reaction can be interrupted and suspended thermoplastics, which are not crosslinked, at the point where the fibers are wetted but have molecular weights higher than the full cure has not yet occurred. This is called uncured thermoset resins but not as high as B-staging, and the resulting material the crosslinked (cured) thermosets. (called a prepreg or molding compound) Thermoset polymers are formed, therefore, can be stored until the actual molding opera- when crosslinks are formed. The crosslink- tion is carried out at a later time. The sus- ing bonds are created through chemical pension of the curing process is overcome by reactions between active sites on the resin heating the resin (and occasionally by adding molecules, sometimes employing the use of an activating chemical), which is done during non-polymeric molecules, such as styrene the molding operation. Usually special (cold) and various initiators, to assist in the pro- storage conditions are required for prepregs cess. The crosslinking process is somewhat and molding compounds as the thermoset Fundamentals of Composites Manufacturing: Materials, Methods, and Applications 159 160 6: Thermoplastic Composites resin will slowly continue the crosslinking The absence of change in molecular reaction even though it has been temporarily weight of a thermoplastic during processing slowed by cooling. With all of these advan- gives rise to a major compromise of proper- tages, thermosets are clearly the preferred ties, which is inherent in the formulation resin for making composites. of all thermoplastic resins. In general, most Thermosets have some disadvantages mechanical and physical properties of poly- too, which have led to the use of thermo- mers are improved as their molecular weight plastic resins in composites as well. Some increases. However, increasing molecular of the disadvantages of thermosets include weight makes processing of the thermoplas- the following: tic composite much more difficult. This is • required mixing of chemicals to effect because resin melting points are increased, the cure, wet-out of the fibers is more difficult with the higher viscosity resins, and the polymers • potentially harmful vapors and chemi- are more difficult to dissolve should solvent cal handling, processing be used to wet the fibers. • limited shelf life, Much research and effort has gone into the • multi-step processing, task of improving the physical properties of • longer times for molding the part (cure thermoplastic resins and yet not making the time), resulting polymer extraordinarily difficult to process by melting or, less often, by solvation. • inability to reprocess (reshape) the Even though compromises on molecular material after it has been cured, and weight and processing are inevitable, some • poor toughness. important properties of thermoplastics are The last of these—poor toughness—needs superior to thermosets. This has led to in- some explanation. Because the crosslinks creased use of thermoplastics in composite tie the polymer chains together, the overall applications. rigidity of the polymer system is usually To fully appreciate the impetus to use increased as curing proceeds. This rigidity thermoplastics for composite applications, reduces elongation and generally reduces it is appropriate at this point to step back impact toughness in thermosets. and look at the entire plastics and composites Thermoplastics do not have crosslinks. marketplace. This includes all the polymer The molding process is simply one of melt- composite products employing thermoset ing the thermoplastic so it will flow into and and thermoplastic resins, as well as the many fill the mold. Then the material is allowed non-reinforced plastics used. This market- to cool and solidify in the molded shape. No place is, of course, immense and getting big- change in molecular weight occurs during the ger every day. In applications too numerous processing of thermoplastic resins. Therefore, to even conceive, plastics are replacing wood, whatever molecular weight is needed in the metal, ceramics, paper, leather, and other final product must exist in the thermoplastic traditional materials. Moreover, they are resin before it is molded. All composite mate- being used in a multitude of unique applica- rials are solids at their use temperatures and tions for which no other material has ever generally at room temperature, regardless of been used. When viewing the entire market the use temperature. So thermoplastics are for plastic and composite materials, that is, solids at room temperature, and after being all products employing polymeric resins, melted during molding, they return again to thermoplastics represent about 80% of the their same solid condition after cooling. total. Thermosets represent the remaining Fundamentals of Composites Manufacturing: Materials, Methods, and Applications 6: Thermoplastic Composites 161 20%. Why are thermoplastics so dominant A brief summary of the characteristics of in the total marketplace? Generally, ther- the engineering and advanced thermoset moplastics have the advantage over thermo- and thermoplastic composites is given in sets because of much faster molding times Table 6-2. Engineering thermoset compos- (simple cooling of thermoplastics to solidify ites (FRP) might be used in automobiles and versus the chemical reactions required for boats. Engineering thermoplastic composites thermosets) and the overall adequacy of the could be used to strengthen traditional plas- properties that can be obtained. tic parts such as valves and football helmets. Still putting the big picture into perspec- The advanced thermoset composites might tive, it should be understood that the vast be used in helicopters and airplanes, whereas majority of plastics materials do not use rein- advanced thermoplastic composites could be forcements and are not, therefore, composite used in submarines and tanks. These uses materials. Hence, the inherent problems of are, of course, merely representative of com- fiber wet-out that come with thermoplastic mon applications that utilize these various resins do not apply. The market for just materials. reinforced materials, that is, the composite For thermosets, the division into engi- materials, is about 20% of the entire plastics neering and advanced composites is based and composites marketplace. Within this on resin type, reinforcement type, preci- more narrow composites market, thermosets sion placement of the fibers, and control represent about 80% of the total material over fiber-resin content during the mold- used, just the reverse from the entire mar- ing process. Generally, the resins used for ketplace. engineering composites are polyesters and In summary, thermoplastics are the domi- vinyl esters. The reinforcement used with nant plastic materials overall and especially engineering composites is almost always in non-reinforced applications. Thermosets fiberglass. An alternate name for the engi- are used in non-reinforced applications for neering thermoset composites is fiberglass specific purposes where they have an ad- reinforced plastics (FRP). For this group vantage because of some unique property. of composites, the placement of the fibers Further, within the reinforced or composites during molding is often quite random as marketplace, which is much smaller than occurs in such processes as spray-up and the total, thermosets dominate and thermo- wet fiber lay-up. Even when more precise plastics are used only in applications where methods such as filament winding, pultru- their unique advantages are important. sion, and resin transfer molding (RTM) are This chapter discusses the characteristics of used, control over the resin-fiber concentra- thermoplastic composites that present those tions is generally less precise than would be specific advantages. the case when using these same processes with advanced composites. The emphasis Differences Between Engineering and in engineering composite processing is often High-performance Composites on throughput. Engineering composites are The world of composites can be separated characterized by their relatively low price into two groups by resin type, thermosets and rather than for any particular outstanding thermoplastics, and then into two additional performance property (except for corrosion groups, the engineering or industrial composite resistance for vinyl esters). materials, and advanced or high-performance As indicated in Table 6-1, the advanced composite materials. Table 6-1 summarizes thermoset composites are distinguished from the differences between these materials. the engineering thermoset composites by the Fundamentals of Composites Manufacturing: Materials, Methods, and Applications 162 Table 6-1. Characteristics of engineering and advanced, high-performance thermoset and thermoplastic composites. Engineering Composites Advanced Composites Thermosets Thermoplastics Thermosets Thermoplastics Resin types Low cost (for example, Traditional commodity Epoxies and specialty High mechanical unsaturated polyester and low cost (for resins (for example, property resins, Fundamentals of Composites Manufacturing: Materials, Methods, and Applications and vinyl ester) example, phenolics, polyimides, usually highly polypropylene [PP], polyurethane [PUR], aromatic (for example, nylon, silicones, and cyanate polyetheretherketone polycarbonate [PC], esters) [PEEK], polyphenylene polyethylene sulfide [PPS], terephthalate [PET], polyarylsulfone [PAS], and acrylonitrile- liquid crystal polymers, butadiene-styrene and thermoplastic [TP] [ABS]) polyimides) Reinforcement Fiberglass (chopped Fiberglass (short) Carbon fiber, aramids, Carbon fiber, types or woven) other high- aramids, other high- performance fibers, performance fibers, and specialty and specialty fiberglass (long fibers) fiberglass (long fibers) Concentration Up to 50% Up to 40% Above 50% and up to Above 50% and up to of reinforcement 65% 65% Processing Traditional thermoset Traditional Precision placement Adapted precision methods curing (for example, thermoplastic methods (for example, methods for spray-up, lay-up, processing (for prepreg lay-up, thermosets and 6: Thermoplastic Composites resin transfer molding example, injection filament winding, specific methods for [RTM], filament molding, extrusion, pultrusion, and RTM) thermoplastics only winding, pultrusion, thermoforming, and and compression blow molding) molding) 6: Thermoplastic Composites 163 Table 6-2. Comparison of advanced and engineering thermoplastics and thermosets. Advanced Advanced Engineering Engineering Thermosets Thermoplastics Thermosets Thermoplastics High cost High cost Low cost Low cost High-temperature Solvent resistance Excellent fiber Standard capabilities wet-out thermoplastic manufacturing High strength High toughness Moderate strength Short fibers High modulus Poor wet-out Brittle Moderate strength Good fiber wet-out High strength Brittle Good toughness types of resins, types of reinforcements, and thermoplastic resins, which are called neat precision of the processes used to control resins. fiber placement. The types of resins used in Molders who use injection molding and these materials have been discussed in previ- other traditional thermoplastic molding ous chapters and the types of reinforcements machines would rarely have the capabil- and molding methods will be examined in ity to mix reinforcements into the plastic detail in subsequent chapters. So, in brief, as this is usually done in an extruder. The the high-performance thermoset resins addition of fibers is often done by the resin include epoxies, phenolics, polyimides, etc., manufacturer or an intermediate resin com- and the high-performance fibers include pounder who might also add colors, UV carbon/graphite, aramids, etc. stabilizers, and other minor components A similar separation into engineering and during the same extrusion operation. The high-performance composites can be made actual addition is usually done by adding for thermoplastic composites, also shown in the short fibers through an inlet port in the Table 6-1. Engineering thermoplastic com- barrel of the extruder. The reinforcements posites are made from relatively low-cost are mixed into the molten resin by the action thermoplastic resins. They are almost always of the extruder screw. This action will often reinforced with short fiberglass strands. break the fibers, especially if they are long. These composites are usually molded using Therefore, the fibers used in engineering traditional processes such as injection mold- thermoplastic composites are short—small ing, extrusion, and thermoforming, which enough to survive the extrusion operation were designed for non-reinforced materials. and pass through the many small clearances The resins are introduced into the process- typically present in molding machines. The ing machines as pellets—small pieces of solid fiber lengths in these pellets are usually only thermoplastic resin shaped like short pieces a few millimeters and, by analogy, are often of spaghetti. These pellets are heated in the called whiskers. Difficulties in processing process until molten, pressed or injected into of the resin and fibers in a molding machine the mold, and then allowed to cool and so- usually limit the maximum concentration of lidify in their molded shape. The normal use fibers to about 40%. of these traditional thermoplastic molding Even though the processes used to mold processes would start with non-reinforced engineering thermoplastic composites are Fundamentals of Composites Manufacturing: Materials, Methods, and Applications 164 6: Thermoplastic Composites relatively common, some minimal machine thermoplastics must be allowed for in pro- modifications must be considered when mold- cessing these materials. ing with reinforced resins. The most obvious change is that all small restrictions in the processing stream need to be opened up as ENGINEERING THERMOPLASTIC much as possible to allow for passage of the COMPOSITES fibers. Those restricted openings might be Dozens of engineering thermoplastic res- in the molding machine or in the mold, such ins are available and, as previously discussed, as the gates. The molder should also realize they dominate the world of non-reinforced that long-term running of fiber reinforced plastics. Most of these resins also can be ob- resins will increase the abrasive wear along tained with short fiber reinforcements. The the flow path of the resin. This is due, of reinforcements are generally added to obtain course, to the higher abrasive character improvement in some specific mechanical of the reinforcement versus a neat resin. property. A few of the most common ther- Therefore, wear should be expected and moplastic resins, neat and reinforced, along machines and tools should be examined of- with their properties, are listed in Table 6-3. ten as wear could change part dimensions. Note that a wide range of properties can be The processes for molding thermoplastics obtained in just the neat resins (0% fiber). will be discussed in greater detail in a later This variety has been developed over many chapter in this book. years as polymer chemists have created The advanced (high-performance) thermo- new resins to fill in the gaps and expand the plastic materials are characterized chiefly available mechanical, physical, and chemical by the type of resins used, the types of re- properties of plastic materials. inforcements, and the types of processes, The choice of resin often depends on many as shown in Table 6-1. The resins used in factors, which might include mechanical advanced thermoplastic composites will be properties, but can also include chemical discussed later in this chapter. The advanced resistance, thermal resistance, resistance to thermoplastics typically include high-perfor- ultraviolet light, resistance to environmental mance reinforcements, such as carbon fibers, stress cracking, electrical properties, or oth- aramid, etc., which are used at the longest ers. Resin choice might be dictated by one of possible length and highest practical concen- these non-mechanical properties. However, tration. As is the case with high-performance at the same time, some improvement in thermosets, the fiber lengths in high-perfor- mechanical properties might be required mance thermoplastics are often the full size over what can be obtained from just the of the part. The fiber concentrations may be neat resin. For example, a plastic valve may as high as 65% of the total in both thermoset require the inherent abrasion resistance and and thermoplastic advanced composites. machinability of nylon but could also require Many of the precision fiber lay-down the tensile strength to be greater than the methods used for high-performance thermo- 5.5–12 ksi (ksi is the abbreviation for 1,000 sets can be used for thermoplastics, provided pounds per square inch) (38–83 MPa) obtain- that appropriate changes are made. These able with neat nylon resin. A logical method modified processes, as well as some processes of getting increased tensile strength in nylon used exclusively with thermoplastic compos- would be to add fiberglass reinforcement. As ites, will be discussed later in the chapter on seen in Table 6-3, tensile strengths of 20–27 thermoplastic processes. In general, however, ksi (138–186 MPa) are possible in nylon with the high melting point of high-performance 30% fiber content. Fundamentals of Composites Manufacturing: Materials, Methods, and Applications 6: Thermoplastic Composites Table 6-3. Effects of fiberglass content on mechanical properties of various engineering thermoplastic resins. Tensile Strength*, Flexural Modulus*, Notched Izod Impact*, Resin ksi (MPa) ksi (MPa) ft-lb/in. (J/mm) 0% Fiber 30% Fiber 0% Fiber 30% Fiber 0% Fiber 30% Fiber Acrylonitrile- 4.8–7.5 13–16 290–400 900–1,100 2–6 1–1.5 Fundamentals of Composites Manufacturing: Materials, Methods, and Applications butadiene- (33–52) (90–110) (1,999–2,758) (6,205–7,584) (0.11–0.33) (0.05–0.08) styrene (ABS) Acetal 6.5–10 14–22 400–500 1,000–1,400 1.4–1.5 .7–1.8 (45–69) (97–152) (2,758–3,447) (6,895–9,652) (0.06–0.08) (0.04–0.10) Acrylic 5.1–10.5 17.5 (121) 189–270 1,800–2,000 .4–1.8 1.0 (polymethyl (35–72) (1,303–1,862) (12,410–13,789) (0.02–0.10) (0.05) methacrylate [PMMA]) Nylon 5.5–12 20–27 40–575 1,000–2,000 .6–1.7 1.5–3.8 (polyamide) (38–83) (138–186) (276–3,964) (6,895–13,789) (0.03–0.09) (0.08–0.20) Polycarbonate 9–10 14–19.5 320–335 680–1,250 12–15 1.8–2.0 (PC) (62–69) (97–134) (2,206–2,310) (4,688–8,618) (0.65–0.80) (0.10–0.11) Polyethylene 2.3–4.3 3.4–6.1 50–310 438–585 .4–4.0 1.2–1.3 (16–30) (23–42) (345–214) (3,020–4,033) (0.02–0.20) (0.06–0.07) Polyethylene 7–15.2 16–23 350–450 1,050–1,730 5.2 1.2–2.2 terephthalate (48–105) (110–159) (2,413–3,103) (7,239–11,928) (0.38) (0.06–0.12) (PET) Polypropylene 4.2–5.4 8.1–8.5 250 750–899 .3–.6 1.1–2.0 (29–37) (56–59) (1,724) (5,171–6,198) (0.01–0.03) (0.06–0.11) Polystyrene 6.5–7.2 7–11 435–450 920–1,300 .4 1.0 (45–50) (48–76) (2,999–3,103) (6,343–8,963) (0.02) (0.05) Polyvinyl 5.9–7.2 8.5 300–378 500 1.5 16 chloride (PVC) (41–50) (59) (2,068–2,606) (3,447) (0.08) (0.87) * Values shown are typical for several grades of each polymer. (Source: IDES database.) 165 among the decreases in properties with temperature which is the ability of the resin to bond to are greater for non-reinforced than for re- the fibers and the ways in which the fibers inforced plastics because the reinforcement interact with the internal crystalline struc. For instance. structure firmly in place.26 mm). Because the molecules are carry much of the load when tensile and higher apart at high temperature (this is.13–0. After impregnation. reinforce- content on various mechanical properties. with several loadings of fiberglass gives some In the process used to make the long-fiber- additional insights into the effects of fiber reinforced thermoplastic resins. This results because the fibers offset each other. prop- increases in tensile strength and flexural erties that depend on interactions between modulus are not uniform. decreases to 6 × 10–5 in. the molecules. As ment strands are impregnated with the can be seen quite readily in Figure 6-1. Note that the ter all. the addition small amount of fiberglass reinforcement. has with 30% fiber addition are 120–200% in only a slight overall increase because the ef- tensile strength and 200–400% in flexural fects of strength and elongation more or less modulus. When the nylon is an engineering thermoplastic resin increases reinforced with 20% aramid. if the elongation and strength are reinforced materials./hr (58. Similar improvements in durability are seen crease because the fibers hold the composite in other resins. toughness can be difficult to rate of non-reinforced nylon is 22. Table 6-3 are almost like whiskers. and increases the tensile strength by 10%. of fiberglass increases the tensile strength Hence. (0. A graphical presentation of the mechani. the Izod impact toughness.166 6: Thermoplastic Composites In every thermoplastic resin. As discussed. these spaghetti- strength increases linearly with fiber content like strands are chopped to normal pellet as does the flexural modulus. When the resin is reinforced with reinforcements are added. As already discussed. and toughness wear capability increases tremendously is a combination of both strength and elonga. This lengths are increased.10 in. An interesting application of reinforced Examination of the notched Izod impact engineering thermoplastics is for wear re- data shows a much different result when sistance. where the toughness of the reinforced mate. Because the elon. Typical increases combination of strength and elongation.5 mm). Impact measures aramid fibers. Note that. the wear rate greatly with the addition of reinforcement. tensile resin. which is a and the flexural modulus. the lengths of the reinforce- gation is such a strong determining factor of ment fibers used in the materials shown in toughness. will generally de. flexural modulus by 40%. This decreased at higher temperatures. the strength of in. that is. the mechanical prop- trend is seen in the notched Izod impact data erties increase significantly. ture of the resin. For example. variation is due to several reasons. however. and notched Izod cal properties of a particular nylon resin impact by over 100%. the toughness of the material. af- flexural stresses are applied.010 in. elongation drops precipitously with even a in contrast to the whisker-length reinforce- Fundamentals of Composites Manufacturing: Materials. and Applications . holds the molecules in place better. typically tern for thermoplastics would be for the Izod ./hr (15 × 10–5 cm/hr). over both non-reinforced and even fiberglass tion. (2. the length—about . such as DuPont’s Kevlar®.2 × 10–5 cm/hr). Hence. If the fiber toughness to decrease with fiber content. the reflection of an expansion). The elongation.9 × 10–5 predict.005–. the wear both changing. Hence. like tensile strength. However. are ins are improved more than others. Methods. some res. the usual (but not exclusive) pat. a process called long fiber reinforcement rial is generally lower than the toughness of increases the fiber length by about 15 times the same resin without reinforcement. For reinforcement fibers have been fully wetted Fundamentals of Composites Manufacturing: Materials. but length of the finished part. the optimal length is about 3 in. ments of common thermoplastic engineering most resins. although the rate of increase fiberglass are sold as rolls. improved mechani. therefore. In general. when fiber lengths are the entire length of the pellet. the in properties with length diminishes. processing. One resin has shown to have a strong entry Even greater fiber lengths will generally into the marketplace—continuous reinforced result in even greater improvements in polypropylene. Effects of fiber content on the properties of nylon. the long-fiber reinforcements will be (7. will be discussed the net result is still longer fibers than the in the chapter in this book on thermoplastic whiskers and. Of course. The that can be used in typical thermoplastic methods used to process thermoplastic resins processes.6: Thermoplastic Composites 167 Figure 6-1. resins. often the entire long fibers are broken during processing. The lengths longer than those used in pellets. Sheets of polypropylene and properties.6 cm). many of the where the fibers are long. Even with great care. different of the long fibers are about the maximum manufacturing processes must be used. Methods. and Applications . cal properties. 6) Polyethylene 5.6 (0. ppm/° F (ppm/° C) for various thermoplastic composites at different fiber content levels. low cost.0) Nylon 5. a property cause of their limited and specialized use.9) 1.7 (0. These materials are less familiar be- resistance anyway. The key properties In spite of the significant improvements in for these polypropylene-fiberglass compos.3) terephthalate (PET) Fundamentals of Composites Manufacturing: Materials. composites could easily be treated as a gen- In general.0 (1. % by Weight Resin 0 20 35 Acetal 4. the high-performance thermoplastic com- which improve upon the wear resistance of posites will be discussed by major family resins that are often inherently good in wear groups.2 (0.3 (1.50) 1. important when mechanical fasteners.2) 1. ease of molding. the properties of engineering thermoplastic ites are high impact strength.4 (1. 4. Coefficient of thermal expansion (CTE). compound (SMC) in automotive panels (such as non-dent door panels). This occurs because the fibers are effects of the addition of reinforcements.7) Impact polystyrene 2. are used to attach composites. Although not shown in Table 6-3.1 (1.2 (1. and Applications .9 (0. Whereas the engineering thermoplastic forcements to engineering thermoplastics.0 (0.5 (1.5) 3.5 (3.8 (1. stiff and hard—highly desirable properties.9) 3. the product is molded. The markets for the poly. such facturer sells fiberglass mat and fabrics in as rivets.1 (2.3 (2.5 (2.2 (1.6) 2. which the fiberglass strands are intermixed increases with fiber content (see Table 6-4) with polypropylene strands. wear resistance is dramatically eral group because of the overall familiarity improved by the addition of fiber reinforce.3) 2.8) 2.1 (0.1) 2. Methods.2) 1. and resins when fiber reinforcements are added.9) Acrylonitrile-butadiene.2) 2.6) Polycarbonate 3. These limitations are directly molding compound (BMC) or sheet molding addressed in the next section.9) styrene (ABS) Polyphenyleneoxide 3. in ladders) and as replacements for bulk and toughness. solvent sensitivity.168 6: Thermoplastic Composites with the polypropylene.0) 1. other HIGH-PERFORMANCE mechanical and physical properties are THERMOPLASTIC COMPOSITES often affected by the addition of fiber rein. although one manu. Table 6-4. The most important limitations are re- replacements (substituting for aluminum lated to thermal stability. Shear strength. of most readers with the neat resins and the ments. Fiberglass.0 (1. Consolidation suggesting a stiffening and internal strength- and wetting of the fibers takes place when ening of the material because of the fibers.9 (1.0 (1.2) 1.2) 1. some serious limitations in properties still propylene-fiberglass composites are as metal exist. high stiff. tics are imparted to the resin in composite The high degree of aromaticity of the poly- applications. In many cases. flame-retardant properties. The polyimides. Methods. This thermoplastic resins—comparing their excellent thermal stability is also char- advantages and limitations. solvent resistance. the stiffness of imide molecule and the accompanying stiff- the backbone is modified (either by making ness of the planar imide rings leads to high it stiffer or more flexible) by the addition of stiffness in the backbone of the molecule some other molecular group or groups that and. The inherent resistance of these materials Figure 6-2. mosets. Thermoset polyimides are seen to The remainder of this chapter will look have the highest thermal resistance of all at the major families of high-performance the thermoset resins in common use. and Applications . have good mechanical properties (especially A general characteristic common to all high stiffness). therefore. and low flammability. these same char- unique characteristics to the molecules. which adds stiffness. performance thermoplastic resins. also properties of the resin. A high thermal stability to the backbone of the typical thermoplastic polyimide is pictured polymer. parisons between the various types of high. These other groups will impart ties mentioned. the high mechanical stiffness. However. resistance (no known reaction to organic strength. Polyimides were introduced in a previ- ness. acteristic of thermoplastic (that is. ous chapter of this book on specialty ther- and thermal stability are key properties. low flammability. Fundamentals of Composites Manufacturing: Materials. excellent solvent degree of aromaticity. Polymers tions where their high strength. non- the structural formula will be shown as a crosslinked) polyimides. these same characteris. In most cases. Thermoplastic polyimide. Therefore. key to understanding the basis of the overall both thermoset and thermoplastic.6: Thermoplastic Composites 169 High-performance thermoplastics are Thermoplastic Polyimides and Related occasionally used in non-reinforced applica. excellent electrical proper- high-performance thermoplastics is a high ties (high resistivity). acteristics lead to high melting points that Therefore. are near the decomposition temperatures. link the aromatic sections together along the thermal stability. they are the focus of the com. and other desirable proper- backbone. thus making thermal processing difficult. in Figure 6-2. and solvents for some). temperature sterilization. a regis- The plastic/composite resin is used exten. Therefore. resistance to most solvents. As with period. This resin is the highest in other applications where the combination performing. rods. which results in a stiff and structur- cal resistance. metal. thus lowering the melting point medical applications use PEI because parts sufficiently to allow melt processing of the can be made by injection molding. Parts and shapes wherein a powdered material (resin. As with A closely related thermoplastic polyimide other modified polyimides. are formed Polyetherimide (PEI) is another poly- into standard shapes and then machined to mer in which an imide/aromatic group is specific sizes and shapes. PEI has excellent to modify them. forced with short fibers or fillers. to particular part specifications. As with tic polyimides has led to several attempts other modified polyimides. The amide gives material have led to its use in space for greater flexibility than the basic polyimide solar array panels. and low electrical conductivity. ther. in its film structure where the aromatic groups are form is Kapton®. this aromatic group is for circuit boards. a linking group. has found applications as ally rigid backbone. For high-volume separated from another aromatic group by applications. LARC-TPI is used polyimide materials. a process (Tg = 537° F [281° C]). up to 500° F (260° C) for extended periods posites are formed by sintering. for PEI is Ultem® (GE Corporation). inserts. The excellent ultraviolet bonded to an amide. The plastics/com. melt-processible resin. Several backbone. joined directly to imide rings without any and in its formable plastic/composite form intermediate atoms. is Vespel®. The shapes are usually made and then machined sintered thermoplastic materials. often rein. Methods. tered trade name of Solvay (formerly owned sively for small washers. can be made by extrusion. which acts as a bridge resistance and mechanical strength of this to another aromatic group. The material. In this case. This causes the powdered particles other polyimide-related materials. because of its excellent electri. adhesive and as a film. but will material. Fundamentals of Composites Manufacturing: Materials. and Applications . group is an ether. PEI is often less posites but making thick parts has proven expensive than the other high-performance to be difficult. the PAI structure has similar processing problems as discussed has an imide group bonded to an aromatic above but. One brand name of PAI is Torlon®. a DuPont trade name. Center has developed a material called inherent low flammability and smoke emis- LARC-TPI that has greater flexibility in the sion. to form polyamide-imide (PAI).170 6: Thermoplastic Composites to solvation by organic solvents also makes extensively as a high-performance structural solvent processing difficult. and by BP Amoco). It is of thermal stability and solvent resistance able to maintain most structural properties is especially important. NASA Langley Research thermal stability. the linking rectly into the shape desired. standard to join together and form a solid mass. moplastic polyimides are difficult to process Another important modification of the by either of the common methods that bring basic thermoplastic polyimide is the com- a thermoplastic material into the liquid bination of the imide with an amide group form—melting or solvation. LARC-TPI has been successfully still have good thermal stability under high- used as a matrix for high-performance com. These can below its melting point and held for some be reinforced or non-reinforced. also a trade name of DuPont. they also can be sintered di. injection mold- or ceramic) is heated to a temperature just ing. and compression molding. To give some flexibil- an insulating material and as a substrate ity and toughness. A common brand name The difficulty in processing thermoplas. group. However. Thus temperatures up to about 800° pump components. thus giving it many of the same PBI can be doped with acid. thus imparting slipperiness melted. with one ether difficulty. even when the other polymer is can be added. PBI resin can be molded.and fire-resistant materials. mal resistance from its reflectivity. and PEKK. the polyimide family of materials without In contrast to most thermoplastic poly- actually employing the imide ring. advantage that most other polymers will not silicone. generally with specific reference to PEEK. Methods. bearings. of time and. but with some Related polymers are PEK. whose structure protective gloves. and stiff. good fatigue of the reinforced grades have as high as 40% resistance. or molybdenum disulfide (“moly”) stick to it. Polymers and fuels. high electrical resistivity. The outstanding properties of the its related polymers are sometimes called molded parts include the highest compres. the material ness and other properties characteristic of can withstand up to 1. and Applications . where “aryl” indicates Fundamentals of Composites Manufacturing: Materials. a DuPont trade name). and even linkages. tions in aqueous solutions. as is the case with thermoplastic linkage and one ketone linkage. organic solvents. the PBI ring structure is still flat in comparison to thermoplastic polyimides. in the case of PEEK. is needed. Some tensile and flexural properties. polyaryletherketones. for short bursts. cams. bases.6: Thermoplastic Composites 171 PEI is available in numerous grades. PBI is often used as a bear- to the resin’s natural abrasion resistance. The imides. the linkages are ether. its hydrophilic character and allowing it to The PBI resin is nonflammable in air and be used for membranes for chemical separa- emits little or no smoke up to a tempera. excellent hardness. PEEK and valves. The Tg for PBI is over 800° F include: gears. The PBI mol. It can be made into fibers with Perhaps the most widely used of the high- excellent fire-retardant properties. In this polymer sever- other protective gear. aramid. Hence. up to 10% polytetrafluoroethylene and good thermal stability. also offers excellent Polyetheretherketone (PEEK) and Related resistance to acids. sive strength of any unfilled resin. It is hydrophilic. and is shown in Figure 6-3. fiberglass. or carbon fiber content. or coating. It most common example of such a molecule is can be used for film casting. in common with most polyimides. low friction. so all will be discussed together.400° F (760° C). encapsulation. ing or seal in machines used to melt other Typical uses for the wear-resistant grades thermoplastics. The properties of all these materials makes standard shapes and then machines are similar. a proprietary molding which has one ether and two ketone link- process is used by a contract molder who ages. a relatively low coefficient of thermal ex- In some applications where wear resistance pansion (CTE).000° F (538° C). slides. which gives it ecule is structurally similar to a polyimide some improved comfort in fabrics but also in- except that the five-member ring is altered. thus increasing properties as polyimides. and ketone. o-rings. Typical applications are seals. from its linkages and. excellent both non-reinforced and reinforced. creases its sensitivity to some polar solvents However. PBI performance thermoplastic resins is poly- fibers are also used in high-temperature etheretherketone (PEEK). Typically. The name of a polymer is derived coated with aluminum for enhanced ther. and the most common of the group. polybenzimidazole (PBI). F (427° C) can be withstood for long periods It is possible to achieve the backbone stiff. and (427° C). the parts to the particular shapes required. ture of 1. PBI. firefighter clothing. PBI also has the (PTFE) (Teflon®. ether. blended with other al aromatic groups are separated by various heat. PBI is available in a solution. polyimides. polyimide-related thermoplastics. polyarylimides. a to solvents. feature of the sulphur-containing groups PEEK was one of the first reinforced is their relative ease in melt processing high-performance thermoplastics to be quali. Polyetheretherketone (PEEK). which being used over most of the other high-per- gives good thermal stability. Methods.172 6: Thermoplastic Composites Figure 6-3. result. but it is far easier to process. is only slightly less then the polyimide and eral family is polyphenylene ether (PPE). compared to the other high-performance fied for use in aerospace applications. much more service data is available The overall properties of the other for reinforced PEEK than for most of the members of this sulphur-containing group other high-performance thermoplastics. and Applications . in Figure 6-4b. stress cracking. The crystal structures also improve fone (PSU). low electrical conductivity. As with the formance thermoplastics. Fundamentals of Composites Manufacturing: Materials. a high amount of aromatic content. which is shown bonded crystalline structure to have any ef. trade name of GE. they have increased Tg. and thermal stability and ease of processing char- excellent toughness. The most Furthermore. Polysulfones and Related Polymers mer backbone leads to a high degree of Polysulfones and related polymers are crystallinity. and high modulus tween the aromatic groups. Thus PEEK is often referred to highly aromatic molecules that use sulphur as a semi-crystalline material. PEEK has excellent resistance common brand name for PPE is Noryl®. polysul- regions. Since its use in several large aerospace parts. As a thermoplastics. plications because of its excellent blend of high solvent resistance. The structure come from the formation of these crystalline of the most common of this group. high strength. PEEK has PEEK is often used in composite ap- low flammability. is given in Figure 6-4a. ultraviolet light. of thermoplastic polymers are similar to Also. acteristics. Structural or sulphur-containing groups as links be- rigidity. The regularity of groups along the poly. Another the solvent resistance of PEEK since the commonly used polymer in this group is solvent molecules must penetrate the tightly polyphenylene sulfide (PPS). who offers the material and low flammability. The thermal stability of PEEK Another polymer that is of the same gen. the familiarity of aerospace engineers PSU. which is also called polyaryl ether. Possibly the most important fect on the polymer. thus PEEK and other related polymers are highly increasing the total volume of PEEK resin aromatic. high strength. Some of the more common brand with the performance of PEEK has led to names are: polysulfone—Udel® (Amoco). in a 50:50 blend with polystyrene. the strength of LCP polymers. and flame- fone—Radel® (Solvay). They are melt-processible with ordered sections in the melt state and high orientation in the solid state. the materials have low thermal expan- sion and low shrinkage. these materials tend to be highly directional. Because of their orienta- Figure 6-4. When molded and so. One of the unique properties of liquid crys- tal polymers (LCPs) is they rapidly change their viscosities with temperature. As a result. This material will be discussed further in the chapter on fibers. Fundamentals of Composites Manufacturing: Materials. These unique properties lidified. Generally. which lead to a high dant. polyethersul. At certain temperatures. the LCPs have good stress-crack resistance. the liquid state changes from having areas of structure to being totally random with a corresponding drop in viscos- ity. Fluoropolymers Liquid Crystal Polymers The polymers that have a backbone of Liquid crystal polymers generally have carbon to which fluorine atoms are pen- long repeating units. sometimes called fluorocarbons or degree of orientation or crystallinity even fluoropolymers. sulfide—Ryton® (Chevron Phillips). tion. are unique among all the in the liquid state. Several LCP matrix materials have been commercialized. resistance. The most common of these are: Vectra® (by Hoechst) and Xydar® (by Solvay). Sulphur-containing advanced thermoplastics. and polyphenylene retardant properties. even without external fibers added. This property allows LCPs to be used as lubricants of high or low viscosity. Three-dimensional representation of a liquid DuPont.6: Thermoplastic Composites 173 composites and other applications where strength and toughness are important. and Applications . Methods. One polymer of this type is Kevlar® by Figure 6-5. polymer materials. The highly aromatic nature of these materials leads to excellent strength and stiffness. In the solid state. depending on the temperature. The high orientation of the linear units is much like the reinforcement obtained from fibers. is high. solvent polyarylsulfone—Astrel® (3M). It is used extensively as a fiber in crystalline polymer. and good thermal stability. A representation showing the three-dimensional nature of the crystalline and amorphous areas is given in Figure 6-5. electrical resistance. LCP materials have some self-reinforcing characteristics. With airplane production rates reaching 28 flame-retardant properties. This results in a high a Florida swamp in 1996. Methods. CASE STUDY 6-1 rocarbons. called fluorinated ethylene installed and production started using Ten propylene (FEP). This material is a woven. rine to the electrons in the fluorine-carbon and low friction properties. This material is called polyvinylidene which requires an 1. PVDF has excellent flame. It is used as minutes without having a burn through. because hand lay-up on an aluminum tool that was PTFE was nearly impossible to mold using vacuum bagged and oven cured for 4 hours. the material gen molecules on the carbons in the basic had to pass the Class E cargo hold burn test. The most common of these materials burn. Fundamentals of Composites Manufacturing: Materials. other matrices has given some advantages thermoset polyester. of course. The first of the fluoropolymers made was In addition. and Applications . Also. designers housed the smoke addition of some fluorocarbon material to detectors in a four-ply. The most common be applied 4 in. electrical resistance. Furthermore. has a good blend of proper. The poor bonding of these should have a cargo hold smoke detection materials is. Like the other weight decreased by 5% while its strength and fluoropolymers. eleven lay-up molds had one of the fluorine molecules is substituted to be made and each tool had to be turned with a carbon and three fluorine molecules. The less fluorine and retaining some of the new material had to comply with all the FAA’s hydrogen molecules on the carbons were requirements for smoke. a The part was then trimmed on a three-axis derivative molecule. router and assembled by hand to finish the propylene (PHFP). such as attraction or bonding with After the crash of Value Jet DC9-32 into any other atom. the electrons are Conversion of the Cargo Hold Smoke held so tightly by the fluorine that electron Detector to Thermoplastic Composites activity. This causes the bond to be short and strong. and flexibility to the polymer. unit. the Federal Avia- resistance to chemical attack and gener. fluorinated polymers containing Ultem® (polyetherimide) resin product. ties with ease of processing. moreover. thus giving high density to the fluo. most commonly known by the trade name The original process made the pan using Teflon® (DuPont Company). glass-reinforced Later. pan-shaped shell. and vertical made. In PHFP. was produced. detrimental to their system. retardant properties. part. glass-reinforced. (10 cm) from the part for 5 brand name is Kynar® (Atofina). bond. twice a day to keep up with production thus giving slightly higher carbon branching needs. Boeing’s Spokane plant personnel soon fiber bonding. Later. Eventually. A mixture of In 1999. of solvent resistance. and thermal per month and with 10 parts per airplane. durability increased. found themselves overwhelmed with orders. However.174 6: Thermoplastic Composites result from the strong attraction of the fluo. a 50-ton thermoplastic press was PTFE and PHFP. which is the current fleet had to be retrofitted. conventional melt-processing methods. its in other matrix materials. in the ceiling of the cargo hold. tion Administration (FAA) and the Boeing ally poor bonding of fluorocarbons to any Company agreed that all passenger aircraft other material. use as a matrix in composites. spares orders skyrocketed since polytetrafluoroethylene (PTFE). Cate Advance Composites’ Cetex® material. since the part was to be installed has two fluorine molecules and two hydro. called polyhexafluoro. toxicity. stability without major sacrifices in matrix. electrical resistance. The an additive to improve chemical resistance part passed all these tests and. the Originally. is low.800° F (982° C) flame to fluoride (PVDF or PVF2). saving Boeing over $500.6: Thermoplastic Composites 175 Because of the ductility of the material. One answer is simple—the higher cost the part could be trimmed using a stamping of the thermoplastic materials effectively press. Where do thermoplastics fit Thermoplastics seem to have special and where are thermosets more appropriate? advantages for the small part that can be Also. There are also lower labor properties. injection molders have been resins themselves more expensive. why do thermosets dominate the costs. the toughness can be difficult to tance to most solvents. However. Methods. the tensile emissions. the usual pattern for ther. smoke. is there likely to be strong competition injection molded from short. Some aerospace applications have been Some questions arise immediately when converted from aluminum to thermoset considering the relative values of reinforced parts because of the weight savings that thermoplastics and thermosets. and Applications . Most of the In the end. them ideal for this application. many available for some resins. costs may actually favor thermoplastics even Typical fiber contents range up to 30%. which also result from use of the weld- reinforced plastics market? Another ques. and heat properties modulus properties. If part performance requirements exceed ness. which provided additional cost savings. A good example of the value the fibers. Impact measures the combined with the natural toughness of toughness of the material. For instance. al. which are stiff and strong. The the reinforced thermoplastic. fiber-reinforced between the two materials? engineering thermoplastics or for the high- Fundamentals of Composites Manufacturing: Materials. if ther. sometimes achieving a 300% increase those easily obtained using epoxies. the molder is able to add the some applications with significant increases fiberglass as part of the molding process. the resin over the non-reinforced thermoplastics. Hence. of the aromatic thermoplastic resins are In every case where the reinforcements inherently flame retardant. production costs were reduced by thermoplastics that would be stiff and strong 80%. For example. and low heat release. ing technology. of these materials are resistant to airline moplastics would be for the Izod toughness hydraulic fluids (Skydrol) and have found to decrease with fiber content since elonga. of including the fiberglass adds to the price of inforcements in thermoplastic resins. application where contamination from that tion will probably decrease faster than the fluid is likely. The Izod impact results are container parts for aircraft. some predict. They also strength and flexural modulus increase have service temperatures higher than with fiber content. strength will increase. tion then arises. can be gained from using thermal welding moplastics can have such good mechanical instead of rivets. possible in tensile strength and flexural stiff. though they are considered high-performance though 40% and even 50% fiber contents are or advanced materials. Not only are the thermoplastic For years. limits the scope of their use. if the elongation and strength are Another major advantage of high-perfor- both changing and often changing in different mance thermoplastics is their general resis- directions. enough to compete with thermosets cost considerably more than basic unsaturated SUMMARY polyesters. The excellent not as clearly understood as the strength and flammability. and toughness is a high-performance thermoplastics makes combination of both strength and elongation. whereas with properties of these materials are excellent for thermosets. but the cost using short fibers (whisker length) as re. First.000. carry of these thermoplastic properties is in cargo much of the load. This is expected because most epoxies. have low smoke are added to the neat fibers. 2. Thermosets cannot be remelt. vinyl ester. thermosets and what property differ- ed and so they can only be recycled into filler ences will be caused by this structural materials. 6. High Performance 3. paratus available.org/cmvs. What are four key properties of compos- 1. Strong. Fundamentals of Composites Manufacturing: Materials. Give three advantages of an advanced thermoplastic composite over an ad- LABORATORY EXPERIMENT 6-1 vanced thermoset composite. All the samples must plastics. Finally. Also compare the results with tough- or extra weight savings. from the American Society for Testing Dearborn. A. Give three advantages of the advanced Toughness of Thermoplastics versus thermoset over the advanced thermo- Thermosets plastic. thermoplastic resin with long. Why do engineering thermoplastics thermoplastic composites with thermosets usually contain short fibers? and examine the effects of fiber length. Obtain samples of flat panels (at least 8 ites that depend strongly on the nature × 8 in. PA: Technomic Publishing Co. etc. the use of thermoplastic composites is rising at twice the rate of thermosets. and Applications . the future the effect of reinforcement content. have the same fiber content (%). 2. which strongly fa. [20. These tests BIBLIOGRAPHY can be Izod. cutting. Cut samples for impact tests. 3. Methods. properties. samples of each resin should be tested. Several countries have mandated difference? recycling of all materials. Charpy. Society of Manufacturing Engineers (SME). 1993. Describe the differences in the nature and thermoplastic resin with short-fi.sme. The sample sizes and 2005.3 × 20. Lancaster. QUESTIONS thermoplastic materials can be recycled into 1. Brent. After testing. Considering the ness data for the neat resins (obtained advantages in toughness.). compare the toughness and Engineering Thermoplastic Composites. or falling dart im- pact. What is the key difference between applications and retain the same value as the the structure of thermoplastics versus original resin.176 6: Thermoplastic Composites performance part that needs special proper. cycle time. depending on the type of testing ap. “Composite Materials” DVD from the other testing criteria should be obtained Composites Manufacturing video series. Identify and explain three differences vors the use of thermoplastic composites. Procedure: 5. and from the resin manufacturer) to assess finishing (drilling. and potentially the most im- portant implication for long-term views. or epoxy with glass have the advantage in each of the four fibers). In between engineering thermoplastics countries where such laws have been passed. for thermoplastics appears to be bright. of recycling thermosets versus thermo- ber reinforcement. MI: Society of Manufacturing and Materials (ASTM). continuous. Objective: Compare the toughness of 4. solvent resistance. mosets and the effects of fiber length. ties such as flammability. and advanced thermoplastics. fiberglass reinforcement. At least three Engineers. www.3 cm]) of the following of the resin? Indicate whether thermo- materials: thermoset reinforced plastics sets or thermoplastics would generally (polyester. results of thermoplastics versus ther. VA: Composites Fabricators Association. Upper Saddle River. Arlington. Methods. Brent. Strong. A. A. Fundamentals of Polymer Resins for Composite Manufactur- ing. and Applications . Plastics: Materials and Processing. Inc. Brent. Fundamentals of Composites Manufacturing: Materials. NJ: Prentice-Hall. 3rd Ed. 1995. 2006.6: Thermoplastic Composites 177 Strong. by examining the differences in the types • Properties and uses of ceramic matrix of bonds that exist in ceramics. weight. So. als and non-metals is based on the tendency terials for composites. metals and non-metals. of the element to give or take one or more tween these polymeric materials have been electrons when forming bonds with other examined and their various advantages and elements. which affect Second. Standing back the non-metals take electrons. which will be when the metal atoms give up electrons discussed in this chapter. can be understood. The non- In comparison to ceramics and metals. metals. The past several chapters have discussed The separation of the elements into met- the most prominent polymeric matrix ma. that is. lighter negative. The differences be. lower First. on the right. There are different ways in which elec- posites trons behave in the bonds formed between the elements (atoms) of the periodic table. The polymer matrices’ disad. vantages are lower thermal stability. ments. • Properties and uses of metal matrix The elements can be divided into two major composites groups—metals on the left and non-metals • Manufacturing of metal matrix com. of electrons surrounding the nucleus. and can wet out the reinforcements There are three possible ways that the ele- more easily. and composites polymers. rials (ceramics and metals). less expensive. and Applications 179 . but that technicality will COMPOSITES be ignored for this discussion. at least preliminar- • Non-polymeric matrix materials ily. a metal can combine with a non-metal. Any the polymer matrices have advantages by charged element. Some elements along the inter- posites section of the periodic table can behave as both metals and non-metals. All the ele- now and taking a look at all the polymeric ments are electrically neutral before bonding matrix materials as a group. whether positive or being easier to mold. the number of characteristics can be seen when they are protons in the nucleus equals the number compared to non-polymeric matrix mate. and lower hardness. a metal can combine with another Fundamentals of Composites Manufacturing: Materials. can combine. they become positively charged.1: Introduction to Composites 179 7 Ceramic and Metal Matrix Composites CHAPTER OVERVIEW the amount of frictional wear. • Manufacturing of ceramic matrix com. stiffness. These overall This chapter examines the following: differences. metals become negatively charged. and others that will be discussed later. Methods. some common with other elements. is called an ion. depending on NON-POLYMERIC MATRIX the circumstances. The metals give electrons and disadvantages pointed out. There are crys. it is of electrons. Further.) the ceramic is placed under force. Ionic bonds are the most important bonds the positive-positive repulsions of the metal in ceramic materials. the layers Therefore. Regular window glass is the sea of electrons. a non-metal can combine with positive ions—a highly unfavorable situ- a non-metal. When the layers of the such a material. This is demonstrated by the brittleness of ceramics. Methods. crystal structure resists movement.180 7: Ceramic and Metal Matrix Composites metal. the bonding is called a metal- called a single crystal. This type of bond is called an ionic bond. The freely lattice of alternating ions. both are called crystals. Most crystal struc. more electrons to form a more stable state. therefore. much When several metal atoms come into close like north and south poles of magnets at. bind the many negative ions and vice versa. the metal structure is not as brittle as form crystals. proximity. These materials are called poly. the major properties of from the metal to the non-metal because a ceramic materials can be ascertained from more stable state is formed in both atoms knowledge of the characteristics of ionic when the electrons transfer. That high bond energy is responsible for the (The sea of electrons is like a lubricant that high melting point of ceramics. This causes bonds. If the entire structure is a continuous When positive ions are held together by a sea lattice structure without boundaries. The lat. This is possible because the donated elec- Most of the time many positive and negative trons can move freely in the spaces between ions join together in a three-dimensional the positively charged metal ions. result in the positive ions coming near other thereby absorbing impact energy. lic bond. facilitated somewhat by is termed a glass. metal crystal move relative to each other. electrons is called the sea of electrons. ions together. It is also possible to form ionic. These bonds are strong ions are cancelled to some degree by the sea and therefore require much energy to break. the hardness of ceramics and their wear metal atom. of electrons that moves between the ions. This ductility gives metal atoms to each other because any movement would greater ability to move when impacted. These combinations result in ation since like charges repel. if forms a slick coating between moving parts. Hence. These positive and negative ions Another Metal Atom will then attract each other strongly. How- bonded materials from atoms that do not ever. The highly mobile group of tice structure is usually called a crystal. Fundamentals of Composites Manufacturing: Materials. These latter structures form the ceramic because the metal layers can a rigid. which usually have different a three-dimensional lattice structure that orientations. characterized by this type of bonding. Third. Ionic Bond—Metal Atom with The resistance to atomic movement and the Non-metal Atom strong bonds between atoms also explains When a metal atom comes near a non. has some similarity to the lattice structure crystalline. where each of the moving electrons cancel repulsive charges positive ions is surrounded and attracted by between the atoms and. and Applications . The ions can be said to bond together. the three different bonds. Metals and most metal alloys are tures are not that uniform. Hence. Hence. they all want to give up one or tract. of ceramics. tals that are finite in size and that meet The metal ions arrange themselves into other crystals. disordered (amorphous) network that move more easily. metals are more ductile than in the crystal will resist movement relative ceramics. the metal to become positively charged and the non-metal to become negatively Metallic Bond—Metal Atom with charged. one or more electrons will move resistance. Some to the energies required to break ceramic or non-metal atoms. Methods. and Applications . and ammonia. energy through the metal. metals. The highly mobile electrons are that the polymer is crystalline or. methane (natural and metallic bonds. ecules can align together and achieve some ally seen in metals. When a polymer gets to be about metals. since in polymers. The elec. These areas are called thermal energy well (except when in solu. the energy gas). points of ceramics. it can be said of metals. a molecular structure similar in some ways trons’ mobility also can be noted by the to the crystal structures of the ceramics and high electrical and high thermal conductivity the metals. means that less energy is Because polymer units consist of mol- required to separate the individual ions in ecules that are long chains. These chains are called lower than the melting points of ceramics or polymers. the melting points of not able to pack as individual atoms or ions metals are generally lower than the melting as they do in ceramics and metals. the this packing never involves all of the mol- electrons are held strongly by the non-metal ecules so there are always some areas that ions. The greater mobil. a characteristic of long chains. Therefore. concepts of crystalline and amorphous were previously discussed in Chapter Two. Even in the crystalline regions. and Many common small molecules are held the energy for untangling the chains is much together by covalent bonds. Remember that melting a polymer 20 units long. As has been out of the polymer chain. (The carry the electrical charge). When this occurs. entangle. the melting points the ability to bond with several other atoms of linear (thermoplastic) polymers are much to form long chains. Some examples less than the energy of breaking the ionic are water. The type of bond in which atoms are forces of ceramics and metals. under certain conditions. it is a solid and can begin to does not mean that the atoms are separated have some structural properties. the polymeric that the chains can move independent of Fundamentals of Composites Manufacturing: Materials. Some polymers form tions where the ions have been broken out almost no crystalline regions and these are of the crystal lattice and the ions themselves commonly called amorphous polymers. In ceramics. have metal crystals. Polymers will shared is called a covalent bond.) Covalent Bond—Non-metal Atom with The overall linear nature of the uncross- Another Non-metal Atom linked polymer molecules gives polymers The third possibility for bonding is when some distinct differences from ceramics and a non-metal atom comes into close proxim. Both of primary forces between the atoms in adjacent the non-metals want to take electrons. it merely means discussed in previous chapters. They reflect light and increased stability by packing together in give metals their shiny appearance. the is done by sharing some of their outer-most forces attracting the molecules together are electrons to achieve stable states for both small when compared with the crystalline atoms. sea of electrons. the atoms are the lattice.7: Ceramic and Metal Matrix Composites 181 metals are less easily broken on impact and matrix materials used in composites are long tougher than ceramics. there are no ity with another non-metal atom. the polymer mol- The mobility of the electrons can be actu. This polymers. polymers. especially carbon. semi-crystalline. therefore. In amorphous regions. more ac- carriers of the electrical charge and heat curately. they do not conduct electricity or are non-crystalline. from each other is relatively small compared not important structural materials. sometimes made of thousands of ity of metal ions. So. However. These molecules are required to separate polymeric molecules mostly gases and liquids and. Therefore. amorphous regions. which is facilitated by the units. carbon dioxide. As a result. therefore. The separation of the atoms Table 7-1. With the exception of carbon-matrix day to approaching 3. oxidation by ceramic coatings. the temperature require- high-temperature capabilities of ceramic ments of materials have gone from a little matrix composites are summarized in Table over normal temperature on a hot summer 7-1.182 7: Ceramic and Metal Matrix Composites other chains. As will be seen in much more de. Temperature limits for from each other out of a chain is the process composites with various matrices. obvious that poly. some mishaps Fundamentals of Composites Manufacturing: Materials. means that polymers are not as strong or as stiff as ceramics and Carbon matrix 4. matrix composites (CMCs) are where poly.649° C) as composites.800 (982) than either metals or ceramics. The aerospace industry gives some mer matrix composites are least likely to be examples of the increasing need for high- used—in high-temperature environments temperature applications. the technology has not fully met the require- ized laws. But if • Everything reacts faster at high tem- ceramics and metals are inherently strong peratures. Type Use Temperature. plification and meant to give some humor.000° F (1. Methods. absorb impact energy.000 (2. In The problems of high temperatures can some applications. The several decades. and Applications . and that requires much higher temperatures than polymeric melting Approximate (although still not as high as many ceramic Composite Maximum and metal melting points). Hence. This move- Ceramic matrix 3.000 (1. achieve better strength and stiffness. their intent is clear: withstanding high tem- peratures is extremely difficult for materials.649) ment. polymers are tougher Metal matrix 1. therefore. however.204) metals. question and the ways that these materials are reinforced will constitute the remainder While these rules are obviously an oversim- of this chapter. Over the last and where high stiffness is required. It is. trix composites are clearly the best choice the requirements for performance at high for high-temperature applications. such as the space shuttle. The relative openness of the polymer ° F (° C) structure also means that polymer atoms Organic matrix 800 (427) can move quite easily and. why are they reinforced to make • The reaction products may be any- composite structures? The answer to that thing. temperatures are even more dramatic. ment and. stiff fibers to make composite materials. and stiff. the inherently lower protected) strength and stiffness of polymers is one of the main reasons that they are reinforced with strong. When time at temperature is considered. which must be protected from airplanes have increased in sophistication. ceramic ma. of decomposition. • Everything reacts with everything at mers are made into composite materials to high temperatures. as is sadly evident. (oxidation tail later in this text. PROPERTIES AND USES OF CERAMIC Much effort has been invested to develop MATRIX COMPOSITES products that can withstand the tempera- The most inviting applications for ceramic tures demanded by our high-tech world. be summarized in the following general. if cracks form from local stress is increased. When such a transformation increases the The following toughness mechanisms in volume of the phase or crystal. created when the material is impacted. To understand the mechanisms by which when the crack encounters the fiber. These reinforced ceramics are. In previous chapters it has been absorbs the energy of the crack along its pointed out that toughness is related to the length. This occurs when the reinforcement has a higher strain Toughening Mechanisms to failure than the matrix. breaking of the bonds. in zirconia-toughened alumina. Moreover. induce pullout of materials seem to limit the applications in the reinforcement from the matrix. in which the movement of the crack in- Therefore. and Applications . ing. toughness also can be defined as duces a phase or crystalline transition in the ability of a material to resist the initia- the reinforcement (toughening) material. Thus. such as a reinforce- compromised. the deflection. In other adding a reinforcing material to a ceramic. However. along the surface of the reinforcement ture/high-stiffness applications. it will be unable to simply move As mentioned. In this case. either acting alone or in concert. time propagation. affected and. of stop crack growth is by load transfer course. in many cases. Simply put. where it must break interface bonds inevitably. This method is especially important they naturally propagate since the ener. tion and propagation of cracks. Methods. to the reinforcement. words. inherently possess the high bond energies Instead. the material re- growth of cracks in ceramic matrix com- sists local concentrations of energy that are posites is transformation toughening sufficient to initiate and propagate cracks. and structural applications for non-reinforced pullout require energy (absorb energy). the reinforcement has arrested the toughness of the material can be sub. the material’s phenomenon crack pinning or crack temperature capability is not adversely deflection. the the reinforcements toughen the matrix. As the fiber elongates. the growth of the crack. this load is transferred to the fiber from section will examine the nature of toughness the matrix. ceramic matrix composites. Some call this stantially improved. and the energy then dissipates ability of a material to absorb the energy through internal atomic motions.7: Ceramic and Metal Matrix Composites 183 have occurred. • Another method used in composites to proved. possibly. the crack stops grow- concentrations that exceed local strengths. if the growing has to be carefully controlled so that the crack encounters a boundary of a strong material’s ability to perform is not severely and rigid material. the brittleness and lack of impact between the reinforcement and the toughness of these non-reinforced ceramic matrix and. However. the energy required for further growth • Usually. When a material’s technol. ment. non-reinforced ceramics through the reinforcement material. Fundamentals of Composites Manufacturing: Materials. ceramic materials are severely limited. This which they can be used. is actually im. That absorbed energy is often sufficient Fortunately. it has been found that by to stop the growth of the crack. it in detail. the crack ceramic matrix materials have been pro- is squeezed by the enlarged matrix and posed. By • Yet another method used to arrest the absorbing impact energy. gy that encourages this behavior is often ogy has not reached the required levels of higher than the energy absorbed in that performance for temperature and time. the crack is deflected and runs that allow them to be used in high-tempera. Stress/strain characteristics of various rein- to concentrate their strength and stiffness forcements for ceramic matrix composites. the micro. can be tailored Figure 7-1. although tions such as turbine blades. magnesium oxide (MgO). point of the growing crack. whiskers impart sufficient tough- Reinforcement Shapes ness for many applications. zirconia (ZrO2). there- Several types of reinforcement shapes fore. and Applications . on consideration should be given to them here. The most common shapes to reinforce ceramics are fibers and whiskers. Continuous fibers. and SiO2). Methods. Most ceramic matrices are from polymer composites. the shape effects of ceramics Many materials can serve as ceramic reinforcements are unique enough that some matrices. cordierite (mixed posites the reinforcements carry the load to MgO. the comprised of: alumina (Al2O3). Sometimes further lateral or cracks can absorb sufficient energy to transverse toughness can be achieved by stop the growth of the main crack. They are chosen. Since continuous or even long-segmented reinforcements force deflection of a crack to travel along the fiber for a longer distance.184 7: Ceramic and Metal Matrix Composites • If the growth of the crack creates mi. Matrix Materials ter. giving toughness whereas in polymer com. However. Flakes and particles are also used but have less significance in changing properties and will not be discussed here. their ability to withstand the environment The shape effects are unique because the and meet the specific requirements of the purposes of reinforcements in ceramics differ application. one mechanism may dominate in a particular Whisker reinforcements do not impart system. but whiskers are much easier to process. the same toughness as continuous fibers. Moreover. However. A comparison of fibers and whiskers the toughness of ceramic matrix composites. The use of long-fiber composites has not completely independent and might occur proven to be highly beneficial for applica- simultaneously and synergistically. In ceramics. into particular orientations. or preforms. in a ceramic matrix is given in Figure 7-1. some other advantages of longer fibers also have been recognized and exploited in vari- ous applications. fabrics. Al2O3. often but not exclusively carbon. the dominant reinforcement shape for have proven to be successful in improving CMCs. mullite (mixed Al2O3 and SiO2). borosilicate reinforcements have a primary purpose of (B2O-SiO2). including some whiskers in the matrix ma- These toughening mechanisms are probably terial. The reinforce- crocracks that radiate from the leading ments can be unidirectional fibers. They are. lith- improve mechanical properties like strength ium aluminosilicate glass (LiO2-Al2O3-SiO2). these longer reinforcements may result in greater difficulty in processing. Reinforcement shapes for polymer matrix composites will be discussed in a later chap. But. and stiffness. in part. Fundamentals of Composites Manufacturing: Materials. these long fibers are more likely to absorb sufficient energy to arrest crack propaga- tion than are particles or whiskers. materials are well known ceramics while Similarly. are automotive ap- sis of the carbon-carbon matrix is a polymer. thermal conductivity and Fundamentals of Composites Manufacturing: Materials. nose cones. space structural elements on opti- carbon-carbon composites as CMCs. As with most of these other siles increasingly share this need to with. This is cal devices. plications. molybdenum the heat and impact damage. the efficiency of a heat exchanger stand high temperatures. and exhaust valves. titanium boride (TiB2). most of these structures have others are chosen for specific applications. however. Al.and coal-fired power plants. oil. microwaves. However. zirconium boride sensors need to be especially protected from (ZrB2). boron carbide (B4C). which are progressively out As noted previously. too. temperature engines continues. Some of the most common uses in. and general ers are increasingly important as engines space structures where thermal exposure is and other devices operate at ever-higher a critical issue. Methods. frictional heating at higher temperatures. small parts that serve as fasteners (such as MoSi2 is an example. are increasingly made from CMCs. high thermal and structural (often isotropic) tions that are rare even for CMCs.660° F [2. As the trend to higher- plications.016° C]) allows applica. some experts classify radomes. O. because the ba. Some of these sensors. These. requirements. cation frequencies than other composites. it is likely clude engine parts. As the speeds Non-automotive power generators also of aircraft increase. temperatures. CMCs compete with carbon-carbon Thus some applications of CMCs include composites. especially those radar. Sensors are being increases with operating temperature. In placed on these structures in key locations this application. Strategic and tactical mis. also typically made of CMCs. increasingly. aluminum nitride the stresses that arise during flight. the ability of CMCs to of the range of metals. CMCs is in heat exchangers. is a strong incentive to increase operating the classification could be either way. Automotive engines operate more this text has treated this type of composite efficiently at higher temperatures. and sialon (a complex “sensor windows. temperatures. rocket nozzles. ties. especially for planes have been shown to operate more efficiently and hypersonic vehicles. possibly even entire automotive Skin areas in the path of exhaust gases are engines. CMCs will require higher-temperature materials are being used as components for gas-turbine on surfaces such as wing leading edges and engines. and Applications . nuclear power generation systems. too. disilicide (MoSi2). so there with the polymeric group. and N). to monitor the heating and. Heat exchang- engine parts. Applications CMCs are generally more transparent to In many applications. Clearly. so. Initially a few parts withstand high-temperature environments were made from CMCs. Space applications include heat shields Another non-automotive application for for space re-entry vehicles. especially turbine blades that more components will be converted and in areas that confine the exhaust gases. requirements. where its high melting bolts and nuts) and fittings that have both point (3. such as piston heads has led to their use in many aerospace ap. reasonable because the carbon matrix has Just as advanced aerospace applications properties similar to those of the CMCs that are increasing toward higher temperature have been discussed. are candidates to be made of CMCs. and nose tips.” covers that protect the compound of Si. and stealth components. boron nitride (BN). Those (AlN). Therefore. silicon nitride (Si3N4).7: Ceramic and Metal Matrix Composites 185 silicon carbide (SiC). However. Therefore. to CMCs. and other telecommuni- requiring good thermal and wear proper. devices. the metal jet of the HEAT round with it. heated plastic melt is pushed through the die and then cooled into the shape desired. matrix material. In addition to photography. beverage MATRIX COMPOSITES drinking straws. For whisker and particle rein- cal discharge machining (EDM). as the CMC is penetrated. As revealed in high-speed traditional tool-steel cutters. of CMCs. (This assumes the not been able to be formed by this method. is made by electri. CMCs are dimensionally stable. Great include such common items as aluminum Britain. reinforcement has a higher melting point Recently. ogy. A similar technology is used for inserts where the diameter of the wire is reduced placed into the pockets of bullet-proof vests as it is drawn through the die. Metal extrusions advanced tanks in the United States. such as the cavities in an powders before they are formed into compos- injection mold for plastics. Methods.) The ceramic been made by adding conductive filler to the particles consolidate with each other and Fundamentals of Composites Manufacturing: Materials. the integrity of the tank. The preform material. and synthetic fibers. conductive CMCs have than the ceramic matrix. These tools have occurs when the CMC is penetrated by the demonstrated far longer wear lives than HEAT round. Carbon fibers have proven to rounds. used to shape materials as they are pushed therefore. This capability has opened While ceramics do not generally have good the pathway for many more tools to be made thermal conductivity.186 7: Ceramic and Metal Matrix Composites resistance to heat shock are important. The principle The abrasion resistance of CMCs has led on which the metal-CMC-metal sandwich to their extensive use as cutting tools for works uses the expansion in volume that the metal-cutting industry. This through a small opening (die) that gives technology has proven to be so effective that shape to the final part. This is especially true when the mor. thus ume. and wire. their abrasion resistance and general hard. Many ceramic matrix materials are solid Some tooling. CMCs have ing point of the ceramic. ite materials. A closely related application for CMCs is Thus. which pushes traditional steel cutting tools. however. forcements with high thermal conductivity One application for CMCs that does not has made CMCs highly effective as heat depend on thermal or wear capability is ar- exchangers. These rounds had been a serious be especially good as reinforcements in this problem since the waning days of WWII application. the presence of rein. In plastic for individual protection. Some familiar plastic MANUFACTURING OF CERAMIC extruded parts include PVC pipe. it shatters and thus greatly expands vol- ness. anti-tank (HEAT) is to move. temperature slightly lower than the melt- piece) be conductive. part manufacturing. These tools are to protect the second layer of metal and. The EDM process requires that is then heated. This expansion is directed outward improving on the accuracy of cutting over through the penetration hole. and Applications . often under pressure. to a the material being eroded away (the work. Some armor consists of layers of CMC reinforcement is a fiber that is continuous in material between metal plates. CMC armor the CMC and oriented so that the direction has been shown to offer unique protection of the fibers is the direction that the heat against high-explosive. when they were first used. Hence. This process forced composites. the whiskers or particles uses a spark to form the shape required in are usually blended with the powder and the tooling by eroding away the unwanted then pressed to form a preform. and other nations use the technol- window frames. a counterforce is applied that helps tooling for extrusion dies. automotive trim. forming conditions. silicon nitride. The method in wetting the fibers. Therefore. in a compact preform. braiding. the final part. employs two or more constituents or organic (usually alcohol) solvent carrier. the fibers and eventually fills the pores in the whisker size. form using chemical vapor deposition (CVD). this method. the properties of ceramic material is infused and this material the whisker reinforced CMC are dependent on reacts with the ceramic coating already on these variables: whisker production method. The slurry is filtered and the matrix material. The high viscosity of with short fibers rather than whiskers or the melt limits this method somewhat. use of a sintering aid. boron nitride with alumina. However. the also called chemical vapor infusion (CVI). This Alternately. pressure. These fiber preforms are then infiltrated The whisker reinforced composites have with the powder material. and Applications . whisker/matrix compatibility. or continuous during the consolidation of the matrix. but it particles. In addition. particle. form and coats the fibers. At this create a preform of continuous fibers using time. While deceptively simple in concept. and then further heated titanium nitride with alumina. called in-situ reaction sin- of the ceramic powders in either a water tering. of course. and turing CMCs is to create the reinforcement time. whisker loading. eliminate any binder. the fiber preform can be infused blending/sintering process can be done with melted ceramic. pressure beneficial are SiC (silicon carbide) in a is applied using a mold that has the shape matrix of Si3N4 (silicon nitride) and SiC in of the preform and. The ceramic and higher toughness than the non-rein. titanium nitride with the matrix and entrap the reinforcement. or knitting techniques. Methods. Another manufacturing method is to and titanium nitride with sialon. Organic binders also has the potential to improve the uniformity might be added to help hold the materials of the distribution of the reinforcing ma- together in a preform after the carrier has terials since they are formed throughout been evaporated. but the results ticle size and shape. process of making CMCs from powders using CVD/CVI is a process in which the ceramic whiskers as the reinforcements is actually matrix is vaporized and then enters the pre- quite complicated as it involves many dif. matrix powder/whisker can be good because bonding of the matrix blending.7: Ceramic and Metal Matrix Composites 187 with the reinforcements in a process called weaving. phase by direction reaction. reinforcements can be mixed with a slurry This process. matrix also can be infused into the fiber pre- forced matrix itself. titanium at higher temperature and pressed to sinter boride with alumina. matrix. a matrix of Al2O3 (aluminum oxide). sintering. A newly emerging technique for manufac- and sintering temperature. this manufacturing method has been Fundamentals of Composites Manufacturing: Materials. the short fiber reinforced can work if the fibers are sufficiently wetted composites generally have lower strength and the infusion is done slowly. This is a slow process. to the fibers is usually excellent. some new then heated under pressure to eliminate the composite structures may be possible with liquid and shape the ceramics and reinforce. titanium carbide with alumina. During the heating. matrix par. Further gaseous ferent variables. which occurs The whisker. The CMCs made with this tech- ments into a convenient form for subsequent nique include aluminum nitride with tita- operations. The impregnated fibers are then pared to the non-reinforced ceramics. Some heated in stages to remove the liquid and sin- of the whiskers proven to be especially ter the matrix. technique. This preform is then heated to nium boride. often by the slurry higher strength and higher toughness com. which react during Wetting agents might be added to assist sintering to form new phases. or fibers. copper. the strength or modulus of the composite also increases. the whiskers common matrix materials are: aluminum. The most common rein. damping control of vibra. The rein. transfer of forces to the whiskers than can tinely added to engineering thermoplastics be done with the particles. Therefore. as would be expected fibers. 1974). whiskers are more of little importance with MMCs. gests that whiskers are more efficient than whiskers. Therefore. When the strength or modulus of the non-reinforced matrix. Hence. in metals. the problem in ceramic dinal strengths of SiC whiskers are within matrix composites with brittle fracture is 5% of each other. Typically. length/diameter ratio. the transverse and longitu- ductile and tough. whiskers. matrix increases. The first production use but both are roughly the same when com- of MMCs was as components of the space pared to having no reinforcement. and Applications . and silicon carbide fibers.188 7: Ceramic and Metal Matrix Composites demonstrated in the laboratory but has not Examples of the changes in properties been widely used on commercial products. nickel. The much higher to improve their strength or stiffness. of MMCs with various reinforcements can be seen in Table 7-2. and modulus values. magnesium. This demon- Property Comparisons strates that the matrix and reinforcement The MMC properties of most importance in MMCs both contribute to the strength are: strength and stiffness improvement over and modulus. Even so. their ability to easily reinforce in all direc- Since metal matrices are usually inherently tions. Rather. the fibers clearly dominate the strength wear resistance. This sug- forcements can be in the form of particles. Today. the effective than fibers when the application MMCs are analogous to polymer matrix com. difference is that. and the modulus and strength data are nearly the various alloys of these metals. of course. From the table it is PROPERTIES AND USES OF METAL obvious that particulate reinforcements will MATRIX COMPOSITES raise the modulus and strength significantly over the non-reinforced material. the most into the matrix than particles. the strength ductivity. thermal con. Methods. Note also Metal matrix composites (MMCs) consist that the 7090 alloy has a slightly higher of high-performance reinforcements in a strength and modulus than the 6061 alloy. metallic matrix. which allows better Just as fiberglass reinforcements are rou. to the values of the reinforcement. electrical conductivity. and control of the coefficient of and modulus of the matrix are much closer thermal expansion. graphite/carbon lus. The reason for this tions. Because shuttle (boron reinforcement in aluminum whiskers are more difficult to incorporate matrix to make tubes. requires multidirectional reinforcement. titanium. the comparisons between different metal ma- composite is stronger and stiffer than the trices. are shown with only 20% loading. same as the 30% particulate data. so the Fundamentals of Composites Manufacturing: Materials. MMCs are common where part specifications An advantage of whiskers over fibers is dictate high performance. This is. higher temperature from polymer matrix composites where stability than polymer matrix composites. than whiskers as reinforcements. posites in that the reinforcement is stronger The remaining data in Table 7-2 allow and stiffer than the matrix. particles at increasing strength and modu- forcements are boron fibers. This is somewhat different non-reinforced metals. because the whiskers have a more distinct and particles. so too strength and modulus values for the fibers are reinforcements routinely added to metals in aluminum indicate that fibers are better to improve strength and stiffness. 0 (213.6 (335.5) 48.0) 52. Properties of selected metal matrix composites.9) 18.7) 240 (1. Reinforcement Matrix Reinforcement lb/in.0 (124.1) 108 (745) Al 6061 Graphite Unidirectional 0.0 (206.9) 117 (807) fiber Cu SiC Unidirectional 0.8) 150 (1.) ping gases. Therefore.230 (6.655) fiber combined values in the composite are more fibers in resin. ticular advantage for some applications.8) 30. Metal by the density.0) 35 (241) Al 6061 30% SiC Particulate 0. in general.4) 30.0 (69. The exceptions would be when the Even with highly conducting fillers. they do have good specific strength and Plots of specific strength versus specific stiffness compared to most other materials.089 (2.7: Ceramic and Metal Matrix Composites 189 Table 7-2. Strength.55 (120.5) 112 (772) Al 2124 20% SiC Whisker 0.5 (127. even if gases are pres- Metal matrix composites do not have the ent. advantage to MMCs is their lack of out-gas- tionately affecting the strength or stiffness. and Applications .072 (2. Density. both obvious advantage over both polymeric and stiffer and stronger than non-reinforced ana. as shown in Figure 7-2. ceramic matrix materials is conductivity.7) 80 (552) Al 7090 30% SiC Particulate 0. Fundamentals of Composites Manufacturing: Materials. Another in some other way adds weight dispropor. tendency to release trapped gases when in a ness are the strength and stiffness divided low-pressure environment like space.9) 31.7) 10.140 (3. Polymeric materials have a (Note that specific strength and specific stiff.034) fiber Al SiC Unidirectional 0. Methods.105 (2.9) 17. the low diffusivity of metals (especially best combination of specific strength and compared to polymers) makes MMCs highly specific stiffness when compared to carbon valued in space applications. How- of an average. logues. Modulus.097 (2. along with other properties that are of par- forced materials are shown in Figure 7-2.0 (206.3 × 106 psi. poly- reinforcement does not increase the specific meric and ceramic materials do not reach strength or stiffness because it is heavier or the conductive levels of metals. ever. One The reinforced metals are.2 (359.103 (2. stiffness of MMCs and various resin-rein.462) fiber Ti SiC Unidirectional 0. sing in space.104 (2.8) 212 (1.1) 120 (827) fiber Mg AZ91C Graphite Unidirectional 0. Further. heavy components matrix composites have little chance of trap- tend to decrease these values. × 103 psi Type (g/cm3) (GPa) (MPa) Al 6061 None — 0.108 (3.0) 18. forging. Polymer matrix milling. cutting. Measurements ing point than ceramics and can usually be on boron fiber reinforced aluminum have reshaped using conventional metal shaping shown a five-fold increase in dynamic damp- Fundamentals of Composites Manufacturing: Materials. Specific strengths versus specific stiffnesses of various composites. The incorporation of a second phase (the therefore. fabrication formability. EDM. through the material by acting as sites for Metal matrix composites have a lower melt. and Applications . A particular advantage of MMCs is post. scattering and attenuation. composites are usually thermosets and. Methods. processes such as casting. reinforcement) into a metal significantly Ceramic matrix composites are high melting affects the propagation of pressure waves and therefore cannot be shaped with ease.190 7: Ceramic and Metal Matrix Composites Figure 7-2. cannot be reshaped after curing. and cold forming. clear other small tolerance zones within golf club heads. In general. In another example. as with particles and critical suspension components. automotive. the corrosion between forced aluminum. The cost increase is 30–40%. manufacturing methods used to make MMCs plications. sports. The the normal steel liners. tion was pumping sandy and dirty water. brake calipers. Melting is Fundamentals of Composites Manufacturing: Materials. anything that can be cast plications.7: Ceramic and Metal Matrix Composites 191 ing capacity. Water. Shrinkage SiC is not as severe as with carbon/graphite. blended into a molten metal. actuator rods. inforcements. sporting goods. sizes are about the same as with non-rein- even worse. strophic failure that can occur with carbon/ finishing costs for MMCs are about twice as graphite. which are added in the barrel. practice. MMCs have been used for and a screw applies pressure and forward applications such as structural rods for space movement to the molten metal and the re- platforms. and numerous other ap. pistons. the aerospace. and casting composite might be wetted by water or. Polycrystalline diamond tools restricted to pitting rather than the cata. the mixing of the fibers and the melt minum MMC block in its engines without is done in a machine like an extruder. impellers. sway bars. The range of tolerances. A problem that must be acknowledged Typical industries using cast aluminum in MMCs is the corrosion that arises when MMCs include defense. and golf club shafts. in Another auto manufacturer is using an alu. mechanical properties are better. sur- ite fibers. However. corrodes and corrosion can be severe if the parts are not carefully processed. As with other composite materials. The final parts may or may manufacturing applications include cutting not be pressed while still hot. Machining of MMCs but it still must be dealt with in the design causes more tool wear than with non-rein- of parts. The corrosion with SiC is usually forced metals. reinforcements. One and whiskers. the matrix and reinforcements automobile company is using MMCs as the simply can be blended and then molded. and aluminum is reinforced with carbon/graph. and Applications . performance heat sinks for electronics ap. Typically. allows the design of high. extruder melts the metal in a heated barrel In aerospace. Some automotive applications depend on the natures of the matrix and include: piston ring inserts. It reports a seven-fold Conceptually the reinforcements could be increase in piston life for its diesel engines. In an environment in which the face finishes. antenna masts for satellites. in pump life when it changed from a steel combined with the low thermal expansion housing to one made of MMC. production rates. and various joints and fittings. matrix MMC.5% in MMCs. is about 1. missile The reinforcements must be small enough body casings. MANUFACTURING OF METAL Applications MATRIX COMPOSITES MMCs have been used in automotive. Carbon reinforced copper is of in aluminum can be cast in an aluminum particular interest for this application. part complexity carbon fibers and aluminum is rapid. When reinforcement ori- ing rods. aircraft stiffeners. the high A pump company reported a 200% increase thermal conductivity of a metal matrix. The applica- of the composite. connect. seawater. is reduced somewhat because of the higher based corrosion of aluminum reinforced with viscosity of the reinforced melts. entation is not important. General the extruder. to pass through as the screw turns and to Sports applications include tennis racquets. Boron reinforced aluminum also much as for non-reinforced analogues. the tools and bearings. Methods. crown of the pistons. If pressed. However. are preferred for cutting MMCs. thus wetting the fibers and distribut- the preform. so special fiber coatings are used to wetting of the fibers.192 7: Ceramic and Metal Matrix Composites usually done under an inert gas atmosphere and still preserves the orientations of the fi- to prevent formation of unwanted metal bers. In this method. Methods. remove the binder and further heated at a Rather than infuse the metal using foils. and Applications . the boron carbide od are the difficulty in retaining the metal and the metals that form the alloy matrix are powder on the fibers as they are oriented combined. composites. The problems with this meth. then covered with another metal foil. especially metal (that is. metal. This heating with compression causes priately for later work. can be used to infiltrate the fibers with the Mixing long fibers with either a powder or a metal matrix. Some reinforcements.) them in the orientations desired. the metal powder is thor. (Fiber volumes above However. (the foils help retain the fibers in place) and The powder-reinforcement mixture is then heated to above the melting point of the pressed into a preform that is shaped appro. This is especially appropri- cess and is similar to the sintering process ate when the shape of the part is complex. done to reform the powder metallurgy billet Just as with ceramics. are not wetted well by molten liquid phase begins to form) to achieve proper metals. In is also a good way to make MMCs that have the case of metals. The fibers An unusual method has been employed to can then be heated and pressed to sinter the make boron carbide reinforced metal matrix metal powders. But. it higher temperature while being pressed to is also possible to melt the metal and cast consolidate the metal powder and bond with it onto the fibers that have been arranged in the reinforcement. the casting mold. which are then blended in A pressure infusion method has proven to an advanced jet mill and compressed at high be more convenient than the powder method pressures to form a billet. An organic binder the metal foils to melt and infuse with the might be added to help retain the shape of fibers. some experts have thick sections. diffusion techniques. In this technology. it is possible to coat the fibers with 50% are characteristic of advanced polymeric the metal powder and then carefully place composites. however. such as pultrusion. The The mixture is then degassed to remove metal-fiber sandwich is then compressed any volatile components and trapped air. In this method. can be the metal matrix. In fact. This is a sintering pro. called powder The fiber layer is laid down carefully in the metallurgy. the temperature at which a carbon fibers. Multiple to blend the reinforcements with a metal layers of reinforcement and foils can be done. Fiber vol- of the fibers would not be preserved and the umes of 50–60% have been achieved using fibers might be broken in the mixing process. thin sheets of the metal oxides and metal carbides. this process is simpler melt would be difficult because the orientation with metals than with ceramics. vacuum diffusion into the final form. A vacuum or pressure assist suggested that the processing temperature is often used to help with full wetting of must be above the solidus temperature of the the fibers. instead of combining them as and the problem of disturbing the orientation molten liquids. powder. matrix material (called foils) are placed un- A more common method of incorporat. The billet is then Fundamentals of Composites Manufacturing: Materials. ing particles or whiskers into a metal is thus making a sandwich structure. proper orientation on top of a metal foil and oughly blended with the reinforcements. Sometimes a subsequent improve the bonding between the fibers and shaping process. they are combined as micro- while the materials are compressed. der and on top of a layer of reinforcement. The preform is then heated to ing the metal throughout the structure. It discussed for ceramic matrix composites. scopic particles. Therefore. perature or high-stiffness applications. Of course. These unit is heated to a moderate temperature to gaps include the following: reliable and low- remove the organic binder in the preform cost forming technology. Methods. such as bicycle frames. Fundamentals of Composites Manufacturing: Materials. However. much like the choice of fiberglass then shaping the resulting mixture into a flat reinforcements is an upgrade to traditional sheet about .5 mm) thick. Whereas ceramic matrix composites are For this application. and China are rapidly achieving good contact between the diamond and the parity. is positioned on top of a metal base that pro. used in commercial applications. it is sprayed with an organic because of some inherent property problem. and diamond to limit even wider adoption of CMCs. Ceramic matrix composites. diamond must be securely attached when Both CMCs and MMCs are increasingly the product is completed. that uses diamond-reinforced pads is the smoothing of silicon disks (wafers). improvement of matrix/ heating press where the entire assembly reinforcement bonding. MMCs are less compelling but. the reinforcement. One particular application less expensive. in some applications. mixing the diamonds (or diamond dust) The new MMC is also about 38% stronger. wear resistance. on the other vides a solid backing and is an attachment to hand. After the sheet is tional ceramic materials would not work properly placed. The diamonds are bonded into where the composite competes well against the top surface of the metal matrix when the traditional aluminum alloys. more common. diamonds have a Al2O3) also can be used. Japan. of the new MMC is more than three times Similar grinding wheels are made by greater than the best modulus of aluminum. (1. These have lower special value because of their hardness and hardness than diamonds but are. Therefore. also makes quality control easier as each interestingly. throughout the matrix. The sheet engineering thermoplastics.7: Ceramic and Metal Matrix Composites 193 shaped to form parts. the choice to The MMC composite is made by mixing the upgrade to MMCs is viewed as routine and metal powder with an organic binder and simple. some technological gaps continue sheet. When these materi- als are fully sintered.06 in. joining technology. the metal matrix needs usually associated with specific high-tem- to be able to bind the diamonds securely. they are strong in the United States. not only facilitates their use in abrasion but compelling. The metal base. The modulus process is completed. an alloy of several metals with nickel metal matrix composites might be chosen as the principal component is used because to simply upgrade a part that is otherwise the nickel will sinter well and retain the made of the metal matrix material without diamonds. CMCs have The diamonds are usually in an array that a unique role that is. is sintered. matrix. they provide excellent CASE STUDY 7-1 grinding action. Then. non-destructive material. the unit is transferred to a testing capabilities. but when the composite terials besides diamonds (such as SiO2 and is used as an abrasive pad. of course. other ma- materials for MMCs. CMC re- After the diamonds have been placed on search and development activity is especially the surface of the matrix sheet. and Applications . Still. can fulfill applications where tradi- the grinding mechanism. Eu- pressed into the sheet slightly to insure rope. Hence. which SUMMARY will be used to make integrated circuits. usually brittleness. adhesive and the diamonds are set in place. presenting diamonds Diamond Reinforced Abrasive Pads to the grinding surface regardless of the Diamonds are not usual reinforcement amount of wheel wear. 38 mm). ceramic. Fundamentals of Composites Manufacturing: Materials. effort in the United States seems focused 5. especially automotive. machining. (See Figure 7-3 for an ex- planation of the wear measurement.) Figure 7-3. What are three advantages of using should continue with vigor. knowledge of the effects where the tool steel is the standard. commercial use. Methods.) 2. along with inspection an extensive design database. tribute to the use of CMCs for struc- formance of these materials are sufficiently tural applications? rewarding that the development efforts 2. duplicate the cutting of Europe and Asia it seems concentrated on the log as was done with the tool steel. complex structure forming. non-destructive mils of wear and as a percentage of wear testing techniques. the development in. (12.194 7: Ceramic and Metal Matrix Composites thermal fatigue. cutting passes as the tool steel. and Applications . 4. (12. and feed depth according to the suggestions of the cutting tool manufacturer. and quality as. Why do MMCs reinforced with whiskers Wear Properties have higher strength and stiffness when Objective: Discover the wear capability compared to the same matrix reinforced of metal or ceramic matrix composites. metal matrix composites versus metals alone? LABORATORY EXPERIMENT 7-1 3. (to the same percentage content) with Procedure: particles? 1. 1. These gaps include the fol- 6. As After cutting for the same number of with CMCs. some technology gaps are limit. Purchase a cast iron log. feed speed. Report the difference in wear as both lowing: casting technology. low-cost fabrication techniques. fracture properties. of defects. (This is a solid piece of cast iron shaped in a long cyl- inder. Repeat cutting of 5-in. (0. commercial uses. compare ing even more rapid acceptance of MMCs in the wear on the MMC or CMC. Wear pattern of a cutting tool. of each pass until the wear reaches .015 In the case of MMCs. Use a newly purchased tool steel (M42 or M2) cutting insert and cut a 5-in. 3. How does this advantage con- derway and the promises of the superior per.7-cm) linear quality assurance criteria. QUESTIONS surance criteria.7-cm) linear pass on the log. After cutting. Give a major advantage of a ceramic Undoubtedly the gaps in both CMCs and matrix composite over a non-reinforced MMCs will be overcome. True the log by mounting it on a lathe and cutting off the outer layers until the cuts are uniform around the surface. Set the turning speed. Using a newly purchased MMC or CMC on high-performance applications while in cutting insert. remove the cutting tool and measure the wear on the tool flank (or relief angle). Much work is un. complex structure forming. joining technology. and passes on the log. 1992.. If the melting points of ceramics are generally higher than the melting Schwartz. Ginburg.7: Ceramic and Metal Matrix Composites 195 4. 7. Brent. and Toaz. Mel M. Inc. NJ: Prentice-Hall. and Applications . No. Mancini. “Ceramic Compos- 6. Vol. John J. erally higher than the melting points of Dearborn.” Composites in Manufac- thermal conductor? Why? turing. David. Engineered Mate- rials Handbook. International En- using carbon reinforcements in an alu.” Composites in Manufacturing.” Manufacturing Engineering. in general? 2005. K. 9. K. W. OH: ASM International. London: Chapman and Hall. www. Plastics: Materials polymeric bonds. ture of a polymer relate to the strength of the covalent bond? How does that Warren. 4.sme. Boca Raton. Ceramic Matrix Com- posites. Second Quarter. Peter. Composites Materials. If the melting points of ceramics are gen. 3rd Ed. MI: Society of Manufacturing polymers. Vol. R. Inc. “Metal Matrix Composites Aid Piston Manufacture. 1997. points of metals. Fourth Quarter. pp. Chawla. cyclopedia of Composites. Metals Park. New York: VCH minum matrix? Publishers.). 7. what can you conclude Upper Saddle River. well? Schuldies. Upper Saddle River. 1993. Ceramic-matrix Compos- relate to the melting point? ites. 8. Which material—ceramics or met- ites—Emerging Manufacturing Processes als—would you expect to be a better and Applications. 10. what can you conclude about Engineers. A. Vol. “Composite Materials” DVD from the 8. Fundamentals of Composites Manufacturing: Materials. D. 1992. 1987. “Scaling Up Metal- Matrix Composite Fabrication. FL: Taylor & that metals conduct electricity so Francis. the relative strengths of ionic versus Strong. 61–62. Bowles. NJ: Prentice-Hall. versus metal bonds. R. Why don’t ceramics conduct electricity Morgan.org/cmvs. L. No. R. 1: Composites. about the relative strengths of ionic Society of Manufacturing Engineers (SME). 2006. New York: Chapman and Hall. 2. Methods.. What physical phenomena are associat- ed with the decomposition temperature and the melting points of polymers? BIBLIOGRAPHY ASM International. Carbon Fibers and as well as metals? What is the reason the Composites. M. Composites Manufacturing video series. 2005. 1991. How does the decomposition tempera. Stuart (ed. 1987. 1990. What is the problem associated with Lee. May. 5. in general? and Processing. Composites with whiskers or par. especially long fibers. In fact. This • Natural fibers means that loads can be transferred onto • Fiber-matrix interactions the fibers along the long axis. their internal molecu- fibers. direction. the influence of This orientation of internal molecules is fibers. • Carbon/graphite fibers This relationship between length and the other dimensions is often expressed math- • Aramid and other synthetic organic ematically using a term called the aspect fibers ratio. the emphasis it through a die also will have the effect of of this chapter will be on the long fibers aligning the internal molecules in the long Fundamentals of Composites Manufacturing: Materials. This that composite materials containing long is accomplished by physically pulling the fibers might be considered a new class of solid but pliable (plastic) fiber in the long solid materials beyond the traditional ma. Each has lar structure is often oriented in the long its own unique applications. length to the diameter of a fiber. Therefore. which is simply the ratio of the • Boron.1: Introduction to Composites 197 8 Reinforcements CHAPTER OVERVIEW with only a minor treatment of whiskers This chapter examines the following and particles. concepts: Fibers are materials that have one long axis (length) compared to the other di- • General fiber characteristics mensions (width and height). Methods. is so dramatic usually produced by drawing the fiber. stretching their poly- world. and Applications 197 . GENERAL FIBER CHARACTERISTICS In addition to the natural length that Reinforcements for composites can be characterizes fibers. whiskers. and/or particles. metals. A tension load Long fiber composites have contributed to on the fiber pulls against the molecular so many major innovations in our modern chains themselves. This gives the fibers ex- are the most common and have the great. the fibers can be efficient in giving reinforce- ment to the composite structure. This process orients the molecules terials—ceramics. merely forming the fiber by forcing matrix material. Therefore. of the finished part. ceptional strength and stiffness in the long est influence on the mechanical properties direction moreso than the other directions. and polymers. along the length of the fiber. silicon carbide. Fibers are cialty fibers materials that have high aspect ratios. In some just improvements over the non-reinforced cases. rather than against a ticles are more likely to be thought of as mere entanglement of the chains. and other spe. meric backbones. although fibers direction as well. The other • Glass fibers dimensions are often circular or near circular. might have after being formed and the treatment causes improved adhesion to the matrix materials some degradation of the surface. thermal clothing. are well known and frequently used for but these non-circular cross-sectional fibers Figure 8-1. are those typical of each fiber type. What was hoped is that the non- are made from melts. have been investigated for a structural effect like that seen in I-beams. and even Fibers are available in many diameters carpets where the advantages include im- as seen in Figure 8-1. Methods. Others have rough circular cross-sections. these properties have little value in smooth around the perimeter since they composites. reinforcement of composites. drawing is usually more non-composite applications such as sleep- effective than mere flow alignment. which have higher perimeters since the fibers are heat treated perimeters than circular ones. and. ing bag filler. therefore. However. Such fibers Some improvements were initially reported. possibly through like a cloverleaf. such composite. Careful choice of the shape might as a tri-lobe design that looks somewhat also result in a stiffer fiber.198 8: Reinforcements direction. Fundamentals of Composites Manufacturing: Materials. and Applications . The diameters shown proved thermal retention and soil hiding. improved properties in the Fibers of non-circular cross-section. Relative size of common fibers. Some are However. strongest effects on composite properties. Another consideration has proven to be As expected. taining mechanical strength and stiffness Also. the tensile strengths of using traditional composite fibers is clearly Fundamentals of Composites Manufacturing: Materials. posite fibers.8: Reinforcements 199 have not been widely used and are not now the fibers most commonly used in composites commercially available. in some applications. why do glass. of overwhelming significance in choosing erties increased with longer fiber length: the materials that are to be reinforcements tensile strength. increased tensile modulus. and light weight. and Applications . and rameters on the properties of the composite aramid dominate the composites market? into which they have been incorporated. the metals Studies have been conducted to determine are clearly higher than the traditional com- the relative importance of various fiber pa. They also are available can be said of modulus—the traditional com- in many oriented forms such as woven cloth. That is the material’s me- flexural strength. Methods. In these charts. For effects on composite properties: increased example. some manufacturing methods are more of a material cannot be overemphasized. general range. that results when a tennis racquet or golf increased flexural strength. Note the and the resulting data are given in Figures wide variation in all the properties listed. goods. mat. and braid (all discussed in a later but other materials are within the same chapter). SiC. (glass. carbon. Of course. The same the length desired. This common metals that might compete against has been done for the materials in Table 8-1 composites in some applications. there is increased hitting speed tensile strength. and strong. and Before discussing each of the fiber types density properties combination is called the individually. specific strength and specific stiffness ties of several fibers commonly used in of a material.046/kg). The rate chanical properties and density. That comparison is by dividing the tensile strength and tensile given in Table 8-1 along with data for some modulus of a material by its density. With elongation. found to be about 60–70%. the premium for weight the part. these are calculated composites is useful. the relatively a satellite can be as high as $10. but Fibers are generally made in continuous not so high that other materials (boron. are about 3 in. So. In these situations. Above that level lightweight composites dramatically improve there seems to be insufficient resin in most the efficiency of operation. stiffness.6 cm) and then the rate stiffness. and elongation. carbon. The mechanical strength. Even elongation. the While aircraft costs per lb/kg are less than upper limit of fiber length is the length of space structures. favorable with long fibers.000/lb minor increases in properties obtained with ($22. the fibers are savings is still compelling. As 8-2 and 8-3. and decreased shaft is lightweight. for composites. which is a of increase rises sharply until the fibers combination of the advantages of strength. knits. the following composite prop. The answer to this question will be a focus The fiber length and concentration have the of this chapter. low weight while still main- long fibers are needed for part performance. applications where the cost of launching However. posite fibers are generally higher in value. Normally. A limit of fiber loading has been for applications like wind turbine blades. a comparison of the proper. Even in sporting referred to as continuous. (7. the reason for might be expected. composites to fully wet the fibers. the weight and mechanical properties Increased fiber loading has the following combination in a material is important. modulus of elasticity. lengths that can be used as is or chopped to and even steel) could not compete. In aerospace of increase in properties rises less sharply. aramid) are quite high. stiff. 0 500 (3.5 166 (1.000) 29 (200) 30 Aluminum 2.6 (standard modulus) Carbon/graphite 1.0 toughness) Aramid (high 1.97 375 (2.999) 25 (172) 2.8 modulus) Aramid (ultra-high 1.8 780 (5.447) 64 (441) 0. g/cc strength.585) 12 (83) 5.5 500 (3.447) 10 (69) 4.5 (ultra-high modulus) Aramid (high 1.7 Carbon/graphite 1.4 523 (3. Tensile Tensile Elongation Fiber Type Density.3 145 (1.8 Flax 1.8 600 (4.7 modulus) Boron (on tungsten) 2.9 500 (3.5 665 (4.4 580 (3.9 SiC 3.5 494 (3406) 27 (186) 2.8 145 (1.5 Spider silk 1.8 40 (276) 7 (48) 15 *ksi = psi × 103.200 8: Reinforcements Table 8-1.8 (intermediate modulus) Carbon/graphite 1. to Break. Modulus. % ksi* (MPa) Msi** (GPa) Glass (E-glass) 2.145) 25 (172) 30 Magnesium 1.447) 60 (414) 1.606) 12 (83) 4.5 500 (3.137) 33 (228) 1.5 116 (800) 9 (62) 2.000) 14 (97) 35 Steel 7. and Applications . Methods.5 molecular-weight polyethylene (UHMWPE) (standard modulus) UHMWPE (high 0.0 modulus) Ultra-high.9 Glass (S-glass) 2.97 435 (2.585) 17 (117) 3.378) 40 (276) 1. Comparison of properties for several key fiber types (representative values for each fiber type.447) 56 (386) 0. 0. bare fibers). **Msi = psi × 106 Fundamentals of Composites Manufacturing: Materials.999) 19 (131) 2.8 70 (483) 10 (69) 20 Titanium 4. 8: Reinforcements 201 Figure 8-2. Fundamentals of Composites Manufacturing: Materials. and Applications . Methods. Specific strengths of various materials. Fundamentals of Composites Manufacturing: Materials. Specific modulus values for various materials. Methods. and Applications .202 8: Reinforcements Figure 8-3. The high Glass fibers as reinforcements have been volume of use has contributed to the con- known and used for centuries. The value of the specific strength dominance is due to the combination of its for the advanced materials is obvious from low price (roughly an order of magnitude less these data. Fiberglass was originally intended as an Manufacturing Processes insulation material and that application The raw materials of glass fibers are continues to be important. and growth in the economy that occurred after ultra-high-molecular-weight polyethylene WWII. than carbon fibers) and excellent properties. the use of this chapter. coal. Almost always made with poly- An interesting property comparison meric resins as the matrix. In this scenario. Therefore. such as clay. During WWII silica sand and various subcomponents. fiberglass was combined with resin to create tional composite fibers are about an order the first modern composites. increased in volume with the tremendous vanced fibers (carbon/graphite. The specific ational boats. and decorative pieces. minor ingredients. automobile bodies. An example persists today as a way to describe parts would be a tether of material used for a great made with fiberglass and. turing facility in 1937. the dominant rein- about 150 miles. thin-walled glass objects such as forcement. there has been in web-like configurations to strengthen little incentive to change to another rein- their fine. These materials of magnitude greater than the metals. airplane parts. Simi. fiberglass was the only commercial reinforce- ments used in composites materials. The specific strengths of the tradi. recre- nitude greater than the metals. by far. Com. usually. and steel only about 20 forcement material in terms of usage. This situation does not apply vases. Therefore. polyester height. That name can support its own weight. and Applications . but really larly. aramid Fiberglass is. when shortages of strategic materials forced such as limestone and boric acid. the specific stiffness values for the ad. to aerospace where performance is highly mercially important continuous-filament valued and there are strong incentives to glass fibers resulted from the joint Owens. Renaissance tinuing low price of fiberglass. had a few wartime applications. text that for several years following WWII offers excellent overviews of the reinforce. Early designs of many products were made around fiberglass and GLASS FIBERS those products have served well. the strength and specific strength of fi- evident as each is discussed individually in berglass are quite good. (The Composite Materials video this material in many consumer products is [2005] from the Society of Manufacturing widespread. change to the more recently developed and Illinois and Corning Glass research. Methods. support a length of about 140 miles. especially when seen in the con- Engineers.) ment for composites. and aramid fibers. products. the entire class related to specific strength can be seen by of materials became known as fiberglass considering a length of suspended cable that reinforced plastics (FRP). Venetian artisans incorporated glass strands for most consumer products. and some manufacturers to seek alternate materials. and Fundamentals of Composites Manufacturing: Materials. carbon/graphite can thermoset resin. which higher-performing materials like carbon culminated in the formation of a manufac. The advantages and disadvantages of As can be seen from Table 8-1 and Figure each fiber reinforcement type will become 8-3. which complements this section. and numerous other consumer stiffness of fiberglass is not as high.8: Reinforcements 203 evident. aramid. pitchers. Fiberglass was used to reinforce [UHMWPE]) are also about an order of mag. This miles. These are dry mixed and melted reheating as shown in the latter part of in a high-temperature refractory furnace. which allow for ease into a machine that cools the glass and forms of transport of the glass and subsequent it into small glass marbles. These processes are called als are added to a blender where they are the marble process and the direct-melt pro. The direct-melt process simply The temperature of this melt varies for each removes the marble formation and couples glass composition. the figure. are used for the manufacture of glass fibers The first process developed was the marble from the molten mixture of sand and the process. but is generally about the melt chamber directly to the filament 2. and Applications .260° C). These marbles Figure 8-4. As can be seen. melted.204 8: Reinforcements fluorspar. The blender then feeds cess. Methods. Two similar processes formation stage. thoroughly mixed. after the glass is melted. Fundamentals of Composites Manufacturing: Materials. In this process. the raw materi- subcomponents.300° F (1. The marble process is shown in Figure the materials to a furnace where they are 8-4. Schematic representation of marble melt process for production of continuous filament fiberglass. The molten glass exits the furnace marbles are formed. fibers are manufactured but only four are ings. The fibers are drawn reinforcements like carbon or aramid. Thereafter they are gathered fibers are still used in various electrical together. which are low-corrosion metal (such used in composites: E-glass. The strength of quartz is approxi- made into the marbles. Fundamentals of Composites Manufacturing: Materials. and Applications . That Glass is an amorphous material that con- conversion begins by feeding the marbles sists of a silica (SiO2) backbone with various into a remelting furnace where a glass melt oxide components to give specific composi- is again created. fibers. The strength than E-glass and has better reten- sizing may contain a coupling agent and tion of mechanical properties at elevated other chemicals to enhance the bonding of temperatures as shown in Table 8-2. of tiny holes (typically 200 to 1. These applications where fiberglass is used rather additives will be discussed in more detail than one of the other high-performance later in this chapter. The fibers are formed by tions and properties. which is mined chiefly in Brazil. the most common type of fiberglass used ing rate and method. (The electrical properties or sizing is applied so that the fibers can have little importance in most composite pass easily through mechanical equipment applications. S- the fibers to the matrix when they are later glass is preferred in advanced composite mixed together to make composites. A protective coating in composites. It the molten glass flows directly into the fiber. E-glass fibers are temperature.200). antenna windows. E-glass ply with air. properties and low cost. and radomes. C-glass. Then. the direct-melt process has Applications for quartz include its use in ab- been sufficiently improved that it is now the latives. Because of their good strength controlled by the hole size in the bushing. electrical resistivity were required. However. These a curing step and other secondary processing data point out the advantages of E-glass in before they are sent to the customer. viscosity of the melt. (mechanically elongated) and then wound Other properties for E-glass. quartz. up on rolls. major process used for making glass fibers. Several types of glass directing the melt into the formation bush. The E-glass fibers have a calcium aluminobo- molten glass flows through the bushing rosilicate composition with maximum alkali holes and forms continuous strands called content of 2%. The diameter of the fibers is devices.8: Reinforcements 205 are graded and inspected and then stored Types of Glass Fibers until needed for conversion into fibers.) without breaking or abrading. Methods. The downstream mately 25% lower and the density is only steps after the fibers have been formed are slightly less than fiberglass. and cool. and quartz. marble process in raw material mixing and Quartz fibers are made from mineral melting. after the melting furnace. similar to Pyrex®. only in applications where its superior soft- Originally. S-glass (and as platinum) plates that have a multiplicity its variation S2). Quartz is used the same as with the marble process. They can then be transported to and C-glass are given in Table 8-3. electrical applications and of C-glass in acid The direct-melt process is similar to the solutions. They were filaments. However. thermal barriers. the use of the marbles resulted ening point temperature and/or superior in improved control over the quality of the electrical signal transparency are necessary. S-glass. the filaments are cooled originally used when strength and high (quenched) by spraying with water or sim. A sizing may S-glass is approximately 35% higher in be applied before the fibers are cooled. is then made into rods that are drawn into forming bushing and plate without being fibers. and Applications . and various to everyday life. low corrosion properties. Examples wall and bathroom panels. Some examples are the ducts for the Many fiberglass products are not readily air conditioning and heating. Even and not just for body panels. mobile bodies. and even auto.413) Applications small parts that are injection molded using Fiberglass reinforced plastics (FRP) have fiberglass reinforced thermoplastics. the manufacture of FRP is often less than the same resin manufacturer. ksi (MPa) E-glass 770 (5. Com. Some consideration other major panel-like applications for FRP should be given to toughness and elongation. one of the first options considered is to make tible to water logging or corrosion.447) 350 (2. Some examples include the Fundamentals of Composites Manufacturing: Materials. housings and cabi. of fiberglass is an easy way to improve part If boat hulls are thought of as panels. fiberglass is forced with fiberglass.206 8: Reinforcements Table 8-2. Methods. FRP has now become to imagine what society would be like with. Some sporting goods use FRP.274) 665 (4. these parameters is not critical. like wood and metal. ° F (° C) Glass Type –310 (–190) 72 (22) 700 (371) 1. fewer parts and therefore fewer places for When most people think of fiberglass.309) 500 (3.585) 645 (4. but for many applications the reductions in building roof structures. Furthermore. show the breadth of fiberglass composites This saves on original assembly costs and use. would be vaulting poles.447) 380 (2.620) 250 (1. Automobiles are a major market for FRP Snowmobile housings are usually FRP. Certainly this is a major application for Thinking more about the injection mold- fiberglass and the reasons are obvious. This decision usually allows painting. the overall cost of the same mold to be used and. strengthened with fiberglass. In a become so widespread in use that it is hard similar product line.200 (8. the use other materials. Temperature. Rather than attempt to list the bodies. Many parts in the walls of swimming pools are usually automobiles are made of fiberglass compos. housings of observable and yet are critically important many types throughout the car. easier to shape (mold).724) S-glass 1. ing of fiberglass composites. snowboards. often. strength or stiffness. the standard material for entire truck cab out them. ites. tremendous pared to other materials that have been used variety exists of thermoplastic parts rein- for boats. can be envisioned such as light rail cars. surfboards. and wear. tub and shower units. probably. bows and arrows. To strengthen parts. and skateboards. In addition to its light weight and applications or even the markets for FRP. lighter. does not require reinforcements. Effects of temperature on the strength of glass fibers. More detailed discussions of applications improves durability because there are simply are in the last chapter of this book. different sections to rub against each other they envision a fiberglass composite boat. Hence. more them out of the same resin but add fiberglass easily colored and. nets for appliances. FRP allows a sig- a few applications will be discussed just to nificant reduction in the number of parts. not suscep.000 (538) Tensile Strength. 193 (0. Today.532 Weight gain after 24 0.382 (750) ° F (° C) Dielectric strength. Al.787) temperature.8 4. especially the Edison for his first successful electric light mains that run under the street.2) 3.810) 0. % Weight gain after 24 42 3. est specific strength and highest specific though carbon fibers were used by Thomas modulus of any material.8 (5. % Weight gain after 24 2. carbon/graphite fiber has among the high- ment of carbon or graphite fibers. Methods. % pipes that bring out water.176 (0.5 1. 10–6 ° F (10–6 ° C) Specific heat at room 0. % Weight gain after 24 39 4. By the 1960s. the development of high-strength/ used in plants where many chemicals are high-modulus carbon fibers did not occur processed.1 hours in H2O. BTU/lb•° F (kJ/kg•° C) Softening point.1 hours in 10% HCl.2 hours in 10% H2SO4. 262 (103) 330 (130) — V/mil (kV/cm) Index of refraction 1.7 0. fibers based hazardous materials.1 (5. fibers were developed and commercial- ized.555 (846) 1.188 (0. Properties of glass fibers. those of glass fibers has led to the develop. Even the circuit boards in computers been patented and offered for commercial and other electronic devices are likely to be sale. are frequently made of on rayon and polyacrylonitrile (PAN) had FRP. especially for until the 1950s.8: Reinforcements 207 Table 8-3.0 24 hours in 1% Na2CO3. Type of Glass Property E-glass S-glass C-glass Coefficient of thermal 2. the mechanical properties CARBON/GRAPHITE FIBERS of carbon fibers have steadily increased The demand for reinforcement fibers through improvements in starting materi- with strength and stiffness higher than als and manufacturing methods. pitch-based carbon reinforced with fiberglass.1 2. In the late 1960s.525 1. 1.1 2.562 1. and Applications .0 (7. Fundamentals of Composites Manufacturing: Materials. Since then.778 (970) 1. and pipes bulb. Storage tanks.7) 4.3) expansion.737) 0. also must be accompanied by good properties with relatively low costs for stretching of the fibers. PAN-based fibers have oxidation step.208 8: Reinforcements When originally developed. tion step. The a difference between carbon and graphite textile fibers are often referred to as acrylic fibers. Tows of fibers from many spools are than the carbon fibers and often by a differ. PAN fibers used series of combs that keep the fiber tows sepa- to make carbon fibers are a different grade rate but adjacent to one another as they go Fundamentals of Composites Manufacturing: Materials. pitch. directed into the stabilization oven through a ent manufacturer. and rearranging) so that the polymers do not Each process offers distinct advantages melt in subsequent processing steps. Pitch is an Today the designations of carbon fibers amorphous mass that must be formed into focus on the modulus and strength specifica. road surfaces and fuel briquettes. for making carbon fibers. and wound onto a later. The graphite fibers were made by pro. Methods. sometimes called the cost and properties. but those intended for carbon fibers cessing carbon fibers through an additional are simply called PAN. and Applications . there was from those used in traditional textiles. Therefore. These rings are critical to the later made fiber for the starting material of the formation of graphite.) Today. The only for longstanding customers for which molecular structure of a PAN-based fiber they were specified many years ago. such as when marketing pitch is used as a binding material for asphalt and some processing issues are discussed. pitch goes tions of each variety.and pitch-based fibers must centrations relative to other atoms and all be stabilized by thermosetting (crosslinking can be converted into a graphite material. so there is no difference between the to separate the components of coal tar or two types. which involves hold- standard modulus products. this text will generally petroleum. and. Both PAN. Notice Figure 8-5. to a lesser extent. through a meso-phase in which the polymer chains are somewhat oriented even though Manufacturing Processes the material is liquid—a liquid-crystal phase. fibers. Thermosetting is done with mod- first carbon fibers made. fibers. PAN fibers process. during the stabilization step is shown in Fig- The PAN-based and pitch-based fiber ure 8-6. a similar ring-based structure is are usually produced at a different facility formed. the demands on performance spool. PAN is a commercially available that rings are formed during the stabiliza- textile fiber. However. use the term “carbon fiber” to indicate both thus making it a suitable starting material fiber types unless the graphite fiber desig. rayon. The current preferred technologies for This orientation is responsible for the ease making carbon fibers use polyacrylonitrile of consolidation of the pitch-based product (PAN). nation is required. Rayon-based fibers were the stabilized. Two equivalent representations of manufacturing processes are summarized in the consolidation process are shown. It is therefore shown as a ready. (The process for formed as strands and then gathered into making carbon/graphite fibers is discussed a group called a tow. The PAN fibers are high-temperature step. In the pitch-based PAN-based carbon fiber process. It has high free-carbon content. In the conversion process. Pitch-based ing the fibers at a constant length against fibers have high modulus and good thermal their inherent shrinkage as they become conductivity. This and disadvantages in terms of both fiber stabilization step. In addition to this. but are now made erate heat and in an air atmosphere. All of these materials have high carbon con. into a carbon/graphite form. have dictated that all carbon fibers meet the Pitch is the material that remains at higher performance capabilities of graphite the bottom of the distillation tower used fibers. 8: Reinforcements 209 through the process. Again. but they are otherwise equivalent. under a nitrogen atmosphere in a step called graphitization. In this step. The molecules within a carbon strand are stretched and aligned. (This step is sometimes also called pyrolization. and Applications .) During this step the fibers are heated to higher temperatures in a nitrogen atmosphere and the tension on the fibers is maintained. The heat and stretching pressure causes the molecules to join together by the elimi- nation of hydrogen (dehydrogenation). Methods. The material on the left is a product of the stabilization process. the fiber diameter is reduced to about one-half the original diameter. These tows are spread (flattened) by passing them over a bowed roller. Two of these molecules are shown in the first part of Figure 8-6. The new structure emerges and is seen to have additional six-member rings at the junctions Figure 8-5. Spreading allows equal access to the heat for all of the fiber strands. Because of material loss and shrinkage during carbonization. the prod- uct of the previous step is shown on the left side of the figure along with another. the fibers are further heated. Hydrogen molecules attached to the interconnected rings are removed by the heat and the chains of rings merge together to form plates. the nitrogen atoms present in the rings are eliminated and the ring structure is further consolidated. This results in the formation of a plate-like structure. This process is depicted on the molecular scale in Figure 8-7. equivalent plate. The next step in the process is carbon- ization. The heating and tension during graphitization eliminates the ni- trogen and new rings are formed that join Fundamentals of Composites Manufacturing: Materials. Manufacturing process for making carbon/graphite fibers. The graphitization structure is shown in Figure 8-8. One is reversed relative to the other. To achieve the high strength and stiffness properties demanded in today’s marketplace. of the two previously separated molecules. The carbon content after carbon- ization is 80–95%. with continued tension. and Applications . The carbon content of After graphitization. Figure 8-7. The result tion. the f ibers are the fibers after graphitization is generally cleaned in an electrolytic bath. Methods. the previously separate plates. This bath above 99%. Structural changes of PAN-based carbon fiber during the carbonization step of the manufacturing process. the surface of the fibers. The differences in modulus and removes debris that might have been formed strength of the fibers are largely dictated by during the heating processes and oxidizes the conditions present during graphitiza.210 8: Reinforcements Figure 8-6. Structural changes of PAN-based carbon fiber during the stabilization step of the manufacturing process. Higher-modulus fibers are processed at is a larger plate with only a few nitrogen higher temperatures and for longer times. atoms on the edges. The oxidation of Fundamentals of Composites Manufacturing: Materials. surface finishes. this finish is an epoxy so that good been demonstrated in the laboratory. called whiskerization. grows ceram. the ic whiskers (such as SiC. Structural changes of PAN-based carbon fiber during the graphitization step of the manufacturing process. While these whiskers greatly in. called pyro- Some manufacturers and. processes the oxidizing agent must be added the fibers are introduced into a bath where intermittently. which is needed for subsequent expensive and thus is not used commercially. and Applications . bility is most often measured by looking at the cess is still preferred because it can be run contact angle of the fiber/water interface. the whiskerization process is bonding. continuously whereas with the solution After washing the electrolyte solution off. Some non-oxidizing treatments also have Usually. potassium permanganate. Gas-phase oxidations and radio the matrix. or Si3N4) on fibers are then wound back onto spools. therefore. the electrolytic pro. Methods. Wetta- hypochlorite. the end as a separate tow. method shows good increases in bonding to bon fibers. However. crease the ability of the carbon fibers to bond droxyls. It the surface of the carbon fiber. have investigated of pyrolitic carbon on the fiber surface. resin can be achieved. or sodium effectiveness of the surface treatment. to the carbon surface and improves to the matrix.8: Reinforcements 211 Figure 8-8. The whiskers should be noted that each tow of fibers that are oriented perpendicular to the surface of started through the process is retrieved at the fibers. examining the wettability of the fiber. TiO2. Therefore. the acid. like hy. The Liquid oxidization can be done by simply extent of the wetting of the fiber by water pulling the fibers through a bath of some is directly proportional to the number of convenient oxidizing agent such as nitric chemical groups attached and. One compatibility with the eventual matrix method. The non-electrolytic surface treatments of car. consists of vapor-phase deposition laboratory researchers. the surface adds chemical groups. After drying. Another non-oxidative method. especially lization. but is also expensive. an appropriate polymeric finish is applied. each Fundamentals of Composites Manufacturing: Materials. frequency (RF) plasma treatments have both The effectiveness of the surface treatment been demonstrated but fiber properties are of the carbon fibers is often measured by lower than with the electrolytic process. In the cross-fiber direction there are • The cost of the fiber has increased bonds.97 to 7. 36 to 600 ksi (248 to 4. (not fibers) is attested to by how easy it is to write using a pencil. These rings are formed by strong covalent bonds so the resistance against the • The modulus increased from 1.78 g/cc) with changes oc. structure. (1. are relatively significantly from $3. plates. A major in. The weakness with costs spread more or less evenly of these bonds in traditional bulk graphite over the entire process.30 per weak Van der Waals bonds that form to hold pound ($8. Some typical a problem for the molder. Hence. were that to occur.0008 ohm-in. the direction of the 4. the price drops. more strength in the fiber axis direction and • The elongation to failure dropped from significantly improving the stiffness (modu- 4.002 ohm-cm) upon each other to form a three-dimensional with most of the change occurring dur.29 per kilogram) the stacked rings in place. are not fully oz/in. They are oriented within the fiber ing graphitization. that there is little alignment of the graphite little by little. values for these changes in a PAN-based such as aerospace. thus adding even occurring during graphitization. plates within a fiber dictates that the slough- facturers have begun making 50. however.88 to $8. Remembering that The manufacturers of the fiber add new the bulk graphite of a pencil is made so plant capacity as the volume increases and.6% with most of the change oc.000–12. changes occurring more or less uni- formly throughout the process.55 to $18. lus) of the fibers. off the production equipment.4 µin. However. do not use the larger fiber are: tows. The standard for many years was on the paper.000 strands ing off of the layers. The ring structure is (10 to 228 GPa) with most of the change also dimensionally stable.5 to 33 Msi tensile force is strong. Fundamentals of Composites Manufacturing: Materials.8 to 1.212 8: Reinforcements spool of original fiber is again spooled at tions. Some applications.3 (1. the sides. For some applica. although process problems associated with Throughout the process several changes handling the larger number of fibers remain have occurred in the fibers. especially • The density increased from 6. Structure • The resistivity dropped from 454 to As shown in Figure 8-9. manufacturing process and therefore have out the process. would per tow in an effort to more efficiently use not be at the end of the fiber but. that is.154 to 0.000 strands per tow. these larger tows seem to work well.137 MPa) with when the fibers are pulled in tension.40 µm) with conceptually similar. (13. Some manu. curring during oxidation. rather. tows with more is separated from the stack and deposited strands. The conversions • The diameter decreased from 550 to of pitch-based and rayon-based fibers are 291. exposed to the thermal treatments of the curring more or less uniformly through. Methods. so that the long axis of the fiber is the same • The tensile strength increased from direction as the long axis of the plates. This is because of the greater pos- sibility that some of the strands. These bonds. it can be extrapolated that the pencil novation to reduce the price has been the mark is formed when one layer of graphite use of larger tows. the plates stack . lower physical properties.94 to 1. the most of the change occurring during force is pulling against the ring structures of graphitization. the end of the process. and Applications .03 those in the center of the tow.20 to 1. the plates. both the tendency for surface abrasion. for PAN-based fibers. Methods. plicates the picture. Still. and rayon-based) further com- little sloughing off of the layers of graph. Three-dimensional representation of the carbon fiber structure. This stabilizes the cross-fiber for the various fibers. property ite. so that the surface of the carbon fibers has pitch-based.8: Reinforcements 213 Figure 8-9. so surface clean. the rearrangements of the atoms and Carbon fibers are available in a variety of molecules tend to eliminate the inevitable grades from many different manufacturers. imperfections that occur along a plate and These grades are generally grouped accord- the non-planarities that can occur between ing to the modulus of the fibers. However. Properties sion. The existence of three direction and increases the size of the plates major types of carbon fibers (PAN-based. sented in Table 8-4. plates. The rearrangements improve the the presentation of property data can be natural stacking of the plates and result in a misleading because of the large number of significant increase in the number of Van der grades and different points of optimization Waals bonds. carbon fibers have a tendency to data for a variety of carbon fibers are pre- abrade along their surface. strength and stiffness increase going from Fundamentals of Composites Manufacturing: Materials. ing via electrolytic treatment and addition Analyses of the data from Table 8-4 tests of polymeric sizing are important to reduce reveal that. Nevertheless. and Applications . Because carbon fibers are made under ten. However. the fiber in tensile measurements taken on fibers at continues to consolidate and form a more various stages of the manufacturing process orderly structure—both are factors that under a variety of conditions. in strength is reached. fibers.5 Intermediate modulus 305 (2.820) 85 (586) 0. in production.413) 64 (441) 1.5 527 (3.447) 33 (228) 1. However. the suggest that both strength and modulus ini.447) 64 (441) 0. the graphitization increases the carbon con- strength goes down and the modulus goes tent of the fiber. % PAN-based Fibers Standard modulus 500 (3.067) 42 (290) 2.5 Intermediate modulus 780 (5.530) 33 (228) 1. For pitch-based modulus will decrease the tensile strength.103) 75 (517) 0.2 Ultra-high modulus 500 (3.0 554 (3.903) 55 (379) 0.633) 128 (883) 0. Beyond that point a The trade-off between strength and modulus trade-off occurs—optimizing for a higher is illustrated in Figure 8-10.4 Rayon-based Fibers 110 (758) 6 (42) — 119 (821) 5 (35) — standard modulus to intermediate modulus and other factors also can have effects.1 880 (6. Tensile Strength.4 Ultra-high modulus 525 (3.6 653 (4.8 512 (3. Methods. a maximum defects are points where failure can begin. the trade-off is not as dramatic. However. the elongation for tization stage in the process.5 640 (4.502) 34 (234) 1. These data tend to increase modulus. and Applications . Elongation to Fiber Type ksi (MPa) Msi (GPa) Break. when going from inter.620) 105 (724) 0. although time the pitch-based fibers is generally lower than Fundamentals of Composites Manufacturing: Materials. increase in temperature and time during mediate modulus to ultra-high modulus.371) 43 (297) 2.7 Pitch-based Fibers Standard modulus 276 (1.378) 40 (276) 2.214 8: Reinforcements Table 8-4.1 924 (6. Tensile Modulus. This suggests that as the up. Properties of various carbon fibers available from manufacturers. The materials. decrease in strength suggests that defects tially increase with treatment temperature are being created in the fibers and these but that after a certain point. These trends confirm what has been seen non-carbon atoms are driven off. at The optimization of modulus is generally least within the range of products currently a function of the temperature of the graphi. there is a greater chance of having a of the molecules at higher temperatures Figure 8-10. One of those thermal similarly to ceramics. and creasingly important. and Applications . The tensile both strength and modulus are critical. therefore. This important for most applications of carbon trend reflects the essentially brittle nature fibers. Therefore. pansion (CTE). For almost all materials. the tion point. In such a material. Trends in tensile strength and tensile modulus with temperature for PAN-based carbon fibers. Methods. As the length of the test fibers in. pitch-based defect within the test sample and. PAN-based fibers are more present in the test fiber.8: Reinforcements 215 for PAN-based fibers. Fundamentals of Composites Manufacturing: Materials. The decrease in strength that occurs when Although mechanical properties like defects are present also can be seen in the tensile strength and modulus are the most effect of fiber length on tensile strength. chance of having a defect in the sample. CTE is positive because the increased motion creases. the more likely the commonly sold in the marketplace. thermal properties are becoming in- of the carbon fiber. whenever a defect is properties is the coefficient of thermal ex- present. however. In for a similar reason—the more material general. the defect serves as a failure initia. and strength also decreases with fiber diameter the lower elongation is not a problem. fibers are being used in applications where the tensile strength decreases. along the major axis of the fiber. Methods. the temperature goes up. This is assumed to arise from the natural conductivity of graphite • racing car bodies and frames. resistance and low break extension (elonga. it fibers are contracting to achieve better is convenient to examine applications accord- symmetry and uniformity in the molecu. tible to fatigue. the following: est and increasing importance is thermal conductivity. ing to the primary property utilized. lar structure (toward the idealized perfect Representative applications based upon graphite crystal). away from the heat source. high stiffness. have low impact • housings for computers. criteria more closely than any other material. high toughness. The thermal • aircraft structural parts such as doors properties of various materials are shown and landing gear assemblies. small motors. The ideal engineering material would have They have a negative CTE indicating that as high strength. Pitch-based carbon fibers have • aircraft control surfaces and. in Figure 8-11. and Applications . and low weight include Another thermal property of great inter. on airplanes). Fundamentals of Composites Manufacturing: Materials. properties: ders them creep resistant and not suscep. • heat shields for missiles and rockets. which ren. • storage tanks (especially when weight is although the price has continued to decrease a consideration such as the waste tanks with increased production. relatively low compressive strength. and the orientation of the rings that lie par. combined smaller. (For the carbon fibers. Carbon fibers are elastic to failure at normal temperatures (meaning that they These applications are based on thermal do not deform before failure). Carbon Applications fibers are the rare exception to this rule. surpassing that ingly. The following applications are based on and a small coefficient of linear expansion. and allel to the axis of the fiber. • high-precision tooling. of most metals. These fibers can be used • helicopter rotor blades and wind tur- as radiators (heat pipes) to transmit heat bine blades. Carbon fibers. ductors of electricity. the sample gets and low weight. Although there are The explanation given is that the carbon some obvious overlaps between categories.) The uses of carbon fiber composites obviously The contraction is stronger in ultra-high depend upon the unique properties available modulus than in standard-modulus fibers. springs. and comings. and electrical control panels.216 8: Reinforcements will increase the size of the sample. strength. except in strongly oxidizing environments or when in contact with certain molten • aerospace antennas (because of the low metals. the CTE with high-performance matrices. • space structures such as telescope However. Carbons have excellent damping coefficient of thermal expansion). • automotive drive shafts and leaf Carbon fibers are moderately good con. stiffness. characteristics as well. increas- high thermal conductivity. meet these is measured in the longitudinal direction. They are chemically inert • brakes. carbon fibers have some short. and missiles. They are also expensive. that is. with these materials. chemical inertness: which is a benefit except that it might com- plicate processing. mounts. rockets. They are brittle. • spacecraft. full fuselages. tion). Thermal conductivities of various materials. • bridge structures (which will not cor. in the paper industry. • circuit boards. These applications are based on electrical Applications based upon rigidity and good properties: damping: • shields against radio frequency inter- • musical instruments. and Applications . • rollers for industrial processing such as rode and have good seismic resistance). nuclear industry. and Fundamentals of Composites Manufacturing: Materials. Methods. • audio speakers.8: Reinforcements 217 Figure 8-11. and and • arms for mounting the heads to read • uranium enrichment centrifuge in the computer storage devices. ference. Manufacturing Process Applications based upon fatigue resistance In 1971. This that the solvent used is hot. cloth. and Applications . the polymer is difficult to dissolve. wholly aromatic (that is. and therefore the improvement in properties that they impart is less significant. currently the major cant intermolecular bonding as illustrated brand. and Aramid • x-ray tables and mounting arms. • heart-valve components. This fiber is sold in the After the polymer is formed it must be United States as Spectra® and in Europe as spun into fibers. These intermolecular bonds yet. Even in solution the polymer Fundamentals of Composites Manufacturing: Materials. a DuPont fiber. For example. with are all polyamides) and so there is signifi- Kevlar®. These are not • artificial joints. These Applications based upon biological inert- other organic fibers are. aramid fibers were introduced and self-lubrication: in commercial products. drying the polymer. Because of high reg- nylon fibers might reinforce tires or conveyor ularity. “Dynema. further increase the strength and stiffness Another high-performance organic fiber is of the polymer. They were origi- • textile machine components. of carbon fiber usage keeps increasing and The synthesis and structure of the aramid the price keeps dropping. Methods. and protection and then as a reinforcement for • artificial limbs. they contain the benzene ring). nally used as reinforcements for tires. and other rubber-related goods. The fibers Most of these applications for carbon fibers are have also found applications in high-strength growing rapidly and new applications are con. the FIBERS strength and stiffness of aramids are high. the volume boats and protective clothing and gloves. such as that used for sails on racing stantly being created. as with other highly aromatic molecules.218 8: Reinforcements • touch switches. bonding. as a group. but they are not generally considered That difficulty can be appreciated by noting with the aramid and UHMWPE fibers. Therefore. After a few years. in the case of nylon. but generally not in dissolving it in an appropriate solvent as il- high-performance applications. the segments are uses as it becomes ever more competitive. they became widely used for ballistic • compressor blades. especially when ARAMID AND OTHER ORGANIC the aromatic rings are in the backbone. high aromaticity. high-performance composites. these price of carbon fiber may continue to drop. Therefore. These materials are certainly compos. belts. There is probably a polymer are shown in Figure 8-12. So. usually ness and x-ray permeability: referred to as textile fibers. Other aramids are available but. and intermolecular belts. ites. However. The poly- minimum price based on the cost of the raw mer is a polyamide having the same chemi- material.” Other organic fibers might be washing. This should further accelerate the number of whereas with aramid. • air-slide valves. have not penetrated the market as fully. linkages join segments that are aliphatic. made of UHMWPE. This is done by filtering. but even that price is subject to the cal linkages (amides) along the backbone as normal price-volume relationships. as in Figure 8-12. and then used as reinforcements. concentrated is because their properties are much lower sulfuric acid. lustrated in Figure 8-13. The most common organic fibers used Note also that the polymer is highly polar (as for reinforcements are the aramids. discussed in this text except in passing. the nylon. properties for these fibers are given in Table However. However. and Applications . dried. able from other companies. These grades are In contrast to glass fibers and carbon designated as Kevlar 29 (high toughness). maintains some intermolecular bonding and this chapter. if the fibers are to be subjected 8-1 and the specific strengths and specific to extensive mechanical operations. thus. The solution is then forced though a plate there are some applications. This is possible because aramid fi. collected. As will be discussed later in carbon fibers. such as modulus are given in Figures 8-2 and 8-3. The differences between the grades are sizing. bers are tough and not. a sizing amid fibers are less dense than fiberglass and can be applied. Therefore. The material emerges matrix and fiber is intentionally weak so as continuous fibers. such as for bal- (spinneret) into which many small holes listic protection. determined by the processing conditions. and 149 (ultra-high modu- surfaces. a coupling agent may be applied forms rod-like crystals. Properties the molecules are already aligned in the long Three grades of aramid fibers are available direction as they are formed. aramid fibers often do not require lus). Methods. and matrix. therefore. spools. to improve the bonding between the fibers crystal thermoplastics discussed previously. 49 fibers that have sizing coated onto their (high modulus). As indicated by the inherent rod-like nature and high crystallinity of the fibers. washed. in the case of aramids. subject which generally give more crystallinity to to the same incidental processing damage the higher-modulus fibers. and intermediate in strength Fundamentals of Composites Manufacturing: Materials. from DuPont and similar aramids are avail- aramid fibers are not drawn. The fibers are then it can be broken during impact and. (The mechanical that occurs with glass and carbon fibers. where the bond between have been drilled.) Ar- during braiding or some weaving. and wound onto absorb more energy. Synthesis of aramid and its intermolecular bonding.8: Reinforcements 219 Figure 8-12. similar to the liquid. 220 8: Reinforcements Figure 8-13. Even though the size for aramid fibers that the other fibers do not of the cable and rod might be the same. fibril failures rather than a brittle failure The elongations of aramid fibers are much like carbon and glass. and Applications . glass but not as high as the outstanding Therefore. which are like fibers within the have the same resistance to compression Fundamentals of Composites Manufacturing: Materials. the fibers break into high toughness. composites are used. and stiffness between glass and carbon fi. Therefore. However. the fibrils do not small fibrils. Manufacturing process for aramid fibers. plus the excellent of a cable consisting of many fibers versus tensile strength. These fibrils arise from the rod-like bers. Tensile strength failure is to the specific strength of carbon fibers. Analogous to this higher than either fiberglass or carbon would be the difference between the failure fibers. The unique failure mechanism of aramids The failure of aramid fibers is unique in is responsible for their high strength and that when they fail. This toughness is one of the most im. Methods. the specific strength of the structure of the liquid crystals as they are aramids is quite high. The believed to initiate at the ends of the fibrils specific modulus of aramids is higher than and is propagated through the fiber by shear. roughly comparable spun into fibers. results in high toughness failure of a solid rod. fiber. aramid fibers fail by a series of specific modulus of carbon. That elongation. cable is tougher because it has many failure portant properties and leads to the majority modes and is far less susceptible to formation of applications in which aramid reinforced of a single defect leading to brittle failure. the offer. Pressure bottles made periods is not unexpected in light of the of aramid fiber composite and carbon fiber thermoplastic nature of the fibers. the negligible decrease in tensile strength at jected to impacts and then tested for reten.) The aramid fibers exposed to several aggressive thermoplastic nature of aramids means that. liquids. (Although carbon fiber also starts as a dicated. thermoplastic polymer. and Applications . Impact toughness of aramid and carbon fiber composite pressure bottles. aramid is resistant to most solvents. Fundamentals of Composites Manufacturing: Materials. This bottles. in general. allow for its unique characteristics. However. the fibers are sensitive fibers. aramid fibers to heat. which is modified to of aramid fibers (932° F [500° C]). the heat treat. Retention of tensile strength is shown for change it into a ceramic-like material. lower temperatures (up to 302° F [150° C]) is tion of original pressure-holding capability. characteristic is consistent with the high Aramid fibers are made by a traditional melting point/decomposition temperature polymeric synthesis. mids is sensitivity to solvents. Since Another characteristic of thermoplastic aramids are thermoplastics. they possess resins that should be considered with ara- many of the same fundamental characteris. As already in- tics. when the aramid fibers are exposed to a high The effect of aramid toughness can be temperature (482° F [250° C]) for extended seen in Figure 8-14. Figure 8-14. Methods. The decrease in tensile strength seen sistance is important. PAN. 8-15. encouraging and indicates that aramid fibers Clearly the retention of pressure strength have good resistance to heat when compared was much higher for the aramid-reinforced with other thermoplastic materials. composites (the same matrix resin) were sub. Therefore. That sensitivity is seen in Figure are rarely used when compressive force re.8: Reinforcements 221 forces as do the monolithic glass and carbon among other things. Only in some of the strongest acids. This is confirmed in data presented in Table ments of carbonization and graphitization 8-5. the positive aspects of aramid ics and metals. the rope gives better protection with a layer of composite material on the against the sunlight because it is thicker bottom. Be. Each for various exposure periods. By contrast. Therefore. The fabric. and a test layer on top of the foam. the rope held creasing impact. (1. of that.222 8: Reinforcements Figure 8-15. such as hydrochloric. nitric. (2. The most investigate the effect of outdoor exposure important positive property is impact dam- on aramid fibers. For example.5-cm) thick structure expected.6 oz/yd2 (170 g/m2) fiber yarns. For this test. Effect of temperature on a high-modulus aramid fiber. over that period. and sulfuric. in a property as the end-point of the test.0 oz/yd2 (203 the sun doing the damage). two aramid age prevention and this can be seen in the products—a rope of . of 5. Weights were dropped onto the sample from the fabric test was terminated after only 5 different heights to show the effects of in- weeks of exposure. Methods. it is prudent to fibers should be re-examined. shows rapid deterioration. As would be of them was a 1-in. with g/m2) fiberglass cloth and polyester resin in its inner fibers only within the woven small the first prototype.5 oz/yd2 (119 g/m2) in the third prototype. tive results. and of cause tests of this type often take 50% loss 3. Polymeric materials are affected by sun. The data show clearly that Fundamentals of Composites Manufacturing: Materials. and Applications . a layer of polyurethane foam on top and therefore protects the inner fibers bet. ter (it is actually the ultraviolet [UV] light of The test layer was made of 6.5 in. aramid cloth in the second prototype. plain-weave fabric were exposed to sunlight prototype surfboards were constructed. are up well for over 24 months losing only 69% aramid fibers strongly affected. In light of the above somewhat nega- light to a greater extent than are ceram.3 cm) and a data presented in Figure 8-16. This is accomplished Bases by making an aramid-reinforced shield for Ammonium 92** the part that can be removed when it is hydroxide (28%) ready for use. Not only is properties. the fiberglass prototype sustains much more the use of a polyethylene polymer for com- damage than either aramid prototype. but of aramid fibers. Applications UHMWPE fibers have molecular weights Several uses for aramids take advantage that are orders of magnitude higher than of its desirable combination of light weight.7%) 100* craft wings and other structures where im- Hydrochloric (37%) 36* pact damage might be expected.5* amazed that a high-performance fiber could (5% solution) be made from polyethylene. Traditional Water (boiling) 98* polyethylene is the highest volume plastic and is used for a wide variety of applications * = 100 hours exposure ranging from trash bags to milk jugs to toys ** = 1. Solvents but the ability to withstand impact damage Acetone 100** is important because they may be subjected Carbon tetrachloride 100** to incidental damage and must not leak. is superior One obvious change in UHMWPE fi- in impact damage protection. The techniques for polymerizing Fundamentals of Composites Manufacturing: Materials. Benzene 100** Ultra-high-molecular-weight Polyethylene Other Chemicals Fiber Synthesis and Manufacture Gasoline 100** People familiar with plastics are often Salt water 99. Sodium hydroxide 97* Aramids have found a special niche in (40%) high-performance pressure vessels. the leading edges of the Voyager aircraft that Hydrofluoric (48%) 94* flew nonstop around the world were made of Nitric (70%) 13* aramid. For example. Chemical resistance aramid fiber used for bullet-proof vests. This higher mo- strength. Acids Other uses include leading edges of air- Acetic (99. and Applications . and especially toughness. In these applications. Traditional polyethylene is not. In posites suggests that something special has fact. Battlefield shelters made of Fibers are Soaked Retention. modulus. % aramid fibers are lightweight while retaining at 70° F (21° C) strength and antiballistic properties.000 hours exposure for children. Therefore. used as a textile fiber because of durability (cracking) problems. however. traditional polyethylenes. half as heavy as the fiberglass). As the name suggests. even the second aramid sample (about been done to the polyethylene.8: Reinforcements 223 Table 8-5. Damage control applications have Sulfuric (96%) 0* also included protecting parts while still in the fabrication stage. Methods. lecular weight improves almost all physical One use is in ballistic protection. not only is the hoop stress high. it is also used as armor for ships and motor- Liquid in which ized combat vehicles such as tanks and per- Tensile Strength sonnel carriers. bers from traditional polyethylene is the molecular weight. and other products does not explain all of the performance Fundamentals of Composites Manufacturing: Materials. UHMWPE have been known for many where high strength and scuff resistance years. Impact studies on prototype surfboard. and Applications . Powders of UHMWPE have been are important. molded into articles such as cutting boards. But just increasing the molecular weight snowboard bottoms.224 8: Reinforcements Figure 8-16. Methods. But poor bonding may occur. structural applications are the specific modulus is higher than anything usually not an option for these fibers.8: Reinforcements 225 characteristics of UHMWPE fibers. of 1–5 million. The oth. and Applications . Bonding to standard polyethylene is folding of the polyethylene molecules does not extremely difficult. Somewhat simi. The starting material for the fibers is the bonding to the matrix is as good as the UHMWPE powder with a molecular weight aramid-matrix bond. The solu. these rods have a high degree of be good. rona or plasma treatment. For this reason. glass or aramid fibers. movement under a load. like competes against aramids. sively in composite applications like those described for fiberglass or carbon fibers? The Properties answer is simply that the UHMWPE fibers The mechanical properties of two of the are not able to withstand the temperatures of most common UHMWPE fibers in the United curing used in many composite applications. Methods. UHMWPE fibers are used for sail- tic protection. In those markets. ness of the bond between the fibers and the ecules in the fiber direction so that the normal matrix. that is. UHMWPE fibers are actually improve impact resistance. The powder is dissolved in UHMWPE fibers are thermoplastics and a solvent so that the normally intertwined therefore have some of the same advantages molecules are free to move completely inde. Fundamentals of Composites Manufacturing: Materials. From Table 8-1 it can be seen between grades but are approximately 290° F that the tensile strength and modulus are (143° C). The molecules chemical inertness of polyethylene. higher creep. Hence. usually with a co- crystallinity (60–85%). States are presented in Table 8-1 and Figures The melting points of the fibers differ slightly 8-2 and 8-3. UHMWPE fibers have much good but not significantly better than fiber. being used extensively for impact and ballis. The resistance of the fibers to tion is then forced through a plate with small solvents and most acids is better than with holes in it (spinneret) similar to what is done aramid. and disadvantages that were noted with pendent of other molecular chains. But UHMWPE has ropes. The basic polyethylene nature of UHMWPE er change is that the manufacturing process fibers brings up the question of the effective- of UHMWPE fibers stretches out the mol. especially. the specific which is less than the load required to break strength is as high as any other material and the fibers. UHMWPE fibers are tough. That toughness has led to these fibers tion of the structural aramid applications. except carbon fibers. In these cases. Hence. are aligned as they pass through the spinneret In light of all its excellent properties. tion is protective clothing and. The solvent is removed and then the aren’t UHMWPE fibers used more exten- fibers are dried. In addition to the high strength and stiff. impact strength. However. why holes. This also called extended chain polyethylene is because slippage along the matrix-fiber (ECPE) fibers. UHMWPE cloth and other fabrics and applications. Extending the molecules bonds uses energy and therefore improves creates rod-like structures. When used in applica- lar in shape to the aramid and liquid-crystal tions where the fiber-matrix bond must polymers. UHMWPE fibers can be treated molecular orientation (95–99%) and high to oxidize their surface. Also. This resistance reflects the inherent when making aramid fibers. aramid fibers. A related applica- same level of protection. where toughness and possibly light one major advantage—it weighs less for the weight are important. Later. This can be The major uses for UHMWPE fibers are anticipated from the elongation data in Table similar to those for aramid with the excep- 8-1. Applications ness. the fibers are drawn. This mate. excellent properties suited to some special- tals in solution and then spin fibers from the ized and important applications. Fundamentals of Composites Manufacturing: Materials. The typical deposition gas for and textile fiber with excellent flame retar.7% PEI content. cuts and abrasions. boron and SiC have and form rod-like polymers that exist as crys. the performance of the entire part is products of relatively simple shape but with improved. boron fibers is BCl3 and H2. and for SiC it is dant properties. The sub- in a sort of self-reinforcing step. Just as UHMWPE can be made into high- By far. illustrated in Figure 8-17. It was found strate filament then passes into a chamber that the strength of polyester doubled with into which a deposition material has been only 0. it also can substrate filament passes through a cleaning be a good reinforcement. Both boron and SiC fibers are made by the tra. thermoplastic. which is heated by resistance from Another rod-like thermoplastic is based on a variable direct current (DC) power supply. a the chapter on special matrices). SILICON CARBIDE. poly-p-phenylenebenzobi. a polyetherimide (PEI). also has been suggested for gas decomposes when it touches the substrate use as a reinforcing material. energy is used when dissimilar materials rub against each other and. at least in the laboratory. the case of boron fibers and carbon in the All of the integration of the reinforcement is case of SiC. A matrix material added as a gas. therefore. solution. OTHER SPECIALTY FIBERS Boron and silicon carbide (SiC) are high- Other Organic (Synthetic) modulus reinforcements. The filament is typically tungsten in by properly coupling it with PEI and epoxy. can be made let-stopping capability give these fibers a into ballistic protection materials. although both fibers have been done at the time the polyester is crosslinked used with both deposition materials. To overcome the oven in which the fiber is heated to remove high cost of this material. is targeted at aramids and as they exit the chamber. This is strong position in the ballistic protection done by forming the polymer into tapes of market. the most important performance fibers by special processing. application of UHMWPE is for ballistic it has been found that another commodity protection. Light weight and excellent bul. termed M5. The deposition soxazole (PBO). These materials High-performance Fibers were originally developed in the 1960s at A few other thermoplastic fibers have Texaco and United Technology under the properties high enough that they have been auspices of the Air Force Materials Labora- used as reinforcements in structural compos. AND protection is improved. Some manufacturers of bullet-proof unidirectional fibers and then compacting by vests have noted that when UHMWPE fibers a patented process. While the total production volume of ites. tory. One approach to making these fibers is these materials is small compared to the to follow the lead of aramids and UHMWPE other fibers discussed. The coated fibers are then wound onto a reel rial. It is speculated that additional high ballistic protection capabilities. be an excellent matrix (as was discussed in In this process. researchers have any lubricants or other surface contami- developed a method to reinforce polyester nants. a mixture of silanes with H2. polypropylene. ballistic BORON. filament. chemistry similar to polyimides. however. and Applications . One example of such a fiber is Vec. The high toughness of has properties that. Methods. Just as a PEI can chemical vapor deposition (CVD) process.226 8: Reinforcements protective gloves. these fibers in gloves protects hands from are superior. The result is a flat sheet are combined with aramid fibers in adjacent material that can be thermoformed to make layers. Boron fibers have been combined with to achieve the high output required for effi. squash. Mirage rudder. and rudder. ciencies and cost. Boron fibers also have been used in sports cause there needs to be time for the deposi. and wettability by a metal primary property required for this applica- matrix. vertical stabilizer. tensile strengths (by elimi. The time required to make the product. Typical reaction time tennis. fibers can be modified to improve tempera. and golf club shafts. Some different SiC crystalline structure on the applications for SiC fibers in an aluminum outside of the fiber. racquetball. and badminton. and recreation products such as rackets for tion buildup to occur. Applications Boron fibers are unique among the high- performance fibers because they combine the usual good tensile properties with good compressive properties. Silicon carbide fibers are often sold as ture resistance. inside the deposition chamber is generally fishing rods. tion is the ability of the SiC fibers to retain A minor change in the gas flows inside the their bonding strength to the matrix even chamber when making SiC fibers creates a during high-temperature processing. Figure 8-17. elements. elements for movable military Fundamentals of Composites Manufacturing: Materials. reinforcements for metals and ceramics. B-1 dorsal longeron. Such changes have allowed several grades of SiC fibers to be made and sold commercially. Most boron fibers are sold as prepreg tapes with epoxy as the matrix. The nating defects). This change improves matrix include aircraft wing structural the adhesion of the SiC fibers to metal ma. The typical compres- sive strength for boron fibers is 1. Methods. the frame and rib truss members and frame CVD process conditions for making boron stabilizing members in the space shuttle.8: Reinforcements 227 trices. F-15 horizontal stabilizer. the diameter fiber and boron fiber reinforcement. a company manufacturing One principal application for boron fibers vapor-deposited fibers will usually employ in a aluminum matrix is as tubular struts in many CVD chambers. These products have the advantages of both carbon As can be seen in Figure 8-1.895 MPa). from 30 seconds to a few minutes. These prepregs have been used to make the following aerospace products: F-14 horizontal stabilizer. F-111 wind dou- bler. Therefore. bination of boron fibers with conventional carbon fiber reinforced epoxy prepreg.000 ksi (6. The of the fibers made by the CVD process is tensile modulus and compressive strength many times larger than the other commonly are both high for this hybrid reinforcement used fibers. and the Hawk and Sea Stallion helicopters’ horizontal stabilizers. and Applications . Chemical vapor deposition (CVD) process Some recent applications have used a com- for making boron and SiC fibers. metals to create metal matrix composites. vapor-deposited fibers is usually long be. skis. aircraft lightning strike protection is to use cific applications. and other natural fibers can be much lower ficient of thermal expansion of the nitrides than synthetic fibers. have been commercialized using a process Some of the properties of natural fibers developed in Russia and later licensed to cited include low cost. Electrical resistivity as normal carbon fibers. SiC fibers One of the problems with aircraft rein- have been placed in a titanium matrix for forced with carbon fiber composites is their drive shafts to give increased stiffness over inability to conduct electricity away from other candidate materials. and Specialty Fibers potential for reducing the stealth of the Several fibers have a unique property or aircraft. difficulty to repair. these fibers conduct a process that is roughly analogous to that heat. Nitrides retain their tain appeal from an environmental viewpoint stiffness and strength at temperatures over for using natural fibers. Likewise. They have been shown to resist reinforcement fibers. has a bright future. The carbon fibers are coated with nickel in conductors. natural 2. and ably good strength. The combination of insulating against used to make boron fibers. For example. complexities in manufacturing. An alternate method of giving properties that direct their use toward spe. costs of these thermal shock better than SiC. While these properties Fundamentals of Composites Manufacturing: Materials. health benefits due to in volume. thus simplifying the for these fibers ranges from 102 to 101 ohm. fibers have been used for some composite Fibers made from basalt (an inorganic parts. low density. carbon fibers. This problem forcement. seem to be growing. cm. especially when carbon and reduced machine wear during manu- fibers are in short supply. especially in countries where the more mineral) have high modulus and reason. and Applications . As can be observed. given in Table 8-1.204° C). sustainability. NATURAL FIBERS Alumina fiber. aircraft is struck by lightning. electricity and conducting heat is especially useful in applications such as heat sinks for electrical devices. the opportunities for these fibers reduced dermal and respiratory irritation. Ceramic armor reinforced with has been remedied by installing a metal SiC fibers has become a major product and mesh in the outer layers of the aircraft skin. In addition.228 8: Reinforcements bridges. biodegrad- firms in other countries. the crons. However.200° F (1. It is such as fiberglass. However. making them either insulators or semi. traditional fibers are largely imported. and missile body casings. Methods. The coef. carbon fibers nickel-coated carbon fibers. Further. facturing operations. mids. While still small ability. Fan blades also critical electronic components when the have been made of titanium with SiC rein. These have been have been exposed to fluorine to produce shown to protect the aircraft and reinforce carbon/fluoride fibers. These fibers natural fibers is sufficient. this mesh has several problems including the added weight. has been explored as a reinforcement tensile strength of flax and spider silk are for aluminum. 40–55 The properties of some natural fibers are Msi (276–379 GPa) in diameters of 3–20 mi. the modulus of these fibers Nitrides are made from organosilicon is somewhat lower than the more traditional polymers. manufacture of the parts and their repair. Basalt fibers generally in applications where the strength of the compete against carbon fibers. and ara- transparent to radar. with a high modulus. This fiber remains stable in less than the strengths of synthetic fibers molten metals and will not corrode. Therefore. there is a cer- is lower than alumina. Efforts in India and Latin America have While the appeal of natural fibers is cer- been similarly successful with hemp and a tainly high. tion synthetic fiber with properties that may decking. and a few automotive be at least as good as some of the high-per. cations for silk. in the United States. Fundamentals of Composites Manufacturing: Materials. maturity. hemostatic not critical such as for tub and shower units. extrac. each from one of its six different of properties because of climate. synthesize a variety of silks for different ap- ated with natural fibers include variations plications. environmentalists fillers rather than strength reinforcements. and general fragility. glues.8: Reinforcements 229 are laudable. plant variety. The major application is auto- some applications do not need high properties mobiles and the marketplaces are Europe and and so natural fibers are acceptable. Even though the resultant wood products and so they are mostly seen as silk material is synthetic. These fibers are often hazardous solvents used in fiberglass. which may be key to making an imita. patches. This natural reinforcement fibers such as flax. Other ma. The fibers proved to be adequate with material and as a rope or net. Mercedes-Benz introduced jute-based worm silk is that a spider has the ability to door panels in its E-Class vehicles in 1994. It is helpful to think of vigorous program of development of natural the forces involved on the thin fiber web fibers for composites. some negative factors associ. components. This Zealand and their work with locally grown invites the use of spider silk as an armor hemp. and aramid manufacturing. and Europe but is also increasingly a motivation environmental stability. harvesting silk glands. is in contrast to the high temperatures and kenaf. of spider silk results in extraordinarily tion technology. molding compound (SMC) in automobiles is performance properties. cations in which strength and stiffness were vascular wound repair devices. as with the New Zealand case. furniture. used in applications such as synthetic lumber. They are shape. This is especially important in to absorb dye. the United States. Medical unsaturated polyester resins for some appli. hemp. sutures. and jute. carbon a replacement for fiberglass. reality requires that some high- variety of other natural fibers such as flax and volume application in a major market needs cotton. to happening. some countries have pursued a impact toughness. The major im- fiber. The movement into using Spider silk is an interesting natural fiber natural fibers as a reinforcement for sheet that has the potential of acquiring high. about 4% of the 400-million-pound facturing method since it is done at room (180-million-kilogram) market comprises temperatures and in aqueous solutions. Methods. In high elongation (35% in draglines and up spite of these problems and because of the to 200% in other silks) and therefore high advantages. extensive softness. The advantage of spider silk over silk. and Applications . One example is New when struck by a fast-flying insect. Most of the natural fibers are formance fibers. dressings. Comparisons of these materials with to adopt natural fibers before they can be traditional high-performance reinforcements taken seriously as a part of the composites show that the synthetic materials have higher market. prosthetic devices. ligament The fibers were also used with polypropyl. luster. devices such as wound closure systems. The uniqueness of the structure techniques. petus for the use of these fibers is that they terial advantages of spider silk are its ability are recyclable. However. would be happy with the projected manu. The difference with based on their proven and long-term use in spider silk is that it has a unique molecular composites with thermoplastics. and other bio-related ene and exhibited acceptable properties for products are especially appealing as appli- non-critical applications. That situation may actually be close properties but. fiberglass. removed when manufacture of the cloth is complete. opposed to a coating being applied as with a ter. John be referred to as both sizings and finishes Deere has made parts for its combines from with no attempt to distinguish them from natural fibers and a soy-based resin. Over the sometimes increased by a weak bond be. The ultimate environmental combination Materials coated onto the fiber surface will may now be possible for composites. in economies. it is possible FIBER-MATRIX INTERACTIONS that during the fiber surface treatment some coating could be added. thus complicating The bonding between the reinforcement the terminology. this larger view will be taken here. Some developmental products practice. Usually a strong the textile industry. years. have been found to impart a slipping between matrix and fibers. fore. these all-natural is a step in the manufacture of the fiber in composites will improve in properties as which the fiber surface itself is modified as experimenters study how to make them bet. There- automotive applications. bonding of the fibers to the matrices and oping countries as a way of assisting their impart desirable fabric qualities. especially those imported from devel. This will continue to be strong. one material often serves both pur- have been created in the United States for poses and so the distinction between sizings interior door panels and similar non-critical and finishes has largely disappeared. The electrolytic treatment synthetic resins and fibers. of carbon fibers is an example of a fiber surface treatment. Methods. drastically reduced. This protection is especially important to ings and finishes. Then. the starch could be removed by ability of the material to absorb energy. While or necessary. and the processing was complete except the toughness of a material.230 8: Reinforcements German automakers continue to use natural mechanical damage. However. They discovered that matrix bond and some of the important starch could be applied from an aqueous considerations involved in the modification solution to protect the fibers. and Applications . When textiles were first bond between reinforcement and matrix is used in automated equipment during the desired so that loads can be transferred effi. Sizings are used chiefly carbon fibers. sizings continue to be important. and matrix is critical to the performance of Sizings have been used for many years in the composite material. when and optimization of that bond. manufacturers found that the fi- This text concentrates on the more common bers were being damaged and their strength methods of strengthening the reinforcement. and other ceramic- for their ability to protect the fibers from like fibers that are brittle and highly sensi- Fundamentals of Composites Manufacturing: Materials. of the part. other materials. Another term that is sometimes the environmental reasons for their adoption confusing is fiber surface treatment. This allows vinyl alcohol. centuries. A narrow distinction was made between siz. one another precisely except where obvious ously both are natural and recyclable. Finishes enhance the fibers. Sizings and Finishes In high-performance composites where Sizings and finishes were discussed briefly the fibers are so critical to the performance when the major fiber types were introduced. is washing the fabric in hot water. which is easily absorbs energy. the fibers had been converted into cloth Although not considered in detail here. most notably poly- tween the matrix and fibers. Obvi. which is the for sewing. However. Industrial Revolution of the 18th and 19th ciently from the matrix to the reinforcement. potentially competing in all ways with sizing or finish. which protective coating to fibers. which typically polymeric materials that remain on are compatible with the glass. A coupling agent with polar and non-polar interactions. finishes are often comprised fiberglass and a resin matrix. They deliver dual-purpose sizing end composed of an organo group. sizings are made of silicon-containing groups. Figure 8-18 il- The finish chosen should be compatible lustrates such a coupling agent and the polar with both the reinforcement and matrix. Methods. This is analo- of molecules that have one type of functional gous to soap molecules where the non-polar group on one end and a different type on end attaches to the grease and the polar end the other. a finish for of the water to the grease and allowing the fiberglass and polyester might have one end grease to be washed away. Today. These types of finishes are called attaches to the water. which is and finish. and Applications . Fundamentals of Composites Manufacturing: Materials. thus forming a coupling coupling agents. For example.8: Reinforcements 231 tive to surface defects. and the other the fibers. Figure 8-18. To and non-polar interactions it would have with accomplish this. compatible with the polyester. the nature of reinforcement/matrix with the matrix. plasma. they interactions involves the recognition of a are subject to water absorption. which alloy with ist. fiber manufacturing compa- patibility problem. the concept of the The development and optimization of a molecule-to-molecule coupling provides a surface treatment for fibers can be ardu- simpler picture. the interface theory in a previous chapter. the development cost of good coupling agents chosen finish is often the same type of poly. even be- detrimental to other properties. metal ions by infiltration. This the use of a finish is sometimes a necessary is thought to exist between the matrix and evil—needed for strength and modulus. only a marginal interaction with the fiber. the coupling takes places as the matrix and bond to the silicon carbide. Regardless of and lithium. silicon-rich environment. the fibers can be treated in a attachments (bonds) to the fiber surface. fiber coupling agents that have given the desired companies often guard the exact nature improvements in mechanical properties of of their coupling agents and finishes with the composites. possibly. However. Therefore. This activates The theory of molecules touching other the surface of the fiber and makes it more molecules to form bonds was introduced as compatible with the finish resin. There approach to improving bonds in metal and also may be selective absorption of the resin Fundamentals of Composites Manufacturing: Materials. which model is chosen. face treatment of the fibers is often done to An analogy of the interphase would be a improve adhesion. Another diffused into each others’ domain. The moisture sensitivity of the composite This is the basis of coupling agent concepts. Methods. three-dimensional interphase. Finishes are often polar to obtain good is called the interphase theory. Further. the interphase is a known to aid the wetting of ceramic reinforce. or corona. The For metal matrix composites. and Applications . This increases the However. its chief purpose is to provide a amount of silicon on the fiber surface and lattice that the matrix molecules can pen- enhances the bond between the fibers and the etrate and then be held in close proximity aluminum matrix. In this compatibility with the fiber or interaction theory. the difficulty and In some cases. flexible. which has led to choices of ous and time consuming. Therefore. region where sizing (finish) and matrix have ments by liquid aluminum alloys. as with carbon fibers. tween the coupling agent and the fiber. Nevertheless. For example. but rather. Although this would seem to solve the com. the use of interphase is a polymer network formed by coupling agents is not as common as with the coupling compound or sizing and into polymeric matrix composites. For this reason. great secrecy. but the coupling agent and. as polar molecules.232 8: Reinforcements Some recent research suggests that actual ceramic matrix composites is to introduce molecule-to-molecule coupling does not ex. it often results in only nies continue to optimize current surface fair reinforcement/finish compatibility since treatments and develop finishes that are the finishes of the matrix resins often have compatible with new matrix resins. tion of several promising matrix materials. is often compromised by the presence of the An alternate view of how molecules interact finish. fibers are often treated with Interphase Theory electrolysis. groups of molecules associate with others Examples of such metals are magnesium through a network of forces. to improve briar patch formed by the coupling agent. which the matrix molecules can penetrate. sur. Therefore. have proven to be barriers to the introduc- mer as will be eventually used as the matrix. the bonding of silicon carbide fibers with The network may have occasional chemical aluminum. but. Nickel coatings are also to the fibers. in fact. of course. The are a liquid and a vapor. But the work of adhe- chemistry. the conditions interphase and reinforcement can be obtained that would determine the work of adhesion by applying the general principles of surface can be approximated. as: (discussed later in this chapter). Predictions of the bond strength between However. The probability of encoun. Determining whether fiber/ma. This unbal- Although the interphase probably has a ance gives rise to a surface free energy. within the limits of a fast pulling the matrix and reinforcement or between the rate and low temperatures. the failure will not necessarily be at the interface. However. It is the tension (that is. forces on the surface molecule are unbal- sponsible for transferring the load from the anced because it does not have molecules of matrix to the fibers. the energy is rationale behind this statement is simply called the surface tension. If the surfaces the main part of the interphase zone. These observations have and B been interpreted as interfacial (adhesive) The work of adhesion can be approxi- failure when. the boundary material is pulled from the other. WAdhesion = work of adhesion for the two trix interphase failure has occurred can be particles difficult. GB = surface free energy of particle B ies of the fracture surfaces of composites GAB = surface free energy of the inter- often reveal fibers that appear to be clean action between particles A of adhering matrix. to define the work of adhesion in terms of the Even if a crack is directed specifically at surface free energy between two surfaces. tering a critical flaw is much greater in the which is the energy required to separate two bulk phases of the matrix and fiber than in particles. is no effect of temperature. that tension failure usually occurs because The energy associated with bonding at the of a critical flaw. and Applications . as with the peel test and B. the contains the energy of dissipative processes Fundamentals of Composites Manufacturing: Materials. but away from. In other words. observed in any real peel strength test) also rounded by other molecules. conditions. true cohesive failure in form a new surface of a unit area. Methods. However. GLV. It is possible are much larger. However. the same material on one side. A the interphase region. GA = surface free energy of particle A Scanning electron microscope (SEM) stud. which in this case means that ing evidence is often needed to affirm these the pulling rate is infinitely fast and there theories. and slightly inside the interphase region the work of adhesion assumes equilibrium (cohesive failure). In reality. some confirm. In this test. G. the pulling rate is some finite num- Adhesion Theory ber and the effect of temperature is present. The interphase would be re. the failure has actually mated using the peel test. The attractive forces on a molecule sion should not be equated to the adhesive in the bulk are essentially equivalent in bond strength since the bond strength (as all directions because it is completely sur. it is the energy of the interphase zone because the bulk phases the bond between the particles.8: Reinforcements 233 onto the fiber. lower modulus and lower strength than the which is defined as the energy necessary to fiber or the matrix. surface is defined as the work of adhesion. one been close to. failure between similar parts same energy as would be required to move a of the interphase) is probably rare within bulk molecule to the surface. The WAdhesion = GA + GB – GAB (8-1) possible failure mechanisms are complex where: but have been studied in adhesion bonding technology. The angle to be measured. This quantity is a relative attached to a tensile machine. The test uses a filament to which energy. the work of dislodge a single drop of resin from a single adhesion can be found. a flaw increases as the length of the fiber Fundamentals of Composites Manufacturing: Materials. There. An analogy is given to car waxes. The above phenomenon is often referred formation. energy. the water readily spreads across the surface. when these energies are included. and Applications . none of the methods gives unambiguous sion can be derived. the surface the other tensile jaws. Hence.234 8: Reinforcements such as viscoelastic deformation. by the tensile test machine and the force to cause the fiber to separate from the resin drop is measured. plastic de. is known for the liquid (usually a single drop of matrix has been applied. The work of adhe- sion in terms of liquids. the fiber is pulled energy of the solid can be evaluated. the water beads be- surface. shown in Figure 8-19. Methods. This test is sensitive to fiber sample Figure 8-19. Some of the flaws could come from handling dur- ing the test. the work of adhe. equation: Single Filament Pullout WAdhesion = GLV (1 + cos U) (8-3) The single filament pullout test shown Since the surface tension between the liq. is cause the wax has low surface energy. suring the angle between a liquid and the When wax is present. resulting in the following results. Therefore. Using the concepts of does not spread on the surface. it is far more likely to bond than solid is high. a large number of samples must be run to obtain reproducible results. In contrast. water) and for the gas (usually air). and vapors Measurement of Fiber/Matrix Bond is expressed as: Strength Several methods have been used to de- WAdhesion = GLV + GSV – GSL (8-2) termine the fiber/matrix bond strength but In terms of the angle. The surface of the solid is said to be “wet- the actual curve of the peel strength is much ted” by the water when the angle is low and higher than just the work of adhesion. This test will not work unless the fiber is stronger than the inter- face. U. it tends to surface tension. After fore. Then. in Figure 8-20 uses a modified tensile test uid and the vapor and the contact angle can machine to measure the force required to be determined experimentally. but for any particular fiber the condition may not be met because of fiber flaws. the surface energy for a bead up. if a surface has high This happens when the surface energy of the energy. After the resin has cured. As noted previously. when the water if it has low energy. This is indicative of low surface given surface can be determined by mea. U. local micro-cracking. and so on. if the surface filament. G. the filament is face energy of the solid relative to the liquid threaded through a hole in a plate and then can be calculated. by observing whether the angle of the attaching the lower end of the filament to liquid on the solid is high or low. The hole measure of the energy of the surface. This condition is generally met. Surface energies determined by contact length since the probability of encountering angle. the sur. to when discussing the energy of the surface. must be smaller than the resin drop. solids. Also. Transverse tensile test. It is also tedious because of the The short beam shear test is the classical fragility of the fibers and the difficulty in test used most frequently to determine fiber/ getting a good resin droplet.25 in. Methods.8: Reinforcements 235 Figure 8-21. Therefore.25 in. (2. aligning the direction of whereas the flexural sample bends when the Fundamentals of Composites Manufacturing: Materials. support span = 1. easy to prepare. The sample is Transverse Tensile Test reasonable in size. which may focus The test is much like a flexural strength test failure into the interfacial region but not except that the sample is much shorter and exactly at the interface of the fiber and the thicker than the flexural sample. and the perpendicular to the direction of the fibers.0 in.5 cm).8 test in which a sample containing unidirec. (0. matrix bond strengths. (3. and Applications . Short Beam Shear Test increases. specimen width = . cm). Fiber pullout test. Typical dimensions for Figure 8-21 shows the transverse tensile the test are: specimen length = 1.5 in. Specimens The major difficulty with this test arises be. matrix.6 cm). the fibers in the sample to be perpendicular to the pull direction is critical to prevent Figure 8-20. In this test. The test apparatus is illustrated in Figure 8-22. are. speci- tional fibers is oriented so that the pull is men thickness = . of the matrix and the fibers.6 cm). shear forces. (0. therefore. equip- cause of the large differences in the moduli ment to run the test is generally available. a fiber/matrix bonds. the critical strength. the specimen is slowly pression and the bottom is in tension. When all the seg- There are many failure modes associated ments have reached this length. statistical version of equation 8-4 is required. The critical fiber length is the Uc  2lc ¤T i i c (8-5) Fundamentals of Composites Manufacturing: Materials. is resists bending and. to determine the relative strengths of the Because of the nature of fiber strengths. the fiber by the matrix. The typical criti- However. The length of the fibers at this fore. it is difficult to predict theoretically. therefore. (0.3 cm) wide. This pulled in small increments and inspected situation requires. This much smaller than the standard tensile test shearing action is understood by noting that specimen. (1. that a shear after each pull. the top of the sample is in com. and Applications . In Equation 8-5. The fiber will begin to break plane be located within the sample at the into small segments as load is transferred to place where compression changes to tension. (7. there. Methods. the short beam shear sample 3 in.6 cm) long and .236 8: Reinforcements minimum length at which the matrix can- not transmit enough tensile stress to break the fiber.0016 substantially the same. which is prepared as a micro-tensile test specimen. capsulating a single fiber in a matrix sample. point is the critical length. Short beam shear test. The equation relating the critical length and the strength between the matrix and the fiber is: T d Uc  c (8-4) 2lc where: Tc = strength between the matrix and the fiber (shear strength) Sc = strength of the fiber (ultimate tensile strength) d = diameter of the fiber lc = critical length The shear strength is inversely proportional to the critical length so small critical lengths indicate good adhesion. usually about force is applied. matrix has fully cured. instead. After the beam shear. the fiber By being short and thick. Eventually.5 in. and averaged: The embedded single filament test de- pends on the determination of the critical d fiber length. That is. the short beam segments become so small that the matrix shear sample forces that shearing action to cannot transfer sufficient force onto them be the major force within the sample. The critical length is determined by en- Figure 8-22. summed. the test is with the short beam shear test and. when comparing materials that are cal length for carbon-epoxy fibers is . to cause them to fracture. this test is excellent in. concluded. the sample. is Embedded Single Filament Test measured. including the short men is illustrated in Figure 8-23.041 mm). shears. The embedded fiber test speci- in all flexural samples. Sc. Figure 8-24a. ment. The intensity of the fiber pat. so. When the fi. carbon. continuous and the fiber breaks. The most common types of failures for polymer matrix composites with high- modulus fibers (such as fiberglass. a charac. circumstance and reflects a weak fiber-ma- tern (sheath) seems to be proportional to the trix bond. the composite fails in its basic allows calculation of the interfacial shear purpose. which arises because points of the composite are at the fibers of the stresses induced in the sample by the themselves. pattern develops into a non-nodal pattern. the birefringence as matrix-fiber separation (Figure 8-24b). friction different from the polymeric matrices. which depend on the effective- ness of the bond and the relative strength and stiffness of the matrix and the reinforce- Figure 8-23. ceramic matrix composites is somewhat bers. It looks like the fiber which the fibers break. The second failure mode is referred to ber fracture is complete. matrix is strong. The matrix has transferred Once the fiber begins to fracture. During tensile pulling it stretches and suggesting separation of the bond between when the bond to the fiber fails. The matrix recedes from the fiber bond strength. the breakage optical birefringence. moduli of the matrix and the reinforce- As a result. This is an undesirable light pattern. the development of the sheath is rapid fiber. The third failure mode is fiber pullout Micro-indentation Test (Figure 8-24c). In this case. the bond be- Another method recently developed to tween the matrix and the fiber is poor. the load onto the fibers and has stayed in teristic birefringence pattern develops at contact with the fibers to the stress level at the broken fiber ends. In this case the matrix separates from the that is. longer breaking can be facilitated by using In the first. the matrix the matrix from the fiber.8: Reinforcements 237 freedom in sample selection and reduces standard deviation in the testing. and Applications . The birefringence is observed by mode for maximum strength and indicates viewing the sample between crossed-polar. Little measure the fiber/matrix bond strength is or no energy is transferred to the fibers and. the micro indentation test. Three segments and the point at which they are no different failure modes are depicted. the test method allows greater ments are often nearly the same. Failure Modes of the Fiber/Matrix Bond The nature of the bond between the fiber and the matrix results in several different failure modes. segment is sheathed in light. Methods. that the bond between the fibers and the izing filters and using monochromatic light. when the bond strength is because it has greater elongation than the low. stress and takes into account factors such The nature of failures for metal and as: local geometric distribution of the fi. Observation of the lengths of the fiber and aramid) are shown in Figure 8-24. This method therefore. the bond between the matrix the fiber segments in a single. pulls back elastically. The failure Fundamentals of Composites Manufacturing: Materials. That is. Embedded single filament test. the sheath appears to surround all fiber. and metal and ceramic matrix composites the residual stresses due to thermal loading. In between the indenter and the fiber. shape and size of the indenter. This is the preferred failure pulling. While this composite can absorb high metal matrix composite in which the bonds amounts of energy and can be of benefit for between the matrix and the reinforcement ballistic protection. Figure 8-25. Common failure modes for polymeric matrix composites. ment of properties from the inclusion of an ite failures. failure and the lack of failure of the matrix. and Applications . modes of these materials are illustrated in most desired for structural applications. Note the random nature of the fiber for structural applications. In particu- Fundamentals of Composites Manufacturing: Materials.238 8: Reinforcements Figure 8-24. In Figure 8-25c the matrix fails before the Figure 8-25a shows the fiber failure of a fibers. Figures 8-25b The most obvious and desired improve- and 8-25c illustrate ceramic matrix compos. This failure point is the situation just prior Influence of Coupling Agent to the failure of the matrix. This is the case crease in mechanical properties. it would not be chosen are good. Methods. In Figure 8-25b the matrix and effective fiber surface treatment is an in- fiber fail simultaneously. the of a coupling agent that enhances the bond strength and modulus are improved. to increase the strength and the modulus of A composite without sizing can be compared the composite by about 50%. As ever. The sized compos- Another interesting trend is the effect of ite is substantially superior to the composite annealing. improves the strength and the modulus of Another property that can be improved the composite.8: Reinforcements 239 Figure 8-25. Annealing is exposing the com. the effect of annealing is not as great as expected. The effect of sizing is roughly with sizing is the resistance to cyclic fatigue. without sizing in its retention of properties posite to a moderately hot temperature above (applied stress) and that improvement in- room temperature but not close to the melting creases with the number of cycles. How- between the matrix and the fiber surface. Methods. it is hoped that both tensile strength and point or decomposition temperature. to a composite with sizing. and Applications . Fundamentals of Composites Manufacturing: Materials. When modulus will be improved by the addition a composite is annealed (or post-cured). Failure modes for metal and ceramic matrix composites. lar. the addition of the sizing greatly the improvement achieved with sizing. through experimental testing. Then. This capability is related directly potential of bodily harm. chosen to specifically counteract a particular One requirement is that the material must threat. Ballistic protection. such as energy of the projectile and. if layered thick enough. Therefore. therefore. but they are not tough and is dependent on several factors. the materials like aramid (Kevlar®) or similar number of layers to stop each particular strong fibers will work. They are naturally tough 240 grain materials and. This restriction leads to other the impact energy. flexibility. the force of the Threat Number of Ammunition bullet must not be so intense that it breaks Level Layers Stopped bones. flexural strength of the material. Sample threat levels It is important to note that strength. The material must dissipate the energy 357 sufficiently and in a short enough time that magnum the body will not be harmed. the threat level is iden- be noted—the material must be flexible. into cloth) stacked to the thickness desired However.30-06 armor-piercing round. to the strength of the material. realistically the personal armor and then sewn into cloth pockets. this requirement.240 8: Reinforcements CASE STUDY 8-1 Moreover. absorb energy. tified so that the user will be aware of the Thirdly. The number of layers is requirements of the anti-ballistic material. tion. they have been shown to spread Bullet-proof Vests the impact energy laterally with great ef- ficiency. almost any mate- They are sheets of fibers (usually woven rial. but another requirement Table 8-6.22 be strong enough that a reasonable thickness rifle bullet or a . The sliding of the feel like a medieval knight encased in hard layers over each other also helps to spread steel armor. For instance. have strength sufficient to stop ballistic personal armor (bullet-proof vests) the projectiles. Many mate- Most commonly. the material must be light weight. or causes 2A 22 9 mm other bodily trauma. sess this property. the shrapnel). will stop the bullets. In this regard. are illustrated in Table 8-6. Methods. the threat may be a . Other fibers. That is. from steel to aramid cloth. These will prevent the bullet from penetrating. will satisfy let-proof vests are not encased in a matrix. and light weight are not the only requirements. bullet Fundamentals of Composites Manufacturing: Materials. injures internal organs. therefore. The most do not spread the energy. Aramid and UHMWPE fibers have been shown to pos. This gives must be reasonably thin and pliable so that the flexibility desired and the thickness re- the individual wearing the vest does not quired to stop the bullets. Carbon and glass obvious factor is that the anti-ballistic ma- fibers tend to break when they are hit. the second restriction must vest is purchased. is that the impact of the bullet must not do major bodily harm. the fibers used in bul- rials. But so will steel threat is determined. 3A 40 Wad cutter. In fact. such as carbon or The ability of a material to serve as anti- fiberglass. 2 32 44 magnum. This terial must withstand the penetration of results in the transfer of much of the impact the bullet (or other ballistic device. the thick- Both threats are measured by the weight ness required is directly proportional to the of the projectile and its velocity of travel. When a bullet-proof plates. and Applications . Hence. This requirement is usually stated in terms of energy dissipa. would suffice. product’s limitations. ing while the fibers are held under ten- impact projectiles). reinforcements and occasionally with Some of the key learning points in the epoxy. Putting it simply. the better they have high moduli and strengths. Methods. The high cost of the boron and the fibers are closely examined during the SiC fibers limits their use even though design process. Thus the composite proper. Carbon fibers have high specific further developments will continue. Some of the layers applications). S-glass (including the improved of the composite. as the sub- of the composite. the needs for armor and the increas. These fibers When fiber reinforcements are put into are tougher than those made of glass or composites. some might • Carbon fibers are the most prevalent be polymeric matrix materials (especially fibers for critical or high-performance those that are shaped). the overall strength. and corrosion-resistant shaped and rigid. An interphase region S2-glass). The major types • The bond between the matrix and rein- of glass fibers for composites are E. strength. Since the threat plications except where there is a high for a vehicle is often more severe. While the technology to sion or by spinning directly from a pitch protect vehicles has already reached a high (carbonaceous mass). would be non-matrix material. all the volume. the types priority on performance. because of their sition using other high-modulus fibers. are modified by the fibers are made by chemical vapor depo- effect of the matrix. However. They are made by pyroliz- be ceramic matrix materials (to stop high. because of cost. the They are used for metal and ceramic more efficient the composite structure. and C-glass. these fibers are used for ballistic pro- ties are a combination of the fiber and the tection. matrix. For example. whis. or on composite properties. Glass fibers of armor are often very elaborate. importance in determining the properties such as tungsten and carbon. often are mainly used for engineering applica- consisting of several layers. Today. Still. and Applications . coupling agent to improve mechanical • Glass fibers are the most widely used of properties. and often do. all reinforcements. the physical properties of strates. between Fundamentals of Composites Manufacturing: Materials. strength and specific stiffness. impart these properties. and graphite fibers are essentially the ing sophistication of weapons suggest that same. • Boron and silicon carbide continuous modulus. or particles. They need the matrix to properties. each of which tions (as opposed to high-performance has a different capability. Because of their high toughness creased because the fiber does not occupy and ability to spread energy laterally. specifically formulated for their electri- contain a matrix. Therefore. the physical properties of the fibers. helmets are cal. which are all formed by the sizing material. carbon. forcement is critical to the performance glass.8: Reinforcements 241 Other armor types may. finish. and so on. study of fibers are as follows: • Fiber strength decreases greatly in the • Reinforcements can be fibers. and others might applications. the overall properties are de. • The most common organic fibers are SUMMARY aramid and UHMWPE. Fibers are the most ture absorption. presence of surface defects and mois- kers. carbon level. Armor for vehicles E-glass dominates in composite ap- is also shaped and rigid. The surface of fibers important and have the largest effect can be treated with a sizing. 9. Why to handle them carefully. some generalizations 8. 2. The least expensive fibers are glass. changing. jaws and run a tensile test. Note the range of results for each are probably helpful in understanding the length.00/ and the additional processing done to a lb ($17. Compare the range of the results for each fiber length. Spectra fibers tensile strength of glass fibers that are are about the same price as aramids. Note the ultimate tensile strength of the costs of production.07/kg) and general fibers are about $8. 2. 1.242 8: Reinforcements the fiber and the matrix. [2.20/kg). a wide range of prices depending.5 cm]) versus those that are long (over 10 in. [25 LABORATORY EXPERIMENT 8-1 cm]). sizings. glass fibers of different lengths with Procedure: aramid fibers of the same length. • Tests to determine the strength of the 5. If available. 1. that is.00/lb rod and a fiber in regard to properties ($33. and embedded single so that there is no slippage. • Coupling agents. Be careful range for fiberglass filaments. Methods. short (less than 1 in. Why would you Fiber Length Effects expect these differences? Objective: Discover the differences in 3. and Applications . However. length. Because the total costs of fibers are determined by the market and 7. Cut 10 of the filaments to 10-in. lengths. and industrial applications. Select 15 single filaments from a tow of Compare the range of values with the fiberglass or carbon fibers. transverse tensile. Plot the average tensile strength versus $1. 3. Average the tensile strengths for each ous fibers. 11. Compare the differences that would the tensile strength of fibers as a function be expected in the tensile strength of of fiber length. they are constantly each filament. tensile test machine that will allow clude fiber pullout. finishes. Aramid fibers cost about the fiber. lengths. strength and most other mechanical 4. repeat the test with aramid on the amount of certification and testing fibers and compare the results. gripping of each filament individually short beam shear. Cut 10 of the filaments to 4-in. (25 cm) tulated and described. 6. medicine. Carefully clamp each filament into the Costs of fibers are an issue in most com. filament. Fibers for aerospace and military applications require far more certi- fication and testing than those sold for use in QUESTIONS sports. has been pos. (15 cm) and surface treatments improve shear lengths.07/kg). in part.00/lb ($33. They usually have a selling price in the vicinity of 10. Describe the differences expected in the around $15.64/kg). posite applications. would you expect these differences? Fundamentals of Composites Manufacturing: Materials. (10 cm) properties of composites. Prepare a fixture for the jaws of the bond between the matrix and fiber in. Distinguish between a finely extruded Military/aerospace fibers are about $15. that must be done.00/lb ($2. same as the high-end carbon fibers. Cut 10 of the filaments to 6-in. general relationships of the prices of the vari. Carbon fibers sell over length for the fibers. Dictionary of Plastics. 1987. rials Park. John Wiley and Sons. Materials to Composite Materials.D. When would aramid fibers be used in and Graphite Fiber Composites. 2005. W.8: Reinforcements 243 4. Gilbert and Rowe.. John W. Delmonte. Surface Properties of Carbon Fibers and Dearborn.L. “Composites. State the purposes for sizings.. Francis Group (CRC title). New York: Interscience BIBLIOGRAPHY Publishers. Technology of Carbon 6. Lee. (ed. manufacturing method using magnetic George. PA: 5. 1987. (ed. Karyn L. based and PAN-based carbon fibers. Handbook strengths. R. Mackenzie. Engineered Mate. George. pp.” NASA Engineers. Reinhold.M. 1982. L. their Composites. Stuart M. 2000. 1961. Roop boron fibers. Based on Real Time Simulation. New York: Mar- 8. OH: Science and Engineering. Peters.. New York: Van Nostrand 11. the matrix as compared to an inter. J. Andrew. Explor- whiskers as reinforcements. Issue 3. OH: ASM International.” Mate- Society of Manufacturing Engineers (SME). finishes.D. Jr. Peter.. and Schalek. 19. Inc. Describe the advantages of three Publishers. and Jensen. Inc. 1. of Composites. Carbon Fiber.” Journal of Morgan. 1978. John. Inc. Drzal. R. 1987. and Processing.sme. 7. types of tests for fiber/matrix bond Lubin. 5th Ed. www. Thomas. Carbon Fibers and ASTM International. 3rd Ed. (ed. 2005. rials Handbook. and Drazl. “Fiber-Matrix Adhesion Measured by Fiber Glass. Lancaster. Mohr. Describe the differences between pitch. MI: Society of Manufacturing Their Adhesion to Organic Polymers. “Stress Transfer in Single Fiber/Resin NJ: Prentice-Hall. New York: place of carbon fibers? Van Nostrand Reinhold. Materials Park. Describe the concept of an interphase Progress Towards Its Marketplace Pres- between the fiber coupling agent and ence. Describe a possible application and a cel Dekker.T. Plastics: Materials Bascomb. A. A New Dictionary of Chemistry. Describe the method of manufacture for Donnet. Miall. vantages of natural fibers. “The Composites Manufacturing video series. Technomic Publishing Co. International face. New York: VCH 10. Al-Ostaz. Upper Saddle River. Engineers’ Guide Callister. Strong.). 3rd Ed. 1993. Contractor Report 4084. Tensile Tests..” Report for MFG 355. July. A.. 1986. Methods. Vol. 2004.T. James F. “Composite Materials” DVD from the Bascomb. ing Its Mechanical Properties and Reviewing 9. Inc. Wheeton.. Whittington’s and coupling agents.org/cmvs.). 1984. August 12. Carley. New York: American Society for Metals. “Spider Silk. Chand. Boca Raton. Dean M.” Journal of Adhesion. 1. Brent. Fundamentals of Composites Manufacturing: Materials. FL: Taylor & ASM International. New York: Van Nostrand the Micro-Indentation Test: Data Reduction Reinhold. L. William P. 3rd Ed. 1991. and Applications .). W. 2002. Encyclopedia of Composites. and 219–239. 2006. 1981. Vol. William D. Jean-Baptiste and Bansal. List three advantages and three disad. tows. ments are simply too fragile and small to be forcement in the final properties of the used individually.) • Preforms • Hybrids FILAMENTS. precursor fibers are formed in other forms. Others forms a continuous filament. rovings. Despite the fact developed over the centuries by the textile that most fiber reinforcements are formed industry and the composites industry has as single filaments. Some the liquid raw material through a metal of these forms are essentially available as die with many holes in it where each hole produced by the fiber manufacturer. the form in which that reinforce. and that might be affected by the form and the yarns type of process that might be used to make • Woven and knitted fabrics (cloth) a composite structure using that particular • Non-woven fabrics (mat) type of reinforcement form. mat. however. the Reinforcements are sold and used in filaments are usually made by passing composites in many different forms. Even A few comments are appropriate here more important. an excellent review of the forms of reinforce- sional laminates ments used in composites [SME 2005]. In the case of are converted into cloth. reinforce- ments are made as single filaments in a INTRODUCTION process called spinning. For efficiency. These technologies have been this way and then converted. (The Society of Manufacturing Engineers [SME] produces • Prepregs videos that complement this text.” This term is used of the form of the reinforcement on the in both precise and general terminology. Still other forms have been de. nature of filaments. strands. Fila- Because of the importance of the rein. This chapter examines the following Therefore.1: Introduction to Composites 245 9 Reinforcement Forms CHAPTER OVERVIEW process by which the composite is made. • Whiskers ROVINGS. STRANDS. They offer • Braided. used as single filaments in either composite veloped specifically for use in composites. or a variety of carbon fiber. TOWS. keep in mind the properties of the composite • Filaments. these single fibers are ment is used makes a major difference in sometimes called monofilaments. The Fundamentals of Composites Manufacturing: Materials. stitched. the characteristics of the composite. and Applications 245 . AND YARNS As discussed in Chapter Eight. is the influence about the word “fiber. they are almost never shared them. and three-dimen. as the various types of reinforce- concepts: ment forms are explored in this chapter. To emphasize the solitary composite. Methods. applications or textile applications. the group is called in which the length is substantially greater a yarn. the standard designation given in Table ing and co-processing. and a length of at least . the fiberglass When formed. aramid.5 cm). Hence. Below that the capabilities of the fiber manufacturer. oc. such as weaving and knitting. Fibers of diameters larger than K industry.246 9: Reinforcement Forms precise definition refers to a single filament the fibers in the bundle. a fiber has a high of continuous fibers. If the strand of fibers is twisted.3–10.0S.20 in. These chopped fibers are called staple fibers. these fibers • C = the type of filament (the example is are often blended with cotton or wool fi. fibers are usually considered to have purchaser. the material is called whiskers. the group of filaments is called a roving. of their tendency to break. Fiberglass manufacturers have developed a As indicated previously. aspect ratio. • 150 = the filament count (example is ester chapter and will be discussed further 15. However. ECG 150 3/2 3. Prac. etc.). They are gathered together into a group and then wound onto a spool or processed further (pos- sibly chopped into staple fibers). length. count of the filaments. the group of filaments is called a tow (pronounced “toh”). Various continuous fiber forms. they are usually continuous.2 C [C-glass] or S [S-glass] identifier).00 in. The identification system in the United quent processing of the fibers in processes States would identify a yarn as. In the composites 9-1. hundreds and sometimes thousands of filaments emerge from the many holes in a single spinneret. which are naturally in the length of be staple fibers and textured fibers). which helps keep Figure 9-1. In the textile industry. cm). when synthetic system to identify the critical parameters for fibers are made. (0. For advanced fibers (carbon. ultra-high- molecular-weight polyethylene [UHMWPE]. • E = the type of glass (the example rep- the fibers are chopped into shorter lengths. where this code represents casionally it is desired to have fibers that are the following: not continuous but longer than whiskers. their products (BGF Industries. staple fibers. This continuous nature facilitates subse. Having all the materials in • G = the filament diameter according to the blend the same length simplifies blend. Fundamentals of Composites Manufacturing: Materials. However. Figure 9-1 depicts the various forms than the diameter.000 yards/lb). The group into which the fibers have been gathered has a specific name. The filament group also can be called a strand. for example.50–4. and Applications . the term “fibers” is The diameter of the filaments and the used generically for any single or group of number of filaments in a strand varies filaments that have a high aspect ratio. staple fibers are used in mat (to be are rarely used in composites because discussed later in this chapter) and in mold. Inc. ing compounds (discussed briefly in the poly. (1. resents E-glass but others could use a usually in the range of . the manufacturing concept. So. Methods. Rather than a specific in the one on compression molding). 1997). In the case of fiberglass. which applies to both advanced and glass fibers. greatly depending on the specifications of the tically. a continuous filament but others could bers. 000. carry designations such as AS4. B 14 (3. another H 39 (10) term. These values help the purchaser match the material with the E 28 (7) actual manufacturing process. These and many other processes bundle (the example is two plies of a will be discussed in later chapters in this 3-strand construction (total of 6 basic book. in a bath of resin and then laid down as • 3/2 = the number of strands twisted continuous strands onto a mandrel (filament together/the number of plies in the total winding). 6. • Fiber types. especially with standard tex- tile fibers such as nylon and rayon. C 18 (4.000.5) fiber length on the spool. In the weaving IM7. core inside diameter. The strands may be fed into systems where they are chopped system uses a number easily deter. Methods. winding and pultrusion. core length. Selected diameter designations • Filament diameters are typically in the for fiberglass products (U. A denier is the weight. the fibers are aligned in the warp.000). × 10–5 Code the spool or creel onto which the fibers have (micron) been wound. from BGF Industries.S. and coated with resin (spray-up) or coated mined by weight. (5–7 micron) range. process. and 50. these conventions are based on the way turer. Nominal Filament Fiberglass and advanced fiber manufac- Designation turers may also designate the dimensions of Diameter. fibers are arranged in a parallel and HR40. The spool’s outside diameter. Dating from the early days of weaving. G 35 (9) Occasionally. of 9. longitudi- actual count is given (typical values are nal. and number of spools per box are some of the values that D 23 (5) would typically be used. K-1100. The machine 3.000. The • To indicate the umber of filaments. and Applications . 12.5) weight. tion of the twist (example is 3 turns per inch in the S direction).000 K 51 (13) meters of fiber. WOVEN AND KNITTED FABRICS (CLOTH) Advanced fiber manufacturers typically identify the following parameters for their Some directional conventions have been products: developed to simplify the discussion of fab- rics.0S = the number of turns per inch in continuous fiber processes such as filament the twist of the final yarn and the direc. Inc.” is used to identify the fibers. or machine direction. T-650/35. A 7-denier fiber is thinner U 98 (25) than a 12-denier fiber. system)* 20 to 30 × 10–5 in. fabrics are woven on a loom. unique to each manufac.9: Reinforcement Forms 247 Table 9-1. array on a loom between two supports. is in weaving and knitting fabrics and in • 3. The most important use of strands strands). P-55S. “denier. brochure (12/97) Strands are used in many composite part manufacturing processes. 34-700. Fundamentals of Composites Manufacturing: Materials. in. This measure is simi- lar to the filament count measurement used * This table and the example in the text were derived to designate fiberglass strands. direction is usually 0°. in grams. the means is simply given in Figure 9-2 where a roll of material manually interlacing the crossing fibers.248 9: Reinforcement Forms A means is provided for other fibers to be The directional conventions for woven interwoven above and below the warp fibers. the interweaving pro. The warp count and positive bias and to the left is negative bias. and Applications . These interwoven. woof. a term from the textile crossing fibers are called the weft. In general. bias. tion of the roll. In is illustrated. The edges of the roll are Another direction is one that cuts across often treated to prevent unraveling. Fundamentals of Composites Manufacturing: Materials. or transverse direction fibers. Note that the warp fibers are in fill. Methods. they are sometimes cess is highly automated. These the fibers at a 45° angle. no the right of the machine direction is called selvage edge is created. Because fabrics are often sold more complex looms. Generally the bias direction toward when fabrics are made for composites. called broad goods. These are In primitive weaving. This is called the edges are called the selvage. fabric also pertain to rolls of fabric. industry. Roll terminology. These the long direction of the roll and the fill or fibers are arranged at 90° to the machine weft fibers are in the cross or short direc- direction. on rolls and are planar. fill count are simply the number of strands Figure 9-2. These characteristics are not just Textile manufacturers have developed dependent on the fiber’s properties but on fabrics with various handling and mechanical the way in which the fibers are formed into the characteristics such as openness. Openness is made by interlacing strands in an al- inversely related to the warp and fill counts. In Drape is the ability of a fabric to hang with. openness is a relative common weaving patterns. In fabrics. and Applications . Figure 9-3 illustrates some of the most strength. shower curtains. and the per inch (or centimeter). drape. is packed the fibers are in the array. Fabric construction forms. drape is the ability of the fabric to conform to the shape of the Types of Weaves mold. out creases and to form graceful folds when These are usually expressed as yarns or ends used as draperies. ternating over-and-under pattern. the sim- fibers. and cloth. Methods. it refers to how tightly plest of all the weaving patterns.9: Reinforcement Forms 249 in the warp and fill directions respectively. In composites. there is one warp fiber for Figure 9-3. Fundamentals of Composites Manufacturing: Materials. like. In other words. other words. description of the space between the parallel • Plain weave (Figure 9-3a). care must be taken in the printed circuit boards. Plain weave used.250 9: Reinforcement Forms one fill fiber without skipping. etc. 5 harness. The pattern gives uniform strands (4 harness. it is usually left moderately other weaves so wetting and air removal open so resin penetration and air re. open-weave the strength of twill fabric is slightly fabric. drape on mild contours. more warp fibers in such a way that the fabric has the appearance of diagonal • Leno weave (Figure 9-3f) is produced (bias) lines. rather stiff weave. radomes. diving boards. There is reduced crimp and so distortion of low-count. and can conform to complex contours and spherical shapes. Methods. fibers pass over one and under two or and aircraft ducts. Satin weaves and is. skis. the part. provid- weaves with only a small reduction in ing a locked effect. Basket weave uses are similar to than plain or basket weaves. Crossover (crimp) in the warp directions than a plain points can pinch the fibers and cause weave. The surface rapid buildup of plies. therefore. It also provides heavy fabrics for higher than plain weaves. A high is the most resistant to in-plane shear strand density is possible. when strand size and count for warp This weave has a high degree of drape and fill are the same. The addi. can be a problem unless a vacuum is moval are fair to good.) Satin weave is • Basket weave (Figure 9-3b) has a pat- used extensively in the aircraft industry tern similar to plain weave except that where complex shapes are common. and under two fill strands. Because the weave satin weave is also less open than most is stable. ducts. Less stable than plain weave. highly pliable. narrow fabrics. pattern is not strictly repeated. Because the fabrics are non-sym- fabrics are used for flat laminates. (There is more on this subject in the chapter on design. The fabric is flatter and • Crowfoot weave (Figure 9-3e) is stronger than an equivalent weight a satin weave in which the stagger and count of plain weave. This weave and other contoured surfaces. The crowfoot and satin weaves defects that diminish the strength of the can incorporate a higher strand count fabric. • Satin or harness weave (Figure 9-3d) mum fabric stability and firmness with is similar to the twill weave but has one minimum strand slippage results from warp strand weaving over four or more this weave. The leno weave is of twill-based composites is smoother used as an inner core for support of thin than plain weave composites. considered to be a are flat. This weave has superior by having two parallel warp strands wet-out and drape compared to plain twisted around each fill strand. and Applications . This weave reduces stability. This weave type and stretch in all directions. design of the part to ensure that asym- tooling. 8-har- strength in both warp and fill directions ness. This tional strength comes because there produces a weave with improved uni- are fewer crossover points between the directional stability and more strength warp and weft fibers. coatings and for tooling and repairs. The crowfoot weave is • Twill weave (Figure 9-3c) has the fill used for fishing rods. and covering wood structures metric lay-ups do not cause warping of such as boats. Fundamentals of Composites Manufacturing: Materials.) then under one fill strand. The fabric those for plain weave but with better is like other satin weaves. It is two warp strands are woven as one over also used for housings. Maxi. is less stable than plain weave so it is more pliable. metrical. These fab- rics obviously have high strength in the bias directions. In applications such as drive shafts. especially when the device is highly shaped (such as a helmet). These conduits are rarely plications in composites. little time expenditure. other fiber properties for both warp and fill. the transfer of energy within the fabric is excellent and so knitted fabrics are of- ten used in ballistic devices. Moreover. thus in woven fabrics. and directional breaking strengths. other fabrics have special ap. the ability to giving a well-fitted reinforcement with contour these fabrics is exceptional. This desirable property is enhanced by the superior crack-stop- ping capability of knitted fabrics. and Applications . triaxial weaves are highly efficient reinforcements. Knitted fabrics. conditioning. This represents an incredible va- riety. where the loading is chiefly along the 45° axis.9: Reinforcement Forms 251 most often in conjunction with other The contouring capability of knits fabrics. variety of fiber diameters. has been useful in forming parts with complex geometries such as conduits In addition to the conventional woven for aircraft electrical wiring and air products. therefore require a highly complex • The looping pattern of weft knitting mandrel for filament winding or hand (Figure 9-4a) gives fabrics much greater lay-up. Therefore. lished to assist users in obtaining the type Fundamentals of Composites Manufacturing: Materials. These fabrics are straight for more than a foot or so and illustrated in Figure 9-4. thread counts. fabric thicknesses. The knitted fabric can be ap- drape and stretch than can be obtained plied over the mandrel as a sock. areal weights. especially because each manufacturer has a separate group of fabric combinations. They are also highly effective when mixed with traditional woven fabrics to obtain a composite with high strength in all planar directions. • The method for triaxial weaves (Fig- ure 9-4b) moves the warp fibers into the bias directions while leaving the fill fibers in the 90° directions. Hence. Methods. extensive lists of fabrics by vari- ous categories and style numbers are pub- Figure 9-4. Properties Fabric properties can depend upon a host of parameters including the follow- ing: type of weaves. The fibers are bound patterns discussed previously. This material. This can occur when an area of the composite part needs special reinforcement because it is subject to high stresses.5– 7. A light coating of binder is ap- will make special orders if the volume is suf. This material is used when a rapid buildup of reinforcement weight is desired. It also serves as a physical barrier to fiberglass strands that may become promi- nent because of the natural movements of the composite. An economical compromise for the molder would be the use of chopped strand mat. it also would be more costly than the chopped spray-up method. [2.252 9: Reinforcement Forms of fabric desired. uniform fabric. While changing to a woven fabric would likely result in higher physical and mechanical properties. It is comprised of a simple. Methods. mat gives the same quality of reinforcement trated by mentioning two fiberglass fabrics that would be obtained in spray-up but with used widely in composites—one thin and the convenience of a lay-up fabric and only the other thick. The thick material is called a small increase in cost. woven roving. Veil is often applied behind a gel coat to mask the underlying composite material and give a smooth sur- face. a manufacturer of boats may be currently using chopped fiber spray-up (discussed in a later chapter) but would like the convenience of a sheet rein- forcement. The chopped strand The wide variety of fabrics can be illus. For example. most weavers onto a belt.6 cm]) and directing these chopped fibers Figure 9-5. Types of mat. and Applications .) NON-WOVEN FABRICS (MAT) Some composite applications do not require the sophistication of a woven rein- forcement. be handled as a sheet. (Note that some veils are made by non-woven methods as explained in the next section. The thin fabric is veil. Fundamentals of Composites Manufacturing: Materials. is a sheet product made by chopping fiberglass into similar lengths as would be typical for a spray-up operation (1–3 in. plied and dried to create a material that can ficient to justify the setup time. Additionally. shown schematically in Figure 9-5a. It is simply a large-count Chopped strand mat is not as rugged roving material loosely woven into one of the as a woven fabric. The looseness is needed to ensure proper wet-out of the fibers. tight weave made from fine strands so that it appears to be a fine. shorter fibers (in chopped mat). a mat veil would be just as acceptable that are all oriented in one direction. the continuous strand mat is extensively in composites. improved melt and bond the higher-molecular-weight mechanical properties. The product inviting for other non-woven products. strand mat but may not need the properties with non-woven polyethylene. to make mats and. of course.9: Reinforcement Forms 253 loosely and so when handled. The fibers out of materials other than fiberglass. ent molecular weights are deposited onto a Some applications require slightly better belt in much the same way that continuous properties than can be obtained with chopped strand fiberglass mat is made. by product so that the integrity of the mat can DuPont). just as in PREPREGS the case of chopped strand mat. and Applications . The temperature of the strand mat. However. results in some fibers being oriented in For example. have no structural properties and so. and tively fixed geometry of fabrics results in more randomness in fiber direction. marketplace. This material is used as a rugged and can be handled without the loss wrap for buildings and in non-tear envelopes. While it is not used mat. wherein 80% of the load is in one direction. therefore. This is logical because veils a sheet material for ease of manufacture. applying a Advanced reinforcements like carbon and light coat of binder. Fabrics with are moderate and/or multidirectional) has 80% of their fibers in one direction would led to widespread use of chopped strand mat rarely be made and would likely not be stable in the fiberglass reinforced plastics (FRP) enough for practical applications. This material has longer strands than lar-weight polyethylene fibers. is made by swirling continuous strands of fiber onto a moving belt and then. In many cases. no binder is or cannot bear the costs of a woven fabric. which some sub-optimal arrangement of the fibers. in non-composite markets is non-woven some care should be taken in handling the polyethylene. These advanced fibers 33–50% as strong as fabric laminates of usually require more precise control of the comparable thickness. which then the chopped mat and. they are loose It is possible. polyethylene fibers of two differ- be retained. Fundamentals of Composites Manufacturing: Materials. The mat is also more materials together. direction of the fibers than can be obtained ties is because of lower fiber content in the with mats. In this product (Tyvek®. A applied. there may be an application directions that are not required in the load. One could be sprayed with a light binder coating. which is illustrated in Figure rolls is sufficient to melt the lower-molecu- 9-5b. However. which is then dried. difficult to handle. Another method has been developed that The low cost of mats has led to many veil allows designers to optimize the fiber orien- materials being made of mat rather than tation and yet still have the convenience of woven fabrics. the technology is not as durable as woven fabric. even the rela- mat. the bare fibers are not woven. the low Therefore. Since as a woven veil. in most The method is to supply a sheet of fibers cases. However. Therefore. therefore. ing pattern of the part. the designer wants to orient 80% cost and generally acceptable properties for of the fibers in that direction so the design many parts (especially those in which loads can be as efficient as possible. Rather. some of the material that has found widespread use fibers may fall from the mat. aramid fibers are often made into woven fab- The composite designer should recognize rics but are rarely made into either chopped that laminates made with mat are only or continuous mats. which is common with chopped among many other uses. the entire sheet is pressed product that fits this niche is continuous between heated rolls. This drop in proper. of fibers. Methods. 254 9: Reinforcement Forms as is done with fiberglass mat products. them carefully into columns and prevents ever. another sheet of resin- other constituents required for full curing. it is important to evaporate the (B-staged) so it is easy to handle does not solvent so that there are no (few) residual run off the fibers. Therefore. another solution to holding the fibers the fibers from crossing over one another. the prepreg line. the time it is from the paper and adheres to the fibers. So. typically 12–24 in. Methods. This method is to Typically. The rolls may from curing prematurely. The thickness of the resin is with the matrix resin. If the entire when the prepreg is rolled up at the end of roll is not consumed during one out-time. it can be applied as a solution. Next. Then the columns are resin and use the same amount desired in carefully drawn together into a sheet so the completed composite. pre. The sand- Since the resin coating contains everything wich of paper. no additional materials can be added ties of the final part. desired in the prepreg. the resin coating After the fibers are properly placed on the must include all of the hardening agent and resin-coated paper. a comb-like device is used to col- coat the unidirectional fibers with the matrix limate the fibers. most prepregs excessive curing of the resin. volatiles that might complicate the final Because the resin is already in place on the cure of the resin or compromise the proper- fibers. the prepregs through rolls where the resin is pressed into must be kept refrigerated to prevent them the fibers to achieve wet-out. Some prepreg to prevent the rolled up layers from new developments in resin technology have touching each other and sticking together. sheets is usually epoxy. resin. This resin because they are fibers pre-impregnated is the matrix. Beyond that time. and fibers then passes needed for curing the resin. in place is now preferred. It is partially cured However. nient widths. (183 cm) or the maximum width of Fundamentals of Composites Manufacturing: Materials. Typically. out of the freezer is carefully noted. These materials are called prepregs layer of resin has been applied. they are available in widths ing fibers in a single direction. (7.6 cm) and as wide as fibers are passed through a device that aligns 72 in. Because the amount of time that a cold storage facility. coated paper is applied on top. The other piece of paper the remainder is placed back in the freezer on which the prepreg sits is wound with the so that the shelf life can be preserved. the resin separates is removed from the freezer. This Usually the top sheet of paper is removed is called the roll’s out-time. The fully wet- must be recertified as acceptable or simply ted prepreg is then wound up and shipped to discarded. to the prepregs. The paper used in this a prepreg is exposed to room temperature is process is coated with silicone so that when critical to its shelf life. that is. Some of these claim that prepreg is used. (30–61 cm) Prepregs are made by carefully collimat. the sheet of fibers is directed onto The resin holds the fibers together in a sheet the surface of a paper sheet to which a thin form. even after a year without refrigeration no Prepregs are supplied in rolls of conve- significant curing has resulted. be heated to facilitate wet-out but the heat- pregs are kept at 0° F (–18° C) for up to 6 ing must be carefully controlled to prevent months. resin needs to be added to these materials. the as narrow as 3 in. wide. How. and Applications . Prepregs in which the carefully controlled so that the amount fibers are all in the same direction are called is equivalent to the final resin content unidirectional tapes. If a viscous resin is The resin coating the fibers in prepreg to be used. However. resulted in epoxy resins that have much This final paper layer is removed when the longer shelf lives. no additional that there are no gaps between the fibers. when a roll of prepreg the prepreg is formed. length. of subsequent manufacturing processes. However. and Applications . unifor.9: Reinforcement Forms 255 the machine on which the prepreg is made. three-dimensional outputs from two-di- the resin. prepregs are now made with near-net to this dimensional conversion. of lay-up and curing of these laminar prepreg Prepregs also can be made with tow. allowing only a small excess some of the raw material suppliers have of resin to accommodate the resin bleed been inventive in the forms they supply and Fundamentals of Composites Manufacturing: Materials. can have improved drape over the permits shaping a prepreg to fit a mold of unidirectional material. An irony (and difficulty) of making com- Traditionally the resin content of the posite products is that they are usually prepreg is given as a weight percentage.(or fiber-) volume percentage is mensional inputs. three-dimensional but the raw materials (re- whereas the resin content of the finished inforcements) used to make them are gener- part is given as a volume percentage. creased. Thankfully. product is desired. and storage and shelf life. The methods tapes are used. a designer must be able to envision age is easy to measure and control. width. prepreg tows have the advantage of include the following: fiber weight per unit carefully controlled resin-fiber content and. which are often built-up laminates. process that occurs in bagging (discussed The lengths are usually specified so that the in Chapter 14). splices. The property of flexibility is ing (crossover) of fibers in woven goods called drape (using the same term as is used diminishes the strength of the prepregs to describe the flexibility and conformability compared to unidirectional tapes. the trend has cal conversion from raw materials to the been toward lower resin content so that final product are important to the success the specific strength of the composite is in. Therefore. the resin-weight percent. viscosity curve with temperature). than most wet impregnation processes. Thus reinforcements are preferred for finished laminates because it layered to get three-dimensional products. depending on the type of Prepregs have a degree of flexibility. unidirectional prepreg This stickiness is called tack. These have some obvious handling Properties advantages and. resin content. of textiles). flow of the resin (that is. This weave. is related directly to the mechanical prop. Because consistent removal of large Composite manufacturers struggle with uni- excesses of resin has become a costly prob. These products will be discussed in a later chapter pre-coated materials are used in automated on vacuum bag lay-up methods. of width. However. Some of the requirements material.and two-dimensional linear or sheet explanation for this is simply that when the materials. higher precision in this property applied from a solution). operations where the application of a wet resin The specifications for prepreg materials would be impractical. workman- ship (drape). formity in thickness and other issues related lem. volatile content (if the resin was therefore. tack. erties through laminate theory (discussed The efficiency and uniformity of the physi- in Chapter 11). Therefore. Methods. STITCHED. the crimp- complex shape. prepregs can be made with woven fabrics. alignment (no fiber crossovers). parts. The prepregs also have a sticky when the optimum performance in a laminar surface because the resin is not fully cured. Historically. desired. DIMENSIONAL LAMINATES mity. The ally one. As with other prepreg are stringent. in making composite prepreg is made. tack retention. weight of the roll is not excessive for easy If a more dimensionally stable sheet is handling. resin contents. AND THREE- gaps/spacing. BRAIDED. If desired. However. several absorbing nature of the composite is further strands are alternated over and under each enhanced because when fibers do start to other to create either a flat or tubular fab. The energy- dimensional materials. thus putting load cess for some composite parts and has been on the longer fibers. Therefore. can. Braids can be built up to create a pseudo. and bicycle frames. turbofan guide vanes. water mandrel. Braided structures have the advantage of which are at the characteristic angle of the bias fiber directions. centuries. aircraft horizontal being explored by composite manufactur. This pre-conversion to higher di. A potential problem. some strands in the braid performance when they are subjected to can be oriented in the 0° direction to give shear forces. These higher-dimensional materi- be covered with braided material. the lost load is again transferred to other ric (like wrapping a maypole or. and Applications .256 9: Reinforcement Forms have already made some of the dimensional When a braided structure is put in ten- conversion. mo- ers. is the loss in Using methodology developed over the properties because of crimping. in that no fibers are actually oriented in the direction perpendicular to the plane of Stitched Laminates the braid. Therefore. the failure mechanism of braiding hair). The inclusion of braided reinforcements include hockey sticks computer controls for this equipment has (see the case study at the end of this chapter). skis. energy-absorbent structures. reinforcement fabrics. the shorter fibers experience the load mensions simplifies the manufacturing pro. therefore. thus giving a shape to the mate. The higher-dimensional materials may also three-dimensional structure. Braiding need not be some three-dimensionality is often highly linear. thus als can usually be handled more efficiently allowing easy buildup of fibers for oddly than lower-dimensional fibers or sheets and shaped products. rial not generally possible with woven or Creating fiber forms that already have knitted fabrics. most of the fibers participate in Braided Reinforcements sharing the load. Therefore. of course. between the strands. sion. furniture. automotive parts. often al- longitudinal strength as well. curved mandrels can desirable. This phenomenon leads Braids are strictly another form of fabric to good mechanical properties and highly although they are usually perceived as three. the relatively stiff matrix limiting the dimen- sional change of the composite structure. This occurs even with shown to result in improved properties. strength is in the direction of the fibers. Because of the many crossover points. braids The direction of maximum reinforcement also have excellent crack-stopping capability. In braiding. led to some amazing options. This is called ultimately improve the mechanical proper- “pseudo” because it is still largely laminar ties of parts. canoe oars. often give indications of imminent failure. gives a characteristic angle for the braid. braids are now made on highly Some of the composite products that use automated equipment. the thickness yields a Composite manufacturers discovered strong product that has many characteristics that if they stitched through a lay-up of of a truly three-dimensional product. resulting in improved braid. The direction of crossover a braided composite is progressive breakage. which are prosthetics. Some braids are made on a core or torcycle seats. stabilizers. fibers. Methods. first and then straighten. some additional ben- Fundamentals of Composites Manufacturing: Materials. reduce manufacturing time. leviated by good braid design. which is affected by which absorbs ever-greater energy and can the number of strands being woven together. fail. Be. This involves stitching laminate is called a trans-laminar rein. The result is an Fundamentals of Composites Manufacturing: Materials. It involves stitching across the woven fabrics have become practical as entire laminate. more relatively weak matrix to hold the laminates complex arrangements of the plies can together in the perpendicular direction.9: Reinforcement Forms 257 eficial properties could be obtained. the with stitching is intuitively obvious. both larger stitching is. Hence. One example bers. in the thickness or z direction. ing fibers or fabrics through a resin bath Stitching and Z-fiber construction work and then into a mold where the laminate because the normal laminate depends on the is cured. except that a weave is also introduced in ing the amount of stitching will increase the vertical direction. discussed later in this text. re. the construction is especially amount of stray fiber accumulation. which are higher stitching densities (stitches per unit woven at the same time in parallel sheets. increas. These improve the general properties of the lami. Less obvious time for manufacture. This is threads and higher stitching densities lower like having weft fibers across the warp and the in-plane tensile strength. This is generally done to reinforcements for composite parts. These tensile strength in the plane of the laminate. which susceptible to impacts and shear. that is. beneficial properties arise because of the This is not surprising because the stitching orientation of the stitches perpendicular to creates discontinuities in each layer of the the plane of the composite layers. in their other properties. least 5% of the total fiber volume is oriented The second approach to stitching is called perpendicular to the plane of the plies. is the improvement in other processes when Instead of stitching with conventional fi. which will be uous pins or rods to hold the layers together. have a major effect on these two properties in particular. involves draw- This is called Z-fiber construction. increased fracture toughness. When at laminate. the laminates are stitched. thus reducing the nate stays neatly layered. is strength- severely restricted size and growth of impact ened. Also. only in selected areas of the laminate. some three-dimensional stitching. Larger stitching threads and fabrics. of fibers in the perpendicular direction. the joint. The forced composite. is always a problem at the entrance of the inforcements in the perpendicular direction curing die. and Applications . multiple layers of fabric. products are like traditional woven fabrics nate as already mentioned. is pultrusion. In making 3-D woven the properties. the perpendicular to the warp. the selective stitching. there is an improvement in delamination The improvement in laminate handling since the layers are sewn together. an alternate approach is to use discontin. The first is called comprehensive weaving machines. In this case. Clearly. Also. area) are both effective in improving the are simultaneously interlaced with strands interlaminar shear and toughness proper. The stitching of the laminate improves the ease layers do not slide around and the lami- of handling the composite. This process. cause the laminate is brittle (because it is stitching has been shown to reduce the crosslinked). give improved properties in the part. Clearly. while other areas are not compromised damage and edge delamination. and forces are most likely. Three-dimensional Laminates Two approaches are common with stitched With the advent of computer-controlled fabrics. that ties. Methods. Unfortunately. If the fabrics are stitched. most common area where such stitching The benefits in properties realized from might occur is at a joint. the stitching include improved compression after advantages are that the area where shear impact. 9 cm) at the tip. of course. especially carbon fibers.5 in. and aramid fibers together preforms for composite structures. (3. the resin is added and cured. the precursor The application of advanced textile fibers. The concept of a preform is to make a ucts is the lack of crimping. (1. appropriate stiffeners (such as T-sections). Comparisons of the mechanical lacks only the resin and curing to be fully properties of composite parts have shown completed. That additional over interlaced three-dimensional products. The preform products. the reinforce- that 3-D products can have a 30% increase ments are arranged into a form that is the in strength and modulus over otherwise same as the finished product will be when equivalent crimped constructions. Using knitted fabrics. ing an automated stitching and lay-down The three-dimensional woven product has machine as a single unit. stitched together. The completed wing was shown to only 3 minutes with the 3-D weave and to have superior mechanical properties and. woven fabrics. crease in formability (the ability to be draped) unidirectional sheets. This advantage reinforcement package in the shape of the is even more important in three-dimensional final product (or nearly so). Thicknesses varied from this technology.8 cm) at the wing root to less 3-D woven fabric without pleating. and held in place. infused into the preform using a VARTM duced from 45 minutes using 2-D technology technique. a helmet was formed from a over 1. There is one more textile- have some unique advantages over woven. manufacturing concept related to the form braided. greatly reduced manufacturing ing (VARTM) process.75 in. are. and Applications . which has further improved dimensional lay-ups have some advantages composite manufacturing. by creating broad goods that are pre-layered Just as non-woven products. and knitted fabrics. The total than . Said another way. such as polyacrylonitrile (PAN). The entire wing was made from and finishing after molding and generally a stitched preform. That advantage is a dramatic in. This rapid time was costs when compared with traditional 2-D assisted by the much higher resin infusion manufacturing methods. concept is the preform. Methods. This permits because the stiff fibers used in composites. a different approach has often been PREFORMS taken. Also. optimization of the structure.258 9: Reinforcement Forms integrated stack of fabrics bound together The near-net-shape preform was made us- in a three-dimensional array. The layers included mat. The advantages materials for fabrication of a prototype air. carbon. rate of 3-D fabrics when compared to equal All forms of 3-D materials allow easy inclu- thicknesses of traditional 2-D lay-ups. do not adapt well to knitting. the elimination of shaping craft wing. which was shaped with improved uniformity of fiber distribution. sion of various types of reinforcements. are technologies like three-dimensional weav- knitted into the three-dimensional shape and ing and stitching has clearly improved the then the entire structure is carbonized to manufacturing ease of making composites convert the PAN fibers to carbon fibers. non-woven three. in some closed-mold operations like Fundamentals of Composites Manufacturing: Materials. and over equivalent 2-D stacks of material. The major advantage of the non-woven prod. of course. Resin was manufacturing time for the helmet was re. In this new approach. However. such pre- at McDonnell Douglas. Many different another advantage that can be critical for fiber orientations were layered and then some parts. such Knitting also has been adapted to making as glass. the vacuum-assisted resin transfer mold. Because they A major project at Boeing (and previously are made to be in their final shape. in one integrated preform. of the fibers. such as mats. Long Beach) used 3-D forms are called net shape. In this method. In both coverage. fiberglass rial suppliers do the kitting for them. movement of layers during with the thermoforming process. after drying or curing. complex shapes are required. The drawbacks of this system of the part. and then cutting to the final shape production. more parts made on each mold). and holding in the proper lay-up. the final preform is three. the fibers are three-dimensional. Alternately. Methods. the screen. rected fiber performing. The multiple forms speed sheets.9: Reinforcement Forms 259 resin transfer molding (RTM) and compres. then thermoforming to create the shape. Another is that the preform material can be cut and then laid up in the is made with chopped fibers and that could Fundamentals of Composites Manufacturing: Materials. It is then ready to be used in a process for preforms is simply cycle time. As the fibers are directed onto cases. The fibers are deposited three-dimensional. The Sometimes preforms are dictated because. molds that are rotated under the stream of terials like fabrics. Another way of making a two-dimensional The use of preforms depends on issues preform is by laying up materials like mat such as quality. they are sprayed with a binder dimensional because all real. In some that will add the resin and cure the final part. with light stitching. A strong suction at the molding stage the operator does not behind the mold assists in getting uniform have to worry about getting the materials coverage. of course. kitting. mold closing. and prepreg fibers and binder. finished parts so that. Some molders request that mate. shorter cycle time will easily jus. the reason shape. The chopped fibers suppliers have sophisticated cutters and are blown into the chamber and directed other material-handling equipment.or desired preform. This process is called them in place until the binder cures. are held in the preform shape. Some common methods of securing that the layers do not move around in the the layered materials would be with a lightly mold during resin injection. repeatability. The disadvantages of the thermoforming tify the increased costs of making a preform method are the cost of the extra step and because of the high value of the product. preforms are needed to ensure common. based on the nature of on the screen in a way that gives uniform the materials from which it is made. the preform is trimmed to net from being made. mats. and or curing. After ther- the molding cycle would prevent good parts moforming. situations. which can make the preform. In other cases. In a more automated method. applied adhesive. final shape and secured. the the usually higher cost of the thermoform- high value of the molds (and the need to have ing-compatible binder. manufactur. compacting the fibers. The layers are then secured are the high cost of the equipment and the in some fashion to hold them in place and poor compaction of the preform. although this is less sion molding. knits. This roving is directed into a chopper located at is often more efficient because the material the top of a chamber. a Some molders have long practiced a skilled operator uses a chopper gun to direct method of improving efficiency by precutting chopped fibers and resin into a perforated and assembling stacks of material so that mold shaped like the part. and Applications . as light binder in the mat must be compatible cited previously. especially where deep draws and with pinning. onto a perforated screen shaped like the A preform can be thought of as two. that already have a light binder coating and ing efficiency (cycle time). or because Another method of forming a preform the production demands are high and parts using two-dimensional materials is by di- are needed in large volume. the layers of be a problem. Some mod- Two-dimensional preforms are made by els of this equipment have several preform laying up traditional two-dimensional ma. and economics. Fundamentals of Composites Manufacturing: Materials. full integration of from layered two-dimensional materials but. Preforms are required for the RTM process and because of the manufacturing efficiency they afford.260 9: Reinforcement Forms be a problem where strengths need to be in the areas where impact is expected. the machines must stop knitting if the resins are the same in layers of differ- on some needles and continue knitting on ent reinforcements. This has the advantage of improving shaped preforms are useful in processes the average properties of the fabric according such as pultrusion and RTM where the final to the average of the two materials. The advantage of hybrids is that the superior properties of the various reinforcement types can be utilized to optimize the part. For Other hybrids are made by laying a sheet preforms the processes would not just make or fabric of one material on top of others in 3-D weaves. Selective placement of fibers within hybrid placed on the top and bottom of the I-beam composites. of course. they would make 3-D weaves to a laminate. are made directly using one of should be possible. but that can be minimized knitting. the value of the preform also increases because labor can be dramatically reduced. A highly practical application is in an I- beam that will likely be subjected to impact. For example. when materials. some worry making a three-dimensional preform by 3-D of delamination. and similar shapes can be created or knitting different fibers into the same automatically using 3D techniques. Methods. glass with carbon. Three-dimensional I-beams. are Figure 9-6. This sorbing properties because energy dissipa- requires sophistication not present in the tion is increased across layers of dissimilar broad goods products. vests and rigid armor applications. it is a process that is growing rapidly (RTM is discussed in detail in a later chapter). The optimized. the aramid section with the carbon materials in contrast. This has improved energy-ab- a particular net shape—the preform. The hybrid lay-up is illustrated in Figure 9-6. When the 3-D weaving of aramid and UHMWPE are alternated to or knitting is completed. An application of this others. usually as a prepreg sheet. all the while maintaining an even method of using hybrids is in armor. the preform is ready give the highest performance in bullet-proof for resin addition and molding. As the by weaving together reinforcement fibers thickness of the part increases. and Applications . There is. and glass with aramid. These fabric. rest of the I-beam is made of carbon fibers. the 3-D processes discussed previously. HYBRIDS Materials that combine two or more types of reinforcements are called hybrids. Layers tension on all yarns. Typi- cal examples would be carbon with aramid. Three-dimensional preforms are not made If the resins are the same. Another part can be made by simply infusing resin advantage of this technique can be achieved into the preforms and then curing. Aramid fibers. T-stiffened Still other hybrids are made by weaving panels. Hockey stick manufacturers reinforcements in the same sense as fibers reported some fiber buckling in the curve and whiskers. of course. of two different forms. therefore. easily in the braiding process. This eliminates These are the fibers left on the ends of the need for a separate matrix introduction spools. give improved performance in the part. Hence. flat particle. The first is milled Then. This process is much faster and more the fibers are placed between rollers and reliable than the old hand lay-up process. blade of hockey sticks. the weaving pattern guar. The resin Fundamentals of Composites Manufacturing: Materials. (If the mate. the whiskers are so much closer braider ships the preforms to the molder. the fibers sold as loose whiskers. They also cause of problems at the ends of the fibers). However. berglass and is braided over a mandrel. metal. Milling is an operation where foot. method of selling whiskers is as a paste in making the reinforcement the warp and the matrix resin. The In addition. Particles are not usually considered prepreg sheets. Methods. This are too small or narrow for fibers to be ef. conventional fiber lengths. the probabil. after final sanding of the blade. These are molder slips the preform over the wooden usually made by chopping and then milling blade core much like a sock is slipped over a regular fibers. The other common throughout the reinforcements (for example. The handles are is not sustained for as long a time as with usually made of wood. or composite. that problem because its curved shape has been is. After the handle is made.9: Reinforcement Forms 261 with thermoplastic fibers that can be later make whiskers from spooling remnants. average and. average. In squeezed as they are rolled. “feel” for the hockey player.2 Although composites have proven to be in. loss of strength and reduced Because whiskers are short. therefore. The milled fibers tomated so that the time to install the sock are often used to make repairs to composites is less than 15 seconds. Practically. those ity of encountering a defect is much lower problems have been solved through the use than with conventional fibers. Below that length the material excellent materials for both the shaft and the is considered to be a whisker. The However. Many fiber manufacturers the fibers to achieve good wet-out. high length to radius ratio. (5 mm). not processible with antees that the matrix is well distributed regular length spools. it is called a difficult to match with conventional. the blade has been a rial does not have a high aspect ratio. on of a braided preform. in a composite. and fill in areas in the pre-cured part that The next step is to apply the resin. the preform process has been semi-au- the length of the fibers. individual whiskers have higher The preform for the blade is made from fi- tensile properties than individual fibers. the blade core Most of the time whiskers are sold in one (made of white ash) is attached to the handle. and Applications . which are slightly longer than the and. the higher proper. fibers are usu. melted to form the matrix. is done by hand and the resin is rolled onto fectively placed. Braided Preform Use in Hockey Sticks ally considered to have a length of at least . This reduces fact. WHISKERS CASE STUDY 9-1 Whiskers differ from fibers in that whis- kers are shorter. to the critical length that full transfer of The hockey stick is made of two parts—the force from the matrix to the reinforcement shaft (handle) and the blade. This has the advantage of ease matrix fibers the weft). of application. fibers used are softer than conventional rov- ties are often not fully realized because of ing fiberglass so they can be handled more end effects (weakening of the composite be.) and. But some textile a difference in the methods of manufactur. knits and braids can be characteristics of open and tight fabrics. examining the nature of the 3-D weaving allow reinforcement assemblies reinforcement is an important aspect of to have a significant number of fibers ori- understanding composites. These cut and shaped assemblies are also can be chopped into shorter lengths so called preforms and generally can be made that they can be blended with natural fibers into composite parts merely by adding the or sprayed into a mold along with the resin resin. built-up materials have little strength in the ties of the composite. These Many composites are made from the materials. this results in little fiber being SUMMARY oriented in the direction perpendicular to the The form in which the reinforcements plane of the broad goods. Place the lay-ups over a container and application of a binder.262 9: Reinforcement Forms is usually a toughened polymer like poly. while not really a different form make the cloth. LABORATORY EXPERIMENT 9-1 Sometimes a broad goods shape is desired. and the fibers are held in place with a light 2. Prepregs are sheets comprised ment assemblies so they do not move. Therefore. The fiber bundles part. have improved perpendicular bundles. ented in the perpendicular direction. Make two lay-ups using fabrics that weaving. these are used makes a difference in the proper. knitting. Preforms are becoming increasingly matrix. are used sional reinforcements can be cut and shaped directly in many processes such as filament so they are in the final shape of the molded winding and pultrusion. called three-dimensional rein- simplest of reinforcement forms—fibers in forcements. Hence. are vastly different in openness. are mentioned in this chap- chosen for their desirable properties but ter because they can be delivered as a paste with others the major focus is on the shape and used as a form of reinforcement. Therefore. The properties are other processes also use preforms advanta- manipulated by varying the over-and-under geously. or yarns (depending on the type of Both two-dimensional and three-dimen- fiber and whether it is twisted). The matrix is added then clamp the edges of the reinforce- in a later step. Methods. pattern of the fibers as they are crossed to Whiskers. lay-ups should be at least four layers The mats are generally randomly oriented thick. but other characteristics Objective: Determine the relative wet-out are lacking. or braiding. temperature in about an hour. These are generally more complex Procedure: than just woven broad goods. properties. called strands. The fibers also can be made into a broad goods form without 1. Fabric Openness as in a woven fabric. Fundamentals of Composites Manufacturing: Materials. The form also makes perpendicular direction. of the part and the ease of conforming the reinforcement to the part’s shape. important because of the rise in the use of Fibers can be woven into cloth. Curing is usually done at room matrix itself. of unidirectional fibers held together by the urethane. and Applications . Some of the patterns are of reinforcement. the RTM as a manufacturing process. Actual parts can be made by assembling the blade is trimmed and finished. layers of essentially two-dimensional mate- rial. But. These non. techniques like perpendicular stitching and ing. rovings. including toughness. These bundles. made. However. although a Real composite parts are three-dimension- post-cure of about 24 hours is common. although cloth is not all the same. The woven materials are called mats or sheets. tows. Then al. (ed. 11. Inc. 1. Discuss the flow rate versus the open. Distinguish between a cloth and a Dearborn. into the middle of the re. What is a disadvantage of preforms? 8.) BGF Industries. William P. Time the flow of the resin through the reinforcement assembly. Joseph C. James F. 10. corn syrup or motor oil can be used in place of the resin. Methods.sme. Brochure. such as 10 BIBLIOGRAPHY oz.Distinguish between a prepreg and a mat. Salamone.). What are two advantages of a 3-D weave over a stitched fabric? 7. (ed. 2005. A&P Technology. 1999. www. 1997.).9: Reinforcement Forms 263 3. 3rd Ed. Upper Saddle River. Whittington’s the container into which the liquid Dictionary of Plastics. FL: CRC Press. Fundamentals of Composites Manufacturing: Materials. Inc. weave and a satin weave. Lancaster. “Why Braided Rein- inforcement assembly so the resin flows forcements should be Part of Your Vocabu- through it and then into a container. (If preferred. Boca QUESTIONS Raton.org/cmvs. Carley. What are the differences between a random chopped mat and a continuous Strong. 1978.) Fiber Glass. Engineers. volume in the container. 3rd Ed. PA: flows can be calibrated and the timing Technomic Publishing Co. Concise Polymeric Materials Encyclopedia. and Applications . performance? NJ: Prentice-Hall. Inc. 4. 2. MI: Society of Manufacturing mat. Explain why crimping diminishes the properties of a fabric. New York: Van Nostrand Rein- 5. ness of the fabrics. A.. De- cember. 2006. Brent. 4. Explain why preforms are gaining in popularity. (300 ml). measured as the time to reach a certain Mohr. Gilbert and Rowe. J. hold Company. 6. Discuss the differences in weaving pat- tern and physical properties for a plain Society of Manufacturing Engineers (SME). Which type of satin weave would be ex- pected to have more drape—8-harness or 5-harness? Why? 5. Pour a set amount of resin. Plastics: Materials strand mat in terms of construction and and Processing. Why do whiskers have more strength than fibers? 9. 3. 1998. List three products for which a knitted fabric would be better than a woven. 1993. (If lary and Part of Your Composite!” preferred. “Composite Materials” DVD from the Composites Manufacturing video series. Give three advantages of a stitched fabric. data was fragmented and inconsistent from ceramics. materials. • the scarcity of standardized tests for Some attempts at standardization have composites. Further. Although these tests were not usually proprietary. the properties of metals. and plastics. the database of composites In general. the innovations in composites • the continuous development of new design and manufacturing were occurring composites. because each design might be made with • the relative newness of composites as new and occasionally surprising results. Fundamentals of Composites Manufacturing: Materials. new materi- of the large databases for these materials als were continually being developed—true compiled over the years. • Quality control principles ceramics. concepts: As will be discussed in more detail in the chapter on design. Even the development including the following: and approval of new designs made the ac- cumulation of standard databases difficult • the complexity of composites. and plastics are known because company to company.1: Introduction to Composites 265 10 Quality and Testing CHAPTER OVERVIEW complicated by the fact that the reinforce- This chapter examines the following ment can be oriented in specific directions. generally dating • Mechanical testing from the 1950s. In essence. The lack of an accepted in the 1970s. • Component materials testing The emergence of composite materials has been relatively recent. and Applications 265 . The initial developments • Thermal and environmental testing were largely made by aerospace companies • Flammability testing who developed tests specific to their own ap- • Non-destructive testing and inspection plications. Methods. The same is not carbon fibers in the mid-1960s. these characteristics • History of composite materials testing make composites very different from metals. In the United because the reinforcement and the matrix States these groups include: American are such different materials. and so rapidly that uniform testing was not able to keep up. and many advanced resins in composites database is due to many factors. thus using their own criteria for acceptance. been made by the major testing and profes- The complexity of composites arises sional societies of the world. subsequent years. the companies rarely HISTORY OF COMPOSITE MATERIALS worked together to develop standardized TESTING tests. Hence. aramid fibers true for composites. This is further Society for Testing and Materials (ASTM). Thus this chapter should be understood that use of a qual- begins with a discussion of the fundamentals ity tool or system does not guarantee its that underlie quality control and all com. plastics. However. Association Francaise good quality practices than they may actu- de Normalization (AFNOR). Whether that will help make a difference. tests will be arranged according to the type reporting or believing that control charts are of property being examined: mechanical. British Stan. the Plastics Industry (SPI). correct use. in the process of of Mechanical Engineers (ASME). These include: Deutsches Institut themselves more credit for implementing fur Normung (DIN). For example. but it does describe the true nature of qual- neering (SAMPE). Underwriters Labo. if non-destructive testing and inspection. the fact that a posites testing. There are spe. company managers reported that tabase for composites and the uniqueness they were more familiar with and more in- possible with each design. National Institute of Standards lustrate the development of a logical plan and Technology (NIST).266 10: Quality and Testing Military Handbook Committee (MIL-HDBK. Advancement of Materials and Process Engi. It is therefore important to should not be allowed to cloud the evaluation understand the overall nature of composites of a company’s position in terms of quality. it the composites industry. In the Materials Association (SACMA). and Applications . It was found that almost without Because of the lack of an accepted da. improvement. may be an overly optimistic judgment by bility. ASM International. guilt or self-deception and composites. which is so critical to long-term success.S. the danger can QUALITY CONTROL PRINCIPLES be that it will fail to invest the time and The fundamentals of quality are straight. The composites ately or that the use is sufficient. molding process for thousands of pieces a 17). Methods. it has been found that most groups have also worked to standardize people. cific tests that have become common within As part of a self-evaluation on quality. Japanese Industrial the familiarity and use of quality methods Standards (JIS). testing of each volved in using quality programs than was composite structure or design is far more actually observed during inspections of their important than is typical for metals. The chapter concludes with a look at managers. especially company executives. and the American Society ity improvement. effort needed to really use the quality tools forward and amazingly simple. for improvement. and flamma. A study was done to evaluate dards Institute (BSI). implemented correctly within a company thermal and environmental. Clearly. exception. methods. erations. testing and quality control. Society of Quality is a process not a destination. However. It then proceeds to discuss company uses control charts in the tracking specific tests for material components—resin of its manufacturing process does not mean and reinforcements—and then tests for the the control charts are being used appropri- composites themselves. (NASA). ratory (UL). the goal is to describe a principled ap- Aeronautics and Space Administration proach to quality using the tools. give tests. Suppliers of Advanced Composite day. ally deserve. the basic approach is similar. American National Standards Insti. National end. A company the process to improve is a unique lay-up truly focused on continuous improvement operation of large parts or a compression will not get caught up in measuring how Fundamentals of Composites Manufacturing: Materials. Society for the This statement is a bit trite from overuse. yet understandable. facilities. a company gets caught in this over-estima- tion of quality performance. and techniques that make sense and to il- tute (ANSI). and the International and techniques in small manufacturing op- Organization for Standardization (ISO). Therefore. Non-U. products. they will up of 20 sets of quality system requirements. requirements. First. that is. But at the same time there has developed To begin to make some sense of the variety a dangerous idea that if a company has of methods for quality control. This. Al. ISO 9000 is Documentation and Certification actually composed of four certification sets: Programs 9001 being the most comprehensive and Documentation and certification of quality 9002. develop. process control requirements. ISO 9000 and the QS 9000 are. This model applies to organizations that In the short run. These are: excellent quality. The primary components of this system with these efforts. The degree of importance of nents of a company’s design and production any one depends on the company’s particular system. has occurred. Certification does not guarantee are to address. It is essentially the Fundamentals of Composites Manufacturing: Materials. companies by competitive pressures. ISO 9002 is made up of 19 sets of quality they provide a way to document. Methods. quality system requirements. In short. the wrong thing. grams ISO 9000 has made an admirable attempt 2. this is because it does not require much more effort to docu- 1. evaluate. for the most part. 9003. for this and training and service requirements. there are five achieved certification then it is a company of primary quality functions that quality tools high quality. Improvement methods certification process. it is likely focused on wide. system requirements. ISO 9001 expects organizations to Certification programs. ISO The focus will be on getting better. requirements for documenting the compo- ment of quality. real. it is just not as easy as 4. If a company measures its qual. Management philosophies national standards that outlines stringent All are important to quality and the improve. there is confusion design. however. install. such as ISO 9000. to continue on the course of improvement. and 9004 addressing lesser sets of (like ISO 9000) is being forced upon many requirements of the organizational system. dards with one single family of standards ity program by how many or what kind of that would be recognized and accepted world- tools are being used. produce. which are not include all management responsibilities. company’s ability to adhere to the require- ments set forth in the standards. ISO 9001 is a quality assurance model made though companies may not like it. discussion. and service and anxiety. There are some interesting issues tem. necessarily compatible with improvement. benefit from those pressures in the long run. essentially the same. Thus assessments of the effectiveness of the ISO 9000 quality program will take precedence over Originally. however. apply this model and meet the requirements are popular and the intent of these programs by developing a comprehensive quality sys- is good. and certify a company’s quality system. System integration strategies it sounds. ISO 9000 was to replace scores merely verifying that some quality tool is of national and international quality stan- being used. Certification is granted based on a stage of progress. product design focused quality plans and systems. and Applications . Documentation and certification pro- ment a poor process than it does a good one. Analysis and statistical tools to include continuous improvement in the 3.10: Quality and Testing 267 many or which tools it is using or not using. 14000 is similar in intent but focused on izing that the tools are simply the means environmental issues. What is ISO 9000? It is a set of inter- 5. check sheets are limits are established to help monitor when used to ensure that all of the required steps a variable is not within the desired range are being done in a process. It uses aver- of tools includes check sheets. flow charts. cal methods can be applied such as statistical As already indicated. capability analysis. and design of experiments (DOE). a bell curve (normal distribution). the cure would be run at control within the specification limits set various temperatures and the hardnesses for it? measured. and training and as Excel®) with little special training needed. of the tools for monitoring a process is sta- cal in nature or related to quality. Then. Most of these them over time. purchasing. process control. as it would cause a change in another variable. process. it must Analysis and Statistical Tools first be determined how well the process or The “basic tools” are so basic that you system is functioning. for 30 days and then plotted according to ISO 9004 primarily focuses on the critical their general values. qual. correlation plots. quality. improvement. Such a plot is shown in Figure 10-1. and plots frequencies called histograms. and Applications . The cor- ISO 9003 is made up of 16 sets of quality relation coefficient. such as cure temperature. The most important might not even consider them to be statisti. process presupposes but does not really re. most spreadsheet computer programs (such ment. for smooth and reliable production. A Pareto quire good quality. However. and customer data are normally distributed. the ISO certification process control (SPC). and plots of occurrence such as temperature or hardness. the task of obtaining bar chart) used for quality purposes. the plotted hardnesses represent roughly pects of management responsibilities. Upper and lower control are intuitive.268 10: Quality and Testing same as 9001 except that product design is related. Correlation plots can be done using not required. SPC stand a process. is running. For example. the hardnesses would be Design of experiments (DOE) then comes plotted versus the temperatures. good it is relative to the process specifica- able in a process. age values of important process variables. chart lists the causes and numbers of prod- portant to the well-being of a company than uct rejects. capable of staying in statistical such as hardness. with its strong relationship Fundamentals of Composites Manufacturing: Materials. Capability analysis is a method of statisti- Correlation plots have to do with running cally analyzing a process to determine how the process. tions. To find out if changing one vari. several statisti- interactions and service. order they occur. and orders them from highest compiling documentation for the various to lowest. DOE. Figure 10-3 shows an example of standards to which it might be certified. hardnesses were measured servicing requirements. In design. service requirements. a Pareto chart. When the ity planning. This list tistical process control (SPC). R2. is shown along with system requirements and is essentially the the equation of the line. This good quality is ultimately much more im. That task is left largely to chart is a special type of histogram (or the company. is the process. The data show that elements of a strong quality system—all as. it is smart to begin with a helps to identify when a process is drifting flow chart showing each of the steps in the out of control. and this example. Methods. To effectively improve a process. Then a into play to help reduce the common cause correlation analysis would be performed to variation that occurs in statistically stable determine how closely the two variables were processes. Thus it focuses on manage. same as 9001 except it leaves out product A histogram is shown in Figure 10-2. In other words. To fully under. Figure 10-2. Fundamentals of Composites Manufacturing: Materials. and analyzing the process when more than sion to higher stages of quality. one variable might be changing. as is the DOE is a method of performing experiments typical case in actual operations. and Applications . supports progres. Methods. Correlation plot of hardness versus temperature. In essence. Histogram.10: Quality and Testing 269 Figure 10-1. to improvement methods. The entire idea behind the most powerful Used properly. is failure modes of a product. In this improve- Failure mode and effects analysis (FMEA) ment scheme. In other words. If this prerequisite un- the purpose of the analysis tools is to deter. or process for a considerable time at improvement. even though benchmarking is laudable. In his view. fied standard is six sigma. and how to best is what Ed Deming preached and. A company might seek an alternative 2. apply the ideas and methods obtained from what his 14 points are based on. Methods. a company will mine how and where the process should be find itself trying to imitate the operation it improved for most immediate effect. the the product or service will be between specifi- elimination of failures. Recognize and evaluate the potential by companies that have not already worked failure of a product. so that new areas for improvement are iden. Figure 10-3. its weaknesses. 99. other companies. or process reduced to the point that the specifications and plans for the elimination of those failure are at ±6S. and the nonconformance rate will be involves three steps: 0. This processes. service. Pareto chart. When problems arise. Quality function deployment (QFD) is a system that focuses first on the desires of the customer and then sets the product or process parameters in accordance with those expectations. either industry standards (benchmarking) or 3. This standard is dif- ficult to achieve and should not be attempted 1. of course. derstanding does not exist. This comparison process is called benchmarking. it is difficult for a company that is just Improvement Methods starting to apply quality control methods. benchmarking requires an and long lasting of the quality strategies is excellent understanding of the company’s the idea of continuous improvement. Most companies find that improvement efforts need to be quantified or at least compared to some standard. Another method for establishing a quanti- tified and worked on for improvement.9999998% of modes. and Applications . and the effects of that failure. in fact. However.270 10: Quality and Testing Another tool that is helpful in identify- ing the causes of a problem or defect is the cause-and-effect diagram (sometimes called the Ishikawa or fishbone diagram). Document the process. Possibly the Fundamentals of Composites Manufacturing: Materials. The most com- mon of those standards is the competition or some industry standard. Identify actions that could eliminate standard for improvement that is appropri- or reduce the chance of the potential ate for their status but does not depend upon failure occurring. service. changes to the process are examined in light of po- tential customer satisfaction.002 parts per million. S. a standard of process deviation is a technique that identifies the foreseeable is set such that the standard deviation. an arbitrary value (six sigma). The hoped for result is. Then is benchmarking rather than intelligently quality efforts should continue the analysis implementing learned methods. The FMEA technique cations. done any other way. they stopped their efforts. quality will never has proven to be highly effective and appli. First. Improvement The system’s overall performance depends programs are. streamlining production flow” and “that tim to the same end as other management factory performance is largely determined by fads. In the book Running Today’s Fac- cable to companies regardless of their state tory. a reminder that if you segment an elephant panied by improvement in the leader. That is why. not an improvement strategy. The other fallacy involved companies and wise.10: Quality and Testing 271 best alternative is to employ the Taguchi the reduction of variation. Too often it is thought that by break- implementation procedures. the process is good a quality strategy is or how broad and continually centered toward the mid-point precise the view is of the system. but they do not ture. blamed TQM. quality issues become tem. In the past. With aspects of the design and production sys. have an ending point. By virtue of its but you will not gain an understanding of title and purpose. In attempting to use The structure and organization of the system TQM. but eventually set. often. achieved it. overflowing on the interdependence in its entire struc- with milestones and goals. the and parts are not stable and ever striving process is continually refocused. For example. the process said. I would say that it all had to do the process whenever the critical values are with reducing variation. or style. an achieve the shortest possible cycle time by excellent concept that lost luster falling vic. be good. not a compilation of the sum of its parts. It is affected by. rather than accept few words. the System Integration Strategies supply chain for any given company usually At its root. Standard and Davis claim that “the of quality implementation. In fact. experience forces this to be the first consid- though the fault lay within their methods. the you may get more “manageable” pieces. it is how the elephant as a whole works. company. this broader focus. its falling was lean manufacturing are brought together in more the fault of improper implementation such a way that there cannot be impact on by impatient and naïve managers than it one without impacting the other. at the root of quality is even more important and. many managers focused on endings determine the behavior.” Thus. Usually. was a fault of the philosophy. all that will have to be Improvement strategies must be directed dealt with are its parts. and affects all chain is likely to be international. ing up the system. Systems theory is by transformational leaders and accom. and having failed to do so. having accomplished a seen and therefore acted on. Today’s world requires astute manage- ment of the supply chain. costly. set goal to improve quality and having once especially early on in improvement efforts. quality improvement and improvement. and Applications . quality is truly a system con. involved only suppliers that were nearby or cept and quality improvement is a system within the same country. core strategy of lean manufacturing is to Total quality management (TQM). as they should be. In this method. only the events are two fallacies. Now the supply problem. which in turn dictates and final results and thereby fell into one of various events. Unfortunately. Early on the broader scheme of who did not accomplish the goals they had things is not considered. In other words. and the process. Deming loss function. “If I had to reduce my message to a is run under SPC but. eration. Fundamentals of Composites Manufacturing: Materials. was founded on the idea of continuous variability. usually actions are shortsighted and reactionary far short of what the company needed to claim whereas later they become more objective success.” Regardless of how within the acceptance limits. This method to achieve low variability. Methods. if processes of the specifications. furnish the called kaizen. favorably impact the appreciably over time and because the tests quality of the products or process. on sound management for success as has The conditions under which testing occurs already been discussed. a good management system for systems of good management will similarly the supply chain is imperative in today’s give positive impact on quality. Testing can be viewed from two different How management sees employees and the perspectives. It is outcome is a future state map. and contin. If non-standard tests are to be performed. standardize. and Applications . speed. This overall Because reinforcements do not change view will. the company will do a value stream both samples. of the specifications of the reinforcements the lean manufacturing method yields great and resins. upon request. in which the various capacities and production systems are de.272 10: Quality and Testing Therefore. Nearly every quality guru has a use properties of the composite by monitor- set of principles (for example. One view is a determination of systems and priorities of the company are the fundamental properties of the composite critical factors in the quality improvement material. Therefore. and bodied in Deming’s 14 points or TQM. shine. The other is to investigate the in- process. This information is used to verify quality management. etc. which helps to put everything in the might be tested at the same time. temperature. sometimes to be performed.) should all follow ues to be. a standard with straighten. the type of equipment. COMPONENT MATERIAL TESTING Management Philosophies Strategy The employees’ quality of life has a lot to do with the quality of a company’s product. if a standard test is special kind of quality awareness. depends expected over its useful life. known properties or a comparison material gram. A “kaizen” is an event whose results of these tests to their customers. Total conditions. global economy. in reducing waste throughout the manu. noted and justified. conditioning. All together. which embod. the specifications of sample without the direct reference to quality em. Methods. an extremely important concept that standard precisely. sustain) pro. Raw Material Testing scribed in terms of downstream demand. The manufacturers of reinforcements and The company then attempts to improve the resins usually conduct extensive tests on current process. possibly using a technique their products and. considering the term that a composite part has the properties “management” as part of its name. organized and disciplined way. Usually. facturing enterprise. This is useful information to the results and improved profits because the design process and flags possible conditions entire system is considered together in an that may need monitoring. generally good practice for molders to obtain ies the change system and path for continu. Other to verify their properties are tedious and Fundamentals of Composites Manufacturing: Materials. Deming’s 14 ing changes in the composite’s properties points) that are counted as fundamental to over time or under various environmental the particular program or method. of course. sometimes management philosophies seek to instill a dramatically. thus en- plant in good order. map of its process(es). the operation of the equipment (such as the Lean manufacturing has been. suring that the conditions are the same for tation. Some of the other can often affect the test results. During lean implemen. these test results so that they are aware ous improvement (Mika 2006). One of the important the conditions of the test should be carefully aspects of lean manufacturing is the 5S (sort. Methods. A flow of mended that molders conduct some verifica. gas is injected and the tube is often heated. Viscosity measuring equipment. In one independently verify the properties of the chromatography method. There- thereby creates a spectrum. mass spectrometry to identify the nature ing sophistication) include Fourier transform of the components that make up the resin infrared (FTIR) and various chromatography mixture. few molders various components of the resin. Another factor affecting the is an indication that the resin has begun to permeation is chemical affinity for the gel. Chromatography separates the stickiness of the prepreg are used as Figure 10-4. tests that measure the flexibility and for each polymer. Fundamentals of Composites Manufacturing: Materials. resin is constantly changing because material (in the most common method) has of its reactive nature. FTIR examines the frequencies of For prepreg samples. Therefore. which is unique fore. and Applications .10: Quality and Testing 273 require specialized equipment. On the other into a small-diameter tube in which a gelatin hand. cure and may not be appropriate for use. If materials penetrate the gel and are absorbed the viscosity has dramatically increased. a small amount of reinforcements. the components of batch is appropriate for use. the viscosity of the the molecular motions in the polymer and resin cannot be determined easily. methods. Some of these tests are solvated or liquid resin mixture is injected discussed in Chapter Eight. it more strongly. Some of the components Testing for viscosity is simple and can be are absorbed more strongly by the gelatin done using relatively inexpensive equipment and therefore they take longer to traverse (see Figure 10-4). Chromatography can be combined with More extensive tests (requiring more test. been coated on the inside walls. The measured viscosity the length of the column. tion of resin properties to ensure that the Under these conditions. it is recom. the resin separate. The retention is can be compared with the viscosity of the a function chiefly of size since the smaller resin as indicated by the manufacturer. If the times and the glass transition temperature. other tests are available to deter. and a determination of problem arises. This test uses a hand-held device. The acceptability of the initiator (catalyst) standard testing laboratories or resin sup- is best measured by mixing it with resin in pliers often have such machines.) needed to lift the prepreg is measured. The variation resin has advanced excessively. the prepreg is pressed against surements is thicker than that recommended a standard surface and the amount of force for gel coats. The force to indent is the hardness. In this test. off) versus temperature. the tests are will be stiff and the drape will be less. the prepreg in these tests can be high. off by the test specimen is compared with lems with the cured composite are evident or the standard material. the sample thickness for good hardness mea- In this test. the extent of cure can be made. the Tg also by the manufacturer and data collected by increases until a maximum is reached when the molder. a test for gel time and peak exotherm as Of particular interest is the transition called discussed in Chapter Three. If data is available from previous Most of the other components in a com. One common device is the the prepreg is placed over a solid mandrel Barcol hardness tester. and Applications . correspond to phase changes and other mo- which has an indenter that is pressed into lecular rearrangements in the sample. a sample of of the indenter. Also. Fundamentals of Composites Manufacturing: Materials. the initiator can be assumed to the amount of crosslinking is essentially be acceptable. The test for flexibility is called the type of hardness tester and the nature the drape test. that posite can be accepted from reliable manu. The test the correct concentration and then running measures thermal transitions in the resin. displayed in a plot of heat absorbed (or given mine whether the part cured properly. However. As the temperatures are similar to those specified amount of crosslinking increases. the higher of a set diameter and the amount that the the hardness value. The increases or A hardness test is possibly the easiest way decreases in the plot are endotherms (heat to investigate the extent of cure on a cured taken up) or exotherms (heat given off) and sample. usu.274 10: Quality and Testing reasonable approximations of the resin’s which is measured on a scale determined by cure state. Tg. Some caution must be ex- own weight is measured. samples known to be properly cured. not generally owned by molders. Methods. the more complete or sample drapes over the mandrel under its advanced the cure. The gel and the differential scanning calorimeter where exotherm tests are directly related to the cure a known standard material is housed. One the part. complete. therefore. The information is suspected. is in storage). If the cure of the ercised in using hardness tests. data can be compared with the Tg of the facturers as shipped unless some specific sample in question. (See ASTM D2583. The and can be performed after assurance that temperature of the chamber is increased the resin and the initiator are themselves and the amount of heat taken up or given acceptable (as discussed previously). In general. of the transitions measured is the Tg. This test requires a large test ma- prepreg advances (usually as it continues chine that is quite costly and. In the DSC test. Another test to evaluate the extent of cure ally by hand or by a force scale. If prob. a small sample of the Curing Tests composite is placed in a sealed packet and It is important to ensure that the cure has then inserted into the heating chamber of occurred properly in a composite. The usually not appropriate for gel coats because stickiness is determined using the tack test. The tack uses differential scanning calorimetry will be less over time as the cure of the (DSC). The fiber and resin densities are to burn off the matrix. which is usually heated the theoretical density of the composite and equipped with a reflux condenser to based on the densities and percentages return the hot solvent back into the heat. The glass transition filler from the resin is the thermo-gravimet- temperature is taken as the point where ric analysis (TGA) test. the theoretical density with the actual density reinforcements are dried and weighed to determined in the laboratory. As depicted in Figure the calculation of the resin-reinforcement 10-5. ness of the composite change. The method. A test method also exists for determining the fiber content of a composite through electrical measurements. Inorganic systems may have the percentage of reinforcement and resin transformations that can be used for iden- determined. fiber. in the composite. Organic systems are lost below a tared crucible and heating to burn off the 932° F (500° C) depending on the nature of resin. If no fillers are pres. testing the composite material when sub- If a filler is present. is assumed to be the void content. After digestion of the resin. The difference determine the percentage of composition. and Applications . of the components and then compare the ing vessel. In the is often a complicated process that depends DMA method. Fillers has to be separated from dynamic mechanical analysis (DMA) and the reinforcement and from the resin. Alternately. This method only MECHANICAL TESTING applies to unidirectional conducting fibers Mechanical properties are determined by in a non-conductive matrix. it will interfere with jected to various forces. expressed as a percentage. off. the sample can be displaced and One test to help sort out the presence of the stresses observed. it is sometimes desirable to for organic and inorganic systems or for a determine the concentration of fiber and mixture of both. In the TMA as a function of increasing temperature. Methods. the The composite density is obtained by the weighed composite sample is placed into buoyancy test. TGA also can be used for stability the reinforcements are not affected by the studies to determine the rate of decomposi- temperatures at which the resin is burned tion at a fixed temperature.10: Quality and Testing 275 Other methods used to determine Tg are percentage. Moisture is generally lost resin in the composite. The sample is then reweighed and the material. However. This method works because tification. This thermo-mechanical analysis (TMA). at about 212° F (100° C) or higher depend- ent. TGA can be used After curing. resin. the percentage of reinforcement can be ing on whether moisture is bonded in the determined by placing a weighed sample in system. This test involves key properties associated with the stiff. off the resin or if the reinforcement will and any other components that might be not withstand the temperature required present. the weight lost. a solvent extraction usually obtained from the manufacturers. In this method. material out of the system. percentages of component contents and If a furnace is not available for burning the densities of the composite. the sample is loaded with a on the type of filler and other components stress and the displacement is observed. the method cannot be used The void content of the composite can for reinforcements such as aramids and be determined from a combination of the UHMWPE. The procedure is to calculate a solvent bath. five forces are important in composite Fundamentals of Composites Manufacturing: Materials. changes in the length or thickness temperature increase is controlled at a fixed of a sample as a function of temperature are rate and a purge gas sweeps any evolved monitored. method can be used. The Figure 10-5. and Applications . carbon-epoxy. compressive. Properties ferent circumstances. The vibration and damping tests measure the response of the Shear strength 18 ksi (124 MPa) composite to loads that are intermittent. Determination of other Tensile strength 315 ksi properties involve these forces but with (2. The former test is for all ping regions of the tensile test machine.276 10: Quality and Testing structures: tensile. The fatigue tests involve flexural loads that are applied repeat. flexural. are given materials in general whereas the latter is in Table 10-1.793 MPa) but applied for a long time. slowly Composite applied forces. Table 10-1. Methods. Flexural modulus 19 Msi (131 GPa) edly over extended periods. The creep tests are like Flexural strength 260 ksi tensile tests in which the forces are static (1. Some of the important for 62% Fiber Test Value properties are determined under standard Volume testing conditions (room temperature.). All of the force types are important to determine the behavior of composites in dif. etc. typical carbon-epoxy composite. For example. Types of forces. Mechanical properties of a torsional. Some mechanical properties for a typical aerospace composite. and shear. specifically for resin-matrix composites rein- forced by oriented continuous or discontinu- Tensile Properties ous high-modulus fibers. Fundamentals of Composites Manufacturing: Materials. Tensile properties are determined using The standard sample for test method D638 procedures such as those given in ASTM is shaped so it will break between the grip- D638 and D3039. impact tests involve forces that Tensile modulus 21 Msi (145 GPa) are added quickly.172 MPa) various changes to testing conditions. 10: Quality and Testing 277 most common shape for non-composite plas. Tensile test specimens. The increased the problem of cutting the specimen into width of the specimen in the gripping zones a dog-bone shape. and Applications . Since this affects the properties of the The standard specimen for composites composite. gular sample. breakage in the desired zone by reinforcing tic test specimens or composites reinforced the ends with tabs bonded to a flat. the tabbed specimen is superior (test method D3039) is illustrated in Figure for continuous reinforcements. the failure zone between the grips. Note that 10-6b. Fundamentals of Composites Manufacturing: Materials. Note that this specimen achieves the tabs in specimen 10-6b are tapered at Figure 10-6. which requires some of ensures that the specimen will break within the fibers in the specimen to be cut short. This latter specimen avoids illustrated in Figure 10-6a. rectan- with short fibers is a “dog-bone” shape. Methods. (The area is the width times the finish (either from lamination or from ma. curate determination of elongation requires there is a resistance to movement. Ac- When a specimen is pulled in tension. If only strain gages. A common example would from a laminate sheet after the tabs have be a spring that is deformed slightly. Elongation is The crosshead speed is generally run at usually expressed as a percentage increase 1–2. The tabs are imparting potential energy. all of the mechanical energy when a sharp edge is present. in length compared to the original length of cause of the brittle nature of the samples. grams. Fundamentals of Composites Manufacturing: Materials. These are attached to the sample the solid material returns to its original during setup of the test. same plies in which the surface is oriented The elongation is a measure of the strain in the perpendicular direction. (5–10 square inch or pascals (newtons per square mm). Other data indicate that the surface meter). in two samples that have the same sample between the pulling forces. Energy is always recovered in width control. the The displacement (movement) of the ma- order of the plies makes a difference in the ten. It is suggested that the samples the sample. the available within the spring to cause it to adhesive is less likely to run over the edges return to its original shape. which is then more likely to be parallel and. terial is called the strain (F). Normally the sile test. In these de- riser (causing early failures) that can occur formations. The length dimension is not chining the edges) can cause differences in important in the calculation because it is properties. therefore. This taper avoids the stress deformation is called elastic.4 in.5 in.2–. Elongation is difficult to measure tering of the sample. and Applications . thus been bonded onto the laminate. Another way of the samples. then used to cause the material to return ture that will not distort or otherwise affect to its original shape and position when the the sample./minute (25–64 mm/minute). Plots of the stress versus strain such as care should be taken to protect the eyes and the type shown in Figure 10-7 are called skin against flying fragments. thickness. Methods. or optical inter- small deformations are considered and ferometers. An orientation in which the surface strain is given as the change in length (Nl) fibers are parallel to the pull direction yields divided by the original length (lo).) number of plies in the same direction. when the force is tension. Be. To prevent fiber fraying of saying this is that energy is returned or along the edges and to give the most precise recovered. Care should be put into the material by the applied force taken in sample preparation so the tabs are to cause the deformation is held within and properly aligned and bonded at a tempera. Generally. especially if they are carbon fiber reinforced. then the the specimen. the units different results from a sample having all the are dimensionless.278 10: Quality and Testing the point where the tabs meet the body of shape when the force is relieved. extensometers. the sample is important in giving less spread the force is usually divided by the area of in the data. the test specimen. waterjet cutters have proven to be the best The force divided by the area is called way to cut the samples. because of the stiffness of the samples. the samples are cut stress is relieved. The break is stress-strain curves or stress-strain dia- often sudden with a large amount of shat. diamond cutting blades with elastic deformations. For distributed over the entire length of the example. yielding units of pounds per be in the thickness range of . the stress (T). Surface ply orientation makes a assumed that the applied force is evenly significant difference in properties too. So that materials of dif- Some data indicate that the thickness of ferent sizes can be directly compared. the center of the tensile specimen. the thickness includes the of the fibers. (0. thickness. It is important to remember that the properties of the individual components of a composite are not the same as the proper- ties of the composite itself. sure vessel can be determined by cutting a ring from the vessel and then pulling on F  T  EF (10-1) the ring with pins attached to the tensile A machine. because it is dominated by the characteristics in the composites. and most importantly. in practice. the tensile test pro- cedures require that the load applied to the Figure 10-7. a more where: common method of determining the tensile properties of a pressure vessel is to pressur- F = force ize the vessel (almost always with water) and A = cross-sectional area simply measure the pressure at which the T = stress vessel bursts (loses pressure). For example. Among the reasons for this difference is some of the load. part being tested be divided by the part matrix. the thickness is not normal- curve for the fiber is linear. The relationship between stress and strain In theory. Such materials are said to have stiffness. This normalizing of the thickness allows for comparisons of data for many parts of many thicknesses. called modulus. the stress-strain tor will generally result in lower values for behavior of the matrix is elastic and then the tensile strength of composites versus the non-elastic. the strength of the composite is not the same as the strength of the fibers even though they carry most of the load. The modulus is bers has on part performance. and composite. evaluates the to as Young’s modulus for the effect that shortening the length of the fi- tensile stress case. Hence. However. Relationships of the tensile strength of fiber. not all fibers are exactly arranged as predicted. Methods. capability will vary from the reported tensile The curve for the matrix begins linearly but strength. and sometimes referred the open-hole tensile test. This indicates ized and. the slope of the stress-strain curve. tensile test is run to determine the effects the material resists deformation of the hole.10: Quality and Testing 279 strongly. The composite curve is elastic tensile strength of the fibers. even though small. However. E = proportionality factor. This is because. correspond. the actual load-carrying that the stress-strain behavior is elastic. which carries little of the load.25-in. the tensile properties of a pres- in the elastic region can be shown by. in real Note in Figure 10-7 that the stress-strain composite parts. For composite materials. This is called F = strain the burst test. called the A modification to the tensile test.6-cm) diameter hole is drilled in If the modulus is large. Fundamentals of Composites Manufacturing: Materials. this fac- then starts to curve. a . Then. In this test. and Applications . matrix. is carried by the matrix. a ing to a steep angle of the curve. therefore. 280 10: Quality and Testing Compression and Compression-After. This Institute of Technology Research Institute situation was discussed previously when (IITRI). other specimens are impacted with a known energy Figure 10-8. Clearly a transition in type of the sample. Then. Pressure is applied only on the end of is in tension. In this Occasionally. a method of determining the fiber-matrix ods differ principally in the way the sample bond strength. Illinois this transition plane pure shear occurs. it is called the four-point bend test. the sample. several flat-panel specimens are made and compared in compressive strength. done. [1. At include those developed by Celanese. and Applications . These meth. is supported by the fixture. the tabbing extends along both sides of two points of pressure are used. and this greatly diminishes the compressive properties. and the bottom opposite the loading force ing. case. The support fixture During the test. have a ten- dency to buckle within the composite. Perhaps two supports and then pressing on the top of the most prevalent of the methods is the Boe. When this is the sample except for a small region (. A control specimen is tested for flat-panel compressive strength.3 cm]) in the middle. While flexural testing is simple and easy The compressive properties can be quite to perform. which the tabbed sample is placed. in particular.50 in. Most commonly the pressing is ing modified test method. A cap is placed on the top of the sample where the compression machine presses. This is called the standard D695. An important test to assess the loss of properties after impact is called the compres- sion-after-impact test. and then tested for flat-panel compressive Impact Properties strength. Methods. which is similar done with a single point of contact as shown to the procedure and fixture given in ASTM in Figure 10-8. The special fixture supports the specimens on their sides and bottom. In this test. to the composite sample. Fundamentals of Composites Manufacturing: Materials. and the National Aeronautics and short-beam shear testing was discussed as Space Administration (NASA). nar sample supported on its sides to prevent buckling when it is pressed on its ends. Flexural test. the mixture between tensile and different from the tensile properties because compressive forces means the flexural test of the difference in the ability of the composite to support a columnar load versus a pulling load. Flexural and Shear Properties There are several methods for supporting The flexural or bending forces are deter- compression test specimens and these have mined by placing a rectangular sample across given rise to various test methods. It consists of metal plates between flexural test or the three-point bend test. the top of the sample prevents the sample from buckling but does under the loading force is in compression not prevent the non-tabbed region from fail. The compressive strengths are Compressive force yields information compared to evaluate the effect of damage about the strength and stiffness of a colum. The fibers. although rarely in composites. Other compression test systems force must occur in the middle of the part. espe- cially when voids are present. the climbing drum peel test accomplished by integrating the equation (ASTM D 1781). it is a commonly used test and is especially useful when flexural forces are those that are likely to be encountered in the use of the composite part. A peel test that gives more system. as is done in ergy without breaking (rupture) is called the stress-strain experiment. property called impact toughness (some- ness—equilibrium toughness and impact times called impact strength) is defined toughness. Other shear tests include: Iosipescu (v-notch). If type of toughness only approximates actual a more severe peel test is desired. Examples would be sandwich panels and certain joints. Generally. is usually so slow that equilibrium conditions Impact toughness is strongly dependent can be assumed. Using calculus. but it is not the only test procedure used for compos- ites. can be done by simply turning the ends of a sample or molding a sample with turned ends developed when a tensile test is performed so it can be pulled in a tensile machine. a relatively long period of time. can be used. the toughness of a material is much more important when the force is ap- Impact/Toughness Properties plied suddenly in an impact rather than over The ability of a material to absorb en.10: Quality and Testing 281 cannot determine basic material properties that are useful for theoretical calculations in design. depicted in comparing similar materials. two rail. Equilibrium toughness is so as the energy absorbed by a material upon named because the speed of the tensile test sudden impact. the rolling toughness performance. A simple test Figure 10-9. This to peel a layer from a sandwich structure. and Applications . a toughness. and three rail. Nevertheless. Test fix- tures for these and other test methods can be obtained commercially. Shear testing is important for samples bonded by adhesives. measures the force required describing the stress-strain curve. Therefore. An example when such forces would be important is in a tub and shower unit where the principal forces are the flexural forces from a person standing on the bottom of the tub. The most important of the tests for these materials view shear as a peel phenomenon (shear- ing along an adhesive plane). It is related to the area upon the ability of the material to internally under the stress-strain curve such as that move or deform to accommodate the impact. Methods. Figure 10-10. this summation is reliable data. There are two types of tough. Simple peel test. An because energy absorption is the summation example of this simple peel test is illustrated of all the force resistance effects within the in Figure 10-9. but it is useful in drum peel test (ASTM D3167). The short-beam shear method is probably the simplest shear test to run. Fundamentals of Composites Manufacturing: Materials. 282 10: Quality and Testing toughness unless the nature of the backbone changes. it will not swing as high after the impact as before the impact. In the Charpy and Izod tests. The sample is clamped in the holder vertically (for Izod) or laid horizontally (for Charpy) and may have a notch cut in it to initiate the rupture. materials with high sample. Hence. the pendulum will generally break the sample and continue its path beyond the impact point. The energy high elongation are often tough. Alternately. vibrate. the the height of the pointer. For example. or higher strength and better sharing of the other impacting device onto the sample. records the strain. crosslinking a flexible polymer will increase impact toughness because of the greater abil- ity of the polymer to transfer the energy. Methods. The Izod and Charpy tests (ASTM D256) utilize a pendulum-impact testing device (illustrated in Figure 10-11). High molecular weight favors high tough. modulus are called brittle (the opposite of Another test to determine impact tough- toughness). thus determines the toughness of the sample. In this test. the drop height. Therefore. The impact force along the polymer chain. the ability of this material to ab- sorb energy by passing the energy from one molecule to another through intermolecular forces makes it tough. even though nylon is crystalline. Rolling drum peel test. The reduction in height (poten- Figure 10-10. A pointer. The results are usually expressed as elongation and low modulus are called tough. This results from the combination of column that guides a metal dart. Fundamentals of Composites Manufacturing: Materials. tup. Crosslinking of a brittle polymer will usually decrease tough- ness because of the increased limitation of motion within the polymer mass caused by the intermolecular bonds. impact toughness (Izod or Charpy) in units and materials with low elongation and high of ft-lb/in. which impactor has an accelerometer attached that causes more atoms to rotate. tial energy) can be related directly to the energy absorbed by the sample. materials that exhibit maximum height of the swing. Crystallinity gives higher strength but lower The weight of the impactor. the sample is placed under a ness. and Applications . ness is the falling dart test (ASTM D5628). (J/m). and measures the energy absorbed on impact and stretch to absorb the energy of the impact. The energy ab- modulus is usually low in these materials sorbed is a measure of the toughness of the (low stiffness). especially if absorbed from the impact is measured from they also have good strength. therefore. However. which is pulled by the pendulum and then This movement is related to elongation or stops at the maximum height. Some of the energy in the pendulum will be absorbed in the breaking of the sample. An iterative process for a simple beam. the length of time the load is Fundamentals of Composites Manufacturing: Materials. This method portion of the deformation). This property is called height and weight of the impactor that causes creep. the results are given as the height at ately recovered (the elastic or short-range which 50% of the samples break. A load is applied over a of raising or lowering the height to obtain a long period of time causing the material to range of “just fail” and “just pass” heights deform. the amount of a relatively short period of time to measure creep is strongly dependent upon the amount results (even tensile tests are completed in of the load. Methods. a small determines the results of the test. However. and the size of the impactor point can all be a few minutes).10: Quality and Testing 283 Figure 10-11. However. a continuously applied load that is less than Some tests lack the accelerometer and that required to give immediate or near measure the toughness by noting the drop immediate failure. This deformation is called permanent set. some is called the stair-step procedure. In some amount of the deformation will be immedi- cases. of the deformation is not recovered. polymeric matrix varied to accommodate different materials materials will often deform over time under and different sample thicknesses. When the load is removed. and Applications . Izod and Charpy impact tester and specimens. Creep In addition to an obvious dependence on The tests discussed up to this point all take the nature of the composite. Creep is illustrated in Figure 10-12 sample rupture to occur. only at high temperatures and for long dura. • Reduce the stress level. and Applications . Further. Adhesives are generally not rein- polymer matrix composites are considerably forced and therefore will creep just as other different and can exhibit pronounced creep plastic and resinous materials do. the sample will eventually F = amount of deformation (strain due to break. If the stress-to-rupture test functions of time and temperature. To = applied stress (usually a constant If a material is loaded for a long period over the course of the experiment) of time. It has These relationships can be expressed by the been observed that initial load cycles modified stress-strain equation. A plot of the stress level versus the amount of deformation. However. not the resin. Increases in any of these parameters sometimes relieve the residual stresses will cause creep deformation to be greater. and the temperature of the mate. • Utilize initial loading cycles. • Increase the fiber content and corre- spondingly reduce the content of the creep-prone resin matrix. that contribute to the creep. let the fiber. Creep test. Figure 10-12. Creep can be especially troubling for tion. and it is creep) useful in developing allowable stress limits Both the modulus and the deformation are in applications. • Select stiffer fibers such as high-modu- lus carbon or use hybrid designs to achieve a higher stiffness. relieve the stresses. The creep at temperatures of 100–300° F (38–149° C) for these materials is higher than for fibers. Methods. where operational loads can cause long-term thus the non-reinforced materials will creep Fundamentals of Composites Manufacturing: Materials.284 10: Quality and Testing creep. with a sub- E = creep modulus stantial load. This is called creep rupture. Some of the methods that can be used to reduce the amount of creep include the following: • Place the fiber orientations in direc- tions of high loads to reduce the creep loading on the transverse or resin-domi- nated direction. applied. is performed at several loads. the times for increases in the amount of stress (T) from rupture will be different assuming constant experiment to experiment will also increase temperature. the time to failure will give the allowable Significant creep is generally observed in stresses for design considerations with the ceramic matrix and metal matrix composites additional allowance for safety factors. In other words. at a high temperature. be the principal load-bearing member of the structure. causing initial micro-cracks and flaws to arrest at T o  E(t . non-reinforced polymers and joints. which rial. T )F(t . • Reduce the temperature. T ) (10-2) fiber-matrix interfaces and creating a more stable substructure within the where: material. composites have several mecha- maximum service life of around 106 to 107 nisms through which fatigue can be reduced cycles. In fiber-reinforced cause creep rupture to occur more rapidly composites. and Applications . • energy dissipation resulting from the One of the major advantages of carbon- viscoelastic effects of the matrix (that is. the adhesive should be the order of one-half the static ultimate as highly crosslinked as possible without strength for conventional aluminum alloys. The fatigue test is per. These types of charts are occasionally that exists within the overall composite called S-N charts (indicating the stress and structure. which samples are prepared. and the number of failures). and then subjecting the sample to intermittent • blunting of cracks at the fiber surface. especially over the largest practical area. The critical which reduces further crack growth and property is re-measured after set numbers transfers the load to the fiber. To ures will occur. Creep is also a This means that after about 106 cycles. This can be minimized by us. the or at least significantly retarded. metals do not. the limit of performance is ing the highest possible fiber concentration taken as the point when the retention falls in the composite. the problem in mechanical joints. This phenomenon energy by breaking matrix bonds but is called fatigue. Composites tend to stabilize early in fa- tigue loading through the following mecha- Fatigue nisms. all are exposed to the may relieve internal cure stresses load with a few being withdrawn for testing through bond breakage and additional at each interval. or level of stress. carbon fibers. becoming excessively brittle. the fatigue endurance limit is on inforced materials. minimize the amount of creep in non-re. such as tensile strength. versus aluminum as illustrated in Figure 10-13. used to monitor the fatigue of various mate. the loss of a few failed fibers than in a non-stressed sample. Figure 10-13 shows a chart flexibility. Their fatigue endurance limit. appear to be better than their Some residual stresses in a material may metal counterparts. is not noticeable to the overall strength of es. of cycles.10: Quality and Testing 285 more than the reinforced composites. each of which absorbs or redirects the Composites and almost all other materials energy to other parts of the structure: are negatively affected by intermittent loads • matrix micro-cracking. In most cases. Methods. whereas stress level below which no significant fail. a composite. In fact. a bolt or rivet. loads over long periods of time. • stress redistribution and load sharing rials. which absorbs applied over long periods. reducing the temperature below 50%. In actual practice. epoxy composites in aircraft applications movements among the polymer chains). in early rupture. is low in this cycle range. is their improved fatigue performance This is also called internal damping. several identical • delaminations between layers. In these cas. The composite aluminum can only safely withstand 50% of material will often creep under the loading of the static load it could originally withstand. does not lead necessarily to catastrophic formed by measuring a critical property in breaks in the fibers. Fundamentals of Composites Manufacturing: Materials. the residual stresses combine with the the composite because the load is redistrib- stresses induced by the creep (migrating uted among the other fibers through load through the polymer structure) and result sharing. or by spreading the stress Fiber reinforced composites. Many aircraft are designed with a Thus. Vibrations can cause distor- will persist. it vibrates. and performance such as in an stiffer the material. vibrations in a composite are When a composite material receives a sud.286 10: Quality and Testing Figure 10-13. That is. tions of function such as misalignments in Fundamentals of Composites Manufacturing: Materials. Methods. which can result in fiber-matrix about the original position in cycles with ever bond breakage and delaminations. especially decreasing amplitude. The speed with which over long periods. They can also affect external attach- rectly to the stiffness of the composite. and Applications . The vibrations might also the vibrations end is called the damping initiate micro-cracks. failures. Vibration and Damping In general. it oscillates movements. so the ments. which could later cause of the composite. to be avoided. the longer the vibrations airplane wing. Vibrations cause internal den impact. Vibrations are related di. bonds. Fatigue testing for various materials. The layers plastic matrix and a ceramic-like fiber. and the CTE in porated onto the composite. This latter method verse CTE. a piezo-ceramic device is temperature that is uniform in all directions. the interaction between have excellent damping characteristics. expansion (CTE). damping is highly desired. which are a mixture of a oriented exactly opposite (–45°). rigid response is needed. In many cases. the fibers are restrain- has been called stress-coupled activated ing matrix expansion in the fiber direction. which are Composites. The transverse direction. surfaces where fast. often a metal. This device Therefore. cal current that drives a motor to counter. the CTE for metals is to bond the composite together with an is usually constant over the entire range of adhesive layer that has high elongation. other fibers in the same sheet. which is incor. the coefficient of thermal senses the movement and sends an electri. Clearly. These differences two layers are.) Therefore. selection of resin and fiber combinations. Methods. The rubbery state above structure. adhesive. This creates an TESTING interlayer that absorbs considerable en- ergy and therefore dampens the structure. these fi. acting in opposite are noted in Table 10-2 where the CTE in directions. incorporated in the composite. temperatures for the solid metal. (Think characteristics. is independent of location within the metal act the vibrations. usually trying to rotate to 0°. In ergy (even without rupturing) and thus other words. they have different CTEs bers attempt to align with the direction of in the direction of the fibers and in the vibration. For plas- This type of material absorbs much of the tics. Further. the composite provides stiffness cause the vibrations to decrease. to the THERMAL AND ENVIRONMENTAL surface of the composite. damping (SCAD) and has been shown to be which is the direction in which the bonding several times more effective than the other of the matrix and the fibers would logically common types of damping. Still another method and ceramic. maintain a rigid aerodynamic surface. This characteristic is important in control- Compared to most metals. the CTE is different energy and therefore dampens the entire below and above Tg.10: Quality and Testing 287 space telescopes. composites provide excellent of the vibrations that occur in an airplane properties for aircraft and missile control floor or in a golf club shaft. Proper additional features can be added to com. damping and it is done by bonding a sheet of another material. Fundamentals of Composites Manufacturing: Materials. the glassy state below Tg. the structure’s elasticity and its need to The many fiber-matrix bonds absorb en. Another method is to orient the Tg expands from two to four times more than fibers in a damping sheet. composites ling aero-elasticity. Temperature Effects Another method is called active damping. on the other hand. As a result. they are also As a result of their improved damping objectionable because of discomfort. therefore. This causes a shearing action in the fiber direction is seen to be at least an the adhesive and that absorbs energy and order of magnitude larger than the trans- damps the vibration. The fibers in both states is substantially higher than the the sheet are at an angle (usually 45°) with CTE for a metal or a ceramic. Metals and ceramics have a response to In this method. often represented by A. have are bonded together with a high-elongation a complicated dependence on temperature. be most effective. and Applications . posites to further improve damping. can such feature is called constrained layer provide that control. One along with fiber and layer orientations. But some and improved “feel” in the aircraft. When vibrations occur. Representative coefficients of thermal expansion for epoxy-matrix composites.4 to 0. As the carbon fibers are converted process built in some residual stresses that. is limited. ics. used in the composite. For most materials. upon heating. Coefficient of Thermal Reinforcement Direction Expansion. This change in structure and. This is done by care- might be expected that the CTE changes in fully selecting the directions of the fibers a similar way. the CTE strength of various metals and composite reflects the greater activity of the atoms at materials. Methods. rotating. they also experience a decrease with temperature. are relieved. be achieved with a zero CTE material.7 to 1. This causes an the structure of the fibers goes through a initial shrinkage in the fibers with heating dramatic change. On the other hand. rienced are great and yet the need for precise tor of the extent to which the fiber has been alignment of various optical components converted to graphite. its high-temperature range allow for the greater movement (vibrating. iron has low twisting. 10–6.288 10: Quality and Testing Table 10-2. and translating). from polyacrylonitrile (PAN) to graphite. activities are also occurring in carbon fibers ly representative. the strong stretching (draw- depending on the nature of the carbon fiber ing) of the fibers during the fiber-making itself. the range of values for and in aramid fibers. therefore. stiff materials tend to expand less perature. which indicate that for them too. These can both are some CTE values for metals and ceram. it a zero CTE material. and Applications . This activity results in composite has high specific strength at room the atoms moving away from each other to temperature. a negative CTE. This is possible telescopes where the thermal changes expe- because the fiber modulus is a good indica. materials experience with increasing tem- Hence.6 (–0. ° F (° C) Glass fibers Parallel to fibers 8 (15) Transverse to fibers 30 (55) Carbon fibers Parallel to fibers –0. Therefore. Also in that figure must not be compromised. The negative results in a significant change in CTE as CTE has a benefit in allowing the creation the fibers move from a plastic-like structure of a composite material that is essentially to a ceramic-like structure.0) Transverse to fibers 4 to 6 (7 to 10) Aramid fibers Parallel to fibers –1 (–2) Transverse to fibers 33 (60) Though the values in Table 10-2 are mere. in both of carbon indicates real variation in the CTE these materials. in important mechanical properties such as The negative CTEs for carbon and aramid strength and stiffness. Such a material has It can be followed by noting the CTE as a great benefits in applications such as space function of fiber modulus. as In addition to the expansion that most the modulus increases the CTE decreases. However. Figure 10-14 shows fibers are highly unusual and deserve some the effect of temperature on the specific discussion. Such specific strength but has good retention Fundamentals of Composites Manufacturing: Materials. which is exactly what occurs. While the polyimide-carbon fiber higher temperature. general rule-of-thumb has been to target 3% as an upper range. less than most matrix materials. Carbon Table 10-3 indicates the degree to which fibers and ultra-high-molecular-weight Fundamentals of Composites Manufacturing: Materials. The goal within the extremes. it is obvious Moisture and Solvent Effects that values for existing resin systems are Composites absorb moisture through the often greater than this goal. Methods. Other materials fall between these equilibrium conditions.10: Quality and Testing 289 Figure 10-14. A strength is carbon-carbon. of properties through a wide temperature the polymer matrix can absorb water under range. although it is typically cracking or delaminations have occurred. However. matrix. Specific strength as a function of temperature. considerable moisture. Fiberglass and aramid fibers can absorb and porous regions or areas where micro. the fiber-matrix interface. The best material for both high industry has been to develop matrix mate- specific strength and retention of specific rials that do not take up much moisture. the fiber. and Applications . Therefore. PEEK. The high-performance thermoplastics are well Epoxy.5 that inevitably occur during aircraft main- (PEEK) tenance. polyetherether- Epoxy 5. consulting Table that most polymers have a significant loss of 10-3. in outdoor ap- a composite is the amount that would be plications. Moisture absorption for neat water absorption. and Applications . Consequently. % materials (polysulfone. moisture. in a significant loss of properties over long rial to the chain decreases water absorption periods. effects of simple environments can result Toughening epoxy by adding aliphatic mate.0 known for their low moisture absorption and toughened resistance to other solvents. Hence. Polymer materials are sensitive to ultra- tion of the amount of moisture absorbed by violet (UV) light. Methods. with atomic oxygen.3 plastics. The polyes- toughened ters are sensitive to many common solvents Epoxy. such as polysulfone (PSU). would be required or. However. there are sev. Note the low Polymer Type Absorption at water absorption rates of the thermoplastic Saturation.0 is a problem because of the occasional spills Polyetheretherketone 0. Just as UV light de- at a typical fiber content of 60%. the rubber toughening is due to the presence of a second phase wherein absorption oc- Moisture curs on the phase boundaries. the amount of moisture that could be properties. and polyamide-imide). Epoxies also have sensitivity to many (121° C) common solvents including the hydraulic fluid used in many aircraft. rubber 9. Even in earthly conditions. with the fiber volume at 60%. the resin grades the matrix materials. aliphatic 4. non-moisture A similar problem exists in near space absorbing part of the structure. it should be remem. However. alternately. and polyamide-imide (PAI) allows polymer composites to be used in applications where polyethylene (UHMWPE) fibers absorb little these and other solvents are present. bered that the fiber is a major. As shown in Table 10-3. in both outdoor and space absorbed in a graphite composite made with applications. the decrease in polymer capability absorbed by the resin matrix. For example. Solvent sensitivity can be a major problem Epoxy.0 ketone [PEEK]. Figure 10-15 shows data from a slightly. the long-term eral factors that influence water absorption. oxygen. the excellent solvent resistance of the high-performance thermo- Polyamide-imide 0. This sensitivity Polysulphone 1. when needs to be determined. Some environments using moisture absorption data for neat of high sunlight are obviously more severe resins (without fibers).0 with some composite materials. Therefore. a surface coating be 2% (40% of the maximum value of 5%).290 10: Quality and Testing Table 10-3. adding rubber increases study in which a fiberglass-epoxy composite Fundamentals of Composites Manufacturing: Materials. a significant safety factor might epoxy. rubber 7. Therefore. Studies of spacecraft placed in orbit ues shown in the moisture absorption data for several years and then retrieved indicate for the resin. The increase in water from (non-reinforced) resins. so does atomic moisture pickup will be about 40% of the val. employed on polymeric matrix composites.4 such as acetone and methyl ethyl ketone toughened at 250° F (MEK). in this regard than others. a good approxima. Comparison of the obsolescence built into their designs. Of (rather than days for boiling water) but course. on the other hand. been seen in this chapter. it may not proximately 10–25 years. be anticipated in far less time than would be For example. Methods. as has correctly reflect the condition of the part af. Fiberglass-epoxy exposure to various moisture conditions. erties degrade over time. composite prop- ter actual service. ture-humidity testing is in the order of weeks mance in real time with accelerated tests. and Applications . Therefore. the value of the accelerated tests is the weeks are better than experiencing the that the performance of the composite can length of years of actual service in Panama. Therefore. However. 3–5 years service and a maximum of ap- even though it was a short test. The temperature-humid. seems to rational basis for predicting the service life Figure 10-15. agree well with the conditions of actual service ronments in an effort to gage the effect of in Panama. that 40 days in the temperature-humidity Figure 10-15 represents data for pressure environment is equivalent to nearly 4 years tanks that were burst (taken to failure) after in Panama. exposure to three conditions: boiling water. some ity conditioning. Most data indicates that the boiling water is more structures are designed for a minimum of severe than the other conditions. the accelerated test indicates required with real-time monitoring. high humidity and elevated temperature Aging and Service Life Considerations (95% relative humidity and 174° F [79° C]). The time frame of the tempera- moisture and attempt to correlate its perfor.10: Quality and Testing 291 was exposed to several high-moisture envi. Fundamentals of Composites Manufacturing: Materials. Few composite products have antici- and actual service in the humid and hot pated short-term service lives or planned conditions of Panama. include bearing strength. accelerated tests usually consist of put. • Verify the data by subjecting the part What is most clear is that under the condi- to real service conditions. however. open-hole tension. and Applications . and loading conditions. a cyclical loading test would be and plastics. and private ting samples into elevated temperature laboratories around the country. model of combustion exists for these materi- • Accelerated aging analysis usually re. fiberglass records over long exposure times so the does not burn and does not. extending the time for the sample. and at various national. temperature. burn has been. there that an extrapolation to real operational is a surprising amount of information that environments can be made. and will be ignored for the purposes of this tion. Concentrate two temperatures to study the loss of a par- on identifying the worst combination of ticular property. aramid fibers.292 10: Quality and Testing of parts needs to be devised. Even less. a major formance records are unknown. con- real performance can then be placed in tribute to the combustion of the material. That is. impact. Some aspects are clear. such as 5. the insulate the inside from the flame. such as when the outer layers of fiberglass to see how a sample behaves over time. only gross including some real exposure data so approximations are possible. Air. when several effects several environmental conditions and combine (as occurs in real fires). posed to a set time. humid. for example. Some minor contributions may the temperature of a sample is the same as arise from the orientation effects of the fibers. at ity. taken by quires modeling the data taken from themselves. their contributions to the fire are thermal aging depend upon the phenomenon generally much smaller than the resin matrix called the time-temperature transposi. als. The a database to give credence to future other common fiber reinforcements—carbon models and extrapolations. and UHMWPE fi- Thermal aging is an important way to bers—will burn under normal fire conditions. Properties often examined conditions. The study of how composites and plastics isting data is inadequate or where per. These area of research at universities. materials to see what is already known about them. but these temperature of the sample can be raised. accelerate composite behavior. duct these tests. compare the baseline (unheated) • Define the service environment in terms sample with materials that have been ex- of exposure time. no comprehensive appropriate. Even so. Keep good tions that normally exist for fires. Methods. These companies may. effects are small and will be ignored. stituents. review the database for those and open-hole compression. can be learned just by making some reason- able observations. compression after • After selecting the materials and con. However. No one has and severe humidity conditions. military.000 hours. Tests for However. Following are craft companies and others who expect their some suggestions for establishing a basis for products to be used for many years often con- predicting service life. fibers. If the yet been able to sort out all of the factors that anticipated environment is repeated occur during the combustion of composites loading. in industry. FLAMMABILITY TESTING • Conduct accelerated aging tests on the materials and components to develop Understanding How Composites Burn trends in performance where the ex. therefore. flexural strength. Fundamentals of Composites Manufacturing: Materials. and continues to be. This principle states that increasing discussion. Methods. for testing is to satisfy the requirements of cations will usually have to be made to the some agency that controls the specifications resin or one of the few inherently flame. bromine. use conditions. Many • Smoke emission/toxicity—how much minor additives. escapes from the material during com- which releases water molecules when bustion and at what rate? heated. The test Fundamentals of Composites Manufacturing: Materials. the best practice is to run terial drip. To reduce that burning. In assessment of overall design for fire safety. some modifi. process. These water molecules tend to • Fire endurance—how rapidly will fire reduce the flammability of the composite. study of the nature of the combustion often made to make the resins less com. Sometimes even color pigments corrosive? can have an effect. These fillers reduce flammability. Combustion Characteristics of Organic • laboratory tests or those usually done Resins and Plastics within a manufacturing facility for in- The following properties are usually those formal studies. Other reasons might resistant resins will have to be used. Other rial? What are the orientation effects on fillers that can strongly affect combustion fire penetration? include those containing halogen atoms such as fluorine. smoke is released? What is the rate can affect the behavior of the combustion of smoke release? Is the smoke toxic or process.10: Quality and Testing 293 Most inorganic fillers do not burn. such as antimony oxide. generally reflecting the purpose for increase the amount of aromatic (benzene) performing the test. the most common methods Flammability tests can be divided into three of modifying the resin are to add halogens or groups. and considered when examining the burning of • full-scale tests used to simulate actual composites and plastics. The reason is simple—most organic resins will The most obvious and prevalent reason burn. • official tests or those performed to meet some official requirement. various market • Flame spread/fire-retardant proper. penetrate a barrier of the specific mate- affecting both flame and smoke. the fire go out? but they may increase smoke density. by far. Other include improvement of the composite mate- chapters have addressed the changes most rials. and Applications . and • Ease of extermination—how easily will iodine. chlorine. One obvious • Heat release rate—how much heat example is aluminum tri-hydrate (ATH). but does the fire spread? Is it different in they can decompose in a fire and strongly different directions? affect the combustion process. brief summary. These categories are: groups within it. or sag as a result of some flammability tests. establishment of a specification. the most important aspect of the composite in deter- Types of Flammability Testing mining the combustion characteristics. droop. for use of the product. • Ease of ignition/flame resistance—how readily does the material ignite? What Official Tests kind of ignition source is required? For numerous reasons. and bustible so they will not be treated here. • Physical characteristics—does the ma- fects of fillers. burning? The resin matrix is. sectors have developed their own flam- ties/surface flammability—how rapidly mability requirements and tests. To understand the ef. often requiring pur. now the Na. The so that preparation costs are low. and most of that all parties performing the tests do them the fundamental combustion charac- in precisely the same way. A brief summary of the most important of the nature of the smoke generated in a the official tests follows. thus limiting tional Institute of Standards and Technol. where the flames never reach. flame spread factor and a heat evolu- posite products and their associated fire tion factor.294 10: Quality and Testing procedures have been carefully specified so range at commercial labs). index. the broad applicability of this test. and Applications . [10. cases.25 in. This index is the product of a The major market or use sectors for com. In light an estimation of the potential effects of these requirements. the material is subjected to a radiant Note that each test procedure is designated heat source. rate study and experimentation. and the costs of the test are modest such as the American Society for Testing ($200–$300). Because satisfy most of the marketing/use sec. The smoke chamber • The cone calorimeter (ISO 5660/ASTM test (ASTM E-662) is designed to mea- E-1354) test. available.2 × 10. it is sometimes referred to × 4 × . • Combustion research has shown that Details about the tests can be obtained from many fire fatalities occur in rooms these agencies. the procedures only after considerable temperature of sample as it burns. Hence. In many amount of data available from this test. rial might be developed. However.6 cm]) as the NBS smoke density test. results are often nization for Standardization (ISO). [15. materials are compared. fire is important. equipment used in the tests has also a model of the combustion of a mate- become standardized. International Orga. The sample size is not by a alphanumeric code in which the agency large (6 × 18 in. appears to be the single. Several advantages of this test the National Bureau of Standards include: the sample size is modest (4 (NBS). as a function of time. The agencies that teristics (ease of ignition.7 cm]) controlling the test procedure is designated. of weight loss. which is only about 10 sure the density of the smoke generated years old. costs test apparatus is a closed box (smoke are usually modest (in the $200–$500 chamber) approximately 3 × 3 × 2 ft Fundamentals of Composites Manufacturing: Materials. thus guaran. As a result of the vast to lab are kept statistically small. especially when different Bureau of Standards (NBSIR. federal motor vehicle been used extensively for many years safety standard (FMVSS).2 × 0. rate of heat control the specifications usually change release.2 × 45. National confusing. rate of smoke release. Federal Railroad and so a wealth of comparative data is Administration (FAR). under both flam- most comprehensive test that might ing and smoldering conditions. weight of sample as it burns. teeing continuity over time in interpreting and yield of smoke) can be determined the test results. Methods. thus enabling chase from only approved sources. places where official of a fire on surrounding areas and oc- tests can be run are usually limited to two cupants. this test was originally developed by tors. groups—commercial testing laboratories and • The principal result of the radiant panel major research facilities such as those owned test (ASTM E-162) is a flame spread by resin manufacturers. The procedures are also under a wide range of heater and igni- studied to ensure that variations from lab tion conditions. this test has and Materials (ASTM). ogy). which are determined as requirements are summarized in Table 10-4. Further. and the military standard (MIL-STD). 4 in./ minute (10 cm/minute) Cargo compartment Fire endurance FAR 25. liner.0) b 200 floor All materials Toxicity NBSIR-82-2532 As appropriate (National Bureau of Standards) Air transportation Cabin and cargo Flame resistance: FAR 25. horizontal. and buses) motor vehicle safety minute) standard) Surface transportation— Seat materials Flame resistance FAR 25. burn length b 6 in.853 (Federal Flame time b 10 seconds. ceiling (American Society for Testing and Materials) Floor structure Fire endurance ASTM E119 Nominal evacuation time r 15 minutes Seat.853 (a–b). 45° FAR 25.50 in.853 (a-l). Ds (4. Methods. and Applications mass-transit vehicles Railroad (15 cm) (buses.4 cm/minute). Sector Component Property Test Procedure Criteria Surface transportation Panels Flame spread FMVSS 302 (federal Rate of flame spread. Fundamentals of Composites Manufacturing: Materials./ minute (6.853 (a-l) Ds (4. and Administration) passenger trains) Panel. Flame spread ASTM E162 Flame spread index b 35 wall.5) b 100 partitions. panels.0) b 200 interior materials Heat release rate FAR 25. class b3 is 4 in.853 (b2–b3).855 Burn length: 6 and 8 in. b 400° F (204° C). FAR 25. partition. Flame time: 15 seconds (commercial aviation compartment vertical. Summary of fire requirements for composite materials in the United States. walls. Peak HRR in 5 minutes: 65 kW-minute/m2 (HRR) ASTM E906 Total HRR in 2 minutes: 65 kW-minute/m2 295 ./minute (10 cm/ (cars. (102 mm) above specimen. Flame time of drippings: 3 seconds aircraft) materials: seat. ducting Rate of flame spread: class b2 is 2. trucks. light rails.853 at 4 in. 10: Quality and Testing Table 10-4. Smoke emission ASTM E662 Smoke density. FAR No flame penetration of liner. (15 and 20 cm) panel. peak temperature liners.855. ceiling. Ds (1. mass loss and flame spread criteria for seats All large area cabin Smoke emission FAR 25. seats 25. heat ISO 5660 cone Criteria currently under development case furniture.4 m2/second. ISO 9750 Average HRR b 100 kW-minute/m2. hull Resin/laminate MIL-R-21607 Resin qualified under MIL-R-21607 or laminate (life boats. average materials) (surface materials) smoke production Organization for smoke production b 1. smoke calorimeter components production Military (U. maximum Standardization) smoke production b 8. Methods. no flaming drops or debris Furniture frames.S. Continued. flame room/corner test spread b 20 in. (International maximum HRR b 500 kW-minute/m2. wall Heat release rate. Ignitability. rescue boats. Navy Structural Peak heat release MIL-STD-2031 (SH) Flame spread index b 20.5 m) from floor. maximum smoke Dm submarines) composites inside (PHR). craft. (0. other release. smoke. Sector Component Property Test Procedure Criteria Marine transportation Main structure. and Applications Marine (high-speed Bulkheads. etc. 296 Table 10-4.3 m2/second. flammability (fire. flame spread index b 100 and small passenger retardant properties) ASTM E-84 vessels) Fundamentals of Composites Manufacturing: Materials. (military standard) or tested to ASTM E84. b 200. 25 kW/m2: PHR b 50 kW/m2 pressure hull Tign r 300s • 50 kW/m2: PHR b 65 kW/m2 Tign r 150s • 75 kW/m2: PHR b 100 kW/m2 Tign r 90s • 100 kW/m2: PHR b 150 kW/m2 Tign r 60s 10: Quality and Testing . fire-restricting and ceiling linings surface flammability. the laboratory tests will general give the same ranking of materials as would be obtained in official tests.5 or 3. nearly immediate results can be assessed.6 × 0.6 cm]. The rate associated with decreased flammability. [7. gas inlets so the atmosphere within it Ds.0 minutes. the ignition sample size. however. LOI test a sample is suspended verti- ated by the burning of a sample placed cally inside a closed chamber (usually inside. v The limiting oxygen index (LOI) test ber contains an optical light source and (ASTM D-2863) is probably the most detector to measure the reduction of accurate of the laboratory tests. expressed as a percentage of the is for building materials. Some of the most common laboratory tests are listed next. The smoke cham. The sample is oxygen/nitrogen atmosphere. and Applications . Figure 10-16. Such a case might occur when a company is trying to adjust the formula or design of a prod- uct. After ignition. In the optical density from the smoke gener.9 × 0. Fundamentals of Composites Manufacturing: Materials. usually 3 × a glass or clear plastic enclosure) as 3 × . The v In the vertical burn test (ASTM D-568 cost of performing this test (about $500 and D-3801).6 m).9 × 0. The sample is ignited • The Steiner tunnel test (ASTM E-84) from the bottom and the atmosphere measures the flame spread and smoke is adjusted to determine the minimum generated by the burning of a sample amount of oxygen required to sustain within a large (25 × 2 ft [7. and extent of burning are reported.10: Quality and Testing 297 (0.6 m]) burning.25 in. Results is equipped with oxygen and nitrogen are usually expressed as smoke density. can be controlled.6 × 0. source (usually a Bunsen burner) is Laboratory Tests Sometimes official tests are either too costly or too time consuming to run. This minimum oxygen con- chamber.6 × 7. Limiting oxygen index test. The sample is small. Also. The chamber cost is moderate ($300–$500). The company might go to an outside testing agency (commercial laboratory or resin supplier) and have an official test run on a candidate formula or design and then use inside laboratory tests to monitor the effectiveness of changes. In this way. Methods. as useful as official tests in ranking the combustion characteristics of widely different materials. Higher numbers are a fire is started at one end. and the shown in Figure 10-16. is called attached to the top of the chamber and the oxygen index. Laboratory tests are not. after 1. the sample is suspended per run) is relatively high. as is the cost vertically so that it can be ignited at of the materials because of the large the bottom. because the nature of the materials are usu- ally similar. The principal use of the test tent. basket. In most of the tests. such as a burning waste resin should be noted. should reformula- Full-scale Tests tions be necessary. which are assumed to correctly request assistance from private testing orga. the standard NON-DESTRUCTIVE TESTING AND procedures often caution against using the INSPECTION results of the test for any determination of Most of the tests that have been described performance in actual burning conditions. most instances. D-635) is similar to the vertical burn Flammability testing will continue to be test except that the sample is supported important in assessing composite behavior. etc. Instead. that burn while the ignition source Full-scale tests often examine tempera- is in contact but go out quickly when tures in and around the test enclosure. full. real parts materials as to their performance in real are rarely tested using destructive tests. vertically. In fact. an entire airplane must To determine actual performance. As a result. be subjected to a series of proof tests that scale tests should be run. proof parts are used to con- failure is considered “bad. the company or successfully completed. Methods. This test is most useful in the enclosure. they can be anticipated and The major problem with the results from worked on before a crisis situation exists.) that can does not burn for the entire time. Only see the value in trying to protect the public self-supporting materials should be and limit liability through testing. and Applications . Dripping of the a likely fire hazard. are nizations (often the same as those who run tested in the destructive tests. Therefore. Therefore. cannot necessarily be extrapolated to being An example is aircraft. In burning conditions.298 10: Quality and Testing withdrawn and the length of burn of the official tests). official tests and laboratory tests is that per- formance in an actual combustion situation can only be speculated. Often.” certified for flight. it is prudent for manufacturers of composite parts to assess the combustion characteristics of their products so that. tested in the horizontal test. because of the tests. smoke generation in and leaking out of guishing. the be used as a framework on which the test time to extinguish is noted. However. the The best that can be hoped for in the official sample is no longer fit for use after the test and laboratory tests is a correct ranking of has been conducted. Fundamentals of Composites Manufacturing: Materials. once the certification is procedures. it is removed are termed self-extin. Some of these testing or- the sample in a set period of time (10 ganizations have even established full-scale seconds) is measured. or a controlled source such as a gas v The horizontal burn test (ASTM burner or an assembly of wooden slats. in this chapter are destructive. Before an airplane is “good. Ignition often simulates of similar materials.” but passing firm performance in simulated actual use. Full-scale tests simulate and exceed actual service condi- are only rarely controlled by standard test tions. coupons and samples from complexity of combustion. real production agency requiring the results is usually free parts are no longer tested in destructive to configure the test. If the sample test facilities (rooms. Materials materials can be attached. This test is less stringent The use of this type of testing in specifications and used when the vertical test cannot will likely continue to rise as more agencies distinguish between materials. that is. vehicles. and heat generation in and measuring the burning characteristics around the chamber. reflect the conditions of the real parts. companies will trim areas. tion (NDE) in which the part is changed. rangement (direction) of the fibers in each of methods. The most important method even though they have frequencies and wave of doing this verification is with ultrasonic properties. as with dense into two groups—non-destructive evalua. Each and matrix have been chosen and the ar. When the ultrasonic waves are associated with defects in the part. the tion. Some have divided NDTs penetration is beneficial. including the its uniformity (as well as some other factors effectiveness and reliability of the manu. This section the laminates and the number of laminates examines some of the most common. instead. electrical current. Methods. parts is useful. Ultrasonic frequencies (20–100 MHz) are just right for General Principles examining carbon-based. the correct fibers defects that are likely to be found. This is because ing changes in that signal when compared the wavelengths are about the same size as to some standard.10: Quality and Testing 299 To gain further confidence in the integrity the energy. material being examined. such as a void increasing the frequency of the wave. Ultrasonic signals are not really electro- cedures. Still others. discussed previously in the section on quality. This is called statistical process Ultrasonic Testing control (SPC). acoustic and. in gen- conductivity. thus facilitating easy Fundamentals of Composites Manufacturing: Materials. on other occasions penetration can non-destructive inspection (NDI) in which no be viewed as a drawback because the waves change occurs in the part. Some required has been worked out. eral. NDT is applied far may be so energetic that they pass through beyond the field of just composites. concrete curing. materials (like metals) or thick materials. the signal ergy of the wave is increased. Wave penetration is also (NDT) have been developed to investigate affected by the density of the material and the nature of the product. and However. quency and wave type that will reveal the sume that the correct design for the part most about the material and the potential has been made. The secret of good NDT is to find the fre- In composites. Another problem weld inspection. and the higher changes are dramatic. wooden beam inspection. the greater the penetration capa- of the parts. Even with superb SPC pro. non-destructive tests as. electrical with high penetration waves is that. However. the changes common defects. They are. they are fundamentally differ- scanning. and characteristics. ent from electromagnetic waves. occasional verification of the actual magnetic. like eddy current. the higher the energy of the wave. Sometimes facturing process. As sions. high-energy waves can be resonance imaging [MRI]). of the methods use electromagnetic signals. space within the composite layers. like ultrasonic and acoustic emis- occur and these need to be monitored. problems during manufacturing can always Others. and many others physically harmful. use non-electromagnetic signals. facturing process is done by controlling the machines. and Applications . use imposed the most important monitoring of the manu. frequency range has its own equipment. That is. By encounter changes in density. resinous materials Most NDT techniques involve sending because waves of these frequencies are high- an energy signal (wave) through or onto ly affected by changes in the density of the the part to be inspected and then detect. printed-circuit-board inspec. In general. Some of everything and cannot distinguish the flaws the most important applications include: from the good material. the en. medical more difficult it is to control and interpret. several non-destructive tests bility of the wave. investigations (like x-rays and magnetic Furthermore. that are beyond this discussion). too numerous to list. part can be distinguished from one another termine the modulus of a material. Ultrasonic signals from these various depths. it has Ultrasonic pulse-echo testing requires access a defect. assuming because of the differences in return times that the density is known. structurally different and. transmitter and the part and the receiver One improvement uses sprayed water. Acoustic Emission An obvious problem with the through. pulse-echo method is the increased sensitiv- ter and a receiver. This is often the stress are detected and compared to other case with parts before they are assembled. ing have taken great strides in reducing. or in signal strength due to air gaps between the manufacturing fluctuations. Still. signal reflected off the backside of the part is A problem with acoustic emission lies in detected on the same side as the transmission the requirement for a standard emission occurred. the method is gaining popu- monly used for field inspections and. Pulse-echo devices also allow detected as losses in the transmitted signal. The couplant in this case is usually water. the need for a couplant. or mission strength is placed between the even eliminating. a couplant mate. is gaining popularity in performance. Methods. method. When the area to be tion. This method is relatively easy to automate therefore. An example of a similar phenom- to only one side of the part. In this type of testing. Quan- return faster than the signals coming from the titative results are also difficult with this opposite side of the part. The output are the most commonly used of the NDT of commercial ultrasonic scanners gives techniques for composites. The pulsed signals are ity it gives to detecting many types of defects. The stress does not need to all stages of composites manufacturing. can detect changes in thickness and simple to interpret. a picture of the internal structure of the Ultrasonic through-transmission testing composite and shows where defects such as is probably the simplest of the ultrasonic delaminations. samples of similar parts. Water and acoustic jelly are allowing much greater portability. The ultrasonic sig. the part defects are located. the entire part. enon is the audible sounds made by wood nal is transmitted into the part and then the just before it breaks. presumably. thus and the part. A difference in the but is not the case when field inspections sound pattern indicates that a sample is are required. be immersed in the couplant. Recent improvements in ultrasonic test- rial that has high ultrasonic signal trans. In addi- common couplants. for precise measurement of thickness and. because larity because of its simplicity and ease of of other advantages. Defects are detected as signals that pattern from a known good part. the transmission method is that both sides of sounds emitted by a sample placed under the part must be accessible. Since the rate of signal travel is One advantage of the pulse-echo method dependent on the stiffness of the material. which devices move (as a coupled pair) across the might be missed by the through-transmis- area of the part to be investigated. transmitter and receiver.300 10: Quality and Testing detection. In the acoustic emission method. wear. contaminants. is that defects at different depths in the ultrasonic measurements can be used to de. thermal Fundamentals of Composites Manufacturing: Materials. This method is com. along well without any couplant material beyond with the transmitter and the receiver can just air. be mechanical. machines are now available that work examined is large. To minimize losses from processes such as corrosion. In actual practice. Another advantage of the is placed between an ultrasonic transmit. monitored as the transmitter and receiver such as foreign material inclusions. and Applications . Defects are sion method. and similar methods. of acoustic emissions to detect minute fluid flows. Evidently. a laser is used with easily detected in these materials. any absorbed water can be detected as This method can detect flaws in compos- the sandwich is heated. ter. instances. finish or gel coat uniformity. dimensional pictures is called holography. For instance. These sample are usually thermal. this can be detected. Radiography especially useful for detecting bond defects has an important role in the inspection of in thick honeycomb and foam sandwich metal-matrix composites. the curing speed. The stresses imposed on the penetrating irradiation such as x-rays. In this method. they may not be way to monitor vibrations on computer hard detected. In the past. defects cannot be phy. jarring. the water will es. However. such as leaks. acoustic emission testing the sample is subjected to a stress (usually has a response rate and sensitivity that are mechanical and often vibrational) and then especially good for this application. Two modes of operation are pos- disks as they come under environmental sible—active and passive. the sample is externally heated and composites and other products is the ability the thermal gradients are detected. an opaque penetrant can be used the test can be done by simply placing the to detect defects. fa- the relative temperatures of the surface of a tigue failures. excessive exposure. However. and stiffness are just some sample and. most constructions. moisture content of type of radiation used in medical practice the sample can be detected. Valve leaks are routinely monitored using portable acoustic emission Optical Holography devices. In the passive interesting application that has relevance for mode. Acoustic emissions are sensitive to many different phenomena in composite manu. polymer composites are nearly transparent A related method is called shearogra- to x-rays and. when a honeycomb The use of laser photography to give three- sandwich material has been exposed to wa. method where two pictures are taken with cape back through the entry crack when the an induced stress in the sample between water is vaporized. This method is and in inspecting metals. therefore. Thermography facturing. Therefore. The high energy of x-rays acoustic detection equipment on the sample is a further deterrent to their use as these and then shining a light or other heat source rays require special precautions to avoid on the sample.10: Quality and Testing 301 stresses are the most common. In composites. If a microwave high-energy waves are the most familiar source of stress is used. because these temperature dif- of the most common properties that can be ferences are affected by internal flaws. impact red [IR] thermography) detects differences in damage. Thermography (sometimes called infra- consistency of fiber distribution. method has had limited acceptance be- cause of the need to isolate the camera and Radiography sample from vibrations. If water has seeped ite samples by employing a double-image into the honeycomb cells. however. and that leaking sound the times of the pictures. In the active mode. a new Radiography is a general term for the phase-locking technique seems to eliminate inspection of a material by subjecting it to this problem. can indicate the location of those flaws. and Applications . Another the emitted heat is detected. In some the same double-image technique as in Fundamentals of Composites Manufacturing: Materials. Methods. this detected. If One non-composite application that is in- the internal flaws are small or far removed teresting is the use of acoustic emissions as a from the surface. which vibrate strongly during composites. permeability. A coil induces an pattern can give an indication of the stresses alternating current in the material. mass. Methods. Shearography has gained The changes in these currents are detected positive acceptance in a relatively short by a magnetic detector and compared with period of time because of this attribute.302 10: Quality and Testing holography with a stress applied between Eddy Current exposures. visual frequencies are not able to penetrate When a resin is liquid. defects therefore. Microscopes also can be helpful in enhancing ted signal. ous application for microwave technology is. therefore. especially those on the surface microwave irradiation to heat the food. If the composite is translucent. Other defects that are often visu- would be different in those areas. or within the gel coat.39 in. However. the size of the those with carbon fibers. its spectra from other samples. Therefore.04–. may be useful in following the degree of fading. thermal. The camera current within a conductive material. microwave Nearly everyone uses visual inspection energy is especially useful in exciting water as a method for detecting some defects in molecules. if an air gap were present. wrinkles. These are shown as decreases in transmit. the penetration depth of this technique is and other methods. and other spectral char- crosslinking. One other obvi. composites that are conductive. and homogeneity. This technique is. are the most commonly detected because ity to apply stress with mechanical. solid. These concentrated in the area and. acteristics. and discoloration. as color irregularities and surface waviness. [1–10 mm]). especially ally detected are blisters. according to their depth and nature and Microwaves can also detect changes in the are a measure of the severity of the damage dielectric properties of a composite. including Because strains are detected. Some of the types of defects clas- in which the resin is especially rich or poor sified include: scratches. in shearography. ally detected defects have been classified tected using microwaves. moisture content is readily de. visual detection of flaws. superimposes them to reveal interference. limited to thereby indicating the strains in the samples. A wide range of visu- Therefore. Areas sustained. abrasions. the extent of cure can be Visual inspection is especially helpful in measured by following the changes in the color determinations and can be enhanced by dielectric properties of the resin. loss of gloss. a currents are affected by variations in conduc- quantitative appraisal of the severity of the tivity. especially those that regularities. In general. can be seen since the dielectric properties and cuts. Fundamentals of Composites Manufacturing: Materials. an An eddy current is an induced electrical image-shearing camera is used. it can carry highly filled composites because of light in- charge much more readily than when it is terference with the opaque fillers. orange peel. porosity. the measurement of the dielectric within the structure and reinforcement uni- nature of radomes and other devices that formity can be detected visually. and Applications . Surface defects great mobility over holography. pitting. Microwave Frequencies Visual Inspection As in microwave cooking. It is takes the signals from the two images and not part of the electromagnetic spectrum. and the abil. Sometimes viewing under oblique The microwave spectrum also can be angled light is useful in detecting surface ir- used to detect defects. especially subtle problems such are small (about . This also instrumentation that detects color matching. therefore. defect is possible. dents. need to transmit electrical signals. limited. Many rac- the use of special lights. Fabrication is done by cutting prepreg The principal applications of leaf springs tape into the desired shape and then stack- are in automobiles and trucks. The springs are placed on the underside of the car in the SUMMARY very restricted space between the rear axle Testing and quality assurance are not only and frame. an application based on the flex. leaf part is then trimmed using a diamond cut- springs are especially useful in cushioning ting wheel. The ability to vary many parameters in ural properties of composites may prove to the composite springs allowed designers to be one of the largest applications of compos. Methods. thus further reducing maintenance. CASE STUDY 10-1 cost. is obtained by stacking the springs. and the real quality of the process tional time of the already pressed mechanic. specific ites. Success is directly related to the level or The composite leaf spring originated in attitude of quality within the organization. The punishment encountered tem. flex locations. Pressure and heat are applied to consolidate cal space required when compared with the and cure the layers in the spring. These ing the layers within a matched metal mold. The main materials First. otherwise ite springs also gave a significant savings in undetectable surface defects. the rear wheels of the car.) However. The failures forced replacement of ment and the employees. Quality durable product than the metal leaf springs is not just a task within the production sys- then in use. The compos- imperfections that result in small. will not improve. The weight savings in some Leaf Springs cases was 3% of the total weight of the car. as well as several primarily on three factors. and Applications . The success of any effort will depend and Ford Aerostar ®. The needed load-bearing capability every successful quality improvement effort. and involvement are integral to resin. consigned to one area that is primarily during racing caused premature sagging involved in sampling and inspection. The principal properties for most compos. This application is leaf springs—those areas of stiffness. The visibility weight over the metal springs—a significant of these dyes can sometimes be enhanced by competitive advantage in racing. the racing circuit out of a need for a more but primarily within management. worth. used in leaf springs are E-glass and epoxy support. thus adding to improve it will cost more than they are to the costs of the cars and requiring addi. Management must have Composite springs proved to have about 20% an attitude that quality begins with them. alter spring rates. and even make progressive springs that are made from stacks of rela. then any efforts the springs nearly every race. springs have the advantage of reduced verti. tively flat strips of a resilient material. resilience within one spring. they are mandated Composite leaf springs have been used by many government and commercial cus- in several vehicles including the Corvette® tomers. and weight. good business practices. trucks and trailers. The cured more familiar coiled springs.10: Quality and Testing 303 Penetrating dyes can be used as a visual longer fatigue life. ing teams also found that the use of com- posite springs eliminated the need for sway bars. about 20%. (The weight savings in just the springs was ite parts are related to tensile properties. Fundamentals of Composites Manufacturing: Materials. Therefore. which eliminated the need technique to detect surface cracks and other for such frequent replacement. If this (permanent set) or fracture of the metal is the primary view of quality by manage- leafs. management’s understanding. Fads are tensile and compression tests are for not new to the business environment and design. in tensile properties when fibers are not • Fiber volume and void content should aligned. tant environmental considerations for facturing process and should. molder. For any operation or organization the correct strategy is critical. the following. important properties. The failure mechanisms for Testing and Materials (ASTM) is the are investigated to verify that design dominant body in the United States for considerations were proper and that defining tests. composite laminates. and Applications . but the release data of the fibers should be monitored. Methods. Testing is the basis for • Moisture and water effects are impor- improvement of a part’s design and manu. of faddish sales talk.304 10: Quality and Testing be willing to invest in the education of em. working properly. terestingly. The American Society structures. therefore. and ceramics. conditions of parts. and be involved manufacturing information about themselves. the standard test methods and the specific These tests have high variability and so tests that might be applied to the actual use many samples need to be run. Special applications also practiced routinely and as an integral part may consider the effects of other en- of every product-improvement project. of delaminations and the extent of dam- Third. wider distribution of data than do results tomography. but they may be more important quality has not been immune to its share in actual use testing. • Toughness is usually determined using The careful manufacturer will understand impact tests (Izod. Charpy. durability and fatigue of composite fully prescribed. lay up a sheet that is roughly 12 × 12 Fundamentals of Composites Manufacturing: Materials. dart drop). plastics. be composites. and acoustic emission. Second. In. and elongation are all time and resources committed to quality. or method being applied. learning points related to testing include thermal cycling. Alignment of Fibers in Tensile Tests These tests generally monitor viscosity Objective: Determine the differences and cure conditions. scale sizes is important to determine • Many standard test procedures are care. success follows the actual content age from impacts. • Important non-destructive tests for com- • Test results for composites have a much posites include: ultrasonic. Tensile strength. Using unidirectional prepreg material. and creep. Key vironmental factors such as solvents. • Tensile tests provide key design and ployees to further this idea. from single component materials like • In-use testing in both small and full- simple metals. manufacturing and quality assurance • Incoming fibers are rarely tested by the were properly done. and fundamental validity of the strategy. • Flexural tests are not as valuable as the program. radiography. be monitored occasionally to ensure Procedure: that the manufacturing method is 1. success is directly related to the tensile modulus. the commitment of management • Compression testing is important in time and other personnel is more important design and in determining the presence than money. LABORATORY EXPERIMENT 10-1 • Incoming resins are often tested by the molder to ensure quality and shelf life. Why are the mechanical properties of 13. Compare the use of five different NDT materials? methods for determining whether a void is present in a thick. ences in tensile and flexural modulus. run in the 45° direction up another sheet in which the middle two layers are oriented at + and – 90°. what are the effects of temperature. Standards and Literature information can be obtained from each References for Composite Materials. Describe the elongation of a material.10: Quality and Testing 305 in. What mechanical properties will change type of specimen. Methods. 12. Cut at least five tensile specimens from strength and flexural strength in both each sheet. as a polymer is post-cured? 8. cord the data. Apply tabbing material to each of the fiber content. run in the fiber direction six layers thick with all of the fibers b. How can the fiber volume fraction be lower stiffness. 7. testing and actual use? Discuss the differ- 7. 1 in. (30 × 30 cm). thermoplastics. Phila- one? delphia. lay meaningful in determining voids than the tensile test? up another sheet in which the middle two layers are oriented at + and – 60°. PA: ASTM. Average the data for each 10. Why is viscosity a good measure of un- cured resin quality? 14. and Applications . Describe creep for both thermosets and 4. Compare the data and plot the results 11. BIBLIOGRAPHY 5. run in the direction perpendicular carefully oriented in the 0° direction. In testing for creep. and direction? sheets. Test the specimens in tension and re. lay c. Why is the compression test more 3. Cure all of the sheets. Using the same prepreg material. What differences are to be expected in American Society for Testing and Materials the following tensile tests and what (ASTM). What would be from hand lay-up without destroying the expected differences in ultimate the part? tensile strength in comparing the two 4. What is the difference between tensile 6. What happens to the tensile strength of a material if the resin does not bond well to the fibers? What happens to the QUESTIONS toughness? 1. Explain the differ- determined for a composite part made ences in the curves. (2. Why are test procedures specified by composite materials often lower than the mechanical properties of the bare ASTM or some other standards orga- fibers? nization used when performing some tests? When would they not be used? 2. 8. Fundamentals of Composites Manufacturing: Materials. indicating changes in ultimate tensile strength as a function of lay-up angle. This tabbing material can be ad- ditional composite material or a metal. to the fiber direction 2. The sheet should be a. 6.5 cm) part. What type of test is normally performed but should be of the proper length and to measure fatigue life? properly tapered. Draw a stress-strain curve for both a stiff material and a material with 3. 5. 1987. 9. Using the same prepreg material. “A Re- view of Fire Test Methods and Criteria for Composites. Lyon. 3rd Ed. Sorathia. Thomas. NJ: Prentice-Hall. Richard. July/August. 1997. Upper Saddle River. MI: Society of Manufacturing Engineers. 10th Edition. Society of Manufacturing Engineers (SME). 2005. 2006. Fundamentals of Composites Manufacturing: Materials. 28. Plastics: Materials and Processing. Usman. Geoffrey. MO: Cook Composites & Polymers. Brent. and Grenier. MI: Society of Manufacturing Engineers. Dearborn. Running Today’s Factory: A Proven Strat- egy for Lean Manufacturing.org/cmvs.sme.306 10: Quality and Testing Composites Applications Guide. 2005. Andrew. Dearborn. Inc. 5th Edition. 1999. A. p. “Composite Materials” DVD from the Composites Manufacturing video series. 2006. Standard. Methods. Ohlemiller. Mika. Dearborn. www. Kaizen Event Imple- mentation Manual.” SAMPE Journal. Dale. Kansas City. and Applications . MI: Society of Manufacturing Engineers. Strong. Charles and Davis. phase. are oriented in specific directions in a plane. instead of ±45° fibers. When the structure of a material is the design same in all directions. Civil and Mechanical Engineering. Fundamentals of Composites Manufacturing: Materials. However. The terial. principal reason for the relative simplicity ±30° and ±60° fibers could be used. • Residual stresses Because composites are often laminar structures. the fibers are often located in planes. do not have fibers. Methods. Therefore. in general. at 0°. Australian Defence Force Academy. When the fibers are directed in all INTRODUCTION directions (random planar orientations). and ceramics. Ph.D. anisotropic. y. the Composite materials are inherently more material is called orthotropic. The University of New South Wales. it is called isotro- • Basic stress types pic. (The example given is not filled with particles. materials • Fatigue reinforced along the principal x. one-component materials such as for example.. non-isotropic or. and z axes • Composites versus metals are called pseudo-isotropic. and Applications 307 . • Vibration and damping the structure is a reasonable approximation • Smart structures of one that is isotropic. their structures are still the only way to get a pseudo-isotropic ma- far less complex than most composites.) * The principal author of this chapter is Rikard Benton Heslehurst. If the fibers complicated in their structures than single. plastics. Even rial approximates orthotropic and is called when these one-component materials are pseudo-isotropic. • Modeling and finite element analysis If fibers are oriented in the vertical and • Lay-up notation planar directions. University College. as in a 3D weave. and ceramics is that the This chapter will present the following: structures of these traditional materials are the same in all directions whereas in • Introduction composites there is a specific directional- • Methodology of composite structure ity. plastics. For example. the mate- most metals. 90°. Because the fibers in most composites • Laminate theory are not equally oriented in all directions. • Rule of mixtures synonymously. especially those off-axis. and ±45°. This • Cracking in composites is because some of the directions. School of Aerospace. the fibers • Symmetric and balanced equations are not really the same in all directions.1: Introduction to Composites 307 11 Composite Design* CHAPTER OVERVIEW of metals. composites are. Note design methodology can be undertaken by that there is a major impact on the a series of development procedures. methodology books. (QFD) method. including 1. • emphasis on the attention to detail There are many fiber and resin materi- required in design and manufacture to als to select from. and the time/cost of manufacturing the Design specification is particularly cru. woven cloth.). tant of the steps in design. ronment. The fiber form selection STRUCTURE DESIGN is generally based on either fabrication The basis of the composite structure convenience or shape complexity. vendors have a preferred list of the • an understanding of how the manu. Choosing the material and manufac- will be produced. Methods. part. These strength-to-weight ratio and stiffness- are outlined in the flow chart shown in to-weight ratio when selecting a cloth Figure 11-1. The most ap. and and resin for the structure. This usually comes down to result is a product that works the first what a company already has available time and meets customer requirements. The se- lection of unidirectional (tape. in the wrong way than. system combinations. fiber form. This method is dis- • an understanding of the influences and cussed elsewhere in numerous design issues of the individual constituent ma. for example. and propriate type of design is a functional the corrosive condition dominate resin specification. terials (fiber and resin) so good designs 2. It is based on what the selection. the • an awareness that there are many fiber choice is either a glass or carbon variables in the design of composite type depending on the application and. Other fibers should be and addressed. this chapter will provide: with traditional materials. vapor/fluid absorption characteristics.308 11: Composite Design The design of composite structures is com. rovings. The other detailed functional specification will part of the step is choice of manufactur- always save time and money. A brief description of each step over a tape form. A good approach to develop- • an understanding of the principle char- ing a design’s functional specification acteristics and issues so that good struc- is the quality function deployment tures and components will result. and Applications . investigated where necessary. mat. structures that need to be understood of course. Design specification is the most impor. such as metals. The end ing method. Most material ior and performance. As such. attention should be given to The development of a thorough and fiber/resin interfacial issues. fiber/resin system combinations from facturing (fabrication) processes are which to choose. or some other METHODOLOGY OF COMPOSITE form is next. temperature range (hot and cold). cally an operational environment issue. Also with respect to the envi- part must do in actual use (function). Typically. Also impacting the manufactur- cial for composite structures as there ing process selection is quality control are many more ways of doing the design of the product’s performance require- Fundamentals of Composites Manufacturing: Materials. Resin selection is typi- follows. plex. The operational environment. turing is like opening Pandora’s box. cost. design. but the first require- closely tied to good composite structure ment is choice of fiber type. etc. as well as fiber/resin achieve the desired outcomes in behav. For example. However. Figure 11-2 laminate’s axial stiffness or strength is just one of several types of design Fundamentals of Composites Manufacturing: Materials. single-ply equivalent property. ments and the number of parts to be requirement is known as a ratio of the produced. and Applications . do not rely solely on these This step can be done using simple results to finalize a design as other sizing charts such as the one shown factors need to be considered when the in Figure 11-2.11: Composite Design 309 Figure 11-1. ±45°. required in the various orientations. Methods. is used to determine the number of plies and 90° directions can be determined. Composite design methodology flow chart. then 3. Initial sizing of the composite structure the percentage of plies in the 0°. when the final configuration is set. strength of the laminate in the principal ite laminate. and Applications . To determine the in-plane directions. Simple sizing chart for laminates. some will even run as a the composite structure.310 11: Composite Design charts that can be used to initially size can be used. Detailed sizing of the composite structure done to evaluate the complete in-plane requires a computer program to evaluate stiffness properties and estimate the the engineering properties of the compos. (Courtesy John Hart-Smith. 1989) Fundamentals of Composites Manufacturing: Materials. Boeing. These simple programs also properties. But this step must be 4. spreadsheet. Methods. a relatively simple program will estimate many of the other physi- Figure 11-2. Methods. The outcomes of the design. Such activities will 2. Typical cost reduction tance and strength characteristics of is achieved through reduced material the laminate. of the structure. stresses (1–2 plane). particularly in estimating to help it meet the design goals with the flexural rigidity (bending) resis. cost reduction. The analysis also materials. investigation of potential interlaminar stress areas. involves performing some form of cially worthwhile. the cost per part can be processing time. failure condition. This is especially so if estimated. Detailed design the materials to be used. The first design review is used to check faster part fabrication. etc. and 5. referred to as first. The detailed design step typically give a good idea if the project is finan. and the manu. on the development of the laminate’s 9. applicable to composite thermal expansion. the individual ply materials. analysis will look for further structural facturing method employed. Here the rationale quences. and stacking se- tional specification. This is compared with other the analysis is to be done thoroughly. posite structures requires significant tion quantity. It is strongly recommended of meeting. leaner manufacturing steps. that detailed stress analysis of com- sumables to be used. material are compared against the design’s func. 1. ply orientation. exceeding. Figure 11-3. in composite structure design are shown in tude of activities such as joint design. Axial and transverse in-plane compres- lead to local ply buildup or thinning sive stresses (1–2 plane). form. or the actual ply orientation uting to the overall improvement or and stacking sequence chosen. Initial costing of the product can now 10. must be used to complete should give an estimation of the initial this phase of the project design. The design detail step covers a multi. Making too changing either one or all of the mate. Axial and transverse in-plane tensile and the effect of damage and reparabil. knowledge of the con. Note information. flexural follows: stiffening with cores. competing products and the functional specification to determine project con- BASIC STRESS TYPES tinuation. Good stress analysis Poisson’s ratio and the coefficient of techniques. degradation of structural performance. such as where required. With this improvements without cost gains. or falling short of that only one aspect be changed at a the requirements guide the designer in time and the analysis re-run. the manufacturing process which parameter change was contrib- selected. The second design review considers the ply failure. making small. In detailed sizing.11: Composite Design 311 cal and mechanical properties. Optimization of the structure involves design. the This review considers improvements to stacking sequence of the plies becomes the design of the composite structure important. The previous steps complex stress analysis such as finite defined the volume of the structure. and the ultimate strength detailed design work just completed. element analysis. and the produc. The basic stress types to be considered 7. ity of the design. 8. and Applications . incremental changes to the mechanical and physical properties. 6. They are usually designated as inclusion of holes and cut-outs. usage. many changes at once will not indicate rials used. Fundamentals of Composites Manufacturing: Materials. and Applications . In-plane shear stresses (1–2 plane). The compres- designated T1 and T2. Fundamentals of Composites Manufacturing: Materials. Stress designation. Figure 11-3. support the fibers and resist this failure nately reacted by the fibers in the 0° and 90° mode. Axial and Transverse In-plane and Compressive Stresses 4. Methods. composite are essentially the same as the in-plane tensile stresses. Interlaminar or through-the-thickness The in-plane compressive stresses in a stresses (1–3 and 2–3 planes). However. sive stresses are designated –T1 and –T2. it or the fill direction for woven cloth support becomes more rubbery and the maximum the transverse stresses. The axial stresses are are therefore controlled by the resin. the Stresses resin plays an important role in compression. These stresses are predomi. The fibers have a tendency to micro-buckle ite structure act in the principal directions and it is the role of the resin (matrix) to of the laminate.312 11: Composite Design 3. while Axial and Transverse In-plane Tensile the fibers take the compressive stresses. The in-plane tensile stresses in a compos. When primarily supported by the 0° plies or the the resin is operated at a high temperature warp fibers in a woven cloth ply. These stresses are compressive strength reduces. The 90° plies or has a degree of absorbed moisture. The compressive strength properties laminate directions. The basic theory of laminate analysis is re- nar stress components: the interlaminar ferred to as Classical Laminate Plate Theory. in the composite structure. There are three interlami. Methods. a pure shear stress the fibers in the 1–2 plane.11: Composite Design 313 In-plane Shear Stresses normal stress T3. the interlaminar field can be transformed into the biaxial stresses are typically taken by the resin. and the two interlaminar The in-plane shear stresses are designated shear stresses. For conventional U12. it can be seen that the ±45 plies play fort expended to design the laminate so the a crucial role in supporting the shear stresses interlaminar stresses are reduced as much as in a composite structure. Out-of-plane stresses induced in composite structures. Fundamentals of Composites Manufacturing: Materials. The interlaminar stresses are also known as the out-of-plane or through-the-thick. possible. Interlaminar stresses are typically concentrated at free edges and where there Interlaminar Stresses are ply variations as shown in Figure 11-4. and Applications . U13 and U23. Based on the well-known Mohr’s circle of two-dimensional composite structures with stress transformation. LAMINATE THEORY ness stresses. Figure 11-4. principal tensile and compressive stresses Since the resin is a relatively weak material along the ±45 degree lines in the 1–2 plane. there is much ef- Hence. When the ply axis of opment of the engineering and physical prop. the mate. Boeing. By laminating with specific ply orienta- verse and shear properties are approximately tions. (Courtesy John Hart-Smith. 1989) Fundamentals of Composites Manufacturing: Materials. Hence. The order Figure 11-5. the in-plane properties are uniform in 10% of the axial ply properties as shown in all directions. erties of a ply based on the fiber angle to the the ply behaves anisotropically. P/6 laminate rial behavior has mutually perpendicular [0°/+30°/–30°/+60°/–60°/90°]. etc. Ply property changes with ply orientation. then the ply trans. Then. Generally speaking. the total that the deformation behavior of the ply resistive force is obtained by simply sum. Methods. carbon-fiber have in-plane deformations. This means principal loading direction. for tion aligned to the ply fiber direction behaves example. P/3 laminate [0°/+60°/–60°]. by the total thickness.314 11: Composite Design The theory is essentially based on the devel. When anisotropically with respect to the ply thickness and dividing behaving plies are subject to in-plane loads. P/4 in an orthogonal manner. If this assumption is the composite will twist and bend. When the greater is the contribution to strength and in-plane properties are uniform. a unidirectional ply or Special quasi-isotropic laminates have equal woven cloth with the principal loading direc. and Applications . is referred to as a quasi-isotropic laminate. laminate [0°/+45°/90°/–45°]. the more 0° plies. That is. the laminate stiffness in the axial direction. unidirectional composite. symmetry is not aligned to the loading axis. numbers of plies in specific directions. is influenced by both in-plane extensorial ming the properties in a particular direction and flexural forces. degrees of symmetry. Uniform properties in a mate- Figure 11-5. the rial mean it has isotropic behavior. as well as made for a high-performance. . In some laminate configurations there B = extensorial/flexural coupling stiffness is coupling between in-plane and flexural behavior and this results in non-zero terms A total representation of the in-plane/flex- in the B matrix.. . . .. ... .. .. A22 A26 B21 B22 B26 ¹¹ ®F 2 ® « N 1 » ¨ A11 A12 A16 ¸ « F 1 » ® 2® © ® ® ® ® © ® ® ¬ N 2 ¼  © A21 A22 A26 ¹¹ ¬F 2 ¼ (11-1) ® N 6 ® © .11: Composite Design 315 is not important for the in-plane properties... the laminate’s behavior « M1 » ¨ B11 B12 B16 ¸ « F1 » (11-3) ® ® © ® ® will be quasi-isotropic. The principal term used in the rule of mixtures approach is the fiber-volume D = flexural stiffness fraction or fiber-volume ratio (Vf).... and as long as there are an equal number of plies in each direction... .. and Jones The flexural behavior relates the radii of 1975.) curvatures to the D matrix to obtain the unit moments as: RULE OF MIXTURES « M1 » ¨ D11 D12 D16 ¸ « k1 » The rule of mixtures approach is a useful ® ® © ® ® ¬ M 2 ¼  © D21 D22 D26 ¹¹ ¬ k2 ¼ method in determining the engineering and (11-2) ®M ® ©D D62 D66 ¹º ®­ k6 ®½ physical properties of plies in a laminate. Tsai 1988... D22 D26 ¹ ® k2 ® where: ® ® © ¹® ® ­ M 6 ½ ©ª .. ... The total k = radii of curvature expression is: The extensorial/flexure couple stiffness re- Vf + Vm + Vv = 1 (11-5) lates the radii of curvatures with unit loads or the in-plane strains with unit moments by: where: « N 1 » ¨ B11 B12 B16 ¸ « k1 » Vf = fiber-volume ratio. ¬ M2 ¼  © B21 B22 B26 ¹¹ ¬F 2 ¼ The overall in-plane behavior of a struc. ®M ® ©B B62 B66 ¹º ®­F 6 ®½ tural laminate is a function of the in-plane ­ 6 ½ ª 61 stiffness and the flexural stiffness proper.. A66 B61 B62 B66 ¹ ®F 6 ® ®N ® © A ¬ ¼© ¹¬ ¼ ­ 6 ½ ª 61 A62 A66 ¹º ®­F 6 ®½ ® M1 ® © . which is the ® ® © ® ® physical volume of fibers to the total ¬ N 2 ¼  © B21 B22 B26 ¹¹ ¬ k2 ¼ ply volume ®N ® ©B B62 B66 ¹º ®­ k6 ®½ Vm = matrix or resin-volume ratio ­ 6 ½ ª 61 Fundamentals of Composites Manufacturing: Materials.. and shear) of the laminate to the load per unit width: « N 1 » ¨ A11 A12 A16 B11 B12 B16 ¸ « F 1 » ® N ® © . .... . D66 ¹º ­ k6 ½ N = load per unit width A = in-plane stiffness (For greater detail in the application of F = strain the classical laminate plate theory refer to Tsai and Hahn 1980. (11-4) transverse.... and Applications . It ­ 6 ½ ª 61 is based on knowledge of the properties and where: volume of fibers and resin that make up a M = edge moment per unit width ply. ural behavior for given deformations follows The in-plane or extensorial stiffness (note that diagonal symmetry is assumed): matrix relates the in-plane strains (axial.. Methods.. where: ties. B. D11 D12 D16 ¹ ® k1 ® ® M 2 ® © . which is gineering and physical properties that can difficult to measure be determined using the rule of mixtures vm = Poisson’s ratio for matrix approach. where: ume of voids and porosity as a result v = major Poisson’s ratio of a ply or single of the process used layer (laminate) The following equations result in the en. please note the following: 1 G 1. vf = Poisson’s ratio for fibers. The void content is assumed to be zero. In using these equations. ¨ Vf Vm ¸ © . (A more extensive listing can be Shear modulus: found in Donaldson 2001). which is the vol.316 11: Composite Design Vv = void volume ratio. Voids are a result of the manufacturing method and the cure process used. ¹ (11-9) 2. Voids reduce the fiber-volume ratio. Methods. However. and Applications . where: Density: T = axial stress strength of a ply or single R = Vf Rf + VmRm (11-6) layer (laminate) where: Tf = axial strength of fibers R = total density Tm = axial strength of matrix Rf = density of fibers Transverse modulus: Vm = matrix volume ratio Em Rm = density of matrix E y  Ez  ¨ ¥ E µ¸ Longitudinal stiffness (modulus): ©1  Vf ¦ 1  m ¶ ¹ (11-11) ©ª § Ef y · ¹ E = Vf Ef + Vm Em (11-7) º where: where: E = Young’s modulus of a ply or single Ey = Young’s modulus in the y orthogo- layer (laminate) nal direction of a ply or single layer (laminate) Ef = Young’s modulus for fibers Ez = Young’s modulus in the z orthogo- Em = Young’s modulus for matrix nal direction of a ply or single layer Poisson’s ratio: (laminate) Ef y= Young’s modulus of the fibers in the v = Vf vf + Vmvm (11-8) y orthogonal direction Fundamentals of Composites Manufacturing: Materials. Gf = shear modulus of fibers ing the fiber. the Gm = shear modulus of matrix individual fiber or resin properties can be estimated. where: In some cases the fiber or resin property G = shear modulus of a ply or single layer cannot be easily determined.and resin-volume ratios. ©ª Gf Gm ¹º 3. by (laminate) measuring the ply property and determin. A complete listing of the various Tensile strength (longitudinal): testing methods for composites materials is T = Vf Tf + VmTm (11-10) available (American Society for Testing Ma- terials 1990). homogenous ¨ 1 ¸ (11-14) laminate approach is the same analysis Vf  ©1 . However. The expression that determines the fiber- volume ratio from the fiber and resin weight In-plane Orthotropic. the fiber. but the ply density and fiber-volume the laminate. analyze the individual in-plane state of the but weight ratios cannot be used directly to laminate and use these results to interpret determine the engineering properties. resin. To de. If three-dimensional stress analysis of the plies the individual fiber and resin densities are not must consider the anisotropic behavior of known. the materials data sheet (MDS) documentation. º (11-13) Each ply has its own individual me- where: chanical and physical properties in three dimensions. tions allow for less complex analysis and thogonal plane initial sizing of composite structures to TmT = axial tensile strength of the matrix be performed. The densities can be found in the purely based on the resin properties. then use Equation 11-6.11: Composite Design 317 Interlaminar shear: where: Gm Wf = weight of the fiber G yz  (11-12) ¨ ¥ G µ¸ Wr = weight of the resin system ©1  Vf ¦ 1  m ¶ ¹ ©ª § Gf yz · ¹ Rr = density of the resin or matrix system º where: The properties of some common composite systems are shown in Table 11-1. there is a difficulty in determin. ratio are provided. some simple assump- TyT = axial tensile strength in the y or. orthotropic and homogenous initially and ing the measured value of the fiber-volume through-the-thickness effects are ignored. But manufacturing safety data sheet (MSDS) or for a complete analysis of the structure. Occasionally the A slightly more detailed approach is to weight ratios of the fiber and resin are used. Gyz = shear modulus in the yz orthogonal plane of a ply or single layer (lami- nate) MODELING AND FINITE ELEMENT Gf yz = shear modulus of the fibers in the yz ANALYSIS orthogonal plane The modeling of composite laminated structures varies from the relatively simple Tensile strength (transverse): to complex. All modeling of composite structures requires computer support due ¨ ¥ E µ¸ T yT  ©1  ©ª § Vf  Vf ¦ 1  m ¶ ¹ T mT Ef y · ¹ to the detail in the lamination of the indi- vidual plies. and ply densities must the through-the-thickness performance is be known. the total structure’s performance. The assumptions made for ease of analysis are that the structure is Generally. An ex- termine the fiber-volume ratio from weight pansion of this approach is to assume that ratios. ratio in a fabrication process. Homogenous ratios is (Heslehurst 2006): Laminate Analysis 1 The in-plane orthotropic. and Applications . Methods. Thus Fundamentals of Composites Manufacturing: Materials. ¥ µ¹ method used with traditional isotropic © ¥ Wf µ Sr ¹ materials. The basic assumption is that © ¦§ Wr ¶· ¦§ S f ¶· ¹ ª º the entire laminate is homogenous. 095 relative density (density of the composite to the density of water) .550 ratio. Vf Matrix volume 0.200 1.200 3. 318 Table 11-1.005 0. Vv 0.005 0.295 0.450 ratio.500 0.600 density (density of the fiber system to the density of water) Matrix relative 1. and Applications Fiber T300 Boron (4) AS E-Glass Kevlar 49 Boron Matrix N5208 5505 3501 Epoxy Epoxy Al Fibers’ relative 1.200 1.545 0.600 1.743 density of matrix. Composite System Carbon Fiber Kevlar® Fiber Boron Fiber Carbon Fiber Boron Fiber Glass Fiber Reinforced Reinforced Reinforced Property Reinforced Reinforced Reinforced Plastic Plastic Aluminum Plastic (CFRP) Plastic (BFRP) Plastic (GFRP) (CFRP) (KFRP) (BFRA) Fundamentals of Composites Manufacturing: Materials.450 0.329 0.750 2.458 2.167 1.458 2.295 0.495 0.000 Fiber-volume 0.500 density (density of the matrix to the density of water) Density of fibers/ 1.824 1.750 2.894 1.167 1.700 0.700 0.200 1.005 0.362 3.200 0.600 1. Methods. Common composite system fiber/resin properties.005 0.560 1.579 1. Vm 11: Composite Design Composite’s 1.440 2.005 0.200 1. Rf /Rm Void ratio.666 0. Note that the out-of-plane deforma- tions due to bending are not truly balanced (this is explained later in this chapter). and Applications . The method also allows for the use of different fiber/resin layers or hybrid Cij = generalized stiffness composite structures. Evalu- in-plane axes of symmetry are aligned with ation of the stiffness matrix. when the plane of symmetry is the same method on. Fundamentals of Composites Manufacturing: Materials. ®T 5 ® ©C51 C52 C53 C54 C55 C56 ¹ ® F 5 ® plane orthotropic behavior on a ply-by-ply ® ® © ¹® ® basis. Beware that the Assuming diagonal symmetry. where: ing sequence. and not like that shown in Figure 11-5. the analysis required 21 tests to This is because they are typically as. The proach is more related to what material individual ply stress state is ignored. For example. This approach re- quires detailed knowledge of the ply stack. One word of caution is i = numerical values 1…6 that the laminate’s properties are typically j = numerical values 1…6 a weighted average over the thickness and this can lead to erroneous results when using However. One important aspect of this analy.. for example. The analysis interrogates the stress state of the individual plies and then combines the data from each ply to arrive at the total laminate performance. Note that the material’s following expression would be used. ­T 6 ½ ©ªC61 C62 C63 C64 C65 C66 ¹º ­ F 6 ½ sis is that the laminate as a whole is also orthotropic such that all angled plies come as a matched pair of positive and negative (11-15) plies. This results in a balanced laminate that eliminates the in-plane anisotropic effects. symmetry or the ply is symmetrical through the thickness). « T1 » ¨C11 C12 C13 C14 C15 C16 ¸ « F1 » ® T ® ©C C22 C23 C24 C25 C26 ¹¹ ® F 2 ® In-plane Orthotropic Behavior of ® 2 ® © 21 ® ® Individual Plies Analysis ®T 3 ® ©C31 C32 C33 C34 C35 C36 ¹ ® F 3 ® The next level of complexity in modeling ¬ ¼© ¹¬ ¼ ®T 4 ® ©C41 C42 C43 C44 C45 C46 ¹ ®F 4 ® composite structures is to look at the in. is necessary. properties are known. then the out-of-plane shear behav- Ply-by-ply Analysis ior is decoupled from the in-plane behavior The most complex approach is to use and only 14 constants of proportionality need three-dimensional. The difficulty in using this ap- smeared throughout the laminate. for example. parallel to the Three-dimensional. Anisotropic 1–2 plane. the laminate does possess orthotropic behavior of a laminate in three-dimensions properties in that its properties vary along was analyzed for a given applied strain. C12 = off-axis properties are not modeled well. of symmetry. the the principal axes. that is. How. anisotropic ply-by-ply to be evaluated. sandwich assumed through the thickness (mid-plane structures. etc.11: Composite Design 319 the overall properties of the structure are analysis. C21. be performed to provide these constant of sumed to vary linearly between the axes proportionality. Methods. C. the principal loading axes. if the ever. shear modulus. The analysis is based on ®T 4 ® © 0 0 0 C44 0 0 ¹ ®F 4 ® dividing the structure into a large number of ®T 5 ® © 0 0 0 0 C55 0 ¹ ®F5 ® small elements and assigning each element ® ® © ¹® ® the appropriate material properties. strain component 6 is equivalent (11-16) to in-plane shear strain Q11 = ply axial modulus.320 11: Composite Design « T1 » ¨C11 C12 C13 0 0 C16 ¸ « F1 » « T1 » ¨Q11 Q12 0 ¸ « F » ® ® © ® ® ®T ® ©C ® 2 ® © 21 C22 C23 0 0 C26 ¹¹ ® F 2 ® ® ® ¬T 2 ¼  ©Q21 Q22 0 ¹¹ ¬F  ¼ (11-18) ®T 3 ® ©C31 C32 C33 0 0 C36 ¹ ® F 3 ® ®T ® © 0 0 Q66 ¹º ®­ F  ®½ ­ 6½ ª ¬ ¼© ¹¬ ¼ ®T 4 ® © 0 0 0 C44 C45 0 ¹ ®F 4 ® where: ®T 5 ® © 0 0 0 C54 C55 0 ¹ ®F 5 ® ® ® © ¹® ® T6 = U12 . the shearing be. and Applications . vice versa havior is decoupled from the normal stresses. only four con- If the shear stresses in the three planes are stants are required to be evaluated in tests: independent. the stress-strain D = deformation behavior is further simplified to: k = element stiffness = EA/L Fundamentals of Composites Manufacturing: Materials. Methods. which is equiva- lent to the axial Young’s modulus Q22 = ply transverse modulus. for the in-plane behavior. Then ­T 6 ½ ©ª 0 0 0 0 0 C66 ¹º ­ F 6 ½ all of the equations are resolved simultane- ously in the form of the load versus deflection (11-17) relationship in terms of the known stiffness of the element. The element stiffness is based on the Young’s modulus of the mate- rial and the element’s cross-sectional area and length: P = kD (11-19) where: With in-plane (1–2 plane) behavior be. and the Poisson’s ratio. then only nine constants of the axial and transverse Young’s moduli. the proportionality need to be evaluated. Poisson’s ratio effect of trans- When there are three mutually perpen. which is equivalent to the transverse Young’s modulus Q66 = ply shear modulus Q12 = Q21. « T1 » ¨C11 C12 C13 0 0 0 ¸ « F1 » Finite Element Analysis ®T ® ©C C22 C23 0 0 0 ¹¹ ® F 2 ® ® 2 ® © 21 ® ® Finite element analysis (FEA) allows de- ®T 3 ® ©C31 C32 C33 0 0 0 ¹ ®F3 ® tailed stress and deformation solutions to ¬ ¼© ¹¬ ¼ complex shapes. verse strain due to axial stress and dicular planes of symmetry. P = applied or internal load ing the primary concern. Thus. stress component 6 is equivalent ­T 6 ½ ©ªC61 C62 C63 0 0 C66 ¹º ­ F 6 ½ to in-plane shear stress F6 = G12 . see Whitney 1987. the main issue individual layers to allow for anisotropic in the application of FEA is what material behavior in the analysis. The through-the-thickness the stress analysis of composite structures properties remain an issue. Finite element analysis of WWII fighter wing diagram of the principal ply directions in a fabricated with composite materials. At the lowest level the 1995. the structural Closed-form Solution Approach components possess the laminate properties that have mutually perpendicular prop.) structural element has global orthotropic properties. In other words. The case study at the end of this chapter provides an example of a closed-form solu- tion approach. (For further read- properties to use. The ply lay-up pattern will aid in Fundamentals of Composites Manufacturing: Materials. and Gibson 1994.) LAY-UP NOTATION The basic principle behind lay-up notation is to ensure that the lay-up pattern achieved in fabrication of the composite laminate is the same as the engineering requirements. as seen in more time for analysis and model building Figure 11-6. but in many cases is within 5% of the more accurate solution. Methods. again. and Applications . It is next level uses the orthotropic properties of not as accurate as FEA. Reddy and Miravete the ultimate choice. see Whitney 1987. and includes the full 3D properties of the In composite materials. the issue of E = Young’s modulus through-the-thickness properties needs to A = cross-sectional area be addressed. and Gibson 1994. The engineering lay-up requirements are set from the engineering stress and stiff- ness calculations. It provides a good initial basis for further detailed stress analysis such as FEA. The basic patterns of ply orientation can be illustrated with a simple Figure 11-6. The most complex approach requires structure showing deformation. The allows quicker results than with FEA. however. The level of complexity is ing. laminate. Reddy and Miravete 1995.11: Composite Design 321 and the individual plies and. The closed-form solution approach in erty variation. The only issue with the closed-form stress analysis approach is that it requires a good understanding of the behavior and aniso- tropic relationships of composite materials. (For further reading. The closed-form solution approach is excel- lent for undertaking the initial sizing stress analysis. The subdivision of the plies requires a significant increase in the number L = element length of elements and processing time increases The solution can be visualized as a plot accordingly (more simultaneous equations to of the stresses in a contour map of the solve). Plies of equal but opposite ply angle (plus/ direction. notation: there are a number of ways to specify the ply lay-up patterns. However. normally with the 0o axis parallel minus orientation) can be shown as: Figure 11-7. is used. Each ply is separated by a slash. (Courtesy Abaris Training. the warp clock. 3. The recognized industry stan. which are also acceptable. shown in Figure tool surface. lay-up notation is taken from the Boeing Some basic rules apply for ply lay-up Drafting Standard. For example: be provided and there should be logic and [notation] consistency in its use.com) Fundamentals of Composites Manufacturing: Materials. that is. and Applications .322 11: Composite Design distinguishing between unidirectional plies to the primary load direction of the part and woven cloth. Laminate notation is written between In any case. To assist in determining the difference be. 2. The basic reference for ply laminate or assembled structure. The notation is written starting with tween plies laid up at angles to the principal the first ply laid down. 1. a key to the notation should square brackets. For dard for its use in notation states that the example: counter-clockwise (CCW) symbol be used on [ply1/ply2/ply3] the main views in the manufacturing draw- ing to show the relative fiber or warp yarn 4.abaris. Directional conventions of the warp clock. Methods. www. 11-7. at the direction. BDS-1330. Symmetry with an odd number of plies • A symmetric laminate has the ply is shown as: orientations mirror imaged about its [0/0/90/0/0] m [02 /90 ] s structural mid-plane as shown in Figure 11-8 with unidirectional tape. For clarification. When the warp direction of the angled from the mid-plane. This is because fabric ply is essential: out-of-plane behavior is a function of ply position away from the mid-plane. When the orientations of the warp di. and fill directions so they are not really rections of fabrics to the laminate’s 0° balanced by themselves.11: Composite Design 323 [±45] m [+45/–45] and SYMMETRY AND BALANCED [45] m [–45/+45] LAMINATES 5. of that ply (FG = fiberglass and C = In terms of structural behavior. but not in the purest sense 12. By this definition. the following carbon): deformation phenomenon will occur. [(0 or 90)FFG/(+45/0/–45/90) C /(0 or • A symmetric laminate does not possess 90)FFG ] coupling between in-plane (extensorial) An example notation for a laminate lay-up and flexural behavior. The properties of the 6. here are the related [0/0/90/90/0/0] m [02 /90] s definitions. Multiple (adjacent) plies can be shown The basic lay-up properties of a composite with a subscript: laminate are defined by the symmetry about the mid-plane and the balance of any angled [0/0/0/90/90] m [03 /902] plies in the laminate. Thus symmetric sequence is shown in Table 11-2. the angled plies must [0/±45F/90/(0 or 90)F]s be co-mingled to have equal distances 11. a 45° ori- 9. as warp/fill direction ply counts can be vidual plies are coded with the material different. 7. Methods. only the plain with warp parallel to +45° m +45F and weave cloth’s 45° orientation plies with warp parallel to −45° m –45F achieve this. and Applications . 8. Combined tape and fabric is shown entated plain weave cloth is effectively as the following. a “T” subscripted • The in-plane deformation balanced outside the bracket designates that the laminate has a positively angled ply entire (total) lay-up is shown: for every negatively angled ply. the indi. A lay-up with mid-plane symmetry uses lay-up configuration have a major impact an “s” subscripted outside the brackets: on the loading and deformation behavior of the laminate. For hybrid laminate lay-ups. This [90/0/–30/–45] T definition does not include 0° and 90° orientations. [0/+45F/–45F/0]s and Generally speaking. laminates show the extensorial/flexural Fundamentals of Composites Manufacturing: Materials. noting that the warp balanced. assuming the same number direction for the 45° fabric is to be ori- of filaments in the warp and fill direc- entated +45° to the laminate’s 0° axis: tions. axis are optional: • To achieve a flexural behavior bal- anced laminate. Note that other weave patterns [0/±45fabric/0] m [0/+45F/0] can have slight variations in the warp 10. First. Fundamentals of Composites Manufacturing: Materials. Example of lay-up notation system. Meaning Notation 45 Fabric (fiberglass) [45FFG /((0 or 90)F/02/90/±45/+45F)C ] s 0 or 90 (Carbon fabric) 0 Tape (carbon) 0 Tape (carbon) 90 Tape (carbon) +45 Tape (carbon) –45 Tape (carbon) +45 Fabric (carbon) +45 Fabric (carbon) –45 Tape (carbon) +45 Tape (carbon) 90 Tape (carbon) 0 Tape (carbon) 0 Tape (carbon) 0 or 90 (Carbon fabric) 45 Fabric (fiberglass) Figure 11-8.324 11: Composite Design Table 11-2. Methods. Symmetric laminate lay-up. and Applications . ) material selection and fabrication process Figure 11-9. Methods. A16 = A26 = 0. B12 = B21 x 0. then it is likely that the matrix is too compliant for the laminate has flexural behavior balance. For example. Fiber fracture will most likely occur as this does not constitute flexural balance final fracture in well-designed composite as D16 = D26 x 0. trated in Figure 8-24): ration. In other words. and B22 x 0. mation and in-plane shear deformation. B16 x 0. B26 x 0. If fiber fracture occurs early in • What is termed a specially orthotropic the composite fracture process. With the ing in composite structures (as was illus- angled plies in an asymmetric configu. and B66 x 0. fiber system. Stiffness coupling phenomenon (Davis 1987). were incorporated in a sealant material and Figure 11-9 summarizes the behavior of loaded to failure then the fiber would more the laminates based on mid-plane symmetry than likely fail first. Fiber/resin interfacial fracture. • In-plane balanced laminates show no 2. Asymmetric CRACKING IN COMPOSITES cross-plies (0° and 90°) result in B11 x There are three major categories of crack- 0. and coupling between in-plane axial defor- 3. 1. However. if carbon fibers so D16 = D26 = 0. Resin or matrix cracking. Fundamentals of Composites Manufacturing: Materials.11: Composite Design 325 coupling matrix as B = 0. Fiber fracture. structures. and angled ply balance. and Applications . (Many of these issues Interfacial fracture is usually due to poor are detailed in Tsai 1988. where the strength of ber/matrix interactions and the interphase the matrix is exceeded. Fracture Process Well-designed composite structures will first experience fracture and cracking in the form of intralaminar matrix cracks. By definition. Methods. for example. Matrix cracking is were discussed. moisture or occur. resin. Fundamentals of Composites Manufacturing: Materials. extensive de- interfacial degradation due to the absorp. Typically. This is often what is termed was presented in Chapter Eight where fi- first-ply failure. of a composite structure made with eight- The most common low-load cracking harness satin glass cloth and epoxy resin. and Applications . Intralaminar cracks generally initiate delaminations. (Some discussion of the fracture process trix cracking. The delaminations are the matrix cracks between the adjacent plies as shown in Figure 11-11. tures (Agarwal and Broutman 1990). interfacial failures are The fabric composite structure will have an indication of poor surface preparation limited widespread intralaminar cracking of the fibers. The angled plies (in this case 45°) show all three failure modes of cracking in the sequences Figure 11-10. Intralaminar matrix cracks will typically appear in high concentration but are often localized as shown in Figure 11-11. Types of matrix cracks in composite struc- just described. The 90° plies will fail early by pure intralaminar cracks. Figure 11-10 delineates the differ- ence between intralaminar cracking and interlaminar cracking of the matrix. There are basically two types of matrix cracking: intralaminar and interlaminar or delami- nations. However. Note that the various ply orientations define individual cracking mechanisms. These cracks appear parallel to the fibers in uni- directional composite plies. The 0° plies will have intra. Sizing the fiber for the resin laminar cracking and likely fiber fracture system inhibits fracture between fiber and with little or no delamination occurring. The ultimate failure mode is fiber fracture as shown in Figure 11-11. intralaminar cracks are within a ply in the matrix and interlaminar cracks are between adjacent plies. Figure 11-12 illustrates the fracture hydraulic oils. Often the interfacial failure as the transverse fibers tend to minimize mode can be associated with fiber/resin the matrix cracks. mechanism in composite structures is ma.326 11: Composite Design problems.) not typically an ultimate failure mode but the early stages of a fracture process. laminations and then final fiber fracture can tion of some fluid. R. The plate density. 2 of composite structures. which is a product of the fiber and ply range of vibration modes for a specially ortho- orientation. the laminate tics are attributed to the polymeric matrix. is substantially smaller than the plate’s in- plane dimensions. The natural frequency over a mance is enhanced by the stiffness proper- ties. The plate aspect ratio. is symmetric and specially balanced such This section addresses the vibration char. tropic laminated plate (that is. which VIBRATION AND DAMPING depends on ply orientation and ply The beneficial vibration and damping through-the-thickness position in the properties of composite structures give plate. Vf . by the fiber and resin densities and the fiber-volume ratio. which is influenced Figure 11-12. 3. R = a/b (11-20) where: a = plate length b = plate width 2. The flexural stiffness of the plate. Composite structure fracture process. ¥ Q µ 1 As a simple example. them yet another advantage over traditional There are several modes of vibration in engineering materials. The vibration perfor- a structure. a flat rectangular ¦§ ¶ Rb · S D 11 m4 . The good damping characteris. particularly at high frequencies. The frequency response of the plate is an out-of-plane behavior and thus is influenced by three factors: 1. Fabric composite structure fracture.11: Composite Design 327 Figure 11-11. that A16 = A26 = D16 = D26 = 0) is given by acteristics (natural frequencies and modes (Whitney 1987): of vibration). and the natural damping X mn  behavior. 2 D12 . 2 D66 m2 n2 R2 . D22 n4 R4 plate is examined. Methods. (11-21) Fundamentals of Composites Manufacturing: Materials. t. and Applications . The plate thickness. there are a lot of potential E 1 (X ) E  f 1 (X )Vf .328 11: Composite Design where: The damping characteristic of materials X = natural vibration frequency is typically given as a loss factor. i and j are integers storage modulus. both functions of frequen- cy. which is a S = plate density function of the applied frequency. and the fiber-volume n = transverse direction of the mode ratio. For example. The storage and loss moduli are derived m = longitudinal direction of the mode from the relationship between the individual shape fiber and resin moduli. The loss Di j = flexural stiffness of the D matrix of factor is a ratio of the loss modulus to the the plate. the longitudinal loss fac- shape tor of a unidirectional ply can be estimated Note for the first mode of vibration. Hence. m by (Gibson 1994): = n = 1. E m (X )Vm variables in the development of the plate’s I1 X   natural frequency. The panel aspect ratio E1 (X ) Ef 1 (X )Vf . and ply orientation. As the load is removed. and Applications . as are most composite properties. The in- creasing load will store strain energy (area under the curve). Methods. The most significant feature of the composite structure that contributes to the damping properties is the viscoelastic behavior of the resin. Under- standing this concept allows some degree of analysis to be undertaken on the damping characteristics of composite materials. and ply orientation. Em = loss modulus of matrix fiber-volume ratio. fiber- volume ratio. Figure 11-13. but is funda- mentally a function of the matrix (resin). which is controlled by the fiber/resin I = longitudinal damping loss factor type and the fiber-volume ratio to some ex- tent. The Em = storage modulus of matrix natural damping characteristics of compos. Figure 11-13 illustrates the typical characteristic behavior of viscoelastic materials. the strain energy released is the area under the lower curve. Damping properties can be tailored. Em (X )Vm plays a major role in determining the natural (11-22) frequency of the structure. Hence. as does the panel where: density. However. the deformation path is not similar to the load application path. Viscoelastic behavior of polymer materials. Fundamentals of Composites Manufacturing: Materials. the key factor is the flexural E = loss modulus rigidity of the panel and thus the position of E = storage modulus the contributing plies. Ef = loss modulus of fiber The damping of composite structures Ef = storage modulus of fiber is more complex in analysis. Vm = matrix or resin-volume ratio ite structures are of great benefit in design. The difference in energy stored and released is absorbed energy or energy loss. through varia- tions in the fiber and resin selection. structure. Methods. b.” Essentially. Active imbedded sensors can elimi- rial. Fundamentals of Composites Manufacturing: Materials. modified by the imbedded sensor to sions for the storage (stiffness) and loss change or reduce the signature of the moduli in the shear and transverse direc. Adaptive structures.) structure.11: Composite Design 329 By using similar micromechanics expres. matrix cracking. the loss factor increases significantly and is dominated by the viscoelastic matrix mate. An imbedded sensor can identify lo. and Kelly and/or function. or adapt in form can be found in Baker. a good proportion and thus extend the fatigue life of a of ±45° plies is important. b. the loss factor can be calculated for c. infrared. Therefore. The inclusion of electronics in the a variety of laminate configurations. FATIGUE cal damage. Matrix cracks self-heal—imbedded of other materials that make the structure capsules break and fill the cracks inform or react in certain situations. 2004. The smart repair patch will indicate if SMART STRUCTURES the patch adhesion has degraded thus Due to the fabrication process. levels) typically results in fiber fracture and interfacial cracking. High cycle fatigue (low 2. Additional discussion of smart struc- The application of smart structures falls tures is presented in Chapter 21 where the into the following three categories: damage prevention and detection aspects of 1. fiber pull-out. (referred hereafter as matrix cracking).) can be matrix stress levels in composite materials. etc. a. a. composite allowing the repair to be changed. or posite materials is either a cracking of the removed material. For c. Changes to the physical properties any given material. whether it is caused by The fatigue damage associated with com- overload. when attempting to design a nate vibration through damping highly damped structure. fibers. The various operation signatures Low cycle fatigue is dominated by the (radar. Health monitoring of the composite smart structures are featured. Figure 11-14 illustrates the structural shape can be changed by low and high cycle fatigue characteristics of external signals or reactive feedback. the smart structure can (A detailed discussion of smart structures sense threats. With in the resin material or re-bond the the imbedded devices the structure becomes fiber and resin. Low cycle fatigue (high stress sensors. these failure conditions through the absorption of fluids and are typically associated with the number of gases can be identified by imbedded fatigue cycles. extreme temperature. for matrix-dominated directions (45–90°) 3. Note. and Applications . stress levels) will more commonly result in a. cracking at the fiber/resin interface b. Life cycle improvement. heal itself. structural skin of a system will im- the loss factor of a unidirectional ply is prove operational performance (such typically dominated by the stiff fiber. With the use of imbedded actuators. but as conformal antennas). Environmental degradation changes (hereafter called interfacial cracking) seen as to mechanical properties can be iden. Dutton. structure. materials can easily allow the imbedding c. composite materials. “smart. tions. visual. or cracking of the resin system tified. 330 11: Composite Design Figure 11-14. Fundamentals of Composites Manufacturing: Materials. Methods. and Applications . Low and high cycle fatigue characteristics of composite materials. aligned with the loading direction. Well-designed than glass fiber composites. The typical S-N curves fabrics and random fiber forms tend to have are based on specific alternating stresses more serious fatigue-cracking problems. Fundamentals of Composites Manufacturing: Materials. Thus uni- havior of composites versus metals is shown directional fibers perform better that woven in Figure 11-16. Note in particular the large the fatigue cracking of the matrix. matrix increases when the fibers are not A further comparison of the fatigue be. This is further composite laminate can tolerate large matrix explained in Figure 11-17 where the global cracks and thus provide a higher level of stresses are proportioned to the fibers and damage tolerance than metals. Figure damage size in a composite material before 11-18 illustrates this effect. Comparison of fatigue crack behavior (Jones 1975). Of particular interest is is different from that of metals where small that boron fiber composites perform better cracks can be critical in size. size and inspection requirements for metals The form of the fiber system also impacts and composites. Figure 11-15. and Applications .11: Composite Design 331 Thus fatigue crack inspection focuses on (alternating stress divided by material looking for small micro-cracking in the resin. Cracking in the it becomes critical. Figure 11-15 the resin (matrix) based on the ratios of their highlights the differences between damage individual stiffnesses. Methods. Note the typically lower strength The behavior of composite fatigue cracking loss of composites. density). Fundamentals of Composites Manufacturing: Materials. Comparative S-N curves for composites versus metals (Jones 1975). Methods. and Applications .332 11: Composite Design Figure 11-16. and boron/epoxy fiber/resin systems. properties are at the lower limit with uni- ber-volume ratios with fiber forms. the quasi-isotropic laminate configuration. there is reduced per- Comparative charts shown in Figures 11-19 formance of glass and aramid (Kevlar) through 11-24 plot the composite system fiber systems against metals with regard with all plies oriented in the 0° direction and to specific compression strength behavior. preform better than the metals for the tensile parison of composites to metals is that there strength-to-weight ratios. However. Methods. A better method of specific tensile strength performance of the comparing the properties is to take advan. graphite/epoxy. composite fiber/resins is clearly superior to tage of the materials’ densities. Figure 11-19 indicates that there is a clear stiffness-to-weight advantage for the graphite and boron fiber/resin composite systems over metals for both the upper and lower limits of the material modulus prop- erty. figuration. This shows the metals and.11: Composite Design 333 the quasi-isotropic laminate represents the other practical lower limit. Aluminum alloy 7075-T6. and Applications . stiffness versus matrix stiffness. Stress distribution effects based on fiber tensile modulus. In the specific shear modulus chart in Figure 11-20. (Kevlar) and graphite fiber composites sys- als over metals due to the lower densities of tems. systems being the best of the composites. composites do not do as well as the metals in comparison. the aramid the distinct advantage of composite materi. The quasi-iso- tropic laminates of graphite and boron COMPOSITES VERSUS METALS are slightly better than metal in the shear A direct comparison of composite proper. The shear Included in this effect are the reduced fi. The compos- ite systems represented are a glass/epoxy. and stainless steel PH 17-4 are the common aerospace-quality metal alloys used in com- parison. titanium alloy 6Al 4V. directional fiber orientations and perform poorly against the metals. in particular. Glass and Kevlar are on a nearly equal footing with metals with respect to specific Figure 11-17. Figures 11-19 through 11-24 compare the properties of four typical composite systems with three common metals. graphite. and boron Another issue to be addressed in the com. aramid (Kevlar®)/epoxy. with graphite fiber is a wide range of composite material proper. only glass. ties available with various fiber orientations. In Figure 11-22. ties to those of metals does not normally Figure 11-21 shows that the unidirectional show the complete story. boron fiber composites have a The unidirectional composite represents the clear advantage over the entire range of upper limit of the composite properties and composites shown. In the quasi-isotropic laminate con- composite fiber/resin systems. Fundamentals of Composites Manufacturing: Materials. modulus-to-weight ratio. 334 11: Composite Design Figure 11-18. Fundamentals of Composites Manufacturing: Materials. and Applications . Methods. Fatigue stress behavior based on fiber form (Agarwal and Broutman 1990). 11: Composite Design 335 Figure 11-19. and Applications . Fundamentals of Composites Manufacturing: Materials. Comparison of the specific tensile modulus of four composites versus three metals. Methods. and Applications . Methods. Comparison of the specific shear modulus of four composites versus three metals. Fundamentals of Composites Manufacturing: Materials.336 11: Composite Design Figure 11-20. 11: Composite Design 337 Figure 11-21. and Applications . Fundamentals of Composites Manufacturing: Materials. Comparison of the specific tensile strength of four composites versus three metals. Methods. and Applications . Methods. Fundamentals of Composites Manufacturing: Materials. Comparison of the specific compression strength of four composites versus three metals.338 11: Composite Design Figure 11-22. Only graphite and are observed at two levels. Shear strength is only improved with more ±45° plies. and there can Figure 11-23. poor between the unidirectional and quasi- isotropic configurations. the residual coefficient of thermal expansion (CTE) stresses typically result in some form of value than most of the composite systems warping of the composite structure. with RESIDUAL STRESSES the pure ±45° angled ply configuration giv. Fundamentals of Composites Manufacturing: Materials. In both cases. stresses originate from thermal variation be- ference between the aluminum alloy and tween the cure and operating temperatures the composite systems should be noted. Residual as shown in Figure 11-24. the extreme dif. Residual stresses in composite structures ing the best performance. and Applications . The individual boron quasi-isotropic configurations show an ply can have residual stresses between the on-par performance with metals as shown in fibers and the resin (matrix). Methods. particularly in heat-cured adhesive property of most composite laminates is joints.11: Composite Design 339 The specific shear strength performance regions. Comparison of the specific shear strength of four composites versus three metals. The of the laminate. the differences between the major issue that arises with the differences coefficients of thermal expansion (CTE) of between the CTEs of metals and composites the fibers and resin. be residual stresses between adjacent plies While the metals typically have a higher in the laminate. and each ply orienta- is the residual stresses that arise in joint tion. Moisture absorption also can lead to Figure 11-23. and the fiber at the interface. the selection of the fiber/resin especially for thin laminates (fewer than 12 combination and the curing temperature plies). and Applications . As an example of this CTE variation. For example. room-temperature operating temperature referred to as NT. the longitudinal (fiber direction) CTE is often much smaller than the transverse direction as shown in Table 11-3. the fiber/resin CTE difference occasions the fibers are pre-stressed prior will produce in-plane direction variations of to infiltration and curing of the resin. looking at four induces residual stresses between the resin typical unidirectional fiber/resin systems. expansion variations in the resin and thus interfacial shear failures. needs to be considered so that thermal Table 11-4 gives the post-cure deformation residual stresses do not cause fiber/resin results of a series of four-ply laminates made Fundamentals of Composites Manufacturing: Materials. Residual Thermal Stresses Large variation in the orthogonal plies’ Residual thermal stresses arise because CTE values can have a significant effect of the variation between the CTEs of the on the laminate’s post-cure residual de- fibers and the resin. and the difference formation. On some composite ply. Methods. this the ply’s CTE. Comparison of the coefficients of thermal expansion (CTE) of four composites versus three metals. In a unidirectional residual stresses in the laminate.340 11: Composite Design Figure 11-24. deformation of the laminate can be extreme. Initially. When a laminate does not have between the cure temperature and the mid-plane symmetry. and Applications .08 –0. the two panels sional deflection of the tube at design load are no longer symmetric and will be warped. Thermal stress As this design project is a prototype.38 –0.3 43.-lb (152 Nm) ultimate design symmetric lay-up.2 22. if the laminate 0/0/90/90 is split The next task is to determine the fol- along the mid-plane.350 in. of 3 in. The tor- is split along the mid-plane. If the laminate 0/90/90/0 torque.9 Resin/fiber CTE % difference 80% 101% 61% 105% Table 11-4.31 8.2 m) in total length between the end still have residual stresses within them.3 27. Carbon Kevlar® Boron Fiber Glass Fiber Fiber Fiber Reinforced Reinforced Type Reinforced Reinforced Plastic Plastic Plastic Plastic (BFRP) (GFRP) (CFRP) (KFRP) Fiber Boron (4) Graphite E-Glass Kevlar 49 Matrix Epoxy Epoxy Epoxy Epoxy Longitudinal CTE per ° C × 10–6 6. the two panels are indi.6 12. is to be no greater than 1°. Common fiber/resin system CTE properties. the residual stresses are balanced in the with 1. which reduces the chance of first-ply Fundamentals of Composites Manufacturing: Materials. Methods. Common fiber/resin CTE properties (Tsai 1988). 11-25 explains this behavior. as shown in Figure 11-26.1 79. the allowable shear A torque tube is to be designed from strain for the design is restricted to 2.00 (per ° F × 10–6) 3. Configuration [0/0/0/0] [0/90/90/0] [0/90/0/90] [0/0/90/90] [0/0/90/0] [0/0/0/90] Symmetric Yes Yes No No No No Post-cured Flat Flat Slightly Warped Significantly Grossly shape warped (oil canning) warped warped from carbon/epoxy unidirectional prepreg minimal weight. How. Torque Tube As a general rule.17 4. turing processes available to manufacture it is by hand lay-up on a deflatable tubular CASE STUDY 11-1 mold.78 –2. It is to be a maximum tape cured at 350° F (177° C).0 (per ° F × 10–6) 16. Likewise. they (1.8 15. one behavior has a critical impact on repair using of the simplest and cost-effective manufac- pre-cured or co-bonded repair patches. constraints. (76 mm) in diameter and 4 ft Though the symmetric panels are flat.22 Transverse CTE per ° C × 10–6 30.11: Composite Design 341 Table 11-3. Figure figuration. The tube is centrally loaded ever.000 graphite/epoxy composite materials at Nstrain. lowing: tube wall thickness and ply con- vidually symmetric and thus are flat.60 –4. Effect of thermal stresses in symmetric and asymmetric laminates.342 11: Composite Design Figure 11-25.5 in. The basic design equations are: in.350 cracking).000 N (11-23) 11-24) J G = shear modulus where: F
= strain = 2.-lb (152 Nm) Maximum shear stress: R = tube radius = 1.000N Uallowable

m a x i m u m a l l o w a b l e s h e a r stress Polar moment of area: Fundamentals of Composites Manufacturing: Materials. (38 mm) TR J = polar moment of area (see Eq. U allowable  b GF 2. failure in the tube (intralaminar matrix T = ultimate design torque = 1. Methods. and Applications . unidirec- tional. (257. (0. For a typical graphite/epoxy.11: Composite Design 343 A major step in the design of the tube is to estimate the shear modulus.713 x106 lb.55 msi (52.91 GPa). but it is not good to have all 45° plies in the configura- Figure 11-26. This can be done by first looking at the range of shear stiffness values for a given composite mate- rial.005 in. and Applications . then t (10. (1. 350 x48 (11-28) GJ  b  3. which gives the circumference to its diameter ratio with the shear stiffness of the design: t = tube wall thickness G 6. where: From Eq. Torque tube geometric description. only six plies are required where: to achieve the design stiffness goal. So the value of the shear modulus as a starting Q¨ 4 4 (11-24) point is: J R  R  t ¸ 2 ª º G = 6.647 mm4) TL 1. with R = 1. G.2 G 1 x(Q / 180) Therefore.4 GPa) where: The unidirectional axial Young’s modulus Q = 3. the effective tube thick- ness is determined: F = angle of twist L = 4 ft = 48 in.0 msi (41.39 msi (33.1 GPa). Methods. which is the ratio of a circle’s is E0 = 29.14159. (38 mm).3 GPa).0 msi (11-27) Angle of twist:   0.713 x106 J R  R  t ¸   .4 2ª º G So. the lowest value of shear stiffness for a 0° ply G±45 = 7. prepreg composite material: G0 = 1.2 m) Q¨ 4 4 3.5 in.22 msi (8.8 mm).5 KN-m2) = . 11-24. Since x = orthogonal direction of plies 76% of the laminate is to contain ±45-degree Fundamentals of Composites Manufacturing: Materials.03 in. which is the highest value of shear stiffness for a ±45° ply GQI = 4. (11-26) Assuming that a ply’s thickness is . (0.46 msi TL (11-25) Figure 11-27 reveals the percentage of G b 1o GJ ±45° plies is 76%. which is the quasi-isotropic value of shear stiffness A relatively large value for shear modu- lus is required for this design.46 msi (203 GPa).-in.13 mm).619 in. tion as there are often axial loads that will need 0° plies for added strength.204 E0 29. Angle ply percentage chart (Hart-Smith 1989). [0/90/±45] combinations. this means five of the six plies are re. to be balanced. plies. as the angled plies need maximize the shear stiffness. [±45/0/±45/90/±45]T In-plane properties: This ply configuration is based on the fol. and Applications .344 11: Composite Design Figure 11-27. Methods. six plies will be used. G12 = 5. The final lami- nate lay-up could be: A detailed analysis of the laminate con- figuration produces the following results. there also should be mize interlaminar stresses and reduce at least one ply in every direction of the the risk of delaminations. E1 = 8. However. • The ±45° plies on the outer surface will quired.97 msi (41 GPa) Fundamentals of Composites Manufacturing: Materials.33 msi (57 GPa) lowing reasoning. As a • The interspersion of the plies will mini- general design rule. E1 = 9.8866 × 10–6/° F (0. • load application fitting and appropriate E11 (longitudinal modulus).07 x106 x0. analysis. (38 mm) ever.5 in. and A12 (principal thermal Fundamentals of Composites Manufacturing: Materials.4 (339 × 103 mm4) cable to composite structures and give good approximations of properties. various steps in the results are checked against the design design and analysis are carried out. the values of the stiffness. How- R = 1.48 · voids. 350 x1. equations. Poisson’s ratio). v12 (principal joint analysis.13 msi (63 GPa) SUMMARY G12 = 6. Next. (17 MPa) • The fibers are linearly elastic and ho- (11-29) mogeneous. cations of the part. With this in mind.02 mm) from the rule of mixtures. it is important to follow a general T12 = 11. dividual constituents are the same Other issues to consider further are: whether they are made by themselves • end fixtures and appropriate joint or made up within the composite.000 Mstrain: designing composites parts complicated. and Applications .15 ksi (180 MPa) chapter has proven to be successful.8149 homogeneous and linearly elastic.07 msi (42 GPa) The complex nature of composites makes Torsional strength at 2. ¥ 11.5 • The composite ply is macroscopically U applied    2. Margin of safety is: • The matrix is linearly elastic and ho- mogeneous. It first requires.005 × 8 plies = 0. Twist: • The interface between the fibers and matrix is completely bonded.11: Composite Design 345 N21 = 0.4848 • areas of local reinforcement. 350 x48 is no transitional region between the G   0.2 (240 mm2) of the rule of mixtures are reasonably appli- J = 0. TR 1.94 ksi (82 MPa) plan for design.75o b 1o GJ 6. Hence.38 ksi the establishment of the functional specifi- (23 MPa) meets the design goals. as do most other design systems. Therefore. (1. Design analysis can be difficult.372 in. and Flexural/torsion properties: • long-term manufacturing approach. The torsional shear stress of 3. The assump- Shear stresses: tions are as follows. The assumptions A = 0. and there TL 1.94 µ (11-30) ¦§  1¶ %  380% • Both the fiber and matrix are free of 2.48 ksi J 0.4926/° C) • damage tolerance. some assistance can be obtained by estimating the properties of the composite t = 0.8149 in. A1 = 0. for strength and performance the • The mechanical properties of the in- design is successful. Then. Methods. The plan presented in this Tult = 26.04 in. especially Geometry: if there is little symmetry to the part.8149 matrix and reinforcement that might (11-31) add a complication of a third material. Select a resin for which the density is Am = coefficient of thermal expansion for known. This unequal distribution of load is a follows: tremendous advantage in composites and is the reason that composites have such high E11 = Vf Ef + VmEm (11-32) specific strengths and specific stiffnesses compared to metals. These advantages also relate to the long-term fatigue advantages of com- posites. These expressions tion of the load carried by the fibers is over are derived from the rule of mixtures as 90%. composite structure can be found from the 4. when the ratio of the moduli is 10 and themselves and the volume fraction of the the fiber volume fraction is 0. they modulus of the fibers. Make the two panels. Em = Young’s modulus for the matrix LABORATORY EXPERIMENT 11-1 v21 = major Poisson’s ratio for composite Fiber-volume Fraction ply Objective: Discover the effect of varying Vf = fiber-volume ratio the amount of fiber in a composite. and Applications . calculate the weights of the fiberglass and the resin The ratio of the load carried by the fibers that will result in two different fiber- compared to the load carried by the entire volume fractions—40% and 60%. load carrying within the composite struc- ture. the fibers carry almost all thoroughly. referring to Figure in terms of the matrix/fiber properties 11-28. Typically. carefully laid up so they are all uni- and especially when the fiber volume frac. (Alternately. v21 = Vf vf + Vmvm (11-33) The unique nature of composites can be an advantage in damping and vibration ap- A12 = Vf Af + VmAm (11-34) plications. Select a fiberglass roving for which the vm = Poisson’s ratio for the matrix density of the material can be obtained A12 = principal coefficient of thermal ex. from the manufacturer. Using the densities. This load ratio is enlighten- for making the composite panels (of ing as it shows how the fibers dominate the 40% and 60% fiber-volume fraction). Em. vf = Poisson’s ratio for the fibers Procedure: Vm = matrix volume ratio 1. The fibers should be the ratio of the moduli is a number over 10. directional. matrix 3. Weigh the fiber and resin components rule of mixtures. is high. Ef . Figure 11-28 illustrates that when the 5. where: The manufacturing methods for compos- E11= principal longitudinal modulus for ites allow the creation of smart structures composite ply that are able to monitor and even self-heal Ef = Young’s modulus for the fibers some cracks. Fundamentals of Composites Manufacturing: Materials.346 11: Composite Design expansion coefficient) can be expressed of the load. Methods. so that lay-up technique.) fibers 2. Be sure to wet the fibers tion.6. the frac- respective ingredients. Vf . is much greater can be made most easily using the hand than the modulus of the matrix. For example. pansion for composite ply the density can be determined experi- Af = coefficient of thermal expansion for mentally. 6. specific tensile stiffness QUESTIONS d. Fraction of load carried by fibers in longitudinal tensile loading of a continuous-parallel-fiber laminate. Describe the effects of the fiber volume 5.11: Composite Design 347 Figure 11-28. Describe the effects of fiber orientation and not just wait to run real-time aging in composite parts. test them 4. unidirectional to which of the panels has the higher tensile strength and stiffness. ing tests on materials and components 2. Methods. anisotropic. tests on the final product? 3. and homogeneous the creep in a composite material with materials. and Applications . 6. Why would you conduct accelerated ag- in composite parts. specific tensile strength c. b. Make a note as a. a polymeric matrix? Fundamentals of Composites Manufacturing: Materials. What techniques can be used to reduce tropic. Poisson’s ratio 1. Define the following terms: for tensile properties. Discuss the differences between iso. After fully curing the panels. Ef = 43 × 106 psi (296 GPa) Singer Island. J. “Mechanics of Composite Laminated Anisotropic Plates. R. v12. B. 4th Ed. Workshop on Composites in Manufacturing. Practical b. L. 2nd edition.. and Applications . VA: American Institute Dayton. Engineers. and Broutman. Australia: UNSW. Strong. Agarwal. Society of Manufacturing Engineers (SME). 2nd Edition. References for Composite Materials. OH: ASM International. [0/45/90]s Analysis of Composite Laminates. ACUN-5: Af = 1.4 tion Requirements. H.sme. July 11–14. Whitney. Materials. Melbourne. Infra- Am = 40 × 10–6/° F (72 × 10–6/° C) structural. Dearborn. Dutton. & Miravete. Composite Design. [452 /–452 /0] Reddy J. 1987. 1987. A. and A11 Gibson.” Douglas Paper 8366. Materials. 21. DC: Scripta Book metrical: Company.348 11: Composite Design 7. Fundamentals of Composites Manufacturing: Materials. 90]s Press. “Composite vf = 0. NY: McGraw-Hill. Natural. OH: Think Composites. Lancaster. “A New Approach to composite with the following constitu. ed.. ASM Handbook. N.” International Conference and PA: Technomic Publishing Co. Fabrica- vm = 0. ASTM Standards and Literature NJ: Prentice Hall. W. als. M. PA: American Society for Testing Tsai.. A. Tsai. Composites. Materials Park. S. M. 1989. Reston. the following composites and discuss Jones.7 × 10–6/° C) International Composites Conference. and Nano-composites. M. Plastics: Materials American Society for Testing and Materi. L. Phila- delphia. Donaldson. MI: Society of Manufacturing Analysis and Performance of Fiber Composites.2 Structures Engineering Design vs. BIBLIOGRAPHY 2005. R. D. Australia: April. J. F. J. Introduc- and Materials (ASTM). Brent. 1990. and Processing. PA: Technomic Publishing Co. 1994. Washington. Vol. 3rd Ed. 1975. and Hahn.org/cmvs. for a unidirectional. Em = 0. D. NY: John Wiley & Sons. [±45.” Invited paper. 1995. July 2006. Lancaster. Principles of Composite using the rule-of-mixtures relationships Material Mechanics. of fiber: FL: MIL_HDBK-17 Committee Meeting. S. 1988. graphite/epoxy Hart-Smith. 2004.5 × 10–6/° F (2. Upper Saddle River. S. Inc. 2001. Composite Materials for Aircraft Structures. Palm Beach. A. NY: CRC c. R. a. 2006. www. D. tion to Composite Materials. Mechanics of Composite whether they are balanced and sym. 1980. Fibrous Composite Laminate Strength Pre- ent properties and 65% volume loading diction. Draw a diagram showing the layers for Sydney. Structural Analysis of Davis. De- velopments in Composites: Advanced. Methods.5 × 106 psi (3. of Aeronautics & Astronautics (AIAA). “Composite Materials” DVD from the Composites Manufacturing video series. Inc. 8. B. J.4 GPa) Heslehurst. T. Baker. and Kelly. W. Calculate the values of E11. 1990. Still other the strength and stiffness of the matrix. this book has focused on designated as 3 but in other places it is called laminate structures (such as that shown in the z direction. The nature of industry calls the plane in which these fibers the core materials will be discussed later in are laid the x-y plane (also referred to as the this chapter. and adhesive materials. this direction is Up to this point. forces • Post-processing operations in the x-y plane can be resisted. can have fibers oriented advantages of a composite structure (that in many directions but all of them are in a is. The composites tional composite laminates. So. like mat. It consists of two face sheets. itself. The adhesives (also discussed 1-2 plane in Figure 11-3 and all of Chapter later in this chapter) are present to hold the 11). But what if the force applied to the com- SANDWICH STRUCTURES—CONCEPT posite is in the direction perpendicular to AND DESIGN the x-y plane? (In Figure 11-3. the synergy between fiber and matrix) plane because the mat is. If one layer or ply of composite is not sufficient to give the • Sandwich structures—concept and strength or stiffness desired. the z-direction strength and stiffness rectional fibers and some. essence. Methods.) In laminate structures. ing this z-direction problem is by making a The use of flat sheets to make composites sandwich structure such as that shown in is logical because. The face sheets arrange fiber reinforcements in flat sheets (top and bottom of the structure) are tradi- that are placed into molds. and Post-processing Operations CHAPTER OVERVIEW along the x-y plane. Joints. In particular fiber orientation. Composite structures are com. more layers of design composite can be bonded to those already • Core material present and the total strengths of the fibers • Other z-direction stiffeners act together in the x-y plane. If the force that is to be resisted is to act structure together. and Applications 349 . if the Figure 11-3). Fundamentals of Composites Manufacturing: Materials. planar. the fibers have little ability to resist it. largely. The materials. All largely disappear in the z-direction. the fibers can be oriented This chapter examines the following in the direction of the force to increase the concepts: strength of the composite. force is perpendicular to the direction of the fi- posed of a series of sheets or plies that have a bers. the fibers are held in their orientation by a The most common method of address- resin matrix. can have of the laminar composite is determined by two directions of fiber orientation. composites are Figure 12-1. a manufactured by using various methods to core.1: Introduction to Composites 349 12 Sandwich Structures. like cloth. by increas- ing the number of layers and by orienting the • Joints fibers in the directions of the forces. Some have unidi. Methods. then the entire sandwich structure is also especially as related to the specific ap- a composite. The term double composite structure • environmental conditions during use. • manufacturing of the sandwich struc- ture. such as properties. a par- other hand. words.350 12: Sandwich Structures. wich composites. terials in a sandwich composite go right to mum structural properties. The trade-offs between component ma- • careful selection of materials for opti. the basic issue of why a sandwich composite Fundamentals of Composites Manufacturing: Materials. it is clear that the material choices and compromises that if the structure is to work properly. and Applications . Therefore. in de. For instance. On the Just as with resin-fiber composites. capability. but not and manufacturing issues as do the simpler good in another. Joints. terials joined together to create something that has better properties together than the These considerations. Both consist of disparate ma- plication. following must be considered: Trade-offs to Maximize Performance • trade-offs in the amount of component and Cost materials for performance and cost. such as cost or manufacturing composite structures. Components of a sandwich structure. and Post-processing Operations Figure 12-1. it is a composite structure overall and are critical as well to the performance of sand- contains composite components within it. all can be better appreciated and understood. In other and manufacture of all fiber-resin composites. Each of these design/manu- Thinking of these sandwich structures facturing considerations will be examined so as double composite structures. so critical in the design components would have separately. the manufacturing methods are chosen. ture. all the considerations signing and making fiber-resin composites must be weighed before the materials and and using them in sandwich structures. and ply that the face sheets are composites and • various other design and use issues. The double composite’s nature is sim. describes the concept of a sandwich struc. the overall composite structure ticular component may be ideal in one area might have some of the same critical design of consideration. the components must work together. 12: Sandwich Structures. lightweight. The web of the I-beam corresponds to Doubling the thickness at essentially the the core of the sandwich composite. that of a non-sandwich composite. still maintaining increase in stiffness of the I-beam and of essentially the same weight. As il- of the core materials yields tremendous lustrated in Figure 12-3. This is a sandwich structure. and Applications . stiffness to an applied z-direction and these correspond to the resin-fiber lami- force. This effect is illustrated in Figure 12-2. Joints. Likewise. Fundamentals of Composites Manufacturing: Materials. Methods. therefore. the I-beam are the upper and lower surfaces especially. The greater thickness the principle on which I-beams work. The thickness is doubled again. the face plates of increases in bending/flexural strength and. the increase in the sandwich composite are principally strength doubles to tenfold over the single functions of the distance between the face skin and the stiffness increases to 37 times plates and not of the nature of the web. A structure quite Structural engineers have long known different from a traditional laminate is the that increases in thickness will give large result when core materials are used to make increases in strength and stiffness. If the weight than the resin-fiber laminates. Strength and stiffness effects of increased core thickness. nates. and Post-processing Operations 351 should be made at all. Note same weight as the resin-fiber composite that the web of the I-beam is relatively thin and adding only the light core material gives and. the a three-and-a-half-fold increase in strength core materials are generally much lighter and a seven-fold increase in stiffness. provided certain overall parameters are Figure 12-2. how chosen for z direction stiffness and strength. maintained. costs since cores are usually less costly than The I-beam is far less capable of spreading face sheets. Comparison of an I-beam to a sandwich composite. the use of more core spread all across the surface of the core. if bonded thicknesses is clearly a compromise that properly together.352 12: Sandwich Structures. less strength and stiffness in the x and y beam. Moreover. will have greater stiffness must be decided for each application. thus material in place of face sheet will reduce diminishing the force in any single location. Joints. and Applications . Typi- and strength than would either material by cally. and stiffnesses and then the amount of core is The design question then becomes. Fundamentals of Composites Manufacturing: Materials. Truly the sandwich is a synergistic designed for the proper x-y plane strengths composite structure. In other words. However. The optimization of component face sheet and the core material. and Post-processing Operations Figure 12-3. but this is reasonable for safety. at constant overall the force. the laminate portions (face sheets) are itself. However. structures. much resin-fiber composite should be used This may result in some overbuilding of the for the face sheets and how much for the composite (since less laminate might be ac- core? If it is assumed that a constant overall ceptable). the core material need reducing face sheet thickness will result in not be as rigid or strong as required in an I. increasing core thickness and spread in a composite. In general. because the force is thickness. When the sandwich is subjected then clearly using core material will reduce to a z-direction force. Methods. there is an important thickness is required in the sandwich as difference between I-beams and sandwich might be used in just the laminate structure. the force tends to be weight. the combination of the directions. The sandwich structures in general. when composites materials. and must be able to withstand the force applied with metallic honeycomb cores. Here the high stiffness of The most common core materials can be a core material is often a disadvantage be- divided into four general types: balsa wood.and y-direction loads. This for every application. ing standard tests (such as those outlined In some materials the orientation of the by the American Society for Testing and core is important. or wich structure. Again. As a result. For example. These generally become worse as ing the nature of composites testing. this chapter has discussed This is characteristic of end-cut balsa. Another critical structural property is This property is sometimes discussed in the ability of the core material to withstand terms of withstanding high dynamic loads.) Hence. and Post-processing Operations 353 CORE MATERIAL a common core material because of its light Properties weight. determining the crush strength of the sand- non-crosslinked polyvinyl chloride (PVC). Some support to the core. They are used with wich structure performance. tance of the core material to crack propaga- However. Up to now. several specific types and all are distinct in the core materials may shatter. to stiffness/brittleness is fatigue resistance. cause high stiffness usually comes with high foams. balsa wood is Materials [ASTM]). but it is oriented so that the direc- tion of the wood fibers is in the z direction. honeycombs. Clearly. forces from the x and y directions will place the core Testing into potential shear and buckling failure Some comments are appropriate regard- modes. Because the entire sandwich structure is bonded together. the core material styrene-acrylonitrile copolymer (SAN).) tion. it is important that the core of the laminate layer. with little natural strength of the wood cells helps give reference to specific core materials. If the com- in the z direction. structural properties of composites and Examples of some of the failure modes of core other materials are usually determined us- materials are shown in Figure 12-4. and stitched/compressed brittleness. Each has inherent advantages materials best in resisting impact damage and disadvantages that should be considered are those with slightly higher resilience. The core properties. property is generally associated with ther- The nature of the core is important in moplastic materials such as polypropylene. Others are not the cells oriented in the z direction because as critical but might be a bonus in the choice that is their direction of strength. x. Still another property that is related directional loading to be sure. a reasonable designer would make tion. Methods.12: Sandwich Structures. The common core materials are gen- Another property of interest is the resis- erally acceptable in stiffness and strength. many of which were Fundamentals of Composites Manufacturing: Materials. of material for some specific applications. (This phenomenon can be posite core is damaged. A similar situation exists core properties are critical to overall sand- in honeycomb materials. high stiffness and the resulting up sandwich composites for testing and brittleness tend to result in high crack propa- subject them to the anticipated maximum z gation. Ta- A property of immense importance in some ble 12-1 lists the common core materials and applications is impact damage resistance or some of their important characteristics. and Applications . the repair method envisioned if you think of the deflections that usually involves insertion of a plug of would occur if the web or core was made of core material and then re-establishment rubber. impact toughness. (These methods are materials be strong and stiff in the z direc- discussed in Chapter 21. Joints. The the core material is increased in thickness. Within each category there are made with highly brittle cores are impacted. absorbs resin for added strength Fundamentals of Composites Manufacturing: Materials. stainless. no outgassing. corrosion resistant.354 12: Sandwich Structures. quartz. easily shaped. fungi resistant. low cost. nickel available. good thermal insulation. fire resistant. Core Material Characteristics and Benefits Balsa wood (end grain) Good shear strength. high strength to weight. good impact resistance Polymethacrylimide (PMI) foam High dimensional stability under heat. and Post-processing Operations Table 12-1. superior thermal resistance Metal honeycomb Aluminum. good dielectric properties Styrene-acrylonitrile copolymer No outgassing. fungi resistant. Common core materials and their properties. titanium. explosion containment vessels. corrosion resistant. excellent thermal insulation. high toughness. high-temperature tolerant. excellent dielectric properties. easily bonded. Joints. easily bonded. good temperature range Polyvinyl chloride (PVC) foam High strength. high thermal stability. no environmental problems with resin or recycling Ceramic foams Unsurpassed thermal resistance. reduces cracks. fire resistant. high stiffness. low thermal conductivity. high stiffness. highly variable cell sizes and densities High-performance honeycomb Carbon fiber reinforced. high fatigue endurance. solvent resistance. high impact resistance. easily bonded (crosslinked) PVC foam (linear) Low cost. relatively high-temperature tolerant. aramid. can be thermoformed. high thermal conductivity Stitched/compressed Excellent drape. excellent dielectric properties. fungi resistant. easily bonded. high impact and fatigue (SAN) foam strength. fire resistant. needs to be fully wetted. and Applications . scrim cloth available. solvent resistance Paper honeycomb Low cost. high strength and stiffness Polyetherimide (PEI) foam Low water absorption. good thermal insulator. fire resistant. superior strength. Methods. carbon-carbon. high strength. sound and vibration dampening. recyclable Engineering plastic honeycomb Tough. easily finished. easily bonded Polyolefin honeycomb Rigid and elastic. low cost. excellent mechanical properties. strong for weight Polyimide paper honeycomb High strength to weight. formerly the National Bureau of Fundamentals of Composites Manufacturing: Materials. Methods. developed for metals. Sandwich failure modes. and Post-processing Operations 355 Figure 12-4. But. test might be devised that allows sandwich sults for traditional resin-fiber composite materials and metals or laminate composites laminates. Many of those tests to actual performance. sandwich materials. then some alternate have been modified to give comparable re. Therefore. peel test. the roller cart interest corresponds directly to the test and test. If the property of include the long beam flex test. the specifications are written around material National Institute of Standards and Technol- properties that may have little relationship ogy (NIST. sandwich Some tests have been shown to be espe- materials are sometimes at a disadvantage cially appropriate for sandwich materials and when compared to other materials if just the many of the most common applications. and Applications . vertical flame test.12: Sandwich Structures. falling dart impact test. if the sile/compression test. this disadvantage is justified. flatwise ten- ture. the climbing drum is important in the performance of the struc. These test data are compared. but few have been modified for to be compared fairly. the core shear test. Joints. the best policy is to test the thermal insulators so the core is often entire sandwich structure for sound protected from direct contact with suppression. These often also include water was being trapped in the honey. quency of the core is a key component ness are often difficult to achieve in absorbing these vibrations. some ing and smoke generation. ticularly sensitive to off-gasses that may These include the following: be emitted by the core materials. and Applications . core material itself does not absorb as might be the case in panels used in water.356 12: Sandwich Structures. Joints. and ships have strict flammability re- craft carriers. the edgewise compression test. Some of the core materials are weight to the aircraft that take-offs especially good in resisting both burn- were compromised. high heat. the resin in the face also might • Water absorption: some composite have a problem with off-gassing. even when the sensitivity to this problem is important. have low off-gas- rine environments. It has structural re- (CTE) between the composite and the quirements and a myriad of other properties face plates. Thermal stability and tough. planes. debonding can occur and most use. composite materials could be subject to • Sound insulation: most core materials degradation in moist environments. However. are excellent sound absorbers. and Post-processing Operations Standards [NBS]) smoke chamber test. the possibility that should be considered ability of the material to absorb vibra- whenever high thermal conditions tions can be critical. It is like the athlete who sandwich structure will be severely competes in the decathlon—it is able to do deteriorated. many things well. and insulative capabilities. Nevertheless. However. sandwich composites are widely used when thermal insulation is required. The U. The natural fre- exist. thermal • Vibration damping: for shipping and degradation of the core over time is a other transportation applications. Some have described the core material of the structural properties of the in sports terms. Consequently. at the same time. • Temperature: the face plates of a when sound is a key part of the appli- sandwich material are usually good cation. Of course. Navy found that quirements. If the CTE difference is too required by the conditions of each particular large. The problem • Flammability: clearly some applica- of water entrapment was especially tions. A related problem sing and are therefore preferred when is entrapment of water. In addition. such as metals and a few water and so might be avoided in ma. Methods. important in aircraft for service on air. performance by adding weight and may diminish strength. The water can adversely affect clean rooms. such as panels for trains. Environmental Conditions During Use A consideration in these applications should be given to the differences in Clearly the core material must perform the coefficients of thermal expansion many functions well. An advantage of the entire structure has unique natural most core materials is their thermal frequencies that must be determined Fundamentals of Composites Manufacturing: Materials. of the polymeric types. Some environmental conditions suggest • Off-gassing: some applications are par- special care in selecting the core material. Some materials have a tendency to absorb core materials. requirements on smoke generation and comb material and was adding so much toxicity.S. 12: Sandwich Structures. OTHER Z-DIRECTION STIFFENERS sure must be taken to prevent absorption of Several methods other than sandwich the resin. fibers in the structure. experience has structures have been developed to improve shown that the correct amount of adhesive the z direction strength and stiffness of com- will wick slightly into the honeycomb cells to posite laminates. some honeycomb ally bonded in place. These fiber methods Fundamentals of Composites Manufacturing: Materials. Yet another method is to materials. adhesive must be strong enough to transfer In almost all sandwich structure appli- the load from applied forces onto the face cations. Testing the a problem and the core material might be entire structure is usually required. and Post-processing Operations 357 for the whole composite. after all. The structure with In one circumstance resin flow into the z-direction fibers also could be made by core is desired. The adhesive is. if the core absorbs resin. this could starve the interface and are shown in Figure 12-5. and some stitched/compressed ma- shape the core so it tapers to a smooth finish terials. The milled fibers give a good bond over the entire surface are short and give some reinforcement to the but not so thick that it becomes a point of resin. Some core materials have a scrim been stitched through the x-y plane laminate sheet (that is. some foams. Methods. subjected to high vertical (z direction) loads. The resin inside the cells tends to done with an adhesive film that is placed keep the cells parallel. Therefore. Another method of sealing the sand- failure. This is strength. sealant. balsa. Some typical plug materials are than the resin-fiber laminate. thus increasing the between the face plates and the core. Experience has shown sandwich material usually need to be sealed. care must be taken to prevent exces- and then bond the faces together or wrap sive resin infusion into the core layer. To achieve this moderate wicking. the ends of the surface of the core. and shaped When the core is of an absorbent material metals or ceramics. greatly weaken the bond. In this case. that tough adhesives work best because they This sealing can be done by several different can elongate slightly to accept small displace- methods. Several resin were absorbed or flowed into the core methods of closing the ends of the sandwich material. a thin mat material) bonded layers to place fibers oriented perpendicular to the top of the core to prevent excessive to the plane of the majority of the other resin infusion. One is to apply a thick resin as a ments without cracking. That is when weight is not knitting or weaving. and Applications . That crush strength significantly. sometimes reinforced with milled The adhesive must be thick enough to fibers along the edge. If the one of the face sheets over the end. injection molded plastics. These materials are usu- like balsa wood. sufficient adhesive is applied Manufacturing of the Sandwich Structure to allow the resin to flow into the core and bond at the interface. The cells of the core The most important part of manufactur- material are designed to have resin within ing a sandwich structure is the bonding of them so that they will be stronger in crush the core material to the face plates. These fiber ma- carefully controlled at the temperature used terials are usually layers of cloth that have for curing. With honeycomb. Joints. the amount of adhesive must be increased accordingly or some mea. One strategy (discussed in give a good bond to the walls but will not run Chapter Nine) uses fiber preforms in which excessively. a non-re- wich is to plug the exposed end with some inforced resin layer that has less strength material. after the core and face plates are sheets and to resist debonding from the bonded to make the sandwich. some of the fibers are actually oriented in the viscosity of the adhesive material must be the z-direction component. their cross-sectional shape. looking strength and stiffness involve the addition down the z axis. also encountered in non-naval airplanes. cation equipment and. are valuable. therefore. they are not dominant in the the hat and J shapes (and others that serve composites market. sandwich construction is now rarely costly than traditional laminar structures. which are so common in sand- norm.358 12: Sandwich Structures. But the problems of water Chapter 16 where fiber preforms are the entrapment. The therefore cannot use preforms that have airplane industry uses these structures z-directional fibers. Many airplanes once used sand- the resin infusion processes discussed in wich materials.) A drawback is that these preforms wich structures on aircraft carriers. the pattern of intersection Fundamentals of Composites Manufacturing: Materials. Joints. Typical examples ing methods utilize laminar structures and are hat stiffeners and J stiffeners. But most manufactur. used in commercial airplanes. These stiffeners are often referred to by the fibers in sheets. were are made on highly specialized textile fabri. especially for manufacturing of structural reinforcing materials or stiffen- methods that do not depend on laying up ers. Other methods for increasing z direction When viewed from the top. and Applications . and Post-processing Operations Figure 12-5. are more Hence. Methods for closing the edges of sandwich structures. The alternate So. (Some exceptions are extensively. that is. even though such z-directional preforms method is to use structural stiffeners in are available. similar purposes). Methods. plex and.12: Sandwich Structures. shown in Figure 12-6. these joining methods are even more com- Another pattern that has much interest. which is like rivet- structure is usually shaped like an egg crate. in the 1940s and 1950s could be a predictor is actually stronger than the orthogonal. The composite materials to each other and to most common is orthogonal. Another construction. Methods. Fundamentals of Composites Manufacturing: Materials. a struc. Both plywood and press. In fact. which design criteria and methods for joining will be discussed in Chapter 20. These forces can. and Applications . While a major consideration. The but not as much use. This development of aluminum joining methods structure. Therefore. and Post-processing Operations 359 of the stiffeners can be of various types. certainly considered besides resin-fiber laminates and some of the steps in aluminum joining sandwich materials. Their most common use is for backing mold faces where access is relatively easy because Mechanical Joining only one composite face is used. In this pat. of course. The butt lap is a simple way of join- Just as the general design criteria and ing two laminates when the edges are to be methods for composite laminates and sand. the offset lap has and is better thought of as a backing mate. This type of composites: mechanical. Plywood is a laminate with its principle of course. diffusion bonding. then manufacture. The first methods for joining the triangular structure is more difficult to aluminum were riveting and bolting. even less. its non-sym- the wood products. This was an early construction and is joining device—rivet. and most recently. less inclination for shear and the double lap rial than as a core material. bolt. etc. (A special structure based on welding and diffusion bonding. composed of equilateral triangles. bonding. but such as welding. especially common The most common of these joint designs are in the fiber reinforced plastics (FRP) mar. is called isogrid. Such structures can be stiff and strong. followed the isogrid pattern is discussed further in by adhesive bonding. more tentative. Joints. Thus ture can be built up using support struts there are two general types of joints in between the laminate faces. join composites to other composites and wich-like structures. therefore. The drawback for both of these joints is the additional material that must JOINTS be used. it does even alter the nature of the way the laminate not have optimized z-direction properties resists forces. to non-composite materials (chiefly metals). the common repair (called doubler repair). ing and bolting in aluminum. of the future pathway of composites join- but is limited in actual application because ing methods.—is still used in applications where weight is not placed through the hole and secured.) stir welding. While some of these methods Some other types of structures that might for joining aluminum may not be directly give increased z-direction stiffness can be applicable to composite joining. In each joint the com- ketplace. other materials are still developing. A mechanical faces. aligned. break the joining device and may strength in the x-y plane. composite structures. Several joint designs have been used to egg-crate structures could be used for sand. The cost is also low for the straight lap is the simplest. uses plywood or pressboard as the posite materials are brought together and a material between the composite laminate hole is created through them. Chapter 24. adhesive are often difficult and expensive to build. reflect the situation of composites. the stiffeners intersect at right angles. This method is similar to a type of wich materials are still developing. Therefore. always present in the joint. For example. tern. and stir welding. screw. and chemical. metry means that shear forces are almost board are. However. ) must be large in ers—aluminum and cadmium-plated being diameter so the forces of closure are spread two of the worst. the tight- Materials of the Fastener ening process must not be so aggressive that The choice of material for the fastener layers of laminate are crushed. is illustrated carbon fiber reinforced composites. in Figure 12-7a. Besides the design of the joint. and Applications . • shape of the fastening device. etc. This problem is reduced by over a large area. and Post-processing Operations Figure 12-6. Methods. the process of joining do not damage the composite laminate. This type of device is important. It is also advisable to use a Fundamentals of Composites Manufacturing: Materials. • strength of the fastener. Mechanical joint designs. Be. or by separating the fastener from the carbon with a glass-reinforced outer • materials of the fastener. rivet end. To help prevent this from cause carbon is electrically conductive.360 12: Sandwich Structures. called a bearing failure. titanium. Joints. or nonmetal (compos- siderations in mechanical joining are: ite) fasteners. other con. using nickel. occurring. especially in joining failure. For example. layer or sealant. Shape of the Fastening Device • hole size. largely in ensuring that it and removed in making the hole. the head of the joining device and galvanic corrosion occurs with many fasten. the end (nut. and The physical shape of the fastening device • loss of strength because of the material is important. vice to ensure that the securing forces will not • Mechanical joints are stronger in peel be excessive. tal degradation (except for the carbon- occurs most readily when the fastener has a metal corrosion). • Mechanical joints are relatively easy to inspect. shown in Figure 12-7c. joining. thermal. simply. failure of the adjustment in the method. If made larger than this. bonds advantages. In addition. The shear. by • The mating surfaces of the materials to making the hole large. water. ite material is removed and. stress concentration points can develop at • Little surface preparation is required the ends of the hole when the joint is loaded for mechanical bonding. small diameter and the joint is subjected to • Different materials. Failure types for mechanical joints in composites. between the matrix of one layer with the Fundamentals of Composites Manufacturing: Materials. This is in contrast to In spite of the problem with mechanical using an adhesive to bond the materials. therefore. it continues to be employed. Methods. permanently fixed. whereas adhesive bonds are an interference fit. and a metal. the bonds between layers of because of one or more of the following a composite laminate are. and other environmen- out failure mode. such as a composite shear forces. of course.12: Sandwich Structures. can be joined with little diameter fastener is. The cleavage failure. largely For example. in tension. • Mechanical joints have little creep. more of the compos. Joints. is from transverse shear forces. ends also may have a tendency to pull out. Figure 12-7d. be joined is relatively unimportant. Chemical Joining Many composite joints are made by form- Advantages ing chemical bonds. torque wrench or some other moderating de. fastener itself. Another problem with a small. This could result in failures of the type shown in Figure 12-7b. and Post-processing Operations 361 Figure 12-7. Hole Size and Loss of Strength • Mechanical joints can be designed for The fastener hole is often drilled to give access. the • Mechanical joints are less sensitive to composite is inherently weaker. and Applications . Fasteners with small heads or loading than adhesive bonds. posite. which is often as those discussed previously in this chapter. The surface of the composite ma. and into the interphase of the adhesive molecules • the curing process. and drying that are joined together by curing them simul. the incomplete cure may actu- • adhesive composition. oxygen and retains the styrene. adhesive between the already cured materi. But. determine whether the matrix cured com- the most common method is to apply an pletely (cured hard) to the outer surface. the outer layer of many polyester bonded to is called the adherend. thus improving the bonding ca- Co-cured bonds are often the strongest pability of the material. Methods. and vice versa. taneously. Placing a peel ply on chemical bonds that can be made between the surface of the part during laminate cur- laminate structures. special attention must be given to When different materials are to be bonded. are often made from the same material as A typical surface cleaning process would the laminate they are supporting and are include: wiping with a solvent or vapor de- cured at the same time as the laminate. Surface Preparation Many polyester and vinyl ester formula- The preparation of the surfaces to be bonded tions contain wax or some other internal is extremely important in adhesive bonding. As a separate step. and Applications . to be made. The material to be joined or result. rinsing with water or an alkaline results in migration of the common matrix solution (if required to remove solvent). co-cur. This is because the uncured matrix molecules can migrate • tooling or holding jigs. Similarly. in the complete curing of the composite all taminants. These materi- Fundamentals of Composites Manufacturing: Materials. stiffeners. The process of curing laminate Sanding or scrubbing with an abrasive materials at the same time and thus causing pad increases the surface energy and area them to bond together is called co-curing. agent that forms a coating on the top of It has a large effect on the permanence of the curing polymer and thus excludes the the bond. Oxygen inhibits polyester curing as does the als and to cause the adhesive to harden in a evaporation of styrene at the surface. wiping again are integrally bonded. ally help to improve the bond between the • application procedure. The same practice with solvent. ing can be done as an alternative to sanding ing requires that the composite materials be since removal of the peel ply will result in a made of the same matrix resin. This greasing. When the matrix is polyester or vinyl Adhesive Joining ester. rinsing with deionized water could be applied to two laminate sections (if required to remove solvent). This results terial must be free of grease and other con. One contaminant that requires the way to the outer surface. in an oven (if water was required). Joints. then molecules across the boundary of the stiff. and vinyl ester materials is not totally cured The effectiveness of adhesive bonding is even when the interior is properly cured and dependent upon many variables. (roughness). present on cured composites. of course. thus creating the same effect as when two laminates are co-cured. including: the normal cure cycle has been completed. If the condition exists and a bond is • shape of mating parts and joint design. and Post-processing Operations matrix of another. This condition can be detected by a slight • surface preparation materials and the softening of the outer surface of the com- method of surface preparation. roughened surface. abrading the surface by sanding or scrub- ener and the laminate so that the materials bing with an abrasive pad. such removal is mold release agent.362 12: Sandwich Structures. laminate and the adhesive. adhesive bonding. the wax or other joints are better than others in this respect. Structural adhesives Fundamentals of Composites Manufacturing: Materials. adhesive from a melt to a solid. large as practical and matched as closely Normally. In these cases. except that. thus reduc- an anodizing method. is a thickening of the material. The adhesive is chosen for cially important in adhesive bonding. Methods. subject to shear. applying the adhesive. But. chemical re- fore. ease of application. Similarly. the single. it is critical to remove extensively in primary structures and for these coatings as part of the surface prepara.) agent often prevents good bonding with an Therefore. however. Several of these are similar to the types as rubber cement. The surfaces to be joined adherend or is somehow pressed against should be mated for shape and general the surface of the adherend (or both). Adhesive Composition When applied. these two joint designs are used adhesive. The double lap largely action within the adhesive such as crosslink- eliminates the asymmetry but requires more ing or polymerization. This not only helps to tive on a gel coat. tion process. on the other hand. and resistance to all the forces are transferred. (Exceptions to hardening adhesives would be ly) bonded joint designs are shown in Figure those that are meant to stay flexible. pastes. adhesive joints do not normally from solvent loss. Titanium. and Applications . as possible in shape. a surface oxide should be carefully treated to achieve a stable surface. Note that layers are be treated with a phosphate fluoride or by “dropped” in a staggered fashion. and Post-processing Operations 363 als are cured hard. thus minimizing their effect. The most common chemically (adhesive. The most common method of the areas of the mating surfaces should be as removal of these coatings is by sanding. or solid (uncured) films.12: Sandwich Structures. but these environmental effects. The single-lap can result from loss of solvent. of course.overlay butt the adhesive that causes some interaction joint is simple but asymmetric whereas the to occur with the adherend. the only of joints made with mechanical fasteners change. some shaping of the mating surfaces a liquid phase and wets the surface of the may be required. adhesives are usually liq- Shape of Mating Parts and Joint Design uids. (Not cost.) This hardening require holes or fasteners. The transfer of forces across a joint If the composite is to be bonded to a and the minimization of stress-riser points metal. or pressure against material. there. if any. the surface of the metal must be in the laminate itself can be accomplished carefully prepared. would lustrated in Figure 12-9. such 12-8. cooling of the joint is simple but is asymmetric and. physical change such that they become hard. In all Depending on the type of joint to be cases. This tapering is il- primer. but it helps to transfer the gel coat completely by sanding before the forces. such as structural strength. by tapering the termination of the laminate the most commonly used cleaning method rather than simply allowing all of the layers is phosphoric acid anodizing followed by a to stop at the same point. to meet the many applications that require The scarf and stepped-lap joints are espe. the joint. repairs. These its ability to bond to the adherend and for its designs allow forces to be transferred across other properties. In the scarf and stepped-lap joints. Most smoothness (except for the slight roughness adhesives go through some chemical or that occurs after sanding or abrading). double-overlay butt joint is symmetric but A wide range of adhesives are available requires additional material. the adhesive goes through formed. The practice is to remove give a good bond. Therefore. adhesive bonding is not effec. In the case of aluminum. Any metal that forms ing the thickness gradually and smoothly. Joints. polyurethanes. where one part systems. withstand a variety of difficult environmen. The following are brief descriptions of each tal conditions such as high temperature. and Applications . groups within this class of adhesives are (The chemistry of crosslinking of epox- epoxies.) Shelf Fundamentals of Composites Manufacturing: Materials. cyanoacrylates. ies is discussed in Chapter Four. Joints. They are gener- either one. The most important polymeric is the epoxy and the other the hardener.364 12: Sandwich Structures. are those used most often with composites. Requirements • Epoxies are the most common of the dictate that most structural adhesives be structural adhesives. silicones. type of structural adhesive. and various high-temperature polymers. Methods. Chemically (adhesively) bonded joints. and creep. pheno- These can be stressed mechanically and can lics. and Post-processing Operations Figure 12-8. adverse solvents. modified acrylics. anaerobics.or two-component thermoset ally two-part adhesives. These adhesives are often with atmospheric moisture.or discussed in Chapter Five) and are. Phenolics are dark col- long. 700° F (371° C) for some formulations. even systems available with one or two when the surface is slightly oily or im. nent systems that cure when in the the adhesive is applied. component systems cure on contact nent systems. However. and Applications . Therefore. After warming. usually sold as two-compo. These adhesives bond that its cure will not be advanced during well to most materials. surfaces. Silicones tougher than epoxies because of their can be formulated to cure at room higher elongation. and weathering ponent to the other adherend. after mixing. The air is excluded when the life before mixing of the components is coated adherends are pressed together. Impact resistance is improved ored. by mating the parts. kept at a low temperature before use so ent atmospheres. which limits applications. one component is applied Silicones are tough and flexible with to one adherend and the second com. These adhesives • Phenolics are low-cost thermosetting can be used on most materials. • Anaerobics are single-component sys- tems that cure by free-radical polymer- ization. Service chipboard markets. They are single-compo. the re- the pot life is short. Methods. Fundamentals of Composites Manufacturing: Materials. the is also an advantage as they are used adhesive is carefully applied to the treated to suture skin together in surgical pro. inhibited by oxygen. Cure times are quite but brittle. Typically. the poly. components. –76 to 480° F from standard acrylics in that rubber (–60 to 249° C). including skin. and can go as high as or other tougheners have been added. They are generally strong properly cleaned. action is initiated and proceeds rapidly. or in the case of This can present a safety hazard but two-component adhesives. Joints. good solvent. as is present in most ambi. The polymerization reaction is Figure 12-9. and Post-processing Operations 365 cedures. two-component systems. moisture. After the surfaces are properly prepared. • Cyanoacrylates are the materials used Application Procedure in superglues. The resistance. long (nearly infinite) but after mixing. These over standard acrylics but is still only materials dominate the plywood and good (rather than excellent). • Modified acrylics cure by free-radical They have good adhesion over a wide polymerization reaction. Cyanoacrylates are relatively expensive and strong but brittle. temperature (room-temperature vul- urethanes are not as strong as epoxies.12: Sandwich Structures. temperatures are moderate. The adhesive (if it presence of even small amounts of is a one-component system) is generally moisture. Tapering to end a section or make a joint. The one- therefore. materials react when the adherends are pressed together. They differ temperature range. so no reaction will take place until oxygen is removed from the system. • Polyurethanes are made by the reac- tion of a polyol and an isocyanate (as • Silicones are available as either one. canizing [RTV]) or high temperature (high-temperature vulcanizing [HTV]). storage. Toughness and strength are moderate. and Applications .2 mm).366 12: Sandwich Structures. the mating surfaces but not be excessively • Adhesive bonds work well on even thin thick. pull-out. Typical thicknesses of the adhesive the materials can be fusion bonded (welded) layer are . and even clamps for room-tempera. drill break-through. additional often reduced until gel occurs and then the resin is often used in structural reinforced part is post-cured. (The post-processing operations com- • Adhesively bonded joints weigh less monly used with composites are outlined in than equivalent mechanical joints.1–0. uses a rod or sheet of thermoplastic resin that is heated and applied between the Advantages layers of laminate. fiber fraying. excess resin are to be bonded. Adhesive bonding has some drawbacks but also some advantages. erties. friction heating. and assem- centrations. therefore. and Post-processing Operations The adhesive should be applied to the • Adhesive bonds are usually less ex- recommended thickness. It should cover pensive. layer is too thick.008 in. the pieces the surfaces to the point of incipient melting. heating After applying the adhesive. (0. trimming. and cured. If the entire ture cures are also used. and then pressing the surfaces together. as well as adhesively bonded. composites. the Composites Manufacturing videos that • Adhesive bonds permit smooth external complement this text. to near-net shapes (that is. and other sim- structure. the adhesive could become an important failure point for the entire • Bearing failures. resin and is not. In compacted to remove trapped air. Joints. is rare. The adhesive is a non-reinforced laminates. as strong as • Adhesive bonding is less sensitive to the laminates being joined. However. the cure temperature is is usually not required. The advantages POST-PROCESSING OPERATIONS of adhesive bonding compared to mechanical Although composites are often molded bonding include the following. metal material) can be used. to be bonded are placed in a holding tool. ovens. ultrasonic The cure most often is done in an autoclave heating. bly into larger structures may be required. However. A related process. composite (delamination.004–. The DVD entitled surfaces at the joint. intentionally to create failure at a specific lo- cation or load rather than risk unpredictable Other Bonding Processes catastrophic failure.) is great and care must • When the loading is first applied. the potential delamination caused by the drilling for damaging or otherwise weakening the required for mechanical joining. If the adhesive cyclic loading. adhe- be taken to maintain the composites’ prop- sive bonds have less permanent set. and induction heat- for advanced composites. Welding is ac- complished by cleaning the surfaces with Workholding and Curing solvent and/or water and detergent. “Composites Post-fabrication & Joining” is Fundamentals of Composites Manufacturing: Materials. shapes). • Adhesive bonds eliminate potential In some of these processes. This is to be avoided unless done ilar joint failures are not a problem. hot-melt ad- hesion. etc. Methods. But this latter situation With thermoplastic matrix composites. almost finished • Adhesive bonds have lower stress con. If materials having laminate gets hot enough for the resins of different coefficients of thermal expansion the two layers to intermingle. ing (which requires the addition of some presses. finishing. addition to conventional heating. drilling.25 in. or plastics. high-strength be increased and the feed rate decreased blade. the damaged portion of the part. Methods. dulls quickly.or carbide-tipped reinforcement material (aramid. tools is recommended for composites. A large positive rake angle. Feed rates are . router cutters. The brittle nature of most composites processes are largely dictated by the type should be remembered in machining opera- of reinforcement with minor modifications tions. but the drills should be specifically tai- ter = . Good success has been achieved with relative to normal values used for metal a bandsaw blade with diamond grit on the machining. the ites differ in some major considerations from damage can only be corrected by removing similar processes for metals. (The rake angle is the angle ting speed = 600–800 ft/minute (180–250 between the tool face and vertical surface of m/minute). and surface cut. (50–100 mm) intervals. The abrasive nature and type of The use of diamond. but especially in aircraft and following values have proven successful for electronic circuit board manufacture. However. fiberglass.000–20.000 ft/minute (180–300 times) cutter life. Drill bits should have a cut burr). should be taken to ensure that the cutting tions necessary. In processes of joining and painting are largely milling.000 settings (speeds. cutter lineal speed = 10–14 in. grit) at 2–4 in. used.002–. circular saws. of a thermoset composite part occurs. For example. Care carbon. and Applications . various abrasive tools. feeds. In most cases. (6 mm) solid carbide (diamond. (dry) or 240 to 320-grit SiC (with water). mm/minute)./ Drilling of composites is important in almost revolution (0. and section is less likely. especially for thermoplastic composites. all cutting operations. the possibility of breaking off the last edge lathes. Joints. lored for composites. In nificantly depending on the resin/fiber sys. The every application. holding fixtures should to allow for the easily melted or degraded provide for backing of the part to prevent nature of the matrix. the part). If overheating cutting. starting at one edge and working toward the Composite materials can be trimmed and opposite edge. an efficient vacuum tem and on the thickness of the materials. cutting edge and a relief cutout (area without Optimum feeds and speeds can vary sig. etc. the machine Sanding should be done at 4. and Post-processing Operations 367 especially valuable to enlarge on the informa. By following this sequence.) make certain process modifica. Cooling or lubricating (preferably with tion contained in this chapter [SME 2005]. (6 mm) thick in the routing process: cut.25 ventional metal-drilling equipment can be in. both edges should be cut and then dependent on the matrix material since these the center section can be cut. which Fundamentals of Composites Manufacturing: Materials. system capable of removing cut material and Typical cutting speeds for machining FRP dust will significantly increase (up to five materials are 600–1. cut with conventional metalworking mills. drilling. cutter speed = 10. to Conventional Metalworking Equipment prevent resin build-up on the cutting tool The equipment and procedures used in and overheating of the part. Con- epoxy/carbon composites approximately .12: Sandwich Structures.005 in. ceramics. the cutting speed (spindle speed) should Sawing should use a fine offset./minute so large that the cutting edge gets thin and (250–350 mm/minute).05–0.000 large positive rake angle without becoming rpm.000–12. etc. and other machining tions. rather than are chiefly surface phenomena. the delamination and backside breakout.) fluorocarbon cutting fluid) may be necessary. and machining of compos.) and cutting bits rpm or more using 80-grit aluminum oxide usually need to be modified. tools are kept sharp to minimize delamina- Cutting. On the other hand. wood.13 mm/revolution). drills with high helix angles and tive drilling of holes. PCD cutters often last more than buildup in the drill. such as a drill. With aramid. and Applications . In this process. found. and then low volumes (1–2 gal/minute [4–8 l/min- cut by the following part of the cutting edge. For a rotating tool. this erode the material. with or parts with two different materials. avoiding the heat this method. which is often done in wide. the drill is advanced into the that arises from shear forces and friction. the fibers are tough and Waterjet cutting is gaining strong sup- tend to shred rather than cut. cleanly cut fibers will jet of water to impact and. The water is then pumped at at the edge of the hole. The inser- aside. the frictional heat dominates the dis- cutting composites (not combined with met. When the drill becomes twice as long as conventional cutters. In repetitive drilling. however. a pointed drill-bit geometry can prevent drill causing hole enlargement. the lower thrust forces on the exit of the hole. cut or result. polycrystalline gradually heated to a steady state with heat diamond (PCD) inserts significantly increase dissipating through the hole wall to the sur- drill cutter life compared to high-quality rounding air and chips balancing the heat steel bits. The hole a preset amount.000 psi In this way. (0. Lubricants and coolants are not (and heat) required to cut. the drill itself is Carbide and. the part to be cut. indication of too high a feed rate or pressure. Waterjet Cutting posites. sipation and the chips melt and stick to the als). peck drilling is recommended for deep the orifice) to give additional cutting capa- Fundamentals of Composites Manufacturing: Materials. which would be an make removal more difficult.25 mm) and then onto performance with these materials. stretched. water to high levels (typically 60. will allow the drill to penetrate into are used such as in sandwich structures. fiber and fiberglass has been used to make In some cases. that if the fibers are preloaded This method utilizes a fine. facilitate chip lifting and removal. a phenom- delamination and fiber breakout because of enon known as drill smear. (usually entrained in the water flow after als. Another problem occurs with the repeti- Therefore. Methods. whereas a cutter with a smaller or tion and retraction (like the pecking of a neutral angle would tend to pack the fibers in woodpecker) is continued until the hole is front of the tool. therefore. and Post-processing Operations means that the tool face is slicing into holes and whenever dissimilar materials the part. ute]) through an orifice having a diameter The tools must be kept sharp for adequate of about .010 in. drilling of sandwich materials up to 40 quality holes per tool life cycle. polished flutes are recommended to the manufacture of printed circuit boards. Joints. Research has port as a method to cut composite materials. The resulting chips used in cutting deep holes since they tend are small and granular (sawdust-like) and to cause the chips to stick together and thus should not fuse together. intensi- requirement dictates a C-shaped cutting edge fier pumps increase the pressure of filtered that cuts from the outside toward the center. increasing the cutting forces completed. often requires major compro- The problem in cutting aramid reinforced mises in machining conditions. composites is quite different from cutting either carbon or glass fiber reinforced com. It is then retracted to positive angle also tends to push the fibers remove chips and dissipate heat. Abrasives can be added With any of the reinforcement materi. The requirements for drilling composites A drill proven successful for cutting carbon can be quite different from those for metals.368 12: Sandwich Structures. such smoothly cut edges and without splintering as a titanium bonded to a carbon reinforced or the use of backup material. especially. high-pressure (stretched) and then cut. In the material with less force. the fibers are engaged by the tool [400 MPa]). composite. When dull. fragile piec- started at an edge or away from the finished es often can be cut best using lasers. fected zone in the vicinity of the cut and they are used widely in the manufacture of can dwell in one spot for some time without printed circuit boards. the cut is much rougher with High-power lasers are often rather large boron fibers than with the comparatively machines that require careful alignment of softer aramid fibers.5 m/minute) laser cutting is generally limited to cutting for 1-in. Be- of initial penetration. and the power of The quality (roughness) of the cut depends the laser. ute (635–3.12: Sandwich Structures. etc. dissipate the incoming light ft/minute (18 m/minute) for . Such machines are usually not portable. energy. The heating problem or if the water pressure builds up because it also may be worsened because of the need to is not penetrating the part. (3. which may material being cut. Water pen. Lasers produce a Waterjet cutting can be initiated at any coherent beam of light caused by the excita- point on the part. which varies with the to cut with lasers because of the difficulty thickness of the workpiece and the type of of removing the waste material. Therefore. Joints. It can cut complex pat. Methods. Fundamentals of Composites Manufacturing: Materials. These cutting those parts where the laser can break through speeds are slightly higher than speeds for before sufficient melted material accumu- soft metals (aluminum. shape is to be cut several times. However. Therefore.125-in. and block further cutting. effectively drilled mechanically.). the normal rule in using lasers is to The use of lasers to cut composites is move the workpiece under the laser rather growing rapidly in those applications where than move the laser head. requires good filtra. These are especially useful for cutting the inherent problems associated with laser sandwich materials. type of material. accurate and rapid cutting when the same which fill the excitation chamber of the laser. cutting are not serious. than most of the mechanical methods and They can be focused or collimated with ap- generally requires only clamping to support ertures to drill holes that are too small to be the part.048 mm/minute). The light is focused onto the workpiece and because delamination can occur in the area then burns or melts the material away. cutting is usually cause no cutting force is exerted. tion and subsequent relaxation of electrons terns and can be numerically controlled for in specially chosen molecules. widening the cut width. the thermal effects of laser cut- The waterjet cutting process is quite noisy ting are sometimes serious detriments to its (requires ear protection). Cutting speeds depend on workpiece (steel. which may be etration between the fibers and laminations is more severe because of the good heat conduc- a potential problem if the laminate has voids tivity of carbon fibers./min- on the hardness and strength of the fibers. This is especially heat glass fibers to a high temperature to melt problematic at excessive water pressures. rounding the cut is a problem. and must be or charred edge or of a heat-affected zone sur- carefully monitored for jet wear.3 in. Thick parts are usually problematic The cutting speed. stainless. mm) thin parts to 5 ft/minute (1. thickness. However. typically ranges from 60 remain in the cut. (25-mm) thick parts. There- Laser Cutting and Drilling fore.18. various mirrors and focusing devices. and Applications . use. For example. In some cases. the creation of a melted tion equipment for the water. and Post-processing Operations 369 bility.) and three lates to prevent further cutting. can be started at any point in the workpiece Waterjet cutting produces less cutting force and are capable of cutting intricate patterns. about . such as CO2. brass. Typical values are 25–120 in. to four times faster than for hard metals (8 mm). It produces no noticeable heat-af. Lasers area and then moved into the desired area. them. etc. 13 mm) span.59 KPa). The presence of a core material stiffness.6 g/cm2) chopped strand mat and 18 oz/yd2 (618 g/m2) knit- 3. The abrasive nature of the diamonds nance platform for an industrial plant. Experience indicates that a The kerf (material lost in making the cut) maximum acceptable deflection for a plat- is typically 10% greater than the diameter form of this type would be equal to the span of the wire. This combination gives the bottom faces are Style 500 aramid cloth thickness desired and has been shown to and the core material is PVC foam. or 3. (0. generally about 100 ft Construction (30 m). thick. All laminar construction of three plies sign calculations considering toughness to of fiberglass cloth. the high The use of a wire saw with abrasives is flexural stiffness of the sandwich material old technology dating back to rock cutting illustrates the advantage of this construction in quarries in ancient Rome. have the toughness and abrasion resistance The relative properties for the three compos. platform is to be 48 × 120 in. mm). • shear strength = 25 in. It is mounted CASE STUDY 12-2 in a cutting mechanism that moves the en. All laminar construction of three plies exterior surfaces will be . Methods. abrasion resistance. The intricacy is reasonably good divided by 100. and Applications . Sandwich construction where the top and ted 0/90° fabric. the wire is impregnated with diamonds.000 psi (517 MPa).5 mm) of aramid cloth. Style 1800.7 J). (2. The laminates will be made from lar® 49. Designing a Platform Using Sandwich tire length of the wire. Other required design criteria are: CASE STUDY 12-1 • stiffness = 75. 5. the temperature is required to withstand is 75 lb/ft2 (.005 in. Assume a normal design safety factor of 2. This is characteristic of a laminate reduces the shear strength of the laminate made from advanced materials (such as by a factor of at least 10 and as high as 100 Fundamentals of Composites Manufacturing: Materials. 9. Style 500 cloth of Kev.10 in. Though cm). In the case of cutting composites. with its favorable z-direction properties. (122 cm) with a turning radius of . Other de- 1. (300 g/m2). However. and Post-processing Operations Diamond Wire Cutting aramid or carbon fiber). Comparison of Various Composite • flexural strength = 300 in-lb (34 J). pared for making a canoe or kayak hull. As long as large crowds of people or more time is required to make the cut using heavy machinery will not be moved over the the diamond wire cutting method than with platform. the deflection would be . for a 48 in. The It is decided that the platform is to be constructions are as follows: made of sandwich construction.5 oz/ft2 (6. (12 reported. required. Joints. Constructions and Three different constructions are com. ites are shown in Figure 12-10.52 psi rise at the cut is usually only a few degrees.-lb (2. two plies of 1. first in one direction and then in the reverse (a sawing action) over the surface to Assume that you want to make a mainte- be cut.48 in.0 oz/yd2 (170 g/m2). The and their strength permit the cutting of es. and x-y plane forces have indicated that the 2.370 12: Sandwich Structures. So. (122 × 305 sentially all material by this method.0 oz/yd2 resist dropped tools. the standard pressure the design waterjet or laser cutting. The aramid The core material needs to be chosen laminate material is lighter weight than the and the principal force to contend with others and has greater tensile strength and is shear. 12: Sandwich Structures. However.6 MPa).9 MPa) (but at significantly high. This is a rather thin core. (If not stiff enough.) It foam is reported by the manufacturer to is even possible that if the panel is not stiff have a shear strength of 87 psi (0.7 is. This means that the core plus The stiffness deficiency can be corrected one-half the skin thickness must be roughly by increasing the thickness of the core.5 panel can be best assessed using a lami- MPa). skin thickness. enough.29 in. To obtain the required 25 in. It a minimum of 25 divided by 87. and Applications .7 J) The stiffness requirement is established shear. Methods. solid meets the shear requirement.48–2. (0. In this case. PVC it might feel like walking on a trampoline. it might sag so much that it could The overall shear strength of a cored panel is slip out of its supports. For example. requirement. Through a series Fundamentals of Composites Manufacturing: Materials. but it construction was chosen. material’s shear strength. the sandwich 1. outlined easily meets the flexural strength er weights than most other core materials). as fiberglass laminates have a shear strength will be seen later. with some core materials. The laminate stack equal to the shear strength of the core times program shows that the laminate proposed the thickness of the core plus one-half of the is only 8% of the required stiffness. and Post-processing Operations 371 Figure 12-10.-lb (2. Most common core materials have The flexural strength of the sandwich shear strengths between 70–360 psi (. For example. the thickness of the core is calculated to prevent the feeling of walking on a sur- from reported (literature) values of the core face that is too flexible. a thicker core is needed to ranging between 12.000 psi (6. Plywood and syntactic foams are the nate stack computer program (as outlined exception. after all. Comparison of laminate-only and sandwich constructions.000 psi (83–97 meet the strength requirement. Joints.000–14. having shear strengths of around in Chapter 11). or . for stiffness that the sandwich cm) thick. MPa). although interest. Steel is common but so is composite. tural stiffness. The Figure 12-11. increase the thickness (number of plies) in Therefore. Ski construction. but this is generally a combination of the sandwich and this rub- more expensive alternative to increasing the ber sheet. a layer (2. and Post-processing Operations of trial and error calculations using the stack and laminated wood core is at the center laminate program. The hard outer shell can be made of any durable material. the stiffness requirement of the ski and provides the desired struc- can be met with a PVC core that is 1. and Applications . Fundamentals of Composites Manufacturing: Materials. A sandwich of reinforced polymer there is some stiffness from it as well.125 in. To provide cushion. The incorpora. core thickness. tion of several different materials is of major The phenolic spacer takes space. usually ultra-high-molecu- Ski Construction lar-weight polyethylene (UHMWPE). The bottom of the ski is a sintered CASE STUDY 12-3 running surface. This The construction of a modern composite material has a low coefficient of friction and ski is shown in Figure 12-11. the stiffness felt by the skier is a the face laminates. thus is a good material to improve sliding. Methods.86 cm) thick.372 12: Sandwich Structures. Joints. It also would be possible to of rubber is placed beneath the sandwich. Also. struction in which core material is bonded Procedure: between composite laminate face plates. are proving to be posites are more diff icult to machine more reliable. trimming. and Post-processing Operations 373 top and the bottom are held together by highly varied. 6. sive strength of each material. for example. pressive strength to the average weight ods. Weigh each sample and note the differ- adhesive used to form the bond must be ences in weight. drilling. cores are being used in record. Further. layers can be combined to achieve a unique These methods all have some negatives. The ability to give z-direction strength and stiffness to a composite structure greatly LABORATORY EXPERIMENT 12-1 expands the capabilities of the material. the amount and type of 3. of various core materials. concepts. wich construction rather than just a Composite joining methods have tradition- laminate. ally been dominated by mechanical fastening methods like rivets. in approximately 6 × 6 in. 2. Fundamentals of Composites Manufacturing: Materials. Several methods are employed steel edges. Nomex® There are more materials in a sandwich honeycomb. determine the compres- is more complicated than that for the aver. Methods. Clearly the construction is including modified metalworking methods complicated and illustrates how various and waterjet. the manufactur- ing process must be compatible with that 4. 1. each joint is unique and often requires considerable design time. These methods. Indicate three changes from traditional Cutting.2 lent between the core and the face panels. age resin-fiber composite. What are the principal reasons why com- still beset with difficulties. However. the complexity is also increased. but combination of properties. post-processing of SUMMARY composites is becoming routine. are becoming dominant. in spite 5. Give three disadvantages of sandwich ingly. cm) squares.2 × 15. generally using standard joint design for each material. and diamond saw cutting. of lower weight. carefully chosen. Give two advantages of using a sand- cated and must be done with great care. an ever-wider assortment of applications. than in a traditional resin-fiber laminate balsa wood. QUESTIONS Manufacturing of the joints is also compli- 1. Increas. the use of core materials from the samples of each material and is increasing greatly. suggestions are rigid foams. less costly. Using a plate attachment on a tensile choice. and particle board.12: Sandwich Structures. and Applications . Joints. with an understanding of the complex nature of composites and patience. Finishing of the sandwich structure test machine. laser. The bonding must be excel. (15. Average the compressive strengths of these difficulties. 4. aluminum honeycomb. Some However. co-curing of parts and adhesive joining materials versus laminates alone. Crush Strength of Core Materials Composite structures can be made lighter Objective: Discover the crush strength and at lower cost by forming a sandwich con. bolts and screws. and than metals? longer lasting than mechanical joints. Cut out three samples of each material can go wrong. However. Obtain a variety of core materials. while 3. and that means there are more things that 2. Determine the ratio of the average com- Composites are joined by various meth. and other metal drilling that should be made post-processing operations for composites are when drilling composites. com used most effectively for adding stiffen- ers to a composite part? Ultracore. MI: Soci- Fundamentals of Composites Manufacturing: Materials.baltek.com Schofield. Inc.tricelcorp. “Rational Design of Core Materials. Brent. 1998. waterjet Strong. Inc. Rohacell®. 6. www. www.com 7.mcgillcorp.com a.com Degussa Gmbh.impactcomposite. www. 2006. 9–15. org/cmvs ting a thin composite part: Spheretex America. 3rd Ed.com Impact Composite Technology Ltd. Inc.benecorinc. Joints. www. A.degussa.” Composties Fabrication. Inc.plascore.diabgroup. October. 1997. Dearborn.374 12: Sandwich Structures. Society of Manufacturing Engineers (SME).com M. laser and Processing.sme. A. C.com Plascore. ety of Manufacturing Engineers.ultracorinc. www.hexcel. c. “Design of FRP Joints. Indicate three advantages and three dis- advantages of adhesive bonding versus mechanical bonding of composites. www. 8. Upper Saddle River. “Composites Post-fabrication and Joining” DVD from the Composites Manu- facturing video series.com Lantor BV. www. Methods.” Composties Fabrication.com Nida Core. 12–19.atc-chem. www.com Hexcel Corporation. diamond saw NJ: Prentice-Hall. www. September. www. R. Indicate the advantages and disadvan. A. Inc.spheretex. tages of the following methods for cut. www. www.com Baltek Corporation. What is co-curing and when can it be Tricel Corporation. 2005.com DIAB Core Materials. www.nida-core.lantorgroup. R. Inc. www. Gill Corporation. Why was honeycomb material removed from naval airplanes? BIBLIOGRAPHY ATC Chemicals. and Post-processing Operations 5. Plastics: Materials b. and Applications .com Benecor. Schofield. www. puts fibers into an open mold and layer of resin is called the gel coat and has then adds resin to the fibers. in this chapter. to qualify for consideration in this • Gel coat considerations chapter. the mold is single-sided (that is. usually fabric or mat. the gel are placed into the mold. the formulation mold simultaneously with the resin. although it might be • Spray-up molding covered by a flexible sheet. • Lay-up molding open) and is not covered by a second rigid mold part during cure. Fundamentals of Composites Manufacturing: Materials. the automatic This chapter examines the following application of fibers to a mandrel. The mold can be made of many materi- • Process overview als but. the fibers are in the form of broad protective and decorative surface for the goods. These will then be followed the mold can be divided into two general by a more detailed discussion of the tooling methods—lay-up and spray-up. which is concepts: addressed in a later chapter).) This first times. part. After ensur- some special characteristics in manufactur- ing that the fibers are fully wetted by the ing and operation that are quite different resin. onstration of the techniques and equipment used in these processes. for example. and Applications 375 . (The inner surface of the mold be- The simplest technique to mold a compos- comes the outer surface of the part after the ite part. • Tooling (molds) In the lay-up and spray-up methods. (For a dem- (mold) in which the parts are made. Because the resin from the resin that forms the matrix for the is added at about the same time the fibers composite layers. the resin is cured.) In The gel coat is intended to be largely a lay-up. So. Methods. It contributes very little to the struc- the fibers are chopped and sprayed into the tural capability. Therefore. see the Composites Manufacturing DVD series from the Soci. a • Quality control and safety better outer surface of the part is created if a layer of special resin is applied to the PROCESS OVERVIEW inner surface of the mold before fibers are applied. these processes are coat is considered first and then the lay-up called “wet. GEL COAT CONSIDERATIONS ety of Manufacturing Engineers 2005. probably the first used in modern part is removed from the mold.” and spray-up processes to make the actual The methods of placing the fibers into composite layers. and application of the gel coat focus on the sumed that the fibers are placed or sprayed appearance of the part and its ability to into the mold in essentially a manual process continue to look good over time. It is as.1: Introduction to Composites 375 13 Open Molding of Engineering Composites CHAPTER OVERVIEW (as opposed to. In spray-up. matching. Fundamentals of Composites Manufacturing: Materials. However. When usually made with isophthalic acid as one properly done. (See the discussion in with the best appearance. The color is clean and free of defects (like scratches.376 13: Open Molding of Engineering Composites The gel coat is applied to the surface of the a promoter has been added to the gel coat mold but. so great care should ments and dyes that are added to the gel be given to ensuring that the mold surface coat by the resin manufacturer. application. good operating diluent (sometimes called the monomer conditions. Methods. The most effective method of applying gel the principal polyester resin in a gel coat is coats is to spray them into the mold. when the part is finally removed by the resin manufacturer. equipment. are more dif- solid materials stay in suspension. Normally mold surface. attention should be given to the complexities of color perception and color gel coat materials. compatibility with other resins. Almost all commercial gel coats are based on polyester or vinyl ester resins. ease of used. the gel that needs to be added by the molder is the coat must release from the mold. the mold is treated with a The initiator should be added just prior to release material (discussed in detail later in using the gel coat. and a trained operator. rapid gel coat. or worn areas). should work closely with the manufacturer Gel coats are typically shipped in drums. The gel coat technology (MACT) generally have higher should be stirred or agitated gently so that solids content and. fillers. this chapter). equipment is working properly as a complete tures. Normally. To enable by which the resin is delivered to the spray these variations. ideally 72–78° F (22–26° C). To allow initiator (sometimes called the catalyst). accelerators (also the resin. The gel coat also Several manufacturers make spraying might be formulated for specific properties equipment that is adequate for applying such as color stability. and Applications . the only ingredient outer surface of the part. thixotropic agents resin. especially in light of the need to cut the possibility of premature curing and low. The prepared. and specialty additives. ficult to spray properly. and high elongation. the gel coat formulation. Another consideration with Color is an important consideration in respect to the mold is the condition of the gel coat manufacture and use. Because Equipment gel coats must resist wear and weathering. of the spray equipment to ensure that the They must be stored at moderate tempera. The resins that are com- temperature effects.) Styrene is the most common reactive justed and operated properly. the gel coat ends up as the the gel coat is to be used. The molder shelf life. some considerations are the method maintenance. Therefore. suggest that color matching can best be done by the resin Materials manufacturer. inhibitors to extend orifice size is also important. therefore. combined with the complexity of curing. or crosslinking agent). most gel coat formulations gun. The choice of nozzle design and called promoters). how the initiator is mixed with the contain pigments. this gives the most even coat of the components. this to happen. which could be negative pliant with the maximum achievable control for resin formulation stability. formulation often can be matched to a dents. The gel coat will replicate the color is created by a combination of pig- the surface precisely. After the mold is specification supplied by the molder. when from the mold. to reduce system. Therefore. processing ease. styrene emissions. spraying Chapter Three on various polyester resin properly requires good equipment that is ad- types. In selecting the equipment to be cure. and properties. and the method of atomization of to control viscosity. Most gel coats are degrees of 77° F (25° C). They may first one above the thickness of the gel coat. in fact. but the initiator concentration (within the initiator. application should be a well-ventilated area In general. should be frequently checked. After the gel coat has formulated with thixotropic agents that will reached ambient temperature. However. and professional shorter than the posts by varying amounts. The thickness Many problems can occur with a gel coat. Temperatures should be within a few outward to other areas. It is possible to adjust Because gel coats are pre-formulated with other parameters to achieve the correct gel all the required ingredients for curing except time. it is better to use a series of passes with an air exhaust system and adequate rather than a single concentrated pass. For most applications. and Applications . correct. If the gel time is not is affected by proper technique too.13: Open Molding of Engineering Composites 377 The ambient environment for gel coat give uniform coating at the right thickness. the initiator concentration can be varied to achieve the time stipulated by the Curing resin manufacturer. by noting which of the extending fingers is Other problems are not detected until long not covered with gel coat. the cure is not instantaneous. Also.8%) and a small sample of initiated gel are formulated to flow together without pin- coat should be sent to the laboratory for holes or bubbles. equipment. Dif- methods to prevent overspray contamina. operator in developing a technique that will This could result from too much initiator Fundamentals of Composites Manufacturing: Materials. It is simply a small piece of metal that conditions under which the application was has two posts that are pushed through the done. inspections should be rou- gel coat until the posts touch the mold. Typical time for a gel coat Application to be ready for the next step in the mold- If the materials. That finger is the after the gel coat has been applied. Troubleshooting guides tween the posts are a series of fingers that are available from resin manufacturers. the gel coat does not immediately become hard.05 mm). tine and vigorous. Be. that is. this characteristic gel time determination. Methods. One problem that has been espe- cure properly. not. extend toward the ends of the posts but are equipment manufacturers. ficult areas should be sprayed first. be discovered for many months A coating that is too thin may not cover or or years. however. the initiator allow spraying on side (vertical) areas with- concentration should be set (usually about out resin sagging or running. most likely to give a good result. is cracking.46 mm ±0. usually because used to check the thickness is called a mil of poor application or problems with the gage. that time it is so highly cured that a good plication. bond between the gel coat and the laminate ity of coating evenly without applying the layer is difficult to achieve. Cracking may occur simply Several manuals are available to assist the because the gel coat is over-crosslinked. the operator is the should rarely exceed 8 hours since beyond determining factor for proper gel coat ap. gel coat too thickly. A coating that is too thick cially difficult for the composites industry could result in cracking. The operator has the responsibil. and envi. or trade organizations that can assist in The thickness of the gel coat is measured identifying the causes of defects. working tion. This time ronment are correct. ing process is about 45 minutes. the best gel coat thickness is 18 mils ±2 Properties mils (0. The device Some are seen immediately. gel coats 1. curing begins immediately the accepted range) is normally not only the when the initiator is added just before spray- easiest parameter to adjust but also the one ing. Therefore. some deterioration of laminate thicknesses or because of binding properties is inevitable. This will affect the appearance and the More subtly. etc. cracking of a cured polymer occurs because energy within the material exceeds the • Proper molding conditions exist (mixing strength of the material. Therefore. although molding problems. To prevent cracks from occurring. called the by sharp edges at corners or around fittings structural layers or the laminate. the mold. • The gel coat thickness is within the As already discussed in previous chapters. subsequently. For ex- like waxes. might be or holes. the molder must test each design and each LAY-UP MOLDING change in materials under a variety of Lay-up molding is one of two methods normal and extreme operating conditions. It also helps to smooth the final extremes of temperature (the differences in gel coat surface because it minimizes the ef- the coefficients of thermal expansion [CTE] fects of changes in laminate thickness.378 13: Open Molding of Engineering Composites being used or from excessively hot curing the part can be operated. Demolding is often difficult gun setup. resin reinforced with composite. even when the placed in use. when the product is seen through the gel coat. or from blooming). it that. but also physically additional stresses could come from general prevents fibers from pushing their way into operation. all polymeric materials degrade over as to the cause. these are fairly easy to identify and obvious Sadly. of the part within the mold. the part may experience stresses the amount of degradation. The veil not only visually than the manufacturer recommends. The energy to crack the gel coat • Other potential stresses.). Subsequently. combined with the residual stresses is common practice to lay a thin fiberglass in the part from molding. be caused by the molding and demolding initiator level. time because the part sticks and. time. such as the conditions a boat or through the gel coat layer (a process called might experience in rough seas. and Applications . shop temperature. The molder must conditions. This thin fiberglass layer is especially true if the gel coat is thicker is called the veil. between application of gel coat and ap- stresses occur in trying to free the part from plication of the laminate layers. The other is spray-up. Fundamentals of Composites Manufacturing: Materials. in various sections of the part). (Some areas Because the gel coat is non-structural. nance. additional stresses may occur gel coat is highly pigmented. This backing material. are eliminated. This material is applied. may have thicker laminates and some may it will be backed with layers of composite even have wood reinforcement added to the material (that is. the range of initiator also monitor and control the manufacturing volume and the conditions of cure should be process so that: carefully controlled. That energy can of the gel coat in the drum. Therefore. but they cannot during curing because it has different stop it.) Stresses also might be generated fibers). gel time. might result in layer onto the gel coat before the composite sufficient energy to crack the gel coat. and good cleaning can minimize ample. commonly used to apply the composite layers These tests will provide the molder with behind the gel coat. Methods. by themselves. such as applying protective coatings insufficient to cause the cracking. the energy could come from performance of the gel coat. the envelope of conditions within which which is discussed later in this chapter. spraying technique. correct range. Proper mainte- two or more causes that are. spray- operation itself. such as de- also might come from impacts. Therefore. The hides the laminate layer. the initiator based on cure temperature. Since most resins are for some parts that. the orientation of fabrics (if any). Generally. Room. the vast majority Broad goods are the most common form of applications use polyesters containing of reinforcements for lay-up. have styrene as the reactive diluent. knits. To select to a wide variety of curing conditions. If only a few parts of any Usually written guides can be provided that design are to be made. Although almost any polyester or vinyl Reinforcements ester resin is a candidate.) The lay-up resins usually the design. (These ment.13: Open Molding of Engineering Composites 379 Lay-up parts can be of almost any size and usually chosen according to two criteria: shape. Fill. or any other of These are generally the least expensive the common textile broad goods discussed polyesters and usually provide adequate in Chapter Nine. cures are common. sonic-driven cutters. Methods. if a resin other than an also allows easy inclusion of inserts around ortho type is used. to name the most com- Just as there is a wide selection of lay-up mon. In fact. a wide variety of resins can be used. can only be made by this most initiators. lay-up is usually the list the available initiators and the effective most effective method of manufacture. temperature ranges. mats. which may have a veil. ranging from manufacturer. the temperature and elevated-temperature initiator manufacturer should be consulted. application. woven cloths. This Fundamentals of Composites Manufacturing: Materials. Lay-up resins are frequently shipped in For ease of handling and speed of applica- drums. lasers. Several the temperature range specified by the resin cutting methods are available. usually because of high ortho polyesters. These can be orthophthalic acid as one of the components. and other polyester resins are described in and the number of layers are dictated by Chapter Three. the molder has Due to the simplicity of the lay-up method the responsibility of adding these curing and the generally manual nature of resin agents to the resin. or waterjets. The should be contacted to check on the compat- wide variety of parts that can be made leads ibility of the resin and initiator. with gel coats. which are compatible with complexity of shape. Because the cutters that use a bed for supporting the resins are often shipped neat (containing broad goods and a gantry system to mount no fillers or reinforcements). The resins should be stored within before they are placed into the mold. however. broad goods are often precut railcars. in large operations. the tion when the same part design is to be made resins can be shipped in tank trucks or tank many times. and Applications . These guides also list acceptable accelerators and other additives Resin and Curing Agents for each initiator. The reinforcements are generally simply ers and other additives are most commonly laid into or onto the mold as indicated in added by the molder rather than by the resin Figure 13-1. The manual nature of the process key parameter. which is usually moderately simple hand-held devices to large automatic narrow—about 77° F (25° C). the resin manufacturer which the composite material is placed. gel coat. They are placed on top of the manufacturer. dies. many initiators (catalysts) can be less expensive overall to use precut broad chosen for use with them. stirring the the cutting head. The actual cutting can be resin while in storage is less critical than done with blades. the cure temperature is the method. Sometimes a molder finds it easier and resins. The choice of reinforce- properties for most applications. The initiator is goods that have been bundled together. the largely manual nature of the temperature at which cure will occur lay-up molding makes it the method of choice and the type of resin. But. 380 13: Open Molding of Engineering Composites Figure 13-1. Alternately. and Curing done. To improve wetting. to be excellent tools for wetting out the sel (bucket) and transported to the molding surface. is called kitting. but this step is optional. Lay-up molding. of the gel coat can be pre-wetted with a thin When the fiberglass is wetted. Small hand-held amount of resin to achieve the desired resin. that is needed is to simply place the rein. and Applications . The reinforcements are placed in the mold forcement pack into the mold. Methods. to ensure full dispersion. If fillers or other Full wet-out and coverage of all the re- additives are used. rollers with ridged surfaces have proven fiber ratio is metered or weighed into a ves. they are also added in the inforcements is done by rolling the resin same mixer. This means the reinforce. the upper surface evenly over the fiberglass reinforcements. the reinforcement can be In normal practice the resin is mixed with wetted external to the mold and then trans- the initiator in a mixing vessel and stirred ferred into the mold and smoothed. the proper into the reinforcements. a change in Fundamentals of Composites Manufacturing: Materials. the resin is distributed area. and the remainder of the resin is poured to cover them as evenly as can be reasonably Resin Application. layer of resin before the reinforcements are ments have been cut and assembled so all placed in the mold. Wet-out. By rolling. When fully mixed. One im. the part or cause safety issues. the formation of bonds between the layers. trimmed or otherwise finished. cured. the thickness of each layer should be applied to the mold. high air nated. Also. Fundamentals of Composites Manufacturing: Materials. The wax forms a layer that prevents can be done appropriately. Additional structural materials. The choices of resin are more limited some resins to prevent air from reacting because the resin’s viscosity must be more with the surface to prematurely quench the carefully controlled to ensure that spraying cure. Because exotherms can damage rich surface. spray-up is the and soak into the primary layer. An the higher skill level needed by the opera- example is wax. The advantage of spray- the repetitive curing and application method. for the structure of the final part. Small and complex parts are usu- softness of the primary layer to facilitate ally not good choices for spray-up molding. and resin are added after the previous layer is inspected for quality. any resin having wax should be mechani- Curing can be done at room temperature cally abraded (sanded) before applying the or at elevated temperature (usually in an secondary layer. the compos. be controlled within the range defined for In addition to the limitations already acceptable cure. However. This can Spray-up molding is used when the part best be accomplished when the resins in the is of sufficient size and simplicity of design two layers are the same. Therefore. the disadvantages of the spray- Care must be taken in the time between up method versus lay-up are the special curing of the primary layer and application spraying equipment required. as is often it is removed from the mold (as discussed the case. that spraying the resin and reinforcement ond layer to the structure before the first layer can be accomplished easily and with good is nearly but not totally cured permits the uniformity. proper curing may not stiffness. mentioned. might be added for increased the layer is too thin. Methods. thus aiding in monitoring the also inhibits secondary bonding. Other times that abrading oven) as desired. if wood panels. These are usually covered with a occur. experiments must be done layer of uncured reinforcement and then to define the range of thicknesses for each cured to bond the wood into the laminate layer so a proper cure is obtained. of reinforcement and resin is not sufficient After the part has been completely cured.13: Open Molding of Engineering Composites 381 color (translucency) is noted as the resin air from reaching the surface. exposed to UV light. it is absorbed. cured for portant point that must be considered is the more than 24 hours. additional reinforcement layers and later). and Applications . Alternately. the inability to between them does not become contami. the more of the secondary layer so that the surface limited choice of resins. Therefore. The procedures and cau. speed with which the fiber and the resin can However. wet-out process. By use of preferred method. such as This is because the resin and styrene soften boats and tub/shower units. However. or has a glossy resin- exotherm. This material is added to tor. adding the sec. should be done include when the primary tions discussed in Chapter Three should be layer has been cured at an elevated tem- observed in the curing operation. such as ite layer cannot be too thick. perature. If one layer structure. control the direction of the fibers. This is called secondary bonding. Some resins contain materials that pollution because of spraying the resin. and will naturally contaminate the surface. It is desired that chemical bonds form between SPRAY-UP MOLDING the primary and secondary layers. up over lay-up for most parts is simply the composites of any thickness can be made. for many composite parts. Coverage of resin just after the nozzle. Spray-up Technique. The fibers are of the part. On one hand. The spray-up method is illustrated in A compromise is required in the length Figure 13-2. Nevertheless. of spraying and coverage into tight areas of Figure 13-2. brought into the chopper as roving and then The operator sprays the resin and the chopped so that they fall into the stream entrained fibers into the mold. and Applications . the length of The high degree of care needed in choos. the chopped fiber should be short for ease ing the type of spray nozzle and the nar.382 13: Open Molding of Engineering Composites Equipment. especially since the uniformity of ences such as the inclusion of a chopping fiber placement is critical to the performance mechanism on the spray gun. mold. and row operational limits required in gel coat Curing spraying are not as important in spraying The spraying equipment used for the the composite materials. composite material is similar to the type some training for the spray-up operator is used for gel coats with some obvious differ. This means must be uniform and the thickness of the that the chopped fibers are entrained with sprayed layer must be within the limits set the resin and together are sprayed into the for good curing. required. Methods. Fundamentals of Composites Manufacturing: Materials. Spray-up molding. of chopped fiber. the verse image of the part. Most molders part desired. This color require room-temperature cures at atmo- difference allows the operator to see the areas spheric pressures. ers add a small amount of dye to the resin Since lay-up and spray processes usually when the second layer is applied. the cost of machining a some attention should be given to making mold is high and it usually requires the use of the mold and its use in the lay-up and spray. Methods. the mold must be machined in the re- terials are deployed prior to cure. This is often difficult to do from a logistics such as for tub and shower units. sive). it is better to find another way to make the mold. the most common are metals and composites. Third. and are added by spraying rather than by hand. great care must be given to ensure are usually met by making the mold from Fundamentals of Composites Manufacturing: Materials. However. expensive machines. panels for even more stiffness is also possible • thermal expansion matching with the as with lay-up. Therefore. Second. • expected wear (metal molds have lower even spray-up uses manual labor as part of wear).13: Open Molding of Engineering Composites 383 the mold (including corners). The addition of more layers for in. several not only the definer of the shape of the part. the part Further. It is conceivable to machine the surface TOOLING (MOLDS) of a mold directly and thus create the shape In both lay-up and spray-up. because cure times are often long and mold must be reflections of each other. the process. the wear on the up processes. many mold.6 cm) range are best. Often. composite molds would be best and this is ness and coverage of the laminate. part will be made against the mold. That is. But for best that it has the exact dimensions and surface mechanical properties and ease of chopping. After the fibers and resin are sprayed into The choice of material depends upon: the mold. in lay-up. Because the mold defines the shape of the The requirements for mold performance final part. a roller is used to make sure the resin fully wets the fiber bundles. because the tooling in open-mold processes is important. and Applications . the factors suggest that that have been sprayed and to gage the thick. true in most cases. Hence. part (composite molds generally match ers and the material placed around the panel better). last for the production of several parts. However. these additional lay. and productivity requirements can be high. characteristics that will result in the type of the length should be long. to ensure that the mold is durable so it will (2. • temperature of the cure (metal molds Curing in spray-up is identical to curing withstand higher temperatures). complications arise when this is attempted. wet-out of sprayed fibers is Many materials can be used for molds but accomplished in the same way as with lay-up. First. attempted. the mold is that will define the parts. mold can be high.5–7. a company standpoint as it requires thinking in the re- may be forced to have a large number of tools verse and mistakes are common when this is to meet production demands. but it provides the surface on which the ma. To make it easier to see where the second (or • cost (composite molds are less expen- later) layers have been sprayed. • pressure exerted (metal molds with- creased structural capability or wood or other stand higher pressures). Therefore. A com- mon method for making composite molds is Mold-making Method shown in Figure 13-3. In spray-up. care also should be taken have found that fiber lengths in the 1–3 in. Therefore. the mold made from the master model is actually. The shape that incorporates all of which the mold is laid up. Fundamentals of Composites Manufacturing: Materials. the use of a multi-axis to obtain the desired thickness. After curing material must be chosen so that the model the gel coat. Books on mold making can explain these intricacies and Figure 13-3. A special hard surface coating is sometimes applied to the master model and finished to the final dimensions so it is more durable. Nevertheless. the methods of making a mold from a master model are the same in all systems. Resin shrinkage during molding the mold so that a high level of crosslinking will result in a part that is smaller than the will be achieved. It is not unusual shaping method. This ing is usually done by conventional cutting layer is cured and other layers are applied processes. in many cases. and Applications . The production mold can be made directly from the master model as shown in Figure 13-3. This shap.384 13: Open Molding of Engineering Composites master model. Mold-making. This is done by creating draft angles of about 2° on the sides. However. this is a simplification since. the process- ing temperatures. and other variables. pattern or. molding process. their advantages. The model can be special tooling gel coat is used to increase made from a variety of materials but the the wear capability of the mold. When the master model is exactly as de- sired. reinforcements are laid onto can be shaped exactly as desired.) a shape that is exactly like the finished The master model serves as a tool on part. For some parts. merely an intermediate from which other models and molds are made. some handwork to use epoxy resins for the tooling because is done for finishing. The master model is also modified to enlarge the opening of the mold slightly so the part can be removed. a occasionally. However. the master model may be made slightly larger to offset shrinkage. the plug. In this case. (This is a topic that will not be discussed further here. It is also common to cure the mold at finished to exactly match the surface of elevated temperatures and/or to post-cure the part. the master model and resin is applied. the surface of the model is prepared with mold release. spe- computer numerical control (CNC) milling cial laminating resins are used to improve machine is the most common cutting and the durability of the mold. Today. of their higher performance versus polyes- The surface of the model is shaped and ters. Again. the fiberglass content. Methods. A gel coat is ap- the geometry for one of the part surfaces plied just as was described for the lay-up is called the master model. This also adds to durability. however. The exact amount of shrinkage is complicated and depends on the type of resin. itself. However. used. cycles to condition a new mold. For most occasions. The PVA sticks paste. have special locations designed for gripping The use of patented materials for the bed and pulling. venient grips to use for lifting and moving If the part shows a tendency to stick. the increased cost is jus. after ity to the mold. criss-cross pattern that resembles the shape When a part is to be removed from the of an egg crate. The are often difficult to remove. sanded.13: Open Molding of Engineering Composites 385 The mold is then removed from the master Proper preparation of the mold surface is es- model and. some parts are easily volves the use of a fluidized bed into which removed. been developed. mold. Because of good mold design and/or Another system for creating molds in. Air is often blown Mold release needs to be added to master into the openings created by the wedges. One method bed is solidified so the shape of the part is used to remove the part is to attach the part retained in the bed. the of braces that support the mold surface so it mold becomes conditioned and the applica- is dimensionally stable while providing con. Sometimes this support conditioning. the the part. as little force as possible should be crate mold. the mold has a technology and still others use various poly- support structure or bracing. cured. to the part but can be easily removed. Gradually. ever the mold’s surface has been repaired or If a higher-temperature surface is desired. thick. To do this means the part must finished. and Applications . part so that the adhesion is broken. the system is called an egg. Other types of release agents have volumes are high. Another method is to insert has made these systems using two-phase wooden wedges between the mold and the technology practical. Then. after the part to a crane and the mold to an anchored base is removed. complex and large parts the part or master model is pressed. Then. Care must be exercised that neither the mold Removal Techniques for Parts nor the part is damaged. were waxes and these are still frequently tified only in those cases where production used. the mold is ready for the first structure is created just by making the mold application of resin. and then machined. models and to production molds so that the Some molders provide for air holes in the parts made on these forms can be removed. the surface of the bed can be and pull. Therefore. after proper surface preparation. mers as the basis for release. the production mold is ity of the mold. mold so that air can assist the part. (PVA Some mold-makers have used a metal fac. this often results in heavy PVA film may be used for this first run. This alcohol (PVA). Because these braces often form a mold release should be reapplied. pecially important at its first use and when- the mold is ready for production use. an alternate method of terwards. the mold release agents are added supporting the mold is to apply a network after each part is removed. The original release agents technique is useful. The metal is usually nickel conditioned for release by adding a mold re- applied by a sputtering process. Some are based on silicone As is seen in Figure 13-3. tion of mold release need not be as frequent. epoxy molding compound can be coated on a film-forming material. is often applied to the mold epoxy material is called seamless molding surface to guarantee release. This struc.) ing to further improve the surface durabil. In these difficult release occasions. dissolves in water. simplicity of the part. such as polyvinyl the surface. While this lease material. These materials ture is needed to provide easy handling for are added several times over several heating large molds and gives dimensional stabil. As indicated previously. Methods. Af- molds. Water Fundamentals of Composites Manufacturing: Materials. and the bed becomes the mold. However. The safety of lay-up and spray-up is con- There are hundreds of molds moving cerned first of all with the resin. The mold is then reattached to the spite of this. In fashion. A mate- through the plant at the same time. so it that permit high volume with low production only should be used as a last resort. This method has great force the manufacturers to devise methods danger of damaging the mold and part. Methods. This rial safety data sheet (MSDS) for each system achieves high productivity by com- material should be filed and easily available. This should be monitored. The methods for spraying up the gel coat into a composite All parts made by lay-up and spray-up mold are standard. It uses manual labor to overcome some Most molders consider lay-up and spray. sure to styrene. of the problems of more automated methods. The part is then fully cured reporting the weight to the operator. It then moves to a de- record of the weight is kept and compared molding station where the part is removed to the “ideal” weight. materials. This can be done until all the desired laminate layers have by weighing the part after demolding and been applied. the operator will be and transferred to finishing. The operator in charge of spraying or laying process is repeated at other spray-up stations up the material is useful. with some creative labor to adjust to the varying conditions and modifications to the traditional methods. the mold is hooked onto an mold. If a in yet another oven. bining the advantages of the assembly line Protective equipment also should be worn with the methods of spray-up and then adds when resins are used. lay-up is the method most often Shower Units used. The mold is taken ite cannot be accurately monitored dur- off the chain and sprayed up in the normal ing the lay-up and spray-up processes. The mold moves to an area where to be increased or reduced and adjust the it is refurbished and then put back onto the spray-up or lay-up accordingly. after the gel should be inspected after removal from the coat is applied. because of the ability of manual tion volumes. Some have the rate of production of parts can reach cooled the inner surface of the part so that hundreds a day in a single factory. it is the process that has the most Fundamentals of Composites Manufacturing: Materials. cost. production line. Another The market demands for high volume and method is to tap on the outside of the mold low price of integral tub and shower units using rubber mallets. up molding to be for low-to-medium produc. However. However. Federal standards elevated-temperature curing to make it all mandate a maximum concentration for expo- work quickly. The mold as early in the process as possible.386 13: Open Molding of Engineering Composites also can be used to float the part. SUMMARY CASE STUDY 13-1 When a simple method for making a part High-volume Production of Tub and is desired. inspection. However. it will shrink away from the mold. These can be met using spray-up mold- ing and accelerating the curing of each layer QUALITY CONTROL AND SAFETY of the multi-laminate part. There also should be intermediate in- overhead chain system that serpentines spections by operators and quality control through the plant and carries the molds inspectors so that problems can be caught from one workstation to the next. passes through an oven and then arrives at One of the problems with open-molding a station where the laminating resin and systems is that the weight of the compos- reinforcement are applied. and able to see whether the total weight needs shipping. a method of feedback to the chain and moves through another oven. and Applications . gel coat versus some other application The tooling for both lay-up and spray-up method such as rolling or brushing? is generally made of composites. This is the outer layer of the 3. However. methods. 8. What is a “neat” resin? ing is made from a master model shaped like 4. 12. the veil. After cutting. 2. thus further improving the mat. Roll to wet the roving. QUESTIONS both have the ability to be modified for el- evated-temperature curing but the exotherm 1. Curing of lay-up and spray-up materials is usually done at room temperature. What is “fiber blooming” and how is it that occurs with curing must be controlled. What are thixotropic agents and why and then can be used to make many parts. Place a surfacing veil onto the top of the coat is applied by spraying in both the lay-up resin. The mold is made by laying after resin has been added? up composite on the master model. fillers. over spray-up? Fundamentals of Composites Manufacturing: Materials. In both 11. but adds the advantage of faster application 9. prevented? This is done by limiting the thickness of each 2. and Applications . Add a sheet of chopped strand mat and requires more expensive equipment and it is roll to wet-out the fibers. Lay a sheet of polyethylene terephthal- ment. are they used? 6. How is the ratio of resin and initiator controlled in the spray-up method? LABORATORY EXPERIMENT 13-1 7. Finish by brushing on a layer of wax lay-up and spray-up. What is the purpose of rolling the fibers the final part. and spray-up methods. Apply more resin and roll to wet-out Some improvement in productivity of lay. Formulate a batch of resin by adding lay-up? What is one advantage of lay-up initiator and mixing. Add more resin and roll to fully wet be kitted together. of a gel coat. Cure by allowing to stand overnight. up can be achieved by using precut broad 6. This mold is then conditioned with mold release 5. 5. The gel 4. part? Procedure: 8. harder to achieve uniform coverage. These can be cut using a variety of top of the wetted veil. Pour a small amount of initiated resin part and is made from a specialized polyester onto the film and spread it evenly. wet-out of the fibers is topcoat. of the resin and reinforcement.13: Open Molding of Engineering Composites 387 opportunity for variation in resin. resin to which various pigments. dyes. This tool. Apply a layer of chopped strand mat on goods. What is one advantage of spray-up over 1. ate (PET) film (Mylar®) onto the pic- The process begins with the application ture-frame mold. reinforce. How are additional reinforcements Making a Laminate for selected areas added to a spray-up Objective: Practice the methods of lay-up. 3. and other additives have been added. What is the advantage of spraying on a layer of composite material. the broad goods can 7. Methods. achieved by manually rolling the fibers onto a mold to which resin has been applied. However. and curing methods. Apply a layer of woven roving on top of Spray-up is similar to lay-up in many ways the wetted mat. it 10. the speed with which the reinforcements can be placed into the mold. NJ: Prentice-Hall. Inc. Fabricating Tips. 3rd Ed. Dow Plastics. Why are the performance character- istics (properties) higher for a resin used to make a mold than for the same laminate resin to make a part? BIBLIOGRAPHY Cook Composites & Polymers.sme. Re- vised Edition. 2006. 16. Society of Manufacturing Engineers (SME). Fundamentals of Composites Manufacturing: Materials. 2005. 10th Ed. Plastics: Materials and Processing. Compos- ites Application Guide. Upper Saddle River. MI: Dow Plastics. 2005. Methods. “Manual Lay-up and Spray-up” DVD from the Composites Manufacturing video series. Indicate a problem that might occur if the resin is heated too quickly during an elevated-temperature cure cycle. www. and Applications . What is a “gel coat” and why is it used? 11. MO: Cook Composites & Polymers.org/cmvs. Kansas City. MI: Society of Manufactur- ing Engineers. Strong. Why is it important to control resin viscosity in a spraying operation? 13. A. Why is it important to control resin viscosity in any process that involves adding resin to fiber reinforcements? 12. Why is a master model (pattern) made slightly larger than the part it otherwise duplicates? 14.388 13: Open Molding of Engineering Composites 9. 10/94. How are the weights of resins and fibers controlled in lay-up? 10. Dearborn. Midland. What is the purpose of the rigid support structure that backs molds? 15. Brent. they are cut to modified manufacturing methods for ad. or fabrics. Since prepregs spray-up methods. to soften the resin is used to anchor the Fundamentals of Composites Manufacturing: Materials. Most • difficulty in aligning the fibers in ex. until the proper thickness is achieved. mated) • Vacuum bagging In contrast to those methods discussed in Chapter 13. Methods. they are not sticky. • Tooling (molds) manufacturing procedures. prepregs have a sticky surface because actly the directions desired. unidirectional fibers. This facilitates • difficulty in optimizing the amount of placement of the prepreg layers in the mold. The prepregs this chapter. These materi- PROCESS OVERVIEW als were discussed in some detail in Chapter Although the wet lay-up and spray-up Nine. This chapter examines the following • difficulty in reducing the void content. and equipment. ated resin. typically other processes are used. epoxy resin and carbon fibers. fit the shape of the mold. concepts: and • Process overview • potential problems in mixing the resin and hardener (including emission and • Prepreg lay-up (manual and auto- toxicity problems). the resin is not fully cured.1: Introduction to Composites 389 14 Open Molding of Advanced Composites CHAPTER OVERVIEW • difficulty in getting full fiber wet-out. The materials most often used for advanced composite parts are prepregs. these are sheet materi- methods described in the last chapter als. and Applications 389 . overcome some of the inherent are carefully oriented so that the fibers are problems associated with the wet lay-up and in the direction desired. resins as matrices. the manufacturing methods • Curing (with and without autoclaves) developed for making advanced composites • Roll wrapping in an open mold involve differing materials. fibers to achieve the highest properties If prepregs are made using thermoplastic possible. These Molded products are made by laying other processes. for have been carefully coated with fully initi- example. come in set widths based on the width of the The major problems that have led to the machine used to make them. which could be used with advanced materials. As a reminder. Layers of prepreg vanced composites include the following: are placed. often in different orientations. • difficulty in controlling the fiber/resin Thus a heating iron or some other method ratio. which will be discussed in sheets of prepreg into a mold. choose a type that is non-aerosol composites. When the prepreg is The location where prepreg lay-ups are ready to be used. and shoe covers to further up and automated lay-up. and recirculated. release products. When the vapor is cooled ously. of course. the procedures using the mold’s surface. by the air conditioning. laminar. The temperature of the room nation from body oils and dirt that might is kept constant in the range of 72–77° F be present on the operator’s hands. • control the fiber-resin ratio. If material remains on the roll of Fundamentals of Composites Manufacturing: Materials. Curing of this contamination is that it is airborne is usually done under conditions of vacuum and cannot be easily removed with filtra- and then pressure. If they must of the open-molding system for advanced be used. Methods. through a double-entry system to keep the Two systems are available for placing the air clean. the silicone vapor is prepregs largely eliminate the problems of picked up by the air conditioning system wet lay-up and spray-up identified previ. When those are applied tent to be maximized. sufficient material is cut from the the ability of that layer of prepreg to bond roll of prepreg for all of the layers of the part with another is compromised. and also reduces the amount of moisture con- tamination. especially when sprayed onto As might be obvious. Such laid-up prepreg other parts can be difficult. problems will be even more obvious as they The contamination is difficult to detect are discussed. to a mold. silicone is present at the delamination which correlates with this text [Society of point. Also. The silicone originates in some mold the number of voids and allow the fiber con. These are manual lay- special coats. Entrance to the room can be prepregs. (Both manual and automated until delamination problems become ap- prepreg lay-up methods are demonstrated in parent and an investigation reveals that the Composites Manufacturing DVD series.390 14: Open Molding of Advanced Composites prepregs in place so that they do not move ability of the finished part to bond with after proper placement. and Applications . contamination is to avoid the use of sili- It is good to keep in mind the overall goals cone-containing mold releases. The workers in the room may have prepreg in the mold. This helps keep the prepreg clean and • minimize the void content. hats. the to be made. clean (22–25° C) and the air is filtered to eliminate cotton gloves should be used to handle dust particles. To avoid contami- trolled room. the bag is opened and the done is usually an environmentally con. The best method to prevent this Manufacturing Engineers 2005]). reduce dust and other contamination. the lay-up. it can settle on the vanced manufacturing techniques solves the prepreg and cause surface contamination. Experience The manual lay-up system involves laying has shown that if silicone contamination plies of precut prepreg into a mold. the freezer. Most often • control the ply thickness. the prepreg roll is kept inside a plastic bag. Prepreg materials are almost always kept • control fiber orientation and location. in freezers to extend shelf life. A special and most difficult problem is Manual Lay-up contamination from silicone. The subtlety assemblages are. prepreg roll is removed. To begin is present on the surface of the prepreg. How the use of prepregs and other ad. After removing the bag from • reduce internal stresses. They are to: and less volatile. These conditions reduce tion. the bag should remain closed (sealed) while the prepreg material warms PREPREG LAY-UP to room temperature. below the material. reciprocating knives. mechanical vibra. Advantages include being able to cut knife that either cuts by vertically impacting many parts of the same size and shape easily. the prepreg material like a guillotine into a minimum mechanical breakdown potential. and shears steel-rule blanking). Standard knives with replaceable between the efficiency of cutting many layers blades (Stanley knives) are probably used and the nodal problem with the cutters. and Applications . Curves nesting as shown in Figure 14-1. the wavelength of the vibrations The sheet of prepreg is then placed on a causes nodes (non-vibration points) along special cutting table where it is cut to the the surface of the long blades. and time-consuming to use. are by far more economi- tions are used to drive a knife at ultrasonic cal. or by penetrating and then potential automated cut-part retrieval and remaining buried in the material and slicing lay-up. Then. The careful types of reciprocating knives can cut many layout of the material to avoid waste is called layers of material simultaneously. many years. the material and then punched through the The reciprocating knife is an improve. which has had one and accuracy. and the Laser and waterjet cutting are gaining blade can be retraced to skip over areas that acceptance for cutting uncured as well as are not to be cut. Compromises must be made years. cured composites. which hin- shapes required in the lay-up. In this method. material with a press.14: Open Molding of Advanced Composites 391 prepreg after the desired amount is cut off. such prepreg. This method uses a method. cutting table often has a urethane or other (1. but they still remain difficult. and labor costs. material may be too high and if cutting is chine. Cutting and trimming also have been done Another method for cutting several layers with carbide-edge cutting wheels (like pizza at the same time is die cutting (also called cutters). It has been used extensively Sometimes this is called the cookie-cutter in the textile industry. poor cut- has been the major method used for many ting results. Again. and good material yield with careful through with rapid vertical strokes. A more widely than any other type to cut pre. is a major development for cutting especially when the alternate methods. maximum amount of shelf life. The major advantages of ultrasonic soft plastic cutting surface that does not get cutting are high speed and accurate cutting permanently marked (self-healing surface). Methods. A template is normally used and the stack thickness of prepregs to about . The ultrasonic vibrations enhance plastic bag and sealed. Some stacks of prepreg can be cut manually or by a ma. Uncured der cutting at those points. is placed over inaccurate. edge sharpened for cutting.75 in. and sharp corners can be easily cut. Manual cutting of uncured prepregs attempted at one of these nodes. which methods is their speed and accuracy. In die cutting. The steel strap has ment over the above methods in accuracy been shaped into the outer profile of the part. the bag should the cutting action of the blade by reducing be returned to the freezer to maintain the friction between the blade and the prepreg. Laser cutting of uncured composites can Fundamentals of Composites Manufacturing: Materials. reasonable compromise is to limit the total pregs. cess. New designs and has been used in the textile industry for materials in these cutting tools (such as ce. Both layout of the cutting patterns.9 cm). of stacked prepregs. as manual cutting. disadvantage is the cost of the machines. The advantage of these Ultrasonic vibratory cutting. this method (manual and powered). a die made from ramic shears) have improved their efficiency hardened steel strap. speeds (several thousand vibrations per the roll should be returned to the protective second). The is similar to the reciprocating knife pro. plastic bristle or soft metal cutting surface being able to cut a wide variety of materials. However. they remain in place. The prepreg the amount of waste material is minimized. robot (using suction tips) and deposited in Occasionally. if desired. it is shown in Figure 14-2. obtained from these projections often justify neously. pieces also should have sufficient drape so The material can even be removed by a they will conform to the shape of the mold. The material is cut by a gantry. Each prepreg piece is placed carefully cured materials because of the potential prob. Fundamentals of Composites Manufacturing: Materials. As before. proper shape. exactly according to the specification of the Several of the cutting methods can be composite part’s design.392 14: Open Molding of Advanced Composites Figure 14-1. enting the part is to project the directional A vacuum is applied to hold the prepreg grid directly onto the surface of the mold against the bed and. also scorch or burn the edge of the material. unacceptable in some applications. Methods. the pieces are placed into rial with water. The roll of prepreg is fed into the around the perimeter of the mold on the machine and it cuts off the proper amount flange. automated using a broad goods cutting ma. a directional reference grid can be marked chine. the prepregs should this is rarely a problem. the mold. The ease and accuracy of material can be held and cut simulta. with difficult shapes. To facilitate this. gloves. the pre- trays that are ready for the manual lay-up preg will have to be cut and shaped. After the materials have been cut to the waterjet cutting may contaminate the mate. several plies using laser projectors. When properly controlled. the cost of the machine. and Applications . Nesting is done automatically so surface. Likewise. making sure the alignment of the sheet is lems water contamination could create. Often. A semi-automated cutting table is Although this is normally insignificant. process. Efficient layout of a typical nest pattern. but many companies only be handled with protective cotton are reluctant to use waterjet cutting on un. mounted cutting tool (of various types) or The prepreg pieces should have sufficient by dies that are automatically placed on the tack that when pressed against the mold material. Another method of assisting in ori- and slides the material onto a cutting bed. bubbles. Because the open mold lay-up. the prepreg roll is quite narrow (about to be cut by knives or shears. Typi- and while the material is still sufficiently soft cally. great care must to fit the mold and stay in place. [5–10 cm]). and Applications . some additional flexibility can be obtained special cutting wheels. or After the first layer of the part has been gaps between the prepreg pieces. However. subsequent layers Thermoplastic prepregs can be used in are placed on top of the first. these materials design of the composite part often requires do not have tack or drape. they that the orientations of the fibers be dif- need to be softened so they can be shaped ferent from layer to layer. waterjets. lasers. 2–4 in.14: Open Molding of Advanced Composites 393 Figure 14-2. trimming to non-criti. After curing. of the hardness of the composite. be given to following the design with exact ing can be done by heating the prepreg with orientation of each prepreg piece. Therefore. The automatic lay-up system begins when cal dimensions and removal of excess materi. Automatic Lay-up Whenever possible. a hot air gun or by tacking it in place with a soldering iron. or by using a prepreg made on a flexible fabric diamond cutters are usually required because instead of a unidirectional prepreg sheet. Semi-automated cutting table. The narrow width allows Fundamentals of Composites Manufacturing: Materials. Methods. placed into the mold. There should be no wrinkles. This soften. a roll of prepreg material is mounted on the al should be done before the prepreg is cured payout drive of a tape-laying machine. to the mold surface. a moderate curvature. The machine chines is the separation of the tape-laying then moves along a straight line and feeds and tape-cutting operations. the machine to the minor surface contours. The ma. An automatic tape-laying ma- parts with gentle and moderate curvature. presses the leading edge of the strip of pre. they work best for flat panels and has been laid. the severe. the lay-up machine cannot be used. accurately position to begin laying the next trip. They can. A recent innovation to tape-laying ma- preg onto the mold surface. If the head need and presses the prepreg onto the mold while only lay the tape. for thermoplastic prepregs. As process is repeated until the entire laminate indicated. Fundamentals of Composites Manufacturing: Materials. A typical example would be a tail or wing Tape-laying machines also can be used section for an airplane. according to rial to stick where it is placed and conform the lay-up design specification. and Applications . however. head cuts the prepreg strip at the proper Automatic lay-up machines are large and angle and then lifts and moves to the correct expensive. it can be reduced in size Figure 14-3. This and quickly lay down plies of a prepreg. chine is illustrated in Figure 14-3. Automatic tape-laying machine. Methods.394 14: Open Molding of Advanced Composites the machines to place a layer of prepreg over simultaneously lifting the paper backing. In this case. If the curvature is too When the edge of the mold is reached. The heating softens the chine indexes the area within which the thermoplastic matrix and allows the mate- prepreg is to be applied. The machine has a gantry-mounted head the head heats the prepreg as it is applied that applies and cuts the prepreg. Then. Also. and Applications . With each debulking. The elimination for subsequent bonding but can be of volatiles helps to lower the void content of smoothed by sanding if the outer sur- the final part. thus eliminating the can be done by another head. The is continued. ging system off the part after curing. The bleeder material is resin that occurs during the curing stage as a mat that absorbs the excess resin. ure 14-4. face of the part is the finished surface. by applying the vacuum as the assembly is 2. reducing the chance of moved after the tape has been laid. then debulking is usually done appropriate mold release. and before the part is cured. If the number of plies in the part is small 1. in this case. Build up the part by placing layers of cured. has another to permit excess resin to flow through it benefit in making composite parts. Methods. up of four to six plies. Fundamentals of Composites Manufacturing: Materials. The procedure for assembling the therefore. Such volatiles may and not tear. one prepreg on top of each other in the pre- or more debulking operations are usually scribed pattern and to the prescribed required. some resin may move out of the prepreg and be absorbed by ma- VACUUM BAGGING terials placed in the bagging system. Apply bleeder material on top of the ging the prepreg system is the movement of release film. Other volatiles may have been sheet or Teflon-coated glass fabric. vacuum bag system is as follows. This ben. air is inevitably trapped that increases the fiber/resin ratio and re- between the prepreg layers. the release material is porous when the resin is less viscous. The part also should be debulked during the cur. This usually occurs after each lay- thickness. This is repeated until the final purpose of the release film is to provide plies are placed and the final bagging system a simple method of pulling all the bag- is assembled over the stack. Place the release film or peel ply entire bagging system is removed and lay-up material over the laminate stack. but it should be strong enough so it can efit is the removal of volatiles that may be be pulled to release the bagging system present in the resin. maybe even boundaries that might exist between prepreg on a different machine to which the mold is layers and. therefore. delaminations. Then the 3. Experience duces the total weight without significantly has shown that better parts can be made if reducing the mechanical properties of the some of the air is removed after the lay-up composite. able to move more freely. precise trimming. This process Bagging Methods of air evacuation is called debulking. tween the layers and into an absorbent layer The cutting. the stack of prepregs is vacuumed.14: Open Molding of Advanced Composites 395 significantly and simplified in its operation. The absorbed into the resin when it was stirred perforations in the release film impart to formulate it with the hardener (before it a texture to the part. 4. If the number of plies is large. which is useful was made into the prepreg). Prepare the mold by coating it with an (up to four). This Even with the greatest care during the absorption causes a moderate loss of resin lay-up process. The bagging system is illustrated in Fig- ing process when the resin is heated and is. Still another advantage of vacuum bag. a result of the nature of the bagging system. A fly cutter can be placed on the head to The molten resin is encouraged to move be- simply cut off the tape (but not precisely). especially during cure Generally. Applying a vacuum. A common material for include residual solvents used in making the release film is a perforated Teflon® the prepreg. in the bagging system. Typical of the temperature and pressure within materials are fiberglass. the type of bleeder and 7. Normally. Vacuum bag system. and on top of the breather material. These should permit immediate reading der vacuum. entire assembly. polyester felt. or pressure. the resin content of the final resin trap placed in the vacuum line to part depends on the ability of the bleeder protect the pump from resin that might material to absorb a measured amount of get inadvertently sucked into the line. Normally. highly porous and must not collapse un. the outer insulation may be carefully controlled when this is done. A vacuum valve is placed so that it is ester felt or mat. there is a variables. The breather material acts It must withstand the temperatures as a distributor for the air (vacuum) and experienced during cure.396 14: Open Molding of Advanced Composites Figure 14-4. nected to a vacuum line that leads to sure of an autoclave. for escaping volatiles and gasses. This cotton. It is important that the bleeder will allow the vacuum to be distributed material has good absorption qualities over the entire part. Therefore. which is to form 5. fiberglass mat. a sticky polymeric tape. This sealant is usually mined for each laminate to be cured. heat. Common bleeder materials are poly. Methods. thermocouple wires and as a buffer between bag wrinkles and leads for other monitoring devices are part surfaces. Along with other a vacuum pump. The valve is con- and does not compact under the pres. 6. Apply a breather material on top of an airtight seal with the vacuum bag. the bleeder. To ensure an airtight seal can serve as breather materials but the where the thermocouple wires enter the amount of resin absorption should be assembly. Breather layers should be inserted above and below the part. the system and give a record of the cur- and cotton. and Applications . The bleeder materials also ing cycle. as well 8. A sealant material is placed around the the amount (thickness) must be deter. resin. scraped off the wires (especially if it is Fundamentals of Composites Manufacturing: Materials. Nylon film is hydroscopic and is strong enough to hold a vacuum. Dry film is especially susceptible to a co-extruded nylon that has been heat damage and cracking when excessively stabilized. they tight seal all around. brittle film occurs when the temperatures of curing. If the nylon Several problems are common with bag. • Bag breakage is catastrophic because bly and push the vacuum valve stem it is often not detected until after the through the bag. For example.) Another technique that there are no leaks. ging material might bridge. (The vacuum bag is similar handled. Further. Dry. They must be addressed early part. bag itself bridges over a region in the ging systems. The wires and leads largely the result of using a sealant must then be embedded in the sealant that is not thermally stable at curing material with. these heavy allow bagging materials to form a bridge bags fit over the assembly and can be across the top of the channel. Good bagging techniques. deep channel may of part is made repeatedly. The vacuum bag is then that are free of pinholes and internal pressed onto the sealant to create an air. Lay the vacuum bag over the assem. that is. it in the valve assembly that tightens on is too late to remedy. Some molders non-pressed areas are not. In practice. properly compressed. These Kapton® polyimide film. temperatures. a part 10. The vacuum should be carefully conformity against the part’s surface. and able to withstand the ment. Vacuum bags can should not be subjected to pinching or be made out of any polymeric film that nicking. flex. 9. bridged area. moisture content in the bag falls below the most common material is nylon or 2%. to the type of cooking bag used to cook meat in the oven. vents the transfer of pressure to the bottom of the channel. the film may be stretched beyond because of the high cost of composite parts its limits during cure and burst as well that can be ruined. This pre- used multiple times. monitored during this period to ensure (See Figure 14-5. therefore. therefore. leaks are (caul) that fits in a potential bridging Fundamentals of Composites Manufacturing: Materials. A fitting is provided part has been cured and. additional seal.) If high temperatures • Bridging occurs when the shape of the are used in the cure (generally above part. stresses should be used. the shape of the mold 400° F [204° C]) a more heat-resistant that makes the part. Methods. the system is areas where bridges may occur allow subjected to a vacuum to debulk the enough excess film to be present for bag fibers. a ber bags are useful. Areas where the bag is ant covering them. does not allow film should be used. usually.14: Open Molding of Advanced Composites 397 cloth insulation). and Applications .Activate the vacuum and check the may have a corner across which the bag- system for leaks. Similarly. subject to moisture change in relation ible enough to conform to the shape of to the relative humidity of its environ- the assembly. Often occurring is the use of a pressure intensifier at the bag/sealant interface. have found that reusable silicon or rub. The most common are as fail to transfer proper pressure to the the following. folded also are susceptible to leaks. When the same type part with a narrow. such as pleats intentionally put into • As discussed previously. Good quality bags the vacuum bag. The most common the vacuum bagging materials to press high-temperature bagging material is against all of the part’s surface. Vacuum bag assembly showing use of a strength reduces by about 7% for each 1% pressure intensifier and pleated vacuum bag. bags could be used for multiple curings. not to cause too much resin ensure that the area receives full pres. (A resin dam is shown in Figure spray-on bags. It is even possible that such include a resin dam around the pe. the interlaminar shear Figure 14-5. Recent developments in spray-on direction in which the molder would bags have shown that they can have high like the resin to move is perpendicular elongation and. in part. Two tasks must be accomplished during cure. It is important to ensure that the void content is low because of the serious negative effects of the presence of voids. of void content present up to a maximum of Fundamentals of Composites Manufacturing: Materials. sufficient bleeder is placed are molded to fit the shape of the part and are perpendicular to the plane of the fibers typically used for many moldings. They are Therefore. Methods. Silicone bags also have been used. When resin starving pressure pad is also shown in Figure occurs. less susceptibil- to the plane of the fibers (face bleed). by debulking during the cure. The silicone so that saturation of the bleeder will not bags are more expensive than the nylon or occur. and Applications . CURING After the bagging system has been as- sembled and the part has been debulked. to flow and thus starve some area sure. However. therefore. but are also more durable and 14-5. Pressure pads are often made of a fully wet the fibers and therefore loads rubberized or flexible material that can cannot be transferred properly from withstand cure temperatures without the matrix to the reinforcements. The spray-on bag essentially bers (edge bleed). These taneously. This is done. As a guide. faster to apply. It always conforms to the shape of is removed and to give good integration the part and gives the proper pressure to all of the layers within the composite.398 14: Open Molding of Advanced Composites area between the bag and the part to however. a technique to encourage able to withstand normal curing tempera- resin movement in the perpendicular tures and may be reusable if temperatures direction and to prevent leakage is to are not too high. Several of the above problems can be • The easiest path for resin to take during resolved by using a spray-on bag instead of curing is along the direction of the fi. the surfaces. the nylon film. The temperatures and times for curing are determined by the nature of the resin and the curing agent. rimeter of the bagging assembly. to ensure eliminates the problem of bag breakage and that the air trapped between the layers leakage. A typical example of the use of a of the part.) The molder should be cautious. Simul. The first is curing and that is done by heating the part. The other is to reduce void content. Most advanced composite systems are epoxy or some other advanced resin. the resin needs to be cured. degrading. there is insufficient resin to 14-5. ity to tearing under high pressure. In the imposition of pressure by vacuum and heat. and one cured without a Autoclaves are not the only method for ap- vacuum. and Applications . the temperature and pressure control system pressure on the bladder is released and it that allows for a programmed heating and collapses. one purpose of These studies clearly show that pressure is a the pressure is to ensure that the layers critical factor in consolidation of thick lami. Autoclaves are often filled with an inert A similar system is used to make airplane gas (generally nitrogen) to suppress any fuselages. designed to define the outer surface of a dating and curing the part. case of a tennis racquet. oxidation may occur in the mold.5% or less. curing. the bagging system. or at the fittings and ing has been confirmed by studies of thick connections. rather. detract from the performance of the part. An respect to the pressure that may be added example is the making of tennis racquets. pass stringent pressure code regula. It can be withdrawn from the part pressurization cycle (similar to that shown or simply left in place if its presence does not in Figure 4-15 in Chapter Four). major difficulty with autoclaves is their high When this is done. Methods. One The preferred manufacturing method for is to cure in an autoclave. This in the finished laminate is 0. This is because they must. The other is to these parts is to wrap the prepreg materials cure without one and either ignore this pres. the bladder. laminates in which the consolidation was Using an autoclave. of the parts remain in intimate contact so nates to achieve optimum properties. of the prepregs as they are pressed outward Most autoclaves are equipped with a is minimal. vacuum and an autoclave to assist in consoli. When the part is cured. consolidating and defining the part’s outer tions. Autoclaves are part when it is pressed against the mold pressure vessels that allow the simultaneous by an internal pressure mechanism.14: Open Molding of Advanced Composites 399 about 4%. The importance of pressure during cur. the assembly is placed inside a clamshell mold. by law. These molds are often Autoclave Curing hinged along one edge and are not designed The prepreg method generally uses both a to exert large pressures. the part. Vacuum also helps by consolidating the This process is called co-curing. around a bladder. labor and cure costs on a per-part assembly so that the amount of movement basis are not usually that high. laminate’s layers. autoclaves are not necessarily the best The molder has two options available with pressurization method for all laminates. because many small parts surface. the fuselage is wound around Fundamentals of Composites Manufacturing: Materials. that bonding and curing occur properly. This was noted in a study of shear strength for two parts. during cure to assist in reducing voids. A reasonable goal for void content cur during the heated curing cycle. one cured Non-autoclave Curing Methods with a vacuum. outward against the inside of the mold. They are. However. in Chapter 17). the internal pres- The vacuum line is led directly to the part. The sure is supplied by pressurizing the bladder. The shear strength increased by plying pressure to a composite laminate. In 20% in the part molded with a vacuum. assemblies can be measured directly and in others in which the bonded together at the same time they are consolidation was mathematically modeled. Using filament winding (discussed oxidation that may have a tendency to oc. After the correct amount of surization step or use some other method to prepreg material has been wrapped around exert pressure besides an autoclave. the clamshell mold is only can be cured simultaneously in an average slightly larger than the size of the prepreg autoclave. Normally. In this application. fact. the prepregs are pressed capitalization cost. After winding is completed. additional wraps are placed on the vessels. part. rolling table that moves one plate relative to The prepreg layer is covered with another the other and thus completes the wrapping release layer and then tightly overwrapped of the prepreg around the mandrel. typical system uses a molded silicone me. Golf shafts and other simple the expansion of the rubberized material tubular shapes are often made by this with heating is the pressurizing force. If the with graphite filament. the pressure was ap. However. When the entire part is tapered. The aluminum layer the mandrel and then the mandrel and pre- is covered with another release layer and preg are placed between padded plates of a then overwrapped with the uncured prepreg. The part is made by laying up prepreg preg pieces are wedge-shaped so that when over a plug mold and then placing the plug wrapped around the tapered mandrel. Usu- then with a layer of aluminum. the mold is heated. rather. If the mandrel area that corresponds to the shape of the is tapered. winding and open molding. and Applications . cures. the manual wrapping and rolling step aluminum layer provides the expansion is assisted with a simple rolling table. also called the inside surface of the mold. combines elements of filament heated to cure the resin. First. which then the shaft.400 14: Open Molding of Advanced Composites a mandrel over which a bladder has been method. using the tack of the prepreg with some ap- Still another method uses a rigid mandrel plied pressure to stick it to the surface of the covered with a layer of release material and mandrel. which is important for high-volume installed. the wrapping motion will assembly is heated. mandrel. The direction of the layers is de- It is also possible to exert pressure using termined by normal laminate design theory. the aluminum expands move the thicker side of the mandrel over a 22 times more than the graphite filaments. laminate assembly is placed inside a clam- shell mold. The mold is tube rolling. The rolling is done by placing the heats the silicone and causes it to expand and mandrel on the top of the prepreg and then compress the prepreg layers. as it is for a golf shaft. matched metal dies rather than autoclaves or Care must be taken to ensure that the begin- any of the other methods discussed here. from an overwrap this case. of shrink film. is the subject of Chapter 15. This method is suitable for cylindri. fibers remain aligned with the length of After closing. The and pressure. the pre- part. pressure. The bladder is pressurized to ROLL WRAPPING push the laminate layers outward against The roll-wrapping method. This ning and ending edges of each wrapped layer Fundamentals of Composites Manufacturing: Materials. A method. The mandrel is then rolled. the production. The similarity It is possible to use a rubberized material to filament winding is the use of a mandrel (usually silicone) to pressurize a composite as the tool on which the fibers are wrapped. greater distance than the thin side as shown thus consolidating the composite layer as it in Figure 14-6. it should be thick enough to prepreg material is manually started around perform as required. Methods. In an autoclave but. Since the ally. When the thickness of the wrap needs to cally shaped parts such as tubes and pressure be greater. the pressure is not from plied by a vacuum and/or an autoclave. however. called trapped rubber molding. prepreg material is cut into pieces dium placed inside a metal mold so it fully that are usually about three times as wide as occupies the cavity except for the molded the diameter of the mandrel. of prepreg and the curing of the part with in the intensifier case. This material is similar to a pressure The similarity to open molding is the use intensifier (discussed previously). the mold inside the molded cavity in the silicone. are spread uniformly around the circumfer. Those who sell the wrapped onto the mandrel. Methods. Such products autoclave as well as the curing temperature. of important to the development of some prod. Those in one zone of the circumference. and Applications . These ends are potential club shafts are made by both roll wrapping stress-riser points and if they accumulate and multi-spindle filament winding. course. Roll wrapping. are price sensitive and the roll wrapping Therefore. which enhances the Fundamentals of Composites Manufacturing: Materials. are then hung vertically in an oven and heated to cure the prepreg. The molds used in an autoclave are usu- The simplicity of roll wrapping has been ally made of metal or composite and must. This tial problem is not real and that the lower shrink tape is usually applied by a simple cost and good reputation of roll wrapping are wrapping machine. After curing.14: Open Molding of Advanced Composites 401 Figure 14-6. method is highly cost effective. the shrink tape is removed and the surface TOOLING (MOLDS) is ground smooth. Today. that zone who sell the filament-wound shafts point to would be subject to failure initiation. the lack of edges in the winding pattern as a After all the designed prepreg has been performance advantage. withstand the pressure forces of the ucts such as golf club shafts. golf ence of the mandrel. egg crating. a layer of shrink roll-wrapped shafts believe that this poten- tape is wrapped around the assembly. The wrapped mandrels evidence of its value. Once the autoclave. Invar molds are shape that is close to the final shape of the especially common in airplane manufactur. A high-performance film adhe- ing where the value of the parts and their sive. Yet another innovation is the use of lined in Chapter 13. is used volumes are reasonably high. Even when used along with an The part is shown in Figure 14-7. Independently heated and the part was cured. also common in composite work. Recently. In some cases. some molders use metal molds and bonded on its edges. three-dimensional part that oth- ing options and may result in significantly erwise would require building in two halves. The tooling epoxies usually cure at the material is bismaleimide (BMI). The ability to heat a tool outside of an oven Such a preformed nylon bladder was tested or autoclave provides additional manufactur. lower costs. A common method of forming a highly The thermal characteristics of the mold complex part is to lay up prepregs around are important in advanced composites to a bladder. the independently heated tooling lay-up was complete. much in the way made from Invar because of its low coeffi. The chopped prepreg is obtained high-performance epoxies reinforced with from the manufacturer as a mat. Table 14-1 solidate the prepregs. can be molded using lay-up techniques. forming the presents the thermal properties of several bladder using silicone is often a difficult and materials that are used in both advanced expensive process. Methods. cloth is made into clothing. however. or of a metal or ceramic con. for advanced chopped carbon fiber prepreg as the mold composites. The finished part molds are well known but not common. The molds electrical connection to the mold. nylon film To reduce the problems associated with sheet can be used for the bladder. on a complex. The mat carbon fibers. elements embedded in their walls. It is unique in an open mold is important for making because the material can be the heating advanced composite parts. hollow part. To make the process more and engineering composite molds. shapes while still realizing the low cost of a ing can affect the cure because the heat-up molding material. are made using the same general system out. The process of using prepreg materials That material is carbon foam. method permits the creation of complex The type. This is done with a simple for advanced composite molds. and may reduce cycle times and provide improved the mold closed. rates of the tooling can vary widely. is common element itself. feasible for low-cost applications. the bladder inserted.402 14: Open Molding of Advanced Composites pressure tolerance of the mold. composition. Many small parts Fundamentals of Composites Manufacturing: Materials. To sistent with the expansion characteristics of obtain good durability. forming a net cient of thermal expansion. to bond the edges. The nylon thermal expansion and yet give a more film used is the same film that is common as durable mold than can be obtained with a vacuum bag material. It is cut into shapes composites. However. the molds are almost always of material. However. the resin used in the part. the tooling is heated independently to CASE STUDY 14-1 reduce the problem of variable heating and Bladder Molding of a Complex Part accelerate the cure by more quickly getting the entire assembly to cure temperature. a new material offers something SUMMARY different that promises simpler molding. and size of the tool. They was found to have excellent consolidation and are generally metal molds that have heating dimensional accuracy. which then is pressurized to con- avoid building internal stresses. This 350° F (177° C). and Applications . the bladder was pressurized thermal control. 011) 113 (0.9 (23.70 0.9) 9.6 0.90 0. Tooling materials (typical properties might demonstrate a wide range based upon mix ratios.11 0.506) Carbon/epoxy 1.10 (417) 0.8–30.60 10 (0. fiber volume.17–0.12 (501) 0.4) (1.928–6.509–4.03 2.45 Not available Not available 0.589) 1.8 (1.402–17.3 (1.0–9.9) Plaster Gypsum based 1.721–6.90–3.256–2.62 (2.18–1.593) 360 (2.303) (10.14 0.684) Composites Glass/epoxy 1.3 (2.12 (501) 0.3) Nickel 8.0 (0. Thermal Mass.2) 3. etc.1 (11.3 (5.4–16.58 1.49–4.).10 22 (0.718) 500 (4.24) 8.6) 6.0 (0.4) Invar 42 8.2–5.3) Zinc 7./in.2) Ceramics MgO 2.0 (0.19–0.60 21.96 (4.178) (4.129) State change* 0.4–1.094) 106 (0.052) 73 (0. (Courtesy of SAMPE Journal) Coefficient of Coefficient of Specific Heat.6) 0.83 (0.0 (34.9) (3.2) Invar 36 8.4 (13.9) (3.54–0.0 0.0–5.2) 12.0) 19.64 (2.89 (3.0) 7.7 (12.2) Steel 7.98 (4. fiber orientation.13–1.253) 0.11 (460) 0.12 (501) 0.6 0. (CTE).2) (2.0) (4.50 3.84–1.90–3.680 (13.86 (3.13 0. Thermal Expansion Tooling Material Btu/lb/° F Btu/lb/° F Gravity Btu/ft2/hr/° F/in.253) 0.673) 746 (6.7) 10.23 (959) 0.9) 6.09 (376) 0.34) 0.1–3.97 (4.9) 2.02 0.5–1. Specific Thermal Conductivity.80 0./° F (J/kg/K) (J/kg/K) (J/m2/K/cm × 106) (µcm/cm/° C) Fundamentals of Composites Manufacturing: Materials.98 0.1–3.6 (17.004) 403 . lamination sequence.395 (11.45–0.3 (14.3 (1.0 (18.266) (13.06) 1.8–2.37 79 (0. and Applications Metals Cu-Be (C17510) 8. 14: Open Molding of Advanced Composites Table 14-1. µin.86 0.676) 1.879–2.88 (3.10 (417) 0.0–42.593–4.00 1.9 (5.0) Cast aluminum 2.08) 8.28–5.48 24.0 (14. Methods.1) 304 Stainless steel 8.86–1.704–22.436) Al2O3 2. 7–3. 404 Table 14-1. Coefficient of Coefficient of Specific Heat.4 (0.253) (1. Thermal Expansion Tooling Material Btu/lb/° F Btu/lb/° F Gravity Btu/ft2/hr/° F/in. µin.8) (1..965–2.0 (0.01–1.59 Not available Not available 1.3) 2.60 160–220 (1./in.30 0.1–1.9–5.00 0. FR-4500 tooling board † Touchstone Research laboratory.80 Not available Not available Not available 27 (48.6) board§ Carbon foam† 0.7) Water-soluble materials Water soluble‡ 0.47–0. Inc. (CTE).74–2.7–173 (0. Thermal Mass. Continued.7) * Two-phase technology Reconfigurable Tooling System (RTS™) material § General Plastics.4 (6.2–1.6 Not available Not available 1.008–0.009) 3.6–5.24–0.27–0. Specific Thermal Conductivity.128–1. and Applications Monolithic 1.1–1. Methods.2 (4./° F (J/kg/K) (J/kg/K) (J/m2/K/cm × 106) (µcm/cm/° C) Graphite Fundamentals of Composites Manufacturing: Materials.3–1.506) Foam Polyurethane foam 0.1–1.7) 0.53–0.5–9. Aquapore® and Aquacore® materials 14: Open Molding of Advanced Composites . CFOAM® ‡ Advanced Ceramics Research. 1. 6. and Applications . thus improving the consolidation of the part. be pressurized without an autoclave. When done manually. directions. orientations so that the design specifications Procedure: can be met. 90°. Add a nylon bag and seal it to the mold. This method provides favorable results for many products. the prepreg Wet Lay-up Composite pieces are cut prior to laying them into the Objective: Practice the methods of pre- mold. especially in the sporting goods industry. any other volatiles present will be removed. 5. 3. Place a breather material on top of the The assembly of prepreg materials can bleeder. After the prepregs have been laid into 2. Place a release material on top of the The bagging system also allows the resin to resin. Lay a sheet of polyethylene terephthal- the mold. compress the parts. 4. tails are made by this method. the part is then cured. This is commonly done with pressure methods 7.14: Open Molding of Advanced Composites 405 Roll wrapping is a simple method for mak- ing tubular parts. Usually the prepreg will be unidi. Compac- tion is done by wrapping the part with shrink tape. Fundamentals of Composites Manufacturing: Materials. Lay these on top of the film Most of the time. autoclave so that the layers will be packed and 0°. thus matching the Figure 14-7. Place a bleeder material on top of the After curing. 8. In the aerospace industry. move between the layers of the laminate. but might be made of metals for longer wear. that include internal bladders or materi. and the part is finished. the bagging system is removed release. Methods. expansion characteristics of the composite part and avoiding stresses that might result and some parts as large as airplane wings and from mis-matched materials. They might be cut with various fiber preg lay-up. Cut sheets of prepreg in 0° and 90° After debulking. Complex part made with a nylon bladder. they are bagged and a vacuum is ate (PET) film (Mylar) onto a picture applied so the air between the layers and frame mold. Invar molds are common because they have a low CTE. The small parts are usually laid up manually whereas the large parts might be done by an automated LABORATORY EXPERIMENT 14-1 lay-up machine if the curvature of the part is Making a Laminate as Compared to a not great. the cure will be done in an in the mold in the order of 0°. The molds for the processes discussed in this chapter are usually made from epoxy reinforced carbon fibers. Apply a vacuum to debulk the assembly. 90°. even tighter. This method uses prepreg that is wrapped around a mandrel. but some parts may material. Put the vacuum port into the bag before als that expand within a closed mold to sealing. thus reducing void content. Obtain a roll of glass fiber prepreg rectional sheet material. use prepreg fabric. 2005. Handbook of have tack or drape? Lay-up and Bagging. curing the part. 7. Christou. 6. and Lucas.” vacuum to a bagging assembly? SAMPE Journal. John. Vol. and Dorworth. Compare with samples made by the Silicone Elastomers. Upper Saddle River. Vol. No- vember/December. Indicate the part property that is im. Boursier. Inc. 3rd Ed. Evaluation. 1. Rick. “New Composite Tooling: Mate- rial and Concept for Aerospace Composite Structures.” Composites Science and Technology. No. why is pre. Dearborn. 42.org/cmvs. November/ cycle. William W.” Manufacturing Engineering. Put the assembly in an autoclave and Seamless Molding Paste (SMP) Technology. Remove the bagging materials and then Cull. Callis. No. Processing of Advanced Composites Utilizing 11. 1991. p. pp. 2006.” cure according to the recommended SAMPE Journal.406 14: Open Molding of Advanced Composites 9. Chapter 13. 6.sme. preg molding more common than wet Young. 2006. Scott W. A. pp. Daniel N. BIBLIOGRAPHY Beckwith. 299–306. What is the purpose of applying a Concept. 42–49. Philippe. Runo. 2006. “Manual Lay-up and Spray-up” and 5. 6. 53–56. Ray A. No. With advanced composites. Douglas J. What are the problems of uniformity Strong. 42. 6. proved when autoclaves are used for Society of Manufacturing Engineers (SME).. Why are epoxies and carbon fibers the Graphics & Engineering. “TRM Trims Molding Costs. “High-tempera- ture-resistant Tools and Master Models: Fundamentals of Composites Manufacturing: Materials. 2006. Kemp. Methods. Vol. 1995. 1993. CA: Mar Mac 2. No. QUESTIONS pp. 53. Outline a non-autoclave method for “Automated Lay-up and Spray-up” DVDs curing a prepreg part. 60–66. 10. Whittier. 7–13. 42. Wen-Bin.” SAMPE Symposium. Rick. pp. SAMPE Journal. December. and Applications . www. Why do thermoplastic prepregs not McCracken. and Porter. Plastics: Materials with roll wrapping? and Processing. What types of parts are made by the roll series. Vol. pp. March. 1989. “Carbon Foam Tooling: Self-heating 3. November/ 4. Louis C. December. 54. 8. wet lay-up method as discussed in April 15–18. and Demonstration. November/December. prepregs? 2006. Brent. 42. most commonly used components of Merriman. “Out of Autoclave cut the part. “Compacting Pres- lay-up? sure and Cure Cycle for Processing of Thick Composite Laminates. MI: Society of Manufactur- wrapping method? ing Engineers. NJ: Prentice-Hall. et al. from the Composites Manufacturing video 6.” SAMPE Journal. Tires and rubber products were molded tion. Therefore. The process is called unique to composites. was invented in 1909 and processed by so it uniformly fills the mold cavity. Some post-molding work is generally required. es- compression molding. compression molding • Part complexity. The amount of scrap molding compound (SMC) molding is minimal. or alternately. cavity of a matched mold in the open posi. During this process elastomers (rubber products). and Applications 407 . and pressure is The earliest fully synthetic plastic.1: Introduction to Composites 407 15 Compression Molding CHAPTER OVERVIEW industry and in others where high volumes This chapter examines the following of small-to-moderate-sized parts are manu- concepts: factured. are well known and the composites indus- this process is widely used in the automotive try benefits from this prior experience with Fundamentals of Composites Manufacturing: Materials. and female halves together.) manufacturing method for composites that The compression molding process is not employs closed molds. While compression molding to make a variety of under pressure. the material is heated so products including electrical components that it cures. The mold is closed by bringing the male using compression molding before 1900. pecially those who process thermosets and matched-die molding. Hence. molding techniques cycles and high-volume production. These videos are excellent supple- This chapter discusses the most important ments to lectures and laboratories. Compression The molding process can require high molding continues to be a major manufac- pressures and so the molds are mounted in turing method for thermoset plastics and large presses. probably better than any other composite • Process overview manufacturing process. Part-to-part reproducibility is good. but that is often not • Preform compression molding extensive. have used a specific amount of material—the charge of compression molding for many years with uncured resin and fibers—is placed into the widespread use dating from the early 1900s. The presses allow rapid mold elastomers. Compared to other composite • Prepreg compression molding molding processes. pheno- exerted to squeeze the composite material lic. The squeezing of • Equipment the material results in low void contents • Bulk molding compound (BMC)/sheet in the finished parts. SME 2005 for a look at the equipment and the mold- ing techniques associated with compression PROCESS OVERVIEW molding. (Consult the performance considerations “Compression Molding” video. and other has low labor requirements. properties. Plastics molders. and heat-resistant handles. Methods. SHEET MOLDING COMPOUND (SMC) The molds are almost always metal be. parts. mold. In other machines the lower mold that no resin can leak between the sides. Few. or the pins may penetrate into the part. a large daylight open. preform molding. Three generalized sought. The knockout pins are attached to pression molding system is shown in Figure an ejector plate that slides to push the pins 15-1. the capacity depends on the area of When the mold halves allow some excess the hydraulic ram and the pressure that the of material to leak between the sides of the hydraulic motor can exert. In both that the charge of material be accurate. then. pins). In some machines. because of the discussed in Chapter Three as part of the Fundamentals of Composites Manufacturing: Materials. Composites molders also benefit abrasive nature of composite molding mate- from the high technology and availability of rial. For ease between the platens and prevent the mold of loading the mold. This type of mold is preferred for composite often lasting for decades. this half slides downward to open. for speed in closing The specific molding procedures dif- the molds. quickly. machines are normally rugged and massive. However. may lodge is called the daylight opening. compression molding equipment. MOLDING cause the pressures involved in compression The natures of BMC and SMC and the molding are so high. The platens have internal heating units. These rods part. and Applications . a small daylight opening is faster. called flash. and part of the closure sequence. closure is BULK MOLDING COMPOUND (BMC)/ much slower. this is a flash-type mold closure. a compromise in opening is reinforcement used. Compression is called a positive-type mold closure. The other mold half is of the knockout pins should not be too small anchored to the base unit. ing is desired. a two. to facilitate rapid closing. ity is also called the machine rating and the The abrasive nature and high filler content machine size. Care must be taken that the part is guide the up and down motion of the molds. if any. composites molding. The most common mold methods for making these materials were material is tool steel and. The press capac. from closing. it requires as Newtons in the metric system. the mold opens by the top mold half sliding If the mold halves fit together tightly so upward. procedures are discussed in this chapter: step hydraulic system is used. fully cured or else the knockout pins might A hydraulic motor provides the force to move damage a soft part. It consists of a heavy metal base onto into the cavity and thereby knocks out the which slide rods are attached. the mold faces are often chrome plated. the molds close prepreg molding. The chrome plating also helps to release the changes have to be made in the equipment molded part. cases.408 15: Compression Molding plastics. Similarly. The parts are normally ejected from the EQUIPMENT mold by using ejector pins (knockout The molding assembly for a typical com. fer slightly according to the nature of the Therefore. thus allowing for good move- ment of the material to fill the mold. However. since there is not leakage of The capacity of the compression press excess material and any shortage of mate- is stated as tons in the English system or rial results in a smaller part. The molds are usually heated used in the plastics industry to accommodate by the platens to which they are anchored. In the first BMC/SMC molding. the diameter one of the mold halves. So. of many composite materials is not compat- The maximum distance between the ible with the flash-type mold because the mold halves when the assembly is opened excess material. in the second part. Methods. and Applications . Fundamentals of Composites Manufacturing: Materials. Methods.15: Compression Molding 409 Figure 15-1. The mold assembly for compression molding. Another layer of coated film occur before the onset of substantial curing. the molding those added to improve flame-retardant compounds are refrigerated and a strict properties. This thickening is shown in so that the resultant material is a paste-like Figure 15-2. the initiated resin and filler paste is begins. As a further precaution added to improve other properties. little movement of the molding center of the mold and not flow at all. and fillers. is placed on top of the chopped fiberglass and This is also shown in Figure 15-2. By is made and when it is used. when curing In SMC. or dough-like mass. Normally. (10. increase viscosity. Therefore. the viscosity of the mixture is not within an SMC is molded by cutting off the proper acceptable range. must the coated film. Adding more styrene will The molds are then closed and the material lower viscosity but this leads to greater air is squeezed to fill the mold and heat is ap. and Applications . if the viscosity is the area of the mold (within about 80%). a series of compromises because. mixture. this can be time between when the molding compound done by placing strips of SMC in those loca- Fundamentals of Composites Manufacturing: Materials. amount of sheet from the roll of molding glass may not flow to fill the mold properly. compound. The added. the curing occurs during manufacture of the viscosity also increases as a result of fillers molding compounds. as the In both BMC and SMC all the components amount of fiberglass is increased to im- necessary for complete curing of the part prove mechanical properties. great care and some experimentation are the closing of the mold spreads the material necessary in developing BMC materials that evenly throughout the mold. This occurs because the resin mixtures of resin (almost always polyester). removing the carrier film. pollution and more brittleness. tially because of heating. In BMC. both of these materials are increases. of course. The resin may flow but not move the fiberglass size of the SMC sheet generally matches with it. the viscosity increases. compound is made. However. the chopped fiberglass is sim. viscosity must rise to a level that is appropri- ply mixed into the initiated resin and filler ate for molding. which is usually formed During molding. if flow properly in the mold. Normally. such as to prevent premature curing. the laying the sheet material into the mold. or to reduce the overall cost of the maximum shelf life is observed. and curing agents. There is also some curing that occurs. the viscosity way of review. BMC and SMC some of the additives in the mixture have a differ principally in the way the fiberglass is natural tendency to increase thickness. proper flow occurs within a range fiberglass is chopped and sprinkled across of acceptable viscosities and.410 15: Compression Molding general exploration of polyester resins. the entire mass may just sit in the Therefore. filler. the initiator Using longer fibers to improve properties is heat-activated peroxide so only minimal also makes flow more difficult. plied by the molds to cure the part. If The mixture’s viscosity is ever changing there is the need to add additional reinforce- until final curing occurs. As indicated spread onto a wide carrier film and then the previously. this raises are mixed into the resin when the molding the viscosity and makes it harder to flow. Then. and If the viscosity of the mixture is too low. Increasing the molecular weight BMC is molded by placing a weighted of the resin to improve properties will also amount of the material into the mold cavity. compound in the mold occurs with SMC. Further. too high. reinforcement (almost always fiberglass). the viscosity drops ini- into logs of about 4 in. and fiber.2 cm) in diameter. continues to wet-out the fibers and the filler. Methods. On the other hand. During the storage ments to some areas of the part. the resin. the sandwich of material is kneaded between Obtaining acceptable viscosity involves rollers to wet-out the fibers. 5–35 When this is done. like automotive parts. Normally. the The heating is efficiently done using radio viscosity problem is solved since the sheet frequency (RF) heating in which the molding essentially covers the full area. heating for food. cycle time = 1–10 minutes. and so some a vacuum assist for withdrawing the air and efforts have been made to reduce it. seconds. The entire mold cycle can be further The molding time is long for some appli. the RF heating tings are: temperature range = 275–335° F raises the temperature to about 130° F (54° C). Fundamentals of Composites Manufacturing: Materials. (135–168° C).000 psi (3. pressure = 500–5. tions before closing the mold. One of vapors from the mold. the methods used is preheating the molding When the part is molded. However. Viscosity variation during the stages of the molding compound process. the cure occurs in about 30 MPa). using knockout pins is the norm. Typical set. and Applications . reduced when fast closing is used along with cations.15: Compression Molding 411 Figure 15-2. With SMC. Methods. extraction by compound just prior to placing it in the mold. compound is subjected to the RF signal in The molding conditions for both BMC and a process not too different from microwave SMC are essentially the same. The the resin over the entire surface of the pre- molding methods are also similar except for form. along with the need to have filler increasing fiberglass content. (J/m ) 7.25 0. the Every mechanical property—flexural. The part cures Table 15-1. (The major change in shrinkage with material is preformed to the approximate fiberglass is between the neat resin and almost shape of the part and placed into the open any significant fiberglass loading. Properties of molding compound with various percentages of fiberglass content. (The fabrication of these preforms was Some epoxy-based molding compounds discussed in Chapter Nine. advantages of higher fiberglass content.) mold.000 (193) Specific gravity 1. and Applications . valuable in making parts used in corrosive sary for each molding cycle.25 0. psi (GPa) 7. viscosity problems in BMC and. Properties Fiberglass Content 15% 22% 30% 2 Izod impact.000 (117) 21.0 (480) 14. generally needed.000 (48) 10. This material has proven to be especially the application of mold release is not neces.5 Fundamentals of Composites Manufacturing: Materials. such as water absorption and flamma.000 (69) 12. environments.5 21.0 (747) Flexural strength.5 21.412 15: Compression Molding even with these pins some mold release is that epoxies bring compared to polyesters. to a lesser ex- compressive.000 (172) Tensile strength. As would be ex. the ability to use more fiberglass.85 Water absorption.02 0. the dry reinforcing in place. pouring the liquid onto the top of the preform als are made by methods similar to those with some minimal effort to evenly distribute used for polyester molding compounds.0 (374) 9.02 Oxygen index 21. % 0. for economy and improved properties. On a well-seasoned mold. The properties of the products wets the fibers.25 room temperature Shrinkage. These materi. This Somewhat surprisingly. products that need higher fiberglass content.500 (86) Compressive strength. ences due to the fiberglass holding the resin In preform molding. which causes adjustments for curing temperature and the resin to flow throughout the preform. Methods.) Resin is added by are commercially available. and impact—improves with tent in SMC.77 1. In those resin. The In spite of the obvious mechanical property effect of glass content is shown in Table 15-1. do not change with fiberglass content. tensile. psi (GPa) 20. The most important single parameter af- fecting the performance of a part made from PREFORM COMPRESSION MOLDING molding compound is the glass content. pre- pected.02 0. ft-lb/in. The mold is then closed. properties that depend chiefly upon the clude ever higher fiberglass contents.000 (165) 28. the shrinkage remains approach is called preform compression mold- constant.80 1. a different molding approach is taken. and compacts the preform to reflect the improvements in many properties the shape of the mold cavity. bility. probably because the measurement ing and it has some advantages besides just is not fine enough to detect the minor differ.000 (138) 24. 24 hours at 0. psi (GPa) 17.000 (145) 25. shrinkage. the small opening created when the mold is cracked open. the phenolics can be conveniently used with this prepreg material can be chopped and then method. Also. Methods. process. However. This means that the fiber content can be over the entire length of the part. vapor at this stage because of the heating the labor component of the molding costs can of the mold and simply escapes through be substantially reduced. the mass of the liquid ma. Engineering and advanced not move appreciably during molding except composites are made using this method. or SMCs. therefore. ing compounds. for compression of the fibers into the cavity. fore. This process is called bump- ing the mold or breathing the mold or. little filler is used in preform prepreg manufacturers. however. However. less often. in- terial is less and this results in faster heating mold movement can be minimized. within the mold and by the closing of the The lack of filler also means that viscosity is mold since some movement within the mold less of a consideration than with the molding is common. done by opening the mold slightly during the the chopped prepregs can be placed in the molding cycle. the molder has greater the prepreg material and the prepreg can be choice with respect to the resin used. longer fiber lengths results in much higher Prepreg molding. means that epoxy resins can be used and. set by the In general. it method of molding using matched dies. faster cures. properties of prepreg-molded parts In essence. can be used effectively achieved with BMC or SMC. Note. advanced composites are more ary attachment and gives good bonding to common in preform molding than the mold. PROPERTIES. The condensate is usually a mold by semi-automated methods. There- of the resin and. Therefore. When prepregs are used. The fiber lengths molding. PART COMPLEXITY. and Applications . of the mold cavity and the lay-up stack. Fundamentals of Composites Manufacturing: Materials. Fi- is removed with knockout pins. ber-resin contents are. that when a polymer placed into the mold. the prepreg flows to create a smooth bound- therefore. BMCs. of the final part can be much higher than Orientation is controlled both by the lay-up would be possible with molding compounds. for making parts that contain inserts. of course. Prepreg the part) rather than being limited to just molding is usually reserved for small parts chopped fibers as in the molding compounds. with careful design compounds. the condensate that forms must the fibers are shorter than when the prepregs be allowed to escape from the mold. the uniformity Therefore. This is are stacked manually in the mold. AND OTHER PERFORMANCE CONSIDERATIONS PREPREG COMPRESSION MOLDING Compression-molded parts are generally Placing cut prepreg strips into the mold not able to achieve the high complexity that and then compression molding is another is possible with the open-molding systems. of course. the fibers in the preform do can be excellent. This gives a reasonably is used that crosslinks by a condensation random orientation to the fibers. This shaped around the inserts. burping the mold. when cured. because larger ones are more easily made in The combination of higher fiber content and open molds with autoclave curing. which is essentially a mechanical properties for parts than can be manual lay-up process. the insert. Other important resins like When lower properties are acceptable.15: Compression Molding 413 within the heated mold and. preform molding permits fibers of the part is usually superior to those made that are continuous (over the entire size of with preforms. The Because the resin is added separately from inserts can be placed at the same time as the reinforcement. During molding. The pressure utilized in an office copier part that operates requirements increase roughly with the at 400° F (204° C) and is required to maintain square of the area of the part.000 parts plication containing calcium carbonate filler per day are not uncommon. the advantages ture-sensitive components. hoods. Production volumes of 1. and lawnmower hous- Also. The resin was applied manually. furniture. dimensional stability of ±. fenders.13 mm). This part cross-sections should be modest in depth and was molded using epoxy SMC around a shaft. sunroofs. (±0. window oven. rear. and Applications . spoilers. bosses. and variable tolerances that could be achieved. not too narrow. binder onto a plenum (rotating screen) and deck lids. (0. Draft ±. motorcycle fairings.005 in. and a polyvinyl acetate low-profile additive. was drilling two . matched-die molding because of the tight This means that ribs. only machining required on the SMC part Undercuts are difficult with compres. electri- When molding compounds are used. building panels. Parts as large A part that encompasses the entire hood as entire cabs for trucks are compression and fender of a large truck was made by molded. The technical require- Other automotive and truck parts made ments were met or exceeded and the com- using compression molding primarily with mercial requirements have proven to be BMC and SMC include: grille opening highly favorable. and rocker special mix formulated specifically for this ap- panels. The automotive and Preform Molding of a Major Truck truck industries are especially important Component users of compression molding. cargo doors. trim then bonding by heating the preform in an panels. Therefore. The are generally not possible. Fins or other thin sections replacing a machined-steel component. outboard may not flow during the molding process. body chopped fiberglass and a small amount of extensions. ings. panels. motor housings.) commercial success. of compression molding have been so great that its use continues to increase for both CASE STUDY 15-1 large and small parts.013 mm) tolerance. (The presses required to do this are preform molding and has become a major several times larger than the truck cabs. roofs. Methods. the molding compounds contain fill. engine covers. underbodies. which may preclude their use in some interior panels. missile exhaust nozzles. large parts require enormous presses to It replaces stainless steel and also serves as mold them.414 15: Compression Molding For example. a thermal barrier to protect more tempera- In spite of the limitations. angles should be 1–3°. aircraft bulkheads.0005 in. cowls. Fundamentals of Composites Manufacturing: Materials. compression-molded parts Another automotive application used should have relatively few changes in depth. It was a garnish moldings. refrig- should be remembered that the fibers are erator cabinets. Aerospace applications include aircraft ers. The preform was made by directing end panels. air deflectors.20-mm) diameter sion-molded parts unless complicated and holes and finishing the surface to assure expensive sliding molds are used. garden-tractor hoods. chopped and relatively short and random. nose applications. and some wing The need to use considerable pressure and body components. dual-wheel fenders. snowmobile hoods. cones. it cal enclosures. light-housing extensions. Sharp corners should Non-automotive and truck applications be avoided since they are not only stress-riser are also prominent including: basketball locations. electronic housings. (0.008-in. but they are places where the fibers backboards. The good elevated to mold parts is also a limitation because temperature properties of epoxy SMC were of the cost of large presses. • Poor viscosity control may lead to in- nents of the truck.1 and 38. compared with a value of 130 for a similar Class-A SMC part.000 parts per year. lines. The principal ad- sional control than open-molding pro- vantages of using compression molding are cesses. Methods. open-molded parts. warping. To be considered Class the resin paste and glass interface are A. Viscosity control is important. low labor and high volumes.8. and Applications . fiber kinks. Three different modes of compression • Labor is less than in other composite molding have been defined in this chap. cracking. lems such as blistering. Fundamentals of Composites Manufacturing: Materials. In the first. chopped. However. sidual stresses. The major disadvantages of compression ed to be superior to the surface obtained with molding include the following SMC. especially inviting for this manufactur. These relate to the type of materials • Air pollution is lower than open-mold- used. compounds are used. The second method is preform molding. ter. are also compression molded. • Either continuous or random chopped SUMMARY fibers can be used. strength requirements resulted in savings on equipment and tooling costs. moving materials in the mold (compared to • Internal defects from poor flow are SMC) and the reduced size of the press and possible. parts requiring high performance • There is little waste. Lower requirements for completely filled molds. BMC and SMC molding ing processes.15: Compression Molding 415 The surface of the finished part was report. The new truck hood had a Diffracto • Regions of high resin flow may orient Sight Index value between 38. • High production rates are possible. include the following. and breakdown of ated grid of a surface. Matched-die or compression molding has • Several resin choices are available. especially where high accuracy and well-defined surfaces are • Higher pressures give good part defini- required. High-performance parts can be performance of compression-molded versus made by this method. In LABORATORY EXPERIMENT 15-1 this method. a surface must register an Index value of possible. because the fibers are • Automation is possible. (Diffracto is an optical • Flow-related problems such as re- scanning system that produces a highly mag. the fibers in some regions.) • Excessive molding pressure can lead to The precision matched dies ensured distortion of the part. molding processes. excellent fit of the part to the other compo. The third method uses prepregs placed Objective: Discover the differences in the in the mold. small aerospace parts splitting. The total The advantages of compression molding volume is over 6. The mold is Compression-molded Parts Compared to closed to distribute the resin and cure the Open-molded Parts part. the dry preform is placed in the mold and resin is then added. an important place among the processes used • The matched dies give better dimen- to make composite parts. 150 or less. Further. are generally not molded using this method. tion and eliminate many surface prob- fore. The automotive industry is. and ing method. weld (knit) nified photo and matching computer-gener. there. 5. Distinguish between preform molding and prepreg molding.” SME Techni- cal Paper. 2. Why does preform molding usually require less pressure than BMC/SMC molding? BIBLIOGRAPHY Childs. “Compression Mold- ing of Structural Composites. tions of the material supplier. List two differences in molding BMC and SMC. Dearborn. Automo- fabricate flat panels.416 15: Compression Molding Procedure: Modern Plastics. pp. Upper Saddle River. 1991. Make a simple compression mold to Molded Truck Hood has Smooth.sme. ficient to make several BMC panels). 2005. “Compression Molding” DVD from 3. A. Society of Manufacturing Engineers (SME). 1987. Plastics: Materials samples made by the opening-molding and Processing. Inc. EM87-556. pp. 37–39. Dearborn. 2006.” October. List two advantages of preform molding over molding with BMC/SMC. William I. “SMC Structural Composites: High Strength at Low Cost. MI: Society of Manufacturing Engineers.” Plastics Engineering.org/cmvs. NJ: Prentice-Hall. QUESTIONS 1. 1989. the Composites Manufacturing video series. and Applications . William I. Give three differences between BMC and SMC. Childs. 3rd Ed. Mold the BMC according to the direc. cut the samples for Engineers. Brent. 6. www. Fundamentals of Composites Manufacturing: Materials. 2. February. Obtain a sample amount of BMC (suf. tive-quality Finish. Why are compression molds usually made out of metal? 8. 4. 3. After molding. 24–25. MI: Society of Manufacturing 4. Methods. process. “Liquid Composite 1. Give three compromises that have to be reached in determining the viscosity of BMC. Which of the molding methods using matched dies is more consistent with making advanced composites? Why? 7. mechanical testing and compare with Strong. concepts: the mold is opened. the molding operation without moving the ratories. In addition. Cycle Besides being the best known of the many times depend on the resin system used but resin infusion technologies for making typically fall in the range of 5–10 minutes. This means that resin infusion can All of the resin infusion technologies share be used to make advanced composite parts some common features. composite parts. resin infusion processes. continuous across the liquid molding processes. and the degree of design flex- PROCESS OVERVIEW ibility in both part size and complexity. lower emissions. These videos are part) into the mold and then carrying out excellent supplements to lectures and labo. are immediately apparent. the abil- a mold and the mold is closed. The basic resin infusion process is illustrated • Process overview in Figure 16-1. low labor requirements. Resin is then ity to use low-cost materials and the speed Fundamentals of Composites Manufacturing: Materials. • Resin infusion technologies The advantages of the resin infusion pro- • Equipment and process parameters cesses. RTM is used in a more narrow sense means that one-piece. resin transfer molding However. and Applications 417 .1: Introduction to Composites 417 16 Resin Infusion Technologies CHAPTER OVERVIEW injected into the mold so that the preform is This chapter examines the following fully wetted with resin. Another phrase occasionally used to number of parts in an assembly. describe the resin infusion processes is An important advantage of the process liquid molding processes. SME 2005 for a is the feature of being able to place continu- look at the equipment and techniques of ous fibers (that is. However. co-cured parts are and “resin infusion” is the more general often easy to make. listed in Table 16-1. in this Inserts can be easily molded in and this text. and the part is extracted. In all of them the dry where the direction of the fibers is critical (without resin) fiber preform is placed into to part performance. low requirements • Centrifugal casting for auxiliary equipment (like freezers and autoclaves). The factors especially appealing in • Preform technology for infusion the current composite world are: the better • Resin characteristics quality possible with resin infusion (good • Core and flow media materials tolerances that are repeatable and excellent • Part design for resin infusion surfaces out of the mold). The resin is cured. (Consult the that might not be obvious at first thought “Liquid Molding” video. Methods.) fibers. they can be as high as 2–8 hours (RTM) is often the general term used for all for large parts like railroad cars and yachts. thus reducing the total term. Hence. separated from the resin as the resin/filler The disadvantages of resin infusion mixture infiltrates through the fiber pre.) However. processes. new parts and those that were previously ficult to add fillers. are not Fundamentals of Composites Manufacturing: Materials. other costs such as the re- used for engineering composites.418 16: Resin Infusion Technologies Figure 16-1. and Applications . This is because ing process. of manufacture allow resin infusion to be form. the process is likely to the fibers do not need to move in the mold. duction in auxiliary equipment needed and In engineering composites. Methods. also listed in Table 16-1. (They are sometimes made by other composites processes. resin infusion the environmental aspects of resin infusion surpasses BMC and at least equals SMC in often result in it being the lowest-cost mold- mechanical performance. The use of infu- about equivalent to BMC and SMC but the sion processes is growing rapidly for both material is slightly higher because it is dif. Basic resin infusion process. be important across the entire spectrum of The operational costs of resin infusion are composites manufacturing. Methods. styrene) • Full wet-out of fibers can be difficult controlled by closed-mold tooling process (resin flow path) • Lower labor intensity and skill levels • Considerable design flexibility: reinforcements. and mixed materials co-cured in place • Mechanical properties comparable to autoclaved parts with low void contents (<1%) • Wide part size range and ability to handle complexity • Near-net-shape molded parts with little trim required • No bagging required • Heating can be integrated into mold • No refrigeration needed (as required with prepregs and SMC/BMC) • Process can be automated Fundamentals of Composites Manufacturing: Materials.000 kPa]) • Restricted resin choice (due to viscosity) • Prototype tooling costs are relatively low • Air entrapment • Volatile emissions (for example. leak-proof molds 200–300 psi [1. lay-up sequence. fittings. Advantages and disadvantages of the resin infusion process (Benjamin and Beckwith 1999).400–2.000 parts • May increase post-infusion process pressure to higher level (for example. and reinforcements possible • Preform and reinforcement alignment in mold is critical • Low-pressure infusion operation (usually less than 100 psi [700 kPa]) • Production quantities only in the range of 100–5. high repeatability quality • Class-A surface finish possible from tool • Tooling costs can be high for large • Surfaces may be gel coated for better production runs surface finish • Mold filling permeability based upon a • Smooth finish on both surfaces possible limited permeability data base • Cycle times can be short • Mold filling software limited or still in development stage • Molded-in inserts. Advantages Disadvantages • Best tolerance control since tooling • Mold and tool design critical to part controls dimensions. inserts. core materials. • Requires matched. ribs. and Applications .16: Resin Infusion Technologies 419 Table 16-1. bosses. are employed. The most com. infusion processes might be divided into two Occasionally the RIM process will inject types: pressurized injection (a characteristic into a mold in which some reinforcement is of RTM). other terms such as as unsaturated polyesters. The most important sion molding except that the mold is closed continuing problem is proper mold design. The fast cure times process most widely employed and has of RIM and SRIM allow cycle times of a few become the common name for all resin in.” each satisfying a particular need or demon. Mold filling analysis software is where it is heated to ensure that it is highly limited to fairly simple shapes (mostly 2D) fluid but not heated sufficiently to cause sig- and by the lack of enough preform perme. process for thermosets. and struc- atmospheric. These modifications. and narrow definition of RTM is used—a pres. This text prefers to retain the tural reaction injection molding (SRIM) are generic “resin infusion” to describe all of similar to RTM. The resin is cured research is aimed at developing more com. Nevertheless. and Applications . However. the number of variations in the process that often referred to as the “injection molding have been developed.420 16: Resin Infusion Technologies negligible. This system is similar mold designs. the major difference is that. and grew from a series of related processes for seem to be under control and diminishing plastics molding. Another precursor process is called reac- strating a new innovation. SRIM are high-pressure processes (often to sure-injected.000 psi [28 MPa]). RTM 4. A further advanced composites. nificant curing. which is done at pressures lower than While transfer molding. neither transfer molding nor RIM are reinforced and the Resin Transfer Molding (RTM) amount of reinforcement in SRIM is usually Resin transfer molding (RTM) is the much less than in RTM. the processes. The earliest was transfer as manufacturers become more familiar molding. whereas RTM is much Fundamentals of Composites Manufacturing: Materials. This process is advanced composites fields that the resin used extensively for automobile bumpers. The reac- in Table 16-2. and vinyl RTM and VAI will continue to be used. seconds to a minute whereas RTM cycle fusion processes. traditional composite resins. This process is similar to compres- with the processes. esters. when the thermoset plastic material is in- Mold (tooling) design is critical to achieve jected. the through a sprue and runner system into the situation is getting better and considerable mold cavity or cavities. In this discussion. the difference is that transfer molding. rather. liquid infusion process. and vacuum-assisted injection already present. Injection is accomplished by placing complete resin saturation within a reason. A suggestion has been made tive materials usually are the components by technical leaders in the engineering and that make polyurethane. but they are manageable. Also. is simply heated in a The acceleration in the number of parts chamber from which it is transferred to the being made by resin infusion is a result of mold cavities. Methods. two materials that react rapidly are mixed mon of the resin infusion processes are listed and injected into a closed mold. however. RIM. such sure. to the injection molding system for thermo- plastics except that the resin is not melted RESIN INFUSION TECHNOLOGIES by a screw but. regardless of injection pres. (VAI). in the heated mold and is then ejected by a plete models and data for predicting optimal knockout pin system. RIM. epoxies. A plunger pushes the resin ability data at the present time. Transfer molding is. In this process. have resulted in tion injection molding (RIM). in RTM. especially in the area of times are usually 5–150 minutes. an “alphabet soup” of names. the thermoset resin in a transfer chamber able time. Comparison of various resin infusion molding processes (Benjamin and Beckwith 1999. and Applications . Process Attributes or Features Developed from non-reinforced plastics (transfer molding) and urethane (resin injection molding [RIM] and structural reaction injection molding [SRIM]) technologies Resin transfer Resin injected into matched mold under pressure molding (RTM) Excellent surface finishes on both surfaces Can obtain high fiber volumes (55–65%) Process called co-injection resin transfer molding (CIRTM) uses different resin systems during process Often termed vacuum-assisted resin transfer molding (VARTM or VRTM) Vacuum pulls liquid resin into preform (no applied pressure) Single-sided tool normally used with vacuum bagging technology Vacuum infusion Requires lower-viscosity resins processing (VIP) Excellent surface finish on tool side only Tooling less expensive than RTM Lower fiber volumes normally obtained (45–55%) Resin film is placed in bottom of tool and autoclave heat/pressure cycle is used to melt and force resin into preform Resin film tiles normally based on prepreg B-staged formulations Normally requires matched die tools for complex parts Resin film infusion Several industry variations exist: (RFI) —Resin liquid infusion (RLI) in which liquid resin replaces resin film sheets in tool bottom —SPRINT™ in which resin layers are interspersed in the preform lay-up and flowed during heat up Capable of producing high-quality parts depending on tooling Thermal expansion resin transfer molding (TERTM) uses a matched die with internal core that expands to provide pressure after RTM infusion of preform Expansion RTM Rubber-assisted resin transfer molding (RARTM) uses silicone rubber tooling inserts that expand upon heating to provide pressure intensification within the tooling cavity after RTM infusion of the preform Seeman’s composite resin infusion molding process (SCRIMP) uses a proprietary infusion tubing and media to speed resin flow and SCRIMP™ or thickness infusion of the resin “SCRIMP-like” VIP “SCRIMP-like” VIP processes use various commercially available flow media to achieve results similar to the SCRIMP process Fundamentals of Composites Manufacturing: Materials.16: Resin Infusion Technologies 421 Table 16-2. Campbell 2004). Methods. as the mold-defined side. resin movement can trap surfaces can be finished. but it must be on the vacuum-only processes. include vacuum-assisted resin transfer The pressurized injection of RTM has the molding (VARTM. applied to similar VIP processes. held firmly shut. This results in The pressure injection pushes the resin a much lower cost for tooling than in RTM. in the mold. VRTM) and vacuum-as- advantage that resin can be pushed through sisted resin injection (VARI). In some cases. and Applications . The with moderate pressure. These commonly steel) are the norm for RTM. Fundamentals of Composites Manufacturing: Materials. In processes to make composites (as opposed VIP. Several names have historically been metal molds (usually aluminum but not un. Whereas simple clamps Because of the lower pressures used in VIP. the more characteristic of standard RTM than increased pressures not only mean that of VIP. part vented in the mold. which is called fiber wash. the vacuum is applied along with pressure ber volume contents as high as 70% and void as a way to further assist in the resin infu- contents of about 1% are possible. the sur- the pressure can also cause fibers to move face quality is not as good as with RTM. The resin uniformity thin composite mold cannot withstand needs to be verified during the development the normal pressures of RTM. vacuum bag is not the same surface quality sometimes even a Class-A finish. Also. This can be done by examining under just vacuum pressures. Normally the molding. There sion of standard RTM. RTM is truly a composite pro. However. Another common mold system uses a thin Parts made by RTM can be of complex composite mold. In is sometimes called light RTM. can be used in vacuum processes. This system resin/fiber ratios throughout the part. but does well process. but are not as well air in many areas and these should all be defined as with traditional RTM. Typical pressures vacuum can be applied at multiple locations are about 30 psi (207 kPa) but can be as high and each can be sealed (pinched off) when as 100 psi (690 kPa). a key feature of vacuum is applied to strategic locations the RTM process is that the resin is injected where the resin is likely to fill last. RIM and SRIM). Therefore. the pressure without distortion. However. from RTM in the pressure conditions under In comparison to the other resin infusion which the resin is introduced to the mold. firmly against the mold surfaces resulting However. common alternate mold type is a vacuum Some manufacturers simply put the RTM bag on one side and a traditional metal or mold in a press. the preform and the resin is infused as in ited by the ability of the resin to flow into other resin infusion processes. Hence. However. the side of the part defined by the in excellent surface quality on all sides. The injector must not the resin is seen to arrive. Fi. the pressure is applied by the atmosphere to the largely plastics processes of transfer against an evacuated system. but the mold must be able to withstand complete mold filling. Therefore. Therefore. ensuring sure. RTM the molds do not need to be metal. The thin mold is filled with geometries. the all areas of the mold. Methods.422 16: Resin Infusion Technologies lower. Vacuum continues only be able to deliver the resin under pres. tolerances are not as finely held as in RTM. this discussion will focus the tooling must be robust. composite mold on the other. even difficult and compacted preforms. these dual is more control over the injection process processes (pressure and vacuum) are really than when only vacuum is used. The most requires more extensive closure devices. However. Vacuum Infusion Processing (VIP) cess whereas the others are more traditional Vacuum infusion processing (VIP) differs plastics processes. A part’s complexity is only lim. All part complex parts. to be applied to other locations. thus reducing the complexity of after RFI processing—all parts co-cured. Expansion RTM volved moving essentially low-viscosity. Methods. In this process.8 m]) wing part made by RFI. (Courtesy Scott the parts that can be made and eliminating Beckwith) Fundamentals of Composites Manufacturing: Materials. infusion (RLI). Figure 16-2 shows a photograph of a large (42 ft [12. the resin does not need to travel as far as in standard RFI. Therefore. many parts can be inexpen. which forces the resin temperature they are films. is forced by the pressures involved in the process. mold Another variation in RFI technology is to support mechanisms are frequently used. Clearly. uses (usually sequentially) so that the resin drops a rubber pad and a metal (usually alumi- in viscosity and infuses through the preform. Resin Film Infusion (RFI) So far the methods discussed have in. a to wet-out the preform. They are The heating of the mold causes the core typically so high in viscosity that at room material to expand. there are some a material that expands when heated is resins that are so viscous that they will not placed as a core within the preform. A complex preform was used in the part. the resin sheet is placed in the along with the preform. num) plate. for fiber wet-out.16: Resin Infusion Technologies 423 Nevertheless. The mold had internal pressure sec- tions that expanded during the cure to give good definition to the many ribs. The expansion RTM process has two liquid resins into molds and using vacuum different permutations. pressures allow thin molds to be used. In the process used. Since the low preforms. Both are placed inside the mold Typically. but the preform must Figure 16-2. tennis racquets. This method is called resin liquid in this chapter. This process is called SPRINT™. racquetball RFI but does not require the fibers to be pre- hardware. the ability to have totally dry and finished sively made by this process. called the and/or external pressure as the driving force thermal expansion RTM (TERTM) process. the resin Products made by the VIP process include must be lower in viscosity than for traditional bicycle parts. and Applications . However. In one. the fiber preform was laid on top of a resin sheet that was placed in the mold. place the liquid resin inside the mold before These will be discussed in more detail later closing. sometimes the mold and then to apply heat and pressure called rubber-assisted RTM (RARTM). normal RTM or VIP processes. The reasonably infuse through the part in the resin is infused and the mold is heated. and component housings for coated as with prepreg since fiber coating snowmobiles and watercraft. method was developed to lay the film resin in The other related process. The pressure on the mold so that the resin need only infiltrate rubber pad presses against the preform and through a small dimension of the preform (usually the thickness) thus reducing the need for it to travel long distances. A variation on the standard RFI process is to intersperse the resin sheets with preform layers. Lower wing section of a commercial aircraft be laminar. 424 16: Resin Infusion Technologies causes the resin to completely wet the fibers. hardening agents. not too complex. there. The process utilizes one-sided tooling and EQUIPMENT AND PROCESS therefore is best suited to applications like PARAMETERS boats where only one side is exposed to view. The manifolds are shaped somewhat process include yachts. The resin then saturates the Commercial parts manufactured using this preform. and piers. While these in-line mixers are Fundamentals of Composites Manufacturing: Materials. called omega channels. several VIP fore. Void contents are somewhat This process has the advantage of molding higher than with RTM or other pressure materials with high fiber contents (as much processes. usually limited to about 50%. These machines usually consist of holding tanks for the resin components. initiators. It is a patented method of resin distri. Injection Equipment Commercial resin infusion equipment is available from a variety of sources. in Figure 16-3. Achievable fiber volumes are as 75% by volume). the controlled distribution of the resin allows SCRIMP™ and Similar Processes several regions to be simultaneously infused. The full name of the SCRIMP™ process is (In Figure 16-3. large flow media to achieve results similar to the parts can be made by this process as shown SCRIMP process. Lately. By means of various manifolds. The outlets of the tanks are often directed toward an in-line mixer that causes the liquids from the various Figure 16-3. (Courtesy Scott Beckwith) into the mold. The holding tanks are often pressur- ized so the flows can be accurately metered or they might be equipped with pumps to meter the liquids. and Applications . and sometimes even for the minor ad- ditives. the bution coupled with the vacuum bag molding choice of low-viscosity resins (unsaturated process. the resin flows is a potential problem.8-m) boat hull.) Although the knitting together of process. However. truck trailers. However. Methods. The SCRIMP process is licensed widely. the polyesters and vinyl esters) seems to have resin is quickly distributed across the part eliminated this problem in most parts. some generalized descriptions are probably valuable to allow comparisons of the various process machines and to understand the range of operating parameters for each of the infusion processes. The driving power for resin movement is a Most equipment for resin infusion has vacuum and therefore the parts are usually been described briefly in characterizing the different resin infusion processes. ging material. flatbed like the Greek letter omega and are. Because the processes use various commercially available resin is distributed widely and quickly. while the vacuum is applied under the bag. Traditional SCRIMP™ processing of 65-ft tanks to flow together and mix prior to entry (19. railcars. there are nine diffusion Seeman’s composite resin infusion molding regions. such a preform has been used in Fundamentals of Composites Manufacturing: Materials. and Applications . the molds are usually placed The preform can be a simple 2D structure in a press or autoclave. need to have separate heaters for the mold. The first ally or by machine. backside of the mold. For simple. INFUSION Preform technologies were discussed in Molds detail in Chapter Nine where the nature of Metals are the most common materials for preforms and the methods of making them RTM molds. used to create backing support for thin jection system might be just a plunger in a molds that might have injection pressures tube into which the pre-mixed resin system higher than would be normally encountered is placed. While these are often not can be heated and this would eliminate the as sophisticated as the commercial types. For ensure that the mold will stay closed during example. These are usually infusion processes must fit inside the mold manually operated but can be machine as. the pre-mixed resin system. Therefore. the potential inaccuracy of the in. This improves overall injection time top (end) of all long pathways. These types of clamps are easy to use. Normally the vents are located to be effective in a laboratory setting is the se. the potential lack of sufficient force be selectively placed. air could be trapped in such places. An advantage to the press or Many molders have made their own resin autoclave might be. composites coated are especially important in the resin infusion with metal (usually nickel). many homemade versions seem to work Two interesting innovations have been quite well. some VIP. that the press injection systems. Further. processes. areas where resin can puddle. especially at high flow rates. Vent ports should be provided at the the mold. The plunger can be moved manu. these clamps. small parts. they allow for a variety to properly inject the resin to achieve full of mold shapes (as does. forcement forms. some resin injection. readily and not move extensively when the when the pressures exceed the capability of resin is flowing. as in were explained. Venting is a significant issue in all resin in- An interesting variable that has been shown fusion molds. the inexpensive to acquire. at the points most distant from the injection quential injection of resin across the length of port(s). but the convenience of acces- limitations on the completeness of mixing are sibility to the mold during filling is reduced present. There are. and generally reliable preform must allow the resin to permeate except for under high pressures. however. the preforms used in resin ing the halves together. especially if and has the potential for improved wet-out. Since the plungers can jection. The problems with this of these methods uses a water bath with simple system are the need to pre-mix the pressure to resist any shape changes in the materials (and the difficulties with mix mold. The second uses mechanical plungers ratios and problems with handling various placed against strategic locations on the liquids). the in. In addition to the load-carrying Several mechanical clamps located around requirements required of all composite rein- the perimeter of the mold are used for clos. the molds can be made of composites special considerations about preforms that or. When pressures are lower. however. Methods. and the limited pot life when using backed system). of course. This will generally that is nearly laminar in construction.16: Resin Infusion Technologies 425 convenient and generally work well. the water- wet-out. for improved surfaces. or eliminated. especially in systems where the long resin flow paths may be a problem because of the resin’s PREFORM TECHNOLOGY FOR viscosity or rapid curing. properly. in the light RTM or VIP process. There should be no gaps or open sisted. Permeation proper orientation when they were molded. This phenomenon can be seen resin can be injected between the sheets in the differences in the permeation rate of and then the entire assembly can be put resin through woven material and through into a matched die mold where it is shaped Figure 16-4. could cure before the preform is fully wet- An important consideration in choosing ted and the mold filled. It is. therefore. (The resin flows along stand-alone unit. The complex preform is used to make Therefore. eral. presumably because it hand lay-up.) that will be 16-4b. The rate is slower been made using other processes. The com. RTM aircraft hinge. which will be subjected to openness of the structure must be related to significant forces in all directions. the flow of the resin and to the conditions pleted part. Another related consideration is the fiber plified the retention of the materials in their volume fraction in the preform. It is possible to place flat the small gaps in between. However. the preform was lightly stitched ness of the structure as shown in Figure to hold its shape. the resin will wet-out the preform. temperature. (Courtesy Scott Beckwith) Fundamentals of Composites Manufacturing: Materials. Note the inclusion of metal inserts used.426 16: Resin Infusion Technologies hockey stick blades. such as in woven material. high-volume part because the preform sim. it is sheets of dry fibers (woven or mat) between desired to have those pathways interrupted flexible (elastomeric) diaphragms that so the resin is forced to flow throughout are sealed inside a mold-like frame. to be both economical and reliable for the more interruptions in the flow. etc. of the resin is strongly related to the open- In this case. blade. made by RTM is shown in Figure (pressure. This phenomenon is preforms for resin infusion processes is how called resin freeze or resin stall out. the resin and the overall excellence of the surfaces. and Applications . Note that at 50% fiber-volume fraction The preform shown in Figure 16-4a is the penetration is extensive and rapid. 16-5. the resin will move most easily in the The preform need not be made as a single. in constructing the preform. to be avoided. At much more complicated than the simple 71% fiber-volume fraction that penetra- 2D preform used to make the hockey stick tion is much less extensive and less rapid. the an aircraft hinge. Methods. direction of the fibers.) Generally. The blades could have knitted/stitched material. of course. In gen. If the resin flow is too slow. The the preform. resin infusion proved has more crossover points and. cannot be used. Resin infusion as a function of the fiber-volume fraction. Some are. The effect of tem- fusion provided that the viscosity and cure perature can be dramatic. But even within these pultrusion. 2D and 3D braided materials.000 centipoise. tations of various options for preforms. That viscosity is a woven fabrics. and Applications . Fundamentals of Composites Manufacturing: Materials. most resin infusion then used to shape the part. To give an idea about viscosities. vinyl variation is like a combination of RTM and ester. three dominant resin types. Methods. and cured. function of the resin type. weight. In general. the molecular warp knits. and the temperature. are listed in Table 16-4. This second is done with unsaturated polyester. cloth laminates. and epoxy. 2D and 3D is 50–1.16: Resin Infusion Technologies 427 Figure 16-5. some common materials RESIN CHARACTERISTICS and their viscosities at room temperature Most resin types can be used for resin in. The normal range of viscosities spray-up (mat). many grades Table 16-3 lists some advantages and limi. much easier to use because the continuously between rollers and inject the adjustment of viscosity and cure conditions resin. It is similarly possible to move characteristics are appropriate. The Viscosity is the single most important preform materials considered are chopped or parameter. Downstream rollers and forms are are simpler. the reinforcement sheets (woven or mat) however. and stitched preforms. Methods. Preform options and their advantages and limitations with RTM or VIP (Campbell 2004). high-throughput material suited for large-area coverage Good in-plane properties Small reduction in in-plane Highly automated fabrication process properties Stitched preform provides excellent damage tolerance Poor accessibility in complex structures and out-of-plane strength curved shapes Excellent assembly aid Fundamentals of Composites Manufacturing: Materials.428 16: Resin Infusion Technologies Table 16-3. and Applications . P4 glass process and P4A carbon process) High in-plane properties Low transverse and Low crimp Good tailoring of properties out-of-plane properties uniweave Highly automated preform fabrication Poor fabric stability process Labor-intensive ply lay-up Good in-plane properties Limited tailoring of off-axis Good draping properties Highly automated preform fabrication Low out-of-plane properties 2D woven fabric process Integrally woven shapes possible Suited for large area coverage Moderate in-plane and out-of-plane Limited tailoring of off-axis properties properties 3D woven fabric Automated preform fabrication process Poor draping Limited woven shapes possible Good balance of off-axis properties Size limitation for off-axis 2D braided Automated preform fabrication process properties preforms Well suited for complex curved parts Low out-of-plane properties Good draping Good balance of in-plane and Slow preform fabrication 3D braided out-of-plane properties process preforms Automated preform fabrication process Size limitation due to machine Well suited for complex shapes availability Good tailoring for balanced in-plane Low out-of-plane properties properties Multi-axial warp Highly automated preform fabrication knit process Multi-layer. Preform or Textile Advantages Limitations Process Low-cost preform approach Lower mechanical properties Low-to-moderate in-plane properties Not used in advanced Chopped Lower fiber volumes technology applications spray-up Several variations (short chopped-fiber materials spray-up. Viscosities of common materials at room temperature.000 Window putty 100.000–70. methods of irradiating the resin have better When a core is present.000 Molasses 5. An interesting variant of normal imide resins have also been adapted for resin processing is to use an ultraviolet (UV) cure infusion processing. some provision penetration power and are just as effective.000. viscosity without shortening its pot life. it must be The infusion processing parameters for short enough to allow for economical cycle a typical resin are summarized in Table times. ture.000–10. as of UV light penetration). However. This technique is limited in the thick.000. pressure. viscosity. 16-5. centipoise Water 1 Blood 10 Kerosene 10 Antifreeze (ethylene glycol) 15 Motor oil (SAE 10) 50–100 Corn oil 50–100 Motor oil (SAE 30) 150–200 Maple syrup 150–200 Motor oil (SAE 40) 250-500 Glycerine 250–500 Corn syrup or honey 2. the CORE AND FLOW MEDIA MATERIALS part is subjected to UV light and cure takes Many (but not all) parts made with resin place. ultrasonic.000 Ketchup or mustard 50.000–10.000 Chocolate syrup 10. freeze does not occur. infusion have cores within the composite ness of the part that can be cured (because structure.000 Peanut butter 150.000.000. The high-performance material.000–250. other discussed in Chapter 12. This allows the temperature to be polyimide process is proprietary and avail- raised and therefore reduces the material’s able for licensing. The pot life is dependent on tempera. Material Approximate Viscosity. such as microwave.16: Resin Infusion Technologies 429 Table 16-4. However.000 The pot life of the resin is also important. These cores can be important. When the material has filled the mold. or radio fre- It must be long enough to ensure that resin quency waves.000–2. vacuum.000–25. must be made for the resin to pass through Fundamentals of Composites Manufacturing: Materials.000. and cure Bismaleimide and high-performance poly- additives. Methods.000 Shortening or lard 1.000 Caulking compound 5.000–3. and Applications . the amount of resin air) to escape. is to allow bagging assembly. Resin characteristics for infusion processing. The flow materials func- the resin to permeate and stay within the tion as a pathway for the resin (and for the core. and Applications . terials. The problem of is less dense than in the surrounding pre- resin infiltration is especially important in form areas. Another method is to use two honeycomb and open-cell foam materials.430 16: Resin Infusion Technologies Table 16-5. however. resin flow on the side of the core opposite the injection through the entire mold is sometimes a port can be wetted by the resin. Some common materials used in the structure will increase dramatically for flow include a screen layer in which the along with the weight and this excess resin resin can flow and layers in which the resin serves no useful purpose. If that happens. even used to improve wet-out of Several types of flow media materials are the fibers in the face sheets. the adhesive layer used to bond the Some caution must be taken. breather material does for air in a vacuum What cannot be done. it is also possible to for the resin that facilitate its movement tailor the grooves so that resin flow can be through the preform. layers of film and allow the resin to move To prevent resin infiltration in these ma. These ma- even channels through the core provided the terials have a similar function for resin as a core is not compromised by their presence. Resin Parameter Desired Characteristics Flow viscosity must be low enough to rapidly wet-out preform Viscosity Viscosity should be in 50–1.000 centipoise range Must be sufficient to allow complete wet-out of entire preform Pot life or gel time Too short—resin stalls out and leaves dry areas Too long—unnecessary cycle time duration Higher temperatures can: —Decrease resin viscosity initially —Shorten infusion time too much —Speed up cure reaction —Decrease time to 1. The flow can be facilitated through done with channels on the sides of the core or the use of flow media materials. While the grooves on or through the Another approach is to add wetting agents core can be a problem. This can be problem. Methods. Some are available only Fundamentals of Composites Manufacturing: Materials. however. resin. This will be a barrier to the flow of areas to the exclusion of the preform itself.000 centipoise limit Temperature controls Temperature controls (heating) can be placed upon: —Mold cavity —Resin mix bowls —Incoming resin lines —All of the above or only certain regions or around it so that the composite laminates Even when no core is present. between the layers to strategic exit points. managed. to honeycomb to the laminate plates should be avoid excessive resin flow through these in place. listed in Table 16-6. fraction desired in the final part and ing of the resin. • Molds must be carefully vented. pos- manufactured by resin infusion include the sibly by use of flow sensors located following. at least. burlap Resin infused with secondary bagging layer pulled off preform’s surface (creates higher permeability and lower fiber volume initially) Double vacuum bagging Vacuum eventually applied across preform to remove voids and provide compaction after resin infusion is completed Core perforations or cross-cut slotting (saw cuts) in core material Perforated. Flow media material enhancement for infusion processing. and removing the without resulting in excessive meeting part.16: Resin Infusion Technologies 431 Table 16-6. • Gating needs to minimize flow paths injecting the resin. slotted cores Creates z direction resin flow to opposite sides of core for complete wet-out under license and others are commercially of resin fronts (decreasing the potential available from standard suppliers. Flow Media Type or Approach Generally Observed Effects Open side of omega tube allows rapid resin flow through tube and lateral flow across the preform Omega tube or perforated tubing surface Perforated holes in tubing act in same manner Spiral cable wrap also a typical substitute Rigid and semi-rigid screen materials used to increase permeability for resin flow between layers Screen materials Materials of choice: plastic mesh. PART DESIGN FOR RESIN INFUSION • Provision must be made to determine Some considerations for design of parts that the mold is completely filled. in • Flow is better in the plane than across the prototype so the flow model can be the plane of the fibers. Fundamentals of Composites Manufacturing: Materials. tool but cannot have large void areas • Consider automation in making the pre- where resin will accumulate. and Applications . strategically in the part (or. • The preform must fit easily within the • Design the mold for easy part removal. accurately made). • Large parts require long flow times. placing the preform in the mold. make the preform accordingly. form. window screen. • Estimate the amount of fiber volume which may require filling and backfill. Methods. for poor resin knitting). to make a part using resin infusion. To form against the inside wall. sliding molds were required. and Applications . Attempts rosion layer. Cen- tools were of epoxy with a nickel coating. termine the relative costs and production The early prototypes were tested for di. the fi- along with the low-cost mold materials. Dodge Viper® Resin infusion is the principal method of SUMMARY manufacturing the major body panels for the Table 16-7 provides a convenient sum- Dodge Viper®. in making these comparisons as it illustrates Fundamentals of Composites Manufacturing: Materials. RTM may even prove to be the method by which standard production CASE STUDY 16-1 prototypes are made. Some manufacturers use this versus the large 3. especially for those models having Resin infusion can be compared with a relatively small production volume. Methods. mobiles. others have re- be the most important advantage of all as ported that the sand cuts the reinforcement the needs for small runs of products to meet fibers and. therefore. This method builds the sides. development CENTRIFUGAL CASTING time for the first production parts was greatly reduced compared to traditional Centrifugal casting is not usually con- manufacturing methods. The up the tank in reverse order so the structural outer skin was an especially difficult part layers are created first. Fillers can be added easily during centrifu- The use of RTM allowed the entire pro- gal casting. This.000 MPa) method effectively for large fiber reinforced presses needed for metal stamping. tions. In this method. from original concept to that adds weight and lowers cost. These pa- partnership with the paint supplier and the rameters differ somewhat from those of other body-panel manufacturer. spinning mandrel that uses the centrifugal The Viper hood was the largest part and force generated to push the resin and fibers required the most complex tooling. The last is the cor- because of the high gloss required. capabilities. Fiber angle is usually random with the low-cost RTM tooling were not suc- because the fibers are often blown into the cessful so a change was made to metal sheet inside of the structure. Sand is one commonly used filler duction process. Saving time may prove to with sand fillers. plastic (FRP) tanks. molding compound (SMC) tooling. Because these adjustments could be made in the original tool set. results in significant market segmentation requirements contin- loss of strength. Eventually the sidered to be a resin infusion process. Chrysler and its composite molding processes and so they partners believed that RTM would become should be carefully considered when choosing a major manufacturing method for auto.000–2. However. kept bers and resin are applied to the inside of a investment low. The other composite molding processes to de- Viper fit that niche exactly. Some per- production automobile. it formed a typical for resin infusion processes. Because this car was the first mary of the various processing parameters RTM application for Chrysler.700 MPa]) presses ment winding.000-ton (41.432 16: Resin Infusion Technologies • Maintaining the seal on the mold The mold was adjusted and smoothed until throughout the injection and cure cycles these parameters were within the specifica- is important. to be done in less formance benefits have also been reported time than usual. trifugal or spin casting of pipes and tanks is The production was done using low-pres- common although not as widely used as fila- sure (150–200-ton [2. ues to increase. Figure 16-6 is especially helpful mensional accuracy and surface smoothness. resin could gel during fill period 20–28 in. Preform etc.) tend to maintain integrity shape and integrity Fundamentals of Composites Manufacturing: Materials. RTM or VIP Potential Effects on Processing or Structure Process Parameter 50–1. damage mold. lightly tacked layers. low fiber volumes.000 centipoise typical processing range for viscosity Processing at 10–100 centipoise. RTM and VIP processing variables and their effects (Benjamin and Beckwith 1999).16: Resin Infusion Technologies 433 Table 16-7. higher temperature also typical Resin viscosity Higher viscosity—preforms often hard to wet out Lower viscosity—more rapid infusion may leave dry areas and voids Too short—resin fails to completely fill preform Resin pot life Too long—process cycle lengthened unnecessarily Helps drive resin into mold and preform Applied too fast—may move preform out of position within mold Resin injection Too high—may cause “fiber” wash of preform.) tend to “wash” and move around the mold cavity reinforcement Tight preforms (braids. textiles. Hg typical process range Helps pull resin into mold and preform Resin injection Aids in reducing void content through part vacuum level Assists in holding mold halves closed Aids in removing moisture and volatiles Commonly used to ensure more complete wet-out of preform structure Multiple injection Sometimes used sequentially to fill long or large-area parts (“pumping” ports action) Rubber/elastomeric inserts have high expansion (high coefficient of thermal expansion [CTE]) Often called “pressure intensifiers” Internal rubber/ Used to provide internal compaction pressure elastomeric tooling Higher fiber volumes (>65%) achievable Low void contents are typical (<1%) Tooling must be more robust to handle induced pressures Infusion pressures usually below 100 psi (700 kPa) Closed mold Pressure often increased to 100–300 psi (700–2. tooling. stitched. pressure or blow seals Too low—cycle times long. etc. Methods.000 kPa) range after pressurization resin wet-out Decreases microvoids by collapsing bubble cavities Sizing or coupling-agent chemistry must be compatible with selected resin Fiber sizing or Sizing level (if too high) can reduce resin flow (lowers effective coupling agents permeability) Loose preforms (chopped fiber. fabrics. and Applications . if that is be better. However. cross-cuts. resin infusion has the potential mold release to the glass plates or use a for making parts with higher mechanical film that can serve as a release layer. Hence.) Molded-in inserts Inclusion and co-curing entirely possible with RTM and VIP processes and fittings Resin flow around can leave dry areas and voids the regions of applicability for several of the LABORATORY EXPERIMENT 16-1 processes in terms of the production volume Objective: Mold a ping-pong paddle us- and part-size considerations. that can be used. pore holes. This is plunger to make the injection. Be sure to put in a and even compression molding.) are acceptable. Apply mold. etc. energy. 5. record the filling pattern as a function Fundamentals of Composites Manufacturing: Materials. which uses path for air to escape and for resin to shorter fibers because they must move in the overflow when the mold is full. bottom halves are glass plates and the Another method of comparing resin infu. ing RTM. (A nice shape that can be used. As expected. and time to Fiber volume wet-out preforms Commercial market—usually 25–55% fiber volume Aerospace market—usually 50–70% fiber volume Foam and balsa core materials used extensively Open-cell and honeycomb core materials require method for Core materials preventing resin flow into cell structure Closed-cell cores typically have some inherent resin path to opposite sides (flow media. Still another method of comparing the 4. Higher fiber volumes usu. are economic competitors to resin infusion. Make a mold in which the top and ing and thermoset filament winding. perimeter of the mold is a metal pic- sion processes is by the length of the fibers ture frame construction. Methods. parison. So it has wider applicability 2. 1. (Continued) RTM or VIP Potential Effects on Processing or Structure Process Parameter Resin flow permeability is inversely proportional to fiber volume Higher fiber volumes (>60%) require more work. use a metal pipe and a of using fiber volumes of up to 70%. Resin infusion has the capability not available. Make a preform for the paddle and a or compression molding—two processes that preform with a core for the handle. Resin infusion has the for the mold is that of a ping-pong advantage that fibers of almost any length paddle. RTM is seen to fit nicely in the area Procedure: of fairly large parts and production volumes. it is close to compression mold. performance than either injection molding 3. Note and higher than any other process. Make an injection port at the center of than injection molding (short fibers only) the bottom plate.434 16: Resin Infusion Technologies Table 16-7. Use a commercial RTM machine to ally mean that mechanical performance will inject the resin. and Applications . In this com. Obtain some RTM-grade polyester processes is by the fiber-volume fraction resin. Set the ratio for cesses achieve higher fiber volumes? initiator to resin at about 1. Methods. Remove the part from VIP processes and why they are im- the mold and trim. Fundamentals of Composites Manufacturing: Materials. of time and pressure. Discuss at least six of the key process 6. What do preforms do for composites QUESTIONS and why are they an important aspect 1. 4. 6. What is the key similarity between structure with a complex shape for an an RFI process and a SCRIMP™ or aerospace application is to be produced. Comparison of RTM to other composites manufacturing processes with regard to part volume and size. The resin should SCRIMP-like process as far as resin be fully initiated if the plunger injection infusion? system is used. Assume that a 60–65% fiber volume 2. What are TERTM and RARTM and what is used. and Applications . If a commercial system 3. allow the variables pertaining to the RTM and part to cure. portant.8%.16: Resin Infusion Technologies 435 Figure 16-6. When the injection is complete. 5. put the initiator in the small key material aspects make these pro- tank on the machine. Discuss the basic differences between of resin infusion technology? RTM and VIP infusion technologies. 1997. 2005. William P.sme. Rowan. Product. Explain how each would be used in the process. Germany: Hanser Publishers.org/cmvs. and Process Engineering. Mazumdar. Resin Transfer Mould- ing. 1998. 2000. CA: Society for the Advancement of Plastics Engineering (SAMPE). Discuss whether pot life should be short or long in resin infusion and how that might affect cure time. 2002. Dordrecht. www. be fabricated for a specific resin infu- sion process of your choice. 1999. Scott W. Resin Transfer Moulding for Aerospace Structures. Sanjay K. 3.). Methods. Resin Transfer Molding: SAMPE Monograph. “Liquid Molding. Composites Manufacturing: Materials. Boca Raton. Teresa M. and Applications . select (identify) at least three materials Dearborn. 2004. 1999. and Paton. Manufacturing Pro- cesses for Advanced Composites. Covina. No.” NY: Elsevier Advanced Technology. Chapter 9. Composites Design Manual. Munchen. F. Potter. Lancaster. that might be selected and explain why. Parnas. Richard S. 8. Liquid Compos- ite Molding. Quinn. Visit a home improvement center and Composites Manufacturing video series. FL: CRC Press. MI: Society of Manufacturing or methods by which flow media might Engineers. BIBLIOGRAPHY Benjamin. What is the effect of temperature in resin infusion processes? 10. Kruckenberg. C. Fundamentals of Composites Manufacturing: Materials. “Liquid Molding” DVD from the 7. Campbell. Kevin. and Beckwith. Why is resin viscosity important in resin infusion processes? 9. James A. (ed. PA: Technomic Publish- ing Company.436 16: Resin Infusion Technologies Discuss the type of preform and process Society of Manufacturing Engineers (SME). NY: Chapman and Hall. The Netherlands: Kluwer Academic Publishers. is spools through the system. long axis of the mandrel as the fibers are Fundamentals of Composites Manufacturing: Materials. (Consult the “Filament Winding” mounted on a carriage or some other trans- video. Then the mandrel (to which the fiber strand has fiber placement. the turning of that expand on its original capabilities. drel. even then enters a resin bath where the fibers are some that could not reasonably be made with soaked with resin. the most important process been anchored) pulls them from the fiber development beyond filament winding. with initiator or hardener so that the only The two filament winding methods that requirements to cure the part are heat and are the focus of this chapter wrap fibers time.) • Process overview • Filament winding FILAMENT WINDING • Variations in filament winding The basic filament winding process can be • Fiber placement understood by referring to the illustration of the standard filament winding machine shown in Figure 17-1. that the fibers be manually fed through all This chapter examines filament winding the parts of the system. which leads to other important varia. The band be used to make highly complex parts. At initial startup. Methods. and then Filament winding is the most important strands from many spools are gathered to- of the composites processes in terms of the gether and fed through a comb or similar number of users and the total number of alignment device so they make a band of fi- parts made. including some related processes been fed through the system. SME 2005 for a look at the equipment port system that moves laterally along the and the techniques of filament winding. The fiber spools are PROCESS OVERVIEW mounted on a rack.1: Introduction to Composites 437 17 Filament Winding and Fiber Placement CHAPTER OVERVIEW These videos are excellent supplements to This chapter examines the following lectures and laboratories and for general concepts: education for those not familiar with this process. After the fibers have in detail. The payoff is explored. called a creel. The resin is fully activated filament winding. The methods differ in the device called a payoff. Fiber placement is a more bers. the process requires tions in the process. The fibers then go through a roller or (with resin) around a mandrel (a core) as wiper system to remove the excess resin and the method of shaping the fibers and resins then through a ring or some other directing prior to curing. The payoff directs the way the fibers are placed against the man. fibers onto a mandrel. and Applications 437 . The number of strands brought together recent development and is a method that can determines the width of the band. therefore. and Applications . sometimes also called circumferential windings or axial windings. They also impart torsional strength and speeds of the mandrel and the payoff and bending strength. The hoops circle the mandrel Layers of helical and hoop paths can be in paths that are approximately 90° to the added successively on top of one another. in place and give strength to the ends of the tern are determined by the relative motion part. Helical windings can system. eventually posite shapes made by other processes. Heli- mandrel to produce patterns of fibers on cal windings are important to hold the hoops the mandrel. from one As shown on Figure 17-2. The angles of the fiber pat. and helical be seen in Figure 17-2. Filament winding machine. that is. Methods. These wind- directions of fiber paths are: hoop wind. Fundamentals of Composites Manufacturing: Materials. They move next.438 17: Filament Winding and Fiber Placement Figure 17-1. They are like hoops is possible to have one layer at one heli- around a barrel. The sequence and angles of the layers from one end of the mandrel to the other in are determined in the same type of laminar continuous loops that are slightly offset from design system used with other laminar com- the previous loop and. windings. being drawn through. be placed at an angle of 0°. ings are sometimes called longitudinal ings. In fact. The helical paths are at all angles layers that change angle from one to the other than approximately 90°. These can all windings or radial windings. The payoff motion create a layer of material that covers the is synchronized with the turning of the entire surface of the part being wound. Hoop windings are impor. It long axis of the mandrel. the two general end of the mandrel to the other. cal angle and then the next layer at some tant to give radial strength to the part being other angle. it is common to have wound. • It does not have to be round to be ture or in ovens or autoclaves. Pipes. flywheels. if the part cannot be cooling-tower coupling shafts. they are usu. of cure. and similar shapes are most commonly made by filament winding. begin with the metal tank as the mandrel and over- wrap with the fibers and resin to impart additional strength. oars. the mandrel simply remains and is not removed. will not sag to the bottom of the part as the chemical storage tanks. air tanks for firefighters. When parts are cured. aircraft waste removed after curing. winding process include the following: ally continually rotated so that the resin low. it can be wound. However. Fundamentals of Composites Manufacturing: Materials. motor cases. rocket- end of the part. wind-surfer masts. the mandrel is turbine blades. missile launch tubes. there may cycle frames. Filament winding patterns. and wind- ended like a section of pipe. according to the laminate’s design. is cured. Clearly. the parts are hung vertically so that drive shafts.and high-pressure pipes. rotate. All. the part • If it is round. natural gas tanks. must have an axis of rotation. however. Alternately. transmission rotated. depending wound. filament winding are important to a wide cal extraction device is usually required variety of markets. on the size of the part and the nature of the Some typical parts made by the filament resin. This is done with the mandrel in place. tanks. Even so. compressed the resin distribution is even around the cir. water tanks. Methods. Several of those techniques will be discussed later in this chapter. the mandrel is fuselage and wing sections. reverse osmosis resin viscosity drops during the initial stages tubes. golf shafts. the mandrel is removed by some other tech- nique. streetlight and utility poles. and Applications . scuba tanks. bi- cumference of the part. pressure vessels. such as tanks for firefighters. If the part is open. industrial rollers. In normal practice. complicated shapes can be made. The use of a mandrel to shape the fibers and resin means that the general shape of most parts made by filament winding is cylindrical (approximately circular in cross-section). A mechani. radomes. the parts made by usually just pulled out one end.17: Filament Winding and Fiber Placement 439 because the draft angle from one end of the part to the other is usually small or non- existent and thus a strong pulling force is required to extract the mandrel. boat be some sagging of resin toward the bottom masts. Some parts. helicopter rotor shafts. Parts can be cured at room tempera. If the part is close-ended like a pressure vessel. In cases like those (and others that will be discussed). Two statements summarize the capabilities of When the winding has been completed filament winding with respect to shape. by allowing the payoff head to move vertically or twist and Figure 17-2. Labor changes in the curing cycle to allow for better requirements are low. resin flow during the curing phase. are dependent the tenacity to be pulled through the system. The void content can be uses fibers and resin in their lowest-cost reduced by increasing the tension on the fibers forms.) designers expect about 3% void content. used in filament winding. Most filament winding composite part and not a mandrel or mold. might have one-tenth the production rate in function to the mold in other composite of filament winding and. it often mance applications. the being wound. but options allow many parts and drip excessively from the part as it is to be made simultaneously. is a over the void content of the parts made by continuous process that uses a die to form the filament winding. but Filament winding is one of the lowest-cost this can be as high as 10% in high-production composites manufacturing processes. In addition. The continu. Adding pressure during the productivity is high so the cost of the ma. largely non-automated processes can make Like most of the other composite processes parts that are much more varied in shape discussed in this book. Slower speed allows for tighter control which is discussed in a later chapter. higher production costs. However. such as hand lay- The mandrel in filament winding is similar up. That is. Therefore. and ultra-high- hr).000 lb/hr (136–1. Complex parts and those intended for molecular-weight polyethylene (UHMWPE) high-performance markets like aerospace are fibers are also widely used. however. The filament winding machine Resins can be too low in viscosity. but that requirement chopped mat. aramid. the per.360 kg/ but carbon/graphite. A possible exception Because the filament winding process is could be the case of staple fibers that have automated. Manufacturing Processes Non-automated processes. Reinforcement Fibers ous nature of the filaments means that the Almost any of the normal reinforcement strength and stiffness of filament-wound fibers used to make composite parts can be parts are excellent. than a mold. is rarely a limitation. Also. however. can be costly. is that the system with which the fiber angles must be con. Therefore. Fundamentals of Composites Manufacturing: Materials. upon the part’s complexity and the precision More likely. these spray-up. usually only one op. simple parts. The fibers need formance of parts is usually better than to be strong enough that they can be pulled similar parts made by spray-up or with through the system. Fiberglass is the most common fiber the range of 300–3. and Applications . such as pipes. time on each mold or mandrel. of course. the fibers and so filament winding could still are often wound at fiber lay-down rates in be used. and resin transfer molding (RTM). As will operations and below 1% in high-perfor- be discussed later in this chapter. could be adjusted for the weak tenacity of trolled. erator is required per machine. a mea. Methods. staple is a natural fiber. (Pultrusion. the cost of molds or tooling is low during winding and by lowering the resin as mandrels are almost always lower in cost viscosity so that the fibers are well wetted. the cost of parts made by filament winding Filament Winding Materials is about one-quarter to one-half the cost of parts made by manual lay-up. much manufacturing processes such as hand lay-up. cure will also reduce the void content as can chine can be spread over many parts. However. If the easily obtained. filament winding is and complexity than the parts that can be a batch process. one part is made at a made by filament winding. Fiber lay-down rates. it might not have sure of the processing speed.440 17: Filament Winding and Fiber Placement Comparison to Other Composite often fabricated at 10–200 lb/hr (5–90 kg/hr). manufacturing efficiencies are been made into a continuous filament. technique gives fast lay down of fibers but Another problem with the long times fiber wet-out is difficult and void contents involved in winding is the volatility of some are high. If the viscosity of tows or rovings that are gathered together. The continuous strands. especially esters. The form toxicity of some resins. the fibers ing are normally chosen. low-performance pipe and low. A typi- permits rapid lay-down of the fibers. therefore. contributor to the overall favorable econom. These grades are used in filament winding are continuous. human exposure directly from the spools. This means that volatile pressure requirement tanks. tinue to be rotated while being cured. balanced for viscosity. Some Regardless of the type of resin. ply to have a heat-activated initiator. and Applications . When they are in an of fibers used is untwisted. pot life. This remain low.000 centipoise. grades that manufacturers have solved this problem by are designed specifically for filament wind. Not only must the material chopped fibers can be sprayed onto the not appreciably cure. where styrene is a inexpensive. smoothly with a wide band. for large parts. although other thermo. Methods. part and possibly leaving some fibers insuf- eter. the parts are usually moved into ovens or mally used in composites manufacturing can autoclaves for curing. this is fine. many parts may be application. major component. The cal range of viscosities for filament winding width of the band is a function of the number resins is 350–2. but its viscosity must mandrel during conventional winding. the resin bath may be used for a considerable ous fibers are being applied. This is the least to harmful vapors is a potential problem that expensive form of fibers and. gases are being released for a long period No preforms or other special fiber shapes of time. and reactivity. However. often pass quickly through the resin bath ously so that a band of fibers is applied to and this means that resin must penetrate the mandrel. is a must be dealt with properly. For example. have precise fiber alignment can limit the which could result in it dripping off the width of the band. Therefore. One method to extend the pot life is sim- ics of the filament winding process. such as polyester. length of time. fiberglass mat is manually wound from the same batch of resin and so laid against the mandrel as the continu. In this part to be wound. continuous fibers open bath for long periods. is much lower than 350 centipoise. It is used almost exclusively for resins. Equally troubling is the potential are required for filament winding. oven or mon resins are unsaturated polyesters. They are pulled from spools through the thus they are suitable to the unique require- wet-out system and onto the mandrel in ments of the filament winding process. The pot life of the resin needs to be long One variation of the filament winding because it may take considerable time for a process uses non-continuous fibers. small-diam. and epoxies. with the requirement that the part con- sets and some thermoplastics are also used. vinyl autoclave heating can be difficult. Almost all types of thermoset resins nor. This means the crosslinking reaction will not Resins begin until the part is heated. The most com. the resin The complexity of the part and the need to will flow excessively when on the mandrel. heating with heat lamps. The fibers are gathered together and fed simultane. closed-end vessels are difficult to wrap ficiently wetted. This multiple-strand method the fiber bundles quickly and easily. Alternately. While this solution Fundamentals of Composites Manufacturing: Materials. For many applications be used in filament winding. viscosity is generally comparatively low so normally several strands (tows or rovings) that wet-out of the fibers is good. Also.17: Filament Winding and Fiber Placement 441 In the vast majority of cases. As previously indicated. For example. not only as a method to or prepreg winding. increases that the resin itself react quickly. it and cost of the part but adds little to is desired that it cure quickly. most manufactur. the uniformity of the heat must be be resin-rich and that wastes money carefully adjusted. Prepregs • Mechanical rollers or squeezers can be To avoid some of the problems associated placed in the resin bath to force the resin with using a liquid resin. the resin should be highly reactive. but also as a way the problems associated with liquid resins to control the amount of resin on the are eliminated. rarely done successfully. If there is too much. filament winding into the fiber bundles. therefore. and cure operations limits the ability to reduce the viscosity greatly. since the excess increases the weight When the resin does begin to cure. the wet-out of fibers winding. Moreover. of heat and shear. some throughout the winding operation. However. it reduces the throughput initiator react quickly. While this is ultimately the course usu- To achieve this reactivity requires that the ally followed. There are some alternatives that be done in an analogous way to thermoset might be used to ensure good fiber wet-out wet winding.442 17: Filament Winding and Fiber Placement is simple. If they did. extruder to apply the resin to the fibers and thus achieve both the advantages of wet • While it is theoretically possible to use winding and the ease of melting using an ex- smaller bundles of fibers. the fiber truder. Methods. The latter total cost. However. there is no fibers. The resin must be When using a liquid resin and depending melted and maintained in a molten state on the resin bath to wet-out the fibers. This is called dry widely used. resins The use of molten thermoplastic resins must be balanced for both pot life and high in wet-winding operations is difficult and reactivity. the part will need to mix the resin and the initiator. requirement can make the pot life require- ment difficult to meet. This is inherent difficulties arise. There. With Fundamentals of Composites Manufacturing: Materials. Therefore. thus give more time in the resin bath. just as the wet-out of fibers manufacturers would be reluctant to is likely the factor that limits throughput in make special bundles just for filament traditional wet winding. The first and most difficult because of the heat involved and the obvious problem is that some fibers might long times that are usually required. it is possible to use an in the resin bath. most of encourage wet-out. the resin viscosity throughput. This will its performance. the price of such with thermoplastics applied by an extruder fibers would likely increase. reduce the resin’s tendency to drip or sag • The winding speed can be reduced and during the early part of curing. it may also require of the machine and. or any other wet method would severely limit • As already discussed. have high viscosities so wet-out is extremely tion of having the resin stay in place difficult. and Applications . the limita. as is done in an extruder. thermoplastics could continue to soak into the fiber bundles are more easily melted with a combination after they leave the bath. Ther- not be wetted in the time that they are in moplastics might begin to degrade under the bath. This method is can be done with prepregs. While it is possible that the resin these conditions. With prepregs. ers prefer to be assured that the wet-out is rather than in a heated resin bath as might complete. Molten thermoplastic resins could be reduced. However. fore. even when the speeds of the fiber on the fibers throughout the winding through the wet-out zone are slow. and resin dripping of the materials at lay-down. This could. However. A touching the mandrel (or underlying mate. which erodes the performance of the part It is also advisable to heat the underlying over time. Perhaps the biggest advantage is paction to allow intermingling of the resin the increase in winding speed possible with molecules across the boundaries of the layers. Pigments and other to the mandrel or underlying layers. This is done with heat lamps. the issues of fiber wet-out. tend to slip. and Applications . and a few additional considerations. prepregs have all of the advantages and and might have a faster curing (consolida- the disadvantages of thermoset prepregs tion) time. the layers must be compacted dur. or similar high-intensity heating methods. These thermoplastic resistant (depending on the type of resin). flow control agents and underlying layers of material when (surfactants) that help prevent the resin applied. in the thermoplastic resin. nied with compaction. as from a roller. Therefore. heating of the part after winding may not sus the liquid resin and the need to compact be necessary. be a tre- the prepreg during cure. However. present with thermoplastic prepregs. the thermoplastic pipe. of sharp sand particles to cut the fiberglass. when they are applied and cure can be useful. to anneal the part molecules in one layer do not mingle with after winding to get the desired crystallinity the resin molecules in other layers. prepregs. they have almost rect defects or damage. It prepreg are laid onto the mandrel. This compaction must occur during thermoplastics for filament winding. When the bands of mendous cost advantage over thermosets. then The biggest disadvantages with prepreg compaction might be adequate and additional winding are the higher cost of the prepreg ver. There is no need to wet-out the If the melting of the thermoplastic done just fibers and so the time to wind is limited only prior to lay-down is complete and accompa- by the action of the machine. The problem of compaction that was nated. materials just prior to application of the resin viscosity. or its equivalent discussed with thermoset prepregs is also with prepreg. lasers. off the part during winding are all elimi. Fundamentals of Composites Manufacturing: Materials. tion might arise as to why anyone would use ing cure. pot life. can be remelted to cor- used in filament winding. of course. With the difficulties involved. add sand during the winding opera- prepreg is usually heated just prior to its tion to give bulk and weight to the part. Methods.17: Filament Winding and Fiber Placement 443 no resin bath. The thermoplastics have When thermoplastic resins have been higher toughness. they Additives are slightly sticky at room temperature. prepreg to further improve the stickiness removing excess resin. More. over. Most filament winding is done without Therefore. It is Prepregs contain initiated resin and so they even more critical because the thermoplastic can begin curing unless the initiator is heat resins are higher viscosity and need the com- activated. Thermoplastic prepregs are not from dripping off the part during winding tacky. the ques- Therefore. controlling resin/fiber ratios. they will stick to the mandrel additives. be totally ignored. Ther- moset prepregs are tacky. that is. can be more solvent always been prepregs. out time. the resin may be necessary. however. Some applications. there is air trapped between the layers. problem with this practice is the tendency rials). especially low-cost To solve this problem. This makes winding difficult. they minor additives also may be used. The the initial phases of cure when the viscosity answer is that it is rarely done but there of the resin drops because of heat and before are some property advantages that cannot the viscosity rises because of crosslinking. is still a problem. After the part is wound and cured. The mandrel serves the function it to melting point. Three of the most Meltable materials used for mandrels include important considerations regarding the polymers. Dissolvable and meltable mandrels are especially useful for parts that have complex 1. The metal gives some strength surfaces and are often slightly tapered to the plastic and provides some chemical to facilitate easy removal of the part. it must meet higher temperature used to melt the mandrel. polished material. but this is less com- 2. cure temperature. This extrac- by breaking it out. The interior support structure tank to weigh less than an all-metal tank. rocket-motor casings. low-melting metals. for natural-gas-powered vehicles. the mandrel is molded at a size Another type of removable mandrel is (diameter) that can be easily removed from made of a solid material. such as sand. Other types of metal liners are For close-ended parts.444 17: Filament Winding and Fiber Placement Mandrels such as polyvinyl alcohol. Just as with molds. end vessel. Further. numerous requirements. technique. Of course.the simplest man. mandrel removal overwrapped with composite material to is more complicated. give strength to the liner. and Such tanks are used to hold air for scuba the mandrel is then taken out of the part. impregnated fibers are wrapped. the tolerances on a mon today because of the danger of damage mandrel are reflected by the parts to be to the parts. the melting of a mold and therefore defines the internal point of the mandrel must be higher than the geometry (shape and surface) of the part. Such might be a major consideration as far as liners are used for applications such as cost and maintenance are concerned. A the mandrel has an axial shaft that allows similar concept is to use a meltable mandrel it to be held and rotated by the winding that can be removed after curing by heating machine. these mandrels are simply dissolved away. For open-ended parts . the the most common. Typically. which the access hole (polar opening) of a closed- is held together by a water-soluble binder. from the mandrel after cure and this Sometimes the mandrel is made out of a removal often means that the mandrel thin. Another drel is usually the best for part removal example of a mandrel left inside a tank is and cylinders of steel or aluminum are the aircraft waste tank. The mandrel might be used for hun- shapes that prohibit easy removal by sliding dreds of parts. the machining of the mandrel ply left inside the part after curing. Fundamentals of Composites Manufacturing: Materials. These cylindrical plastic liner is combined with a thin metal mandrels must have smooth. In this not practical. salts. One method is a col. the materials used Because the mandrel is critical to the to make the part must be able to withstand the filament winding operation. collapses. brittle material that can be removed is mechanically extracted. Each part is removed the mandrel out. mandrels tion often requires that the mandrel be made of plaster were used for years to make strong and tough. resistance. divers and firefighters. the mandrel is sim- required. and eutectic mandrel are the following. Soluble salts are The mandrel is the tool around which the also used. When close tolerances are In still other cases. somewhat like an umbrella. In this case. Methods. Collapsible mandrels also can be used in One of the most important new meth- open-ended parts when the size of the part ods of mandrel removal is to use a shape is such that mechanical removal by pulling is memory polymer for the mandrel. For example. and Applications . made on it. the high-pressure tanks that contain fuel 3. This allows the lapsible type. The mandrel made to ensure that the expansions are is then used for winding as normal. the part is cured. machine and part assembly rest must be ed to a temperature that will allow the mol. the wrapping process. The chilling locks the molecules in the part and the mandrel should be place in their expanded state. Further. such as pipe diameters. or low depending on its complexity and tial sagging occurs especially in parts the ease of part removal. To compensate for the increasing drel. and reheating can be elastomeric material is squeezed dur- done many times with the same mandrel. of course. able to support the loads. such as poles. The machine many sizes and are specified by the length of must be able to rotate such a part eas. pressure on the mandrel also increases. • There is generally a change in the diam. Not is increased as winding progresses. The mandrel must not ex- the winding is complete. This is espe. important. Then it is quickly • A calculation of thermal expansion of chilled. The most common type of filament winding • If the part is large and especially when machine is the basic machine shown in Figure the mandrel is heavy. the accumulated stand curing temperatures. especially if thin. It should not ecules of the mandrel to move. These basic machines are available in becomes a major concern. expand. of the mandrel before winding.17: Filament Winding and Fiber Placement 445 First. the mandrel is expanded to the of concrete) will support the load. chilling. Fundamentals of Composites Manufacturing: Materials. but thick which allows the mandrel molecules to again parts are often a problem. after curing. After compatible. winding. cost is a consideration. One method soften. and remain inside the part such as plastic each of these requires a different man- liners. A company may have many different cially true with mandrels intended to part sizes. The cycle of heating. Thus the floor on which the entire determines the maximum length of the part. While at that be assumed that the floor (even if made temperature. slightly. which ily. expansion is to put a layer of elasto- This will. If the sagging is too much. As the thickness • The mandrel must be able to with- of the part increases. mandrels for these types of that might be used for part removal applications have interior pressure that might lead to very costly mandrels. the part weight 17-1. • Even though one mandrel will be used The constriction pressure could cause for many parts. The mandrel will then shrink back of dealing with the problem of thermal to the shape it had when it was first molded. only is the cost of the mandrel itself • The mandrel can sag because of gravity. The part will expand are heated to above the cure temperature. size desired for winding. the spindle that can be accommodated. The ing. and Applications . ing the curing process by the expansion Considerations involving the mandrel of the mandrel and thus protects the include the following. wrapping of the part could be adversely Filament Winding Machines affected. part from internal expansion pressure. pand so much that it damages the part Then. the mandrel to collapse. the shape memory mandrel is heat. Another method is simply to choose an eter of the mandrel with the pressure of alternate material for the mandrel. but the cost of using a par- Sometimes the part diameter is small ticular type of mandrel might be high and the length is so great that substan. allow it to be extracted meric material over the outer surface from the part. the part and mandrel wound around it. Methods. the elaborate methods pressure. which determines operation because there is no carriage that the maximum diameter of the part. The band is moved wound onto the mandrel. the fibers are fibers on the mandrel. An. More details about the possible axes of mo. Even more axes of motion are possible. the ditional mandrels was relatively inexpen. espe- fiber placement is discussed. A different type of filament winding ma. lay down of the band over the curved ends of Tensioners are usually mounted on the creel tanks. Polar machines are simple in fixtures and the machine. polar One innovation to the basic machine that machines are less common than standard has already been mentioned is the addition filament winding machines. This problem can be controlled through the other common axis of motion is achieved by use of tensioners. They are also faster than stan- can vary over a wide range. or carriage. Therefore. path by manually moving a sensing device modated on existing machine bases. this change could be accom. Methods. A controller links the carriage speed. Machines with 30 precise and complete coverage of the layer spindles are commercially available. mandrel rotation speed. This also allows improved tem is used to apply tension to the fibers. The size of the machines are avoided.and four-axis machines are becomes slack and automatically apply ten- the most complicated that are routinely used. sion to adjust it. However. winding machines realized that adding ad. the mandrel is mounted vertically in Winding is done from one end using low- this machine and a rotating arm winds the angle winding. which is located across the surface of the machine by tipping inside a ring. and Applications . The most common because the standard machines are more additional axes are for the payoff device to flexible in the types of parts that can be move perpendicular to the plane of the man. of varying surface thicknesses to be wound The slow down in winding that occurs more easily. In this method. end as for a closed-end pressure vessel. Polar machines cannot make parts drel. This is because the principle change motion so that the desired fiber paths can was simply the addition of the turning be laid down. but is most helpful in laying when the fibers go around a closed-end down a smooth band when making a curved vessel can cause the fibers to become slack. simple product.446 17: Filament Winding and Fiber Placement and by the clearance of the mandrel holding the mandrel. A valuable feature available on many If the parts being made were not too large controllers is the ability to input the fiber in diameter. made. the problems lengths range up to 100 ft (30 m) or beyond associated with the ends of the mandrel for special orders. They sense when the fiber line although three. After making as many input stops as possible are the space required (diameter of desired. Then the con- power from linkages. A controller is an important part of the tion will be given later in this chapter when modern filament winding machine. the controller can smooth the path the parts). dard horizontal machines. Typi. and other axes of sive. Some type of brake sys- rotating the payoff. the makers of filament more than just a single. to be applied. This is largely of other axes of motion. This in-and-out motion allows parts that differ greatly from spherical shapes. the possible limitation in turning and display it for verification. cially when the machine is to be used for Several years ago. Winding must be reversed. The over the surface of the mandrel in a desired major limitations on the number of spindles path. The ring rotates and applies Fundamentals of Composites Manufacturing: Materials. fittings that hold the additional mandrel. Another type of machine makes a continu- chine is the polar winding machine. cally. ous pipe that is on an open-ended mandrel. and the normal loads troller can calculate the paths that will give associated with turning. To accomplish this feat requires Figure 17-3. hoop windings the polar machine. to the preceding wrap with no gap between off slowly. Because of that difficulty. Such ar- burst strength that would come from higher eas also may be points of crack initiation. become areas of weakness since they do not ously. This type of pipe does not have the have reinforcement in those areas. Winding pattern conventions. angle (hoop) winding. angle is measured from the bandwidth to the However. because of the specialty nature of axis of the part. scribe the helical pattern. the next helical slanted surface. to the other and then back again. some conventions have been es- Winding Patterns tablished for the critical parameters that de- The basic winding patterns for the stan. cult to apply and describe. No gaps like a braiding operation. The on the more common standard machine. but it is sufficient for Helical windings are much more diffi- low-pressure systems. This convention is that one complete circuit is includes areas that are slightly divergent or a full traversing of the part from one end convergent as well as shapes that are non. Methods. wrap must be applied immediately adjacent The hoops are applied by moving the pay. The full circular cross-sections such as square beams back-and-forth motion of a complete circuit or oval tubes. this discussion will focus would have a winding angle near 90°. Therefore. The winding polar machine (polar) have been identified. This is somewhat fiber band next to the previous edge. The hoops have a tendency to is shown in Figure 17-3b. Fundamentals of Composites Manufacturing: Materials. Those conventions dard machine (hoop and helical) and for the are illustrated in Figure 17-3a. slide when laid on a highly curved or highly After one complete cycle. and Applications . winding angle is important to resist forces Hoop windings are applied to the portions that might be applied to the part. Another of parts that are essentially cylindrical.17: Filament Winding and Fiber Placement 447 the fibers onto the mandrel as the mandrel should be just enough to put one edge of the moves away from the ring. The lateral movement of the payoff the wraps. The wound pipe is should occur between the bands as these will pulled off the mandrel and cured continu. no end or pole piece around which to wrap.448 17: Filament Winding and Fiber Placement considerable calculating and is one reason On an open-ended part. The part must have an axis of easier. In actual practice. to attach many small posts around the ends • band width (actually the critical factor of the part. pattern was done for a spring on the door Further. the mandrel requires that the winding pat. This path allows the fibers to be adjacent to each other but separated by the placed under tension and remain without ridges between the grooves. in place. These some overriding design requirement suggests slots are filled with fiber as the mandrel otherwise. its movement in one direction. slippage. there is. These posts are usually about is the effective band width). 2 in. turns. therefore. winding but the mandrel is unusual. of a large commercial jetliner. The ally available to give the desired results. helps reduce the force necessary to close When the calculations are done. mandrel’s surface has a series of slots that Therefore. The spring is made by filament combinations of angles and speeds are usu. Then. The winding path that makes alignment of This means that when the carriage completes the wraps occur depends on several factors. (5 cm) high and arranged around the entire diameter of the part on each end. with the • speed of rotation of the mandrel. VARIATIONS IN FILAMENT WINDING and a great circle on a sphere. unless go around it in a helical fashion. the angle usually selected. When these are in place. The spring is drel over the entire layer must be a whole mounted to the plane so it goes into twist- number. The great circle One of the major limitations of filament is important in close-ended vessels because winding is the shape of the part that can following that path makes winding much be wound. is hooked by one of the posts. reverse and anchor the fibers on the end is • length of the part. so its surface can be covered by the travers- tions of a few degrees of angle off the geodesic ing of the carriage and the payoff. In this case. ing tension when the door is open and then also part of the calculation. • diameter of the shaft that goes through the part and around which the wind. the payoff device ings are made in closed-end parts (the takes the fiber band just beyond the end of opening in the end has a fitting in place the part and then turns so the fiber band called the pole piece). The tions to these general shape requirements shape of the domes should be designed so that involve additional equipment that adds geodesic paths are available. Methods. This anchors the fiber band to the post. When cured. and proper rotation of the mandrel. Some examples of geodesic paths the spring is wound off the mandrel. a helix on a flat-sided cylinder. but also must be generally linear layer against those below it will allow devia. that machine controllers are so valuable. An interesting variation in the winding tern repeat exactly an even number of times. the return • speed of movement of the payoff. several the door. Excep- path without having slippage problems. are hoop windings around the circumference of a cylinder. is the angle that gives the geode. other motion capabilities to the standard Fundamentals of Composites Manufacturing: Materials. These requirements are. path will be exactly right to allow alignment To achieve complete and even coverage of of the bands. One method to allow the machine to • diameter of the part. of course. and Applications . the friction of one rotation. the fiber bands are not sic path. there is noth- including the following: ing to anchor the fibers so that the carriage can reverse its path and have the fibers stay • winding angle. the number of rotations of the man. tion on some fiber placement machines in TUS system. the filament winding but can be made with complexity of the carriage and. This fibers on the other and. The fiber lay-down rate for axes of motion and using more sophisticated fiber placement is low compared to filament controllers to coordinate all of these motions. portions of the “T” are wound in the normal Therefore. setting desired While the general physical arrangement angles. and Applications . some axes of motion needed to make some One augmentation to the standard ma. fiber placement was developed to way except that as the hoop windings are overcome these limitations. winding. been made. parts were still not available on even the chine is done to make T-fittings. Such parts would not be possible with standard filament winding. called requirements are very costly. In the LO. usually only 20 lb/hr (10 kg/hr). fila. applied to one of the sides. FIBER PLACEMENT A fiber placement machine requires a The desire to use filament winding for a highly sophisticated controller and high wider variety of shapes led to the develop. Still. which onto the mandrel. This action is be required for essentially any shape and to repeated frequently. filament winding. not need to be under tension when applied Another method for creating non-stan. Parts as simple as a curved walking of the mandrel and carriage is similar to cane are difficult to make using standard a standard filament winding machine. It uses a sophisticated fiber placement system. Further. The round most advanced filament winding machines. ring and down its length. LOTUS. control system and a non-standard winding There are as many as nine axes of rota- machine to create curved tubes. made by fiber placement as compared to fila- ment winding machines were including more ment winding. the mandrel is held stationary comparison to standard filament winding while the fiber source spins around it on a machines that may have only three or four. precision in its head and carriage. bicycle frames. Methods. automobile frames. therefore. makes latter advancement meant that the fibers did the “T” strong. Several such modifications have sion when wrapping the mandrel. especially. Other possible parts could include of the payoff head. method that has been used commercially to The most important limitation was that any extent. and high operating costs.17: Filament Winding and Fiber Placement 449 machine. As a result. Instead. including devices like wheelchairs and walkers. which eliminates many of ment machine costs over ten times as much the shape restrictions inherent in standard as a standard filament winding machine. although fiber placement is capable traditional filament winding were present of wet winding. to the mandrel. These ment of a highly automated system. Parts made commercially with fiber place- furniture. areas of concavity. are significantly greater. they were placed dard shapes is the LOTUS system. and medical ment have undulating surfaces. many of the limitations inherent in Further. In light of these high capital costs traditional filament winding still used ten. the number of fiber Fundamentals of Composites Manufacturing: Materials. an operator (or The concept of fiber placement was to automatic robotic arm) pulls the fibers from include all of the axes of motion that could one side of the “T” to the other. A fiber place- fiber placement. The developers of fiber Other factors also increase the costs of parts placement realized that in actual use. even concave is named for the shapes of the parts that mandrel surfaces could be made with the can be made using it. This creates a crossover include in those axes of motion some that that ties the fibers on one side of the “T” to pushed the fibers against the mandrel. prepreg winding is the only in even these highly sophisticated machines. exhaust ducting for engines. the plane travel. However. the part were required to be smooth. To accomplish this. Therefore. Nevertheless. The major manu- Engineers saw this as a way to improve the facturing methods utilizing this concept are productivity and quality of aircraft manufac. the demand for highly lages was made continuously over about a sophisticated manufacturing will continue 24-hour period. Starship’s fuselage. the methods Filament winding is intended for making developed for the Starship are the basis for parts that have an axis of rotation and. and Applications . wrapping.) The part was then veloped for filament winding of the Beech assembled with the wings and engines. espe. The entire assembly was then placed for composite parts in the future. Beech Starship. a flexible ment are aerospace parts that have unusual membrane was installed over the winding shapes. techniques. As heat was applied. Several of the fuselages fiber placement is becoming more important were built. the outer surface of the clamshell mold. the part and mandrel were throughput for fiber placement are likely to placed inside the clamshell mold. inside an oven. as the number and mandrel. Nevertheless. the facture a filament-wound fuselage for the most prominent in terms of usage. (The fibers Fundamentals of Composites Manufacturing: Materials. the outer surface filament winding were to be used for an was smooth because it had been defined by application in which the outer surface of the mold. Fiber placement seems destined inner diameter was just slightly larger than for high volume and has the possibility of the outside diameter of the part as it was becoming a key manufacturing technology wound. normal way. proven to be successful. The pressure surface of a part is quite uneven because was continued throughout the cure. When it is not defined by a mold. Filament winding is. So a team was assembled to manu. number of commercial parts being made by The secret to solving the problem of the fiber placement is small in comparison to rough outer layer of a filament-wound part filament winding. Then winding was done in the size of composite parts increases. Therefore. by cutting it just ahead of the cockpit. The costs of machines and the After winding. cure the part. (De- ing) would have to be done. the elas- tomeric membrane placed over the mandrel CASE STUDY 17-1 was inflated from internal pressure. but in the end the company because of its ability to make parts of almost elected to manufacture the part by other any shape. Methods. filament winding. The dream of many aerospace engineers SUMMARY has been the fabrication of the fuselage of Making composite parts on a mandrel has an airplane in a single winding operation.450 17: Filament Winding and Fiber Placement placement machines in operation is small aircraft that promise to revolutionize air- (less than 20 at this writing). in manufacture of a new round of corporate general. After winding and curing. was to use an external clamshell mold to Most of the parts made by fiber place. like an The part was removed from the mandrel aircraft skin. The mold’s improve. and roll turing. if the fuselage was removed. The first of the Starship fuse- cially in aerospace. a convex cross-section. to increase. need to cut the fuselage. fiber placement. by far. That in- Starship flation pressed outward on the overwrapped A limitation of filament winding has been composite and moved the composite materi- the lack of definition of the outer surface of als slightly outward and against the inner parts. This problem signs for later aircraft have eliminated the was solved in the fabrication scheme de. extensive machining (grind. Filament winding from the part. CA: Fundamentals of Composites Manufacturing: Materials. the wrap- ping can be done manually. 4. and a host specifications of the prepreg manufac- of industrial products. 2nd Ed. 6.. Procedure: 2. D. mandrel.) In spite of this limitation. 1999. Filament Winding Composite ylene is a good material for this purpose. well casings. Humphrey. golf-club shafts. oil drilling risers. Wrap shrink tape around the wrapped Peters.and close. Obtain sheets of prepreg material. Hang the mandrel vertically in an cases.3 cm) overlap between ended). Some of the most obvi.5 in. about . bicycle components.) 3. turer. W. Because the mandrel is placement processes. 2. QUESTIONS LABORATORY EXPERIMENT 17-1 1. oven and heat to cure according to the softball bats. List four factors that affect the helical winding path of a close-ended vessel. tapered. Wrap the prepreg around the mandrel. moving the tape along its surface.17: Filament Winding and Fiber Placement 451 are applied under tension and if the surface Usually. Methods. machined from a steel rod. (5 cm). The advantages of filament winding are its high productivity and the capability to 7. remove the shrink-wrap automate the process. shafts. If a roll table is not available. the prepreg should be cut on the same taper. rocket-motor 6. (These are generally mance pressure vessels. No wonder it is such a highly valuable with a thin layer of resin or paint and and widespread composites manufacturing allow to cure. cores for each of the wrappings. reinforced pipe. system. The width of the cuts should be suffi- 5. the width of the wrapping ma- were concave. Describe how helical wraps are an- 3. tanks (both open. Either cellophane or polyeth. Cotton gloves should be worn for this task.. Covina. Give two reasons why filament winding Roll Wrapping a Golf-club Shaft is so commonly used to make fiberglass- Objective: Make a golf-club shaft. R. Structure Fabrication. is best done by mounting the mandrel many important parts are appropriate for in a lathe or other turning device and filament winding. F. aircraft structures. Sand or grind the surface to remove the received great support from innovations in bumps caused by the shrink-wrap. Describe roll wrapping and point out three major differences between it and 4. T. Secure or make a mandrel shaped like ing is used extensively for high-perfor- a golf-club shaft. The wrapping the concave area. Cut the sheets of prepreg to size so that chored on the ends of an open-ended they will wrap around the mandrel. the fibers would bridge over terial is about 2 in. (1. Discuss three major differences be- cient to obtain four or five thicknesses tween the filament winding and fiber of prepreg. filament winding. Wipe the surface clean and then coat trol. and Floral. Use ous are: pipes. S. part. is a conceptually simple process that has 8. industrial rollers. machine manufacturing and electronics con. BIBLIOGRAPHY 5. Give two reasons why filament wind- 1. 9. After curing. and Applications . Dearborn. A. MI: Society of Manufacturing Engineers. Brent. and Applications . Strong. NJ: Prentice-Hall. 2006. Plastics: Materials and Processing. 2005.sme.452 17: Filament Winding and Fiber Placement Society for the Advancement of Material and Process Engineering (SAMPE). Society of Manufacturing Engineers (SME).org/cmvs. Methods. Upper Saddle River. Fundamentals of Composites Manufacturing: Materials. 3rd Ed. www. Inc. “Filament Winding” DVD from the Composites Manufacturing video series. process—pultrusion—gives an indication of often mats or cloth. machine direction. The Pultrusion is a continuous. the the reinforcement preform to include some materials are pulled through the machine fibers in a direction other than just the wherein they are formed by a die in a man. Therefore. especially since it is • Pulling an infrequently seen manufacturing process • Cutting and trimming [SME 2005]. ishing processes are performed. The to shape metal and plastics.) system. the pultruded part is moved composite manufacturing methods were to a cutter and trimming station where fin- developed. therein is the fundamental uniqueness the die. pultrusion molding is less widely practiced than other compos- • Process overview ites molding processes. The name of the die. The puller provides the force for As a process. Then. Upon exiting die. the cost Fundamentals of Composites Manufacturing: Materials. (Extrusion wetted reinforcements then enter the heat- processes push the material through the ed die where they are cured. can be directed into the basic concept used. movement of materials through the entire riod following World War II when modern system. Possibly because of its uniqueness. Methods. high-volume fibers are wetted by the resin and then are manufacturing process used to make parts further formed as they converge toward the of constant cross-section. A schematic as already indicated. pultrusion is unique to of the process is given in Figure 18-1. Pultrusion is a continuous process with ing of the reinforcement fibers through the high material utilization (scrap rates are machine. pultrusion dates to the pe. A veil is also commonly ner similar to the extrusion processes used added to the reinforcement preform. and Applications 453 . composites because it depends on the pull.) • Shapes and applications The pultrusion process begins with con- tinuous fibers being drawn from reels and formed into a general shape that allows for PROCESS OVERVIEW orderly movement into the resin bath. In pultrusion. If desired. additional reinforcements. • Reinforcement preforming (The “Pultrusion” video from SME’s Com- • Resin impregnation posites Manufacturing series is valuable as a supplement to lectures and laboratories and • Die forming and curing for general education. and This chapter examines the following because the shape of products is restricted to concepts: constant cross-sections.1: Introduction to Composites 453 18 Pultrusion CHAPTER OVERVIEW the relatively high cost of the equipment. Although similar to extrusion. usually less than 5%). the formed part enters the pulling of pultrusion. While most fibers are in the machine Fundamentals of Composites Manufacturing: Materials. the roving packages can be mounted.454 18: Pultrusion Figure 18-1. some success has been achieved and low costs of pultruded products. Some of these manu. pultrusion is a rapidly than prepreg lay-up in open molds. Methods. The roving is drawn from fiberglass pack- chine manufacturers. per part and the productivity in terms of reinforcements. Parts made of fore. advanced performance parts that would metals that have constant cross-sections are typically be made with carbon and aramid now being considered for substitution with fibers are usually not made by pultrusion. There- increasing production method. bundles build mass in the part without re. Fiberglass in other forms as cycle time are the best of any composites well as aramid and carbon fiber are also ac- manufacturing process as shown in Figure ceptable. However. yet convenient to handle because the large fiber aligned with the machine. They are kept separated. ages that are. generally. composites because of the good performance However. pultrusion is less precise 18-2. Roving is modate them. and Applications . A variety with mixtures of reinforcement types to cre- of pultrusion machine designs in many sizes ate hybrid composite structures. When the concept of pultrusion is first quiring a high number of strands to be used. people generally assume that all Another advantage of the pultrusion process of the fibers are oriented in the machine di- is the ability to use a wide variety of different rection. introduced. The Continuous fiberglass roving in high. Schematic of the pultrusion process. The creel is a stand on which needed for a full pultrusion operation. Because of these excellent economic and in controlling the over-direction of the fibers production factors. It is mobile so the strands of reinforcement can REINFORCEMENT PREFORMING be aligned properly with the pultruder. strands are directed into a collection plate count bundles is the principal reinforcement into which holes have been drilled to accom- material for most pultruded parts. are commercially available from several ma. mounted on a mobile facturers also supply the auxiliary equipment roving creel. (Polyimides are not generally The broad goods are cut to relatively nar. Commercial slitters are available that or cloth) to the fiber stream. direction in pultruded parts.) Polyesters have the row widths so they can be easily formed to dominant share of the pultrusion market. Thus additional be used in pultrusion provided they are low resin is not needed to wet out the mat and enough in viscosity to wet-out the fibers in cloth and so they can enter the fiber stream a bath and that they will cure in a relatively after the resin bath.) short duration.18: Pultrusion 455 Figure 18-2.01 in. and Applications . it is possible enter the die. The broad goods enter the stream just before or just after the resin bath. Methods. (61 cm) diameters. Fundamentals of Composites Manufacturing: Materials.03 cm) the top and bottom) of the main stream of increments. These narrow widths are usu- to have fibers in other directions by adding ally made by slitting standard width broad broad goods (usually continuous strand mat goods. (0. fibers. (183 cm) and done by introducing relatively narrow widths 24 in. (When only a small amount of broad goods is used. suited to pultrusion. This is normally can handle widths up to 72 in. Cost and productivity of composites manufacturing methods. The rolls can be of the broad goods from the sides (or from cut in widths indexed to . RESIN IMPREGNATION there is often sufficient resin already on the Most of the resins used for composites can machine direction fibers. only have gives more complete cures. other places where sticking may occur. that is closer to the final shape of the part. which lowering the viscosity of the resin by adding is recirculated into the resin bath. That characteristic is higher shrinkage relatively rapid cure that must take place upon curing than most other resins. espe- double bonds along the chain. formed because of the many carbon-carbon multi-initiator systems are often used. This closed chamber Increasing the number of crosslink sites eliminates the vapors from styrene and other also increases the shrinkage. Methods. The sion. in the die. The mixture of initia- epoxies and vinyl esters. three crosslink sites at the ends of the chains. Therefore. the num. formulation. a better solution is to lower the molecular Resin Injection weight of the resin. This while the product is in the die is difficult to high shrinkage is from the many crosslinks accomplish with a single initiator. which is favor. cially with thick parts.) crosslinking is possible embrittlement. Typically. The unfavorable consequence of high to make phenolic are especially hazardous.456 18: Pultrusion In addition to the obvious cost advantage of The resin must have a relatively long pot polyesters. One initiator begins the curing at the release of the part from the mold. This forming guide assists in ensuring full rene vaporization is quite high. thickness. (The vapors from the monomers used able. wet-out and squeezes off excess resin. another characteristic gives them life (time in the bath without curing). Ideally. This initial gel the mold and the forces needed to pull the formation helps prevent styrene boiling later part through the mold. The vantages of lower shrinkage than polyesters intermediate initiator provides a smooth and also an inherently greater tendency to continuation of curing. fittings. There- a distinct operational advantage in pultru. and ity. However. they move into a cure quickly and therefore have a faster forming area where they converge into a shape pultrusion speed. of the secondary and finishing initiators. profile geometry. ed just prior to the die. If this is done. The use of a multi-initiator system offers flexibility in Resin Bath the choice of initiators so that these factors The resin is most often applied in a resin can be addressed while the productivity of bath. heat-activated initiators are used. The selection of the initia- problems associated with polyesters. so that wet-out is rapid. and pulling speed. The resin bath is often open and so sty. The exotherm from this initiator Epoxy resins are occasionally used in pul. the other two most tors usually allows shorter curing times and common resins in pultrusion. die temperature. The initiators are included in the multi-initiator shrinkage is helpful because it enhances mixture. and Applications . Finishing initiators stick to the die. Many of the problems associated with an ber of crosslink sites should be increased so open resin bath can be eliminated with resin the cured product has sufficient molecular injection. thus a lower temperature and gels the part into a reducing the tendency of the part to stick to dimensionally stable B stage. (Epoxies are much better ensure complete cure and reduce residual adhesives than are polyesters. tor system should be based on resin reactiv- ers have Teflon®-coated the dies. resins. Resin injection also reduces the concerns of Fundamentals of Composites Manufacturing: Materials. The viscosity of the resin must be low the pultrusion line is optimized. is generally sufficient to begin the initiation truded parts. pultrud. fore.) To reduce the monomer content. Therefore. they have the disad. The resin injection system is locat- weight to achieve the desired properties. styrene is not an optimal solution. This is especially After the reinforcements have passed true with relatively thin-walled parts that through the resin bath. In comparison. Typical continuous nature of the caterpillar system speeds for pultrusion are 2–4 ft/minute (0. tem.2 m/minute) for parts . Hence. portion through which the RF power op- erates is normally made of ceramic so the DIE FORMING AND CURING RF signal can penetrate through the part. ing system also allows the part to exit the die nique to help wet-out is to heat the resin just before it is fully cured. the reinforcements are gen. The ing step for the pultrusion process. the resin into the fiber bundles. Reaction ment material with radio frequency (RF) time is often fast. The part must because injection occurs just before the die be rigid enough to pass into a post-curing and. The shaped internal cavity of the die gives final shaping to the part as it is cured. The oven to complete the cure. ing the speed of the caterpillar belts.5 cm to 4. serious limitations. thus reducing the potential of crushing or ment material converges around the mandrel damaging the part when it is pulled. This signal imparts energy to the part and pacted as it enters the heated die. Sizes of parts can vary from 1 in. to initiators on-line just prior to injection into 15 ft (2. (0. thermal heating or in place of it. the part prior to injection.6 m) in diameter without the pultrusion system. after the forming guide. This reduces its viscosity enters a forming device immediately after and improves fiber wet-out. In this way.18: Pultrusion 457 pot life because the resin can be mixed with thick. Methods.1–7.04–3 in.6– gives a constant and uninterrupted pulling 1.6 cm) force. It uses two synchronized continuous Hollow parts are made by placing a mandrel belts to press against the pultruded part in the die. Another tech. This method can be used with part with a polyurethane or other fast-react. best procedure is to inject the resin before Another modification of the standard cur- full compaction is achieved. The forming device makes minor jection is done under pressure. pulling can be easily regulated by adjust- The curing process is the rate-determin. A potential problem with resin injection Dies are usually made of tool steel and is fiber wet-out. reinforcement enters the die. The wetted material converges and is com. This and is shaped by the mandrel and the inside system has the advantage that the speed of surface of the die. Similar success has been pulled through the die at a rate appropriate reported when the part was heated with to ensure that the part is cured as it exits microwave or ultrasonic energy. parts of non-uniform cross-section can be An interesting possibility when using resin manufactured. In this case. Therefore. The reinforce. Also. an alternate resin bath. Fundamentals of Composites Manufacturing: Materials. bands so that the temperature throughout The first is the caterpillar pulling sys- the die can be carefully controlled. and Applications . The die ing polymer matrix is possible. therefore. the in. PULLING Normally. the die. The surface of the belts can of the die. Further. behind the place where the wetted be shaped to match the shape of the part. method of curing is to allow the part to exit erally compressed when the resin is injected the die before it is fully cured. the die will have several heating Two types of pullers are in common use. injection is to use a resin-like polyurethane Some improvement in the curing time that is injected as two components and then can be obtained by heating the reinforce- polymerizes when the two mix. The mandrel is attached to the rear and pull it. the die. The time for wetting out can be costly. the size of the die the fibers is typically less than the time in a is kept to a minimum. which forces changes in the shape of the part. a pultruded power. It then is causes it to cure. Therefore. when the other reaches the end of its travel The handrails were faster to install than zone.4 cm). and is called the double-clamp system. pultrusion machine. Methods. Two methods are used must be cut for final packaging and shipping. These studs and bolts have been used in numerous applications includ- SHAPES AND APPLICATIONS ing new electrical plants built by General A wide variety of standard pultruded Electric for a European consortium of elec- shapes are commercially available. While one is clamping and is similar to that used for metals. In the A cutting saw is the most common method first. That way the cut is straight pieces but the labor to make the parts is across the part. pulling. and I-beams. a signal actuates the saw. 90° angles. they are quite abrasive. Since composites are made of both resin Standard bolts are also pultruded. However. A clamp part 3 ft (1 m) square with many internal on the saw table is activated to hold onto ribs requires a complex mold and a large the part. the two pulling devices that alternately clamp system for marketing these standard parts and pull the piece. boxes.1 cm) thick. water absorption. and flexural properties along with indica- The other commonly used pulling system tions of hardness. The square gratings are about 3 ft (1 m) in Since pultruded parts are continuous. els in the direction of the part and with the These have the advantage of using standard same speed. Making a a sensor. together. the clamp loos- is minimal and the integrity of the grate is ens and the saw table returns to its initial superior because all the sections are cured position. The trical companies. the faces of the clamps One interesting product made by pultru- can be shaped to conform to the profile of sion is grating for chemical plants and other the part. U-channels. industrial locations. The pull with this system also can be metal systems and will require less main- constant and uninterrupted. large grating as a continuous piece and then When the desired length of part has passed slice off each individual grating. Clearly. These gratings have rectangular openings that are about 2 in. As with the tenance. CUTTING AND TRIMMING (5. Each of the parts uniform pressure against the part as they has a specification for tensile. caterpillar system. Composite bolts also can be made or diamond tipped so it will wear longer. The saw is similar to a and flat strips in which holes have been woodworking table saw except that it trav- drilled to allow the rods to pass through. to make the parts using pultrusion. uses sets of opposing wheels to pull the sys. the labor When the cut is completed. flat strips. Standard shapes have been used for nal position so it is ready to clamp and pull handrails in Chicago’s transit system. they overall dimension.1 cm) square and 2 in. There are coefficient of thermal expansion. tubes. the other is retracting to its origi. The saw slides along with the part. The tem. the grates are assembled from rods of cutting the part. Another method is to pultrude the The saw is mounted on a sliding table. high. by pultrusion. Therefore. are made from rods onto which threads have the cutting blade of the saw is usually carbide been cut. and Applications .1–25. pull it. (5. For example. they can be easily mounted on pressure standard U-channels are available in widths pistons so that they are always exerting a of 2–10 in. (5.458 18: Pultrusion A modification of the caterpillar system shapes include rods. The wheels have the advantage that sizes available also vary widely. These and fibers. Fundamentals of Composites Manufacturing: Materials. compressive. The most efficient use of inherent advantages over competitive steel carbon fiber was to incorporate it in the top beams. a pultrusion-friendly grade structures. Most importantly. sive support structures with composites. The design also incorporates in bridges.18: Pultrusion 459 While standard shapes are a large busi. The lighter weight of composite of phenolic was developed. which is the major carbon fiber more than doubles the stiffness reason that steel beams have to be replaced of the beam. For the bridge variety of parts made by this method is application. it was going to explore the pos- exploding. tional I-beams provide about 2. the resin chosen was phenolic. Moreover. Working with frequency interference common to metal Georgia-Pacific. trucks. standard phenolic. and electrical conduits. the composites are not elec. decided to explore another automobiles.000 pultruded buss bar cover for the electrically ksi (41 MPa). To reduce corrosion. Morrison Molded for applications like roll-up door panels for Fiber Glass Company (now Strongwell). However. This shape is and therefore it moves more easily with less shown in Figure 18-3. In addition to the innovative structural shape. force. door supports for ogy (NIST).to ten- trical conductors and so they are much safer fold improvement in torsional rotation than the metal equivalents. ladder rails. Pultruded parts are used The manufacturers. powered people mover at Disney World. extensive 0/90° and ±45° stitched fabric primarily in painting and other maintenance are required the web.500–3. sibility of pultruding a beam with a shape Booms for mechanical lifters mounted on and dimensions designed specifically for trucks and used to access power lines is an maximum stiffness and strength. the new nature of composites also led to the use of a beam projected a flexural modulus of 6. in the Daniel Boone National Forest (Ken- ness. the majority of pultruded parts are tucky). The final beam was 24 in. and Applications . The presence of not subject to corrosion. (61 cm) high In remote areas. The product had beams may not seem like a big advantage. custom shaped. aircraft flooring. and safety. The bridge is a composite structure could vastly simplify footbridge. eliminate the electromagnetic and radio. The composite beam that a double-flange design with internal weighs less than its metal counterpart does ribs would be the best shape. The non-conductive ksi (17–20 MPa) flexural modulus. the composite beams Because of the desire for low flammability. the lighter weight of the and 60 ft (18. Ladders used by over standard I-beams. composites are and bottom flanges only. The new design offers an eight.000 ites for similar reasons. for steel. ease of bridge beam shapes eventually suggested of operation. Whereas conven- utility companies are also made of compos.3 m) long. a longer pot life and lower viscosity than but bridges could be built with less mas. the composite beam utilized a com- bination of fiberglass and carbon fiber to CASE STUDY 18-1 achieve its high performance. automotive tional Institute of Standards and Technol- leaf springs. sidewalls for automobile transport under a development grant from the Na- railroad cars. The potential benefit over steel. portation truck and carried to the location a pultruded beam was developed for a bridge by a team of about 10 installers. It was removed from the trans- transportation and installation. Modeling important application because of cost. (No crane Fundamentals of Composites Manufacturing: Materials. Therefore. the majority of the beam was made Composite structural beams have several of fiberglass. For cost pur- Optimized Pultruded Beams poses. Methods. In pultrusion. the part’s placement in a pultruded part. Fundamentals of Composites Manufacturing: Materials. Pultruded beam with internal stiffeners. Procedure: Therefore. pultrusion is SUMMARY a rapidly growing process. Operational problems like buildup of resin 3. cross-sections must be generally uniform. or other lifting devices were needed. Resin baths can be a major obtain the fiber content. Place the sample into a muffle furnace and fiber at the opening of the die and low and heat at about 1.) Higher source of air pollution. reliable manufactured parts of relatively the throughput rate is high. Custom 2. need to be addressed in each manufactur. eliminated by using resin injection. the growth will be The material usage is high because of the even faster. and rods are commonly done. Analysis of a Pultruded Part The disadvantages of pultrusion have limited its use to products in which they Objective: Discover the nature of fiber are not significant. but that problem can performance beams that can be used for ve. be reduced by covering the bath and nearly hicular traffic are under development.000° F (538° C) for compaction. weigh it to ing operation. I. constant cross-section. 4. After cooling the sample. Weigh the part (or a portion of the part) shapes are also possible but they must be of to obtain a reference weight. which creates voids in the part. The process simple geometry. beams. shapes such as tubing. In spite of the limitations. 3 hours. 1.460 18: Pultrusion Figure 18-3. Hence productivity is the best of all composites LABORATORY EXPERIMENT 18-1 manufacturing processes. can give high reinforcement content. gineering applications. Obtain a pultruded composite part. angles. Pultrusion delivers low cost and ability to make the part to net shape. Also. Methods. As composites Pultrusion has some major advantages become more widely accepted for civil en- as a composites manufacturing method. and Applications . Inc.” SME Technical Paper. Dearborn. “Pultruded Beams Re- flect Design-for-manufacture. “Pultru- sion—Flexibility for Current and Future Automotive Applications. QUESTIONS 1. 1997. cloth or mat is pulled into the die along with fibers. IL: Akzo Nobel Polymer Chemi- cals LLC. Dearborn. Fundamentals of Composites Manufacturing: Materials. Gordon L. Upper Saddle River. Chicago. pp. gate the direction of the fibers. List three considerations for the manu- facturing process when using epoxy resin in a pultruded part. EM87-346. MI: Society of Manufacturing Engineers. 2006. 2005. and Applications .sme. BIBLIOGRAPHY Akzo Nobel Polymer Chemicals LLC. Brown. 23–26. 5. Jr. “Pultrusion Guide. Plastics: Materials determine how the lateral fibers were and Processing. 3rd Ed. “Pultrusion” DVD from the Compos- ites Manufacturing video series.18: Pultrusion 461 5. What is the purpose of these broad goods? 2. Carefully examine the part to investi.org/cmvs.” Publication PC2002. Attempt www.” High-Perfor- mance Composites. Karen. 4. 3. to see the placement of the fibers to Strong. May/June. Suggest three reasons why composite beams are not immediately certified for use in vehicular bridges. Fisher. Brent.. added and whether the longitudinal NJ: Prentice-Hall. MI: Society of Manufacturing Engineers. 1987. Describe what the cut would be like if the cutting saw was not moving with the pultruded part. In some pultrusion operations. A. Describe how you would introduce a stitched fabric into the pultrusion process. 2002. Methods. fibers are in the central portion of the part. Society of Manufacturing Engineers (SME). Hence. Then the for thermoplastic composites are examined. reinforcement. There are some disadvantages associated kers). the advantages of thermoplas- This chapter examines the following tic composites are: concepts: • overall cost savings of up to 25%. materials • molding conditions are more flexible. gener- ally because of faster mold cycles. If the fibers • higher processing temperatures than are long. If the fibers are short (whis. • Wet-out of thermoplastic composite • indefinite shelf life. non-reinforced thermoplastic. permit some unique methods plastic materials resulting from the neces- of processing that hold great promise for sarily high molecular weight of the resins highly efficient and low-cost molding of causes serious problems when attempting thermoplastic composites. the thermoplastic composite. can be pro- cessed like a standard thermoset composite. this chapter As the various manufacturing methods will first look at wet-out methods. and Applications 463 . Some of these to wet-out the fibers (see Chapter Six. with thermosets. and Molding of thermoplastic composites is • most high-performance thermoplastics strongly dependent on the length of the have excellent solvent resistance. • Processing short-fiber thermoplastic • ability to make either high-performance composites or engineering (general) materials us- • Thermoplastic composites molding by ing the same process. traditional thermoset processes • ability to remold to repair mistakes. especially high-performance ther. tackiness. the unique properties of thermo. plastics. Fundamentals of Composites Manufacturing: Materials. Ther- have already been realized. Methods. The inherently high viscosity of thermo- moplastics. • problems with lay-up because of lack of However. then the thermoplastic composite with thermoplastics: can be processed much like a traditional • more difficulty in fiber wet-out. moplastic Composites). • Thermoplastic composites molding by • many are highly fire resistant with low unique processes smoke generation. thermoplastic composites will be examined. and some important adjustments. processing of short-fiber thermoplastic resins some advantages and disadvantages of these and long-fiber resins both by traditional ther- materials versus thermoset composites moset methods and by methods unique to should be kept in mind.1: Introduction to Composites 463 19 Thermoplastic Composites Processing CHAPTER OVERVIEW In general. nated. the has already been melted.1 bers are needed (over about . sible for most of the common engineering ized. they are Hence. This is pos- mined when the polymer is first polymer. [0. the fibers are the entire readily soluble in any reasonable solvent. thus protecting the fibers. for in the extruder. For parts requiring fibers longer than tion can be diluted to obtain a low viscosity whiskers. of course. Because the molecular weight must be thermoplastics but is not feasible for some high to have good properties. However. Therefore. discourage most manufacturers from Then. resin. which is solvent after the fibers have been impreg. cm]) into the barrel of the extruder at thermosets have a distinct advantage. the most common method fibers are called “whiskers” or “short fibers” Fundamentals of Composites Manufacturing: Materials. however. merely raising the temperature generally This is then used as feed stock in molding does not work. in this text the extruded length. which cannot pass through an and thus facilitate fiber wet-out.464 19: Thermoplastic Composites Processing WET-OUT OF THERMOPLASTIC for wetting out short fibers is simply to add COMPOSITE MATERIALS the fibers to an extruder in which the resin Since thermoplastics do not crosslink. located downstream of where the fibers plastic resins. molecular weight of the polymer is deter. must be meltable in an extruder. the amount of shearing is most thermoplastics. the resin/fiber strands using this method. the viscosity of the high-performance thermoplastics that of the thermoplastics (even when heated) is have high melting points. other methods of wet-out are the problems and costs associated with us. In high-performance thermoplastics. Most Several methods have been explored to extruders have a vent port conveniently solve the problem of wet-out using thermo. and Applications . extruder. therefore. Methods. The resin. whisker-length fibers (about . bers and longer chopped fibers that might be allow for good wet-out. Therefore. degradation begins to minimized. length of the pellets. also high.6 cm]). By adding the fibers downstream to a level where wet-out is easy. many times longer than the whisker-length solvent thinning is rarely a good option. sets. The occur before the viscosity is low enough to re. The resulting polymer/solvent solu. required. [0. especially of removing the through a bath of molten resin. a point where the resin is melted.04 in. as will be discussed viscosity is to dissolve the thermoplastic later in this chapter. Hence. seems confusing in light of the continuous fi- ing the viscosity of the resin and. that are chopped to about . Hence. Further. operations on conventional thermoplastic Another obvious method to reduce the processing equipment. the combination “long fibers” by the manufacturer. One method is to pull the fibers ing a solvent. these fibers are called they are sheared. fibers used in the extruded pellets. in applications where long fi.25 in. This means that thermoplastics The mixing of the fibers and the ther- will not wet the fibers as easily as thermo. Some- Most polymeric melts will thin when what confusingly. moplastic is done by putting the short. fibers and resin are extruded into stands ally make wetting out the fibers easy. The first is simply to raise the are melted and so this is where they are temperature so the viscosity of the resin falls added. because of costs and practicability. Therefore. done by the Verton® proprietary process. especially about the same as the extruded pellets). (0. after cooling. This term of heating and shearing can result in lower. This method is used used in materials such as bulk molding com- extensively when the fibers are short and pound (BMC) and sheet molding compound the shearing will not seriously degrade their (SMC). However.6 cm).25 in. are not this case. many of the are chopped to the desired length (usually most desirable thermoplastics. Therefore. No Pellet-length Property Short Fibers Reinforcement Fibers Tensile strength. coating is very thin and is often a resin like tic. fibers is shown in Table 19-1 where various Some resin and prepreg manufacturers properties of samples made from short fibers have tried dusting the fibers with solid resin and the longer fibers are compared. impregnation of the fibers left in place and incorporated into the final can occur. extruded. These fibers fill in a gap between This method is illustrated in Figure 19-1a. The a protective skin to help prevent the resin exception is. These two dusting methods thermoplastics. ksi (MPa) 15. The heating lowers the viscosity of the While some care must be taken to enlarge thermoplastic resin but is generally not the restrictions in the molding equipment.0) 1. ksi (MPa) 11. However.5 (196) Tensile elongation. especially with high-performance after molding.0 (186) 28. % 60 4 4 Flexural strength. full wet-out is often a product or. The powdered resin is generally ap- composites molding was to stack thin sheets plied after the fibers have been wetted with a of the thermoplastic resin on top of the fi. Mpi =10 0. Further. small amount of water or water-soluble resin bers. some of the powdered resin falls off the tempted in the early days of thermoplastic fibers. longer fibers can bundles. by heating and pressing the polyvinyl alcohol. and Applications . The polymeric is lower in viscosity than the thermoplas. Wet-out oc- be obtained as thin films since they can be curs when the fibers are heated in the mold.30 (9. (GPa) Heat distortion 150 (66) 490 (254) 495 (257) temperature (HDT). However. the whisker-length and continuous fibers.” tics.0) E6. processes. One manufacturer has also applied a poly- lar to that obtained during the making of meric coating over the dust-covered fibers as normal thermoset prepreg materials. ° F (° C) Fundamentals of Composites Manufacturing: Materials.9) 1. This creates a configuration simi.45 (10. The along with other wet-out methods that will improvement in properties with the longer be discussed later.19: Thermoplastic Composites Processing 465 and the Verton fibers are called “longer” or viscous than most engineering thermoplas- “pellet-length.5 (321) Flexural modulus. The resin coating can be thermoplastic. the shearing action from be used in many injection molding machines pressing the fibers and resin films together and other traditional thermoplastic molding is insufficient to give much resin thinning. and reported excellent wet-out even though Another method of wet-out that was at.0 (262) 46. can be easily removed problem. Comparison of short and longer fibers in injection molded nylon samples.41 (2. which are inherently more are shown in Figure 19-1b and c. if desired.8 (81) 27. sufficient to obtain penetration of the fiber such as the gates in the mold. of course. The thermoplastic materials can often so that there is some adhesion.0 (103) 38. Table 19-1. that the thermoset from falling off the fibers. Methods. Cyclic oligomers will. The cyclic oligomers are small enough in molecular weight that their viscosity is acceptably low. For example. polymerize during molding. thus giving ex- cellent wet-out of the reinforcement fibers. These methods could reach a molecular weight of 500. just as they can be polymerization. method of wetting the fibers is to co-mingle Mechanical properties are largely dependent or co-weave the reinforcement fibers with on molecular weight. also have Fundamentals of Composites Manufacturing: Materials. when the prepreg is heated during molding. and Applications . before crosslinking. The process of coating with cyclic oligo- mers is done by melting the powdered cyclic oligomers and simply mixing with or coating onto the fibers to make a prepreg. usu. or some Thermosets. The molecular weight of the extruded into films (as discussed previously).000. however. A special. knits. Another new and potentially dramatic change in the method of wetting out the fibers is the use of cyclic oligomers (short- chain polymers).000 whereas a post-polymerized. proprietary catalyst is necessary to get the molecular An interesting and not fully explored weight high enough to yield good properties. of 50. Co-weaving is when the two fi. cy- ally with one being the warp and the other clic thermoplastic of the same type of resin the weft (see Figure 19-1d). linear polymers. cyclic polymers can reach extraordinarily Co-mingling is when the reinforcement and high values. preforms. when heated. thus the oligomers fibers made of the matrix thermoplastic have poor properties and only become good resin. are simply wetted by the thermoplastic fibers co-mingled with the reinforcements.466 19: Thermoplastic Composites Processing other fibrous form to be made using textile technology. applications might have a molecular weight ber types are woven or knitted together. properties needed. Then. The chemical process involved is a catalyzed breaking of the ring structures of the initial oligomers and then a joining of the opened rings into long. the creation of such preforms or fabrics could result in more complex parts which. This technology seems ideal for resin transfer molding (RTM) and related technologies because the problems of resin infusion are largely eliminated. allow cloth. braids. thus increasing in molecular weight. the cyclic oligomers polymerize into chains that are long enough to give the mechanical Figure 19-1. a normal engineer- thermoplastic fibers are mingled together in ing thermoplastic used in traditional plastic the yarns. Thermoplastic wet-out methods. Since textile technology is quite advanced. Methods. Many thermoplastic matrix resins can when the molecular weight increases with be extruded into fibers. the molecules of the resin and the with the thermoset. Such products structing the flow path. Since the fibers are critical to in- THERMOPLASTIC COMPOSITES creasing mechanical properties in the direc- Extrusion tion in which they are oriented. The die might even have an thermosets. be necessary to give the part enough stiffness Figure 19-2b shows the change in orien- to be removed from the mold. the fiber orienta- PROCESSING SHORT-FIBER tion can be changed laterally to the machine direction.19: Thermoplastic Composites Processing 467 poor mechanical properties. it is logical that they also can be used tion part would be stronger in tension in the to form these reinforced thermoplastics into machine direction. Such a die is shown in Figure 19-2. The polymerization wall of the die. Methods. the die could be square shaped analogous to the crosslinking reaction of or wide and flat. The degree of alignment is activation heat for PC is somewhat higher increased by making the restricted flow than the melt point and so the resulting poly. and Applications .) materials where the forces on the part are Other shapes are made by changing the generally perpendicular to the plane of the shape of the opening in the die through which product. the the melt of resin and fiberglass must pass. This type of alignment is common created by the cyclic oligomer method. The major difference between inner mandrel and thus force the resin-fiber these new cyclic-based thermoplastics and melt into the space between the mandrel and traditional thermosets is that after the the outer die body to create a hollow tubular thermoplastic polymer is fully formed. the fibers can be are made by using a die that is shaped in the turned to orient perpendicularly outward.) shapes other than the pellets used in sub. only two resins are being flow. a machine-direc- fibers. Fundamentals of Composites Manufacturing: Materials. With PBT the polymerization have the uniformity of alignment shown. By dramatically expanding the flow path. whereas the Note in Figure 19-2a that the fibers are thermoset cannot be remelted. The resins have tation that can be achieved with a change been demonstrated in pultrusion and RTM. narrow section such is triggered by increasing the heat after the as the area between the mandrel and the catalyst has been added. (However.) In reinforced thermo- much as a thermoset hardens in the mold. mer is a liquid and must be cooled after it is of course. (The die makes a continuous rod tube. The die is mounted on the end of the orientation may not be highly desired in a extruder. (Figure 19-2a is. Figure 19-2c shows that by partially ob- sequent molding operations. path longer and narrower. cross-section of the desired product rather This orientation results in a part that is than the simple round hole used to make especially strong in compression. the direction of flow. it is certainly valuable in some sheet that is then chopped to make the pellets. this change Since extruders are used to combine many results in a tube that is much stronger in the conventional thermoplastic resins and short hoop direction. While this pellets. some minor cooling might short fiber reinforcements are aligned. It even occurs in non-rein- thermoplastics are polycarbonate (PC) and forced extrusions where the molecules polybutylene terephthalate (PBT). polymerization reaction of the oligomers is For example. in the geometry of the die. it shape. generally aligned in the direction of the At this time. Therefore. idealized as actual parts do not polymerized. As plastics. is still processible by melting. become aligned because they are forced to lymerization of both types of cyclic oligomers flow through a long. The po. These in extrusion. temperature is lower than the melting point but the alignment is certainly strongly in so it simply hardens to a solid in the mold. it offers high productivity due to short molding cycles. Note that elongation dramatically drops when fibers are present. The plastic Figure 19-2. This would be expected because the fibers. The purpose of this zone. screw has these same zones and that. and excellent detail can be obtained. Methods. in which the root of the screw Figure 19-2d shows a combination die is thick (the flights are shallow). In a typical injection molding machine. which are stiff and strong. it is parts. the nature of the fiber orientation added in the metering zone. Most engineering thermoplastics are readily processed by injection molding. carry much of the load. fiber direction has a major effect on the At the proper time in the mold cycle. and Applications . screw stops rotating and advances. mechanical heating. This is a good compromise when build up pressure. when In all extruded thermoplastic composite fiberglass is added during extrusion. Note that an extrusion forces on the tube are from all directions.468 19: Thermoplastic Composites Processing Injection Molding For years. Typical fiber contents range up to 30%. The ma- terial then moves into the melting zone. In every case. the performance of parts. Orientation effects in extruding thermoplastic is melted through combined thermal and composites. the resin enters the machine from a gravity-fed hopper. in which electrical heaters are placed around the barrel and the root of the screw gets thicker to provide mechanical heating. after the resin is important to understand and control as has been melted. Injection molding is widely used because the process is easily automated. The screw has deep flights in the zone under the hopper—the feed zone. is twofold: that gives a generally random orientation to to ensure that all the resin is melted and to the fibers. A rotating screw advances the mate- rial. injection molders have been using short fibers (whisker length) as rein- forcements in thermoplastic resins. the tensile strength and flexural modulus increase with fiber content. Sometimes the increases in a property may be as much as 300% over the non-reinforced thermoplastics. This Fundamentals of Composites Manufacturing: Materials. although 40% and even 50% are available for some resins. and is conveyed by the screw into the metering zone. The properties of these products are excellent for some applications with significant increases possible in tensile strength and flexural stiffness as shown in Table 19-1. and Applications . Typical machine sizes range from interpenetrate with the fibers and resin from 1–50 oz (30–400 g). They are removed from the part after runners. These the screw prevents the melt from flowing points are critical because they may be so backward. Two measurements of machine the gates. The flow lines meet in a region between to be made. if any. of the melt and allowing sufficient time for force (90–13. gates. called the sprue. with few. This allows the fibers to turn ran- with sliding inserts to allow production of domly as they flow to fill the area. and possible. area of the part and the restrictions in it becomes a place where the mechanical the sprue. The melt flows through a network constricted that the fibers are not able to of channels. thus used for non-reinforced resins. Molds also oriented throughout the part. multiple injection points (gates) are present The size of the injection molding machine in a mold. If they do not interpenetrate. Fundamentals of Composites Manufacturing: Materials. as is usually may be equipped with unscrewing devices the case. Random- hollow parts. the resin-fiber melt. This situation is shown in Figure is determined by the size of the part or parts 19-3. to flow into narrow sections. This same problem The latter type is called a family mold be. For proper strength of the part. Some molds have ances should be much larger than might be hot runner systems that do not solidify. The fibers must have ample clearance The mold can be either single or multi-cav. Typical values are 10–1. machine that orient the fibers are the places into the mold. and internal cavity clear- it is ejected from the mold. In the simplest mold. is the pressure required to hold the mold a boundary will exist between the flows. flow through them at all (or only with great ties.500 kN). If the section ity. cause several parts that go into one assembly If it is desired to have the fibers randomly can be molded simultaneously. parts. to allow for and the section either fails to fill or has resin simultaneous production of various parts. The actual entry points into the cavities difficulty). the restriction points the sprue and runners solidify along with the must not be too confining. cost to the mold. to the mold cavi.500 tons. Interpenetra- major considerations in determining this tion is improved by raising the temperature pressure. and fibers and resin flowing from one gate must sprue). That means the part. and at the gates are properties are much lower. runners. or other thin sections in the Knockout pins eject the part. All such modifications to the ization is also increased if the temperature of simple one-cavity mold add complexity and the melt is high and the flow rate is low. closed against the injection pressure. A check valve at the end of where the flow path is restricted. the fibers bridge over the top be either identical or different. to allow for good flow of are called the gates. making trimming of the part unnecessary. In this region. runners. Another major consideration in mold- The mold is opened after sufficient cooling ing reinforced thermoplastics is the width time is allowed (often only a few seconds). the actual meeting size are required: shot size and clamping of the flows is called a knit line or weld pressure. the runners. The Because fibers do not cross that boundary. thus reducing the cost of of fibers meet as would be the case when the final part. The clamping pressure the other gate. The cavities in multi-cavity molds may is too narrow. the of the melt to be injected (parts. Hence. the flows to mix. The shot size is simply the volume line. ribs. fibers. Methods. the flow path should be as wide as to allow for internally threaded parts.19: Thermoplastic Composites Processing 469 motion injects the molten material through The locations in the injection molding the nozzle and a channel. can occur in corners that are too sharp. but may add productivity Some problems can occur when two flows to the operation. of walls. A phenomenon related to low elongation is THERMOPLASTIC COMPOSITES seen even in some of the molding processes such as blow molding and thermoforming. the stretch is restricted and the fibers actu- plastic parts. their use is not common. In this molding. This is the entry of the melt into areas of fine detail probably because the presence of the fibers or into narrow flow paths. ations. will have holes or other defects. the plastic molding processes such as rotational molten resin is poured into the mold. The advantages in mechanical ally become points of breakage in the flowing properties can be outstanding. therefore. must be kept in mind. the manufacturing method used with thermoplastic composites is likely to mimic one of the thermoset manufactur- ing methods. of the particles is hindered. the raw mate- much better with reinforced products. However. Hence. the semi-molten resin must stretch and THERMOSET PROCESSES There are critical applications where the properties of the fiber are important and. is stretched too far. the fusing thermoplastics by other traditional thermo. plastic film. if the reinforced material fiber orientation. The higher performance re- quirement of the part will also. thermoforming. require that the resin be one of the high- performance resins discussed in Chapter Six rather than one of the traditional engineer- ing thermoplastics. The thermoplastic be- Fundamentals of Composites Manufacturing: Materials. and Applications . the fiber length must be consid- erably longer than is possible in traditional thermoplastic molding processes. Methods. in rotational molding. When fibers are present. For can move freely. rais. reduces the elongation so dramatically. the material partially melts and becomes sticky. In MOLDING BY TRADITIONAL both. the presence of fibers may restrict casting. in general. injection molding is a viable flow into the mold. some critically important differences with multiple gates. Also. method for producing reinforced thermo. In these applications. fiber flow restrictions. rial is a thermoplastic powder that is tumbled ing the temperature usually means that the inside a heated mold. During the tumbling and mold cycles will be longer. Even though the molding of thermoplastic composites may mimic the thermoset pro- Figure 19-3. Flow lines and knitting in an injection mold cesses. and process.470 19: Thermoplastic Composites Processing In general. blow molding. In casting. heating process. which may require some changes in The reluctance to use reinforced thermo- the equipment. If fibers are present. thus coating the inside Other Traditional Thermoplastics surface of the mold. Although properties can be example. Eventually the particles Molding Processes fuse into a solid mass that has the shape of While it is possible to mold reinforced the mold. breaks occur and the part and fiber mixing are important consider. operating conditions plastics in traditional thermoplastic processes may need to be changed (especially raising also may be because of the difficulty in get- the temperature of the melt) so that fibers ting good flow of the resin-fiber material. for thermoplastics. thermoplastic previously. Because many thermoplastic resins can be after it is shaped in the mold. and Applications . such air gun or direct heating tool. The other com- The manufacture of thermoplastic pre. temperatures required to obtain good flow Fundamentals of Composites Manufacturing: Materials. period of time. Refrigeration is Because thermoplastics are solids at not necessary and no other precautions are room temperature. The most sive and more difficult to work with than are common method of wetting out the fibers for their lower-temperature counterparts. the problems of stiff- applying the hot. and bleeder. wet methods are not applicable can be used in lay-up. typical plished by heating the prepregs with a hot bags for thermoplastics are polyimides. This softening is usually accom. therefore. release. The plastic prepregs are available and have been disadvantage of this material is the curing used in several commercial products. However. Therefore. One major advantage for thermoplastic resins. or aluminum foil. ponents such as the sealing tape. also must be high- tures required to melt high-performance temperature tolerant. are heated promise is cloth made from both the rein- to cure and turn into a solid. Further. breather. thermosets. pregs must account for the higher tempera. in contrast. which can withstand 700° F soldering iron. They must be softened (slightly melted) so The bagging step for thermoplastic ma- that the drape can be improved sufficiently terial should be essentially the same as for to allow them to be applied to the contours thermosets. Therefore. Higher temperature thermoplastics and their much greater bagging materials are generally more expen- viscosity compared to thermosets. Unidirectional and fabric over thermoset prepregs is that thermoplas- prepregs are generally available.19: Thermoplastic Composites Processing 471 comes liquid by heating (melting) and then. the fibers effectively prevents wet methods the cloth-like texture of the material means from being used. and reinforcement fibers. advanced composites. such as polyetherimide An advantage of thermoplastic prepregs on carbon fibers. The problems as. such the resin fibers melt and thoroughly wet the as polypropylene resin on fiberglass. thermo. the bagging materials of a mold. Thermosets. The heating also improves tack must be able to withstand the higher tem- so that one layer will stick to the layer peratures and pressures normally required under it. Such a material was presented with thermoplastics. a prepreg since it contains both matrix and Open Molding reinforcement in a sheet form. forcement fibers and the fibers of the matrix curing in the normal sense does not exist material. of this material is that it is highly conformable sociated with melting the resin and then (good drape). and have no tack. a heat gun or soldering iron is not needed. thermoplastic prepreg is to heat the resin Molding of thermoplastic prepregs and simultaneously shear it by pulling the must also account for the much higher resin and fibers through a roller system. Therefore. Methods. without drape. However. Further. but it has special relevance in melts are much more viscous than uncured this discussion on molding with prepregs. Therefore. The hybrid woven material is. tacking with with thermoplastic resins. The time and the pressure needed to ensure that prepregs are engineering composites. it is cooled to made into fibers. (371° C). a material that holds great solidify. highly viscous material to ness and lack of drape do not exist. tics have infinite shelf life. such as a as Kapton®. neither wet that layers will have less of a tendency to slide lay-up nor spray-up can be used effectively relative to each other. it In general. For example. thermoplastic prepregs needed to ensure their usefulness over a long are stiff. essentially. Therefore. thermoplastics is difficult and rarely done Thermal expansion becomes more critical commercially. which must be moved a resin bath.” That is. Hence. Methods. Most high- performance thermoplastics melt in the Liquid Infusion Molding 500–700° F (260–370° C) range. Instead of attempting to wet the Fundamentals of Composites Manufacturing: Materials. Many of the molds used with difficult. wet filament winding prepreg. shape of the mold. There- in the mold. The resin is hard to liquefy with- thermoset composites will not work as they out some device like an extrusion screw.472 19: Thermoplastic Composites Processing characteristics and compaction. if the prepreg has been shaped to fit sures must be high to inject such a viscous the contours of the mold. well unless the temperature and pressure Even if the material can be injected. the problems of maintaining between the layers of prepreg and into the the thermoplastic as a melt will be present. the mold must be heated. of course. an alternate method is avail- except that a special heated shoe is attached able that allows filament winding with ther- to the applicator head. matic lay-down machines for thermosets. To keep the resin liquid while it In addition to the concern about the effect is being injected. Whereas the which softens it and gives it the tack and thermosets require the high temperatures drape necessary to stick to the mold or to to cure the resin. Fortunately. als used during molding. As the thermoplastic moplastic resins to be done with only minor prepreg tape comes between the head and modifications to the standard thermoset the mold. they usually too high to effectively wet the fibers seek to return to their original shape. liquid infusion molding with about the coefficient of thermal expansion. is rarely done in commercial practice. the thermoplastics require previously laid layers. and Applications . it will not adhere material as the molten thermoplastic resin. the tape is heated by the shoe. the injection pres- fore. it is hard to maintain as a liquid because of the high heat involved to at- A problem with the lay-down of ther- tempt to lower the resin’s viscosity. compared with the 250–350° F (121–177° C) curing Just as wet lay-up is impractical with temperatures for epoxies. Further complications come from the need for higher forming pressures Filament Winding in thermoplastics because of the higher If filament winding is attempted with viscosity of the resin. process. the viscosity is prepregs tend to be “springy. A cooling shoe is the high temperatures to melt it. Moreover. there is concern In summary. are made of low-temperature materials. Moreover. Even moplastic composite prepregs is that the at the high temperatures. the problem of wetting out to relax. These machines resemble auto. Further. its have been applied for sufficient time so that high viscosity results in fiber movement these forces of recovery have been allowed and. mold thermoplastics. using thermoplastics in materials and autoclave fittings and cou. the fibers are moving relatively Some machines have been developed for rapidly through the resin bath so the wet-out the automatic lay-down of thermoplastic time is short. liquid infusion molding processes like plings must be able to withstand the higher resin transfer molding (RTM) is also very temperatures. join together into a solid mass. the fibers. of the high temperatures on the materi- which also can be a problem. This is placed just after the heated shoe to re-so- so the resin will form to the shape of the lidify the tape and ensure that it remains mold and so that the layers of prepreg will in place. in the mold design because of the elevated temperatures. The heating of the resin prior plies high-intensity heat that can be focused to injection can even be done with a small directly onto the prepreg tow just before it extruder. The pre-impregnated tow bath are also present in pultrusion. too. preg tow. in pultrusion. but this has been less successful An interesting capability available for than the laser. although the resin tends to solidation results in good fiber wet-out. In this successful operation.19: Thermoplastic Composites Processing 473 fibers during the filament winding process. sures that the bonding will be effective. To Still. etc. as opposed to liquid infusion methods on the mandrel are heated by merely mount. This cooling is often rapid so the overall to the mandrel or layers of material that time in the mold can be at least as short as have already been applied. the resin-coated while the fibers in the tow are spread to fibers pass into the die where they are heated facilitate wet-out. will be sticky when the new can result in degradation and other prob- material is laid down. Pultrusion the material used in the winding operation The problems of a wet thermoplastic resin is prepreg tow. Then the die sections be- the mandrel. sion line is often slow enough that this con- moplastic resin. with an autoclave are often done to ensure The savings potential would be great in that the material accepts the shape of the using a high-production method. Some prepreg tow is even and consolidated. the materials already case. This heat softens the prepreg yond that point can be cooled to solidify the tow and gives it some tack so it will adhere part. the layers of material moplastic in the resin bath to temperatures already on the mandrel also may be heated high enough to give a good working viscosity so that they. Methods. end of the die. stocking standard parts and sizes that could Fundamentals of Composites Manufacturing: Materials. The extruder can also used high-intensity lamps to heat the pre. the continuous heating of the ther- facilitate this process. like RTM. One Several heating methods have been used method to alleviate some of these resin bath in commercial production.) and problem. It ap. and Applications . shearing action of moving through the die The tow is applied in a standard filament helps thin the resin and improves wet-out. channels. The fall off when this is done. hat structures. heated consolidation. with thermosets and possibly shorter. The resin then passes through more material laid upon them. meter the resin into the die. pultrude standard shapes (rods. pultruded thermoplastic products is to The tendency of the thermoplastic ma. then post-form them to create structural molding in a clamshell mold. However. the resin can be injected into a ing a high-energy heating lamp so it heats small area in the mold and little resin motion the area of the fibers that are about to have is required. Therefore. lems that have already been discussed. The speed of the pultru- made by coating the tow with powdered ther. plates. In one highly problems is to use resin injection. Inventories could be reduced by of the materials. such as mandrel and that there is good consolidation pultrusion. thus imparting good efficiency to is laid onto the mandrel. terial to retain a previous shape can be a I-beams. The pressure as. material is made in an operation in which the they are not as severe as in filament wind- thermoplastic can be heated and/or sheared ing because. The prepreg the die and is further heated and consolidat- tow about to be laid onto the mandrel and ed before being cooled and solidified at the other materials is heated with a laser. Others have also the heating operation. or bagging members fitted to the specific application. winding machine that has been modified The die temperatures can be staged so the to allow heat and pressure to be applied fibers are heated through the die until good at the point where the fibers are laid onto wet-out is achieved. (This is similar to the concept of the raw material is placed into a heated mold kitting discussed in Chapter Seven. the blanks with thermoplastic composites. be thermoformed. the fibers are discontinuous. external melting of the thermo. the solid thermoplastic could When the blank is ready. This means that the fi- of thermoplastic composite blanks. too. and Applications . different enough that they are considered in One interesting modification used with the section on unique thermoplastic molding stretch forming is the use of prepreg in which methods. when the softened prepreg is MOLDING BY UNIQUE PROCESSES deformed into the mold. largely because the order and orientation of the sheets within melting by this simple contact method is far it. The mold closes on the hot thermoplastic less efficient than heating by combined shear composite blank and molds it to the shape and thermal heating as is the case with in an desired.) and then cured under pressure rarely occurs For manufacturing efficiencies. it is conveyed be placed directly into the mold and then into a cold matched die mold. These are bers slip in the mold to conform to its shape. prepreg sheets of thermoplastic resin with The slippage of the fibers is lubricated by reinforcement fibers that have been laid up the molten resin.474 19: Thermoplastic Composites Processing be later shaped to fit specific needs. This. Methods. the complexity of the part that can be to compression molding. One conceiv. However. can be placed onto shelves in a frame so that able method of using compression molding they can be automatically fed onto a belt and a thermoplastic resin would require that that carries them into an oven. Because the fibers cannot stretch very posites. This softening point is similar to and the thermoplastic injected onto them. Hence. according to the design of the final part. That pultrusion of thermoplastic composites is is. The blanks the thermoplastic be melted outside the mold are heated to the point where the resin is and then injected into the mold. they are molded using stretch forming is limited. which follows. ing. Therefore. which is the condition of plastic and subsequent injection into the the thermoplastic sheet when it is ready to mold has proven to be difficult. The methods used have similarities far. the injection molding screw. the layers of the prepregs are oriented and practical and commercially viable. The most important process for molding If some movement of the fibers in the thermoplastic composites is shown in Figure blank can be tolerated. vacuum forming. Alternately. Because the blank is clamped. This process is called flow Fundamentals of Composites Manufacturing: Materials. the sag point in traditional thermoplastic Either way. tacked together as they are to appear in the fi- nal part. These prepregs are made from fibers that are chopped but THERMOPLASTIC COMPOSITES still highly aligned (usually over 99%). They might be fully consolidated but Compression Molding need not be if little movement of the sheets Traditional compression molding where is expected. The process begins with the formation light or eliminated. This type of matched die for shaping thermoplastics has excellent molding is therefore called stretch form- possibilities for molding thermoplastic com. The blank is melted by the heated mold. The fibers softened and will flow easily under moder- could be in the thermoplastic as part of the ate pressure but not to the point where the melt or they could be placed into the mold resin melts. the use of matched die molds the molded shape. the fibers separate Thermoplastic Composites Molding and the prepreg material stretches. the clamping can be 19-4. prepreg must stretch as it is deformed to However. has clamped to hold it in place and to maintain proven to be ineffective. the time in the the deformations of molding are not great. Therefore. To improve repeat. to limit travel of the press platens. Methods. flow forming is done any process in which a flexible die is used.19: Thermoplastic Composites Processing 475 Figure 19-4. for thin panels where cools and solidifies. The flexible die can be shaped to match the Because the mold is cold. (In prac- resin and to control the movement of the fi. The overall pro.) slowly (that is. However. consolidation and shaping of the material ability. If the flexible increased sufficiently to cause the die to de- die is backed by a hydraulic reservoir. If the flex- metal mold. (Hydrostatic pressure is that pressure result- The pressures involved in matched die ing from pressing by a flexible material or a molding are generally low. the part rapidly metal die. and Applications . The combination of less than the typical thermoset curing time rigid and flexible dies will still provide good in compression molding. the mold is only a few seconds. Often. tice. Thermoplastic molding with preheating of thermoplastic composite sheets. the mold is closed slowly). two ible die is not completely filling the cavity flexible molds can be used. the flexible die. flexible die need not be exactly matched to duction cycle is typically 2–10 minutes—far the opposing metal die. a mechanical stop is usually installed because of the applied hydrostatic pressure. This process is of the metal die. the pressure often can be called flexible die forming. Because of the high viscosity of the process is called hydroforming.) variation of the standard matched die The pressure of the system can be varied process is to use one flexible mold and one to assist in definition of the part. Under some circumstances. the form and completely fill the cavity (therefore Fundamentals of Composites Manufacturing: Materials. a fluid—in this case. the term “hydroforming” is applied to bers as much as possible. forming. highly efficient and does not cone.476 19: Thermoplastic Composites Processing giving good shape definition to the part). or a high-intensity lamp. variability of the parts is often Figure 19-5. However. This method high-temperature elastomers. the parts can be formed incrementally. cargo-floor panels. likelihood of fiber damage. attached to the ends. kick panels. therefore. The com.25-in. That bending opera.6-cm) thick and. when the process is from a press and die or might come form a controlled by pressure only. Thermofolding Incremental Forming An interesting process can be used with Thermoplastic composites permit a spe- thermoplastic composites because of the cial type of molding for large parts. might be compromised. These problems are The advantages of using flexible dies difficult to overcome. laser.7–1. matched metal dies. thermofolding has cost of the flexible dies and. and x-ray panels. rather than by bending slowly and using good pressure. can be used for the entire flexible die require heating of the entire material. savings can be realized. pressibility (hardness) of the flexible die is One of the problems with thermofolding typically 60–70 Shore A. excessive. which is sufficiently is that the fibers may not stay aligned prop- firm for compression while also giving good erly in the bend area. Figure 19-6 illustrates conformity to the shape of the metal mold. tial molding or consolidation. Instead ability to reform the material after an ini. the alignment of the design carbon fiber laminate. heat is trans. bent needs to be heated. instead of using flexible tool that presses the hot material a mechanical stop to define the movement into the forming jig. or it might cause the fibers to slip (0. The panel formed are small. it might kink the resin. The section to be formed Fundamentals of Composites Manufacturing: Materials. that assume that a thermoplastic panel needs is. (0. that the angle of the finished part is correct. Even though the die is cold. of forming these parts all in one operation. substantial tooling cost could be made by thermoplastic pultrusion. Therefore. That or as a heat-barrier cap on less expensive may be important if fittings or some other rubber dies (but these will quickly become material that is thermally sensitive has been brittle and require replacement). because gener. Because the sections to be bent at 45° in its center. The pressure to bend the material can come plex shapes. and Applications . therefore. such as a heating element (like in an oven). The movement might create a thickness of the blank and the nature of resin-rich/fiber-deficient zone. For example. Only the portion of the laminate that will be ferred to it by the heated laminate (blank). The process is shown in of the molds. Methods. high temperatures required to mold high. but can be minimized in the hydroforming method. and then bent When the amount of deformation of a com- to the proper angle. to the softening temperature (sag point). incremental forming tion usually employs a jig or form to ensure might be used. This is especially important for highly com. a section at a time. heating This can be a serious problem with the can be done with directed heating sources. a performance thermoplastics. are the inherent lower Despite the difficulties. Hydroforming can consolidated thermoplastic laminate (blank) use shaped or unshaped flexible dies. ponent is not excessive. three common problems caused by fiber Although pressures vary according to the movement. heated in the middle (only). and can result in squeezing the Thermofolding is done by heating a pre- resin out of the prepreg. the decreased enclosures. they are typically 100–250 psi the fibers. been used commercially to make avionics ally lower forces are required. Therefore.72 MPa) for a . such as sili. is. Thermofolding. The the curvature or deformation of one molded deformed part is then heated to a moderate Fundamentals of Composites Manufacturing: Materials. the deformation of the thermo- areas to be formed. These transition zones link plastic composite part must be modest. adjoining area which is. For this to is to use transition zones between each of the be possible. Figure 19-6. Methods. In transition molding. in turn. Hence. a cold part is forced A key to the success of incremental forming into the shape desired and held. is placed in a mold and heated. In this incremental fashion. Deformation at corners.19: Thermoplastic Composites Processing 477 Figure 19-5. the entire Transition Molding part can be formed. heated and formed. That part is area to the next. and Applications . the transitions are formed and then the mold is shifted to the smooth and the fibers remain in alignment. added so that the critical failure areas have ing ducts using thermoplastics and glass extra reinforcement. the ability to quickly thermoplastic blank through a series of mold them (usually by injection molding) rolls that are set so they impart some shape decreases and the advantages of short-fiber- change to the part. generally about 20 ft (6. for instance. Further. as the required industrial ladders for utility. Fundamentals of Composites Manufacturing: Materials. the temperature for stress relief is material is then heated and consolidated 350–365° F (177–185° C) and the time for with pressure. The molding The ladder has proven to be a tremendous temperature is unique for each resin and success. As the applicable for long parts is to move a heated parts become larger.478 19: Thermoplastic Composites Processing temperature for a long period. additional material is For the deformation of air condition. but does not conduct electricity so a narrow range. as the amount of ma- A difficult problem exists in trying to make terial increases (in this case. and then molded in are too heavy. The layered thermoplastic composite from the center without excessive flexing. heated in an oven. tic sheets are presently thermoformed and then backed with thermoset material (as. If the temperature is too it can be used by electrical utilities. forced thermoplastics are relatively small parts where fast molding cycles are critical Roll Forming and the desired properties of the part can A modification of thermoplastic molding be met by short-fiber composites. besides injection molding. The the resin molecules to move and relieve the prepregs are laid in the mold and then. Again. dropped onto a conveyor for one person to carry. it must be within resistant. The method cooling to remove it from the mold. Aluminum ladders line.1 m). that is. cable. Methods. but But what if some other thermoplastic mold- by passing the part through many such ing process. relaxation is 15–20 hours. and con. The molding cycle for such a process A method was developed for producing can be as low as a few seconds since all that the ladders that has proven to meet all of the is required to happen in the mold is shaping requirements for strength and length with of the softened material and then sufficient weight under the maximum limit. The entire prepreg fibers. a viable alterna- CASE STUDY 19-1 tive could be thicker reinforced thermoplastic Lightweight Ladder sheets. in luxury spa tubs). The most common applications for rein- tion may occur. more than unsaturated polyesters. the original high SUMMARY surface quality can be lost and delamina. low. simply because it costs long enough to reach the rooftops of houses. a major change in the part can used to make the parts? Where thermoplas- be achieved. This allows uses thermoplastic composite prepregs. each set of rollers can be quite small. Even traditional pultruded a compression mold under moderate pres- polyester/fiberglass ladders are too heavy. sheets are stacked in the proper sequence and still be light enough (under 55 lb [25 kg]) for the application. The shape change for reinforced thermoplastics diminish. they The thick thermoplastic sheets could be must be strong enough that. however. no stress relaxation will occur. If the temperature is too high. only specific locations. made by the process illustrated in Figure they can withstand 200 lb (91 kg) suspended 19-1a. the thermoplastic be- struction companies. It is light and strong and corrosion can be critical. and Applications . in strain induced by the deformation. fully extended. were roller sets. sure. The ladders have to be comes less competitive. thickness increases). Obtain some thermoplastic composite the shorter shelf life of thermosets can be prepreg material. in the fold region. with the new wet-out technologies 7. has been treated with mold release. 4. for thermoplastic composites is bright. A good shape for the blank is a of these materials are resistant to airline square about 18 in.19: Thermoplastic Composites Processing 479 Are there any critical advantages that are unique to thermoplastics and have been might tip the balance toward reinforced ther. fluid is likely. (0. joining. The advantage Objective: Learn about the advantages in welding is the shorter time required for and limitations of thermoplastic forming. Note any fiber deformations that occur now being used. it is necessary to bor costs resulting from use of the welding obtain the molding specifications from technology. etc. although Thermoforming of Thermoplastic thermosets usually can be adhesively bonded Composites better than thermoplastics. There are also lower la. Several traditional dramatically increased forming speed thermoset methods have been modified to ac. or bend. 1. the resin. Procedure: In some environments and operations. However. Thermoplastics have essentially unlimited shelf life. Lay up the prepreg into a blank that Another major advantage of high-perfor. high-perfor- might be higher? Thermoplastics can be mance composite applications. Cut the blank into strips that are about Some aerospace applications have been 2 in. For instance. Consolidate the blank in a heated applications where contamination from that press. thermoplastics can com. is at least five layers thick. Thermoplastics seem to have special 6. Methods. It is best to mance thermoplastics is their general resis. (5 cm) wide. Fundamentals of Composites Manufacturing: Materials. Thermoplastics also can be welded much more easily than thermosets. Other methods integrity in the bend area. and machined much more easily the advantages in toughness. cutting. developed to make them competitive with moplastics even though the material costs thermosets even for continuous. and than thermosets.). solvent resistance. and note the differences in laminate commodate thermoplastics. some blank. lay it onto a can be injection molded from short fiber bending jig and press the strip into the reinforced engineering thermoplastics. pete effectively against common polyester 8. chipping. drilled. Considering cut. The inherent elongation of finishing (drilling. or LABORATORY EXPERIMENT 19-1 cracking. The pressing can be done manu- for the high-performance part that needs ally with an insulated metal block that special properties such as flame resistance. Repeat the forming method using a fiber reinforced plastics. ing operations to be accomplished with far less worry about delamination. Heat the center portion of the strip with parts because of the weight savings that a focused heater. hydraulic fluids (Skydrol®) and have found 3.5 m) on a side. use different fiber orientations in the tance to most solvents. converted from aluminum or thermoset 5. Therefore. When the strip has reached the proper advantage for either the small part that molding temperature. the prepreg manufacturer. 2. or extra weight savings. and Applications . a problem. cycle time. The temperature for can be gained from using thermal welding molding will depend upon the nature of instead of rivets. the future the thermoplastic resins allows these finish. NJ: Prentice-Hall. J.. 3. Give three methods commonly used to wet-out thermoplastic composites and explain the advantages and disadvan- tages of each. “Thermoplastic Composites Rapid Processing Applications. “Roll Forming Continuous Fiber-reinforced Thermoplastic Sheets: Experimental Analysis. Brent. Composites Manufacturing video se- ries. High Performance and Engineering Thermoplastic Composites. 1989. Give three advantages of thermoplastic composites over thermoset composites. Strong. Lancaster. Upper Saddle River. J. Arnt R. and Bhattacha- ryya. D. Strong. Inc. 27A.sme. and Applications . Why is fiber wet-out a particular prob- lem with thermoplastic composites? 4. Dearborn. Society of Manufacturing Engineers (SME). private communication. www. A. Mander. Methods. pp. What is a thermoplastic composite? 2. MI: Society of Manufacturing Engineers. Fundamentals of Composites Manufacturing: Materials. Brent. 2005. BIBLIOGRAPHY Dykes. 329–336. S. 5. Discuss four advantages of the matched- die-molding system for thermoplastics. Plastics: Materials and Processing. PA: Technomic Publishing Co.” Composites: Part A. Auckland. Discuss three changes that must be made in filament winding to accom- modate thermoplastics. New Zealand: Center for Polymer and Composites Research. 3rd Ed. 1996.. University of Auckland.org/cmvs. R.480 19: Thermoplastic Composites Processing QUESTIONS 1. A. 6. 2006. 1993. Offringa. • Damage and its effects • damage assessment. in which the damage is severe. it should be structure should be capable of withstanding repaired unless the damage is so severe that the required residual strength load level. the key issues in concern is with the hidden. a deterioration of the strength damage but on the estimate of whether there and stiffness. it should be repaired or the part should obvious and. compromised. posites are specifically structured to maximize Often. especially when hidden. the matter of damage and its performance of the part could be seriously prevention and repair are important topics. This chapter examines the following • prevention. and Applications 481 . a repair fundamental problem is that. • Damage prevention • repair specification. using the philoso- be scrapped. however. an airplane has been shot off by a rocket. Hence. • Repair Understanding the Problem DAMAGE AND ITS EFFECTS High Impact and Primary Damage The philosophy of damage to composites The most straightforward situation is that has been expressed as: If the damage is vis. example. the phy of damage to composites. if a single bullet is achieved.1: Introduction to Composites 481 20 Damage Prevention and Repair CHAPTER OVERVIEW • understanding the problem. but there are some Sometimes the assessment is obvious. The non- compromise the overall performance of the visible damage could be so extensive that part. may is significant non-visible damage. For significant problems associated with detect. concepts: • detection. if a major portion of the wing of ing damage in composite parts and their re. the part should be scrapped. Possibly the most important and has penetrated the door of a vehicle. because com. seems logical. or dealing with damage and repair are: low-impact damage. to scrap rests not on what is the obvious mize weight. and mini. Methods. and • Smart structures • repair evaluation. Therefore. If the damage is not visible. the decision to repair or directional strength and stiffness. On the other hand. even in the case In light of the philosophy and the nature of severe high-impact damage. • Damage assessment • repair accomplishment. much of the of composite materials. therefore. Fundamentals of Composites Manufacturing: Materials. It is readily ible. collateral. It may seem obvious. it pair to ensure that the required strength or seems reasonable to just replace the entire other performance property (per the design) wing. An assessment of the effect of the me- molding. The factors might result in microcracks. occasion. or it might be damaged within the manufacturing facility. use safety factors of 1. The boat for low-impact damage is high. and Applications . the boat might be hit by road itself. prepared by hail or other falling objects. over the boat and carrying various tools that Some composite parts are very large. the potential for damage is damage. aging. blades over 100 ft (30 m) are common. However.6 × 1.625 × . However. rocks. humidity. Methods. During can occur during the manufacturing process transport. have already been applied.5 × 1. Of often the most difficult to assess because it Fundamentals of Composites Manufacturing: Materials. It was determined that the dry crane. 1 × . of course. practice is to pry the walls of the boat free These types of results have led designers to using wooden wedges which are. damage is other sections of the boat are welded to it. owner must be constantly careful not to An example of the manufacture of a large bump against piers. The boat is loaded are routine. The are clearly a possibility. Several problems secured onto the transport vehicle. Yachts of 60 ft (18 m) are made (with high potential for bumping) and then daily in several factories. The boat is for shipment. considered often include: temperature and After the boat is taken from the mold. Workers are moving all general prevention and remediation. All of these tectable with the naked eye. the if the overhead crane does not perfectly line examples given here are illustrative and will up the boat and the cradle. Then.482 20: Damage Prevention and Repair Low Impact and Collateral Damage course. and in bumps are possible.3 cm]). fatigue and vibration. Rock. the inspections revealed that about then walk on the surface again to apply each 55% of the damage is small in size (less than of the layers of fiberglass/resin laminate. the boat must be set in place (usu- The sources of damage are. ally in a cradle). these large parts must be moved or passing vehicles. This lifting could cause microcracks. load- it is moved to an assembly position where ing. the workers will walk careful assessments of damage have been on the cured gel coat to apply the veil and made. In all of these steps. and 28% is large steps may cause damage to the layers that enough to be readily seen.500 in. the part may be twisted or bent as dium damage (barely visible) was then it is lifted out of the mold with an overhead made. during de. shipped. Even after manufacturing has been debris such as rocks kicked up by the tires completed. shock. Wind might be dropped onto the boat. They may then walk on the surface again about 17% is medium sized and barely de- to apply wood reinforcements.25 to 1.50 and these ally. Air is often forced safety factors allow for the normal property into the space to attempt to lift the boat out degradation that occurs because of opera- of the mold. static strength was reduced by 70% and the If the part sticks in the mold. But this can be a problem too numerous to enumerate. pounded into the space between the factors do not account for visible damage. section is assembled. and other boats. the potential age) and then placed in service. and placed unloaded (another high potential for dam- into service. [2. as each serve as conceptual triggers for understand. and damage. After the gel coat has been sprayed into In the case of large rocket motors on which the mold and cured. common wet static strength was reduced by 90%. further stresses and ing the nature of composite damage. Microcracks (or worse) which is always assumed to be repaired. enormous. unloaded. This air could cause flexing that tional and environmental effects. Then. the boat is moved out of the plant et-motor cases with diameters of 30 ft (9 m) to a transport vehicle. boat and the mold. boat is used to illustrate the potential for To say the least. Finally. Some of those tests. such as stress. (Logically. Energies of that level are used to simulate impact. presented that can be taken (beyond changes samples are routinely tested for the effect of in the resin and reinforcements) to minimize damage by drilling a hole of a standard size the damage to a composite part. if allow for damage and manufacturing defects the damaged area is a major portion of the provided a limited focus. in the other half of the samples. the changed by damage. The brief discussions failure strain was plotted versus the ratio of about damage largely concerned the impact the hole diameter to the total width of the strength (toughness) of the materials. the non-damaged area is recommended inclusion of safety factors to carrying most of the compressive load. So. then the effect of the damage will be This section looks at how material choice higher than if the damaged area is small might be altered for parts where damage is compared to the non-damaged area. composite samples cracks. because the effects of the dam- are more regular or.) either frequent or catastrophically impor. predictable. Then some specific steps are a hole is a model for damage.20: Damage Prevention and Repair 483 is usually random whereas the other factors water or heat. These are to simulate use conditions Fundamentals of Composites Manufacturing: Materials. samples were then tested in compression The discussions have provided information to determine the strain to failure. compression test. (The curves forklift attempting to raise a composite part for each of the resins were similar so an av- and bumping it as it slides the forks in place) erage curve is shown. at least. the slight impact from a with three types of epoxy resin. Because on the fundamentals of the materials and the it was learned that the effect of the damage optimization of their properties. The subtleties in design that can be aged samples and the drilled samples are used to minimize the effects of damage will reasonably similar indicating that drilling be considered. A hole of the same Until now this book has focused on the diameter as the damaged area was drilled nature of composite materials and the pro. Even energies four times that level using one type of carbon fiber were made (as. dropped from 3 ft (1 m) results in 6 ft-lb (8 Figure 20-1 illustrates the way some tests J) of kinetic energy. In Figure 20-1. are part in actual use. or tension on open-hole samples in which Sometimes these tests will also subject the the forces applied are less than the ultimate laminate to environmental factors. These cess of composite design and manufacture. Open-hole tensile tests are sess the effect of damage on composite also common when tension is the major force materials and parts. part. that will be encountered by the composite like the Izod and Charpy impact tests. Other Other tests commonly done to test the tests monitor the changes in properties of effect of impact include cyclic compression laminates after they have been damaged. (usually . So.) Half of the samples can cause damage that is still not detectable were impacted with sufficient energy to with the naked eye. The sample.25 in.6 cm]) and then doing a A variety of tests have been used to as. but not on was dependent on the ratio of the dam- how the properties of a composite might be age area to the total area of the part. for example. and Applications . what is the level of kinetic energy The conditions may also represent what from casual impacts? A 2-lb (1-kg) hammer might be encountered in real-life use. create an internal area of damage. Methods. The size of the damaged area was determined DAMAGE PREVENTION using ultrasonic testing. [0. age are magnified under those conditions. the curves from the dam- tant. In the open- can cause fiber breakage and matrix micro. Therefore. direct measurements of toughness. hole compression test. and Applications . These toughened resins significantly for example. epoxy. as Using the various impact tests as guides. Methods.484 20: Damage Prevention and Repair Figure 20-1. However. higher impact energies is obviously beneficial to composite performance. Sometimes these tests also include toughened epoxy’s higher strain to failure at thermal cycling (hot and cold). in repeated aircraft takeoffs and minimize the effects of impact damage. Thermoplastic res- ins are even better than toughened epoxies in Material Choice minimizing the effects of damage. The most obvious choice for ent from thermosets. The landings. discussed in a previous chapter. Open-hole compression test as a simulation for damage. Fundamentals of Composites Manufacturing: Materials. the option to improving epoxy toughness is a toughened use a thermoplastic may not be practical. the processing some resins have been found to be especially of thermoplastics is often significantly differ- damage tolerant. in which the forces are repeatedly applied as. therefore. consistently has a smaller indentation for Another method of improving impact dam- the same impact energy. discussed in Chapter Nine). tape is chosen. However. This system pact than were carbon fibers. The reason is simply that the crossover points in the fabric are places where energy is transferred. capability of the fiberglass to arrest crack As is the case with the depth of indenta. fabric is chosen. there- fore. The depth increases with to withstand the impact force. The When the damage area can be determined fiberglass arrests the propagation of cracks by an ultrasonic machine. Fundamentals of Composites Manufacturing: Materials. This measure is age resistance with fibers is to incorporate especially useful when an ultrasonic tester fibers of two different types in a laminate. The results revealed that fabrics are better at resisting impact damage than tapes since they have a higher strain to failure. Fiberglass used for crack arrestment. Com- posite samples were made with unidirectional tape prepreg and woven fabric prepreg using the same resin and fibers. A variation combines two fiber types by The choice of reinforcement fiber has a placing the tougher fiber. Methods. The can be plotted against the impact energy. samples of carbon fiber com. In this test.20: Damage Prevention and Repair 485 The depth of the indentation is another strength. mixed into a carbon fiber laminate. A struc- for a standard epoxy and for a thermoplastic ture of this type is shown in Figure 20-2. such as aramid. and Applications . impact than is the epoxy. This effect on the surfaces most likely to receive an was discussed in Chapter Eight where it was impact and using fiberglass or carbon fiber shown that aramid fibers were substantially elsewhere to make a hybrid structure (as better in minimizing the damage from im. for impact tough- way to measure the damage from impacts. ness. the impact damage and minimizes the extent of damage. major effect on impact damage. not transferred well across the boundaries mizing the damage area for an equivalent of different materials. This effect criterion for impact resistance is the depth arises from the ability of the stitched fibers of the indentation. impact damage is reduced are impacted at various energy levels. which is ap- increasing impact energy for both the epoxy plied in the direction in which those fibers and thermoplastic. Therefore. the impact energy is spread quickly and its effect is minimized in the impact location. As another composite made with thermoplastic might be expected. The form of the reinforcement also can affect the extent of the impact damage. fiberglass strips are sometimes of the impact damage. the thermoplastic is better in mini. for Figure 20-2. The effect of 3D stitching is an impor- posites made with a standard epoxy and tant factor in impact damage resistance. These samples were then impacted at various levels and the strain to failure was measured. is not available to determine the actual area For example. these crossover points are also places where the fiber is squeezed and this effect reduces fiber strength. but the thermoplastic are oriented. growth arises from the fact that energy is tion. The when composites are stitched. Fortunately. the more different the layers are. and Applications . The reason for this behavior is ers that differ from each other contributes likely because the larger size of the real parts to the improved impact resistance of hybrid allows distribution of the impact force over composites. therefore reducing the damage placed on the surface that is likely to be im- in the immediate vicinity of the impact. are used in com- impact. That direction of the fibers and their contribu- characteristic means that the energy from an tion to the pressure-holding capability of impact is passed deeper into the composite the tank.486 20: Damage Prevention and Repair minimizes costs but gives improved impact have a [0/90/0/90] rather than [0/0/90/90] or protection. when two layers of 0° prepreg are sure vessels. posite vessels. The [10/80/10] had a loss of strain age characteristics as do full-scale real parts. it is better to are much more effective and important in Fundamentals of Composites Manufacturing: Materials. but the interface between the tough spreading of the energy reduces the local fiber (usually aramid) and the structural fiber damage. failure indicated that the [10/80/10] was less therefore. tion. [0/90/90/0]. Tests have shown that small impacted and then the strain to failure was samples do not have the same impact dam. In this case. The samples were is scale-up. the problem is adjacent. two types of winding is worse. The hoop wraps crack-resistance point of view. improving impact toughness. ergy is passed most easily from one layer Of course. ballistic protection. bine the aramid and fiberglass in the same Actual samples of carbon fiber and epoxy fabric by interweaving or mixing the fibers were made to test the effects of layer direc- into the same tow. In general. from a angle to the axis of the tank. it is better to spread the energy later. measured. the severity of the damage filament winding. The property works cussed. Methods. the energy from an impact is passed associated with the interrelationship of the directly from one layer to the other. en. As discussed in the chapter on and. It also would be possible to com. the testing is conservative. hoop and helical. The poor transfer of energy between lay- size samples. Not only can a tough fiber be a wider area. they predict worse impact damage affected by the impact. of the fibers in the layers are the same. and high-strength fibers in adjacent layers. Therefore. to the next in the laminate if the directions the greater is the effect. for example. Hence. the samples predict (such as carbon or glass) further dissipates worse behavior than the actual parts and so the energy. and even when the types of carbon fiber are One design factor that impacts damage different. This pacted. For Fiber direction is also important in pres- example. to minimize the effect of an patterns. The helical wraps are at an oblique layers overtly different. with high-modulus tolerance is fiber direction. The hoops go around the tank ally so it will dissipate over a wider area. resistance than is actually the case in full. to failure of 27% whereas the [40/50/10] had The small samples show a lower strain a loss of 40%. The lower loss of strain to to failure for a particular impact energy. This at approximately 90° to the long axis of the is done by making the directions of adjacent tank. as a result. the design of the composite can be when the resins in the layers are different optimized for damage tolerance. One sample was a [10/80/10] lay-up and An issue that needs to be considered the other was [40/50/10]. This property has been used effectively in bullet-proof vests where layers of aramid and ultra-high-molecular-weight polyeth- Design Changes ylene (UHMWPE) fibers have been placed In addition to the material-based concepts in alternating layers to achieve optimal for improving damage tolerance already dis. So. This type of protective shell is comparing damage in thin-walled vessels usually made of composites. protective shell. For best samples.) This method is rarely used DAMAGE ASSESSMENT except when the composite part is costly or The initial method of assessing impact dam- highly susceptible to any decrease in prop. The aramid spreads the wall thicknesses suggests another design impact and the cork underneath ensures factor that affects impact toughness. In addition to the cost of making walls have less deflection and therefore less the protectant layer. an external material that has been used successfully is a skirt. is being shipped. In this case. External Protectors which is used to cover critical areas of the tank. an energy-absorbing material can ing little flexing are more damage tolerant be added inside the shell. To Fundamentals of Composites Manufacturing: Materials. A case where these conditions apply fore. that is. a rule of thumb for design of pres. another disadvantage micro-cracking. There. the damage from an is the weight added to the total assembly. age is to visually inspect the damaged part. even as remains with the composite as it is bonded a percentage of total thickness. and be jettisoned. have worked well are cork with an aramid Examination of pressure vessels of several hard shell on top. These are especially use- walled vessels and. just before the launch. decreases. than highly flexed parts. The hypothesis was con.20: Damage Prevention and Repair 487 containing the pressure in the tank. impact on a thick part is more likely to be It is possible to make a removable outer compressive as opposed to flexural in thin. in general. and readied for firmed by wrapping the pressure vessel on launch. This sure tanks is to increase the design tolerance means that the integrity of the cases must to “bury the hoops”. Also. because compression ful for space vehicles and missiles since the strength is usually greater than flexural. erties. (The external protector can be removed just prior to use. The most common type will absorb some or all of the impact energy. any less impact damage than the unsupported reasonable material is acceptable. The high cost of launching materials the breakage of these fibers would be much means that the weight of the rocket motors worse than breakage of a similar number (and all other space-shuttle components) of fibers or layers of fibers in helical wraps. sitions zones where the vessel changes from ite material with an external material that hoop to helical wraps. if the hoop fibers were in the outer is with the rocket-motor cases for the space layers of the tank and they were impacted. must be kept to a bare minimum. Some materials that the hoop wrappings is less likely. closer to the inner surface of the tank and One external protectant method is simply cover them with helical wraps toward the to put a layer of shock-absorbing material outer surface so that accidental impact of over the composite. shuttle. which has little deflection. design safety factors are quite low. protection. and Applications . On pressure vessels. of skirt is illustrated in Figure 20-3. Then. A straightforward method of reducing the These areas are usually the ends and the tran- damage from impacts is to cover the compos. put the hoops be guarded carefully. the damage area. is no particular problem with weight or cost the thin-walled samples on the steel core had (assuming that the shell is recoverable). Sometimes this type of layer vessel increase. but since there also tested without the steel core. it can a steel core. stiff composites hav. to its outer layer to ensure that it remains This is postulated to occur because thick in place. Therefore. Methods. stored. As that the energy is dissipated before it reaches the thickness of the walls of the pressure the composite. protective shell can be used while the part the damage is less. Therefore. visible on the surface. damage. If only one side of the possible causes of the damage. several types of damage when caused by light impact. In this testing (NDT) should be used to assist in view. the depth of the damage and attempt to de- mon NDT methods and their applicability. for deciding the amount away from the impact point and extensive of repair that must be done to correct the delamination can occur toward the back. especially composites industry. may be barely have been defined with visual references. these definitions and the ac- breakage below the surface. the well-known and difficult problems with In an effort to relate the visual assessment any composite structure is the hidden dam. Table 20-1 lists com. laminate can be inspected. Some impact damage. However. the inspector should note (measure) further assessment. One of discussed later in this chapter. and Applications . termine the class of damage according to the Fundamentals of Composites Manufacturing: Materials. Although not be considerable matrix cracking and fiber quantitative. They are also useful in assessing side of the laminate. do that the structure must be accessible to The effectiveness of NDT testing will be inspect for the extent of the damage. If possible.488 20: Damage Prevention and Repair Figure 20-3. Methods. one impact side. there could These are listed in Figure 20-4. The damage companying diagrams are useful. Of course. especially will typically spread in a cone-shaped area in field situations. nondestructive angle is the direct perpendicular view. to previous damage assessment data in the age issue. it is prudent to Experience has shown that visual inspec- assume that the hidden side has received tion needs to be done carefully and from sev- greater damage than is evident from the eral different viewing angles. A sacrificial skirt as a protectant against impact damage on pressure vessels. and Applications . Common non-destructive testing (NDT) methods and their applicability. Test Method Optical Non-destructive Through Transmission Thermography (NDI) Methods Dye Penetrant Pulse Echo Inspection Tap Test Visual X-ray Defect Abrasion ¬ G O O O O O G Dent ¬ G O O O O O F Scratch ¬ ¬ G G O G ¬ ¬ Crack ¬ ¬ G F O F ¬ ¬ Cut ¬ ¬ G F O ¬ ¬ ¬ Gouge ¬ ¬ F F O F G ¬ Delamination O F ¬ ¬ F ¬ G ¬ Hole ¬ ¬ ¬ ¬ ¬ ¬ G ¬ Inclusions O O ¬ ¬ ¬ ¬ O ¬ Porosity O G F ¬ G O O F Voids O G F ¬ G O O ¬ Debonds O ¬ F ¬ F ¬ O ¬ Key: ¬Ê = Good G = Some capability F= Fair O = Little capability for practical purposes Fundamentals of Composites Manufacturing: Materials. Methods.20: Damage Prevention and Repair 489 Table 20-1. 490 20: Damage Prevention and Repair Figure 20-4. Types of defects defined for damage assessment classification. system shown in Figure 20-4. The inspec- surface surrounding the damage should be tor should also look at the damage with an done with specific attention to disruptions oblique viewing angle and several different in the surface smoothness and inspection for light-source angles so that collateral damage hairline cracks, which would indicate that might be detected. Careful comparison of the the damage energy radiated outward. Fundamentals of Composites Manufacturing: Materials, Methods, and Applications 20: Damage Prevention and Repair 491 Visual inspection can be enhanced by us- to small areas where damage is already sus- ing a small tap hammer to note the sound of pected. If a large area needs to be inspected, the composite in the vicinity of the impact tapping gets tedious in a hurry. So for large point. This is called the tap test and it is areas, such as a survey of an entire bridge done by tapping on the surface of the com- deck, other inspection methods, such as posite part and listening carefully for chang- thermal imaging, may be much more ap- es in the sound from one place to another. propriate. The standard, against which all sounds are Clearly, experience is a great benefit in to be compared, is simply the most common using the tap test, both in recognizing the of the sounds heard when tapping the part standard sound and in detecting differ- in a known non-damaged area. In other ences from place to place along the part. words, the part is assumed to be regular Some standardization has been attempted and undamaged in general, with deviations by specifying that a standard tap hammer from that sound arising from defects or be used in the test (as has been done by the other non-uniformities. The part is tapped Federal Aviation Administration [FAA]). If gently back and forth until a subtle change this is not readily available, a specific coin in tone is detected, from a clear sharp ring to (a quarter in the USA), can be used as the a duller thud. Then the inspector backs off a tapping instrument. The force of the tap is, bit, maybe .5 in. (1.3 cm) or so, taps again, of course, still a variable that requires some and makes a mark indicating the boundary experience to exercise properly. with a felt-tip pen. The steps are performed Sometimes damage occurs and is not de- again from about 1 in. (2.5 cm) away and so tected, especially if it is slight. The person on until there is an outline of the irregularly doing the damage might not realize that shaped area of damage. damage has occurred or, perhaps, the person A limitation with the tap test is the thick- seeks to hide the accident. However, even ness of the part. The test works best when slight damage can result in a significant the parts are relatively thin and the defect loss in composite properties. Therefore, a is close to the surface. Also, since the test method for detecting even light impacts has detects differences in acoustic resonances of been developed. This method, illustrated in a defect compared to surrounding areas, only Figure 20-5, involves painting the surface of those defects that have different vibrational the composite and then over-coating with a characteristics are picked up. Generally, clear resin containing easily broken micro- those would be laminar-type defects such capsules. The upper layer is cloudy because as delaminations. A further limitation is on of the light diffraction of the microcapsules. parts with complex geometries where the If an impact occurs, the microcapsules break, vibrations might be affected by the shape of thus revealing the paint layer. The change the part from one area to another. Attempts in surface color is easily detected and would have been made to reduce the variability of lead to investigations of possible damage. the tap test by providing a machine-like tap- After initial visual and tap hammer inspec- ping device and an instrumented detection tion, the methods for NDT discussed in Chap- system. In general, these improvements have ter 10 are the principal means for assessing not proven to be sufficiently better to offset the extent of the damage to composite parts. the cost and convenience of the simple tap method. SMART STRUCTURES The tapping test inspection method actu- Wouldn’t it be nice if inanimate objects ally works quite well, but is clearly limited such as bridges, airplanes, and even houses Fundamentals of Composites Manufacturing: Materials, Methods, and Applications 492 20: Damage Prevention and Repair grammed manner. This learning and adapt- ing is usually accomplished by the inclusion of an artificial neural network (ANN) into the smart structure. Applications One important application of smart structures would be bridges and other civil engineering structures. Here the structural components (walls, decking, etc.) could sense when repairs are needed, such as from cracks or corrosion, and then report the location and the extent of the problem. The sensors could also activate motors that could dampen the structure during an earthquake to mini- mize shaking damage. Alternately, a smart airplane or boat could sense cracks, leaks (either externally or internally as with fuel), or excessive forces. The responses could be to report the problem and its extent, and initiate the Figure 20-5. Use of paint-filled microcapsules to detect application of a sealant, which has been damage. preloaded into the critical space. Or, with more sophistication, a sensor could acti- vate motors that might actually change the could sense when they had been damaged shape or stiffness of the outer structure to and then repair themselves, just as living minimize the effects of the forces and thus creatures do? These self-healing structures prevent damage and/or improve operational are already in research and development. performance. A small-scale model of an F/ They are called smart structures. A-18 fighter has already been made and is A smart structure or system incorporates under test in wind tunnels to verify these sensors and actuators into the material of performance concepts. NASA has also flown the system in such a way that enables it to full-scale demonstrators of the F-111 and sense the environment and then respond the Hornet with re-shapeable wings that appropriately in a preprogrammed manner. flex and change their aerofoil shapes. Typical smart structures or smart material Most smart structure concepts are still systems are composites, although this is in the research and development phase not a requirement. Composite structures but some have found their way into actual especially lend themselves to the inclusion commercial use. One of the most common of sensors and actuators because of the way applications of smart composites is for they are made (in laminar structures). the damping of vibrations. Sensors detect A closely related type of structure is called excessive vibrations through piezo-electric an intelligent structure. Intelligent struc- devices, which then apply an opposing cur- tures are smart structures that have the rent to stimulate changes in the structure added capability of learning and adapting and counteract the vibrations. Noisy home rather than simply responding in a prepro- appliances are silenced by smart structures Fundamentals of Composites Manufacturing: Materials, Methods, and Applications 20: Damage Prevention and Repair 493 that sense the acoustic waves being gener- • requires a large number of the devices ated by the appliance and then cancel those spread throughout the structure to waves through active damping. sense and regulate actions. Components and Techniques Fiberoptic Devices Smart structures can be categorized by Fiberoptic devices are similar to the the type of device used to do the sensing or normal fiberoptic cables used to transmit actuation. The most common of these devices telecommunication signals. When embedded are: piezo-electric, fiberoptic, shape memory in composite structures, the output light alloys, electro-rheological fluids, and other signal of these devices changes in relation electro-oriented techniques. to conditions of the surrounding environ- ment. For instance, if the structure moves, Piezo-electric Devices the fiberoptic will change in diameter, thus Piezo-electric devices are made of either changing some components (frequency, am- ceramic or polymeric film, both of which are plitude, phase, polarization, etc.) of the im- electro-mechanical transducers; that is, they posed optical signal. These changes in signal change electrical signals into mechanical can be detected and related to changes in the motion and vice versa. If an electrical signal structure. Other examples of environmental is applied across a piezo-electric device, the changes that can be detected might be tem- device shape will change (usually length) perature, pressure, rotation, acceleration, because of the change in electrical voltage. acoustics, chemical composition, radiation, Alternately, mechanical deformation of the fluid flow, and liquid level. device will result in a change in the voltage When fiberoptic devices are used for trans- output. Hence, the device not only senses mitting signals in normal communications, changes in the structure that it might be the system operator desires to minimize the embedded in, but also gives an electrical very effects that allow them to be used as sen- signal that can be amplified and used to sors. That is, the operator wants to minimize change the characteristics of the structure changes in the signal, which might be caused in which it resides. by environmental effects on the fiber. Thus, Advantages of piezo-electric devices using the fibers as sensors is inherently include: counter to their use as signal transmitters. This duality obviously complicates the in- • ceramic devices can be used as both the terpretation of the data obtained from using sensor and the actuator, and these devices. • rapid response time (although the films The advantages of fiberoptic devices are just sensors). include: The disadvantages include: • ability to sense many different ef- fects, • ceramic devices are brittle and have a small range of mechanical motion, • highly compatible with composites (be- which limits their ability to sense or con- cause both are fibers), trol large spatial deviations directly; • sense both general and local changes, • some potential applications cannot use and electrical devices, thus prohibiting the • largely immune to electro-magnetic use of piezo-electric devices; and interference. Fundamentals of Composites Manufacturing: Materials, Methods, and Applications 494 20: Damage Prevention and Repair The disadvantages of these devices include: which occur slowly, so it is difficult to obtain rapid response, • glass is brittle and easily damaged with relatively small movements, although • susceptible to fatigue, and some polymeric optical fibers may not • relatively low in efficiency. have this problem, and • getting the signal out of the device with Other Techniques the proper interpretation (the general Several other methods have been inves- nature of the environment must be tigated as components of smart structures. well characterized—they are really Some of these include: only sensors). • electro-rheological fluids, which change Shape Memory Alloys their viscosity as a result of an applied electrical field (used primarily for Shape memory alloys have a “memory” damping); because of a transition that occurs within them between two separate phases. For • electro-strictive materials, which con- example, a metal might switch back and strict when an electric field is applied; forth between crystal structures, such as • magneto-strictive materials, which con- between a martensitic phase when cooled strict when a magnetic field is applied; and an austenitic phase when heated. This and allows the metal to remember the shape it • various types of more traditional actua- had when it was cool (or hot) even when it is tors and sensors in combination. subjected to the other conditions. Therefore, when a material is changed from one phase to the other by changing the temperature, Barriers to Implementation the material wants to change shape. But if Many of the same barriers that inhibit the constrained, the material will exert tremen- rapid adoption of composite structures also dous forces on itself. These forces can be used slow the introduction of smart structures. to sense and change the configuration of the These barriers include: assembly in which the shape memory mate- rial is placed. These materials are, therefore, • lack of design data (especially the effects used as actuators in smart structure applica- of inclusion of sensors and other smart tions. Most of the shape memory alloys are structure components); titanium-based, although other materials • high initial cost (smart structures can also possess these properties. have the cost of added components to The advantages of shape memory alloys the already high cost of the composite, include: plus the additional cost of installing the components during manufacture • ability to exert high forces and generate of the smart structure); high strains, and • increased durability problems of the com- • they are ductile, thus resisting impact posite structure because of the presence damage. of the smart structure component; The disadvantages include: • adequate methods for quality control • limited ability to sense changes, and inspection; and • sensitive only to temperature changes, • repair difficulties. Fundamentals of Composites Manufacturing: Materials, Methods, and Applications 20: Damage Prevention and Repair 495 In all of these, the problems of smart struc- of external components, trimming must be tures are added to the already significant done with great care in the presence of leads problems of adopting composite materials. used to connect the devices to the external This fact is especially true in fields where portions of the system. composites are new, such as in infrastructure Successful monitoring and modification of applications (for example, civil engineering physical parameters hinges on the existence structures). Some of these challenges will and knowledge of a unique relationship be- be solved as the promise of smart structures tween the physical parameters of interest becomes realized. For example, although the and the properties that can be modified. In initial costs will be high, the costs over the life other words, what does the data mean and of the structure might be considerably lower how do you use it? In general, researchers when maintenance, inspection, and structural have been able to make test smart structures, failure costs are included. put them into service, correctly interpret the The smart structure devices (components) data from the sensors, and use that data for themselves present additional challenges. For structure modification. All of this has been ac- example, some components are notorious complished in real time, at least for some sys- for being fragile (especially the ceramic-based tems. These experiments seem to imply that devices), which raises the question of long- the promise of smart structures is, in fact, term durability of the entire system. This also achievable. However, large-scale commercial points to the increase in system complexity, implementation is still in the future. which already includes the fibers and matrix. Structures that can be made smart while Now sensors, actuators, connectors, proces- maintaining the majority of their convention- sors, communication links, power, and feed- al properties offer tremendous advantages back all compound the situation. However, over the same structures without the technol- this complexity is not surprising in consid- ogy. Smart structures are able to respond to eration of another self-sensing and repairing changes in the environment, permitting their mechanism—the human body. Surely just the use in a greater number of applications and/ sensing components of the body (nervous sys- or over broader operating ranges. In addition, tem) are many times more complex than even structures can be made smart to increase per- the most complex of smart structures. formance while simultaneously saving weight In addition to the complexity of the sys- by eliminating over-design. Through in-situ tem, there are some problems arising with health monitoring of the structure, safety the methods of manufacturing the smart can be increased tremendously and cost cut structures. How should the devices be in- by extending service life and eliminating stalled? If the device is a fiberoptic line, the need for frequent in-service structural it can be filament wound along with the inspections. Thus the potential for greater reinforcing fibers. However, if the structure safety promises enormous benefits, especially is made of chopped strand, that option is in industries where it is a critical issue, such not open. Piezo-electric devices are usu- as the commercial airlines and automotive ally installed manually, which raises the and construction industries. Liability could question of manufacturing uniformity from be significantly reduced with more accurate structure to structure. Even some seem- failure predictions. ingly simple manufacturing steps are vastly more difficult because of the presence of the REPAIR smart structure components. For example, In the early days of composite aircraft because current technology requires the use structures, it was common to design and Fundamentals of Composites Manufacturing: Materials, Methods, and Applications 496 20: Damage Prevention and Repair build them based on conservative assump- the damaged area, thus adding to the tions about material strength and durabil- thickness of the part. This method, at ity. This was because there was significant least conceptually, doubles the amount variation in material properties and many of material. The damaged area need unknowns concerning longevity. Thus the not be removed when using a doubler. safety or engineering factors were high. In A doubler can be either bonded or these traditionally “overbuilt” structures, bolted over the damaged area. Often, there was a tremendous advantage—inher- especially in thick solid laminates where ent damage tolerance. the composite can tolerate a bolt repair, Today, the design factors are smaller. simply covering the damaged area with Laminate schedules and ply orientations are another pre-cured composite laminate carefully optimized. There is improved con- section or a piece of sheet metal is ef- trol during manufacturing processes such as fective and sufficiently strong to give a prepreg or resin injection of fiber preforms, long-term structural repair. Close-toler- vacuum bagging, and oven or autoclave cur- ance bolt holes must be used. Careful ing. The resulting products are strong, light- attention must be given to the overlap weight laminates with high fiber-to-resin distance, fastener size, the number of ratios. Laminate thickness is being reduced rows of fasteners used, and edge dis- with these materials and processes; thin- tance. Another consideration is the po- skinned cored structures, using honeycomb, tential for corrosion problems if carbon foam, or balsa wood cores are popular. While fiber composites are involved. these can be excellent structures from many 2. Flush-type bonded repairs are placed points of view, repairs to damaged structures into the damaged area. In these repairs, have to be more than just “patches.” The a repair patch of uncured laminate is repair must actually return the structure placed into the damaged area and then to very nearly its original design strength cured. However, before doing the repair, as the rest of the structure cannot just the damage needs to be removed. pick-up the load. As the optimal strength limits of the material are approached in Damage Removal well-designed structures, the more critical After the inspection and damage deter- and difficult repairs become to assure the mination is completed, the marked area of structure retains its full load-carrying capa- damage may or may not need to be removed bility throughout its lifetime. from the structure, depending on the type of While the initial thrust in making opti- repair to be made. mized composite structures was initially Damage removal is usually done by either pursued in aerospace applications, many grinding or routing (cutting). For cutting, advanced composite industrial and civil en- a wheel or circular saw is recommended. gineering structures are now quite similar in Cutters with reciprocating blades, such as design and fabrication to aircraft structures. in a jigsaw, should be avoided as the rapid These also must be repaired to near original up-and-down motion of the blade causes design properties. Therefore, the nature of delaminations along the edges of the cut. repair has become increasingly important. The best cutting technique uses a high blade Two main categories of repairs are usually speed and gentle pressure while moving considered. along the cut at a low feed rate. It is best to 1. The use of an external doubler in- remove damage in an oval or circular fashion volves placement of the repair onto to avoid stress concentrations at corners. If it Fundamentals of Composites Manufacturing: Materials, Methods, and Applications 20: Damage Prevention and Repair 497 is necessary to have an odd-shaped damage In a high-performance advanced compos- removal area, ensure that the corners have ite structure, the fibers are oriented in spe- as large a radius as is practical and avoid cific orientations to carry the design loads. sharp corners at all costs. The only way to get a repair to carry these For carbon fiber structures, a diamond- same loads is to match the ply orientations of grit-edge blade is best. These blades are the original structure with the repair plies. expensive but last a long time, and the cost Therefore, the original ply orientations and per cut is the cheapest of any blade. Carbide materials must be determined. In the pre- blades will last a short time, and ordinary ferred repair design, the original structure high-speed steel blades will be dulled to will be matched exactly, ply-by-ply. uselessness almost immediately. For ara- It is important for the repair to be able to mid fibers, the best damage removal is by transfer the loads in the remaining original cutting. Minimum fuzz is achieved with a structure into the repair plies, and back split helix router bit, operated at high speed, out again. The most efficient way to do this typically between 20,000 and 27,000 rpm. is through a large adhesive bonding area, A reversed steel-toothed blade in a circular which attaches the repair to the non-dam- saw also may be used. (DuPont, the maker of aged structure. The best way to achieve a Kevlar® aramid fibers, offers a free cutting large bonding area is by creating a gradual, and machining manual and can provide more flat taper, called a scarf, as the interface be- information on aramid cutting, drilling, tween the repair and the non-damaged area. routing, machining, etc., including suppliers A scarf repair is illustrated in Figure 20-6. of specialty bits.) This is most often done by sanding away from the edges of the prepared hole. Design Stepping is an alternate to a scarf for the After the damaged areas are completely interface. A stepped repair is illustrated in removed, the new repair material can be Figure 20-7. Although stepping may be oc- applied according to the repair design. In an casionally used instead of a smooth scarf, it ideal repair, the purpose is to try to match and induces stress concentrations at the corners not exceed the original structure’s strength, of the steps and is difficult to achieve without stiffness, and weight. There are obviously damaging underlying plies. other concerns, such as a good long-lasting In conventional marine structures, taper adhesive bond, the smoothness of the repair, angles of anywhere from 7:1 to 14:1 (length cosmetic appearance, etc. However, structur- to thickness) are used. In heavily loaded ad- ally matching the original strength, stiffness, vanced composite structures, flatter angles and weight are the foremost goals. are often used, anywhere from 20:1 to 60:1 In any composite design (including for being common. Sometimes aircraft repairs repairs), it is important to realize that the will go out as far as 100:1. Obviously, the fibers carry most of the load. The matrix flatter the taper angle, the more surface resin is weak, brittle, and serves primarily to area for the bond and the more gradual the transfer the load uniformly through the fi- load transfer from the original structure into bers, keep them in alignment, prevent them the repair plies and back out again, and the from buckling under compressive loads, give more undamaged laminate that has to be the part shape, and protect the part from the machined out. environment. These are all important func- If a relatively flat scarf, for example 40:1, tions, but it is still the fibers that carry the was done that exactly matched the original actual structural loads. ply lay-up sequence, somewhere between Fundamentals of Composites Manufacturing: Materials, Methods, and Applications 498 20: Damage Prevention and Repair Figure 20-6. Scarf-type repair. Figure 20-7. Stepped-type repair. Fundamentals of Composites Manufacturing: Materials, Methods, and Applications 20: Damage Prevention and Repair 499 60% and 100% of the original strength To give an extreme example of a stiffness- (tensile, compressive, and shear) of the part critical structure, consider a pole-vaulter’s would be maintained. So, for a .25-in. (0.6- pole. In use, it is bent through an extreme cm) thick skin, a 40:1 taper gives a scarf angle and, of course, also experiences com- length of .25 × 40 in. (0.6 × 102 cm). The pression and tension loads. If it was damaged total full strength is not obtained because and repaired, care would need to be taken the fibers in the repair and in the original to not create a stiff spot, which would cause part are cut. Also, the fibers must transfer the pole to unnaturally flex just at the edges their loads through a new structural adhe- of the repair. Such a stiffness discontinuity sive bond, which did not exist in the original would cause the pole to fail at the edges of structure. The fibers themselves do not cross the repair at a much lower bending load the bond line. Typically, to get back to 100% than normal. Therefore, to repair a pole- strength, extra repair plies would need to be vaulter’s pole, a large, flat, scarf area would added. This increases the weight and thick- be prepared with a low taper angle. Such a ness of the repair. technique is sometimes called feathering. Bending stiffness is more a function of the However, since the thickness would be care- thickness and ply position of the structure fully matched to control the bending stiff- with some dependence on the type of matrix ness, the expected result would be a decrease and fiber (carbon being much stiffer than in tensile and compressive strength. fiberglass or aramid). All else being equal, bending stiffness goes up approximately with Bonding the third power of the increase in thickness. Since heavy structural loads must be This means that if the repaired area is the transferred across the repaired area through same thickness as the original structure, it the bond lines, the adhesive bond itself must will have about the same bending stiffness. be structural. The type of adhesive is impor- But if the repair is twice as thick, it will be tant, as is the preparation of the surfaces to about eight times as stiff! So a full-strength be bonded. There is no ideal adhesive that repair, attained by adding extra repair plies, will solve any bonding problem. However, will be stiffer than the original. A stiffer epoxies, acrylics, and their derivatives, such repair patch will attract more load and ef- as methacrylates, are generally the best for fectively weaken the structure. This may be most repair purposes. Polyester resin does fine or it may be a disaster! not make a good structural adhesive. The consequences of the changes in Epoxies, while strong, are intolerant of properties need to be considered carefully. dirty surfaces so meticulous surface prepa- If tensile and/or compressive strength are ration is crucial to achieving a long-lasting most important, (for example, in a structural bond. Bond deterioration due to a poorly column) then a repair that is stiffer than prepared surface is seen over time, espe- the original will probably be fine as long cially when there is exposure to water. Bond as the compliance requirements (in case of strengths deteriorate much more rapidly an earthquake) are considered. However, when initial surface preparations are poor a helicopter rotor blade experiences large than with properly prepared surfaces. The bending loads. Thus an overly stiff repair difference between a structural bond that halfway out on the blade would be a problem lasts one year, and one that lasts 30 years, as it would induce large stresses around the can literally be the difference in the type of periphery of the repair, possibly leading to rag used in solvent wiping, or in the cleanli- premature failure. ness of the solvent itself. Fundamentals of Composites Manufacturing: Materials, Methods, and Applications 500 20: Damage Prevention and Repair Surface preparation for bonding is actu- 10. Trace out on additional pieces of clear ally a long and involved subject, with many film the outline of each repair ply so subtle points just now being well under- all will neatly fit in the “contour map” stood. But briefly, it is prudent to be very created on the surface by the scarfing. clean in preparing the scarfed surface. Do 11. Mark on the templates the orientation not blow compressed air on it to get rid of of each ply. dust. Compressed air is full of oil and water. 12. Cut out replacement plies from the Clean, reagent-grade solvents and clean, same material as the original structure. one-use only, disposable rags should be used. If this is not available, consult with ven- Surfaces should not be touched with hands dors to find a close substitute. Original after scarfing unless clean gloves are worn. materials or very close substitutes are The surface should be thoroughly dry before a must for heavily loaded, lightweight, applying the adhesive. Further, the cleaned structural repairs with small safety surface should be protected with a taped-on margins. piece of paper if the person doing the repair takes a break between steps. The basic se- 13. If working with prepreg, apply a layer quence for conducting a damage assessment of film adhesive to the entirely clean and structural repair is as follows. scarfed area. If wet lay-up is being used, apply a thin layer of the epoxy resin to 1. Gain access to the part from both sides, the scarfed surface. if possible. 14. Lay down the innermost, smaller ply 2. Clean and dry the surfaces. first. If there is a hole through the 3. Remove any gel coat and/or paint by structure, it will need support with a careful mechanical abrasion, not with released caul plate on the backside if ac- paint strippers. cess is available. If there is not backside 4. Inspect for damage visually and by access, then one technique is to bond by tapping. using an oval hole rather than a circular 5. Mark out the damaged area. one with a larger oval on the backside to act as support for the “filler” ply. 6. Remove the damaged area of the struc- ture. If it is thick and the damage is not 15. Continue to lay up one ply at a time, all the way through, then the damaged working up toward the larger surface plies may be ground away until solid plies plies. Be careful to match the ply ori- are reached. entations of the original structure. 7. Carefully taper (scarf) the surface by 16. Once the top ply is in place, add any sanding away from the edge of the extra repair plies with each being about damage. Use at least at a 12:1 taper for .5 in. (1.3 cm) larger all the way around lightly loaded structures and up to 40:1 than the original top ply. The ply orien- for heavily loaded structures. tation of the extra ply or plies should 8. Ensure that the scarfing is done slowly match the original outer ply. and carefully by a skilled artisan. 17. A sacrificial outermost ply of thin 9. After the scarfing is completed, cover fiberglass may be added to act as a the surface with a smooth, taped-down sanding ply. sheet of clean paper or plastic film to 18. Vacuum bag the repair using standard protect it from dirt, moisture, grubby bagging techniques as described in a fingers, etc. previous chapter. If using prepregs, if Fundamentals of Composites Manufacturing: Materials, Methods, and Applications 20: Damage Prevention and Repair 501 the repair has more than four or five the original laminate. The difficulty with plies, or if it has a complex contour, this situation is that the repair is contained then it is strongly recommended to within a much larger part, which cannot and perform intermediate debulking steps probably should not be put into an autoclave. using a vacuum bag to pre-compact and For this purpose, portable curing systems, consolidate the plies. which cover only the repaired area, have 19. Cure the repair. Use high temperature, been developed. Figure 20-8 is a diagram if required, in a controlled oven. If an of such a heating system. This system uses oven is not available, carefully use heat a vacuum bag (normally reusable) to cover lamps or heat guns and multiple ther- the repair area. The system is sealed with mocouples to monitor and control tem- vacuum “tacky” tape and then a vacuum peratures evenly. If a room-temperature and heat are applied. The cure cycle is set wet lay-up is being used to create the by a controller; thus a precise thermal curve repair material, most structural epoxies is developed. still require a high-temperature post- When repairs are made to aircraft, the cure to develop full strength in a reason- Federal Aviation Administration (FAA) re- able time. However, some epoxies can quires that a record of the repair be made. be fully cured to reasonable strength That record must show the cure cycle of the numbers at room temperature. These repair material. Thus these portable repair may be fine if high temperatures will systems usually have a recorder for the tem- not be encountered by the repaired perature and the time. structure in service. 20. After the cure is completed, debag the CASE STUDY 20-1 repair and inspect it for delaminations, Self-healing Composites de-bonds, or other flaws. Living bodies are amazing organisms. 21. Clean it up carefully and sand it smooth When they are damaged they can heal (do not cut the fibers in the top ply un- themselves. Inspired by that capability, less it is a sacrificial sanding ply). Apply researchers at the University of Illinois Ur- paint or gel coat as appropriate. bana-Champaign have developed a compos- Doing a repair the right way is not diffi- ite material that can also heal itself. It even cult, just time-consuming, requiring a high bleeds for a short while before completing level of training and attention to detail. How- the healing process. ever, it is possible to repair critical structures The self-healing material is made by correctly and with good confidence that the mixing epoxy resin with a small amount repairs will last. It has been done every day of organometalhalide (Grubb) catalyst and in the aircraft business for many years and microspheres containing the “healing agent” is now being done in the marine industry (dicyclopentadiene [DCPD] monomer). commonly. When the epoxy is cured, both the catalyst In addition to curing the adhesive used and the microspheres are encapsulated in and to make the repair, the layers of material distributed throughout the matrix. If the com- that make up the repair itself must be cured. posite receives a blow of sufficient magnitude If the repair is to mimic the properties of to initiate a micro-crack, the microspheres the original laminate, it must be made of the rupture as the crack expands through the same materials. Further, it must be cured matrix. The rupture of the microspheres using the same cure-cycle parameters as releases the DCPD monomer, which “bleeds” Fundamentals of Composites Manufacturing: Materials, Methods, and Applications 502 20: Damage Prevention and Repair Figure 20-8. Portable heat system for curing the repair area. in the area of the crack. As the DCPD bleeds, The healing mechanism has been con- it comes into contact with the catalyst, which firmed by optical and scanning electron is distributed throughout the matrix. The microscopy. Mechanical testing has revealed catalyst triggers polymerization. Because that, with some optimization of the critical of the rapid polymerization capability of parameters, 85% healing efficiency (recap- DCPD, the resin quickly solidifies and bonds ture of original fracture toughness) was the sides of the crack together. Hence, the obtained. crack is “healed.” This situation is depicted This autonomic (from the same root as in Figure 20-9. “autonomy”) healing technology has obvious The secrets of self-healing technology lie applications in products such as tubs and in the choice of material and strength of the showers, which are susceptible to thermal walls of the microcapsules. If the walls are too cracking, electrical applications where crack- thick, they will not rupture when the crack ing might cause electrical failure, in fatigue- approaches. If they are too thin, they will be prone products, and in any application where broken in processing. The toughness and hidden cracks might shorten product life. stiffness of the walls of the microcapsules and the strength of the bond between the SUMMARY microcapsules and the matrix are relevant Because composites are usually brittle control parameters. The amount of catalyst materials, impacts often result in damage to and the concentration of microcapsules are the fibers and the matrix. When composites also important considerations. have been optimized for weight and perfor- Fundamentals of Composites Manufacturing: Materials, Methods, and Applications and especially in critical applications. It is then im- pacted. and then impacted with a weight suf- ficient to cause visible damage. The repairs attempt specimen from the repaired laminate. Also. 3. This can rarely mens and compare the strength. because repaired laminates. 7. Be classify the damage so that the repair process sure the repaired area is in the tensile can be more effective. LABORATORY EXPERIMENT 20-1 Scarf Repair Objective: Compare the strength of a re- paired composite to the original material. the tap test to identify the extent of the this damage can be catastrophic. reduce damage effects. great efforts have gone into preventing dam- age or into reducing its effects. Fundamentals of Composites Manufacturing: Materials. (0. Therefore. (The sample can be supported on a metal ring of a reasonable diameter Figure 20-9. After curing the laminates. Make two composite laminates that are as nearly identical as possible.25 in. and elongation of the original and shorter than in the original. Inspect the damage visually and with mance. The reality is that damage is inevitable. Cure the repair materials. These methods also help to laminate and the repaired laminate. So. damage. Self-healing composite. Nev- ertheless. It is also sometimes scarf area using the techniques of fit- possible to change the design of the part to ting and pressing. Sometimes. 5. The other laminate is supported so that it has space underneath. there is inevitably lower performance than if there were no adhesive present. Cut tensile specimens from the control and quantify it. methods have been developed to inspect 8.20: Damage Prevention and Repair 503 an adhesive layer holds the repair patch. and Applications . material changes can be made to reduce the 6.6 cm) thick and constructed from layers of epoxy prepreg. technique. repairs can come quite close to their intended targets if they are carefully designed and executed. Place uncured epoxy prepreg into the effect of the damage. Perform the tensile test on the speci- part to its original values. It is suggested that the laminates be about 10 × 10 in. Remove the damage area using the scarf without much of a performance penalty. 2. to return the properties of the composite 9. Methods. (25 × 25 cm) and about .) 4. stiff- be done because the fibers in the repair are ness. set one aside as a control. Procedure: 1. Strong. and White. Which lay-up would you expect to have the smaller impact damage. Dearborn. Upper Saddle River. Methods. 2001. 409. QUESTIONS 1. R. [0/45/0/45] or [0/45/45/0]? Why? 6. White. 683–699. Society of Manufacturing Engineers (SME). BIBLIOGRAPHY Kessler. 2001.. 794–797.” Letters to Nature. M. pp. What is the tap test? List two precau- tions that should be observed to make the test more accurate. 2. Part A32. What are two advantages of using a stan- dard damage classification system? 5. 15 February.504 20: Damage Prevention and Repair 10. Composites Manufacturing video se- ries.org/cmvs. et al. Fundamentals of Composites Manufacturing: Materials. Why does a hybrid composite suffer less damage than an otherwise equivalent single fiber composite? 7. S. Repeat the experiment with different scarfing angles and change the lay-up technique by laying the largest ply down first as opposed to laying the smallest ply down first. What is a scarf repair and how does it differ from a step repair? 3. What is the advan- tage to its use? 4. Explain how a self-healing polymer works. NJ: Prentice-Hall. MI: Society of Manufacturing Engineers. 3rd Ed. S.” Composites. and Applications . Plastics: Materials and Processing. 2006. pp. A. Vol. “Autonomic Healing of Polymer Composites. www. R. Inc. 2005. “Self- activated Healing of Delamination Damage in Woven Composites.sme. Describe feathering. R. Brent. generally at a purposes: lower cost than the backbone resin system itself. The ability of styrene to accomplish both • Contamination in the plant purposes has resulted in lower costs overall • Disposal. and Applications 505 . inside. for instance.1: Introduction to Composites 505 21 Factory Issues CHAPTER OVERVIEW Materials. then. Methods. Generally. such as methyl methacrylate. • Problem of emissions and how to deal because of the predominance of styrene in with them the unsaturated polyester and vinyl ester • Governmental regulation resin market. Styrene forms resins and vinyl ester resins for two major a part of the cured polymer. imparts stiffness to most cured systems (and cosity control so that the fibers can be some brittleness) and generally enhances the wetted. because allow the solvent to be extracted from such a this chapter may be examined by itself and solid part and. and recycling and improved performance and manufac- • Factory simulation turing efficiencies. as a presented. relatively inexpensive diluent. styrene 1. are called concepts: reactive diluents. 2. However. However. It could not be effectively removed TO DEAL WITH THEM after molding because the cured resin would Some aspects of the information in this and be so stiff that the solvent would be trapped succeeding sections have already been dis. It is able to Fundamentals of Composites Manufacturing: Materials. which is unique to this chapter. only at the risk of part because a stronger focus is needed on some degradation. to serve as a crosslinking agent for the Besides being effective. styrene is also a resin. Other reactive diluents exist. New material is also the solvent removed during curing. and physical properties of the finished product. waste. which simultane- This chapter examines the following ously accomplish both purposes. to dilute the mixture for effective vis. When it has been crosslinked. the material is treated here performance resins must be solvated and again in some detail. a diluent that was non-reactive. Several epoxy and other high- of the points. are difficult to use and more costly. and. This would require that the diluent be removed during PROBLEM OF EMISSIONS AND HOW molding. the excellent reactivity of sty- Purposes of Styrene rene during crosslinking results in it being Styrene is added to unsaturated polyester used up during the reaction. Imagine. result. like styrene. the focus in this section will • Material storage be almost exclusively on styrene. Only long and careful heating would cussed in earlier chapters. This higher crosslink density nor- vinyl esters was to modify their existing resin mally increases brittleness. whereas under starved conditions. multiple styrene Reducing Styrene Content molecules join together to form long cross- There are some strategies being pursued links. the heat distortion temperature viscosity for fiber wet-out could be reduced. The amount of sty. therefore. the ex. the base resin was to shorten the molecu. the shorter polymer chains mean that the carbon-carbon double bonds occur Modification of Existing Polymer Systems relatively more frequently. ultraviolet light lar chains. also reduced the amount of styrene available ant (HAP) because it forms a potentially for crosslinking. and Applications . the amount of crosslinking has also changed. density approximately cancel one another. Hence. contributes to easy wet-out of resin systems has been successfully reduced.) The reduction in planation surrounding them is complex and the total amount of styrene contained in the beyond the scope of this book. The extent intermolecular entanglement and. would normally lead to lower overall concepts behind the changes rather than brittleness since styrene is inherently brittle. The resin manufacturers realized that if Thus the brittleness is about the same as it the viscosity of the base resin were lower. Recent federal govern. The effects are much more important in gel Fundamentals of Composites Manufacturing: Materials. but it also gave quick results. Lower overall styrene content and higher ment regulations in the United States and crosslink density occur simultaneously companion regulations in Europe and many with low-molecular-weight resin systems. the details. This means that the viscos. styrene content and the increase in crosslink cially. higher number of crosslinks being formed ufacturers of unsaturated polyesters and overall. Other properties. other countries are now forcing reductions in The lower amount of styrene available for the level of styrene vapors permitted in the crosslinking results in a “starved” situation air. the systems so that less styrene would be needed. chalking. crosslinks. and therefore. ity of the resin is lower. to reduce the molecular resistance. and solvent resistance will be increased by The first method to reduce the viscosity of higher crosslink density. the reduced level of styrene dic- ideal from a functional standpoint. cracking. (Under excess styrene conditions. “How has crosslinking changed the result- reinforced plastic (FRP) parts must be moni. ing polymer’s properties?” tored and controlled. resulting in a The initial effort by almost all of the man. the nature of the dangerous vapor. Shorter chains have less smoothness. thus. amount of styrene needed to achieve good Generally. such as blister resistance. styrene is nearly However. However. also may be affected. Therefore. The question styrene emitted in the manufacture of fiber is. of the effects must be evaluated on a case-by- flow more easily. Therefore. However. that is. and surface weight of the resin. each of the crosslinks is reduced. tated by viscosity control requirements has styrene is listed as a hazardous air pollut.506 21: Factory Issues easily dissolve most of the important resins rene needed in these lower-molecular-weight and. Therefore. However. by resin manufacturers to reduce the styrene each crosslink is formed with only one or content of their products. in the cured poly- the focus here will be on the direction and mer. However. Methods. and the exposure time that workers are during crosslinking. This starving means permitted to accumulate during the course that the number of styrene molecules in of their work. the would be in the unmodified resin system. the reinforcement. two styrene molecules. effects on brittleness from the reduction in This strategy was not only prudent commer. case basis with each resin and application. This ness or higher heat distortion temperature. It spect to other components and when they are Fundamentals of Composites Manufacturing: Materials. and Applications . the new resins might have not used. molecular-weight molecules has a tendency these alternate components might give ad- to make the molecules slide over each other ditional benefits such as increased tough- more easily. resin properties two scenarios. the glycols and then the second is added ing the nature of the base polyester resin. of the polymer. mation. chemical polarity effects. distribution of the acids could be random. Rather. practice. Methods. This is not just a shift are investigating. tried. it is safe to say that all of A particular component could be forced to the major resin manufacturers are working group together or to be dispersed to the ends on innovative new resin structures that will depending on its relative reactivity with re- enable the styrene content to be reduced. lower viscosity allows less styrene to be Therefore. If two diacids are mixed to- can be significantly changed. the bility comes from their molecular shape and presence of a significant quantity of low. At the same time. (For example. the effects need to many new products will be announced. be evaluated carefully. or at least no major weight distribution can be skewed to have reduction in properties as a result of the more low-molecular-weight component. In decrease in styrene. An example found that by varying the types and quanti. The resin manu. reasons. the the differences between ortho and iso res. Therefore. two very different pletely new diacids and glycols are being polymers could be formed. before is anticipated that within the next few years. of such a change would occur under these ties of diacids and glycols. However. Some resin manufacturers call this The sequence of components along the the clean-slate approach. So. Even when common components. Resin producers have making the polyester resins. it is a glycols (like neopentyl glycol) are known to change in the statistical spread of the mo. But there is a limit to which these styrene concentrations can be made by changes are effective so other methods of varying the sequence of addition of the reducing styrene also may be needed. the result could be preferential po- In addition to different combinations of sitioning of the second diacid at the ends previously used components. thus lowering the viscosity. Some of the acids and to lower molecular weights. these changes can be made without Some resin manufacturers have found significant changes in the properties of the that new resin systems requiring lower resin. These changes occur because mixtures of multiple Developing New Polymer Systems types of diacids and glycols. backbone resin also can be altered by chang- facturers are reluctant to disclose the details ing the addition sequence because of differ- of these changes because of competitive ences in the reactivities of the components. are often used in of diacids and glycols. be more soluble in styrene than the other lecular weights of the polymers. a few basic concepts can illustrate rent resin systems is a change in molecular some of the directions the resin producers weight distribution.) However. some com. later. if one of the diacids is added to Therefore. changing gel coat resins.21: Factory Issues 507 coats than in laminating resins. many possibilities exist for chang. gether and then added to the glycols. the molecular weight of only reduced styrene content but improved the resin can be reduced and the molecular physical properties. This increased solu- the average molecular weight is still high. ins lie in the choice of acid that is reacted. which have Polyesters are made from the reactions different reactivities. Without disclosing any proprietary infor- Another modification being made to cur. diacid and the glycol components. Hence. Some have called these changes one. some using a component other than a diacid and alternate monomers. Another example is rene requirement. and vinyl esters. methyl group on the benzene ring). phenolics. and Applications . melamines. Wet-out of fiber- to have more options available for doing so glass remains excellent since only enough of than unsaturated polyesters. For example. polyurethanes. therefore. known as acrylic. to as mixtures). MMA also polymers are higher in cost than the basic offers some improved properties such as polyester. DCPD. Methods. which have lower vapor glycol. epox. This adduct has low a lower vapor pressure and thus lower air molecular weight and.” The net result vapor pressure. (Short chains such The properties of a vinyl ester also can as these are sometimes called oligomers. The net result is a resin t-butyl styrene. Such units chemical reactivity but that have a higher are often called adducts because a few molecular weight and. but the properties of the blend lower smoke generation. allow lower concentrations to be used to ies. at using completely new monomers that are ing of unsaturated polyesters and vinyl not like styrene at all. These is methyl methacrylate (MMA). thus allowing problem. the resin manufacturers are attempting Substituting Other Monomers to create shapes and chemical natures that Styrene is not the only monomer that favor lower styrene contents. Vinyl esters tend same in the cured product. same viscosity used with the monomer alone. vinyl toluene is of mixing DCPD with maleic acid and eth. for the use of less resin or discovering new stage and two-stage additional polymers. therefore. such as dicyclopentadiene (DCPD). Using known principles and new technolo- gies. pollution potential. One approach is to choose leic acid and glycols to form a low-molecular. A major limitation to using with fast cure cycles. is con- full polymerization has been done (referred sidered a hazardous air pollutant (HAP). alternatives. blended achieve acceptable viscosities. Therefore. maleic. the cost of producing the dimers and similar between vinyl esters and unsaturated trimers is significant. MMA may be more compatible blends with unsaturated polyesters include with some polymer systems and. applications. good stiffness. This material also has a ferred to as copolymers) or as blends after high vapor pressure and so it. good reinforcement alternate monomers is their higher cost. but has glycol. acts as a reactive diluent for unsaturated Occasionally. similar to styrene (having just an additional ylene glycol is an adduct of DCPD—maleic.508 21: Factory Issues added. The prime example esters with other polymer types. pressures. the reactive diluents.) be changed significantly by modifying the Performance of these materials is almost the nature of the backbone. Of course. a lower units are “added together. sometimes blends can be done as monomers (often re. the the dimers and trimers is added to achieve the specific natures of the changes are different. therefore. Again. too. print hiding. a polyester resin is made polyesters and vinyl esters. are being investigated as styrene This material can be used to react with ma. good Another approach is to simply combine moisture resistance. a low sty. Some of the interesting However. Some manufacturers have been looking Another major area of focus is the blend. cost is a can be substantially better. good fiberglass wet-out. and two or three styrene molecules together good air bubble elimination when compared and then use these dimers and trimers as with many conventional resins. but the concepts discussed in this section are However. polyesters. Fundamentals of Composites Manufacturing: Materials. monomers that are similar to styrene in weight chain of only a few units. In general. Lewis (Lewis 1979) articulated well this The use of highly thixotropic materials problem when he said. this concept is really using wasted in what seems like an unnecessary an old technology for a new purpose. they will form best if allowed to is inevitable. “Of all tyrannies. To alleviate these problems. or sprayed. Lay. even though of the film-forming systems contain excess you may not agree with or appreciate their thixotropic agents to ensure that the resin actions. governmental will form some films. The company is to the resin mixture. but they also experience the thrill want to do is collect taxes or shut down a of power when. the are they able to enact the changes that they better. Hence.” C.” the thought of receiving a call from the gov. I’m from the govern. The idea Film-forming materials work best on hori. a can. smooth and spread easily when brushed. This adhesion problem has role that it (as a bureaucracy) and many of been alleviated somewhat by creating adhe. Non-horizontal surfaces To make matters worse. as a place of power and influence. These films contain While it is good to have some element of so- carbon-carbon double bonds. in themselves. crosslinking to occur through the film. sit for some time. And. reduce solvent escape. alienation of those with different opinions if sprayed. quiescent (that is. non-turbulent). Hence. This is why may be better to live under robber barons some paints are thick when in the can but than under omnipotent moral busybodies. problem with this method has always been One of the reasons why businesses are the potential for poor bonding wherever the so distrustful of government is the activist wax is present. some ing your company and society. but those who torment us for our own good will torment us without end. Adhe. its employees (as individuals) have assumed. and Applications . This power Fundamentals of Composites Manufacturing: Materials. and that means lots of money improved. sion-promoting films. for GOVERNMENT REGULATION they do so with the approval of their own Business executives laugh (and cringe) at conscience.” For most people. company? Seemingly. mental service because they see government ment and I want to help. are self-serving and reactionary. When officials have this attitude. sleep. The and counter-productive effort. The robber baron’s cruelty may sometimes rolled. It this technology for some time. have been used for many compelled to turn to a lawyer to fight the years to exclude oxygen so that cures can be government. thus allowing ciety leading in various progressive causes. not be able to have such power. that they might be wrong just does not occur zontal surfaces and when the materials are to them. it seems that these activists assume that sion between materials on both sides of the their opinion is “right” and that all others film is thus promoted.21: Factory Issues 509 Suppressants if a company does receive such a call from Yet another strategy is to form a surface the government. often formed by adding wax fied enough to handle it. they might company for some alleged violation. Methods. tyranny sincerely exercised for the good of The paint industry has successfully used its victims may be the most oppressive. who is there to help the layer to suppress the emission of styrene. S. in other settings. his cupidity may at some point be satiated. It is like your mother giving you a stays on the vertical surfaces and becomes spoonful of medicine “for your own good. Not only the fewer contacts with the government. It seems that all government officials envision. Some people seem to have entered govern- ernment saying “Hello. no one feels quali- ers such as this. but they are not as activists believe that they are actually help- effective. quiescent. Methods. with high quality. Hence. Interestingly. fines of the city and allowed them to specify Therefore. He was a member of the sculptor’s guild in ments. Individual artisans became Historical Perspective the primary makers of goods (since this was The role of government has been and can before factories were created). which solicited legal and their desire to control the economies of protection from the local governments. ernment had little choice but to allow him lated and individuals who were especially to sell his goods even though he was not a adept at a trade moved to the city where they member of the guild. People could he refused to be bound by its rules. was forced to produce its own food. the rise of power and prestige of the kings ciations. They sought to establish a quality declined in power. A look at became so powerful that they dictated the past interactions of government and busi. called guilds. Cities began to be repopu. and plunder on the highways. the monopoly could become artisans in that trade. the city hall and the church. nature of government policy toward manu- ness may help to form some suggestions for facturing. reducing the power of the guilds. of the guild was broken. There was little travel because factors contributed to the weakening and the barbaric tribes that had conquered the eventual demise of the guild system. But. and Applications . the guild members had to guarantee a to bureaucracy rather than their insight high standard of quality. but left it when his apprenticeship principle production unit. clothes. wool.510 21: Factory Issues often comes because of their faithfulness leges. He believed that the qual- About the year 1000. they formed trade asso. shoes. each family that grew among the members of the guilds. Since travel with reasonable safety and goods his work was obviously excellent. The their countries. The prime example of this was Michelangelo. two tiny villages. occurred throughout Europe over the next quality products than did the common family hundred years or so and thus the guilds producer. was completed. The Western Roman Empire regularly robbed first of these was the rivalry and competition travelers and traders. the kings named a particular the price of the products. the implementation ity standards established by the guild were of the feudal system resulted in less thievery restrictive on his creativity and. meager farms that were grouped around With the coming of the Renaissance. the picture painted here is not so that the goods could be made long term the total view. leather. along with monetary policy (or improvement of the currently antagonistic more) in most medieval cities. preferred rates and/or with high quality. Hence. The power of situation. The guilds be quite beneficial to industry. The guilds were also and performance in directing and leading required to establish a system of training change. the origins of trade the guilds can be appreciated in cities such associations and professional societies can as Brussels where a visitor to the central be seen in the historical view.D. the gov- could be shipped. cloth. Kings in this period (roughly governments granted the guilds exclusive 1500–1750) sought to purchase goods at rights to sell their products within the con. company as “purveyor to the crown.” which Fundamentals of Composites Manufacturing: Materials.) most people lived on small. therefore. standard and raise the price so their special Another factor was equally important in skills could be rewarded in the marketplace. It was a time when the family was the Florence. The apprentice system was the result. and farm imple. This was To accomplish this. square of the city sees that the guild halls In the early Middle Ages (approximately share the perimeter of the main plaza with 500 to 1000 A. but for those privi. Similar situations The artisans generally produced higher. Hence. The government. this system. give trading companies exclusive territories Governments. This country was founded on the marketplace). With the growth of free markets. tance in their negotiations. government should be highly responsive to tions for workers and high prices and poor public wants. ship. the merchant class (which included the in. and the preferred nobles even took an ownership po. Eventually. those companies Asia. was This system of government manipulation of to control industry by governmental owner- industry and trade was called mercantilism. the activists within (about 1750–1900). companies need some assis- forced the kings into limited monarchies. Clearly industry of the “common man” or diminution of the thrived when given the freedom to do so importance of doing what the public feels (subjected only to the natural forces of the is correct. the greed principle that government derives its powers and shortsighted practices of industrial lead. can intimidate almost any com- took over control of the government and pany. This policy was by associations. Fundamentals of Composites Manufacturing: Materials. the formation of factories government still see industry as a great evil resulted in far too many companies with that must be controlled. There should be no disparaging Revolution were strong. took two different Dutch East Indies Company) in efforts to courses of action to control industry. the opponent of industry. Smith and oth. and Applications . from “the consent of the governed” and so ers of the day resulted in atrocious condi. which were responsive to (such as the Hudson Bay Company and the the publics they served. The public was outraged and sition in these companies. the kings were forced to retreat from favor. Again. the American Composites Manufacturers such as Adam Smith. guided by the doctrines of Karl Marx. Simultaneously. and Latin America. who wrote the classic. Social- Because the crown favored some companies ism. The other course gained great power and did not need to be nor of action was for government to become an did they want to be part of a guild. Kings would also demanded that something be done. That was the path power of the guilds was weakened. Government officials must first remem- The economies of the European and ber that they are ultimately responsible to American nations during the Industrial the public. ing with the government on styrene emis- ers advocated that the government stay out sion standards. at the expense of others. taken by some governmental officials in the With the rise of the Industrial Revolution United States.” child labor. For example. Today. increase the total exports of their countries. the ability of guilds to monopolize Role of Government trade was over. The merchant class resources. That is a role The political and economic policies of this that trade associations can fill. These were the days over all others. however. monopolies. Sometimes the kings or their of the “robber barons. One. Association (ACMA) is the entity negotiat- Wealth of Nations. still exists in parts of Europe.21: Factory Issues 511 gave that company a competitive advantage quality for consumers. new merchant class were formed by writers. government excellent quality and prices for any king to and industry are often confrontational in the have only a few favorites. Negotiations between a single company dustrialists) grew in political power so that and the government are often not balanced. United States. Hence. called laissez faire. Africa. in 1776. There is hope for amicable of direct involvement in industry and just relationships between governments and let the natural forces of the marketplace industries when interactions are facilitated dictate what would occur. with nearly unlimited ing specific companies. In various forms. Methods. not considering by MEP engineers and then establishment what the government has done to “earn” of programs designed to help companies their share of profits. This out of their profits. industry is an system. Role of Industry tion. ment has done much. without the company that is responsive to custom- favoring one company at the expense of its ers and the public in general. internal demands by the populace must urge ber that. on the industry of the na. This includes and current in their technology. good facturing Extension Partnership (MEP) quality. has proven to be highly important (fundamental) constituency of beneficial to the population in general and government. This help is often company. Fundamentals of Composites Manufacturing: Materials. working to accomplish this is the Manu.512 21: Factory Issues Government officials should also remem. ultimately. go to to create an infrastructure that supports a third-world country and see the problems and promotes industry. the pool of the government to purge itself. In reality. government should government. They have created the Government also has the responsibility climate for success. However. This gov. Hence. Utilities. Industry also has the role of improving ture support is not present. the public’s needs and desires help industry improve. This does not just mean eliminating air China to meet the needs of that country’s and water pollution. the dominant industrial system Historical precedent and modern practice in the world today. Therefore. Just as with competition. everything from roads to utilities to banks ernmental responsibility can be critical to to education. resources on which government depends is based. that the government is a partner in the to assist companies. Roads should be that a company must endure just because good. historically and today. which are government the infrastructure and economic climate regulated. The most respon- role in assisting and regulating industry. through the National Institute of Standards Most companies pay from 30 to 50% of and Technology (NIST). therefore. clearly in countries where such infrastruc. corruption in government is a company do this? Because these acts will rampant in some other parts of the world. of various taxes. capitalism. international pressure and to the ultimate customer—the public. If you doubt this. and reasonable salaries sponsored by the Department of Commerce should be part of management’s focus. Further. a company is responsible ruption exists. People pay taxes out of the wages they Each industrial executive strives to make a receive from industry. All are affected by the govern- a company’s success as can be seen most ment and its policies toward business. these profits suggest that government has a legitimate must be made responsibly. One program already should be the ultimate focus of the company. that is. Why should United States. to a real ex- ment (and usually from state governments) tent. sible method is to have a long-term plan for This should be done fairly. Although not necessarily a problem in the and helping the local charities. That means. must be fair in their pricing are not friendly to companies. improve the culture in which the company This should not be tolerated. the govern- where needed. Too often company executives see initiated through assessments conducted their profits drained away. environmental concerns. The MEP receives their income to the government in the form significant support from the federal govern. Where cor. Industry pays taxes profit for the investors in the company. promoting education. Methods. fair prices. Great efforts the environment in which the company ex- are underway to build the infrastructure in ists. It means supporting industrial growth. the little league team. operates. and Applications . After all. is. Government is association should also represent govern. the association. Methods. Associations facilitate the inter- such meetings are also important and should actions between government and industry. Work within your company or within govern- the Society of Manufacturing Engineers has ment to fulfill the role that is appropriate. Each branch understands ing that has some governmental control is its role and respects the roles of the other the storage of hazardous or potentially haz- branches. They ment/industry relationships. Only rarely and reluc- technology can be exhibited. role of government. join an association precedent. The purpose of these regulations public—and so they should seek ways to is to prevent excessive exposure of workers benefit the public. elect individuals who see the proper manufacturing concepts of all types. at most levels. The government has sug- Just as with the branches of government. responsible for the macro scale and does ment to its member companies. necessarily. a professional society) government in the United States have a and stay active in it. If it does so. They check each other and balance the power There is hope for a better world through but they do not. be fostered. for individuals. It is sometimes too easy for a politician to criticize and suggest radi- The New Relationship cal solutions that are outside the legitimate The cooperation between government. realm of governmental action. That two. ardous materials. have mutual respect and cooperation! hostility. and assum- ing partisan politics can be overlooked. Support it with time and similar separation and interrelationship. The reasoning is that Fundamentals of Composites Manufacturing: Materials. often facilitated by climate for doing business is established. How does the individual help? First. the three branches of (or. Industry operates at the micro level. They also help industry with functions that portant for keeping the members informed are too costly or too difficult for the company and provoking new ideas. In relationships as they should ideally exist. the Society for the Advance. Turn these industry. In fact. personal contributions. tantly should government enter the micro- ated with these exhibitions are training and sphere. been a valuable source for information on Second. composites. The social aspects of that it do so. general manufacturing and also composites. is key to improving govern. be safely stored within the active work zones mately responsible to the same people—the of a factory. important.21: Factory Issues 513 Role of Associations and Societies will help them see their different roles as It has already been indicated that asso. This common ground to these materials. In the world of to do alone. the Other roles for associations (and profes. its best work at that level. it must remember that educational functions—another important it enters only because the public is insisting role for associations. At this level the way communication. interactions with their customers. the a macro and micro scale. ciations should represent industry in some A helpful model is to view things on both governmental negotiations. After all. have direct control over their products. Magazines and journals are im. and associations is not without politicians away. and their sional societies) include being a forum where local environment. Third. and Applications . Usually associ. an ment of Materials and Process Engineering effort should be made to understand the (SAMPE) has been especially active. the MATERIAL STORAGE three branches interact with extraordinary Another aspect of composites manufactur- cooperation. gested certain amounts of material that can industry and government are both ulti. Conversely. Methods. ides should not be stored because of the Besides the mandated or regulated storage inherent instability of these materials. • Great caution should be taken to ensure • Resins should be stored out of direct that peroxide initiators and chemical ac- sunlight. Therefore. such as dust. A method an explosion. the properties of regarding material storage have been re. and foreign objects. mixed materials. they can be elimi- Fundamentals of Composites Manufacturing: Materials. the cured resin and the cure itself can inforced by insurance agencies. even resins storage facility. amounts for materials. the exothermic effect can cause were to occur. be opaque (they are generally metal) do not mix directly. • Normally. that the initiators should be stored inside Cautious storage practice suggests that the building because it is air-conditioned means be provided so the resin tank can and overheating through a failure in the be emptied into a container large enough refrigeration unit or a mistake in leaving to spread its bulk over a large area and the unit open will be less likely to cause thus dissipate the exotherm. as is often the case with gel coats. the amount of material that can be out of the mixture. strike directly onto the resin. Therefore. such as cobalt naphthenate. The resin container should celerators. to minimize that these fillers have a tendency to settle danger. Even in the absence of peroxides. Most experts support the of doing this is to have the tank in outside storage concept. but especially gel coats. water. They should be stored below 86° F (30° tices are just wise. some storage prac. spills that might occur. • Most resins. Two opinions exist ture-controlled facilities. UV light can CONTAMINATION IN THE PLANT initiate the polymerization reaction. not be damaged. Some people think that protected with inhibitors can cure it should be located outside the main pro- prematurely. and Applications . stored in the areas where people routinely they are sometimes difficult to get back work is regulated. They see be compromised. safety which the resin is stored surrounded alarms should be installed to signal if the by a concrete retaining wall. When the curing reaction duction building so that if an explosion begins. possibly flammable situation. C). the building itself would rapid heat buildup and result in a dan. a refrigerated storage facil- • Resins should be stored in tempera. often obvious. exposure is high. into suspension. If the tem. polyethylene containers (four containers nies would be wise to investigate the maxi. Therefore. are should be gently stirred during storage. When fillers are part of the resin mix- the potential for leaks and other accidental ture. peroxide initiators are because many of these materials are highly shipped in non-returnable 1-gal (4-L) flammable. Excessive quantities of perox- the materials they use. Therefore. Further. The other opinion is gerous. The wall temperature of the refrigeration unit also functions to retain any leaks or exceeds a safe level.514 21: Factory Issues when the material is inside the work areas. to a case) and 5-gal (20-L) polyethylene mum recommended storage amounts of all containers. If the solution is not Many of the governmental restrictions uniform throughout. ity is often required. Some examples follow. the dangers from fire. Many contaminants. Compa. not only the dangers from exposure but. relative to the location of the initiator perature rises excessively. they should so that ultraviolet (UV) light does not not be stored in the same location. When this happens. adherence been molded using a silicone mold release. some contaminations are much during the initial stages of fixing since heat more subtle. Migration through the theory. Silicone contamination makes to remove. and generally fixing occurs by heating the mold or if they being aware of the problems that can occur are applied to a heated mold. The problem with be used. most consider the disadvantages Some mold release companies have too great and simply avoid using silicone- suggested that their mold releases can be containing mold releases. which are known to be difficult other parts. silicone-containing mold releases can sprayed onto the surface. the problem of if materials are contaminated. and Applications . this person touches another part or The general agreement that silicones an area where bonding is to be done. vacuuming rather than contamination. This prevent good adhesive bonding is further problem is made even worse when cotton reflected in the procedures for intention- gloves are used in handling the parts. In with the mold release. Fundamentals of Composites Manufacturing: Materials. putting “fixed. Then. evaporation While some successes may be achieved of the solvent or water carrier in the mix in using silicone-containing mold releases. This the general rule in the industry. Even if are contaminants that are easily transferred the fixing of the mold release occurs through by contact or those that are airborne and chemical reaction. If that nated materials (like resins). that the amine group causes the material to The contact transfer occurs most often deposit and adhere to various automobile fin- because a person touches a part that has ishes and metal surfaces. thus making any contamination subsequent bonding of molded materials more problematic. contamination may be actually made worse However. they are often in circumstances where the ecules. This is especially true of amine-modi- through the plant. simply. as is ally causing a delamination to occur. the contamination problem could plant. Because of these added present as these are more easily volatilized. concerns. a “semi-permanent” mold release. the molder must take cross-contamination is further worsened special care to avoid cross-contamination when low-molecular-weight components are and clean carefully. special solvent or by grinding off the molded nating parts that are not directly involved surface to smooth it prior to painting). Methods. to other surfaces would be worse too. with the entrainment of some silicone mol. However. prevented. if subsequent bonding is not to be air is especially great if the mold release is done. air through spraying or. This process is said to create sweeping in the vicinity of easily contami. These silicone molecules then migrate surface of the part is specially cleaned before through the air in the plant (sometimes even bonding or painting occurs (such as with a into the air conditioning system). The gloves procedure stipulates that silicones be placed retain the silicone for long periods of time at the site where adhesive bonding is to be and so contamination is routine. The result will be an induced Silicone molecules are carried into the delamination. thus cross-contaminating fied silicones. A manufacturer of these difficult or impossible because it interferes amine-modified silicones. contami. which are used with the ability of the adhesives to stick to for automobile polishes. Hence. notes specifically the molded part. The most important of these causes volatilization of the silicone.” thus decreasing the amount of cross- lids on containers. The most troublesome of these is be worse in the initial stages because of the silicone-containing mold releases.21: Factory Issues 515 nated by good upkeep of the facility. Silicone higher reactivity and bonding of the sili- materials have a reputation for migrating cones. with or without mold travel through the air conditioning of the heating. Further. schedules. Often. routings. cal regulations on disposal also should be etc. the materials back for proper recycling. they can tionships of different production decisions. than the traditional fillers. a computer program. AND RECYCLING FACTORY SIMULATION Great caution should be exercised in dis. such as solvents. DISPOSAL. cycle time. like most composites. technology. throughput. there are five jobs to be performed on five care should be taken so as not to mix the different machines. and Applications . know what it takes to achieve these goals. facturing. the manufacturer must deal resins and peroxides separately.). In composites manu- Some regulations in Europe have man. should the manufacturer deal with this complexity. thermoset materials cannot be remelted Case Example and reused in a product that was similar to World-class manufacturers not only have the first use (as can most thermoplastics). with numerous interdependent variables facturers simply mix these materials and that all seem critical for proper operation: the cure them. In general. be produced—and this is a simple situation. Further. For example. compet- be consulted for safe disposal methods. tem operates. turing systems pose nearly insurmountable the manufacturer of the material should challenges for manufacturers. WASTE. Rather than attempt to dispose of the etc. constraints (budgets.) must be met while satisfying multiple consulted. Simulation has proven to be an effective tool Under no circumstances should solvents be in helping to sort through the complex issues placed into the sewer. While the value of these fillers is not and control over the cause-and-effect rela- as high as the original materials. improved mechanical properties. Therefore. Planning and managing today’s manufac- posing of any liquid materials. clearly defined goals and objectives. assuming that to be crosslinked is not important. but they Thermoset materials. carbonate. Lo. such as calcium rial is the oil on human hands. Methods. ing objectives (cost. Something clearly needs to be done to help which are not readily polymerized. Each is summarized in manufacturer has the obligation to accept this section. should wear clean cotton gloves to in the new composite. and being able to identify from recycled composites are actually better key leverage points for best achieving the Fundamentals of Composites Manufacturing: Materials. How- ever. resulting in slightly prevent contamination. Other liquid materials. be disposed according to local regulations. the original system simulation. including the cured resin. Again. in such materials as bulk molding compound success requires understanding how the sys- (BMC) and sheet molding compound (SMC). Simulation is typically conducted using can usually be disposed to a landfill. such as rials are polymeric and can bond to the resin prepregs. Solid materials. Concentrations do not need to number of resources. most manu. be exact since the quality of the material schedules. etc. often be used in place of the normal fillers In even the smallest manufacturing systems. This is because the recycled mate- operators who touch raw materials.516 21: Factory Issues Another transfer contamination mate. can be ground to small particles and used as This requires a thorough understanding of fillers. knowing what is to be achieved Some users have found that the fillers made with the system. product mix. simulation is typically performed dated that all materials used in commerce on one of two levels: process simulation and should be recyclable. it is possible that there peroxides and the accelerators directly since are 120 different ways in which the jobs can that mix could explode. surrounding manufacturing decisions. study showed that only a small percentage wound onto a mandrel. however. To illustrate the nature performed off-line. In the in the process. the system is ABS Pipe Company manufactures a highly able to run at only about 60% of its theoreti- specialized type of filament-wound pipe. The pipe is then sten. Sometimes a ciled with labels and stacked and bundled step upstream from the bottleneck would for shipping. causing the bottleneck Figure 21-1. Due to various inefficiencies. The secondary operations are experience a problem. It cal capacity. management studied each step for its product so the sky is the limit. The In an effort to improve manufacturing company enjoys virtually unlimited demand productivity. ten times the cost of the raw materials. costing the company millions of is able to sell its finished products for nearly dollars a year in lost revenue. Process flow for ABS Pipe Company. Methods.21: Factory Issues 517 desired objectives. It was fairly easy to find the manufacturing process. and Applications . Fundamentals of Composites Manufacturing: Materials. additional are combined using a proprietary process. consider the shown in Figure 21-1. The process sequence is of the manufacturing challenge. the raw materials slowest step in the line. following example. and then heated of lost production was due to problems at and cured into pipe. this “bottleneck” operation. ing the process. and Applications . a system map. filament winding. For in- fect relationships. such as the strapping machine. Not surprisingly. the ideal machine setup conditions. gaining an understanding of the system ties. would simulation is “Uh-oh. even with years of experience. Management Software is available to model process is under pressure to do something. might be modeled for the least cost. Users can enter decisions that are the “best” in some sense. Managers must make filament winding process. A natural reaction to the thought of using tion.518 21: Factory Issues to run out of work. In a put incoming. matter of minutes. Because of its complex. Or. Rather Process simulation is used to analyze several separate causes contribute to the what happens to material and tooling under problem in complex ways. but what control and performance characteristics for should it be? a number of different processes. Mold filling. The and understanding the injection molding poor performance of the system is costing process and its effect on part properties. there is no single cause for the Process Simulation poor productivity seen at this plant. Methods. However. and amount needed is not too great. Management is a defined set of conditions for a particular at a loss to know which of several possible manufacturing procedure. Simulation of bottleneck operation. most of the catch up. ous location. one at ABS Pipe Company. for example. however. space between stations. can be modeled ing process until the bottleneck was able to and analyzed. and injection and holding pressures. and better tools for troubleshooting quality problems training at certain critical operations. the turning of the mandrel (thus using computer simulation. Other times the bottleneck would is intended to solve. the speeds of the payoff Problems of this complexity are best solved device. which suggest system well enough to identify cause-and-ef. the number of Fundamentals of Composites Manufacturing: Materials. however. simula- get so far behind that there was no place to tion tools are easier than ever to use. In this case. the up and was functioning properly again. Under consideration to simulate pressure forces on the mandrel or are: additional or faster capacity at the the pattern of fiber laydown. causing work to back No one wants to use a tool that is more dif- up and stop the bottleneck operation from ficult to use than living with the problem it producing. a downstream opera. better quality control. and warpage analyses are powerful winder. when to shut down and start up the filament cooling. In short. newly made pipe.” go down temporarily. difficulty of the decisions that a manufac. required to find the data and prepare for Sometimes problems at the bottleneck were the simulation is valuable in understand- actually caused by improper work at a previ. additional storage processes. For is difficult. Today. it sounds too difficult. Often the bottleneck would then effort in simulation involves gathering data be idle waiting until the curing oven heated and preparing presentations. better rules for has been conducted for years. giving the angle of laydown). requires that they have quirements. and the effort until the new pipe had a chance to reach it. ram veloci- ity. these include cooling times strategic planning. and the software interprets the clearly defined goals and understand the data by simulating results. information on part design and quality re- To do so. A filament wind- improvements would have the most impact ing process. The goals are created by jection molding. and profiles for temperatures. enormous amounts of money. It can be This example illustrates the nature and useful for determining machine settings. including some of those involved in the turer must make. such as plastic injection molding. such as the the workers would stop the entire pipe-mak. and operational questions.21: Factory Issues 519 fibers in the bundle (to give the width of the tems. Using the modeling constructs avail- laydown). which have modeling building blocks Design questions: called modeling constructs. and no disruption for modeling simple processes with little or to the current system. for improvement risk-free. and tooling should be data describing the dynamic behavior of sys. and monitor and statistics are gathered and automatically correct the various machine processes dur. Furthermore. graphical animation of the system being modeled to System Simulation better visualize how it behaves under dif- ferent conditions. However. techniques. When it comes to analyzing and improv- During the simulation. the no interdependency or variability. used? Fundamentals of Composites Manufacturing: Materials. of alternative designs and the effectiveness of In practice. summarized for analysis. such as ProModel® or ProcessSimula. might be used to address. manufacturing simulation is alternative operating policies. the user builds a model angle are given. results are visual and quantitative with per- what is seemingly a simple process might be formance statistics reported on all measures quite complex because of interactions often of interest.” performance setup. that captures the processing logic (that is. 2004. reduce cycle times. Methods. see Harrell et that satisfy defined feasibility constraints al. tion software provides a realistic. Modern simula- ing production. no waste of time. These packages 1. Hence. and Applications . as a quick and effective way to design and State-of-the-art simulation technology even improve operational performance. which simulation ware. pendencies and variability. As the model is “run. it is necessary for understanding the interac. Typical design performed using commercial simulation soft. one of special goal-seeking algorithms. overlooked. tor®. Simulation gives manufacturers The choice depends on the complexity of the unlimited freedom to try out different ideas system and desired precision in the answer. (For a provides optimization capability. but scenarios tem simulation technology. What type and quantity of machines. Not that comprehensive treatment of the use of sys- the simulation itself optimizes.) can be automatically run and analyzed using To analyze a manufacturing system. the following methods might be chosen: Because simulation accounts for interde- • Construct a simple flow chart. enabling process engineers the constraints of the system being stud- and molders to quickly optimize machine ied. There is virtually Flow charts and spreadsheet models are fine no cost. are listed as follows. which are unobtainable using other analysis • Build a computer simulation model. The benefits of process simulation have why each step follows after another) and been significant. it provides in- • Develop a spreadsheet model. and the number of wraps at each able in the package. the user can in- ing the entire production process. Further. are specifically designed for easy entry of equipment. Simulation helps evaluate the performance tions of the system over time. Simulation of production even make changes to model parameter systems is becoming increasingly recognized values to do “what if ” analysis on the fly. system teractively adjust the animation speed and simulation is used. computer simulation is often used even for seemingly simple systems Application and certainly for any complex one. sights into the complex dynamics of a system. Fundamentals of Composites Manufacturing: Materials. What is the best way to allocate re.000%. What is the impact of machine downtime for simulation often exceeds 1. Cost 7. size? Because simulation accounts for inter- 4. simulation is an sources for a particular set of tasks? invaluable tool. Its usefulness increases as 6. The real savings from simulation come ized? from allowing designers to make mistakes and work out design errors on the model 15. Should storage be centralized or local. What is the effect of vehicle or conveyor rather than on the actual system. with on production (reliability analysis)? payback periods frequently being only a few 13. 10. and Applications . dependencies and variability. and discover- work best? ing and correcting operating inefficiencies. What is the production capability 8. months or the time it takes to complete a duction? simulation project. What methods and levels of automation necessary capital investments.) to use? 4. What is the optimum unit load size? uncertain. How large should the buffer and storage identifying and eliminating problems and areas be? inefficiencies that would have gone un- 6. an operational nature. How many operating personnel are 7. it provides ducing a set of jobs? insights that cannot be obtained any other way. For important system decisions of 5.520 21: Factory Issues 2. method (kanban. What is the best way to schedule pre- illustrated by the rule of tens. What type and size of material handling system should be used? Economics Savings from simulation are realized by 5. What is the best production control (throughput rate) for a given configu. What is the best layout for the factory? noticed until system implementation. What automation controls work the is also reduced by eliminating overdesign best? and removing excessive safety factors. which are added when performance projections are 8. By identifying and eliminating un- 9. This principle ventive maintenance? states that the cost to correct a problem 2. The con- speed on part flow? cept of reducing costs through working out Operational decisions: problems in the design phase rather than after a system has been implemented is best 1. The return on investment (ROI) 12. 14. How many shifts are required to meet increases by a factor of ten for every design production requirements? stage through which it passes without being 3. Methods. What is the effect of setup time on pro. How much time does a particular job needed? spend in a system (throughput)? 3. What is the optimum production batch detected. How balanced is the production line? it is not uncommon for companies to report 11. Where are the bottlenecks (bottleneck hundreds of thousands of dollars in sav- analysis) in the system? ings on a single project through the use of simulation. What is the effect of a preventive as variability and interdependency increase opposed to a corrective maintenance and the importance of the decision becomes policy? greater. What is the optimum sequence for pro. manufacturing re- ration? source planning [MRP]. etc. a major manufacturing stereos and electronic components for ste. which was acknowledged to be gen. Japanese quality standards process stimulates creative thinking and were enforced and.S. The turing practices were still being used by the second line. U. Similarly. After several years. the Japanese com- second line was producing similar products pany was again allowed to sell directly to the for a Japanese name brand. component feeder lines. had a defect licensees. company and then to a Korean licensee. visits were made to the Japanese rate of less than 2%. and Applications . Something surprising was discovered after CASE STUDY 21-1 a day of tours and discussions in the plant. values. pany could do to improve the quality of the facturing were interviewed to discover what American line. then made the products and sold them in the erally of only moderate-to-low quality. A designer cannot only techniques. It was not be the deciding factor on whether a foreign their way. Thus. of quality was present in the commitment of the Japanese company. firm placed a full-time manufacturing/quality tion. The difference was in the expectations. One produced pany then licensed some of its products to a fairly popular brand sold in the United other companies. workers could many of the critical issues in manufacturing. On being told the best that problems they had with the quality in their could be done was to learn from the Japanese offshore operations. situations even though many of the changes ing foreign product quality. Two production lines were restrictions to the United States. even more. Quality in Foreign Manufacturing The plant manager asked what the com- Several companies that do offshore manu. the attitude results in good design decisions. the Japanese line.S. he responded with “But it is not and service quality an absolute necessity in how our company [the Chinese company] domestic or international markets. or more accurately. imperative and that commitment was in Example one is an electronics firm in force even from 2. Not only is high product engineer.000 miles away. the way of company is able to sell its product. Methods. most companies that have opened inter. The U. the licenses were not revoked. not see how to adopt the methods to other Because of the inherent questions surround. and commitment demanded by try out new design concepts to see what the Japanese marketing company who was the works best. thus allowing the Japanese company and the The facility was the same and so were the licensee to sell against each other. their management or company culture and fore. in other countries. customer for the Japanese line.21: Factory Issues 521 Lastly. southern China that produced portable In example two. However. There. However. Through simula. line one In an effort to see if Japanese manufac- had a measured defect rate of 10–11%. but it does things. which States. decision makers can play what-if games engineer in the Chinese plant to ensure that with a new system or modified process before the quality methods of the Japanese firm were it actually gets implemented. simulation actually makes design. This com- operating within this plant. but the visualization brings real. company in Japan was placed under import reo products. Fundamentals of Composites Manufacturing: Materials. edged as having good-to-excellent quality. This engaging followed. ing systems exciting.” Even with daily interactions serves as a convenient probe to discovering with the Japanese engineer. the Japanese firm had national operations expend significant effort significantly higher quality for the same to maintain the levels of quality achieved reason—commitment to good quality was domestically. good quality may would have been simple to do. one acknowl. The Japanese ism to the whole process. culture.2 Startup regulations 2. ity details).3 Inflation 3. The cultures of the countries seemed attitude of employees. is poorly laid out or the plant is messy and The Japanese plant was. The efficiency of factory operations can podge of motivational signs and slogans.7 Financing 4.6 General uncertainty on cost of regulations 3. even worse. can ex- country.8 Inadequate infrastructure 4. Obstacles to business in lesser-developed countries.3 Fundamentals of Composites Manufacturing: Materials. cultural characteristics of the Japanese Table 21-1 shows the types of obstacles company (such as lifetime employment. SUMMARY Moreover. The World Bank has surveyed com. the Korean company viewed itself as a low-priced alternate to the admittedly superior Japanese product. If the manufacturing process become more successful and compete better. Obstacle Survey Score Corruption 4.5 Tax regulations 4. plode.7 Foreign currency regulations 2.8 Regulations on foreign trade 3. a study dirty. and close attention to qual.522 21: Factory Issues The Korean company had almost none of the issues are outside the control of the company. Table 21-1. the Korean plant was a hodge. mean the difference between profit and loss urging the employees to work harder to for a company. great care should be taken panies and found that the majority of difficult to ensure proper storage of these materials.4 Policy instability 4. off an exotherm so high that they burst into tant in doing business in a lesser-developed flames. lesser-developed countries.5 Price controls 2.4 Terrorism 2. and Applications . Methods. Instead. in contrast. which tolerates the lackadaisical dures. resins can harden or.0 Crime and theft 3. Therefore. The improper storage of liquid materials ing practices. with high automation and and poor quality. presents a serious potential for disaster. they can set Usually other issues are even more impor.5 Safety or environmental regulations 3.7 Labor regulations 3. to be readily apparent in their manufactur. commonly encountered in doing business in quality circles. Materials. It is a reflection of the technically advanced equipment and proce. the result is not just contamination of quiet efficiency. such as peroxides. The The above examples are focused on quality. Gino.. Harrell. Saeid.-H. C. R. p. Plant Productivity. of assembling the data and putting it into Berdine. 2–10. London: Collins. and Mackulak.” AIIE Transactions. p. Cave. “System Improve- associated with modeling the process to ment Using Simulation. CAM Developments in therm)? Computer Integrated Manufacturing. cess. Ghosh. and 1999 Winter Simulation Conference. This has tremendous benefits beyond just simulation. May.910–1. Germany: Springer-Verlag.. Alex. and Merten.913. L. and McComas. “Modeling & Simulation Provide Key resin manufacturer. pp. 3.. A. QUESTIONS Hopp. “How 4. Fundamentals of Composites Manufacturing: Materials. Walton.21: Factory Issues 523 The advantages of simulation are chiefly Mott. New York: McGraw Hill. Jack R. 1986. proper storage of a resin.” Indus- trial Engineering. “Integrating Discrete Event Simulation with Statistical Process BIBLIOGRAPHY Control Charts for Transitions in a Manu- Bateman. Dissen. 1979. Chen.. develop a checklist that can be used to verify Hancock. What is the danger of storing resin in Factory Physics. 1993. to CIM Implementation Philosophy. and Kouzani.” Orem. Kochan. facturing Environment. Royce O. Charles R. What are the problems associated with Simulation Pays Off. eds. Royce. G. Charles. 2. Kao. that the procedures of the resin manu. “An Example of Simulation to Improve facturer are being followed. J. 1988. pp.. 1997. Simulation Using Pro- Model. What is the result of mixing peroxide Lewis. A. 2. Hooper. 2004. Nahavandi. Abbas. Law. Gerald T. “Simulation Optimization for LABORATORY EXPERIMENT 21-1 Process Scheduling Through Simulated Understanding the Dangers of Improper Annealing. pp. and Charnes. Yücesan.. D.” Proceedings of the 2002 Winter Storage Simulation Conference. E. Give three reasons for using simulation Nembhard.. Neil E. What is the procedure that should be followed if the resin overheats (exo. and Lim. Objective: Discover the dangers of im.” Proceedings of the Gogg. M. February. UT: PRO- improve efficiencies. 1999. God in the and a cobalt naphthenate accelerator? Dock: Essays in Theology.. 37–39. Using the storage suggestions. M. 2002. 6. S. 1. Berlin. and Applications . W. Robert E. However. 180. “FMS: Fumbled the simulation package assists the system Manufacturing Startups?” Manufacturing designer in thinking deeply about the pro- Engineering. 104. 2001. Robert A. 1977. 3. C. Harriet Black. Phoenix. M. Snowdon. 1. 2nd ed. and practices. Procedure: Glenney. Visit a composite manufacturing facility March. J.” Manufacturing Engi- using a silicone mold release? neering. A. ed. Wallace J. 5. Thomas J. and Spearman... Ming-Shu in a production plant. New York: Irwin/McGraw- large quantities? Hill. July. Biman. 1. Bowden. Obtain the storage suggestions from a 1985.. Methods. and do an inspection of their storage Harrell. Discuss whether it is better to store resin inside or outside the plant. M. the process MODEL Corporation. Bowden. NJ: Prentice-Hall. P.. Sturrock. pp. 3rd Ed. The Shingo Produc- tion Management System — Improving Process Functions. Inc. eds.. and Manivannan. F. J. J. 5–8. B. “Introduction to the Art and Science of Simulation. S. Methods. Andrew P. 1998. Dillon. eds. Nembhard. T. Shingo. D.” Simulation in CIM and Artificial Intelligence Techniques. and Wich- mann. San Diego. MA: Productivity Press.524 21: Factory Issues AZ. D. Medeiros. Schriber. H. J. Fundamentals of Composites Manufacturing: Materials.S. NJ: Institute of Electrical and Electronics Engineers. 7–14. Watson. W.” In Proceedings of the 1998 Winter Simulation Conference. M. J. Plastics: Materials and Processing.. E. K. 1987.. A. eds. Shigeo. 1992. Evans. Robert E. Trans. Cambridge. Strong. Retti. T. Carson. A. and Applications . E. Upper Saddle River. and G. “The Nature and Role of Simulation in the Design of Manufacturing Systems. Piscataway. 2006. Farrington. CA: Society for Computer Simulation. Brent. Shannon.. pp. which is the case ing. a success of a business. Brent Strong (sometimes with assistance from other authors) and published in various issues of Composites Manufacturing (American Composites Manufacturers Association). and are not part of the discussion here. ing company. This is the number that indicates Most companies use the income state. low may be in the 15–20% range. • Managing technology Because of its importance. ing processes The cost of goods sold is the next line on • Planning the income statement. in the course of its normal business. * Some of the material in this chapter was written by A. These costs The revenue amount represents the total include the salaries and expenses of the sales amount of money that comes to a company force. the revenue is from sales of management and the accounting function. An example income gross margin of 40% of revenues is considered statement is shown in Figure 22-1. For a The next category is general and account- manufacturing company. Normally. and usually shipping costs. (Slightly to be good.1: Introduction to Composites 525 22 The Business of Composites* CHAPTER OVERVIEW the company’s products. Fundamentals of Composites Manufacturing: Materials. Methods. The ECONOMICS OF COMPOSITES value of the cost of goods sold is subtracted MANUFACTURING PROCESSES from the revenue to determine the gross Income Statement margin. This includes the costs of corporate examined here. such as sale of an asset. the costs of making the product. There may occa- This chapter examines the following sionally be other sources of revenue for the concepts: company.) Some of the basics of business Sales expenses are shown below gross economics can be understood from a brief margin because they do not relate directly to examination of the income statement. Commodities on which the margin is shown are typical for a mature manufactur. but the values can have gross margins substantially one shown is a common format. but these are usually termed “extraordinary income” • Economics of composites manufactur. the cost of goods sold will be examined in more detail later. The amounts higher. although some products with high different versions are also used. This line is critically • Corporate creativity important for a manufacturing operation. and Applications 525 . whether the manufacturing costs are in line ment as a simple method of determining the with the sales of the company. It is • The ethical process a total of all the costs associated with making the product and getting it ready to be sold. This includes federal. is the major difference between the two. Each of these categories can be subdivided so that specific costs become more obvious and. Alter- nately. and minor additives. two different manufacturing processes are The taxes for most areas in the United being compared and the labor component States are about 40%. This model might be used when labor income statement. most companies that are is an especially high component of the cost making a profit will choose a formula that of goods sold. labor. Example of an income statement. routing. inspection. the second method gives a better measure of the wasted material because it notes the waste explicitly. and de- the company and is shown above taxes in the sign. the material costs for a company that makes composite bath and shower units might be divided into resin. needed in filament winding. For example. the labor could be There are formulas for calculating deprecia. In theory. Filament winding has the profit of the company. costs would be better because it gives more visibility to this problem. assembly.000) with be divided among the stockholders of the com. state. the material costs might be figured as the total amount of material in the products sold plus the amount of material wasted in the plant. because the hand Fundamentals of Composites Manufacturing: Materials. at least in theory. the major differences being the much higher pany (dividends) or used for other purposes time required for hand lay-up.500 versus 3. Because it is considered an expense of fabrication. These profits can fewer labor hours (1. the second method of accounting for material Figure 22-1. and other miscellaneous Figure 22-2 illustrates a comparison of the taxes that might be assessed. in a plant in which the amount of waste is high. Methods. Depreciation is. However. and Applications . For example. Cost of Goods Sold and manufacturing and assembly were com- The fundamental costs that comprise the parable in the percentage of time dedicated cost of goods sold are material. more easily controlled. municipal. these two accounting methods should give the same material costs. classified according to functions. kitting. goods sold. initiator. An example of when this situ- maximizes the depreciation (thus reducing ation might be especially valuable is when taxable income). and for each process. money Another variation of the cost model sub- set aside to repurchase the manufacturing divides the labor component of the cost of equipment when it has passed its useful life. difference is the greater amount of support ration and approved by its directors. therefore. The costs of these materials can be determined as the total amounts purchased from the various material vendors. It reflects versus hand lay-up. Offsetting this outlined in the company’s articles of incorpo. labor hours required for filament winding The bottom line is net income. fiberglass. such as: tion. Other opera- tions—quality assurance. Therefore. However.526 22: The Business of Composites overhead. filler. the case of making a front cross. the particular process are considerably higher volume of parts made. and the efficiencies than for an alternate process. lay-up took twice as much overall time. therefore. Based upon a produc. and Applications . the more highly costs are fixed and can. each Comparing Composites Manufacturing of these actually consumed more time. assuming that the same part is largely because of the high costs of the could be made by all processes. Methods The third component of cost of goods sold. have the lowest overall costs Fundamentals of Composites Manufacturing: Materials. especially ing processes are difficult because the costs when the costs of a machine or tooling for a vary according to the nature of the part. generalities over many parts made by a tion volume of 40. becomes less expensive because the machine As might be expected. Comparisons between various manufactur- overhead. Figure 22-3 gives a com- fiberglass reinforced plastic cross-member parison of several composites manufactur- are lower than for a steel equivalent. Labor comparison—filament winding versus hand lay-up.000 units. be spread automated processes. for of each manufacturer’s operation. How. However. example. some comparisons are possible based upon member for a minivan. pultrusion and fila- over many more parts. process to make an equivalent part is used ever. the steel part for comparison. This ing processes. the costs of a particular process. Consider. An aluminum machines used to make the steel part. at high production rates. ment winding. also can be important. Methods.22: The Business of Composites 527 Figure 22-2. which are the lowest. but they also have low materials costs because they use Life-cycle Costs tow and wet resin. the product is to be discarded. when materials are less than thermoplastic ther. This result is not unexpected in costs consist of three components: Fundamentals of Composites Manufacturing: Materials. Over the life of the product largely because the costs of tooling and there are other costs. and tooling. and Applications . than just the price of the product as it is Resin transfer molding is next lowest. is prepreg lay-up with an cycle of the product. And eventually. with pultrusion being lower than filament light of the high material costs. not only have low labor costs.528 22: The Business of Composites Figure 22-3. the real cost analysis est cost of any of the methods. Cost comparison of manufacturing methods. Therefore. high tool- winding largely on the basis of lower-cost ing/equipment costs (with an autoclave). The costs of any real product are more cost forms of the principal raw materials. more costs. originally sold. there are still moforming. These highly automated processes high labor costs. even higher should look at the costs over the entire life than aluminum. The high. the life cycle autoclave. In general. the next higher cost. Methods. the leader who can The costs of operation are. They are often delegated to Fundamentals of Composites Manufacturing: Materials. because of governmental action. salvaged. The a dramatic competitive advantage. of low consequence (individual- as $1. they must be or the government mandates it. the expensive equipment used to form evolutionary. On average.000 for a moderately sized vehicle. flat panels of automobiles seems futile because our current view of are generally made of steel but highly curved the future is likely to be different from the panels are made of composites (usually sheet real future when it arrives. at least on some models. Operational decisions are value of money. They in- made of composites would weigh about 75% clude making the sales call. and Strategic environment. to a savings about $6. After the materials are the business). automobiles. when change is no longer slow or turing. These times defy predictions. cost to dispose. The savings could be as much easily made. the decisions—deciding what to do right now value of composites can be estimated from a to run the business. as much as a steel car. and self-forc- The cost of disposal is relatively minor ing (that is. molding compound [SMC]). The first type is operational is directly proportional to weight savings. the remainder of the car is dis- 2.00/lb ($13/kg) of weight purchasing. the value of composites rises Decision-making sharply because of their significantly lower There are three types of decisions required weight compared to steel.22: The Business of Composites 529 1. customers and government to make these demands. the costs for steel products. and posed to a landfill or chopped into filler. For composites. cost to operate. This is simply especially when they are about the future. almost surrealistic way. manufacturer has little incentive to improve the old methods of planning will probably these costs unless the customer demands it not work today. However. paid plan properly in these times will achieve by the purchaser of the automobile. and overhead. PLANNING It is the costs associated with materials. and Applications . However. Methods. of course. Hence. Structural. if random. “Predictions are hard. Since fuel savings in a business. This would translate making the product. In such an Operational. However. shipping the product. the automobile is posal factor will have to be considered in used as an example because the three cost evaluating the type of materials used in the components are widely understood. they must be made to continue for an automobile.” because steel is a lower-priced raw material Yogi’s statement is especially true in a time. like now. These are the reduction over the life of the car. But. The cost to manufacture is the cost that has been considered thus far in this chapter. These are simply deci- weight savings calculation. la- Predicting the Future bor. if this cost becomes significant 3. ly). In a strange. the costs of manufacture are generally higher than As Yogi Berra said. This is at day-to-day (maybe hour-by-hour) decisions of 2007 fuel prices and accounting for the time normal operations. getting the order. and at the high volumes typical of manufac. the dis- To illustrate these costs. a car sions required to get the job done. the part is highly curved or has some other How can you plan for the future at a time unusual characteristic. Therefore. cost to manufacture and sell. then composites can when change occurs so quickly? Planning be justified. straightforward. frequent. adapted to meet the new reality of rapid the high cost of fuel is now forcing both and dramatic change. Change today is episodic and and join it can be easily justified. and scheduling. the adopt the new way of thinking (paradigm) essence of the role of managers is to formulate so that the entire organization can move to and then implement structural decisions. somewhat complex. Thinking structural decisions include those affecting about the nature of change. of moderate consequence. Further. are not self-forcing. basic principles of the company. Suppose the position is that Therefore. and logical paths of improvement. Structural deci. Those basics might include the following: The second type is structural decisions. has articulated a certain basic positioning amine the company and its overall direction. Another way of saying new position. then confusion occurs in the After that. or. fact. of the company. a formal procedure for analyzing the basic and maintenance assistance to the user Fundamentals of Composites Manufacturing: Materials. you will realize company organizational charts and report. and in handling them. it is about maintaining the status quo operating procedures. the employees of the company sions are made infrequently. workflows. make. Methods. Change occurs because a leader sees the Structural decisions are usually made by new position and then influences others to middle and upper management. installation. principles. these are decisions made on desired position? an occasional basis that have to do with Notice that these questions really focus on the way the business is organized. senior management should manufacturer in the area of corrosion-re- schedule the times when strategic planning sistant pipes. If some aspect of the company is original purposes and nature of the company. are extremely will know the guidelines that must be used complex. and self-forcing. This is only accom- usual purposes of structural decisions are plished by the leader’s repeated reinforce- related to developing efficient and productive ment of the desirability of moving to the systems. The leader must make sure that all facets Strategic decisions do not typically come of the company are aligned with the basic up in the normal operation of a company. achieved by giving full design. but he/she must also instill a this is that strategic decisions are related deep understanding of (or adoption of) the to the values of the company and they be. For instance.530 22: The Business of Composites middle managers or operators and controlled positioning of the company can be useful. Further. Strategic deci. The the envisioned position. transition. moving forward along predictable sions are intermittent. During these planning times. at best. not aligned. by standard operating procedures. which are related to the company’s funda. that can accrue from that change. that management is not about change. Typical how the company will change. relatively easy to The process of change is about leadership. have severe consequences. likely done only as major changes occurred. • What does the company want to be? These are periodic decisions that provide limited guidelines for daily activities. strategic planning sessions were minds of the employees. this position will be should be done. the leader must not only instill a vision of the mental purposes. Alignment means that procedures The founders of the company probably did and practices reflect the basic values of the strategic planning when they established the company. In fact. suppose that the leadership which forced the senior managers to re-ex. to be most effective in strategic the company will be the foremost composite decision-making. In ing relationships. pricing policy. and Applications . etc. In • How should the company get to this other words. This is so come the underlying principles on which that when new situations arise during the all other decisions are made. new position and reiteration of the benefits The third type is strategic decisions. While these worries are Fundamentals of Composites Manufacturing: Materials. Although extremely important for long- alignment with this position will not occur term viability of a company. because it is having trouble getting a sales The business makes money because of price high enough to pay for this service. especially Strategic decision-making can be sum. books. If sales and production. (Some of history’s best personal creativity. is a nearly perfect idea-killing As a result. The following sections provide marized as follows. destroy the trust of the employees in the with its need for predictability. consider the competition. most of them only focus on improving egy to employees. therefore. of course. company should revise and communicate however. To do otherwise is to create confusion in the company and CORPORATE CREATIVITY in the marketplace. Therefore. leaders of the company. innovation. place of action in these two areas. 1. ligent leader will remember that strategic get crunch that particular month. conformance to accepted norms. These should be guided these non-aligned moves are required. the intel- trips to customers’ plants because of a bud. In fact. statement. • Strategic decisions concern the future. Too often companies get tion. the best strategy planning should machine” (Dresselhaus 2000). Therefore.) environment to promote creativity. Make Creativity a Centerpiece of • Strategic decisions are the realm of Corporate Strategy leadership. require the creative process and how that can be some effort to assemble this data. Similarly. in companies.22: The Business of Composites 531 companies who buy the pipes. Knee-jerk decisions “[A] traditional bureaucratic structure. the strategic if the chief financial officer of the company decision-making process does not create refuses to allow emergency maintenance immediate business. leaders need to understand readily available. analogies to sports. and Though creativity is the subject of many even war are useful in communicating strat. employee morale. Often. thinking can be stimulated by comparing a company’s strengths and weaknesses against Improving Corporate Creativity the competition (benchmarking). to be done in an environment in which data on avoid having the corporate climate kill ideas the competition and the marketplace are and creativity. lagging sales. sistency can be preserved. Few discuss changing the leaders have come from the military. linear logic. values. poor production. games. some steps that have been demonstrated to improve corporate creativity. Leadership worries about into a mode of planning and forget to move cash flow. no amount of planning can take the its new basic strategic position so that con. decision-making is done infrequently and misalignment might occur if the company that the company needs to move ahead to drastically reduces its design department realize the vision. tates of the most recent ‘long range’ vision It must. but this certainly • Strategic decisions are based on basic is not the case in most companies. This will. usually the focus is on many other things There is a word of caution in regard to besides creativity or its practical manifesta- strategic planning. Making creativity center to the corporate strategy may seem obvious. • Strategic decisions concern change. and the dic- Strategy is often about winning or losing. the by the decisions made in planning sessions. or forward and actually change the company. Methods. Strategic influenced by the corporate climate. However. and Applications . as reward for city man did not understand is that the cows their efforts and as role models for others. Re-examination The additional costs in payroll are usually In one of the best of the creativity books. breaking.” Corporate leaders should give a significant competitive advantage. allow employees to be creative because piece of corporate strategies and initiatives. Gordon MacKenzie (MacKenzie 1998). noted the lazy cows that were porate strategy. Methods. even if no breakthrough focus. is described by author. large and small. “One day. ‘Glass breaks. titude is worth the small amount of time off When creativity is a corporate priority and of normal projects. 18 of these personal projects are strategically criti. There What’s more. many people can be promoted to a level action. Give Time and Opportunity to be be fostered by senior management through Creative thoughtful actions that challenge creativity Some creative companies. into milk even though there is not apparent ever. ways of preventing glass from breaking. them worked. which thrive off new ideas. the company organization just standing around in the field. employees have time about that?’ The directive to the lab then to think deeply. and Applications . In do just the opposite. read broadly. part of their time (such as 10%) to non-as. and otherwise became: ‘We’re going to prevent glass from practice the skills of creativity. Corn- sist) that all employees devote a meaningful ing’s president said to the head of research. ask (in.” What the can and should be promoted. . Establish a Culture of Paradigm to help them in their managerial duties. and five made money . Stressing the cows to produce more of incompetence by moving them out of their will not result in more milk but. some disgust. probably. For compa. Thus. like 3M. we’ve noticed that the more is so much that must be done in a typical senior the executives. For others.532 22: The Business of Composites certainly legitimate. creative people require the back up of others (usually assistants) 4. . the more likely they company. Why don’t you do something signed projects. “How can you allow your producers bureaucratic duties.’ The lab came up with 25 different nies like 3M. allowing time for creativity end result was the now-famous Corelle® line can result in major breakthroughs that could of dinnerware. Fundamentals of Composites Manufacturing: Materials. How. He said to the dairy where their creativity is not swallowed up in farmer. single trend we’ve observed is the growing Sometimes managers are reluctant to acknowledgment of innovation as a center. In actively try to spark creativity and ask chal- all companies. He describes the city 2. that the manager keeps pressure are to frame their companies’ needs in the on everyone to keep busy. This situation context of innovation” (Kelley 2001). occasion- changes to keep the stars of creativity in jobs ally munching the grass. area of strength (Peter and Hull 1969). increased lenging questions. with When creativity is the centerpiece of cor. are performing the miracle of turning grass to positions of leadership (visionaries). they believe it to be a waste of time. new leadership roles. everyone is involved: “The biggest ideas are ever produced. The cal. These creative people to be so lazy? They must do more. Reward and Support Creativity fellow who went into the country and. many can be reduced employee involvement in the company and or eliminated by encouraging creativity in the resulting improvement in employee at- problem solving and creating new products. in others (Thompson 1992). Charles Thompson reports a story that il- lustrates well how a creative culture can 3. worth it. Prototype Early and Often for individual creativity (MacKenzie 1998). suggested that U. teams are usually much more creative than any single individual. how do you make an actual is the best practice for achieving a realistic pyramid larger? This is not an easy task! view of new products. ing before fitting it in place. acceptance climate encourages creativity. you would have to do considerable shap- The most effective tactic to create motiva. urgency because the greatest profits would be nothing but an outer encasement. Therefore. but try grow or die!” However. Thus. it is has been suggested that it be a tree (MacK- amazing how effective people can make the enzie 1998). urgency of goals. company might take to facilitate growth? It gency about new product development. the holder of the most This chapter has. Every mity and cooperative actions. but at the same time all of us should run together. Quoting a Honda man. corpo. “We must ing the concept that “It is OK to fail. hopefully. patents. because of the shear weight of the structure. It tunity. When the entire What is the alternate structure that a climate of a company has this sense of ur. layer would not be attached to the rest. Create an Atmosphere of Urgency and then add blocks one row at a time on When there is a strong motivation. most top of the new base. relied strongly on a creative and proper management should include some hard-working team. Use Teams and Brainstorm Often done better because people are trying to help Many companies seem to believe that each other out. The task of managing people is difficult.22: The Business of Composites 533 5. and Applications . workers down below. are gained at the beginning of a product’s That type of growth would be tenuous. The first organizational analogy is a Prototyping is not only a practice that pyramid with management at the top and the helps identify problems early in the develop. Even Thomas Edison. passing the encourage individual creativity. Besides. to fit with the people are more creative. To grow a pyramid you would have to add another row at the base all the way around 7.” nizations—one demanding obedience and conformity and the other giving more leeway 6. life. Charles Thompson wrote in his book the effective manager also knows that pro- (Thompson 1992). Like in a rugby game. methods to encourage creativity. especially those doing [new product development] team members manufacturing. ball left and right. creativity is something done by isolated Pyramids and Trees geniuses. Management sees ment process. Top management is the trunk development process. In truth. tion from employees. “I am always telling the ductive companies. Therefore. existing pyramid. However. etc. the future and proclaims that. When finished. Methods. fit. the pyramid would be higher. giving support and direction to departments is improved and jobs just get the entity. tion is urgency—urgency from competition.S. growing is difficult to fail when it costs the least. This trunk-management is also Fundamentals of Composites Manufacturing: Materials. ager. the new rows would have rate leadership should instill a climate that to be tapered. not just any block would motivates all employees to be more creative. when you step back and think The use of prototypes to identify mistakes about pyramids. and reaching the goal as There are two different models for orga- one united body. require significant unifor- that our work is not a relay race . However. .” This failure. it is also important in convey. . but the outer urgency from possible loss of market oppor. Cooperation between of the tree. one of us should run all the way from the managers must find ways to solicit coopera- start to the finish. rules. Methods. understood. By defining and supervisors are the branches that give ethics in terms of the basis on which deci- support to the actual producers—the leaves sions are made. So.” situations and ways to do things wrong that Another point is that quality is best con- attempts to cover them all is simply impos. moral principle or values” (Webster’s Ninth each will provide for its own consistency in New Collegiate Dictionary 1983) by which the decision-making process. When the basis of the process is more producers can be supported. However. Of greater practical value is an un. It is virtually impossible to define the way to get quality is not just by inspection many ways unethical or improper acts could (100% testing) or by just monitoring the be committed. The best sible. and Applications . By analogy. There are rules for administering quality.” or “The product must be good enough THE ETHICAL PROCESS to meet its intended life.” in example two it is “Always maintain But these attempts have proven to be mostly product integrity. The Process of Ethics which comes from the roots. according to the underlying basis on which Fundamentals of Composites Manufacturing: Materials. but there is certainly room to try something but ultimately they must be based upon different (should cross-fertilization be pos. To restate the persons conduct their lives. then moment-to-moment deci- ity is allowed because the actual producers sions can be made in keeping with these see a wide view.” or “Ship only product that delights the customer. If the basis is ethical. surroundings (the sun and air). some underlying principle. is defined as. fruitless because there are so many differing “Always serve the customer. ing the entire enterprise as a whole and then derstanding of the basis on which a code is working hard to see the future and control built. Several attempts principles for each example more generally. and have no The process of making ethical decisions structural limitations except to be attached is much like the process of making qual- to the tree itself. Even more precisely.” and in example three. it has been suggested that and the buds. there should be all aspects of the manufacturing process. versus by a set It is best to have a “target-centered manu- of basic standards as to what they should facturing process” where the principle is to do. which will ultimately result in ethics are the result of a process based on the cash crop. then there is really no way to govern “reduce variation. All the leaves and buds ity decisions in a manufacturing process. Creativ. such as “Keep sible. The managers Here is a critical observation. seem to sense their collective responsibility. receive energy from their principles. then by seeing them in light of the entire phi- the system or code used to direct every day losophy and climate of the company and life will be ethical. as a study. have been made to establish such a code for the basis of example one is “Always keep the companies. Growth is simple because the principle. with moral duty and obligation” and “a set of because they are based on certain principles. and government. It is the process by which decisions structure just extends the branches so that are made. professions. the established rules that create good qual- ity. ethics are best implemented sions are made. “The ferent and will cause different actions to be discipline dealing with what is good and bad taken in deciding on the quality.” This is enhanced by see- at all. if people will be governed process (statistical process control [SPC]).” These What are Ethics? three examples of rules are somewhat dif- Ethics.534 22: The Business of Composites the conduit for nourishment (cash flow). an understanding of the basis on which deci. trolled by controlling the process. for instance). only by what they cannot do. and Applications . and live. today many of the concepts methods should be established to imple. emergence of two English words directly Ethics is a process. much like quality. Follow. Technological developments are driven by human needs and wants. at least. depth. Methods. such as simplic- ference. that pur- reduce our frustrations with technology and pose is generally to extend human capabilities. Similarly. process. symmetry. But the most important part of the However. When originally any cost as its underlying principle. the part that will really make a dif. acting. it can be seen that quality and included the disciplines of craftsman- decisions will be made so that any product ship and art. terms with the effects of technology in their or doing—technology requires thoughtful life. extends human capabilities for impacts in the global economy. The philosophy science” or “gadgets. The artistic side of crafts- that can “get by” will be shipped. Congress’ Office of Tech- Technology is one of the defining aspects nology Assessment (1988). technology Another perspective of technology is that dramatically impacts the way we work. some reasonable values. should exploit it to the benefit of our world. will be acceptable within ship and art is further reinforced in the the company. MANAGING TECHNOLOGY When John H. elements of beauty and art. Then. often. What is Technology? often confuse wants with needs—we need The word “technology” seems to have a car for transportation but we want to many meanings.. used. and elegance. tools. is the articulation of the basis for ity. play. from techné—technology and technique. Technology has purpose. thus indicating that this connection decisions. it is concluded that technology thought and in light of the vision and val. or thinking. A market-driven economic Fundamentals of Composites Manufacturing: Materials. As such. the decisions.” at least The close relationship between craftsman- in the short term. everyone has to come to tools or know-how. techné meant the making of something ing this principle. S. our perceptions of ment the decisions that are made most technology are opposed to art and beauty. To some it means “applied drive a Corvette®. between art and technology is desired and appreciated. For instance. and why people transportation. traffic will share some perspectives on technology. Given the society-permeating these perspectives. of technology or. he described of our time. Gibbons was the Direc- tor of the U. It is ubiquitous and is woven technology as “applied human knowledge. Likewise. manship is retained in the word “artisan. of course. People. a calculator extends human ca- apprehensive about it? How do we gain the pabilities to quickly do math functions like knowledge and capability to take full advan- the square roots of numbers. therefore. using a system of roads. balance. should enhance and be guided by artistic ues of the company. technology is not just nature of technology. etc. and machines. the principles by which it and to others “a complex social enterprise or operates may be good or bad.” ethical decisions that just “get by. the best of technology does contain process. its signals. it is “human ingenuity in action.” seamlessly into society.” The origin of the word “technology” assume that a company has making money at is the Greek word techné.22: The Business of Composites 535 the company does business. However. The basis should be established with careful Therefore. Do we like it? Do we hate it? How do we action(s). an tage of technology in our lives? This section automobile.” Given learn. This basis will help everyone “Elegant solutions” are often found for prob- make more consistent and satisfying ethical lems.” and. not let ourselves become resentful or even For example. etc. some Luddites might suggest ogy was initially welcomed. Technology has been products and services are not successful or with us from the beginning of civilization profitable. no new eliminate the tail pipe emissions from mil. and Applications . is generally seen as the trigger new technologies are driven by human val. ed. generally. success in the third the summer that does not have air condi. It should be not- realize that in 1900 in New York City alone. Therefore.” Of course. Some to the negative impacts it has on people and people lament that the technology was ever their jobs. some have negative attitudes man capability and. impossible) to assess with the entire culture of society. solved some toward all technology. That is the phase where After having partaken of technology and the original technology has been modified its benefits.? They have entered the third phase of we really want to go back? technology adoption.” really? power for making electricity. ues—improving the quality of life. all new be “free” of technology. However. often finding that they from the horse urine blistered the paint on have sufficient electrical power to export it the cabs.536 22: The Business of Composites system responds to human wants and needs the point in time that would be considered to with products and services. In addition. it is difficult to go back and give to overcome the problems identified in the it up. phase also requires that the public be posi- tioning? Who wants to give up computers tively responsive to the changes. However. in fact. Luddites (a term problem. many new 4 million pounds of horse manure daily? nuclear plants have been built. profits.S. from the Industrial Revolution [1800s]) are The second phase of technology then oc- people who are anti-technology. trains. Methods. They paint curs. nology. that in many other countries. A further appreciation for the attitudes recognition. however. Luddites generally want us to adopted. Do U. for the creation of civilization itself. Anti-technology Values This phase is successful because the technol- While most people gratefully consume or ogy to be adopted has increased some hu- use technology. However. An obvious example of these two go back to the “good old days. These values differentiate of people toward technology can be gained the technologies that people consume and by understanding the three phases of tech- those that are forgotten. the problems with the a negative picture of technology and point adoption of the technology are seen. What is the difference horse manure contributed significantly to a between these European countries and the tuberculosis epidemic in New York City. The first phase is technological adoption. the horses had to be stabled away from countries use nuclear power as the principle the cabs at night because the ammonia fumes source for electricity. The deployment and adoption of and. However. Fundamentals of Composites Manufacturing: Materials. and photocopiers and go back to the days of the third phase requires not only technologi- typewriters and carbon paper? Who wants cal improvement but also attitude change. after that going back to the horse and buggy days problems at Three-mile Island and concerns would improve air quality because it would about disposal of nuclear waste. or automobiles? It more than just engineering—it must deal is even difficult (really. The technol- For example. Both of these Also. to go back to the days of cross-country travel It is again seen that technology viability is without airlines. nuclear plants have been built in the United lions of cars and trucks. do they States for over two decades. the horses for horse-drawn taxis produced especially Belgium and France. In this phase. Who wants to own and drive a car in second phase. phases is seen in the development of nuclear how good were the “good old days. air-borne bacteria in the to other countries. and/or wanted are in a position of power. concerns are being become available. Competing in the Global Market families. It is clear that those who have tech- plans for distribution and sales. not as an evil.S. compete Fundamentals of Composites Manufacturing: Materials. This is manufacturing jobs? Should we become Lud- referred to as “cultural lag. this change in soci- those who resent the technology and have the ety should be viewed as an opportunity and highest frustration level with it. it works. Technology is making the labor. There are early adopt. progress is generally associated with economic well-being—of individuals. reason why jobs are moving overseas. These late adopters are often jobs overseas.) once thought ers—those who acquire and use the new were particular to our advanced economy gadgets. when the only difference is economic well-being. which has impacting the U. and systems as soon as they (Friedman 2006). ing people in many countries to acquire the gies at varying rates. Still others wait until the technology We cannot stop the growth of technology becomes so ubiquitous that they are forced any more than a person can stop the waves to use it just to continue to function in the of the seas. more technology. players. cultural values and so. Technology is Why don’t we all embrace and adopt the enabler for many of these offshore jobs new technologies immediately? While slow because it allows overseas manufacturing adoption of some new technologies can be to be competitive with manufacturing in associated with cost. they need to be aware of the it may be the answer to the problem of job phenomenon of cultural lag as they develop drain.22: The Business of Composites 537 Cultural Lag the world a level playing field.” Some people wait dites? Should we capitulate and give up on until a new technology is a little more mature domestic manufacturing jobs? To fight for before acquiring it. Technology and Globalization therefore.S. Clearly. nor can we stop the growth of modern world. Manufacturers in highly developed coun- gies.S. However. ing it. must adopt a progressive at- new technologies. and nations. but they are a little more titude toward technology. balance of trade and our very low wages. The U. and Applications . posed to purchasing beta VCRs and laser disk It is cumulative and thrives on innovation. devices. These earlier adopters are expressed about the number of manufactur- sometimes referred to as “techno-geeks. alters our perceptions of time and space. such as computers and the Internet. It benefits and see others using it before adopt. and comfort the late adopt. not less. Technolo. capabilities that we (the U. cial change often are the reasons why most Should a country fight technology to save people lag behind the early adopters. This is allow- People embrace and adopt new technolo. developed countries. Companies nological knowledge have power over those should excite the early adopters.S. These are the people who waited and It is pervasive and irreversible. companies. cultural lag can impact market develop new technologies that are needed penetration. Likewise. tries will have difficulty competing head- have spurred globalization. In society. Now. creative innovators who ers. the U. however. Methods. These people embrace jobs. It requires purchased VHS VCRs and DVD players as op. Technology to-head in labor-intensive manufacturing deployment in many developing nations is environments like that of China.” ing jobs being sent offshore. can. reassure that lack knowledge of technology and how the mainstream. The answer to the problem of job drain is. but cal devices. specialized knowledge and ways of thinking. Technology is not really the As companies develop new technologi. They want to make sure of the that technology is powerful and dynamic. We must recognize conservative. Several practices a composite fuselage requiring 7. that they are outside the realm of feasibility. materials. the ity.000 and stay more creative. Figure 22-4 compares the dynamic planning in which alternate paths critical elements of the cost of goods sold are explored is now the preferred way to plan for an aluminum versus a composite fuse. (NSB’s) Task Force on National Workforce Policies for Science and Engineering has SUMMARY also raised concerns about the declining Even though composites are often highly numbers of students pursuing engineering favored for their performance. strategically. therefore. whereas a com- areas are connected to ingenuity.000 me. receive the highest profits. are not preparing students to understand Because the fabrication costs for com- technology. This issue was confirmed placement. Therefore. Because of the subdivisions so that the costs can be studied uncertainties of today’s world. therefore. less costly.500 parts. and qual. of business is creativity. These aluminum fuselage. not so high It is clear that a nation must have “excel. school systems sembly costs. that planning needs to be more is a good example of composites economics than just an outline of the path the com- and the division of the cost of goods sold into pany will take in the future. a vertical take-off and (NRC’s) Center for Education (Pearson and landing aircraft. lence in discovery and innovation” to con. at least. Further. to understand them fully and discover meth- ods that might be used to reduce them. This method has high capital costs by the Committee on Technological Literacy but is automatic and. is being made using fiber Young 2002). (CTL). but the much higher costs for assembly company that is creative is the company that of aluminum more than offset the lower will develop the products first and. The costs of a composite fuselage are Another of the most important aspects higher for fabrication. Planning The decision of whether to make a helicop. a group of experts convened by the The savings have been so good that the fu- NAE and the National Research Council’s selage of the Osprey. For example. lage. technology develop. One of the methods called for schools to prepare “technologically employed for fuselage structures is fiber literate” students.000 parts. the thinking. ter fuselage out of aluminum or composites However. how it is developed. William Wulf. were identified to help the company become chanical fasteners would require 85. (National situations require that the composite costs Science Board 2003). Methods. CASE STUDY 22-1 Other aspects of business are also im- portant to make good composite parts and Composite Fabricating Economics— to continue to be competitive in the ever- Helicopter Fuselage shrinking manufacturing world. this is the logical place to impacts life and work (Wulf 2000). and Applications .S. and creativity. and technology management. in a world of change is critical to success. Fundamentals of Composites Manufacturing: Materials. aluminum fuselage would have 10. and how it posites are high. also be favorable or. He has attempt to save costs. critical posite fuselage would have 1. costs in the other elements.538 22: The Business of Composites in the areas of design. President of the National Bonding composite parts as an alternative Academy of Engineering (NAE). costs should be analyzed in detail tinue to lead in the global economy. Increasingly.S. most real-life and scientific careers in the U. has ex. The National Science Board’s placement. to mechanical fastening further reduces as- pressed alarm that the U. mechanical fasteners in a corresponding ment. a system of more accurately. Fundamentals of Composites Manufacturing: Materials. As identified herein. Composite versus Metal Cost Comparison Technology is a critical element of today’s Objective: Discover the differences in world. competitors. Along with ethical behavior. needs to be inherent to the company and Within this highly technological world. Elements of the cost of goods sold for an aluminum versus a composite helicopter fuselage. profitability. being technology to other materials and manufac- ethical is a process and. the its culture. the intent of helping. When done with performance and marketing were given. because it has demonstrated superior should be ethical. much like quality. and Moreover. Some perspectives on company needs to work within an environ. Methods. this dissent can make teams more effective and the company more LABORATORY EXPERIMENT 22-1 responsive to its customers and suppliers. the composites industry exists. Ethics is also a critical factor in long-term dependent on recently developed technology. Customers. and Applications .22: The Business of Composites 539 Figure 22-4. the Internet is a critical tool. No industry is more sensitive to it costs for a simple part made of either a than the composites industry because it is composite or a metal. the use of the Internet for improved company ment of healthy dissent. in others in the industry expect that a company part. turing methods. ISBN 1-57675-094-9. “Business’ Killer App: The Web.. Nashville. Keshavan. National Science Board. Brent. What is the cost of goods sold? MacKenzie. CA: Select Press. Thomas L. 3. 2000. New York: Simon Senge. Summarize the report. ISBN 0-7575-2277-7. 2006. The Fifth Discipline. and Schuster. Using the Internet or the library. on Innovation. San Francisco: Berrett-Koe- hler Publishers. Inc. and Giroux. IA: Kendall-Hunt Pub- 0-9644294-7-0. ISBN 1-881052-58-3. Give three situations when dissent ence and Engineering Workforce: Realizing would be valuable. “The Sci- 6. Royston M. A. A. Serendipity: Ac- businessweek. Tech- BIBLIOGRAPHY nically Speaking: Why All Americans Need to Know More About Technology. TN: Abingdon. ISBN Pre-1500. 2002. Peter M. 1989. G. 2005.. Nair. nosaurs. Strong. Kelley. Methods. ISBN 0-670-87983-5. Albany. The Art of Innovation. Self-deception. ISBN 0-9679209-0-6. Friedman. and quality.” http://www. August 14. OR: Dresselhaus search for a case study that compares Design Group. eds. New York: apr2002/tc20020415_3981. 2. 1994. The Peter Principle.htm.. Business Week. New York: Doubleday.nsf. The World is turing method is lower in cost and those Flat: A Brief History of the Twenty-first areas where it is more expensive. each is appropriate. indicating the areas in which the composite’s manufac. New York: Farrar. History of Creativity. 1988. What is meant by the process of ethics? Leadership. 1998. Straus. 1990. 2000. Portland. Thomas. Break-Out Creativ.” Online version at http://www. 1989. the costs for the same part made using Easum.” video. April 15. What are the three types of decisions Surviving with Grace. Leadership and DC: National Academy Press. Crandall. New York: W. Century. A Higher Standard of 4. America’s Potential. Laurence J. ISBN 0-471- 60203-5. “Technology Education: to lower the costs of the composite’s The New Basic. and Applications . Rick. ity. 2001. Stephen R.com/technology/content/ cidental Discoveries in Science. Gordon. Describe two similarities between ethics Publishers. San Francisco: Berrett-Koehler 5. Give the reasons for your findings. and Hull. T. Dubuque. H. be harmful.. and Young. Fundamentals of Composites Manufacturing: Materials. Inc. J. 2003. Arbinger Institute. Suggest methods that might be used Gibbons. New York: Penguin made in a company and describe when Putnam. 1998. Orbiting the Gi- 2. What is meant by “the bottom line?” ant Hairball: A Corporate Fool’s Guide to 3. Dancing with Di- either a composite or a metal. ISBN 0-67166-3984. 4. William M. Raymond. 1998. NY: Delmar manufacturing method. Inc. ISBN 0-385-49984-1. Washington. 1969. lishing Company. ed. John Wiley and Sons. Peter. ROI: Return 1. Seven Habits of Highly Effective People.540 22: The Business of Composites Procedure: Dresselhaus. Pearson.gov/ 7. Morrow. Give two situations when dissent would nsb/. Roberts. 2002. Publishers. 1. William F. Corte Madera. Covey. QUESTIONS New York: Doubleday. Methods. Wheatley. New York: Harper Perennial. 2006. and Applications . Wulf. IA: Kendall-Hunt Publishing Company. 2000. Brent. 1983. Inc. Margaret J. 3rd Ed. Upper Saddle River. Springfield. 1992. Webster’s Ninth New Collegiate Dictionary. 1500-Present. A. Dubuque. 10–12. Plastics: Materials and Processing. Strong. Thompson. ISBN 0-06-096901-6. A. Fundamentals of Composites Manufacturing: Materials. ISBN 0-7575-2692-6. pp. W. MA: Merriam-Webster.22: The Business of Composites 541 Strong. “The Standards for Tech- nological Literacy: A National Academies Perspective. The Technology Teacher. Brent. 1992. 59 (6). Leadership and the New Science. San Francisco: Berrett- Koehler Publishers. A. History of Creativity. Charles. What a Great Idea. 2006. NJ: Prentice-Hall. the makers of steel Fundamentals of Composites Manufacturing: Materials. and the entire process of making. Some advantages of com- INTRODUCTION posites go beyond the normal weight savings and molding capabilities traditionally cited. illustrate some traditional and specific ap- plications. the the adoption of composites in automobiles. IsoTruss® Some breakthroughs in composites that • Critical market—armor have the potential to increase their use far • Breakthrough markets—commercial beyond the current levels and even beyond and corporate airplanes what can be reasonably imagined will be • Future-today markets—unmanned discussed. and Applications 543 . Weight savings has always than the smaller but higher-technology mar. Not all composites uses can be discussed in Further. been an advantage that composite manu- kets.1: Introduction to Composites 543 23 Composites Applications CHAPTER OVERVIEW Some specific composite products will This chapter examines the following be discussed. The sizes were given in Figure 1-2 (in Chapter 100% composite body of the 1953 (and One of this text). be surprising even though the market for fiberglass reinforced composites. but rather to with the breakthrough technologies. Other discussions will look • Learning lessons—space structures at products that might be reasonably made internationally. manufacturing pro- cesses. However. which are instructive for a variety TRADITIONAL COMPOSITES MARKETS of reasons. including comparisons of the • The ultimate composite structure— types of manufacturing that might be done. The lessons learned about concepts: composite materials. for Land transportation is a major market some. This surprise is because subsequent years) Corvette® demonstrated the largest markets are discussed less often the capabilities of this material to the auto- in the popular press and even in classrooms mobile industry. • Introduction transporting. Methods. The objective of this chapter turing add to the potential of great success is not to attempt such a task. innovations in composites manufac- any single book. These breakthroughs are the vehicles result of years of accumulated familiarity with composites. an advantage versus steel. to really appreciate the full facturers have tried to use as a reason for breadth of the composites marketplace. This order will. The traditional composite uses will be presented by markets in the order of Transportation the size of the market. and using composite materi- • Traditional composites markets als are shared. traditional markets should be considered as While composite’s weight savings is certainly well as those that are more leading edge. most difficult body panels for composites Truck tractor bodies and sleeper units.000 miles (1.6 lb (4. Other auto. (1. BMW and Volkswagen environmental conditions of cold. Methods. made of reinforced nylon. some cars (such as the 2004 Cor. further er panel. Even though the tooling costs. The composite version re- is only . allowing repair or re- automobile makers seeking improved per.609. which bolt/snap With increasing frequency and volume. The use of composites has allowed con- fiber hood is made with an inner and an out.2 mm) thick. composites heating and air conditioning vantage over metals. The outer panel truck pickup box. Many of these and boot). Like the fiberglass sheet composites have made greater penetration molding compounding (SMC) hood used on into truck than into automobile manufactur- the regular production Corvette. duces the total weight by 50 lb (23 kg). The economics of these materials has properties of composites also must be impor. In 1. where the molding strong market for many years. This is because composites have truck cabs are made by spray-up with resin had problems with sagging in hot weather. Interior parts have been a as at the front and rear. Truck makers view vette® Z06 and later models) have used the weight savings and low maintenance carbon fiber as the reinforcement in hood requirements of composites as strong eco- panels. promise of weight savings is always part of Most automotive composite parts are the investigation into using composites as a made with SMC or bulk molding compound replacement for steel. the carbon ing. placement with minimum downtime. Hence. such exterior parts. cycle times. The motive makers are examining carbon fiber truck has been field tested for more than for use in high-performance automobiles. Early problems with paintability The most common body panels made of and smoothness have largely been solved for composites are highly shaped sections. lb (9. to capture have been the large horizontal as well as entire trailer bodies are routinely surfaces like the hood and the trunk (bonnet made of composite materials. heat. The total box load-carrying of 150 different automotive applications for capacity increased to 1. The formance are switching to composites for ap. For example.5 improving their economy. transfer molding (RTM) growing rapidly as Recently.048 in. especially if the material con. Some composite side ducts have the advantages of easy shaping panels are proven to have good “non-dent” (molding) and low weight while meeting capabilities. the reality is that other (BMC). the rather modest strength and stiffness tains a high amount of thermoplastic.8 kg) In light trucks. structural inner panels are corrosion resis- plications other than body panels. parts consolidation. especially relatively flat corrosion. The greater stiffness of carbon helps nomic incentives for their adoption. and Applications . Thus prevent sagging. The outer panels were their regular production vehicles. an alternate process.000 km) over extreme the 2006 model year. lighter. and have both introduced carbon fiber parts into off-road operation.000 lb (450 kg) versus Fundamentals of Composites Manufacturing: Materials.3 kg) and that weight is 10. solidation of many parts in trucks. been improved by the continuous lowering of tant for them to be used in automobiles. and lower areas that are easy to form. on for easy removal. in addition to weight savings and the ability large portions of most automobile bodies are to be molded include freedom from rust and still made of steel. therefore. In excess tant and tough. capability of composites gives them an ad.544 23: Composites Applications have been successful in creating new grades fiberglass composites have reached regular of high-strength steel that allow parts to be automotive production. The carbon fiber hood weighs 20. Desirable properties made thinner and. The requirements. a recent innovation is the lighter than the SMC hood.000. After a serious crash that on an overhead conveyor system in a process would probably have destroyed a metal reminiscent of an automobile assembly plant. pulleys. tory in which the molds move through the the weight savings was the driving force for various spray-up booths and curing ovens composites use. is large and diverse. compartment. ent. bonded U-joints was found to have an ulti. water and performance of carbon fiber compos- pumps. rods. a drive flame retardant is important in some of these shaft made from epoxy/carbon fibers with applications. oil pan. Some of the products mental automobiles with favorable results. valve tappets. The driver compartment and tub/shower unit. (FRP) is also used extensively in the molds tive steel box. aggressive Some of the components that seem likely research programs are defining the value to be replaced include: valve covers. Initially. Methods. As more aggressive governmental weight mate torsional load capability equivalent to reduction (fuel efficiency) goals are enacted. but that did little damage Large whirlpool spas are made by spray-up. a major corrugated fiberglass patio/car park covers. to the composite compartment (the driver However. The composite material’s in comparison to metals. often in a highly integrated fac- of epoxy/carbon composite material. and even some ites. energy management. for making many of the parts already dis- Many transportation applications con. and intake-valve stems. and of the crashworthiness of composite body lack of corrosion. they are so large that they are was unhurt). cussed. At pres- than the metal shaft. For example. have been used for many years. Construction The use of composites for automobile The construction market for composites frames has been examined in a few experi. especially Fundamentals of Composites Manufacturing: Materials. However. Some engineers have even suggested joining technologies. However. the use of carbon fiber is restricted to Several metal engine parts have been a few highly specialized applications and targeted for replacement with composites. and Applications . composite material is now the rarely moved through a factory the same way standard in Formula One cars. light weight. cylinder head. such as In addition to the weight savings. These products are made surrounding structure in the car was made by spray-up.23: Composites Applications 545 the 600-lb (270-kg) capacity of the competi. processing methods and a nearly total replacement for the engine by economics. frames was shown in a MacLaren Formula Another traditional product is the tub or One racing car. as the smaller tub and shower units. energy management. and crash targeting the engine block. Fiberglass reinforced plastic because these can be cleaned and. valve-spring retainers. advantage was crashworthiness. Some of the research being pursued internal parts like pistons and connecting includes: carbon fiber composite durability. The laminate layers separate) and this gives an product competes against sheet metal (often increase in the energy-absorbing potential galvanized steel). A significant proof advantages are low cost. Items as large as boxcars and light rail Fiberglass reinforced wall panels are espe- cars are now commonly made from fiberglass cially important for the institutional market composites. the composites will become more competitive composite shaft would result in a 60% weight and carbon fibers will begin to compete for reduction with only somewhat higher cost the transportation market share. some concept cars. The ability to make the composite tinue to be explored. Composite This product is made by pultrusion or lay- structures collapse progressively (as the up of fiberglass mat and unfilled resin. the metal shaft it would replace. deployed across the to the concrete pillars. of course. The collapsed bridge To date. but is not good in levered from the support vehicle. is deployed across the gap. many more bridge cm) high and 20 in. (50 cm) wide and comes installations are likely to occur. Approximately 70% of all Fundamentals of Composites Manufacturing: Materials. The rails. When duty automotive traffic and a few compo. If the beam were too heavy. The weight and by wrappings of composite (in tension). beam across the gap. All of these composite parts with composite simply extends the life of are made in highly reproducible processes the columns. A related in 20 ft (6 m) sections. These parts are forcing the concrete and preventing it from used within structures to add strength or flaking off. Note that tension. number of installations currently in test. the weight of the beam must be as little as Hence. Composites are just the opposite. It uses epoxy and carbon fibers stringent fire codes. therefore. the bridge tracks term (10–20 years) data. The second purpose for wrap. composite fibers in bridges are structure is carried in a truck or attached limited to those for pedestrian and light. (100 and time to collect data. This application ers have adopted the name “fiberglass” and could. parable metal bridges. length can be calculated using simple can- Although actual field tests have not been tilever beam theory. the next highway overpass pillars with carbon fiber can be unfolded from the end of the previous composite. self-supporting bridge to cross are often highly decorative. angle beams. purposes for wrapping these columns. For new construction. shafts. There are two major tubes. the weight of the overpass can be possible. The first step is undoubtedly limiting their application in the deployment is to extend a support to higher-tolerance automobile bridges. It formances. the supported by the concrete (in compression) weight of it could tilt the support vehicle but the concrete itself will be supported and the bridge would fall. the composite are highly complementary The beam is. the nents of heavier automotive traffic bridges. and other simple parts is a growing first is to remediate old columns by rein. wrapping to build upon. These tracks are full-size bridge structures and the limited about 10 ft (3 m) wide and 4 ft (1 m) high. laboratory tests on are rolled across the beam. These panels A portable. The mass production of standardized ing are encouraging. plastic composite. I-beams. market for composites. ribs. be enormous in the volume made it synonymous with any reinforced of fiber used. and Applications . The sections are con- application is the wrapping of concrete nected so that as one is extended. to a military vehicle (such as a tank). therefore. This is a box-shaped With additional experimental installations composite beam that is roughly 39 in. they can be and can cross much wider gaps than com- used for mass transportation applications. the panels will meet even the most (NATO).546 23: Composites Applications for hospitals. The mechanical properties of section and then lowered to the horizontal. boat manufactur- wrapped with composite. disinfected easily. has been found that the likelihood of the column collapsing during an earthquake Marine is significantly reduced if the column is In marine applications. Methods. carrying vehicle is positioned on the edge of The lack of performance data for composites the gap to deploy the bridge. a ravine or small river is encountered. Concrete has good gap in this unfolding manner and is canti- compression properties. After the support beam installed for sufficient time to gather long. will have predictable per- ping the columns is seismic protection. and. Therefore. When flame and ravines and small rivers has been developed smoke retardant resins are used (especially by the North Atlantic Treaty Organization phenolics). on ships and for other components in which Another corrosion product often used signal transmission is to be maximized. If the liquid is not water over metals. It is used as The major problem encountered in using walkways in many industrial plants.000 able.524 m) and at hydrostatic pressures of • seamless construction. commercial • high strength and durability. and manned structures have been generally • minimum maintenance. decks. materials such as concrete. weight (to transport are increasingly used for housings for and install). Submersibles have been developed and successfully used • almost any boat design or size is mold- (remote control) at depths as great as 5. tanks. which may interfere with ger are now constructed of glass fiber rein. storage. bubbles or voids. The major benefits Composites have found wide use in pressure of using glass fiber reinforced composites in hull and buoyancy structures in underwater marine applications include: applications (submersibles).789 kPa). although some components that complement these struc- use vinyl ester for improved resistance to tures represent the majority of the corrosion water blistering. and ductile iron. although usually not for hulls. However. Corro- In high-performance (racing) boats. strength at given weights.200 ft (366 m). The combined is- as mine-sweepers. successfully used. The grating is Fundamentals of Composites Manufacturing: Materials. signal transmission. The structures are nor- mersibles. Methods. and Applications . dry rot. For water transport/ or aramid. except in the case of specialized boats such steel. mine-sweepers. 2. fiber-cement. outboard motor shrouds. However.000 psi (13. aramid wound structures also have been Other marine applications include sub. polyester resins dominate. forced plastic materials. well casings and the various of fiberglass and polyester. Difficult liquids may composites has led to their use as radomes require epoxy. product business for composites. These are generally made Pipes. in chemical plants is grating. as the predominant pattern to optimize the and kayaks. portion of the corrosion product business. composites sues of cost. glass. but composites in these structures seems to be especially where the chemical environment ensuring that they are fabricated without might corrode metal grating. rust. canoes. Military boats also use composites ex. is fiberglass epoxy and polyesters.23: Composites Applications 547 outboard pleasure boats 15 ft (5 m) and lon. although and water logging. and corrosion resistance favor many components on ships because of the composites for the transport and storage of reduced maintenance of these structures other liquids too. the resin of The excellent radar transparency of some choice is vinyl ester. sealed mally filament wound with hoop windings pontoons. the choice of resin is strongly The masts and spars of sailboats are usually dependent on the nature of the fluids that will made of composites—often carbon fiber and/ be transported or stored. The most common material for these applications • freedom from corrosion. com. sion products are usually made with fiber- posites also have taken a major position. In some high-performance boats. and limited to depths of 1. Water the entire hull and even the deck are made transport and storage is the highest-volume from carbon fiber and epoxy. and Corrosion Products other structures. hovercraft. Composite pipes are rapidly replacing other tensively. However. ft (1. The most prominent use for composites in the marine industry is for hulls. and sometimes even when it is. durability. which are now routinely processed in because of the presence of dissimilar mate- many applications. been obtained. tors. tethers bonded together to make the board. There- to hold the platforms. Since the substrate from essentially zero on the incident surface must provide the proper electrical. ing. in printed circuit boards. Typical quickly become dull. common materials for high-quality sub- strates are glass cloth and epoxy. Most boards are made ing operations.548 23: Composites Applications usually made by extrusion but some lay-up to the greatest electrical conductivity on the and even RTM gratings are commercially rearward surface. is the drilling of the holes. the use of composites for oil drill. composites Although more costly for the equipment. The use of composites as a substrate for A market of immense potential but cur. tated by price and its mechanical. The most to grow tremendously in the near future. Fundamentals of Composites Manufacturing: Materials. and The use of tough resins in the couplings may • paper/epoxy. and physical properties. which encountered with metal components in these gives some shear strength. Some significant problems of fabric reinforcement material. the can be fabricated to absorb nearly all the lasers last much longer and generally allow radar energy that impinges upon them. resist shear forces. boards are made by bonding a substrate to Some opportunities for composites include a conductive material. In particular. yield sufficient performance. have been suggested as ways to solve these • glass cloth/melamine. These for oil drilling and related oil-field activities. Some. but are still used ex- examples include circuit boards and insula. tanks. turization and that trend is especially true ity varies continuously. Mechanical drills ductive nature of these materials. Liners and exterior coatings • glass cloth/phenolic. composites resist the warp require that high-performance resins be and twist common in printed circuit boards used. which are cations include offshore platforms. Electrical One of the problems encountered in the The most common uses for composites in use of composites for printed circuit boards electrical applications utilize the noncon.) have been challenges that need to be • nylon cloth/phenolic. rials (substrate and copper foil). is usually done by fabricating the part with a The future of electronics is toward minia- tapered impedance in which the conductiv. Laser drilling is also used widely. Methods. and the underwater fore. such as copper foil. the design of the composite should housings used to encase some of the drill. printed circuit boards is one of the most rently limited in actual sales is components important electrical applications. worked on. als would be: posites. The composite-metal inter- face must be able to withstand shock forces. In spite of the The choice of the substrate material is dic- difficulties. especially in offshore wells. electrical. and then etching the circuit pattern onto times the high temperatures (up to 400° F the copper. and Applications . or in discrete steps. Other oil-drilling appli. As substrate material for printed [204° C]) and highly corrosive environments circuit boards. But the composites also have some • paper/phenolic. etc. Typical materi- applications are solved by the use of com. This increases in throughput speed. • cotton cloth/phenolic. problems and some promising results have • glass cloth/silicone. the pipes. abrasion resistance and the composite-metal interface (joints. is expected thermal. Under certain conditions. tensively. problems. available. and well casings. thermal. • glass cloth/epoxy. The use of composites in consumer/sports ponents. bobsleds for the 1988 Winter Olympics was ity. archery bows and arrows. weight. is the removal of heat generated weight savings. snowboards. An ambitious program to develop six new Because carbon fibers conduct electric.375 in. structural Carbon fiber laminates are also used for design. however. and Fundamentals of Composites Manufacturing: Materials. made of . The shape The number and variety of sports equip. some electrical undertaken with composites as the likely applications requiring conductivity have construction material. Additional layers are sometimes added and lightweight. These ap. tracks. For example. car. tough. The design param- been identified for them. A difficulty in further reducing size. namic drag over sleds used previously and racquets (tennis. bobsleds and bobsled competitions. tapered mandrel. water skis. strength and sensitivity of the rod. Materials now design utilizes a hollow tubular construc- being investigated for boards include poly. periments after the other design factors had ues to grow at a tremendous pace. at least to some extent. Solving the anticipated loads has been a major ad- these problems requires greater density vantage. of the chassis was refined in wind-tunnel ex- ment uses for composites is large and contin. The second layer of longitudinal tion of fiberglass reinforced polyester or fibers gives the rod sensitivity because the epoxy insulators. and Applications . The use of composites for rifle stocks and rifle barrels and stocks. runners. A related application is vibrations of the fish are readily transmit- the tools used by electric company service ted along the fibers. In some cases. tailor the placement of the fibers to match ponents poses additional problems. Polyester fiberglass poles to adjust the stiffness and strength to meet have proven to be excellent materials for specific requirements. Some of the been implemented. and however. interface with the athletes. The longitudinal fibers people to work on the power lines. tool handles. The distance between com. as prevalent as All current sled designs were reviewed and the applications in which the composite is a new design was proposed with a chassis nonconductive. Methods. mechanical high-performance battery plates. (9. seems obvious from a stiffness. tion to minimize weight and optimize the imides. These The inner spiral (hoop) windings give the insulators have been made of ceramics for strength needed to eliminate the pinging many years. and ceramics. bicycles. These also increase the bending strength of the devices need to be non-conductive. particular material’s stiffness. aramid. baseball and softball bats. and aerodynamics. composite sleds are skis and ski poles. the brittle nature of or collapsing of the hollow tube when it ceramics has led to the widespread adop. components. quartz. However. the wires are insulated from the pole. a typical fishing pole in the substrate material. handling and control.23: Composites Applications 549 and mechanical environment for the com. fishing poles. in actual runs. and squash). racquetball. gave good handling and speed performance pole-vaulting poles. For example. eters included the following considerations: bon fibers are used as brushes for motors. is flexed. The composite bobsled uses for composites in the sports equipment chassis showed a 40% reduction in aerody- industry include the following: golf clubs. The rods Standoff devices are used to ensure that are wound on a removable. strength. safety. the ability to in the circuitry. it is part of the miniaturization applications is generally dependent on the process. plications are not. Now. rod. the standard for bobsledding and other sled tent poles.53 mm) honeycomb core covered by six layers on each side of graph- Consumer/Sports ite/aramid cloth with epoxy resin. the flight of the bullet be thought of as analogous to the bone and changes as the rifle is used. A composite leg proper wrapping of the fibers. and interior panels and compartments. fan blades. by covering the composite structure with ture change due to a non-zero coefficient of flexible foam. Typical applications include housings for motors. The low-maintenance requirement coupled with easy molding and low costs have made the use of composites advantageous to the appliance market. Composite leg/foot prosthesis. The composite can. Methods. The popularity of these vehicles signals tremendous growth in this market. But. For people who have had a leg or foot am- which is overwrapped with carbon fiber epoxy putated. The roundness comfort and mobility. These thick- change with heating from repeated firings. ducts. leading However. (Courtesy plastic sheets is especially inviting. composite prostheses offer a chance composite. in- factory transporters. Figure 23-1. Most appliance composites are reinforced with fiberglass. The composite barrel casing is limbs are usually of carbon fibers in epoxy. for short limbs. thermal expansion.550 23: Composites Applications maintenance point of view. The concept of thermoforming thermo. therefore. A light person may in the recreational market is for mini. The overwrapped barrel is about for greater mobility and capability over any four times stronger than steel. dune buggies. and even some street mini-cars. the composite is shown in Figure 23-1. utility carriers. This means that maintenance is substantially reduced over metal components. Applied Composite Technology [ACT]) Fundamentals of Composites Manufacturing: Materials. casing can have a zero coefficient of thermal The composite structure is typically ta- expansion. with the tendon structure of the leg. This means the performance pered in thickness from about 20 layers in and accuracy of the composite rifle does not the toe to 80 layers at the top. four to five times stiffer than steel. and Applications . The barrel is five to six also used. Appliances Fiberglass has a natural advantage in wa- ter applications because it does not corrode (rust) as many metals do. The barrel is Medical actually constructed of a lightweight metal. This market includes golf carts. fiberglass/epoxy is to improved accuracy. which means other artificial limb material. require as few as 15 layers at the toe and transport carts. These devices are roughly shaped times lighter than steel and that gives better like a foot and leg but are flat. since steel needed to simulate a normal leg is achieved barrels expand and contract with tempera. Composite better safety. Many of these applications are made with thermo- plastic composites because the cost demands are tight and the structural requirements are low. nesses vary depending on the weight and A large-volume application of composites activity of the person. transporters for elderly people. Moreover. along with the constant difficulty of any prosthetic re- maining attached to the body. its high-tech image and the technological The problems with the composite mate. the body can be taken apart and inspected for damage such as broken bones. developments that continue to emerge from rial include interlaminar shear. Several standard sizes tables on which x-rays are taken. is used in some aerospace applications. which is the device ure 23-2.23: Composites Applications 551 50 layers at the top. For example. rays are often made of composites. the are offered to meet most weight and activity arms and other moving parts of portable x- combinations and legs can be custom built. This capability has proven to be espe- cially valuable in making surrogate human bodies for research into the effects of vari- ous traumas. a recent research effort developed a torso and the underlying skeletal structure. Fundamentals of Composites Manufacturing: Materials. The aerospace industry is the largest at the top where the prosthetic device is consumer of carbon fiber as shown in Fig- bolted to the holder. and Applications . Carbon fiber markets. great progress has been made in these problem areas and artificial limbs allow good athletic capabilities as well as near-normal walking and running. strong enough to give good flexural strength and fatigue resistance. The near-perfect re. this Fatigue failure is also a concern. However. Useful lives of the devices have been several years. The layering of the composite helps give the impetus for their use in this instance is the feel that is desired. which is being used to investigate the effectiveness of bulletproof vests. The the entire composites industry because of metal device is much heavier and stiffer. The ability to tailor composites to the same tensile stiffness and strength as human bones allows these com- parisons to be meaningfully made. The surrogate body is instrumented to detect the degree of trauma from a shot fired into the bulletproof vest it is wearing. To verify the extent of the damage. Therefore. but their transparency to x-rays. even though fiberglass that couples the artificial leg to the person. it remains highly important for greater than with a device made of metal. The structure is probably for their lighter weight rather than flexible enough to give good springiness. However. especially it. Aerospace turn of energy (no stress-strain hysteresis) Even through the aerospace market is of composites means that the movement and only about 1% of the total composites mar- jumping capability with the device are far ketplace. Also. Methods. The near transparency of composite materials to x-rays has led to their use for Figure 23-2. Composites can be tailored to have almost the same mechanical properties as human bones. tions for composites. In tilt-rotor aircraft. fiber components more quickly than com- Hence. carbon fiber extensively in missile motor housings and composites are often the key to acceptable in the launch tubes from which the missiles performance. For many years the most compelling eco. especially when the missiles are mounted on aircraft. However. Thus the designer must choose which are made from fiberglass or combinations material is least likely to be affected in a way of fiberglass and carbon fiber. This is because Composites crack when exposed to high stealth technology depends. Some space vehicles. such as for the Hubble telescope. its use is increasing as weight second largest market for carbon fibers.552 23: Composites Applications discussion of the aerospace industry will savings and stiffness become ever more criti- focus principally on carbon fibers. and Applications . the A-6. Military aircraft adopted carbon cause of the negative CTE of carbon fibers. use carbon-carbon nage on the F-18. empennage. the wing skins and empen- as the space shuttle. applications included the empennage and the preferred support material is carbon speed brake on the F-15. Initially. Especially in the case of military helicopters. While not all of these Industrial missile applications use carbon fiber (some Industrial products are important as the are fiberglass). Later waste vehicles commonly made of carbon fiber system versions operate with a vacuum and include struts and other support members. Originally. which were the the waste system on aircraft operated with a greatest single weight component of many flush system that required the tanks to with- space vehicles. the wings. Estimates components of aircraft such as access doors suggest that the cost to launch 1 lb of weight and engine cowlings. entire planes like the B-2 and the composites.536/kg). carbon fiber in space vehicles because of the extremely composites were used in some non-critical high cost of launching weight. levels of radiation. This is possible be. Fundamentals of Composites Manufacturing: Materials. structures because the coefficient of thermal With continued good performance. the use expansion (CTE) of the composite parts can of carbon fiber composites has continued to be tailored to be near zero. Other components of space stand positive internal pressure. being designed. Aircraft parts are also a significant mar- nomic incentives for carbon fiber usage were ket for carbon fibers. metals and even ceramics are also Helicopters are also important applica- affected by the aggressive space environ. the casings of rocket motors. F-22 are made of composites. The advent of stealth technology has A problem in the use of composites in pushed carbon fiber composites even more space is their susceptibility to radiation. such on the F-16. therefore require the tanks to withstand an Carbon fiber is especially useful in support internal negative pressure. developed to improve the crack resistance of Therefore. but still the problem persists. increase. Some coatings have been on the properties of carbon fiber composites. Most helicopter blades ment. carbon fibers were used to make for many years is waste tanks. composites in parts where its superior heat and fuselage of the AV8B. and the wings of resistance is critical. Composites are used forcement. are fired. Methods. Some of the military aircraft required. strongly into military aircraft. to some extent. tion for composites that has been important Therefore.000 ($4. the empennage fiber composite. One aircraft applica- into space is about $10. An application that is similar to space carbon fiber is becoming the standard rein- vehicles is missiles. cal to performance. when high-precision orientation is mercial aircraft. The bodies of that is detrimental to the particular part many helicopters are also made of composites. 23: Composites Applications 553 These products often rely on carbon fiber need to be placed in highly confined areas composites because of their ability to save where heat loss by other methods is difficult. there have been several disasters re- of composite materials (usually fiberglass). How- and other components are increasingly made ever. they Columbia was related to the loss of or dam- must be easily stoppable so they cannot be age to a few carbon-carbon areas. Every launch specific strength and specific stiffness of car- has been watched with great interest by a bon fiber. the Royal Air Force motor housings. have flown and landed successfully with some based) for heat removal is poised to become damage to the TPS. the design constraints The most important aerospace application strongly favor carbon fiber over fiberglass as is the space shuttle. Other World War II. energy costs. The board investigating the Columbia Space Specific stiffness is the principal factor in Shuttle accident announced their preliminary the use of carbon fiber composites in indus. Hence. Even though other missions The application of carbon fiber (pitch. which are massively large. fibers seems to be ideal for these applica- ingly. findings and recommendations in 2003. Carbon fibers are one of the in another part of the TPS system other than best thermal transport materials. Careful consideration of this pitch-based carbon fibers are superior to oth. As the size of products decreases. the industrial market is starting to notice. In general. increas. Carbon fiber composite housings will The use of fiberglass and. Methods. However. system (TPS). The light weight and stiffness are especially important The Columbia Disaster to ensure efficient movement and accurate location of the arm. bia’s last flight. disaster leads to important lessons for the ers in heat transport properties. something if optimized for this application during the tragically different occurred with the Colum- fiber manufacturing process. the breakup of the when they apply pressure. of fiber reinforced plastic (FRP). especially in Europe. The concept National Aeronautics and Space Administra- of thermal management with carbon fibers tion (NASA) and even for the manufacturers has already been proven in spacecraft. carbon fibers in wind-turbine blades is a rapidly growing market. Now. Clearly. such as Lesson 1: Learning from History in the case of laptop computers. the need to It is helpful to consider a story from remove heat becomes more critical. the specific stiffness an integral part of the thermal protection of carbon is highly desirable. The industrial market has long The high thermal conductivity of carbon had many fiberglass applications but. Just trial rollers. As STRUCTURES the blades get larger. It has brought great the reinforcement. These rollers must not deflect as most people suspected. large moving machine members. especially the carbon-carbon area. such as activator the war (1942–1943). During the middle part of applications are for items. This is due to the higher technological innovations. carbon fiber products are being used. tions. be common for many items. Composites are not only used for large portion of the population of the United the blades. lated to the space shuttle. These disasters A similar application is the use of carbon are examined here so learning can come fiber composites in robot arms or similar from them. increasingly. the damage sustained was a major market. but wind-tower motor housings States and people in other countries. which are often small and (RAF) was flying daily bombing runs over Fundamentals of Composites Manufacturing: Materials. and Applications . LEARNING LESSONS—SPACE Operating efficiencies favor large blades. that is not what he characteristics. Manufactur- brilliant discovery. However. The areas to be armored were anti-aircraft fire was so intense that on al. The broken window theory grew out of an How could that be? He then realized that observation made in New York City in the he was looking at only the planes that had 1990s. the mathematician made a produce unanticipated results. ing a signal that anything goes. Fundamentals of Composites Manufacturing: Materials. These invitations to more serious crimes. they had some damage on other flights was obviously not inherent limitations on altitude. The German aircraft. In a city. a mathematician known for his for criticality of various areas (although ability to carefully analyze problems was some critical areas were obvious). shot down. that are critical to success. to never compromise the integrity of critical face of the airplanes. Those areas. About 20% of the planes were in half. The RAF could not continue to What does history have to do with the Co- sustain that level of losses. They are observed on the surviving planes. It has direct application to the Co- survived the flights. saw. the plane would be lost. product characteristics should be protected ematician reasoned that. lumbia accident? It is logical that the areas gestions for reducing the losses all seemed to on the Columbia where damage occurred have some problems. and aggressive panhandling are all of the planes where no damage had been the equivalent of broken windows. Further. people walking by he had not seen damage. such as graffiti. The mathematician began What does the lesson have to do with FRP his analysis by examining the planes that manufacturing? Some combinations of manu- were returning. moreover. For instance. of the plane and when damage was received and the sense of anarchy will spread from the there. send- The mathematician’s suggestion was. quite simple. critical and so those flights survived. Soon. more windows will be broken. The not survive must have been those planes theory is this (Gladwell 2002): if a window is that received damage in the areas where broken and left unrepaired. and the number of airplane losses was cut ing damage. he found that there were some Lesson 2: The Broken Window Theory areas on the planes that were not damaged. the sug. which resulted in the ac- could not fly higher because they were not cident. asked to help. rela- therefore. Previous TPS pressurized and. That protec- squadron as a whole. which led to a suggestion ers should make the effort to clearly identify that resulted in a significant reduction in the the areas or the properties of their products number of planes that were lost. the anti-aircraft damage tion should include testing and determination would be random over the entire under-sur. answer is that NASA had not really tested Finally. These critical What was the brilliant discovery? The math. After examining the planes that had returned. not so many that the weight was excessive most every run most airplanes were receiv. Methods. he will conclude that no one cares and no one is reasoned. were critical areas. public that the RAF put armor only in the areas disorder. He recommended tively minor problems. must have been the critical areas in charge. taking the entire with special care and robustness. the planes during the flight.554 23: Composites Applications German-occupied territory and airplane were the critical areas for survival of the losses were devastatingly high. Why the RAF could not cover the bottoms of the didn’t NASA realize how critical damage planes with armor plate because the planes in specific areas could be? The probable would be too heavy to take off. and Applications . building to the street on which it faces. The planes that did lumbia accident and the FRP business. After several days of these facturing defects and end-use environments examinations. But. accident. the lesson is as intended and to monitor with ongoing simply this: the company will work better if vigilance the capability of the manufacturing it takes care of the small problems. Non-destructive testing on fixed and everyone has the responsibility to the actual shuttle and destructive testing do their best to fix it. process. stop people from jumping to take care of even the small problems. clamp down on muggers and various other relatively minor Lesson 3: Testing and Quality Control crimes. A combination of declining budgets and but the board’s report points out potential the growing body of data indicating that improvements that may have prevented the some loss of TPS would not cause cata. product recall). combination of circumstances not tested or Tests of the shuttle after each flight should manufacturing/installation defects. now required on each flight. the testing methods currently employed in- come accustomed to seeing missing or clude: physical tap. In summary. Board suggested that NASA implement a portantly. on the control panel was suggested. and visual tests.S. weight gain. Testing and quality control are not problems that seem to be inherent in the just a series of hoops to be blindly jumped system should be solved because the ultimate through. in making sure that the part will perform For the FRP manufacturer. Given that the design was qualified (tested These should be upgraded and new methods to be sure that it was able to meet all re. The opportunities for a problem to nent. Similar cases where testing has strophic failures induced some measure of been considered to be merely a method of tolerance for little problems. and shuttle while it is in orbit. ultrasonic. result might be a disaster (such as a massive gan to immediately repair broken windows. the incidence of major crimes also are Critical declined dramatically. Such imaging is repair processes. refurbishment. longevity and performance of each compo- cern. The criminals realized The Columbia Accident Investigation that someone was in control. materials. Methods. eddy current. ernment has the capability of imaging the complex assessment.23: Composites Applications 555 When the officials of New York City be. it is important remove graffiti. lation to accommodate the curved surfaces What was the problem with the testing of the vehicle. which led to disaster. damaged TPS on returning space shuttles. Even more im. the generally brittle nature of the can be initiated. an attitude was developed among strong program of testing of the reinforced the city officials and among the populace carbon-carbon composite TPS components that even the smallest problem needs to be of the shuttle. Every manufacturer should remember window did not get fixed and eventually the that quality testing is a method to assist building was destroyed. identified to assess the structural integrity quirements). and custom tailored instal. . radiographic. Further. This toler. the complexity of the fabrication The board also noted that the U. so develop are many: extreme temperatures of that routine maintenance and replacement operation. Some of NASA engineers and officials had be. and Applications . Fundamentals of Composites Manufacturing: Materials. The broken mon. Gov- processes. . done before the accident? Maybe nothing . the missing/damaged TPS of the composite supporting structure and was considered to be either evidence of a attaching hardware on an ongoing basis. be made and directed toward evaluating the The TPS has long been an area of con. human-intensive installation. assuring compliance rather than a method ance eventually led to an accumulation of of ensuring performance have been com- problems. especially those made of composites. the turnstiles in subways. Methods. Vacuum is also an tion hardened. are evident at all orbits over about 18 miles (30 km). materials and man-made debris can ten present in the resins. of small molecules.03 for of space is directed toward the development Teflon® to 3. These molecules can then be out of something. the tendency to react understanding their behavior in the many with atomic oxygen) is nearly no reaction environments to which they are exposed (designated as 0 in the table) for metals. neutral environment consists of a va- hit the shuttle’s leading edge (reinforced riety of gases. space diation (at least short term) are with structures often have very large sur. selecting materials and efficiency (that is. atomic species is oxygen. reactive with many organic materials. Therefore. One major problem with • Radiation. provides special challenges. The most important of these was created for the re-entry heat to reach un. the materials must be light trolled electrical charging and discharg- enough that they can be launched economi. This may common double-atom molecules found have been of sufficient severity that a path on earth. Much of the However.556 23: Composites Applications Lesson 4: Materials are Critical to Success travel for significant distances without An old saying asserts: “Everything is made diversion. Even though the vacuum of tin oxide along with special efforts to space increases with altitude. some of which exist as carbon-carbon composite). and Applications . At electrons and protons that causes uncon- the same time. ing as well as the dielectric breakdown cally. of the thermal insulation on the structure. This is the loss such as aluminum. Plasma is an environment of requirements of survivability in space. design in fault tolerance. diminished by using stable conductive coatings on the materials such as indium • Vacuum. Natural space monomer or co-reactant. its effects ensure grounding of the devices. These effects are space vehicles are subjected follows. One guess to the contamination such as optics or from the scenario of failure was that some solar arrays. sometimes one that is sensitive materials from which it was made. The solutions face areas to facilitate heat dissipation are to build the components to be radia- through radiation.” Clearly the Columbia captured by and deposited on another accident occurred because of failure of the surface. and/or provide shielding with a metal gassing of the plastic. The possibility of en- the out-gassed molecules are able to countering debris is expanding rapidly Fundamentals of Composites Manufacturing: Materials. can be seen in Table 23-1. such as unreacted • Micrometeoroids/debris. which are of. for polymeric materials. A list of the environments to which of the materials. which is highly protected and critical subsurface elements. The which holds the external tank to the shuttle. of materials that can meet the stringent • Plasma. to the aging effects observed on earth. the re- work that underlies the exploration and use action efficiency can range from 0. As In the case of materials for space vehicles. • Neutral atoms and atomic oxygen. causing damage single-atom species rather than the more to the brittle carbon-carbon areas. electronic components. the reaction including Columbia.9 for Mylar® (a polyester). which is the most efficient of the heat the most serious problems from ra- transfer mechanisms. environment that encourages out. Although radiation has a a vacuum environment is the inability degradation effect on polymers similar to transfer heat through convection. The scarcity impact the space structure as it flies of all molecules in the vacuum means through space. 4–2. and Applications . materials when exposed to a wide variety of The development cycle for complex vehicles environments. launch and and so those properties should be guarded landing).9 as the number of launches continues ation of consequences and contingencies.5 Polyester (Mylar7®) 1. the importance of understand. Knowledge is not only obtained from are encountered by space vehicles for which actual excursions into space (generally with much of the testing cannot be duplicated on great difficulty. Methods. tained multiple impacts and are periodi. mation that can be applied in many other Even though these special environments areas.50 Carbon 0. Atomic oxygen reaction efficiencies for common materials. (with margin) to withstand the expected the space program is a rich source of infor- environment. subsystems. the investment for initiation of potentially catastrophic events. Material Reaction Efficiency (Tendency to React) Aluminum 0 Gold 0 Polytetrafluorethylene (PTFE) or Teflon7® 0. to improve performance (payload to orbit) puts special emphasis on making Conclusion the structure only just strong enough Though space vehicles are specialty items. should explicitly include in planning. erties of the materials cannot be overempha- sized at NASA or any FRP manufacturing • Launch environment.7 Silicone (room-temperature vulcanizing 0. A typical This insight should lead to an early evalu.443 [RTV]) Polyimide (Kapton7®) 1. in the case of the shuttle. because of their desirable properties.5 Epoxy 1. satellite investment is $400 million and a Fundamentals of Composites Manufacturing: Materials.9–1. but from the the ground. Composites are the materials of choice structural loads a spacecraft normally for many applications. provides significant insight into the life is 5–15 years. and time). The shuttle windows have sus. including space appli- encounters are during the launch (or cations. Designing for reduced weight with great care. The importance of maintaining the prop- cally replaced. Hence. The highest site.03–0. and as the satellites now in orbit fall which is something every FRP manufacturer apart. space hardware that must first be tested as ing the material properties and behaviors components.7–2. even environments not antici.5–3. and then as part is important. a space vehicle can be very high. cost. Studying what happens to of a total system. averages about 10 years and the operational pated.23: Composites Applications 557 Table 23-1. the contributions to the nation via the mysteries of the universe and life on the products developed initially to meet the Earth and beyond. the solar system. sadly. but the potential 1. They adopted the following long-term goals: are low-volume products. Conduct human and robotic missions goals (see Table 23-2). These processes in space to support research collateral applications are important to endeavors in space and on Earth. is real and. in ways never intended. as reflected in NASA’s mission and 3. 5. Materials are critical. Anticipate and plan for all of the con. manufac- 4. Even if • Research. in the war in Iraq). have been many. 4. unique challenges of space. and manufactur. only the anticipated environment. modified for space applications. and flight to preserve public safety. work as planned. Methods. which were sub- sequently passed into the general economy 2. Such Table 23-2. Develop cutting-edge aeronautics and 1. turers should remain alert for the potential design. NASA. but 3. investment with a single detail gone awry. and the universe. Provide safe and affordable space Though there are many applications access. ity control processes do not become rote. NASA has be made in ever-increasing numbers. and be launched into an incorrect orbit.558 23: Composites Applications launch vehicle adds to this price tag. They might knowledge and understanding of Earth. and combinations of environments and the revolutionary space vehicles. possible. smart aircraft. Each of these failure modes and related technologies. Space vehicles contin. 2. as composites are developed and things to come. results of less-than-perfect manufactur- ing processes. The mission of the National investments are risky when you consider Aeronautics and Space Administration the things that can go wrong to wipe out the (NASA) (Harris et al. and manufacturing are keys value these materials can bring to business. human and catastrophic failure of the Columbia. Fundamentals of Composites Manufacturing: Materials. and Applications . tial to hit land and require destruction in • Advance human exploration. They might development of space. be derived from this tragedy. their selection. materials. verify. Nevertheless. exploration. For our solar system and probe deeper into NASA. orbital transfer. they might not transfer advanced aeronautics. Space vehicles might self-destroy (usually • Advance and communicate scientific due to a propulsion problem). Use our understanding of nature’s (commercialized). space. and the commercial there are nevertheless some lessons that can development of space. and whose designs. interplanetary transportation ing will never produce the highly dramatic capabilities to enable research. They can be harbingers of bigger Finally. Stay vigilant that the testing and qual. space vehicles continue to To fulfill this bold mission. develop. and they achieve the right orbit. space systems technologies to support ceivable potential consequences of highways in the sky. use. 2002). Create a virtual presence throughout for profit has proven to be very high. veer off course during launch with poten. Take care of the small problems as they to a product’s ability to perform in not come along. to planets and other bodies in our solar ue to be important for the military (evident system to enable human expansion. they found that manufacturing the and tanks. Those It is probably obvious that architectural concepts are generally based on the concepts trusses are based on simple geometric forms. and still in most which contained these iso structures. automated manufacturing methods reasons. and testing methods could all be manufacturing capabilities. trying to optimize composite performance for roof and bridge trusses are made of wood weight. Institute) confirmed NASA’s assessment of stiffness. cal resistance is a key requirement for pipes However. quality requirements for broad-based properties and control. chemi. but also discussed in this section. compromised for manufacturing and cost however. The structures showers and autos. An architectural truss. Several years ago. For example. in a bridge. stiffness. The of composite materials even within today’s difference. but were difficult to ease of repair are important for boats. Struc- aerospace applications today. the structural efficiency of isogrid structures. stiffness. of course. NASA and higher strength. equipment because of the complexity in- weight. composites have gained terms of stiffness and weight). Typically.23: Composites Applications 559 New materials. greater stiffness. and strength have been volved in making the overlaps. such as triangles. and Applications . The truss also can be self-support- cost. make using automated or semi-automated In some non-aerospace applications. although some composite bridges is “yes. These concepts keys to remaining competitive. is that the isogrids Fundamentals of Composites Manufacturing: Materials. the wealth of information on the fundamentals trusses are closely related to isogrids. and strength). isosceles triangles. can help product designers so that they can be more efficient in saving weight and adding stiffness and strength to products. called isogrid. it might be asked whether anyone is still ing as. for instance. adding a filler will usu. yet fillers are common throughout the composites industry. market share against other materials for Several researchers (especially those at a variety of other reasons too (usually in Stanford University and Virginia Polytechnic combination with the advantages in weight. developed a flat structure. the reasons for tural materials based on this isogrid pattern using composites remain the same. Methods. as is done by composite properties and the compromises the truss network that supports the roof of that have been made for manufacturing and a house. which is the type turing of many composite products. ease of molding is critical for tub/ isogrid materials was difficult. But over were some of the most efficient possible (in the past 50 years. and strength. processes. is a rigid framework decreases stiffness and strength. designs. of beams. were developed. THE ULTIMATE COMPOSITE STRUCTURE—ISOTRUSS® What Does “Iso” Mean? Why are Composite Materials Used? In the context of structural materials. Such a framework can be used In light of the wide array of important to support another structure. In this way. In the original ap. ally increase weight and decrease strength. The answer or metal. which are joined together Structures based on these concepts hold a to form the support network. and weatherability and could be made by hand. Eventually. this optimization process to continue. plications of composites. The textbook answer for why composites “iso” refers to a pattern of interconnected are used is lighter weight. of “iso” structures and composite trusses. the use of What are “Trusses?” chopped fiber increases the ease of manufac. Similarly.” Some unique concepts are allowing have been made. For example. it might op. such as of the truss and orient the fibers in the di. Other structures could include efficient structural form. tensile. the concept is good for Everything else is empty space. util- ness. natural market is poles for weather moni- toring. The fibers are directed. aerospace structures like the space station The IsoTruss concept is simply this: use or even airplane and missile components. Methods. are potential ap- rections where they will carry direct loads. the structure would be tremendous advantages lead to some in- made of composites so that the weight. been implemented outside trusses with the same bending or torsional the laboratory. whereas the the much lower material cost of IsoTruss trusses are open structures. The optimization is directed semi-automated and even fully automated toward saving weight. stiff. Therefore. If so. an still just dreams. Their components. Ready gular patterns except that the triangles are markets would include construction sup- connected in a unique three-dimensional port beams and even deep-sea oil-drilling manner. For example. at twice been proven and the automated methods are the optimal diameter of a steel structure. plications. Manufacturing was moved IsoTruss is less than one-twelfth the weight. teresting applications. especially in areas difficult to access Understanding IsoTruss Structures because a fully assembled IsoTruss tower The IsoTruss structure is built on trian. however. the length and height. The semi-automated methods have not yet ameter in steel tubes. as much as An early challenge was manufacturing the possible. torsional. This makes IsoTruss an extremely platforms. They were originally flexural. Recent advances have suggested are achieved. and manufacturing methods based on filament maximizing strength. and high strength in a tubular ner—for carrying tensile and compression configuration. IsoTruss structures winding and braiding. This is because much less that they. loads. Ideally. uses composites in their most efficient man. and compressive made mostly by hand using mandrels that loads anticipated. gaining stiffness. can be easily carried by a helicopter.560 23: Composites Applications are essentially flat panels that have been An important additional consideration is reinforced by the grid pattern. strated using full-size samples (hand-made timize the structural aspects of triangular structures) as shown in Figure 23-3. This concept most products that require lighter weight. In short. The costs of manufacturing key enabler is the ability to increase the IsoTruss have proven to be extremely high. like isogrids. are also essentially material is used in an IsoTruss to achieve two-dimensional structures. composite reinforcement for the structure Even highly commercial products. in the directions of the various IsoTruss structures. bicycles and pack frames. but Fundamentals of Composites Manufacturing: Materials. And that is the lesson to stiffness at equal diameters. the original had points at which the fibers could be tied concepts of optimizing composite materials together. These advances have have approximately half the weight of metal not. high stiffness. A unique new structure is called IsoTruss®. This well be made from Isotruss structures. and strength could be optimized. It might be asked The light weight and strength of the whether a structure could be built that is Isotruss structures can be easily demon- fully three-dimensional. For example. An additional be learned. structures versus conventional compos- A careful analysis of trusses will show ite structures. The thickness the same (or better) performance versus a is less important in these structures than conventional composite structure. and Applications . Such ity poles and freeway sign supports might a structure now has been developed. diameter beyond an equivalent optimal di. to a country where labor costs are low. but that concept has evolved. However. nylon was locally available. The advantages of using steel included the simple technology for manufacture of the helmets. the U. moderate performance ny- of this type is good. nylon was found Applications to provide only the bare minimum in ballistic Lightweight and effective armor is essen. But that armor needs to everywhere except in Great Britain. These helmets were and strong as these just seem too good to not manufactured by molding with either 100% succeed. at the same time. It also had excellent insulation capabilities in both hot CRITICAL MARKET—ARMOR and cold climates. the products still have to mid and then coating with a phenolic resin be manufactured. armor was almost always made from traditional materials such as metal plates. Other improvements included better head coverage and more space for ventilation. several parts of the world. Another helmet then began to be used in Too little armor and little benefit is gained. that encouraged its use in helmets.S. the future for structures moderate cost. and Applications . the U. Nylon had a number of qualities to be most difficult. these helmets were found to provide only marginal protection against fragments. be designed to meet the perceived threat. Methods. By the early part of the 1980s. At the time. was discontinued tial to saving lives. However. However. Full-size IsoTruss structure. such as mobility. and reasonably good impact pro- tection. Army experimented with fiber-reinforced inserts in the helmets. are sacrificed.S.23: Composites Applications 561 Too much and other important factors. That process has proven and curing. low cost. Products as lightweight lon composite helmet. military had developed the first all-composite. that has resulted in high transportation costs Other countries such as the United and difficulties with supervision. added weight and reduced the air space between the head and the helmet. This develop- Figure 23-3. A good example to illustrate the move from tradi- tional materials to polymer composites is the evolution of the military helmet. During the Vietnam War. These inserts improved bal- listic protection but. (Courtesy Brigham ment resulted in even better ballistic protec- Young University) tion without altering the weight of the helmet. 100% fiber-reinforced helmet. even though the design is nylon fabric or a mixture of nylon and ara- highly optimized. Thin steel was the principal helmet material of WWII and remained in use until the 1980s. protection and. In WWII. These helmets Fundamentals of Composites Manufacturing: Materials. as a result. Kingdom and South Korea decided to use a Nevertheless. developed because the need for armor is not tured by laying up ultra-high-molecular. armored boats. usu. some of the applications will re- In the latter part of the 1980s. tank operators. It was manufac. land-mine containment tubes Law enforcement Police and security-guard vests. Hence. firearm barrels Fundamentals of Composites Manufacturing: Materials. The first to use this by a simple word change—from the word technology was the French army. ment of these helmets. personnel carriers. weighed 2 lb (1 kg). shrapnel. pressure bottles. Most of the modern that the change in perception is underway. and Applications . vehicle interiors. naval armor. to a certain point. riot shields. bomb blanket Other products Safety helmets. special gear for various duties (pilots. or even from fires. radomes. crashes. the helmet now could be against bullets. engineers and design. No attempt is made resin content performed better in ballistic to quantify these markets because they are. composite material applications rely on However. bodyguards. now recognized. Methods. Current position in modern armor such as helmets growth in many of these markets suggests and bullet-proof vests. Table 23-3. Actual and potential markets for armor/protective materials. explosions. bus and taxi-driver shields. Moreover. resistance. In the develop. knives. police helicopters. artillery gunners) Military armor systems Vehicle exteriors. land-mine demolition gear. armored bank trucks.” The protection in weight by about one-half. body bunkers.562 23: Composites Applications were reinforced only with aramid. the resin concentration largely. combat vests. some of tough and strong fiber reinforcements. special forces. riot gear. untapped and still in development. store operators in high-risk areas). ambulances. let-proof vests the only applications. Some other applications for modern armor ers learned that. hunter vests. to exploit these markets. aircraft-vulnerable sites. However. was lowered to approximately 12%. armored personal cars. engine-fragment containment. another quire a change in people’s minds to be fully helmet began to be used. butcher aprons and arm guards. But these are not material was typically a woven prepreg with the only materials nor are helmets and bul- phenolic as the matrix resin. body armor for at-risk people (public figures. the basic concepts and details of materials ally aramid (like Kevlar®) or UHMWPE (like and manufacturing used in composite armor Spectra®). explosive-containment boxes (aircraft cargo). impacts from falling or Composite materials have taken a leading flying objects. Major Market Category Specific Product Examples Military personnel protection Helmets. The basic types in the United States. a major change weight polyethylene (UHMWPE) fibers in a in that perception and a more ready accep- 0o and 90o cross-ply. Reduced “armor” to “protection. lower are listed in Table 23-3. medics. which was then bonded tance can be achieved in some of the cases with a thermoset resin. fuel cells. which are the two most common should be understood. fire protection. 175 ft/sec are reasonably well understood. thus manufacturers ity).23: Composites Applications 563 Performance was run in which rounds of each type were Almost all armor applications begin with fired into the armor. Its literature sets out the procedures this basis alone. Most applications other the test procedures can be legitimately than body armor focus entirely on penetra. penetration from various missiles. 50% of the rounds penetrate. The whether the fabric is woven or cross-plied standard (NIJ Standard 0101. the velocity at which the probability of pen- forded by a particular armor material. impacts against the surface of the armor grain bullets to a maximum velocity of 1. The velocity at which 1. Higher classifications give protection against larger bullets at higher Energy Dissipation velocities. JSP 158. The most (358 m/sec). (that is. The complication is. Armor materials work because they dissipate For instance. increase with fiber or yarn strength (tenac- all control of the tests. and agent) can all make major differences in velocity of the bullet against which protec. course. Moreover. all are related to penetration. The result of the test is an assessment of the protection level af. armor pen- tion unless they are also considering some etration analysis is complicated and simple additional danger such as fire or explosion correlations can be difficult. The number of major dangers: rounds that penetrate the vest is then plot- ted for each velocity. type of matrix. this assessment considers the firing many shots into the vest and noting ability of the material to protect against two the velocity of each round. varied somewhat. important of these is the ability of the armor To establish the classifications and de. is and found from the graph that is made. This capability requires that the Fundamentals of Composites Manufacturing: Materials. Therefore. uct and. the presence of a sizing or coupling Each classification lists the type. of By far. choose the type that will meet that threat. fabric weight.03) establishes unidirectional. The dissipation phenomenon is ft/sec (425 m/sec). This value is obtained by body armor.395 material. V50 tends to shock. size. and Applications . a purchaser of the body Underlying all of the factors discussed pre- armor must evaluate the likely threat and viously is the concept of energy dissipation. called V50. therefore. such as lay-up sequence. in the yarn increases. and the strength of the six formal armor classifications plus a seventh bond between the fiber and the matrix special one. no agency has taken over. material to quickly (nearly immediately) termine the rating of various body-armor spread the impact energy sideways into a materials and configurations. the tendency among tection is the National Institute of Justice consumers is to compare the materials on (NIJ). cations and testing methods of the NIJ. Type II provides multiple-hit the energy of the bullet or other missile that protection against . FMJ 124-grain complicated but some of the mechanisms bullets to a maximum velocity of 1. 2. blunt trauma. For etration is 50%. Great caution should be ex- for testing and analyzing for penetration ercised in making these comparisons since and blunt trauma. the values. that all of these and other factors ing armor performance is to use the classifi. a special test wide area. and the number of layers. Body-armor manufacturers frequently The leading authority that has established report the V50 value for a particular prod- most of the standards regarding armor pro. and 9-mm.357-Magnum. are largely on their own to specify the protec. but will decrease as the number of filaments tion level in these other areas. the most common method of report. Methods. In general. tion is provided. such as mechanical strength or the introduction of aluminum structures (re- stiffness. However. is also being actually reduced. Their work was achieve the best performance. the methods of manufacturing are matrix. including thermosets and ther- boring fibers connected through the fabric moplastics. be absorbed. then additional energy can armor capability alone and in combination. radar. traditional fibers are being investigated for ting or heating. propeller tors must be simultaneously optimized design. steering and flight control mecha- and several compromises must be made to nism. This might be caused by shattering against an outside layer AIRPLANES of the armor. Another recent finding is that in flux. a time of great op- more energy is dissipated when adjacent lay. The addition of secondary materials. the total energy dissipated is such as ceramics and metals. aramid. Wright brothers’ plane. portunity even though the risks are high. The armor market is certainly the structure. and overall design. if Some applications eliminate the matrix alto- the bond between the fibers and the matrix gether. had innova- It is probably obvious that many fac. Therefore. in addition to high These might be treated in special ways or strength. other round of material optimization. it soon enhanced by the development of flight seems certain that optimizing for ballistic control surfaces (like ailerons). quiring new alloys). many aspects of the If the fiber can internally absorb energy total armor market are changing. Moreover. are being investigated as well. The as backing materials. Ceramics and ceramic compos. UHMWPE. the basic shapes of existing pass energy more efficiently from one layer products are changing and new products are to another. and Applications . In addition to the many investigations of sipation—the sliding of the fiber against the materials. is too strong. and manufacturing techniques. thus requiring an- finding is that energy dissipation can be al. Methods. the fibers must have sufficient used in unique lay-up patterns to optimize elongation so they move or give slightly to energy dissipation and cost. What has tradition- balance the need to have a strong matrix-fi. tered by changing the directions of the fibers On top of all the material and process in adjacent layers. materials. Several matrix transfer some of the load to other neigh. tions in the lightweight engine. such as internal split. So. mass-production Fundamentals of Composites Manufacturing: Materials. At this moment. or fiberglass composite designs. ally been done by hand lay-up may now be ber bond to transfer the energy throughout done by resin transfer molding (RTM). bond eliminates another source of energy dis. itself. ers are of a different material (such as aramid next to UHMWPE). Some sequences seem to investigations. New and by some mechanism. This is because the strong investigated.564 23: Composites Applications fibers must be strong enough so they do not Looking into the Future immediately break when impacted. for some. BREAKTHROUGH MARKETS— Yet another factor in energy dissipation is COMMERCIAL AND CORPORATE breaking up of the bullet itself. Aerospace Needs a Breakthrough ites have proven to be especially useful for The history of aerospace has traditionally this purpose. moving the energy laterally in being created. the manufacturers of armor must also being re-examined. properties. weave or through the matrix. especially in combination with been full of exciting innovations in materials. This is. which were protection will force some decrease in other separate from the primary flight surfaces. A recent in weaves and preforms. This the structure with the need for some slippage change may require completely new concepts to give additional energy dissipation. medium-sized airplanes). not currently available for technology. Kingdom. serviced by the current fleet selection. and cargo-car- cies kept pace with the developments in rying capacity (up to 60% more). It will also help made. pressurization study conducted for Boeing Market share is a major focus and. the 787 will ranges to compete in niches not adequately be certified to allow higher pressurization. and Applications . The 787 promises impressive improve- jet engines. aluminum. it would constitute the ac- but the breakthrough advances were not. by consolidation. the 787 is dedicated to the use of ad. fuel carbon fibers and new resins). minum as the preferred materials for parts. The overall design and efficien. computer control (fly by wire). Indeed. the plane will not be “black manufacturing has taken away from that in. Price This means that customers will feel bet- and politics are dominant marketing forces. Methods. complishment of the dream of composites Fundamentals of Composites Manufacturing: Materials. reinforced plastics (FRP). some weight savings serious potential in aircraft manufactur- and other minor advantages were achieved ing.600 composites (including the introduction of km]) for a medium-sized airplane. niques that will work their way into other posites has been mostly “black aluminum”. Therefore. ing saw throughout the 1990s. thus removing some of the will be largely made of composites. Inevitably.85. There was little effort to use the advantages The Spectrum Civilian Aircraft of molding and part unification. speed (up (from bombsights to missiles).500 miles [13.” Designers will consider com- novative spirit. The com- small companies where innovation was most pany is also looking at incorporating smart likely to occur. new weapons efficiency (20% improvement). composite products. develop new composite manufacturing tech- vanced composites. this wide The Boeing 787 Dreamliner focus will improve composites manufactur- More than any commercial plane ever ing throughout the world. The market is now dominated structures into these components to monitor by a few large companies with tremendous their health. Up to now the use of com. including fiberglass that is. As now A strong conservatism in design and conceived. which are Developing the ability to manufacture inherent with composites but lacking with lightweight. ments in range (up to 8. capital investments. ter during flight as confirmed in an actual not necessarily innovation and performance. The number of aerospace plane’s performance goals. perhaps at the Farnborough Air Show in the United because of the erosion in market share Boe. low-cost aircraft represents aluminum. ment toward using composites. Their bureaucracies Because the composite structures are seem reluctant to change much beyond just stronger and stiffer than the previous metal making airplanes with seating capacities and ones used on other airplanes. These materials and manufacturing techniques performance breakthroughs come directly so that the entire aerospace industry was from the new attitude of Boeing’s manage- infused with excitement. The majority of companies has been reduced dramatically the primary structure. the need for a As has been the case with previous Boeing new direction and new innovative spirit has aircraft. they have been used to replace alu. fuselage and wings.23: Composites Applications 565 techniques (remember Rosey the Riveter). an international consortium of part- become critical to its recovery of position. and stealth to Mach 0. This conservatism has been posites as unique materials with properties caused by liability fears and by the nature of that can be of advantage to achieving the the marketplace. ners will actually build the various systems for the final assembly. shown in Figure cured structures has to have great appeal to Figure 23-4. Seven basic sections are bolted together and then prototypes of the Beech Starship were made the other components such as the engines. some important new in. integrally stiffened. co- aircraft. largely political and conventional methods. This aircraft. or Dreamliner. and interior lighter. Methods. However. by filament winding. bureaucratic problems forced the company to use more traditional manufacturing and What it All Means for Aerospace design methods. development. These prototypes were electronics. and low-cost. Spectrum® all carbon fiber composite aircraft.566 23: Composites Applications manufacturing. The concept of that has been used to create the Spectrum large. The weight is about (flying characteristics) than traditionally 70% of a comparable corporate jet made by made versions. Boeing is inclusion of integral stiffeners is an impor. There are three areas of opportunity Even though the Starship was a great emerging for innovative composite structure technical success. (Courtesy Rocky Mountain Composites) Fundamentals of Composites Manufacturing: Materials. and had better handling materials are added. on the lookout for new and innovative ways tant step in a new manufacturing process of manufacturing composites. The is the Boeing 787. the stagnant commercial jet-liner market principally involving integral stiffening. and Applications . These two realized but not fully commercialized. stronger. tubing for fuel. the concept 23-4. is made of a single shell for the fuselage of a low-cost. The most glaring break in novations have been made since its time. single-unit aircraft body was and a single piece for the wings. In the 1980s. but that seems the advancements being made for the new. and you suspect that the enemy soldiers are nated by an aging fleet that begs for re. inte- development. In fact. piston-driven aircraft. cost. Sim- The landscape of composites manufac. They are probably firing from efficient airplanes. like World War II. in the past. for example. up to see because of the heavy fire. Smarter means eration aircraft emerging to bring private the elimination of costs and using materi- jet convenience to corporate and personal als suited to the application without being travel. but you do not out-of-the-way airports seems to merge know their location. Computer. grally stiffened aircraft structures. General Aviation’s predicted total rejuvenation because of much lower growth numbers are impressive. In addition. the windows but you cannot put your head age navigational systems will make it pos. unless you move forward. fuselages. you are under heavy rifle fire The small aircraft market is still domi. manufacturing processes. 2-4 place. piston-driven aircraft. convenience of air taxi services using small heard the sounds of tanks.and space. materials and pro. The a block or two away. pler means fewer parts and streamlined turing is dotted with a myriad of new-gen. a battle. technology. cessing companies cannot ignore the needs of and wings. Right now.23: Composites Applications 567 any airframe company that wants to take the reported. This opens the door materials and processes that can be easily to breakthrough experiments and product adapted to a number of large. currently in various stages of development. Methods. that major automotive bold steps to develop. on the ground behind a wall. It may place will not be able to resist the temptation breathe new life into the industry reminis- to adopt the new high-performance airplanes cent of the 1930s and 1940s. qualify. costs and improved performance. The market. they could experience a changed on 9-11. turing must be simpler and smarter. co-cured. AirBus to optimize its composites structures The next 100 years of aircraft manufac- for cost savings and increased performance. lighter. It will take innovative companies to directly FUTURE-TODAY MARKETS— address the cost of composite structures and advance the technology to the next step of UNMANNED VEHICLES acceptance. soldiers in your of the private. You know that during previous generation airliners will enhance the viability wars. You have. You also sible for these airplanes to be flown with a hear machine-gun fire but that seems to be minimum of training and instruction. and certify new companies are spending heavily to document materials and processes. It is situation would probably ask a companion Fundamentals of Composites Manufacturing: Materials. The Scenario Another area of opportunity lies in the Imagine you are a soldier in the midst of small. Lightweight. Your squad has advanced into an The adoption of composite materials and enemy town with the object of capturing a processes will truly bring this generation of large cache of weapons believed to be in workhorse aircraft into the age of modern a building two blocks ahead. however. If Boeing and other aerospace/aircraft frustration at airports because of delays and companies take advantage of the new small- inconvenience experienced since the world aircraft technology. and more arms cache. hiding in the houses between you and the placement with stronger. You seem to be effective structures have every right to be safe for the moment but obviously will not included in basic airplanes as they do in the be successful in capturing the arms cache so-called high-performance genre. Affordable business jets ease the exotic. foolhardy. Right now you are lying well with small aircraft. and Applications . 568 23: Composites Applications to cover them and they would jump up and With the use of the plane to scan around run forward. (At least that is what the mov- corners and over the buildings ahead, and ies said they did. They seemed to either get the robot to fire beyond your immediate killed or win a Medal of Honor.) Right now, horizon of vision, you successfully capture however, you are not sure if that is the wisest the arms cache. course of action. Is the preceding scenario taken from Just at this moment of indecision and some science fiction movie? It could be! But peril, you remember that your company it is much closer to reality than you might has been given a new tool. It seemed a bit imagine. The world of unmanned aerial ve- “James Bond-ish” at the time, but now it hicles (UAVs) and unmanned ground vehicles seems worth a try. You reach in your pocket (UGVs) is not just futuristic; it is already and take out a small box containing a min- here in surprisingly sophisticated applica- iature, hand-sized airplane. It looks like tions. And, of course, the potential is truly something that you might have flown as a astounding! science project in high school. You flip the on switch, the propeller starts and you let it go up Unmanned Air Vehicles into the air above your head. You now look at UAVs are any aircraft that operate with- the carrying box and see that it has a screen out an on-board pilot and typically fly with on which the street in front of you is pictured some level of autonomy. Historically, UAVs from the viewpoint of the little airplane. have their roots in military applications and The box also has controls that allow you to current applications are still mostly military. move the plane around; just like playing a Civil activities are limited but have great computer game. You send the plane forward potential. The U.S. military’s involvement and see where the enemy soldiers are hiding. with UAVs started in the early 1900s, and You fly the plane to the next block and see they have had active roles in all major con- that a machine gun guards the street over flicts since the Vietnam War. Recent combat there, thus telling you that trying to move in Kosovo, Afghanistan, and Iraq has proven up that street is foolhardy. You then try the that modern UAVs are vitally important, street on the other side and see a tank wait- especially in urban environments. ing to block any advance there. Hence, you Current UAVs range in size from full-scale must move forward, but with the knowledge aircraft down to systems that fit in the palm of exactly where the enemy lies, that seems of your hand (see Figure 23-5). These aircraft less formidable. are loosely classified into three categories You use a radio to call an unmanned golf- based on size: full scale (wingspans in excess cart-sized robot vehicle that is carrying a of 50 ft [15 m]), tactical (wingspans around few small tactical missiles. Upon your com- 25 ft [8 m]), and mini/micro (wingspans be- mand, the robot moves, fully guiding itself low 10 ft [3 m]). around obstacles, into position about 100 ft Full-scale “endurance” UAVs, such as (30 m) behind you. Then, you maneuver the the propeller-driven Predator and the jet- unmanned plane directly over the position of powered Global Hawk, have nearly become the nearest enemy soldiers hiding in front household names in recent years. The of you. Taking the global positioning system Predator has been used extensively in (GPS) coordinates, you then relay them to the U.S. War Against Terror (Afghanistan the control unit of the robot and instruct it and Iraq), primarily for reconnaissance but to fire a missile. The enemy position is de- also for limited attack missions. One crucial stroyed, thus allowing you to advance safely. advantage of these aircraft is their ability to Fundamentals of Composites Manufacturing: Materials, Methods, and Applications 23: Composites Applications 569 missiles. It has been used for several strikes initiated by the military and the CIA. In De- cember 2002, for the first time in history, a manned and an unmanned aircraft engaged in combat when an Iraqi MiG-25 shot down a Predator after the Predator fired at it. Global Hawk has a wingspan of over 130 ft (40 m) and is capable of carrying a 3,000-lb (1,361 kg) payload. The sensor suite contains synthetic aperture radar, an electro-optical camera, and an infrared camera. Continu- ous flight time is 36 hours. The system is designed to perform most routine flight operations autonomously, thus allowing Figure 23-5. Unmanned aircraft made, in part, with car- the operators to concentrate on mission bon fiber composites. (Courtesy American Composites execution while simply monitoring the Manufacturers Association [ACMA]) aircraft’s performance. Communication with the ground crew can occur through satellite persistently collect data. Both the Predator links, meaning the system can be remotely and the Global Hawk can stay airborne for operated from anywhere in the world. The a day or more. The importance of persis- first developmental Global Hawk flew in tence was seen during the initial phases of 1998. Due to the terrorist attacks of 9-11, the current Iraq conflict. The single Global several of these developmental systems were Hawk that was deployed flew only 3% of the rushed into service in Afghanistan and Iraq. aircraft imaging-collection sorties, yet col- In total, Global Hawk flew only 15 missions lected data on 55% of all air-defense-related, during Operation Iraqi Freedom, yet pro- time-sensitive targets. vided over 4,800 images in near real time. Predator is a lightweight, high-endurance The system located at least 13 surface-to-air craft with a wingspan of just under 50 ft (15 missile batteries, 50 SAM launchers, 300 m) and a payload of 450 lb (204 kg) for up to canisters, and 70 missile transporters; it also 40 hours. It provides surveillance imagery imaged 300 tanks. During these missions, the from synthetic aperture radar, video cam- UAV and its sensors were operated remotely eras, and infrared cameras, which can be from Beale Air Force Base in California, thus sent in real-time not only to the operational reducing the logistical requirements in the commander but also directly to the front-line field by more than 50%. soldier. These UAVs have been operational The next phase for this class of UAV is since 1995, and in total have flown over an armed system that can perform surveil- 100,000 hours. The UAV ground-control lance, suppression of enemy air defenses, station is built into a single 30-ft (9 m) and precision strike missions, all without a trailer and houses a pilot and three sensor human in the loop. operators. Although the ground-control sta- Tactical UAVs include Pioneer and tion must be located at the place of take-off Shadow, with wingspans of approximately and landing, the UAV can be monitored and 15 ft (5 m). Pioneer gained fame during the controlled from anywhere in the world via first Iraqi conflict. After enemy troops real- satellite links. An armed version of Preda- ized that the presence of this UAV meant tor exists, which carries AGM-114 Hellfire imminent 2,000-lb (907-kg) naval gunfire Fundamentals of Composites Manufacturing: Materials, Methods, and Applications 570 23: Composites Applications rounds would soon land on their position, every foot soldier. One or more air vehicles they surrendered to the unmanned aircraft. would be part of a soldier’s normal gear. A Flight times are on the order of 5–6 hours, wrist-mounted control station and video and payload capacities are around 70 lb (32 screen, not much larger than a common kg). Payloads typically consist of a gimbaled wristwatch, would be worn. These MAVs electro-optical and infrared camera. Line- would perform under supervised autonomy, of-sight data links transmitted video to the where the user would provide only high-level ground user in real time. The all-composites commands such as takeoff/land, waypoint Shadow UAV has been extensively used by path following, loiter, etc. For combat in the U.S. Army in the Afghanistan and Iraq urban or forested environments, the soldier conflicts. The fleet logged over 75,000 flight could have his/her own personal eye-in-the- hours as of early 2006. Brigade-level UAVs, sky automatically loitering over the current they provide support to the ground-maneu- position and providing real-time video of ver commanders. Tactical UAVs have the the tops of nearby buildings or the next advantage of providing battlefield aware- clearing. For this to occur, the airframe and ness at a cost approximately 1/100th that of ground station must obviously become even a manned platform, and with significantly smaller. BlackWidow is probably the most reduced risk to human life. well-known, micro-sized vehicle, having a The mini/micro air vehicle (MAV) class wingspan of approximately 6 in. (15 cm). is an area of intense growth and interest. Other aircraft, such as the one developed at Loosely, “mini” refers to crafts with wing- the University of Florida, are even smaller. spans from approximately 10 ft (3 m) down Aircraft of this size have demonstrated the to 6 in. (15 cm), while “micro” refers to wing- ability to locate and image in real time a 3 ft spans below 6 in. (15 cm). These aircraft are (1 m) target from 1,640 ft (500 m) away. designed to fill the need of short-range, lim- UAV materials and construction are as ited-duration, “over the hill” reconnaissance, varied as the aerodynamic designs. It is ap- providing situational awareness. Likely the parent, however, that composites will con- most widely employed aircraft of this class is tinue to be the material of choice for UAVs the Pointer, with a wingspan of approximately of all sizes. In addition to being lightweight, 8 ft (2 m) and a flight time of 90 minutes. This composites offer quick build time, fewer fas- UAV carries an electro-optical or infrared teners, and resistance to corrosion (from salt camera and a short-range (approximately 6 water, for instance). UAVs of the mini class miles [10 km]) line-of-site communications are commonly constructed of metal and/or package. The Pointer system, including plastic skeletons with Kevlar skins. Larger ground station, fits in several hand-carried UAVs, on the other hand, employ primar- cases and can be transported and operated ily fiberglass and carbon fiber composite by two users. More recent systems, such as materials. Raven and DragonEye, are similar in opera- The future of the U.S. military market ap- tion and capability, but with wingspans on pears solid. UAV capabilities have expanded the order of 4 ft (1 m). The requirements for from a single “eye-in-the-sky” in the early this class of aircraft include a wide range 1990s to persistent intelligence surveillance of operational environments, simple user and reconnaissance today. The excitement operation, all-weather operation, automatic in the military market is not unique to the collision avoidance, and low cost. U.S. According to the American Society of An eventual military goal for MAVs is to Aeronautics and Astronautics. As of 2005, provide personal situational awareness for over 500 UAV platforms were on record and Fundamentals of Composites Manufacturing: Materials, Methods, and Applications 23: Composites Applications 571 over half of the nations in the world had sensors could look for survivors of disasters some type of UAV in their arsenals. Fund- like avalanches, floods, and earthquakes in ing by the Department of Defense for UAV areas too remote or hazardous for manned development and procurement has quite surveillance. Super-sensitive chemical sen- literally exploded in the past 5 years, from sors could detect the existence and nature of an annual budget of $363 million in 2001 to terrorist bombs and possibly even effect the an expected $3.5 billion in fiscal year 2009. removal of such devices. The bulk of this funding has been earmarked Current technology allows for an autopi- for Predator, Global Hawk, and Joint Un- loted toy airplane with a wingspan of 12 in. manned Combat Air Systems (J-UCAS), (30 cm) and an on-board video camera to formerly known as Unmanned Combat Air enter the market below the $100 price point. Vehicles (UCAVs). Smaller systems stand to (So, an unskilled 10-year-old boy could send benefit as well from this significant increase his toy plane down the street to “survey the in spending. wildlife” at the neighbor’s backyard pool!) Potential commercial applications are The primary hold-up for release to the civil- widely varying, including border patrol, po- ian market is unresolved issues of operating lice surveillance, search and rescue, forest unmanned vehicles in commercial airspace. fire and wildlife monitoring, detection of Several concerns have delayed the process, fish schools, large-facility security, mail and including autonomous collision avoidance and package delivery, and even recreation. Aerial the possibility of malicious overriding of the surveillance currently performed by manned autopilot system. The urgency of appropri- helicopters and aircraft represents an ap- ate regulations is well recognized, however. plication where unmanned aerial vehicles In 2004, the Defense Science Board Task could have a large impact. For example, law Force on UAVs issued a report calling on all enforcement in U.S. cities with over 250,000 U.S. government agencies to work toward people cumulatively uses nearly 500,000 making UAVs an official part of military and flight hours each year of piloted aerial sur- civil aviation. “The DOD has an urgent need veillance. At a cost of $500/hr, this represents to allow UAVs unencumbered access to the $244 million in spending each year. Statistics National Airspace System (NAS) outside of are similar for traffic/news applications. restricted areas . . . here in the Unites States Endurance UAVs equipped with electro- and around the world.” As soon as these optical and infrared cameras could autono- regulations are established, the commercial mously fly along the border and detect illegal UAV market is destined to explode. crossings at remote locations. Large indus- The “brain” of the UAV is the autopilot, trial facilities such as oil refineries might which is becoming ever-more sophisticated use UAVs to perform aerial inspections of and capable, varying as widely as the appli- the sites, including visual, audio, or chemical cations for computers themselves (especially monitoring (when mounted with a suitable artificial intelligence applications). As UAV chemical sensor system). Such chemical sys- systems push to smaller platforms, the auto- tems open the possibilities of using UAVs to pilots themselves are also becoming smaller. enter highly hazardous areas such as dam- aged nuclear power plants, chemical leak Unmanned Ground Vehicles zones, war areas, and other places where Imagine the following situation: You are the environment must be monitored before driving on the highway and pass a moving actual human entry can be made. It is even vehicle that has no human driver. You are possible that UAVs with infrared or other shocked and move a lane away just so that Fundamentals of Composites Manufacturing: Materials, Methods, and Applications 572 23: Composites Applications you are safe from this strange vehicle. You run from Barstow, California to Primm, are, however, captivated by the concept of Nevada. The winner would receive $1 mil- a driverless car and you want to observe it. lion. However, all the vehicles foundered in You therefore slow the speed of your car the desert. No vehicle traveled more than 8 to match the other vehicle. After cruising miles (13 km). together for some time, you discover that Undaunted, DARPA sponsored another the unmanned vehicle performs precisely race—the Grand Challenge 2005. More than as would a vehicle driven by a human driver. 190 teams entered the competition, with 23 Moreover, you discover that the unmanned competing in the final event. Five teams vehicle is not being guided by a remote op- finished the 132-mile (212-km) course over erator (there are no radio transmissions to desert terrain. All of the vehicles were totally or from the vehicle). The vehicle is, truly, autonomous; that is, no radio guidance was self-driven. allowed. The vehicles had to follow an un- Is the preceding scenario frightening to known course without human assistance. you? Does it seem impossible? Hardly . . . a Due to this incredible advancement in similar situation actually occurred in May technology and vehicle capability, DARPA 2006 as engineers tested—in remotely announced in May 2006 that it would hold piloted mode—unmanned vehicles in the the Urban Challenge 2007. This event will western Utah desert. feature autonomous ground vehicles execut- ing simulated military supply missions safely The Grand Challenge and effectively in a mock urban area, such Spurred on in part by the success of un- as the scenario given at the beginning of manned air and underwater systems, the this section. United States Congress, in conjunction with Even as teams from across the United the U.S. Department of Defense (DoD), has States prepare for Urban Challenge 2007, mandated that one-third of all military land numerous military organizations are ask- vehicles be autonomous (unmanned) by 2015, ing for and awarding contracts to compa- and two-thirds by 2025. In response to this nies for their unmanned vehicle solutions. mandate, the Defense Advanced Research Although the military has implemented Projects Agency (DARPA)—the central re- for tactical use a number of unmanned search and development organization for airplanes, relatively few land vehicles are the DoD—created the Grand Challenge as a currently in use, and none of them are com- field test intended to accelerate research and pletely autonomous. development in autonomous ground vehicles. The lack of autonomous ground vehicles is DARPA’s purpose in holding the Grand Chal- due in part to the complications of traveling lenge was to bring together individuals and across the Earth’s surface, which is differ- organizations. Representatives from industry, ent from traveling through the air. Planes the research and development community, fly through a three-dimensional (3D) space government, the armed services, academia, where all obstacles (other aircraft) are iden- students, backyard inventors, and automotive tified. But land vehicles travel on a two-di- enthusiasts gathered in the pursuit of a tech- mensional (2D) plane where obstacles (think nological challenge. The end goal would be to of them as disturbances in the 2D plane) may help save American lives on the battlefield. be unidentified and collision avoidance is es- The first Grand Challenge was held in sential. As noted previously, however, safety 2004. The goal was to conduct a field test of in the air will become an increasing problem 15 autonomous ground vehicles that would as the number of UAVs increases. Fundamentals of Composites Manufacturing: Materials, Methods, and Applications 23: Composites Applications 573 Humans rely primarily on vision to drive a the industry can imagine uses beyond the vehicle, and other senses allow them to travel current horizon. a designated path and respond to obstacles by maneuvering around them. Unmanned CASE STUDY 23-1 vehicles must also have this ability to sense surroundings, travel a specified course, and The Wonder of Flight maneuver around obstacles. Airplanes are special. Few products in the The state of autonomy in unmanned history of the world have been identified so vehicles is in its infancy. Currently, most completely with technological progress as unmanned vehicles are known as remotely has the airplane. That may arise from the piloted vehicles (RPVs). All functions of an innate desire of human beings to fly, perhaps RPV are controlled by a human operator as a demonstration of our ability to conquer including propulsion and collision avoidance. all obstacles that nature might impose. Or, it Sometimes this is also referred to as tele- might come from our marvel at the apparent presence. RGVs are semi-autonomous. They impossibility of a gigantic airplane lifting off have some ability to automatically react to the ground so effortlessly and carrying us observations of their surroundings. RGVs quickly to a distant destination. Most people are still controlled by a remote operator, but are also amazed by the latest innovation in do not require 100% attention. The Mars airplane technology and desire to understand rovers are good examples of RGVs. The fi- how it works, at least a little bit. Those in the nal class discussed here are autonomously composites field identify with airplanes, even guided vehicles (AGVs). They are able to ob- though they work outside the industry. serve their surroundings and react to them In many ways, the development of the air- based upon an “attitude.” AGVs are provided plane has led to some of the greatest human a series of objectives and perform them with achievements as well as some moments of little to no human input. The “attitude” great sadness. The airplane has affected wars gives them the level of aggressiveness that and peace as has no other technology. The they will use to complete the objectives (wait developments of the airplane and its child, at the stop light forever or run it). space travel, were dominant technologies in The levels of autonomy can be thought the 20th century. However, something else of as a linear progression from today with is special about airplanes, which is not quite RPVs as the norm to tomorrow where AGVs so readily apparent. It will become clear as are commonplace. the technologies that have enabled human flight are examined. Conclusion The technology of air and land unmanned Wilbur and Orville Wright vehicles is moving forward at a dynamic, In at least one critical way, the Wright some might say frantic, pace. The military brothers were typical of those who dreamed applications are currently spurring this of flying ever since ancient days. They were amazing growth. Eventually, civilian applica- visionaries and scientists and added yet an- tions will become even larger in volume and other critical element to the development of complexity. In this field, creative energies sustained human flight. That new element have just begun to be applied. The future for was entrepreneurship. Wilbur told his father, unmanned vehicles is exciting but unknown. as the two began their quest, “I believe that The one certain thing with unmanned ve- flight is possible, and while I am taking up hicle technology is that innovators within the investigation for pleasure rather than Fundamentals of Composites Manufacturing: Materials, Methods, and Applications 574 23: Composites Applications profit, I think there is a slight possibility of design for propellers using wind-tunnel achieving fame and fortune from it.” experiments and built them in their bicycle The Wrights were highly innovative, shop. With assistance from their machinist, self-taught engineers whose experimental they designed and built a four-cylinder inter- skills were honed in their bicycle shop. They nal combustion engine, which they mounted followed in the footsteps of the visionary on their newest version plane. They seemed scientists of the 1800s who learned about to have all the pieces separately worked out, flight from using gliders. Wilbur wrote but would they work together? The broth- the Smithsonian Institution in 1899 (then ers were confident and somewhat in awe of headed by another pioneer flight scientist, their good success. Orville wrote, “Isn’t it Samuel Langley) asking for a summary of the astonishing that all these secrets have been information that had already been learned. preserved for so many years just so that we The Wrights made several interesting glid- could discover them!” ers and kites to test their theories of wing The Wright brothers took their new model design and control methods. Almost none to Kitty Hawk where they had become minor of these worked well. Then a breakthrough celebrities to the locals. A few local witnesses occurred. gathered on the sand dunes on December 17, The Wrights had been traveling regularly 1903 to see whether the Wrights would be from their home in Dayton, Ohio, to Kitty successful. That morning, Orville climbed Hawk, North Carolina, because of the strong onto the lower wing of the bi-wing plane and and almost constant wind along the North guided it for 12 seconds over 120 ft (37 m) Carolina shore. On the way back to Ohio, along the shore. A local caught the flight in a they realized that many more experiments photograph that seems to suggest a hesitat- needed to be done but that the prove-out ing feeling of success. That same day, more trips to North Carolina to test each new de- successes came (best: 852 ft [260 m] for 59 velopment would be prohibitively expensive. seconds) and with them the confidence of They conceived of a way to test the models knowing that powered human flight had in their shop in Ohio. They invented the been achieved. They dubbed the airplane wind tunnel. “Flyer I.” Then their entrepreneurial spirit The next breakthrough occurred when kicked in. they realized that they should break the Newspaper reports of the Wright broth- problem of flight down into several ers’ success followed quickly. However, smaller problems. They worked on con- most of these reports were inaccurate and trol, leaving thrust and lift alone. Then, not very credible. The problem was that when they felt that they had a method for the Wrights did not follow up with public control, they would work on one of the other flights. They wanted to make sure that elements. For instance, when investigating the technology and patents were carefully lift, they tied off the control mechanism so worked out before they gave the world a that they could see the effects of lift more look. They moved their work closer to their clearly. They finally had the details of glider home in Dayton and soon (1904) built the flight worked out and successfully built and Flyer II, which became the first plane to fly flew (many times) full-size gliders in 1902. in a circle. In 1905, they built the Flyer III, They seemed to have worked out many of which could stay in the air for over half an the lift and control problems. hour and perform most of the maneuvers The thrust component was then tackled. that would be required of a reliable and The Wright brothers invented the modern controllable commercial airplane. Fundamentals of Composites Manufacturing: Materials, Methods, and Applications 23: Composites Applications 575 Finally, in 1908, the Wrights began a se- given a hero’s welcome in France and the ries of public flights to advertise their Model United States. A bi-plane. They began taking orders and During these golden years, the visionary started producing planes at the rate of four a engineer-entrepreneurs of the United States month. However, just looking at their planes were busy building airplanes and learning was enough to give competitors ideas on how to improve the technology. Companies how to improve them. The Wrights became established during these years included: so involved in various patent lawsuits that Martin Company, Douglas Company, Lock- they failed to keep ahead of the technology. heed Company, Curtiss Aeroplane and Motor Soon, new technologies were developed Company, TWA, North American Aviation, and being flown by others. The Wrights Northrop Aircraft, and Boeing. Most were tried to maintain control over the market, started by one or two people using garages but the advances were happening too fast and other available space (such as behind a and were too different from their patented barbershop, a cleaners and dye shop, a small technologies. The death of Wilbur in 1912 hotel, a church, and an apricot cannery) as from typhoid fever seemed to end the era of their initial manufacturing locations. Each the Wrights. Orville continued on, but his company seemed to be headed by tremen- enthusiasm had waned. dously dedicated individuals who, like the Wrights, had vision, engineering skill, and Military Impetus and Civilian Circus entrepreneurial instincts. These American Airplanes came into warfare use during companies and similar companies in Europe WWI. Their role was first reconnaissance would prove to be vitally important in the and then active engagement in battles. Euro- development of the airplane, especially dur- pean airplane manufacturers seemed to have ing WWII. a lead in providing military planes for WWI. The Fokker was the plane of Germany’s Red WWII and the Modern Era Baron while the Sopwith Camel was the While the Germans clearly understood plane favored by the British. By the end of the importance of air power at the begin- WWI in 1918, airplanes had demonstrated ning of WWII, the allies had strangely lagged (crudely, to be sure) all of the roles that behind in military aircraft development. military airplanes would play in the future, Consequently, the German Luftwaffe was a except troop transport. powerful force left largely unchecked during Civilian uses for the airplane, except for 1939 and early 1940. The biggest problems flying the mail, seemed to focus around encountered by the Luftwaffe seemed to be air shows, air races, and contests. Barn- the weather and its own mistakes. For in- stormers would fly around the country stance, during the evacuation from Dunkirk, entertaining people with acrobatic stunts when both the English and French armies and rides for those who were brave. This were being hurriedly transported from Eu- was a golden age for airplanes, in large part rope just ahead of the German advance, the because they were so unusual and fun. Add- Luftwaffe was grounded by the weather. This ing to their allure was the accomplishment allowed for a relatively uneventful evacua- of Charles Lindbergh in 1927. He flew an tion across the English Channel. War experts American plane from New York to Paris in believe that if the Luftwaffe would have 33 hours, non-stop, and unaccompanied. attacked the transport ships during those In the days of dead-reckoning navigation, days of evacuation, the British and French this was truly a major feat. He rightly was armies would have been so decimated that Fundamentals of Composites Manufacturing: Materials, Methods, and Applications 576 23: Composites Applications they would not have been able to repel a Ger- as an important part of the aerospace indus- man invasion of England. But, the weather try further accelerated this consolidation of saved the troops and the golden oratory of aerospace companies. Winston Churchill dissuaded Hitler from the invasion, which might have been successful The Current State and would have changed the war. Aerospace is now dominated by a few Not too long after those disastrous days very large companies. Innovations are made of the early war, the British aviation indus- incrementally and over long periods of time. try developed the Spitfire—a fighter that For safety, this is probably good. But for wreaked havoc on the German bombers dynamic market development and progress, that were trying to win the Battle of Britain this is likely bad. Entrepreneurs within the without an invasion. Eventually, the Ameri- large aerospace companies find it hard to can aviation industry joined with the British get support for something really different and subjected the Germans to day and night and innovative. bombing. Similarly, air power also proved Even those aerospace engineer-entre- to be pivotal in the Pacific part of the war, preneurs outside the large companies who eventually leading to devastating bombing want to develop a new aerospace technology runs on the Japanese mainland, undoubtedly find that major developments require tre- shortening the war. mendous infusions of capital. There are, of When WWII was over, many engineer- course, small aerospace contracts for these entrepreneurs within the major airplane people. However, these contracts are highly manufacturing companies were given per- restricted and usually suppress rather than mission to explore the possibilities of air- encourage innovation because of the need to craft for civilian applications. Many of these meet rigid specifications. engineers laid the foundation of the vast The large aerospace firms and similar and extremely successful modern aviation firms in other industries need to learn a few industry. Others felt restricted by the size lessons. First, they must find a way to devel- of the major airplane companies. So, they op internal innovations from engineer-entre- began to explore applications on their own, preneurs. This will probably require that the eventually developing the products and tech- big companies give profit possibilities and nology that would be the basis of the fiber- company time to those employees who want glass reinforced plastics industry. Still others to be innovative. Also, the big companies recognized the need for new materials and need to be willing to take risks. That means manufacturing techniques, many of which they must be less focused on their quarterly were developed by engineer-entrepreneurs reports and more on their earnings in 10 in big and small companies. years. It may also mean that lawyers need With the growth of the civilian aircraft to find ways to protect the companies from business and the many people who flew as liability suits. The investors of Wall Street passengers, safety and government regulation must recognize this vision and be willing to became major factors in building airplanes. not only allow it to happen but encourage it. These restrictive factors were best handled When that occurs, the large companies will by ever larger and more complex companies promote management that understands how building ever larger and more complex planes. to make the companies grow through innova- These companies began to acquire the small tion. The recent development of the Boeing entrepreneurs and then to merge together 787 Dreamliner suggests that some of the among themselves. The emergence of space entrepreneurial spirit has returned to the big Fundamentals of Composites Manufacturing: Materials, Methods, and Applications 23: Composites Applications 577 companies. Some of the fighter aircraft also in aerospace, which might require a com- show this innovative spirit. But, these seem plete rethinking of the supply-and-demand to be exceptions rather than the rule. picture. Where then are the visionary engineer- Composite materials are well character- entrepreneurs of today? The true visionary ized and are being refined constantly. New engineer-entrepreneurs are in small busi- developments seem to happen daily. The nesses. There they can experiment and in- manufacturing methods are also changing novate. They can test new markets, fail, and to provide far greater productivity. The then recover to try again. Like the Wright potential for composites has never been brothers, these modern engineer-entrepre- brighter. neurs learn from the past but also recognize that they need to develop new science and LABORATORY EXPERIMENT 23-1 technology. They are surprisingly agile in the Objective: Become acquainted with a way they approach products and markets. professional organization dealing with com- They are the future of industrial growth. (In posites technologies. fact, over the last 10 years, the net produc- Procedure: tion of new jobs in the United States has been exclusively in the small business sector. 1. Attend a meeting of a professional Big business has produced no new growth organization like the Society for the even though it represents two-thirds of the Advancement of Materials and Process gross national product.) Engineering (SAMPE). The SAMPE Many of the visionary engineer-entrepre- website (SAMPE.org) can be consulted neurs are in FRP and advanced composites, for information about local chapter but probably not in the big companies. They officers who can then be called to get are owners of small shops where products are the date, time, and location of the next manufactured for new and exciting markets. meeting. It may be possible for the en- They may even be making old products but tire class to attend together. using new materials to make them better. 2. If it is not possible to attend a meeting of a professional organization, contact SUMMARY one and request information. The breadth of composites part usage 3. Obtain a copy of the proceedings of a is immense. These products are used in conference of a professional society and markets as diverse as: automobiles, buses, give a summary of one of the papers and trucks; various construction products presented at the conference. such as panels and wrappings for concrete bridge pillars; pipes and tanks that defy cor- QUESTIONS rosion; electrical circuit boards; golf clubs 1. Why is the 787 Dreamliner such an in- and racquets of many types; housings for novative airplane? appliances; medical devices like artificial 2. What are two breakthrough technolo- limbs; and, of course, a multitude of aero- gies of the small aircraft? space products. The growth of composites use continues 3. What are two major motivations for to be strong. Fiberglass-based composites using composites in automobiles? continue to gain market share in all of the 4. What is the chief reason for composites traditional markets. Carbon fiber-based not being adopted to a greater extent in composites are poised for breakthroughs automobiles? Fundamentals of Composites Manufacturing: Materials, Methods, and Applications 578 23: Composites Applications 5. Give three ways to make a composite HQ, ISBN 0-16-067541-3. Washington, DC: tank and discuss the relative advantages National Aeronautics and Space Adminis- and disadvantages of each. Which would tration. be favored in a developing nation? Strong, A. Brent. 2006. Plastics: Materials 6. Describe the mechanism involved in and Processing, 3rd Ed. Upper Saddle River, stopping a bullet in a bullet-proof vest. NJ: Prentice-Hall, Inc. 7. Give two reasons why a composite rifle Tribble, Alan. 1995. The Space Environment, might be preferred in an Olympic shoot- Implications for Spacecraft Design. Princ- ing competition. eton, NJ: Princeton University Press. 8. Recognizing that the Wright brothers were technical and entrepreneurial, Warren, C. David. 2001. “Carbon Fiber in why isn’t their airplane company still Future Vehicles.” SAMPE Journal, Vol. 37, in existence? No. 2, March/April. BIBLIOGRAPHY The Associated Press. 2005. “Critics Scruti- nize Cost of Shuttle.” http://www.usatoday. com/news/nation/2003-02-04-shuttle-crit- ics_x.htm. Curry, Andrew. 2003. “Taking Flight: How the Dropouts from Dayton Changed the World Forever.” U.S. News & World Report, July 21. Epstein, George and Heimerdinger, M. William, eds. 2003. “Celebrating the 100th Anniversary of the Wright Brothers’ First Flight.” SAMPE Tribute to the Centennial of Flight. Los Angeles, CA: Society for the Advancement of Material and Process En- gineering. Gladwell, Malcolm. 2002. The Tipping Point. Boston: Little, Brown and Company, p. 141. Harris, Charles E., Shuart, Mark J., and Gray, Hugh R. 2002. “Emerging Materials for Revolutionary Aerospace Vehicle Struc- tures and Propulsion Systems.” SAMPE Journal, Vol. 38, No. 6, November/December, pp. 33–43. National Aeronautics and Space Admin- istration. 2002. “Celebrating a Century of Flight.” NASA Publication SP-2002-09-511- Fundamentals of Composites Manufacturing: Materials, Methods, and Applications 1: Introduction to Composites v Acknowledgments Special thanks to Rik Heselhurst, Ph.D. publisher of this text, for permission to use at the School of Aerospace, Civil and Me- these materials. chanical Engineering, University College, Special thanks to David Sorensen of the The University of New South Wales who Utah Manufacturing Extension Partnership was the principal author for the chapter on who has developed and taught me much of design and who contributed significantly to the information on the methods of plan- the chapter on repair. Also thanks to Scott ning. I also thank Bill Angstadt of Angstadt Beckwith who made special contributions to Consulting for insights into the new plan- the chapter on resin transfer molding (RTM) ning methods that must be used in today’s and to many figures and tables throughout world. Further thanks to Dixon Abell of the text. Poly Processing Company for his insightful Many thanks also to the American Com- discussions. And thanks to Whitney Lewis posites Manufacturers Association (ACMA). of the Manufacturing Leadership Forum In particular, thanks to Andy Rusnak, the who helped greatly in the production of the editor of Composites Manufacturing maga- figures. zine. I have been a contributing editor to I want to especially thank Rosemary this magazine and have had many pub- Csizmadia of the Society of Manufacturing lished articles. With ACMA’s permission, Engineers who has edited this book. She has substantial portions of these articles have gone far beyond just checking for grammar been used in this text. In that regard, I also and agreement errors. She has also given in- give thanks to the co-authors that assisted sightful help in content and organization. in writing many of the ACMA articles. Those co-authors include: Scott Beckwith, Perry Carter, Tom Erekson, John Green, Charles Harrell, Val Hawks, Mike Hoke, David Jensen, Barry Lunt, William McCarvill, Mike Miles, Frédérique Mutel, John Richards, Christopher Rotz, Deryl Snyder, and Troy Takash. Similarly, I am the author of a text en- titled Plastics: Materials and Processing, which is currently in its third edition. As some of the topics in that plastics text and in this present composites text overlap, I have borrowed some concepts and text from that text. My thanks go to Prentice Hall, the Fundamentals of Composites Manufacturing: Materials, Methods, and Applications v 1: Introduction to Composites 579 Glossary A reinforcements) to improve some specific property. ablation The gradual eroding of a mate- adduct A material added to a normal mix- rial, which is often the result of slow burning ture to alter the reactions or products of its combined with abrasion from rapidly flowing reactive components. The resultant material hot gases over the surface of the ablative may be called the adduct, which is short for material. adduct product. accelerators Chemicals that react with organic peroxides to create free radicals. adherend The material that is to be bond- They are often used to achieve room-temper- ed when an adhesive is used as the bonding ature curing. Cobalt compounds are the most agent. common type. (Also called promoters.) adipic acid A non-aromatic diacid that acid number A measure of the amount imparts toughness and weatherability to of residual diacid monomer in a polyester polyester thermosets. polymerization reaction. Residual diacid is advanced composites A group of com- generally detrimental to polymer properties posite materials using either thermoset and and so maximum values for the acid number thermoplastic resins. They are generally are often set in the polymerization process. characterized by the use of reinforcements acoustic emissions A non-destructive having higher mechanical properties than method to monitor the structure of a com- fiberglass and resins with higher thermal, posite part by recording acoustic emissions chemical, and mechanical properties than from a sample and then comparing those to unsaturated polyesters or vinyl esters. Also emissions from a known good sample. called high-performance composites. activation energy The tendency or lack aliphatic Polymers that have no aromatic thereof, for a bond to resist being broken by content. a chemical reaction. alkyd An alternate name for unsaturated addition polymerization The method polyester materials. The name derives from of linking monomers to form polymer mol- a contraction of alcohol and acid. ecules, which employs an activation of the monomer, usually with a peroxide free-radi- allylic A type of unsaturated polyester that cal. It occurs in a series of chain-reaction-like contains a particular arrangement of atoms, steps in which other monomers are added to including a carbon-carbon double bond. the growing chain. amorphous region The regions in a poly- additives Materials combined with the mer in which the molecules are not packed basic composite material (resin system and into a crystalline structure. Fundamentals of Composites Manufacturing: Materials, Methods, and Applications 579 This generally improves the me. which are not equally direction and negative bias is generally to oriented in all directions (also called non. aspect ratio The ratio of the length to the broad goods A general name for fabrics diameter of a fiber. filler. to polymers. of a resin when it is partially crosslinked. strands in an over-and-under pattern. to break the bond. ecules become solids. the left. Sometimes excess resin. and Applications . B-staging The process of partially reacting a resin so that it reaches a stable B-stage. blooming A process in which fibers mi- anti-foaming agent An additive that grate through a gel coat and reach the sur- prevents or reduces the tendency of a resin face of a composite part. bond energy The energy required to antioxidant Materials that prevent or completely separate two bonded atoms and. stiffness. a ring with hydrogen molecules attached. aramid fiber A high-performance rein- braids Fabrics made by alternating several forcement that is an aromatic polyamide. bridge molecules The co-reactants. or other planar materials. isotropic). which serve as the links in cross- which a heterocyclic group is bonded to an linked polymers that use addition reactions aromatic group. ging system whose function is to absorb chanical properties of the part. thus preventing the degradation of proper- bond strength The stability of a bond. which impart strength.580 Glossary anisotropic Describes the majority of bias is generally to the right of the machine composite materials. bisphenol-A A monomer that can be used annealing Exposing a part to an elevated to improve the water/chemical resistance. bleeder material Part of a vacuum bag- linking). or free-radicals as the crosslinking method. Positive cure of some resins to allow the condensate Fundamentals of Composites Manufacturing: Materials. the mold slightly and quickly during the pal or machine direction of a fabric. and fiberglass basket weave A weaving pattern that has made by low-intensity mixing. breathing the mold See bumping the tardant characteristics. attraction A secondary bond between B-staged resin A stable intermediate stage molecules occurring especially when the mol. Methods. breather material Part of a vacuum bag- ging system whose function is to allow air aromatic A group of carbons arranged in circulation throughout the assembly. mixture to foam. B bulk molding compound (BMC) A mix- ture of polyester resin. The most common brand of aramid fiber is Kevlar®. It is generally two warp fibers and two weft fibers jointly used in compression molding for applications alternating in a regular over-and-under such as automotive panels and parts. bumping the mold A process of opening bias The direction that is 45° off the princi. therefore. pattern. ties from oxidation. called post-curing. usually expressed in terms of bond energy. flame re. and strength of polyester ther- decomposition temperature) for an extended mosets. period to advance the amount of cure (cross. retard the reaction of a polymer with oxygen. like aromatic heterocycle A molecule in styrene. and other properties mold or burping the mold. temperature (but not near its melting or toughness. a mat structure. which is also carbon. non-carbon atoms are driven out of the ma. it is similar to the charcoal residue when wood burns. caterpillar pulling system A puller type cis isomer The arrangement of atoms in used in pultrusion. Maleic acid part and pull it along. has high strength and stiffness. without actually tardant and chemical-resistance properties. sphere). and Applications . through elimination of hydrogen molecules chlorendic acid A diacid monomer added and atomic rearrangement. burping the mold See breathing the cavities The areas in a mold into which the mold or bumping the mold. This rial made by chopping fiberglass into staple improves the speed and effectiveness of the lengths and directing the fibers onto a belt reaction. This is also the name for a step in composite (made porous by a carbonization the manufacture of carbon fibers during reaction) with new resin so that the pores which the planar carbon rings are formed will be filled and the properties improved. such as phenolic. Methods. enhances chopped strand mat A sheet mate- the reactivity of a chemical reaction. and low in which carbon fibers are surrounded by toughness. resin is introduced to forcefully infiltrate the fibers. carbon matrix composites See carbon- carbon composites. a matrix. it involves two continu. is a cis isomer. being consumed in the reaction. consisting mostly of carbon atoms arranged in a hexagonal planar structure which. caul A pad used in a bagging assembly to clamshell mold Molds that are often intensify the pressure in a particular area of connected on one edge and open simply Fundamentals of Composites Manufacturing: Materials. called a pressure intensifier. chemical vapor deposition A method terial through a high-temperature pyrolysis for impregnating the porous carbon matrix process. which have carbon-carbon composites A composite high melting points. Also called breathing the mold a part within a vacuum bagging system. burst test A method of determining the centrifugal casting A process in which pressure-holding capability of a pressure fibers are placed inside a mold. charge A specific amount of material in- troduced into the mold. and then rotated as the then adding fluid until it bursts. to polyester thermosets to impart flame re- catalyst A material that. peroxide initiators are sometimes where they are sprayed with a binder to form erroneously called catalysts. which two key groups are on the same side of ous synchronized belts that press against the a carbon-carbon double bond. ceramic A material characterized by C ionic bonds formed between metal and non- metal atoms (actually ions). Also called spin casting. char The material formed when some fore. carbonization A step in the manufacture of carbon matrix composites in which the chemical polarity See polarity. Also called carbon matrix composites. It is only rarely used in composites. high stiffness. degrade because the term is interchangeable with graphite of pyrolysis (burning in a low oxygen atmo- fiber. C-glass A type of fiberglass formulated to be especially resistant to attack from chemi- carbon fiber A reinforcement material cals. melt flows and solidifies to make the part.Glossary 581 to escape. there. usually of vessel by filling it (usually with water) and cylindrical shape. Today plastics. Also or burping the mold. in which a small molecule (such as H2O) is sional change that occurs in a sample under created in the reaction and separates from differing thermal conditions. the rest of the products and reactants by colorants Materials that give color to a condensing out of the solution (or. words. This addition turing goods. such as a fiber and a matrix. colorants. across the entire surface of a laminate. This type of bond is characteristic of manufacturing method in which the raw polymeric materials. each one being ture made by swirling continuous fiberglass in a separate phase. because one compression-after-impact test A test end of the coupling agent is chemically in which the sample is impacted and then similar to the fiber and the other end is tested in compression to determine the de. co-curing A process in which parts are compression properties Those charac- cured and bonded during a single heating teristics determined by pressing on the ends cycle. materials. and overhead. structure. Each reaction ecules in crosslinking reactions. Methods. Fundamentals of Composites Manufacturing: Materials. in other composite. of a columnar sample. Styrene is the results in the elimination or condensation of most common co-monomer for unsaturated a small by-product molecule. the clam-shell mold requires only matching mold compresses the material minimal pressure and is used chiefly to de. They can be either a dye or pig. each having two active end with two types of reinforcement fibers. cost of goods sold The cost of manufac- and other minor constituents. co-mingling Mixing fibers of different condensation polymerization The types into a yarn. the small molecule separates as ment. often done with reinforce. ing product is in the form of resin pellets. which employs two differ- thermoplastic resin. material is placed into a mold and then a Normally. but also can be done ent monomers. which includes the costs of is usually done with extruders and the result. materials such as reinforcements. in which the electrons are shared by the compression molding A composites atoms.582 Glossary to allow the part to be put in or taken out. compounder A resin processor that takes co-reactant See co-monomer and cross- neat resin from the manufacturer and adds linking agent. crease in properties that might occur because covalent bond A bond between atoms of fiber and matrix damage. method of linking monomers to form poly- ment fibers and with fibers made of the mer molecules. coefficient of thermal expansion condensation A type of chemical reaction (CTE) A measure of the amount of dimen. droplets). while it is being heated to cure. Also called continuous fibers Those fibers that tra- a co-reactant or crosslinking agent. chemically similar to the matrix. groups that will react with each other over co-monomer A name for the bridging mol. and generally consisting strands onto a belt and then spraying them of fibrous reinforcements being surrounded with a binder to hold them into a mat and held in place by a resinous material. matched-die molding. polyester crosslinking reactions. Also called fine the outer surface of a part. and over again when mixed. verse the entire dimension of a part. composite materials Solid materials continuous strand mat A sheet struc- with at least two components. labor. and Applications . coupling agent A material that im- comprehensive stitching Stitching proves bonding between two materials. Glossary 583 co-weaving Mixing of different fibers in a are somewhat analogous to crystals in metals cloth. crimping The result of the crossover of fibers in a woven. the bridges are the crosslinks. at which a material begins to decompose crosslinking agent The solvent or co-re. resins. This results from breaking the actant that forms bridges between polymer primary bonds of the material. or other textile material. joins polymer bonds together. to the important in ceramic matrix composites. especially polyesters and vinyl esters. can be done with reinforcement fibers or cure time The time to complete the cure with fibers made of the matrix resin. This method is similar to crack pinning. of 9. molecules. dart drop impact test A test for tough- Crimps decrease strength in most reinforce. acid groups (COOH). in grams. surface of the sample and the energy ab- crosslink A bond in thermoset resins that sorbed during the impact is measured. polymer mix. rolls can be mounted so that the fiber can be withdrawn easily. or braided fabric. coat but may also extend into the laminate curing agent A hardener. polymer molecules. they do not cure com- like a reinforcement. The cure of some acts as a barrier to the passing of a crack. and Applications . thus creating thermoset decomposition point The temperature materials. Often used as a mono- crystalline region A zone in a polymer mer in making polyester thermosets. daylight opening The distance between crosslink density The number of cross. of a composite part. usually expressed as a ratio of the ac. the opened molds in a compression molding links. Fundamentals of Composites Manufacturing: Materials. of styrene. to arrest the growth pletely to the surface. or degrade. This can be prevented of a crack through a matrix. like wax. creep The gradual movement of polymer D chains when subjected to modest loads over long periods of time. Methods.000 crowfoot satin weave A weaving pattern meters of fiber. a molecule layer. damping The speed at which vibrations decay. therefore. cracking A series of surface breaks in a curing The process of forming cross- composite part generally present in the gel links. is inhibited by oxygen and the evaporation crack pinning The ability of a material. Debulking also might be actions that create bonds or links between used to consolidate a preform. This is highly by adding a coating material. that will react with an epoxy to form a creel A stand or platform on which fiber crosslink. prepreg materials. tual number to the theoretical maximum. which and ceramics. crack deflection A method of toughen. debulking Removal of air from a stack of crosslinking The series of chemical re. knitted. the in which groups of molecules pack closely diacid is often the component that has together. ness in which a weight is dropped onto the ment fibers. These zones exhibit properties that the unsaturation needed for crosslinking. denier The weight. cured hard Curing of the matrix com- ing a composite in which the reinforcement pletely to the outer surface. knit. in which the warp strands skip over or under diacid An organic compound that has two several weft strands in a random fashion. machine. engineering composites Composite drape The ability of a fabric to hang with. In a prepreg it is its ability to formance metals but do not have the high be shaped. elastic deformation A stress-strain dipropylene glycol A glycol monomer that deformation in which the material returns adds toughness to thermoset polyesters. ejector pins Pins mounted in the com- diglycidyl ether A general name given to pression molding press system. broad goods and then pressed through to egg-crate mold A mold in which the the material. which uses two clamps electron conjugation Electrons spread that alternately grasp and pull and then re. eddy current testing A non-destructive it imparts some improvements in properties test method that can be used on electrically and cost. through ether linkages. The lower edge bleed The flow of resin along the edge of the die is sharp. adds toughness to thermoset polyesters. over several atoms. properties of advanced composites. used in pultrusion. Also see colorants. which results in chemical double composite structure A sandwich stability of the bonds. often used in molding compounds. The drape test A method of assessing the cure fibers are usually short and the resins are state of a prepreg by measuring the amount typically inexpensive. The die is made in the shape of the part to be cut. fiber-reinforced plastics (FRP) materials and Fundamentals of Composites Manufacturing: Materials. and Applications . thus making the cut. The method exam- die cutting A method of cutting textiles ines the surface currents created because of and uncured prepregs in which a steel die the internal structure of the composite. Also dimensional stability of the mold surface called steel-rule blanking. Also linked to the remainder of the molecule called knockout pins. The action of the two clamp. to its original shape when the stress is re- double-clamp system A pulling system lieved. a core material. ties. E-glass is the most widely used type of difunctional Having two reactive glass fiber for composites. monitor the completeness of cure. fiberglass with generally acceptable proper- thus. Because it is the least expensive type of sition temperature of a resin or composite and. as occurs in aromatic lease and retract. which are molecules that contain two glycidyl groups used to eject the part from the mold.584 Glossary diallylphthalate (DAP) and diallyl dye An organic material that imparts color isophthalate (DAIP) Allylic materials to a composite. conductive composites. molecules where there are alternating single ing stations together gives a smooth pull. is improved by supporting the back with a diethylene glycol A glycol monomer that series of interlocking braces. groups. It is placed on the plane of the fibers in a bagging system. materials that compete with many low-per- out creases. (DSC) A method to determine the glass tran. structure consisting of composite laminate elongation The strain to failure. is used as the cutting tool. dicyclopentadiene (DCPD) A chemical that can be used as a monomer along with E diacids and glycols to make polyester resins. Methods. usually face sheets bonded on the top and bottom of expressed as a percentage. The group includes all that it drapes over a standard mandrel. and double bonds. E-glass A type of fiberglass that is es- differential scanning calorimetry pecially useful in electrical applications. under the tensile curve is the equilibrium fiber placement A composites manufactur- toughness. ties because of an intermittent load applied epoxy group A three-member ring con. Also called thermoset engineering composites. using a multi-axis head. Also called a strand or filament. negligibly small in comparison. which moves the unmelted resin ahead in the tive groups. A low epoxy molar mass number barrel. volume of the composite. Methods. F filament A single strand of fiber. during a tensile test. The term emphasizes fer molding (RTM) and other resin infusion the essentially linear nature of the polymer processes. indicates that there are few atoms between fiber A material characterized by a single active groups and. The area tion. This the automatic forming of many more shapes grouping is formed by the reaction of an than could be made with filament winding. organic acid (or diacid) and an alcohol (or fiber surface treatment A step in the fiber glycol). over a long period of time. Also fatigue The decrease in composite proper- called industrial composites.Glossary 585 most short-fiber-reinforced thermosets. These mate- equilibrium toughness The toughness rials are excellent reinforcements as they can determined under equilibrium conditions be strong and stiff in the major axis direc- and. ites. ing method in which continuous fibers are Fundamentals of Composites Manufacturing: Materials. ing method that places fibers onto a mandrel ester A grouping that contains COOC at. Also called an oxirane group. fiber-volume fraction (Vf) The ratio exotherm peak The time it takes to reach of the actual volume of fibers to the total the maximum temperature during cure. in the fiber-forming device (spinneret). the number of long axis (length) and other axes that are crosslinks per unit of weight is high. f ibers An alternate name for ultra. generally so that least expensive of the glycol monomers used bonding with the matrix is improved. generally. an epoxy molecule divided by the number of ac. manufacturing process in which the surface ethylene glycol The most common and of the fiber is modified. which is characteristic of the epoxy repair so that the entry angle is gradual. polymer. which are stretched and then formed fiberglass reinforced plastics (FRP) into fibers. in making polyester thermosets. usually a cured forcement. The process allows oms arranged in a particular pattern. feed zone The portion of the injection epoxy molar mass The molecular weight of molding screw (and the extrusion screw). therefore. is simply bolted or bonded over with advanced or high-performance compos- the damaged area. tion perpendicular to the plane of the fibers filament winding A composites process- in a bagging system. Usu- ally filaments are the output of a single hole face bleed The flow of the resin in a direc. Generally made from unsaturated polyester external doubler A repair system in and vinyl ester resins with fiberglass rein- which the repair material. taining two carbon molecules and an oxygen feathering Extending the edges of a scarf molecule. It is located under the feed hopper. Also called the extended chain polyethylene (ECPE) fiber-volume ratio. chains. and Applications . the material should be contrasted laminate. fiber wash The inadvertent movement of high-molecular-weight polyethylene fibers caused by resin injection in resin trans- (UHMWPE) fibers. verse fibers. migration of small portions of polymers on flexible die forming A process in which a solvent-soaked paper. and Applications . curing of the repair material. thermal transition that occurs in solid poly- aged material). to impart some meet. Above the transition. species. acid used in making unsaturated polyesters. This type of repair requires meric materials. which is used in design. essentially the G same as a sizing. rather. tion mold. one or more dies in a matched die set is made gel time The time to reach gelation or the of a flexible (rubber-like) material for mold.586 Glossary coated with a resin and wrapped around a often are made by the decomposition of a mandrel and then cured. gel coat The outer layer of a composite flash Excess material that leaks out of a material. bent. FRP See fiber reinforced plastics. or trans. Methods. with increased temperature. The test sample is supported between geodesic path The path on a surface that two posts and then pressed on the upper side allows fibers to be placed under tension and mid-way between the supports. lidification. function of the part in actual use. It serves as a protective coating. flow forming A method in matched-die glass A ceramic material in which the molding of thermoplastic composites in atoms (or ions) do not form crystal struc- which the fibers are allowed to slide. the condition when crosslink- flexural properties The properties of a ing begins to dominate the nature of the material determined when the material is thermoset resin. ing the composite. exist in a rigid disordered flush-type repair A repair method in network. finish A coating placed on a fiber to im- prove the bonding between the fiber and the matrix. It is a trans isomer. bers interwoven above and below the warp fumaric acid A common unsaturated di- fibers. occasionally. These materials are useful quite pliable or leathery whereas below it in starting various chemical reactions and the material is rigid. filler Solid materials ground to fine pow. today. usually characterized by an un. peroxide molecule. these are the fi. the requirements are based on the other beneficial property. first-ply failure The initial failure condi. which the repair materials are placed into glass transition temperature (Tg) A the damaged area (after removal of the dam. tures but. which marks the onset. functional specification A document ders and added to the resin mix to reduce containing the requirements a part must overall cost and. gate The entry to the cavity in an injec- tion of a composite. fill In a woven fabric. the material can be bonded electron. A finish is. gel point. Also called gelation or gel point The onset of so- hydroforming. woof. ing of thermoplastic composites. mold. gel permeation chromatography An flash-type mold closure The type of analytical tool that assists in determining mold closure system in compression molding relative molecular weight by observing the that allows flashing. remain in place without slippage. Also called the weft. Fundamentals of Composites Manufacturing: Materials. of coordinated free-radical A highly reactive chemical multi-atom movements within the polymer. A curing agent for epoxy molecules. ring. made from carbon fibers. the fiber to above 99% carbon. impact toughness The toughness (energy like cross-section. requires application of heat to effect a cure. often an epoxy. such as the imide monomer in making polyester thermosets. it is attached to other organic groups ing at angles other than 90° to the axis of through the additional carbon atom. Methods. Also called determined by a specific test. I harness weave A satin weave in which impact strength See impact tough- the skips are long. usu. transition molding. it is often used as a than one type of atom. bromine (Br). onto the mandrel in filament winding at a ally. thermoplastic composites. therefore. thus converting the same type to extend the polymer chain. 90° angle to the axis of the mandrel. planar structure which. Also called flex- ible-die forming. It is large part is formed in sections. hat stiffener A stiffener that has a hat. which are often added to polymers to flexible (rubber-like) material for molding of improve fire-retardant properties. reinforcement that has not been cured. is introduced into the porous matrix after heat distortion temperature (HDT) The the part has been pyrolyzed. hoop windings The pattern of fibers laid green preform A mixture of resin and. maximum temperature that a plastic or incremental forming A method of form- composite material can tolerate without ing thermoplastic composites in which a distorting in a mechanical application. glycol An organic compound that has two heterocyclic A ring group having more alcohol groups (OH). (HTV) A type of resin. but today the term hexa A curing agent used with novolac is interchangeable with carbon fiber. hybrid reinforcements Schemes that H combine two or more different fiber types. homopolymerization The reaction of a ized fibers are further heated to drive off the polymer with itself or with another molecule of nitrogen and hydrogen. which contains both carbon and nitro- graphite fiber Originally a reinforcement gen atoms. It is phenolics. the mandrel. and iodine more dies in a matched-die set is made of a (I). Fundamentals of Composites Manufacturing: Materials. impregnation The step in the making of heat capacity The measure of a material’s carbon matrix composites in which new resin tendency to absorb heat. chlorine (Cl). Also hazardous air pollutant (HAP) Materi. which graphitization A step in the manufac. and Applications . called impact strength. halogens The chemical atoms fluorine hydroforming A process in which one or (F). als that emit potentially dangerous vapors.Glossary 587 glycidyl group An organic group con. helical windings The pattern of fibers taining the epoxy ring and another carbon laid onto the mandrel during filament wind- atom. has high high-temperature vulcanization strength and stiffness. ture of carbon fibers in which the carbon. hardener A molecule that will react with an epoxy to form a crosslink. ness. a reinforcement material consisting mostly high-performance composites See ad- of carbon atoms arranged in a hexagonal vanced composites. absorbed) when a material is impacted. which acts as a reinforcement. the elements NCO are double-bonded. the fiber-coupling agent interaction. knit line The area in an injection-molded interlaminar cracking Matrix cracks part where flows from two or more cavity between two plies. It is important to have Interphase Theory A view of the interac. manner. posites in which the reinforcement is placed Fundamentals of Composites Manufacturing: Materials. and Applications . ion A positively or negatively charged latent A property that is hidden under atom. in which the coupling agent forms a three. formability. a hardener ionic bond A bond between positively and that will not react or reacts very slowly at negatively charged ions. It imparts superior toughness and in-situ reaction sintering A process for water/chemical resistance. requires certain quality records to be lay-up A system of manufacturing com- maintained. monomers to make unsaturated polyester mon materials of this type. inhibitor A chemical that absorbs or isogrid A pattern of stiffeners wherein otherwise deactivates free-radicals and thus they are arranged as equilateral triangles. The same type of network would also apply to knockout pins See ejector pins. J intelligent structure A structure with sensors that can learn and adapt rather J-stiffener A stiffener in which the cross- than simply respond in a preprogrammed section is shaped like the letter J. entry points meet.588 Glossary industrial composites See engineering isocyanate A combination of atoms in which composites. intralaminar cracking Matrix cracks L within a single ply. making ceramic matrix composites in which isotropic When the structure of a material two components in the ceramic material react is the same in all directions. sional planar surface. overall efficiency. knitted fabric A material in which the dimensional network into which the resin traditional warp and weft fibers are looped molecules penetrate and thus form a phase to create a fabric with high drape and con- between the coupling agent and the matrix. extends the storage life of polyester resins. if there is a coupling agent pres. The bonding is along a two-dimen. als for a lay-up before the actual molding ent. it is a bond typical room temperature and then reacts quickly in ceramic materials. Interface Theory A view of the interac. resins. isophthalic acid (iso) A saturated. of the fiber and matrix with the coupling operation to simplify molding and improve agent. certain conditions. Also called the weld line. aromatic diacid often included in the mix of like chemical reaction. at elevated temperatures is said to be a ISO 9000 A certification program that latent hardener. initiator A chemical that starts a chain. peroxides are com. Methods. K tions of fiber and matrix that involves the actual touching (bonding) of the fiber and kitting Cutting and assembling materi- matrix or. good interpenetration of material across the tions of fiber and matrix with a coupling agent knit line. during the sintering step and create a second phase. For example. of metals. a solid turns into a liquid. Methods. single type of metal atom or from mixtures this is the machine direction. lattice by a sea of electrons. molding (and extrusion) screw that has a Thus. ergy absorbed when microcracks are created maleic acid A common unsaturated diacid at the point of the main crack. in which the reinforcement has melting zone That portion of the injection a higher strain to failure than the matrix. light resin transfer molding (RTM) A matrix The continuous phase of a com- resin infusion process in which the mold is posite material that surrounds and binds made of a lightweight composite. molding.Glossary 589 into the mold and then the resin is added and master model The shaped material from worked into the fibers to cause wet-out. It operator who is applying a gel coat to moni- is easily converted into maleic and fumaric tor the thickness of the gel coat. leno weave A fabric in which two warp matched-die molding See compression fibers twist around a fill fiber. which is 0° to the axis of the point. material that has a relatively high melting ment winding. therefore creating a smooth. termining the fiber-matrix bond strength. maleic anhydride A common monomer mil gage A small device that allows the used in making unsaturated polyesters. a thermoplastic. tion molding (and extrusion) screw that has shallow flights so that the shear forces are high on the resin. The resultant Fundamentals of Composites Manufacturing: Materials. it is the same as the warp growth of a main crack is arrested by the en- direction. liquid molding processes A general melt-processible resin A resin that can term occasionally used to refer to all resin be processed by melting. defect-free metering zone That portion of an injec- molded surface. infusion processes. especially useful in ceramic matrix as the freezing point for most materials. composites. The metal atoms (ions) are held longitudinal windings The pattern of together by metallic bonds. microcracks A method in which the In woven fabrics. It is surrounded with ment. rollers) to reduce their length. This is the same page. resulting in a fibers laid down on the mandrel during fila. used in making unsaturated polyesters. It is micro-indentation test A method for de- a cis isomer. milled f ibers Fibers that have been mandrel A core onto which the composite chopped and then milled (passed between material is placed and then cured. high ductility. crack stops growing. and high strength. sate for the natural shrinkage of polyesters. together fiber reinforcements. metal(lic) bond The type of bonding pres- low-profile or low-shrink system A ent when positive (metal) ions are held in a method of using certain fillers to compen. changing flight depth. pump the resin out of the machine. metal A material formed from either a longitudinal direction In woven fabrics. the energy of the crack’s propagation heating coils so that the resin will be melted is transferred to the reinforcement and the in this area. acids to form diacids. tion on a machine in which the product runs. which a mold is made. melting point The temperature at which load transfer A method of crack stop. mandrel. and Applications . This zone ensures that all M the resin is melted and creates pressure to machine direction The principal direc. when a crack encounters the reinforce. that has excellent styrene compatibility. the number of monomer units that with short chains that will later be polymer- have been joined together. It is novolac A B-staged phenolic made by the referred to as the general-purpose polyester reaction of an excess of phenol in an acid thermoset resin. thermosetting phenolic. Usually the nucleophilic atom (random planar orientations). Fundamentals of Composites Manufacturing: Materials. Ortho is a low-cost monomer the testing. thus minimizing the orthogonal structure A pattern of stiff- amount of wasted material. in other oligomer A low-molecular-weight polymer words. modulus The slope of the stress-strain O curve. N openness A relative measure of the space between fibers in a fabric. als having fibers directed in all directions tive charge. and Applications . test method to examine the structure of a nesting Arranging broad goods (textiles stressed composite by using photography and prepregs) so that the various shapes created using lasers. which can for the carbon-carbon double bond group be later molded. eners in which the stiffeners intersect at net shape Making a pre-molding and resin right angles. A two-step resin. These are will have a negative or slightly negative useful in reinforcing pastes and in other charge. environment. adds weathering and chemical/water resis- optical holography A non-destructive tance to thermoset polyesters. fit closely together. orthophthalic anhydride A monomer ing thermoplastic requires the addition of a that converts to ortho under polymerization curing agent (typically hexa) to form a full conditions.590 Glossary materials are usually whiskers. the stiffness of a material. molding compound A combination of olefinic unsaturation Another name fibers. cure from the B-stage with heating. operational decisions Those decisions that have to be made immediately for the neopentyl glycol A glycol monomer that continued operation of the company. length of the polymer chain or. the result. the finished product’s shape after molding. monofilament A single filament. aromatic diacid often included in the mix of nondestructive tests (NDT) Tests that monomers used to make unsaturated poly- do not destroy the sample in the process of ester resins. and filler premixed. neat resin A resin that contains no rein- forcement or filler. term emphasizes the solitary nature of one-step resin A resole phenolic that will filaments. This Also called pre-polymer. orthotropic Describes composite materi- nucleophile An atom that seeks a posi. ized into higher-molecular-weight materials. resin. Methods. addition reinforcement package that is near orthophthalic acid (ortho) A saturated. resins used for repair and potting. that is commonly the basis for polyester molecular weight A measure of the thermosets. monomer A single atomic unit that can open-hole tensile test A tensile test in be made into a polymer. which a hole is drilled in the middle of the sample so that the effect of fiber shortening can be determined. Glossary 591 out-gassing The loss of monomer and plastic A non-natural polymeric material other gaseous components of a plastic or that has been formed and shaped. permeability The tendency or rate at polybenzimidazole (PBI) A high-perfor- which a gaseous material passes through or mance thermoplastic. numerous Fundamentals of Composites Manufacturing: Materials. polarity A measure of the chemical nature P of a molecule as determined by the uneven- ness of the distribution of the electrons pattern The master from which a mold within it. closed-end vessel on which the shaft is tem that provides release of the entire bag. like structure. oxirane group See epoxy group. es- out time The amount of time that a pre. volatile components have been removed from polyetherimide (PEI) A high-perfor- coal tar or crude oil. highly crosslinked parts. and Applications . carbon fibers. a single molecule but. ters or alkyds. Nature rarely allows encountering in a regular over-and-under pattern. as the precursor material for forming carbon polymer A material composed of many matrix composites and other carbon-rich atomic units that combine into a long chain- materials (such as carbon fibers). polyester A polymer that contains ester phenolic A thermoset resin made by the re. mance thermoplastic. stiff. the mandrel to create the fiber lay-down Also called chemical polarity. It is often polyester thermoset (PT) A group of B-staged to form either resoles or novolacs polymers. ment winding operation. high concentrations of electrons tend to be payoff The guiding device through which attractive to sites in other molecules where the fibers pass just prior to being placed the electrons are relatively sparse. into a solid. Also called a release film. patterns. The term resin in a vacuum environment. ites. and low-priced resins. plain weave A weaving pattern character. linkages. This phe- onto the mandrel in a filament winding nomenon affects solvent resistance and other operation. Sites within the molecule having is made. They are normally crosslinked by the pitch The material left behind when more free-radical crosslinking mechanism. also called unsaturated polyes- and then cured to achieve flame-retardant. pole piece The fitting in the end of a peel ply Part of the vacuum bagging sys. Methods. plug The shaped material used as a master pattern from which a mold is copied. The payoff is moved relative to chemical-dependent natures of the polymers. action of phenol and formaldehyde. polymer molecule A single polymeric ized by the warp and weft fibers alternating chain. sometimes refers to the matrix material. pecially for composites made from fiberglass preg is out of cold storage. mounted. It is occasionally used mance thermoplastic. The shaft turns the part in a fila- ging assembly from off the top of the part. permanent set The non-recovered change polyamide-imide (PAI) A high-perfor- in shape of a part due to creep. rather. polyacrylonitrile (PAN) A thermoplas- pendant When a group is attached by tic material that is a starting material for dangling from the polymer backbone. which are the most common low-smoke. of all thermoset materials used in compos- pigment Inorganic colorants. pyrolysis A step in the manufacture of positive-type mold closure A mold-clo. it is a control parameter the value of the concept of a polymer mol. fiberglass types and is a good transmitter of electromagnetic radiation. ing material for making carbon fibers. Methods. method that uses x-rays to examine the inner premix A general term for bulk molding structure of a composite. processing viscosity The viscosity of a release film Part of a vacuum bag system mixture measured during the course of the po. to monitor the extent of polymerization. crystalline form of silicon operations are carried out. fibers. They are consumed prepreg tow A prepreg material made in the curing reaction. long-chain molecules (polymers). of polyester thermosets. (alcohol) groups. prepreg A sheet made of fibers or cloth reactive diluent Chemicals that are sol- onto which a mixture of liquid resin and cur. onto a tow or bundle of composite material that provides strength. carbon matrix composites in which the cured sure system in compression molding in which composite is heated in the absence of oxygen the mold halves fit tightly together and do to drive off the non-carbon atoms. preform An assemblage of reinforcement plies shaped to be near the final shape of the R product. and other properties. It lacks only the resin and curing radiography A non-destructive test for completion. vents and co-reactants in the curing process ing agent (hardener) has been coated. It is usually filament winding operations where wet resin a fibrous material. application from a bath is either difficult or release agent Material that is applied undesirable. and Applications . that provides release of the entire bagging Fundamentals of Composites Manufacturing: Materials. and z axes. made from regener- pound (SMC) materials. the time in a resin dioxide. molded part. lymerization reaction. post-curing See annealing. tion process. It is often used to quench A chemical added or a procedure protect wire ends and other small electrical carried out to stop the curing or polymeriza- components. by coating a resin. compound (BMC) or sheet molding com- rayon A type of fiber. not allow flashing to occur. Q pot life The working time of the resin while the fiber wet-out and other pre-curing quartz A pure. pseudo-isotropic Materials that are rein- polyol A molecule having multiple OH forced along the principal x. ecule is in simplifying the representation of promoters See accelerators. y. This material is especially useful in stiffness. to a mold surface to assist in release of the pressure intensifier See caul. propylene glycol A glycol monomer that polymerization The process that con. ated cellulose. which can be used as a start- pre-polymer See oligomer. It is stronger and stiffer than other bath without appreciable crosslinking. Hence. which is a thermoset reinforcement The separated phase of a or thermoplastic. potting The process of encapsulating an assembly or part in resin. the polymer. is low in cost and gives excellent styrene verts small atomic units (monomers) into compatibility in polyester thermosets.592 Glossary polymer molecules in a single mass. The term sometimes (RTV) A resin type. can be machined to ripening The gradual thickening of a give a high-temperature-resistant mold. especially when thicken. it is a thermoset seamless molding paste An epoxy-based and will fully cure upon heating. especially if it is a high-performance roving A group of fiberglass filaments. often an epoxy. satin weave A weaving pattern in which resin stall-out See resin freeze. mold to wet the fibers and form the part. the warp or weft fibers skip over or under several of the other types of fibers. S resin freeze When a resin cures prema- turely and. too much resin from an area of the part so that the fibers are not properly wetted. od in which prepreg materials are wrapped resin A polymeric material that has not around a mandrel and then cured. preform is placed into a mold. along with the preform. the mold is a core material. that refers to the matrix material even after will cure at room temperature. Then heat and pres- sure are applied to cause the film to melt and infuse the preform. after curing. preform is placed into the mold. This resin starving Transferring (bleeding) fabric has high drape. and which. Also called moplastic resin is soft enough to flow under a resin stall-out. Also roll wrapping A composite molding meth- called a peel ply. all resin infusion processes. Methods. Attractive forces between Fundamentals of Composites Manufacturing: Materials. bag and create an airtight assembly. of electrons that move about and bind to- The resin is then cured to form the part. runners The network of channels in an resin film infusion (RFI) A process in injection mold through which the melt flows which a resin film is placed inside the mold from the sprue to the cavities. A one-step resin. vironment. molding compound. therefore. moderate pressure but is not fully melted. resin infusion technology A general sandwich structure A structure consist- term describing all processes in which a dry ing of two face sheets of composite laminate. shaping. cured laminate. secondary bonding Adding more lay- ing is desired. and then resin is introduced into the sheets to the core. thus resin transfer molding (RTM) A method increasing the amount of surface area on of manufacturing composites in which a dry which the bonding of the repair can occur. Most tube rolling. and Applications . scarf A type of repair patch in which the sides of the repair are sloped (tapered). and adhesive to bond the face closed. does not completely fill sag point The temperature at which a ther- the mold during resin infusion. the mold is closed.Glossary 593 assembly from off the top of the part. Also called yet been formed into its final shape. resins are liquids or low-melting solids at room temperature vulcanization room temperature. and then resin is injected into the sea of electrons The highly mobile group mold (under pressure) to wet the fibers. so that a certain viscosity can ers of laminate material onto a previously be achieved prior to molding. composite. sealant Part of a vacuum bagging system resole A B-staged phenolic resin created in whose function is to adhere to the vacuum an excess of formaldehyde in an alkaline en. gether the positively charged ions in a metal RTM is also a general term that describes material. without the material used to coat the surface of a mold addition of a curing agent. Then. Such a coating is sometimes lected areas of a laminate (as. which causes the particles to join together stabilization A step in the manufacture (consolidate) and form a solid mass. therefore. spinneret The metal plate in which holes are shearography A non-destructive test drilled and used as a forming device to make method that uses laser photography and fibers. specific modulus The tensile modulus of a material divided by the density. This time is limited by the spray that is directed into the mold. especially sizing A material coated onto the surface when the molecules are solids. strength than other types of fiberglass. Then a second film tangle them. often smart structure A structure or system treated to prevent unraveling. in which the individual and then chopping the fiberglass so that it strands of fiber were actually spun to en- covers the entire surface. regions that are crystalline and some that are not. called a size and is generally not distinguish- in a joint). sintering A process in which a powdered sprue The channel that connects the material (resin. assume their original molded shape. and fiberglass in (turned). spinning The process of forming a fiber. of carbon fibers in which the rings are Fundamentals of Composites Manufacturing: Materials. at some later time. selvage Edges of a roll of material. that incorporates sensors and/or actuators so that the environment and state of the semi-crystalline A polymer with some structure can be monitored. While synthetic fibers are not actually spun ture of polyester resin. or metal) is heated mold to the nozzle of an injection molding to a temperature just below its melting point. facturing in which the reinforcements are shelf life The time that the uncured resin chopped and then entrained in a resin can be stored. are formulated to give higher of modulus and weight. the material achieving a measure of the combined effects can be reheated to the softening tempera. the terminology comes from the which the fiberglass is mixed with the resin/ ancient method of forming natural fibers. of modulus and weight. which causes the molecules to relax and spin casting See centrifugal casting. and Applications . sheet molding compound (SMC) A mix. and specific strength The tensile strength then chilled to lock the molecules in the new of a material divided by the density. terial divided by its density. of a composite. able today from a finish. of a fiber to prevent damage to the fiber dur- selective stitching Stitching in only se. The natural tendency of many resins to spontane. fibers are then rolled to ensure good fiber ously (although usually slowly) cure. with paste is laid on top and the material is spray-up A system of composite manu- worked by wheels to wet the fibers. It is. raised to a softening point. for example. wet-out. thereby S-glass This type of glass and its vari- achieving a measure of the combined effects ant. ture. ing processing.594 Glossary the molecules cause adherence. thereby shape. The liquid raw material passes through shearing software to analyze the structure the holes to form the fiber filaments. filler. ceramic. modified in shape. machine. that can be molded at one shape. Methods. used in some aerospace and other specific stiffness The modulus of a ma- high-performance applications. S2-glass. The result is an indication of the stiffness as a function of shape memory polymer A polymer the weight. filler paste by doctoring the paste onto a film like wool and cotton. a small metal hammer (or strain The deformation of a sample in a even a coin) is used to lightly tap the surface mechanical test. tensile properties Those properties strand A general and somewhat imprecise determined by pulling on the ends of a term that usually refers to a bundle or group sample. has also been used interchangeably with aromatic diacid occasionally included in fiber and filament.5–4 in. staple fibers Continuous fibers that have stretch forming A type of matched-die been chopped into lengths of approximately molding of thermoplastic composites in . surfactant A material that changes the stiffness The resistance of a material to energy of a surface and facilitates the coating deformation. the edges of the flush repair are stepped. Fundamentals of Composites Manufacturing: Materials. T ing three-dimensional character to the lami- nate. (1. The term terephthalic acid (tere) A saturated. called the elongation. and Applications . the modulus. The strain to failure also can be sibly damaged areas. molecules in the bulk of the material). stitched fabric A laminate in which the fabrics are stitched with a fiber. that are made periodically to provide limited stepped repair A repair design in which guidelines for daily activities.2–10 cm). of the surface by the resin mixture. Tere imparts high heat distortion that are fundamental to the nature of the temperature tolerance to the polymer. company and affect company values and tetrabromophthalic anhydride A halo- underlying principles. sound between known good areas and pos- nal length. which the blanks are clamped and the fibers ral fibers that are inherently in the length stretch to fill the mold’s shape. Methods. that allows for the essential unpredictability textile fibers The set of organic fibers of the world. thus impart. gen-containing diacid that imparts flame-re- strategic mapping A method of thinking tardant properties to polyester thermosets. surface free energy The energy pres- thus increasing the amount of bonding area ent due to the imbalance of forces on the when compared to a straight-sided repair. range of the chopped continuous fibers. In the test. structural decisions Determinations steel-rule blanking See die cutting. and the surface tension The surface free energy geometry of bond angles on the courses of for a liquid-gas interface. which is usually expressed of the composite to determine changes in as the change in length divided by the origi. chemical reactions. sample in a mechanical test. used extensively in textiles (such as clothing. of untwisted continuous filaments. of resin and hardener that will give complete tap test A test used to assess impact dam- reaction of all active sites. age. state by noting the force required to lift a stoichiometric ratio The relative amount prepreg sheet from a standard surface. The stitches are oriented in the direction tack test A method of assessing the cure perpendicular to the plane of the fabrics. Staple also may be natu. the mix of monomers to make unsaturated strategic decisions Determinations polyesters.Glossary 595 formed through crosslinking and atomic stress The force per unit area applied to a rearrangement. molecules at the surface of a material (in steric interaction The influence of the contrast to the balanced forces that exist on sizes and shapes of atoms and molecules. the electrical charge distribution. contained aging as extending the time. propagation of cracks. thus causing fabrics. is softened and then bent at the softened toughening agent See toughener. it contains a carbon. The term usually applies to all thermofolding A thermoplastic molding advanced fibers but not. called toughening agent. the crack’s thinner A material added to a resin mix. This is often done by stitching the material to solidify. is used to exert pres- toughened epoxies An epoxy resin that sure on a laminate.) and as reinforcements in some resultant composite. transition molding See incremental thixotrope An additive that imparts high forming. especially when the energy which sample flaws are detected by compar. Also Composites that use textile-fiber reinforce. in remelting. etc. aging is based. Alternately. transverse direction Especially in woven time-temperature transposition The fabrics. Addi. can be change increases the volume of the material crosslinked and become a thermoset. These additives usu- applications such as conveyor belts and tires. which the reinforcement experiences a phase thermoset polyester A polyester resin or crystalline structure change induced by that is unsaturated. When the phase carbon double bond and. it is the ing thermal photographs (usually taken with resistance of a material to the initiation and infrared cameras). of the fabric to give high strength in the bias toughener A material added to a resin directions. growth is arrested. Fumaric tional heating of the shaped part will result acid is a trans isomer. ments offer modest improvements over non. trans-laminar reinforced composite A thermoset Resins that are liquids at room laminate in which at least 5% of the fibers temperature. Methods. viscosity to the resin mixture. transformation toughening A method thermoset engineering composites See of toughening a ceramic matrix composite in fiberglass reinforced plastics (FRP). region. therefore. Fundamentals of Composites Manufacturing: Materials. toughness The ability of a material to thermography A non-destructive test in absorb energy. of the shaped part will not result in remelting. triaxial weave A fabric in which the warp rated into it or that has increased flexibility fibers are oriented along the bias directions in its structure. results from an impact. It assumes that raising the trapped rubber molding A process temperature of a material is equivalent in in which a rubberized medium. to fi- method in which only a portion of the part berglass. tow A group of filaments gathered to- reinforced materials. which can be reacted to form are oriented perpendicular to the plane of the bonds between the molecules. thermoplastic Resins that are solids at trans-isomer The arrangement of atoms room temperature. ally have high elongation (like rubber). has rubber or thermoplastic resins incorpo. of a carbon-carbon double bond. the direction that is perpendicular to principle on which accelerated thermal the principal or machine direction. and Applications . and then cooled to solidify. mixture to increase the toughness of the tube rolling See roll wrapping. in which two key groups are on opposite sides shaped. Additional heating the laminate. in the vicinity of the crack end. the formation of a crack. gether. typically.596 Glossary carpets. within a closed mold. ture to reduce its viscosity. which can be melted. and Applications . weight. (0. These are the most damaging light compo. viscosity is increased with molecular weight ethylene (UHMWPE) fiber A type of and aromatic content. ester thermoset (PT) and alkyd. viscosity The thickness of a liquid.1 cm) long. Also called the fill. high-performance fiber made from high- molecular-weight polyethylene. ultrasonic vibratory cutting A method weld line See knit line.Glossary 597 twill weave A weaving pattern in which veil A lightweight fiberglass fabric used to the over-and-under pattern of the warp and hide fiber patterns and give a smooth surface weft create a diagonal pattern in the fabric. The polymer chains are stretched and then formed into W fibers. which is equivalent unidirectional fibers and a suitable resin. ultrasonic testing A non-destructive weft In a woven fabric. UV inhibitor A material that enhances the resistance of a composite to the adverse results of ultraviolet (UV) light exposure. these are the fi- ylene (ECPE) fibers. to the composite lay-up. or trans- through it. Y V yarn A bundle of filaments that has been twisted to assist in keeping the filaments in vacuum bag Part of a vacuum bagging a group. particles. It is made by loosely weaving large roving strands. to the energy of the bond between the two unsaturated polyester (UP) See poly. Methods. Also called extended chain polyeth- warp In a woven fabric. ing of fibers by the resin. woof. woven roving A heavy fiberglass fabric unsaturation The presence of a carbon. vinyl ester A group of polymers that have properties somewhat like the epoxies but that U can be cured like unsaturated polyesters.04 in. system whose function is to form an airtight Young’s modulus The modulus in a ten- seal over an entire assembly. these are the fi- method used to detect flaws in a composite bers interwoven above and below the warp sample by monitoring ultrasonic signals sent fibers. two-step resin novolac phenolic that will vibration The oscillation of a material cure from the B-stage with the addition of struck with an impact. used to rapidly build up reinforcement carbon double bond. woof See fill or weft. Resin ultra-high-molecular-weight poly. bers arrayed in the machine direction. sile stress-strain curve. nents for polymers. Fundamentals of Composites Manufacturing: Materials. verse fibers. a curing agent. work of adhesion The work required to unidirectional tapes Prepregs made of separate two particles. cally about . ultraviolet (UV) The component of light whiskers Short reinforcement fibers typi- that is in the ultraviolet range of frequencies. of cutting textiles and uncured prepregs in which a knife is driven by ultrasonic wet-out The complete and uniform coat- vibrations. and Applications . Methods.598 Glossary Z z-fiber construction A laminate system that is similar to stitching but uses rods or pins oriented perpendicular to the plane of the fabrics to hold the laminates together. Fundamentals of Composites Manufacturing: Materials. .INDEX Index Terms Links 3M 173 532 A ablation 128-129 (Figure 5-9) 579 abrasion 490 (Figure 20-4) ABS Pipe Company 517-518 (Figure 21-1) accelerated testing 291 (Figure 10-15) accelerators 65-66 74 101 376 579 acid number 51 579 acoustic emission testing 300-301 579 acrylic 78 365 activation energy 130 579 active damping 287 actuators/sensors 494 adaptive structure 329 addition polymerization 21-22 (Figure 2-2) 579 additives 42-43 56-57 65-66 69 72 (Figure 3-9) 76 80 (Table 3-4) 151 443 505 579 adduct 508 579 adherend 362 579 This page has been reformatted by Knovel to provide easier navigation. 2-2) 579 alkyd 50 67 579 allylic 67-68 579 alumina fiber 228 American Composites Manufacturing Association (ACMA) 10-12 511 American National Standards Institute 266 This page has been reformatted by Knovel to provide easier navigation. 12-9) 579 adhesives/sealants 149 adipic acid 55 579 advanced composites 7-10 (Tables 1-4. . 2-8. Tables 2-1. epoxy 104 364-365 surface free energy 233-234 (Figure 8-19) 595 surface tension 233 595 theory 233-234 work of adhesion 233 597 adhesive joining 121-122 362-366 (Figures 12-8.Index Terms Links adhesion.14-5) advanced thermoplastic composites 164 advanced thermoset composites 161-162 (Table 6-1) aero-elasticity 287 aerospace products 551-553 564-567 576-577 aging/service life testing 291-292 Air Force Materials Laboratory 226 Airbus 567 aliphatic materials 31-41 (Figures 2-7. 1-5) 161-164 (Tables 6-1. 6-2) 389-406 (Figures 14-1 to 14-7. Table 14-1) 579 automatic lay-up 393-395 (Figure 14-3) filament winding 399-400 585-586 manual lay-up 390-393 open molding 389-406 (Figures 14-1 to 14-7. Table 14-1) roll wrapping 400-401 (Figure 14-6) 451 593 trapped rubber molding 400 596 tube rolling 400-401 (Figure 14-6) 596 vacuum bagging 395-398 (Figures 14-4. Index Terms Links American Society for Testing and Materials (ASTM) 265 294 304 353 American Society of Mechanical Engineers (ASME) 266 amine hardener 94-95 (Figures 4-11. Tables 23-1 to 23-3) aerospace 551-553 564-567 576-577 appliances 550 aramid fiber 222 580 armor 561-564 (Table 23-3) bismaleimide 140 boron fiber 227-228 carbon/graphite fiber 216-218 carbon matrix composites 133-134 ceramic matrix composites 185-186 construction 545-546 consumer/sports 549-550 corrosion products 547-548 dicyclopentadiene (DCPD) 153 584 electrical 548-549 fiberglass reinforced plastics (FRP) 206-207 filament winding 439 graphite fiber 216-218 This page has been reformatted by Knovel to provide easier navigation. . 4-12) Amoco 172 amorphous polymer 25 36 (Figure 2-8) 181 amorphous region 36 (Figure 2-8) 181 579 anaerobics 365 annealing 580 anisotropic structure 307 580 anti-foaming agent 43 580 antioxidant 38 580 anti-technology values 536 appliances 550 applications 109-111 543-578 (Figures 23-1 to 23-5. 2-2) molecules 32 (Figure 2-7) ASM International 266 aspect ratio 197 246 580 Association Francaise de Normalization (AFNOR) 266 ® Astrel 173 asymmetric laminate 342 (Figure 11-25) Atofina 174 atomic oxygen 290 556-557 (Table 23-1) attraction 25 580 autoclave curing 399 automatic lay-up 393-395 (Figure 14-3) autonomously guided vehicle (AGV) 573 axial windings 438-439 (Figure 17-2) This page has been reformatted by Knovel to provide easier navigation.Index Terms Links applications (Cont. Table 8-5) 580 armor 561-564 (Table 23-3) aromatic 169 580 bisphenol A 56 80 (Table 3-3) 580 heterocycle 138 580 materials 31-41 (Figures 2-7. 2-8. .) industrial 552-553 ® IsoTruss 559-561 (Figure 23-3) marine 546-547 medical 550-551 (Figure 23-1) metal matrix composites 191 polyimide 139 polyurethane 144-146 silicon carbide fiber 226-228 silicone 146-148 transportation 543-545 ultra-high-molecular-weight polyethylene (UHMWPE) fibers 225-226 597 unmanned vehicles 567-573 (Figure 23-5) aramid fiber 218-226 (Figures 8-12 to 8-16. Tables 2-1. . energy 130 580 covalent 181-182 582 fiber-matrix 105-106 234-239 (Figures 8-20 to 8-25) 580 fusion 366 ionic 180 588 metallic 180-181 589 repairs 496-502 (Figure 20-8) secondary 25 381 593-594 This page has been reformatted by Knovel to provide easier navigation. Leo 122 ® Bakelite 122 Barcol hardness test 274 basalt 228 basket weave 249-250 (Figure 9-3) 580 bearing failure 360-361 (Figure 12-7) Beech Starship 7 benchmarking 270 bias 248 580 binder 1 bismaleimide (BMI) 139-140 (Figure 5-13) bisphenol A 56 80 (Table 3-3) 580 BlackWidow 570 bladder molding 402 405 (Figure 14-7) bleeder material 395 580 blooming 378 580 Boeing 174-175 565 567 575 Boeing 787 Dreamliner 565-566 Boeing Drafting Standard 322 bond.Index Terms Links B Bakeland. ) strength 130 234-239 (Figures 8-20 to 8-25) 366 580 Van der Waals 212-213 boron fibers 226-228 (Figure 8-17) braids 256 261-262 580 brainstorming 533 breather material 396 580 breathing the mold 413 580 bridge molecules 62 580 bridging 397 British Standards Institute (BSI) 266 broad goods 248 580 broken window theory 554-555 B-staged resin 580 B-staging 124 159 580 bulk molding compound 68 408-412 (Figures 15-1. (Cont.Index Terms Links bond. . Table 15-1) 580 bullet-proof vests 240-241 (Table 8-6) bumping the mold 125 413 580-581 burping the mold 125 413 581 burst test 279 581 business ethics 534-535 business obstacles 522 (Table 21-1) business planning 529-534 butt joint 364 (Figure 12-8) butt-lap joint 359-360 (Figure 12-6) This page has been reformatted by Knovel to provide easier navigation. 15-2. aramid 221 (Figure 8-14) manufacture 208-209 (Figure 8-5) market 551 (Figure 23-2) pitch 208 591 polyacrylonitrile (PAN) 208 591 properties 212-218 (Table 8-4.Index Terms Links C capability analysis 268 carbon-carbon composites 134 581 carbon fiber 207-218 (Figures 8-5 to 8-11. 5-11. . Figures 8-10. Table 8-4) 581 applications 216-218 carbonization 209-210 (Figure 8-7) 581 coefficient of thermal expansion 215-216 582 graphitization 209-211 (Figure 8-8) 587 impact toughness vs. Table 5-2) 581 activation energy 130 579 applications 133-134 bond energy 130 580 bond strength 130 580 carbon-carbon composites 134 581 carbonization 136 581 chemical vapor deposition 135 581 electron conjugation 131 584 green preform 134 587 heat capacity 131 587 high-performance thermosets 130-136 (Figures 5-10. 8-11) rayon 208 592 recipe 208 stabilization 208-210 (Figure 8-6) 594-595 structure 208-213 (Figures 8-6 to 8-9) tensile strength/modulus 215 (Figure 8-10) 595 thermal properties 215-217 (Figure 8-11) carbon matrix composites 130-136 (Figures 5-10. 5-11. Table 5-2) impregnation 135 587 manufacturing process 134-136 (Figure 5-11) performance criteria 131-133 (Figure 5-10) This page has been reformatted by Knovel to provide easier navigation. .) pitch 130 591 production flow 135 (Figure 5-11) properties 136-137 (Table 5-3) pyrolysis 135 592 stabilization 131 594-595 steric interaction 131 595 testing 131-133 (Table 5-2) thermal stability 130-131 carbonization 136 209-210 (Figure 8-7) 581 casting 190 catalyst 61 101 376 581 caterpillar pulling system 457 581 caul 397 581 cause-and-effect diagram 270 cavities 469 581 Celanese 280 centrifugal casting 153 432 581 ceramic materials 180 581 ceramic matrix composites 179-188 (Table 7-1. Figure 7-1) applications 185-186 chemical vapor deposition (CVD) 187 581 chemical vapor infusion (CVI) 187 crack deflection 183 583 crack pinning 183 583 in-situ reaction sintering 187 588 load transfer 183 589 manufacture 186-188 microcracks 184 589 properties 182-184 (Table 7-1.Index Terms Links carbon matrix composites (Cont. Figure 7-1) 194 (Figure 7-3) This page has been reformatted by Knovel to provide easier navigation. 11-4) engineering thermoplastics 168 (Table 6-4) cold forming 190 collateral damage 482-483 colorant 43 582 This page has been reformatted by Knovel to provide easier navigation.) reinforcement shapes 184 (Figure 7-1) 245-263 sintering 187 594 toughness 183-184 596 transformation toughening 183 596 ® Cetex 174 C-glass 205 581 char 127 581 charge 581 Charpy test 282-283 (Figure 10-11) chemical joining 361-362 chemical polarity 37 581 chemical resistance 223 (Table 8-5) chemical vapor deposition (CVD)/chemical vapor infusion (CVI) 581 boron fibers 226-227 (Figure 8-17) carbon matrix composites 135 581 ceramic matrix composites 187 silicon carbide fibers 226-227 (Figure 8-17) Chevron Phillips 173 chlorendic acid 55 581 chopped strand mat 252-253 (Figure 9-5) 581 cis isomer 52 581 clamshell mold 399 581-582 Classical Laminate Plate Theory 313-314 cleavage failure 360-361 (Figure 12-7) co-curing 362 399 582 coefficient of thermal expansion (CTE) 287-288 (Table 10-2) 341 (Tables 11-3. Tables 11-3.Index Terms Links ceramic matrix composites (Cont. . 11-4) 582 carbon/graphite fiber 215-216 comparison 340-341 (Figure 11-24. 5-11.Index Terms Links Columbia disaster 553-559 (Tables 23-1. 11-4) 582 compounder 66 163 582 concept of 1 construction 370-372 (Figure 12-10) core material 353-357 (Table 12-1. 15-2. Tables 23-1 to 23-3) business 525-541 (Figures 22-1 to 22-4) carbon-carbon 134 581 carbon matrix 130-136 (Figures 5-10. Figure 12-4) covalent bond 181-182 582 cracking 183-184 325-327 (Figures 11-10 to 11-12) 332 (Figure 11-16) 377 583 design 307-348 disadvantages 2 (Table 1-1) double structure 350 584 dye 43 584 economics 525-529 (Figures 22-1 to 22-3) 538-540 (Figure 22-4) This page has been reformatted by Knovel to provide easier navigation. 23-2) co-mingling 466 582 co-monomer 62-65 582 competing globally 537-538 composite materials 582 additives 42-43 56-57 65-66 76 80 (Table 3-4) 151 443 579 advanced 7-10 (Tables 1-4. . 6-2) 389-406 (Figures 14-1 to 14-7. Table 5-2) 581 compression molding 407-416 (Figures 15-1. Table 14-1) 579 advantages 2 (Table 1-1) applications 109-111 543-578 (Figures 23-1 to 23-5. 1-5) 161-164 (Tables 6-1. Table 15-1) 474 582 coefficient of thermal expansion 287-288 (Table 10-2) 341 (Tables 11-3. Figure 6-1) 245-263 584-585 engineering thermoset 161-162 (Table 6-1) 375-388 (Figures 13-1 to 13-3) fatigue damage 329-333 (Figures 11-14 to 11-17) 585 fiber-matrix bond 105-106 234-239 (Figures 8-20 to 8-25) 580 fiber wet-out 41-42 45 100 380-381 383 442 464-467 (Table 19-1. 23-2) 561-573 (Table 23-3. 5-2) 161-164 (Tables 6-1. Figure 19-1) 597 fiberglass reinforced plastics (FRP) 161 203 206-207 585 fillers 42-43 73 103 586 flammability testing 292-298 (Table 10-4.) engineering 7-10 (Tables 1-4. Figure 6-1) 584-585 engineering thermoplastic 7-10 (Tables 1-4. Figure 1-2) 543-559 (Figures 23-1. 1-5) 161-168 (Tables 6-3. Figure 23-5) 576-577 This page has been reformatted by Knovel to provide easier navigation. . 1-5) 161-168 (Tables 6-1 to 6-4. Figure 10-16) high performance 57 85 115-157 (Figures 5-1 to 5-17. 6-4. Tables 5-1. 6-2) 168-176 (Figures 6-2 to 6-5) 356 365 375-388 (Figures 13-1 to 13-3) 515 579 587 591 history 4-7 industrial 588 industry structure 13-15 (Figure 1-3) intelligent structure 492 588 ionic bond 180 588 laminate sizing 310 (Figure 11-2) 594 markets 10-13 (Table 1-6.Index Terms Links composite materials (Cont. ) matrix 1-5 (Table 1-2) 19-46 (Tables 2-1.Index Terms Links composite materials (Cont. 2-2) 589 metal matrix 188-194 (Table 7-2. . Table 14-1) 451 455 (Figure 18-2) 471-472 pigments 42-43 76 591 prepreg 14 103 109-111 159 253-255 390-395 (Figures 14-1 to 14-3) 442-443 473 592 property comparison 3 (Figure 1-1) 33-35 (Tables 2-1. 7-3) metallic bond 180-181 589 net shape 258 590 non-polymeric matrix 179-182 (Table 7-1) open molding 375-388 (Figures 13-1 to 13-3) 389-406 (Figures 14-1 to 14-7. 2-2) 318 (Table 11-1) 333-341 (Figures 11-18 to 11-24. 11-4) reinforced vs. non-reinforced materials 17-18 (Table 1-7) reinforcement 1-5 14 (Table 1-2) 73 103 109-111 159 163 184 (Figure 7-1) 193 197-243 (Figures 8-1 to 8-25. Tables 8-1 to 8-4) 245-263 (Figures 9-1 to 9-6) 267 357 379 390-395 (Figures 14-1 to 14-3) 440-441 454-455 473 485 592 self-healing 501-503 (Figure 20-9) shipments 12 (Figure 1-2) smart structures 329 491-495 594 This page has been reformatted by Knovel to provide easier navigation. Figures 7-2. Tables 11-3.. 3-9. Table 19-1) 596 thermosets 47-83 (Figures 3-1 to 3-4. 8-3) 289 (Figure 10-14) 594 surface agent 42-43 temperature (use) limits 182 (Table 7-1) thermoplastics 159-177 (Figures 6-1 to 6-5. Table 15-1) 474 582 advantages 414 applications 414 assembly 409 (Figure 15-1) bulk molding compound (BMC) 68 408-412 (Figures 15-1. 6-2) 376 596 tooling 110-111 383-386 (Figure 13-3) 401-404 (Table. Figures 8-2. Figures 8-2. 15-2. Tables 6-1.Index Terms Links composite materials (Cont. . Table 15-1) 580 breathing the mold 413 580 bumping the mold 413 580-581 burping the mold 413 581 charge 407 581 comparison to other processes 435 (Figure 16-6) daylight opening 408 583 This page has been reformatted by Knovel to provide easier navigation. 14-1) trans-laminar reinforced 267 596 vs. to 6-3) 463-480 (Figures 19-1 to 19-6.) specific stiffness 190 (Figure 7-2) 199-203 (Table 8-1. Tables 3-1 to 3-5) 105 (Table 4-5) 128 (Figure 5-8) 159 161-164 (Tables 6-1. 8-3) 594 specific strength 190 (Figure 7-2) 199-203 (Table 8-1. 15-2. metals 333-340 (Figures 11-18 to 11-24) compounder 66 163 582 comprehensive stitching 257 582 compression-after-impact test 582 compression molding 407-416 (Figures 15-1. 15-2.) ejector pins 408 584 equipment 408 flash-type closure 408 586 knockout pins 408 588 machine rating 408 machine size 408 of truck component 414-415 part complexity 413-414 positive-type closure 408 592 preform 412-415 592 prepreg 413 592 press capacity 408 pressure requirements 414 resin viscosity 410 597 sheet molding compound (SMC) 68-69 (Figure 3-7) 408-412 (Figures 15-1.Index Terms Links compression molding (Cont. open molding 415-416 compression properties 582 compression strength 338 (Figure 11-22) 582 compressive force 276 (Figure 10-5) compressive stresses 312 condensation polymerization 23-24 (Figure 2-3) 582 cone calorimeter test 294 constrained layer damping 287 construction products 545-546 consumer products 549-550 contamination 76 514-516 continuous fiber 199 204-205 (Figure 8-4) 246 (Figure 9-1) 582 continuous strand mat 252-253 (Figure 9-5) 582 control of properties 50-51 Convair Aircraft Company 15 copolymer 78 508 This page has been reformatted by Knovel to provide easier navigation. . Table 15-1) 594 thermoplastic composites 474 596 undercuts 414 vs. Index Terms Links co-reactants 62-65 (Table 3-1) 73 159-161 582 core material 353-357 (Table 12-1. 22-3) composites vs. comparing manufacturing methods 455 (Figure 18-2) 527-528 (Figures 22-2. Figure 12-4) crush strength 373 flammability 356 off-gassing 356 properties 353 (Table 12-1) resin infusion 429-431 (Table 16-6) 593 sealing edges 358 (Figure 12-5) selection 356-357 sound insulation 356 temperature 356 testing 353 355-356 (Figure 12-4) use conditions 356-357 vibration damping 356 water absorption 356 Corning Glass 203 532 corporate creativity 531-534 correlation plots 268-269 (Figure 10-1) corrosion products 547-548 corrosion resistance 120-121 (Figure 5-5) ® Corvette 6 cost. . metals 539-540 epoxy 109 helicopter fuselage 538-539 (Figure 22-4) life-cycle 528-529 of goods sold 526-527 582 polyurethanes 145 thermoplastics 164 (Table 6-2) 596 thermosets 164 (Table 6-2) 596 cotton fiber 229 coupling agent 148-149 231-232 (Figure 8-18) 239 582 This page has been reformatted by Knovel to provide easier navigation. Index Terms Links covalent bond 181-182 582 co-weaving 466 (Figure 19-1) 583 cracking 183-184 325-327 (Figures 11-10 to 11-12) 332 (Figure 11-16) 377 485 (Figure 20-2) 490 (Figure 20-4) 583 behavior 331 (Figure 11-15) delamination 327 (Figure 11-12) fatigue damage 329-333 (Figures 11-14 to 11-17) 585 fiber fracture 325 first-ply failure 326 586 fracture process 326-327 (Figure 11-11) gel coat 377 586 interfacial fracture 325 interlaminar 326 (Figure 11-10) 588 intralaminar 326 (Figure 11-10) 588 microcracks 589 stress 332-333 (Figures 11-16. 11-17) 595 creel 437-438 (Figure 17-1) 454 583 creep 106 283-285 (Figure 10-12) 583 TM CrossCheck device 111-112 crosslinking 28 31 48-49 57-65 (Figure 3-6. . 4-4) 118-120 (Figure 5-4) 124-125 138 141 583 agents 62-65 (Table 3-1) 73 96 159-161 376 583 B-staging 124 159 580 bridge molecules 62 580 catalyst 61 581 This page has been reformatted by Knovel to provide easier navigation. 4-3. Table 3-1) 91-104 (Figures 4-10 to 4-15. Tables. Tables 4-3. Table 3-1) 583 unsaturated polyesters 57-65 (Figure 3-6.Index Terms Links crosslinking (Cont. Table 3-1) vinyl esters 118-120 (Figure 5-4) 597 crowfoot satin weave 249-250 (Figure 9-3) 583 crystalline region 36 (Figure 2-8) 180-181 583 cultural lag 537 This page has been reformatted by Knovel to provide easier navigation. 4-4) initiator 58 376 588 phenolic 124-125 591 polyimide 138 polyurethanes 142-144 reactive diluent 61 63 (Table 3-1) 505 592 silicones 146 (Figure 5-16) 365 solvents 63-65 (Table 3-1) steps 58 62 thermoplastic composites 159-161 596 thermoset polyesters 57-65 (Figure 3-6. .) co-monomers 62-65 582 co-reactants 62-65 (Table 3-1) 73 159-161 582 curing 63 73 98 (Figure 4-14) 100-102 104 125 583 cyanate esters 141 density 31 97 583 dicyclopentadiene (DCPD) 152 584 epoxy 91-104 (Figures 4-10 to 4-15. Index Terms Links cure 28 48 63 65-66 70-76 (Figures 3-8. . 4-13) 98 (Figure 4-14) 100-102 (Figure 4-15) 111-112 exotherm 62 70-71 (Figure 3-8) 585 extent of 104 filler 73 103 586 film 75 flame retardants 73 gelation 70-71 (Figure 3-8) 586 heat 74 hexamethylene tetramine (hexa) 125 587 This page has been reformatted by Knovel to provide easier navigation. 3-9) 398-399 457 583 accelerator 65-66 74 101 376 579 additives 65 76 579 agents 80-82 94-96 (Figures 4-12. 4-13) 125 379 583 and contaminants 76 and pigments 76 591 and resin grade/type 75 autoclave 399 by-products 94 clamshell mold 399 581 co-curing 362 399 582 control 65 76 crosslinking agents 73 583 epoxy 94-96 (Figures 4-12. Index Terms Links cure (Cont. Table 19-1) 596 thermoset polyesters 65-66 72 (Figure 3-9) 78-79 583 time 70-71 (Figure 3-8) 583 two-step resin 125 597 uncured reactants 99 This page has been reformatted by Knovel to provide easier navigation. .) inhibitor 65 72-73 103 376 588 initiator 58 74 376 588 ® Intelimer 78-79 lay-up molding 379-381 mold heat 73 monitoring 111-112 one-step resin 124 590 options 78-79 oxygen 73 part thickness 75 457 permanent set 283 591 polyesters 104 591 post-curing 75 104 457 592 prepreg 399 promoter 65-66 74 101 376 592 rapid 154 rates 101-102 (Figure 4-15) reinforcements 73 592 repairs 501-502 (Figure 20-8) spray-up molding 383 594 styrene 73 temperatures 100-101 tests 274-275 thermoplastic composites 159-161 463-480 (Figures 19-1 to 19-6. Index Terms Links cure (Cont. Table 20-1) 500-501 collateral 482-483 crack 183-184 325-327 (Figures 11-10 to 11-12) 332 (Figure 11-16) 377 490 (Figure 20-4) 583 cut 490 (Figure 20-4) defect classification 490 (Figure 20-4) delamination 490 (Figure 20-4) dent 490 (Figure 20-4) design effects 486-487 detection 490-491 (Figure 20-5) effects 481 external protectors 487 (Figure 20-3) fiber direction effects 485 gouge 490 (Figure 20-4) This page has been reformatted by Knovel to provide easier navigation.) unsaturated polyesters 65-66 72 (Figure 3-9) 78-79 UV light 74 597 vacuum bagging 398 597 water 75 wax 75 cured hard 362 583 Curtiss Aeroplane and Motor Company 575 cut 490 (Figure 20-4) cutting 190 367 cyanate esters 140-142 (Figure 5-14) cyanoacrylates 365 cyclic oligomers 466 cycloaliphatic epoxy 90 (Figure 4-7) D damage 481-504 (Figures 20-1 to 20-9. Table 20-1) abrasion 490 (Figure 20-4) assessment 484 (Figure 20-1) 487-491 (Figure 20-4. . .Index Terms Links damage (Cont.) high impact 481 hole 490 (Figure 20-4) intelligent structure 492 588 low impact 482-483 measuring 485 nondestructive testing (NDT) 298-303 488-489 (Table 20-1) 590 open-hole compression test 484 (Figure 20-1) prevention 483-487 (Figures 20-1 to 20-3) primary 481 reduction 487 reinforcement effects 485 592 removal 496-497 repair 495-502 (Figures 20-6 to 20-8) sacrificial skirt 488 (Figure 20-3) scratch 490 (Figure 20-4) self-healing composites 501-503 (Figure 20-9) simulation 484 (Figure 20-1) smart structures 491-495 594 tap test 491 595 -tolerant resins 484-487 damping 285-287 327-329 (Figure 11-13) 356 583 dart drop impact test 583 daylight opening 408 583 debulking 395 583 decomposition point 26-27 (Figure 2-4) 583 defect classification 490 (Figure 20-4) Defense Advanced Research Projects Agency (DARPA) 572-573 delamination 327 (Figure 11-12) 490 (Figure 20-4) Deming. Ed 270 272 Denier 247 583 density 316 dent 490 (Figure 20-4) This page has been reformatted by Knovel to provide easier navigation. 11-4) 321 339-341 595 warp clock 322 (Figure 11-7) 597 Deutsches Institut fur Normung (DIN) 266 diacid 49 51-55 (Figures 3-2. .Index Terms Links design 307-348 adaptive structure 329 finite element analysis 320-321 (Figure 11-6) lay-up 321-323 (Figure 11-7) 344 (Figure 11-27) 588 methodology 308-311 (Figure 11-1) modeling 317-321 (Figure 11-6) of experiments (DOE) 268-269 of repair 497-499 (Figures 20-6. 20-7) of smart structures 329 594 quality function deployment 308 stresses 311-313 (Figures 11-3. 3-3) 79 (Table 3-2) 583 diallyl isophthalate (DAIP) 67 584 diallylphthalate (DAP) 67 584 diamond wire cutting 370 dicyandiamide (DICY) 101 dicyclopentadiene (DCPD) 57 151-153 (Figure 5-17) 584 die cutting 391 584 diethylene glycol 56 80 (Table 3-3) 584 differential scanning calorimetry (DSC) testing 274 584 difunctional 49 584 diglycidyl ether of bisphenol A (DGEBPA) 88 (Table 4-1) 584 diluent 61-65 (Table 3-1) 73 99 108 159-161 505 dipropylene glycol 584 directed fiber preforming 259 ® Dodge Viper 432 This page has been reformatted by Knovel to provide easier navigation. Index Terms Links double-clamp system 584 double composite structure 350 584 double-lap joint 359-360 (Figure 12-6) 364 (Figure 12-8) Douglas Aircraft 5 575 DragonEye 570 drape 249 255 274 584 drill smear 368 drilling 367 369 dry winding 442 DuPont 7 170-171 173-174 218-219 dye 43 584 dynamic mechanical analysis (DMA) 275 E economics 525-529 (Figures 22-1 to 22-3) 538-540 (Figure 22-4) eddy current testing 302 584 edge bleed 398 584 egg-crate mold 385 584 E-glass 205 584 ejector pins 408 584 elastic deformation 278 584 electrical. . discharge machining (EDM) 186 190 products 548-549 properties 39 resistance (epoxy) 108 electron conjugation 131 584 electro-rheological fluids 494 electro-strictive materials 494 elongation 278 584 embedded single filament test 236-237 (Figure 8-23) emissions 76-78 505-509 end-capped polyimide 138-139 This page has been reformatted by Knovel to provide easier navigation. Index Terms Links engineering composites 7-10 (Tables 1-4. 4-13) 96 98 (Figure 4-14) 100-102 (Figure 4-15) 111-112 583 cycloaliphatic 90 (Figure 4-7) diglycidyl ether of bisphenol A (DGEBPA) 88 (Table. 4-12) -based vinyl esters 118 (Figure 5-3) catalyst 101 581 cost 109 creep resistance 106 583 crosslinking 91-104 (Figures 4-10 to 4-15. 4-4) 583 cure 94-95 (Figures 4-12. Figure 6-1) 584-585 coefficient of thermal expansion 168 (Table 6-4) 582 fiber reinforcement 166 168 245-263 592 fiberglass content effects 165 (Table 6-3) 168 (Table 6-4) notched Izod impact toughness 166 open molding 375-388 (Figures 13-1 to 13-3) properties 165 (Table 6-3) 168 (Table 6-4) shear strength 168 wear resistance 168 engineering thermoset composites 161-162 (Table 6-1) 375-388 (Figures 13-1 to 13-3) environmental effects 35 (Table 2-2) epoxy 85-113 (Figures 4-1 to 4-15. 1-5) 161-168 (Tables 6-3 6-4. . Tables 4-1 to 4-5) accelerator 101 579 adhesion 104 364-365 amine hardener 94-95 (Figures 4-11. 1-5) 161-168 (Tables 6-1 to 6-4. Table 4-3. Figure 6-1) 375-388 (Figures 13-1 to 13-3) 584-585 engineering thermoplastic composites 7-10 (Tables 1-4. 4-1) 584 electrical resistance 108 fatigue resistance 106 585 fiber-matrix bond 105-106 fiber wet-out 100 597 filler 103 586 This page has been reformatted by Knovel to provide easier navigation. 4-3) room-temperature vulcanization (RTV) 101 593 shear strength 105-106 This page has been reformatted by Knovel to provide easier navigation.) flame retardant 91 (Figure 4-8) flammability resistance 109 flexibilized 92 (Figure 4-10) 107 glycidyl group 85-86 (Figure 4-1) 587 group 585 hardener 92 94 (Figure 4-11) 96-97 (Table 4-4) 101 112-113 587 heat distortion temperatures 90 (Table 4-2) 587 high performance 85 161-164 (Tables 6-1. . 6-2) 375-388 (Figures 13-1 to 13-3) 579 587 high-temperature vulcanization (HTV) 101 587 homopolymerization 96 587 imide-based 91 (Figure 4-9) inhibitor 103 588 initiator 96-99 376 588 latent hardener 101 588 matrix 288 (Table 10-2) 589 molar mass 97 585 novolac-based 90 (Figure 4-6) 590 nucleophile 92 590 oxirane group 85-86 (Figure 4-1) 591 pot life 102-103 111-112 592 prepreg 103 109-111 390-395 (Figures 14-1 to 14-3) 592 promoter 101 592 properties 104-109 (Table 4-5) reactive agent 94-96 (Figures 4-12. 4-13) resin ratio 112-113 ring 86-87 (Figures 4-2.Index Terms Links epoxy (Cont. Tables 4-1.) shelf life 102-103 111-112 594 shrinkage 104 smoke 109 128 (Figure 5-8) solvent/diluent 99 108 stoichiometric ratio 97 595 strength/stiffness 106 structure 85-91 (Figures 4-1 to 4-9.Index Terms Links epoxy (Cont. . 4-2) tetra-functional 89 (Figure 4-5) tetraglycidyldiaminodiphenylmethane (TGDDM) 89 (Figure 4-5) tetraglycidylmethylenedianiline (TGMDA) 89 (Figure 4-5) thermal stability 107-108 toughened 92 (Figure 4-10) 106-107 596 tri-functional 89 (Figure 4-4) uncured reactants 99 use 85 UV resistance 108-109 597 viscosity 100 597 volatiles 100 water absorption resistance 108 equilibrium toughness 281 585 esters 50 585 ethics 534-535 ethylene glycol 55 80 (Table 3-3) 585 exotherm 62 70-71 (Figure 3-8) 585 expansion RTM 423-424 extended chain polyethylene (ECPE) fibers 225 585 extensorial stiffness 315 external doubler 496 585 external protectors 487 (Figure 20-3) extrusion 467-468 (Figure 19-2) This page has been reformatted by Knovel to provide easier navigation. 9-3) 252-253 (Figure 9-5) 262-263 595 face bleed 398 585 factory. Table 21-1) material storage 513-514 523 process flow 517-518 (Figure 21-1) recycling 516 simulation 516-521 (Figure 21-1) waste disposal 516 failure mode 355 (Figure 12-4) 360-361 (Figure 12-7) failure mode and effects analysis (FMEA) 270 falling dart test 282 fastener materials 360 fatigue 585 damage 329-333 (Figures 11-14 to 11-17) resistance (epoxy) 106 stress behavior 334 (Figure 11-18) testing 285-286 (Figure 10-13) feathering 499 585 Federal Aviation Administration (FAA) 126 491 174-175 501 federal motor vehicle safety standard (FMVSS) 294 Federal Railroad Administration (FAR) 294 feed zone 468 585 This page has been reformatted by Knovel to provide easier navigation. . contamination 514-516 government regulation 509-513 emissions 505-509 hazardous air pollutant 506 508 587 issues 505-524 (Figure 21-1.Index Terms Links F fabrics 247-250 (Figures 9-2. Table 9-1) 585 filament winding 440-441 585-586 flax 229 fracture 325 glass 203-207 (Figure 8-4. Table 8-4) 551 581 characteristics 197-203 (Figures 8-1 to 8-3. . 8-3) 246-247 (Table 9-1) 586 graphite 207-218 (Figures 8-5 to 8-11. Tables 8-2.Index Terms Links fiber 197 245 585 alumina 228 aramid 218-226 (Figures 8-12 to 8-16. Table 6-4) 464-465 (Table. 19-1) continuous 199 204-205 (Figure 8-4) 246 (Figure 9-1) 582 damage effects 485-487 denier 247 583 directed preforming 259 direction 485-487 drawing 197 filament 205 245-247 (Figure 9-1. Table 8-4) 587 hemp 229 hybrid 260-261 (Figure 9-6) 587 jute 229 kinking 477 (Figure 19-6) knitted fabric 251-252 (Figure 9-4) 588 lay-up molding 379 This page has been reformatted by Knovel to provide easier navigation. Table 8-1) comprehensive stitching 257 582 content 167-168 (Figure 6-1. Table 8-5) 580 aspect ratio 197 246 580 basalt 228 boron 226-228 (Figure 8-17) braided 256 261-262 580 carbon/graphite 207-221 (Figures 8-5 to 8-14. 16-5.Index Terms Links fiber (Cont. Table 16-3) 454-455 592 prepreg 14 103 109-111 159 253-255 390-395 (Figures 14-1 to 14-3) 399 413 442 455 (Figure 18-2) 473 588-589 592 596 properties 199-200 (Table 8-1) 207 (Table 8-3) 251-252 pullout test 234-235 (Figure 8-20) roving 245-247 (Figure 9-1.) length 242-243 464-465 (Table 19-1) manufacture 203-205 (Figure 8-4) mat 252-253 (Figure 9-5) milled 261 357 589-590 monofilaments 245 590 movement 477 (Figure 19-6) natural 228-230 nitrides 228 non-woven fabrics (mat) 252-253 (Figure 9-5) out time 254 591 particle 261 placement 449-450 585 polybenzimidazole (PBI) 171 591 preform 258-260 425-428 (Figures 16-4. Table 9-1) 593 selective stitching 257 594 silicon carbide 226-228 (Figure 8-17) silkworm silk 229 size 198 (Figure 8-1) specialty 228 spider silk 229 This page has been reformatted by Knovel to provide easier navigation. . Table 9-1) 595 strength 199-203 (Table 8-1. . 8-3) 595 stitched laminates 256-257 strand 245-247 (Figure 9-1. Table 9-1) 597 z-fiber construction 267 598 This page has been reformatted by Knovel to provide easier navigation. Figures 8-2. 9-3) woven roving 252 597 yarn 245-247 (Figure 9-1. Table 9-1) 596 ultra-high-molecular-weight polyethylene (UHMWPE) fibers 223-226 597 unidirectional tape 254 597 veil 252 597 Verton 465 -volume fraction 315 317 346-347 585 wash 422 585 wet-out 41-42 45 100 380-381 383 442 464-467 (Table 19-1. Figures 8-2.Index Terms Links fiber (Cont. Figure 19-1) 597 whiskers 163 184 246 261 597 wood 229 woven fabric 247-250 (Figures 9-2.) spinning 245 594 staple 246 440 595 stiffness 199-203 (Table 8-1. 8-3) 206 (Table 8-2) surface treatment 230 585 textile 595-596 three-dimensional laminates 257-258 tow 208 245-247 (Figure 9-1. Table 9-1) 585 This page has been reformatted by Knovel to provide easier navigation. . Adhesion Theory 233-234 bond 105-106 234-239 (Figures 8-20 to 8-25) 580 coupling agents 148-149 231-232 (Figure 8-18) 239 582 fiber pullout test 234-235 (Figure 8-20) fiber surface treatment 230 585 interactions 230-239 (Figures 8-18 to 8-25) Interphase Theory 232-233 588 short beam shear test 235-236 (Figure 8-22) 281 sizings/finishes 230 594 surface free energy 233-234 (Figure 8-19) 595 surface tension 233 595 traverse tensile test 235 (Figure 8-21) work of adhesion 233 597 fiber-volume fraction 315 317 346-347 585 fiberglass 5 203-207 (Figure 8-4) 586 applications 206-207 content effects 165 (Table 6-3) 168 (Table 6-4) diameter 247 (Table 9-1) filament 204-205 (Figure 8-4) 585 in crack arrestment 485 (Figure 20-2) manufacture 203-205 (Figure 8-4) properties 206-207 (Tables 8-2.Index Terms Links fiber-matrix. 8-3) reinforced plastics (FRP) 161 203 206-207 (Tables 8-2. 8-3) 585 roving 246 593 shin guard 154 types 205 fiberoptic devices 493-494 filament 204-205 (Figure 8-4) 245-247 (Figure 9-1. 17-2) 447 587 longitudinal windings 438-439 (Figure 17-2) 589 LOTUS system 449 machine 438 (Figure 17-1) 445-447 mandrel 437-439 (Figure 17-1) 444-445 589 materials 440-443 patterns 447-448 (Figure 17-3) payoff 437-438 (Figure 17-1) 591 polar winding machine 446 pole piece 448 591 prepregs 442-443 592 reinforcement fibers 440-441 592 resins 441-442 585-586 shape memory polymer 444 594 staple fibers 246 440 595 This page has been reformatted by Knovel to provide easier navigation.Index Terms Links filament winding 399-400 437-452 (Figures 17-1 to 17-3) 472-473 585-586 additives 443 579 applications 439 axial windings 438-439 (Figure 17-2) comparison to other processes 435 (Figure 16-6) 440 527 (Figure 22-2) creel 437-438 (Figure 17-1) 454 583 dicyclopentadiene (DCPD) 153 584 dry winding 442 fiber wet-out 442 597 geodesic path 448 586 helical windings 437-439 (Figures 17-1. . 17-2) 447 (Figure 17-3) 587 hoop windings 437-439 (Figures 17-1. Table 5-1) 591 testing 292-298 (Table 10-4. behavior balanced laminate 315 323 force 276 (Figure 10-5) properties 586 testing 280-281 (Figure 10-8) flow forming 474-475 586 This page has been reformatted by Knovel to provide easier navigation.Index Terms Links filament winding (Cont.) thermoplastic composites 472-473 585-586 variations of 448-449 wet-out 442 597 fill 586 fill direction 248 (Figure 9-2) fillers 42-43 73 103 586 film stacking 466 (Figure 19-1) film/wax 75 395 592-593 finishes 230-231 (Figure 8-18) 586 finite element analysis 320-321 (Figure 11-6) fire resistance 38-39 55 first-ply failure 326 586 flame retardant 73 91 (Figure 4-8) 122 flammability. . Figure 10-16) flash 408 586 flash-type mold closure 408 586 flax fiber 229 flexibilized epoxy 92 (Figure 4-10) 107 flexible die forming 475-476 586 flexible molds 149 flexible tooling 149 flexural. char 127 581 core materials 356 epoxy 109 phenolics 125-127 (Figure 5-7. . Tables 8-2. 8-3) applications 206-207 content effects 165 (Table 6-3) 168 (Table 6-4) diameter 247 (Table 9-1) filaments 204-205 (Figure 8-4) 245-247 (Figure 9-1.Index Terms Links flow media materials 429-431 (Table 16-6) fluorinated ethylene propylene (FEP) 174 fluoropolymers 173-174 flush-type bonded repair 496 586 flying car 15-16 (Figure 1-4) forces 276 (Figure 10-5) foreign manufacturing quality 521-522 (Table 21-1) forging 190 fracture process 326-327 (Figure 11-11) free-radical 21 60 586 freezing point 25 fumaric acid 52 586 functional specification 586 fusion bonding 366 G gates 469 586 GE Corporation 170 172 gel coat 55 375-378 586 gel permeation chromatography 51 586 gelation 70-71 (Figure 3-8) 586 General Aviation 567 geodesic path 448 586 Georgia-Pacific 459 glass 180 586 glass fiber 5 203-207 (Figure 8-4. Table 9-1) 585 in crack arrestment 485 (Figure 20-2) manufacture 203-205 (Figure 8-4) This page has been reformatted by Knovel to provide easier navigation. Index Terms Links glass fiber (Cont. 8-3) reinforced plastics (FRP) 161 203 206-207 (Tables 8-2. Table 8-4) 587 applications 216-218 carbonization 209-210 (Figure 8-7) 581 coefficient of thermal expansion 215-216 582 graphitization 209-211 (Figure 8-8) 587 impact toughness vs. 8-11) rayon 208 592 recipe 208 stabilization 208-210 (Figure 8-6) 594-595 structure 208-213 (Figures 8-6 to 8-9) tensile strength/modulus 215 (Figure 8-10) thermal properties 215-217 (Figure 8-11) graphitization 209-211 (Figure 8-8) 587 green preform 134 587 This page has been reformatted by Knovel to provide easier navigation. aramid 221 (Figure 8-14) manufacture 208-209 (Figure 8-5) pitch 130 208-209 (Figure 8-5) 591 polyacrylonitrile (PAN) 208 591 properties 212-218 (Table 8-4.) properties 206-207 (Tables 8-2. . Figures 8-10. 8-3) 585 roving 246 593 shin guard 154 types 205 glass transition temperature (Tg) 26 274 586 Global Hawk 568-569 571 glycidyl group 85-86 (Figure 4-1) 587 glycol 49 55-56 (Figure 3-4) 80 (Table 3-3) 587 golf-club shaft 451 gouge 490 (Figure 20-4) government regulation 509-513 Grand Challenge 572-573 graphite fiber 207-218 (Figures 8-5 to 8-11. 14-2) 527 (Figure 22-2) 579 comparison to filament winding 527 (Figure 22-2) die cutting 391 584 nesting 391-392 (Figure 14-1) 590 reciprocating knife 391 semi-automated cutting 393 (Figure 14-2) steel rule blanking 391 595 ultrasonic vibratory cutting 391 597 hardener 92 94-97 (Figures 4-11 to 4-13. 17-2) 447 (Figure 17-3) 587 helicopter fuselage 538-539 (Figure 22-4) hemp fiber 229 Hercules. . 7 heterocyclic 138 587 hexamethylene tetramine (hexa) 125 587 high-impact damage 481 This page has been reformatted by Knovel to provide easier navigation. Inc.Index Terms Links Grubb catalyst 501 H halogen 38-39 55 587 hand lay-up 390-393 (Figures 14-1. Table 4-4) 101 112-113 587 harness weave 249-250 (Figure 9-3) 587 hat stiffener 358 587 hazardous air pollutant 506 508 587 health monitoring 329 heat 73-74 capacity 131 587 distortion temperature (HDT) 27 45 90 (Table 4-2) 587 stresses 313 helical windings 437-439 (Figures 17-1. Table 5-1) 356 365 591 polyimides 136-139 (Figure 5-12) polyurethanes 142-146 (Figure 5-15) 356 365 silicones 146-151 (Figure 5-16) 365 515 vinyl esters 115-122 (Figures 5-1 to 5-5) 505 597 high-temperature vulcanization (HTV) 101 587 histograms 268-269 (Figure 10-2) history of composites 4-7 hockey stick 261-262 Hoechst 173 hole 490 (Figure 20-4) homopolymerization 96 587 hoop windings 437-439 (Figures 17-1. 6-2) 168-176 (Figures 6-2 to 6-5) 375-388 (Figures 13-1 to 13-3) high-performance thermosets 115-157 bismaleimide (BMI) 139-140 (Figure 5-13) carbon matrix 130-136 (Figures 5-10. 6-2) 375-388 (Figures 13-1 to 13-3) 579 587 high-performance thermoplastics 161-164 (Tables 6-1.Index Terms Links high-performance composites 85 161-164 (Tables 6-1. . 5-11. 17-2) 447 587 horizontal burn test 298 hybrid reinforcement 260-261 (Figure 9-6) 587 hydroforming 475 587 This page has been reformatted by Knovel to provide easier navigation. Table 5-2) cyanate esters 140-142 (Figure 5-14) dicyclopentadiene (DCPD) 57 151-153 (Figure 5-17) 584 open molding 375-388 (Figures 13-1 to 13-3) phenolics 122-130 (Figures 5-6 to 5-9. Index Terms Links I Illinois Institute of Technology Research Institute (IITRI) 280 imide-based epoxy 91 (Figure 4-9) impact strength 281 587 impact toughness 40 221 (Figure 8-14) 281-283 587 impregnation 135 455-457 587 income statement 525-526 (Figure 22-1) incremental forming 476-477 587 industrial composites 588 industrial products 552-553 industry structure 13-15 (Figure 1-3) infrared thermography 301 inhibitors 65 72-73 103 376 588 initiator 58 74 96-99 376 588 injection molding 465 (Table 19-1) 468-470 (Figure 19-3) in-plane deformation balanced laminate 323 325 in-plane orthotropic laminate 317 319 in-plane stiffness 315 in-situ reaction sintering 588 inspection 298-303 ® Intelimer 78-79 intelligent structure 329 491-495 588 Interface Theory 232 588 interfacial fracture 325 interlaminar cracking 326 (Figure 11-10) 588 interlaminar shear 317 interlaminar stresses 313 internal damping 285 This page has been reformatted by Knovel to provide easier navigation. . Index Terms Links International Organization for Standardization (ISO) 266 294 Interphase Theory 232-233 588 interply slip 477 intralaminar cracking 326 (Figure 11-10) 588 ion 179 588 ionic bond 180 588 Iosipescu (v-notch) testing 281 ISO 9000 267-268 588 iso resin 53 55 isocyanate 142 588 isogrid 588 isophthalic acid 53 588 isotropic structure 307 588 ® IsoTruss 559-561 (Figure 23-3) Izod test 166 282-283 (Figure 10-11) J J stiffener 358 588 Japanese Industrial Standards (JIS) 266 joint unmanned combat air system (J-UCAS) 571 joints 359-366 (Figures 12-6 to 12-9) jute fiber 229 K kaizen 272 ® Kapton 170 471 ® Kevlar 7 173 218-219 240-241 (Table 8-6) 333-340 (Figures 11-18 to 11-24) 562 570 kinking 477 (Figure 19-6) kitting 259 380 588 knit line 469-470 (Figure 19-3) 588 knitted fabric 251-252 (Figure 9-4) 588 knockout pins 408 588 This page has been reformatted by Knovel to provide easier navigation. . .Index Terms Links Kynar® 174 L laboratory experiments 17 (chapter 1) 45 (chapter 2) 80 (chapter 3) 112 (chapter 4) 155-156 (chapter 5) 176 (chapter 6) 194 (chapter 7) 242 (chapter 8) 262 (chapter 9) 304 (chapter 10) 346 (chapter 11) 373 (chapter 12) 387 (chapter 13) 405 (chapter 14) 415 (chapter 15) 434 (chapter 16) 451 (chapter 17) 460 (chapter 18) 479 (chapter 19) 503 (chapter 20) 523 (chapter 21) 539 (chapter 22) 577 (chapter 23) laissez faire 511 laminate 405-406 analysis 317-321 (Figure 11-6) asymmetric 342 (Figure 11-25) balance 323-325 (Figure 11-8) cracking 183-184 325-327 (Figures 11-10 to 11-12) 332 (Figure 11-16) 377 490 (Figure 20-4) 583 damping 285-287 327-329 (Figure 11-13) 356 583 delamination 327 (Figure 11-12) 490 (Figure 20-4) density 316 fiber-volume fraction 315 317 346-347 585 finite element analysis 320-321 first-ply failure 326 586 flexural behavior balanced 315 323 in-plane deformation balanced 323 325 in-plane orthotropic 317 319 in-plane stiffness 315 This page has been reformatted by Knovel to provide easier navigation. ) interlaminar shear 317 lay-up molding 378-381 (Figure 13-1) 405-406 455 (Figure 18-2) lay-up notation 321-324 (Figure 11-7. 11-17) 595 stitched 256-257 stress analysis 321 symmetry 323-325 (Figure 11-8) 342 (Figure 11-25) tensile strength 316 testing 353 355-356 (Figure 12-4) theory 313-315 (Figure 11-5) three-dimensional. Table 11-2) life cycle 329 528-529 longitudinal stiffness 316 open molding 375-388 (Figures 13-1 to 13-3) plate aspect ratio 327 Poisson’s ratio 316 properties 318 (Table 11-1) quasi-isotropic 314 Rule of Mixtures 315-317 shear modulus 316 sizing 310 (Figure 11-2) 594 specially orthotropic 325 spray-up molding 381-383 (Figure 13-2) stiffness 325 (Figure 11-9) 332-333 (Figures 11-16. anisotropic 319-320 transverse modulus 316 vibration 286-287 327-329 (Figure 11-13) 356 597 viscoelastic behavior 328 (Figure 11-13) void volume ratio 316 Landec Corporation 78 LARC-TPI 170 laser cutting/drilling 369 latent hardener 101 588 This page has been reformatted by Knovel to provide easier navigation. .Index Terms Links laminate (Cont. Tables 16-1 to 16-7) 589 advantages 417 419 (Table 16-1) centrifugal casting 153 432 581 comparison 421 (Table 16-2) 435 (Figure 16-6) This page has been reformatted by Knovel to provide easier navigation. Table 11-2) leadership 530 leaf spring 303 lean manufacturing 272 leno weave 249-250 (Figure 9-3) 589 life cycle 329 528-529 light RTM 422 589 lightweight ladder 478 limiting oxygen index (LOI) test 297 (Figure 10-16) Lindbergh. 14-2) 527 (Figure 22-2) prepreg 390-395 (Figures 14-1 to 14-3) 455 (Figure 18-2) 592 productivity 455 (Figure 18-2) reinforcements 379-380 592 resin 379-381 secondary bonding 381 593-594 vacuum bagging 395-398 (Figures 14-4. 14-5) wet-out 380-381 597 lay-up notation 321-324 (Figure 11-7. .Index Terms Links lay-up 259 344 (Figure 11-27) 380 421 (Table 16-2) 435 (Figure 16-6) 455 (Figure 18-2) 588-589 lay-up molding 378-381 (Figure 13-1) 405-406 automatic 393-395 (Figure 14-3) cost comparison 455 (Figure 18-2) curing 379-381 583 debulking 395 583 kitting 259 380 588 manual 390-393 (Figures 14-1. Charles 575 liquid crystal polymers 173 (Figure 6-5) liquid molding processes 417-436 (Figures 16-1 to 16-6. . Figure 16-6) 593 rubber-assisted RTM 423 TM SCRIMP 421 424 (Figure 16-3) TM SPRINT 423 structural reaction injection molding (SRIM) 153 420 thermal expansion RTM 423 thermoplastic composites 471-472 474-478 (Figures 19-4 to 19-6) vacuum-assisted injection 420 vacuum infusion processing 421-423 (Table 16-2) 433-434 (Table 16-7) load transfer 183 589 Lockheed Company 575 long fiber reinforcement 166 464 longitudinal direction 247 589 longitudinal stiffness 316 longitudinal windings 438-439 (Figure 17-2) 589 LOTUS system 449 low-impact damage 482-483 low-profile additive 69 This page has been reformatted by Knovel to provide easier navigation. 16-5. Table 16-3) 592 reaction injection molding (RIM) 420 465 (Table 19-1) resin characteristics 427 429-430 (Table 16-5) resin film infusion (RFI) 421 423 (Figure 16-2) 593 resin freeze/stallout 426 593 resin transfer molding (RTM) 153 417 420 422 433-434 (Table 16-7.) core and flow media materials 429-431 (Table 16-6) disadvantages 419 (Table 16-1) equipment 424-425 expansion RTM 423-424 fiber wash 422 585 molds 425 part design 431-432 preform 425-428 (Figures 16-4.Index Terms Links liquid molding processes (Cont. Table 8-5) 580 constructions 370-372 (Figure 12-10) core material 353-357 (Table 12-1. 15-2. . 14-2) 527 (Figure 22-2) Manufacturing Extension Partnership (MEP) 512 manufacturing safety data sheet (MSDS) 317 marine products 546-547 markets 10-13 (Table 1-6. 23-2) 561-573 (Table 23-3.Index Terms Links low-shrink system 69 104 589 M machine direction 247 589 machine lay-up 393-395 (Figure 14-3) 421 (Table 16-2) 435 (Figure 16-6) machining 367 magneto-strictive materials 494 maleic acid 52 589 maleic anhydride 52 589 managing technology 530 534-538 mandrel 437-438 (Figure 17-1) 439 444-445 589 manual lay-up 390-393 (Figures 14-1. Table 15-1) 474 589 material safety data sheet 99 material storage 513-514 523 material structure. Figure 23-5) 576-577 Martin Company 575 master model 384 589 mat 252-253 (Figure 9-5) matched-die molding 407-416 (Figures 15-1. Figure 1-2) 543-559 (Figures 23-1. Figure 12-4) damping 285-287 327-329 (Figure 11-13) 356 583 double composite 350 584 This page has been reformatted by Knovel to provide easier navigation. anisotropic 307 580 aramid fiber 218-226 (Figures 8-12 to 8-16. Table 12-1) 593 vibration 286-287 327-329 (Figure 11-13) 356 597 materials data sheet (MDS) 99 317 386 matrix 1-5 (Table 1-2) 19-46 (Tables 2-1. (Cont. Table 11-2) milled fibers 261 357 589-590 non-isotropic 307 orthogonal 590 orthotropic 307 590 polyimide 136-139 (Figure 5-12) pseudo-isotropic 307 592 sandwich 349-374 (Figures 12-1 to 12-11. 7-3) metallic bond 180-181 589 metals vs.) epoxy 85-91 (Figures 4-1 to 4-9. 12-7) mechanical property testing 275-276 (Table 10-1. . 4-2) graphite fiber 208-213 (Figures 8-6 to 8-9) isotropic 307 588 laminate sizing 310 (Figure 11-2) lay-up 344 (Figure 11-27) 588 lay-up notation 321-324 (Figure 11-7. Figures 7-2. composites 333-340 (Figures 11-18 to 11-24) metering zone 468 589 methyl methacrylate 78 508 microcracks 589 micro-indentation test 237 589 microwave testing 302 This page has been reformatted by Knovel to provide easier navigation. Figure 10-5) medical products 550-551 (Figure 23-1) melt-processible resin 170 589 melting point 25 (Figure 2-5) 589 melting zone 468 589 metal 589 metal matrix composites 188-194 (Table 7-2. 2-2) 288 (Table 10-2) 589 mechanical joints 359-362 (Figures 12-6.Index Terms Links material structure. Tables 4-1. Index Terms Links mil gage 377 589 Military Handbook Committee 266 military standard (MIL-STD) 294 milled fibers 261 357 589-590 milling 190 367 mixtures 78 508 modeling constructs 519 modified acrylics 365 modulus 279 590 moisture effects 289-291 (Table 10-3. Figure 10-15) molar mass 97 585 mold 383-386 (Figure 13-3) 401-404 (Table 14-1) assembly 409 (Figure 15-1) bumping/burping 125 413 580-581 clamshell 399 581-582 closure 408 egg-crate 385 584 flexible 149 heat 73-74 liquid molding 425 master model 384 589 materials 403-404 (Table 14-1) -making method 383-384 (Figure 13-3) part removal 385-386 pattern 384 591 plug 384 591 release agents 148 385 515 592 resin transfer molding (RTM) 425 593 seamless molding paste 385 593 This page has been reformatted by Knovel to provide easier navigation. . . 15-2. Table 15-1) 580 diallyl isophthalate 67 584 diallylphthalate 67 584 premix 68 592 ripening 70 593 sheet 68-69 (Figure 3-7) 408-412 (Figures 15-1 15-2. Table 15-1) 455 (Figure 18-2) 474 596 molding compounds 66-70 159 408-412 (Figure 15-2. Table 15-1) 590 alkyds 67 579 allylics 67-68 579 bulk 68 408-412 (Figures 15-1 15-2. 23-2) National Bureau of Standards 128 (Figure 5-8) 294 355-356 This page has been reformatted by Knovel to provide easier navigation. Table 15-1) 594 thermoplastic composites 159 unsaturated polyesters 67-70 159 viscosity 410-411 (Figure 15-2) 597 molecular weight 25 590 monofilaments 245 590 monomer 19-20 (Figure 2-1) 49 376 590 monomer additives 56-57 80 (Table 3-4) Morrison Molded Fiber Glass Company 459 ® Mylar 556 N NASA Langley Research Center 170 National Academy of Engineering 7 National Aeronautics and Space Administration (NASA) 266 280 492 553-559 (Tables 23-1.Index Terms Links molding 69-70 122 144 377 386 407-416 (Figures 15-1. reinforced materials 17-18 (Table 1-7) non-woven fabrics (mat) 252-253 (Figure 9-5) North American Aviation 575 Northrop Aircraft 575 ® Noryl 172 novolac 124 590 novolac-based epoxy 90 (Figure 4-6) 590 nucleophile 92 590 O offset-lap joint 359-360 (Figure 12-6) olefinic unsaturation 51 590 oligomer 19 78 466 508 590 one-step resin 124 590 open-hole compression test 484 (Figure 20-1) open-hole tensile test 279 590 This page has been reformatted by Knovel to provide easier navigation. .Index Terms Links National Institute of Standards and Technology (NIST) 266 294 355 459 512 natural fibers 228-230 neat resin 142 163 290 (Table 10-3) 379 590 neopentyl glycol 56 80 (Table 3-3) 590 nesting 391-392 (Figure 14-1) 590 net shape 258 590 neutral atoms 556 nitrides 228 nondestructive testing (NDT) 298-303 488-489 (Table 20-1) 590 non-isotropic structure 307 non-polymeric matrix composites 179-182 (Table 7-1) non-reinforced vs. advanced composites 389-406 (Figures 14-1 to 14-7. Table 14-1) 579 automatic lay-up 393-395 (Figure 14-3) cost comparison 455 (Figure 18-2) debulking 395 583 engineering composites 375-388 (Figures 13-1 to 13-3) 584-585 equipment 376-377 gel coat 55 375-378 586 high-performance thermosets 375-388 (Figures 13-1 to. 13-3) high volume 386 laminate 375-388 (Figures 13-1 to 13-3) lay-up 378-381 (Figure 13-1) 390-393 588-589 materials 376 386 molds 383-386 (Figure 13-3) operator 377 productivity 455 (Figure 18-2) quality control 386 roll wrapping 400-401 (Figure 14-6) 451 593 safety 386 spray-up 381-383 (Figure 13-2) 594 thermoplastic composites 375-388 (Figures 13-1 to.Index Terms Links open molding. . 14-5) veil 252 378 597 openness (fabric) 262-263 590 openness (weave) 249 operational decisions 529 590 This page has been reformatted by Knovel to provide easier navigation. 13-3) 471-472 474-478 (Figures 19-4 to 19-6) tooling 383-386 (Figure 13-3) trapped rubber molding 150 400 596 tub/shower units 386-387 tube rolling 400-401 (Figure 14-6) 596 vacuum bagging 395-398 (Figures 14-4. Index Terms Links optical holography 301 590 optical properties 39 organic materials 218-226 (Figures 8-12 to 8-16. Table 5-1) 356 365 591 piezo-electric devices 493 This page has been reformatted by Knovel to provide easier navigation. Table 8-5) 293 ortho resin 53 orthogonal stiffener 359 orthogonal structure 590 orthophthalic acid 53 590 orthophthalic anhydride 590 orthotropic structure 307 590 out-gassing 556 591 out time 254 591 Owens Corning Fiberglas Company 5 Owens-Illinois 203 oxirane group 85-86 (Figure 4-1) 591 oxygen quench 73 P Pareto chart 268 270 (Figure 10-3) part design. complexity 413-414 damage tolerance 486-487 for resin infusion 431-432 thickness 75 particle 261 part removal 385-386 pattern (mold) 384 591 payoff 437-438 (Figure 17-1) 591 peel ply 395 591 peel test 281 (Figure 10-9) pendant attachment 33 591 permanent set 283 591 permeability 38 591 peroxides 66 phenolics 122-130 (Figures 5-6 to 5-9. . .Index Terms Links pigments 42-43 76 591 ping-pong paddle 434-435 Pioneer 569-570 pitch 130 208-209 (Figure 8-5) 591 plain weave 249-250 (Figure 9-3) 591 plasma 556 plastic 19-21 591 plate aspect ratio 327 plug (mold) 384 591 Pointer 570 Poisson’s ratio 316 polar winding machine 446 polarity 37 591 pole piece 448 591 polyacrylonitrile (PAN) 208 591 polyamide-imide (PAI) 170 591 polybenzimidazole (PBI) 171 591 polybutylene terephthalate (PBT) 467 polycarbonate (PC) 467 polycrystalline 180 polyester 47-83 (Figure 3-5) 57-65 104 591 597 polyester thermoset (PT) 591 polyetheretherketone (PEEK) 171-172 (Figure 6-3) polyetherimide (PEI) 170 174-175 591 polyhexafluoropropylene (PHFP) 174 polyimides 136-139 (Figure 5-12) polymer 19-21 (Figure 2-1) 181 591 This page has been reformatted by Knovel to provide easier navigation. 2-8. 2-2) 579 amorphous 25 36 (Figure 2-8) 181 579 antioxidant 38 580 aromatic 31-41 (Figures 2-7. 4-4) 118-120 (Figure 5-4) 124-125 138 141 583 crystalline regions 36 (Figure 2-8) 180-181 583 curing 28 48 62-63 65-66 70-76 (Figures 3-8. Table 3-1) 91-104 (Figures 4-10 to 4-15. . Table 4-3. 2-8. Tables 2-1. 4-13) 98 (Figure 4-14) 100-104 111-112 124-125 159-161 274-275 283 362 376 379 383 398-399 457 463-480 (Figures 19-1 to 19-6.) additives 42-43 56-57 65-66 69 76 80 (Table 3-4) 151 443 579 aliphatic 31-41 (Figures 2-7. 2-2) 580 attraction 25 580 bismaleimide (BMI) 139-140 (Figure 5-13) characteristics 24-25 chemical polarity 37 581 colorant 43 582 crosslinking 28 31 48 57-65 (Figure 3-6. Table 19-1) 501-502 (Figure 20-8) 583 This page has been reformatted by Knovel to provide easier navigation.Index Terms Links polymer (Cont. 3-9) 80-82 94-96 (Figures 4-12. Tables 2-1. Index Terms Links polymer (Cont. . Tables 4-1 to 4-5) fillers 42-43 73 103 586 fire resistance 38 fluoropolymers 173-174 freezing point 25 glass transition temperature (Tg) 26 274 586 heat distortion temperature (HDT) 27 45 90 (Table 4-2) 587 imide group 138 (Figure 5-12) impact toughness 40 221 (Figure 8-14) 281-283 587 inhibitors 65 72-73 103 376 588 liquid crystal 173 (Figure 6-5) melting point 25 (Figure 2-5) 589 modifying existing 506-507 molecule 19-20 (Figure 2-1) 591-592 naming 24 new 507-508 This page has been reformatted by Knovel to provide easier navigation.) cyanate esters 140-142 (Figure 5-14) decomposition point 26-27 (Figure 2-4) 583 definition 19 591 dicyclopentadiene (DCPD) 57 151-153 (Figure 5-17) 584 diluent 62-65 (Table 3-1) 73 99 108 159-161 dyes 43 584 electrical properties 39 environmental effects 35 (Table 2-2) epoxies 85-113 (Figures 4-1 to 4-15. Table 19-1) 596 This page has been reformatted by Knovel to provide easier navigation.Index Terms Links polymer (Cont. . 4-2) surface agent 42-43 thermal properties 35-37 thermoplastics 8 27-31 (Figure 2-6) 160 463-480 (Figures 19-1 to 19-6.) oligomer 19 78 466 508 590 optical properties 39 pendant attachment 33 591 permeability/resistance to gases 38 591 pigments 42-43 76 591 polyurethanes 142-146 (Figure 5-15) 356 365 pot life 65 102-103 111-112 429 441-442 456 592 pre-polymer 20 592 properties and control 50-51 377-378 secondary bond 25 381 593-594 semi-crystalline 36 (Figure 2-8) 172 181 594 shape memory 444 594 shelf life 65 102-103 111-112 594 silicones 146-151 (Figure 5-16) 365 solidification 25 solvent 37-38 62 99 staining agents 38 structure 85-91 (Figures 4-1 to 4-9. Tables 4-1. 4-4) 118-120 (Figure 5-4) 124-125 138 141 583 dicyclopentadiene (DCPD) 57 151-153 (Figure 5-17) 584 difunctional 49 584 exotherm 62 70-71 (Figure 3-8) 585 freezing point 25 gel permeation chromatography 51 586 homopolymerization 96 587 This page has been reformatted by Knovel to provide easier navigation.) thermosets 8 27-31 (Figures 2-5.Index Terms Links polymer (Cont. . Table 4-3. 2-6) 176 596 toughening 43-44 (Table 2-3) 484-485 596 ultraviolet (UV) resistance 39 108-109 290 597 uncrosslinked 181 vinyl ester 115-122 (Figures 5-1 to 5-5) 505 597 viscosity 31 (Figure 2-6) 41-43 410 597 polymerization 21-27 48-51 (Figure 3-1) 592 acid number 51 579 addition 21-22 (Figure 2-2) 579 attraction 25 580 bridge molecules 62 580 co-monomer 62-65 582 condensation 23-24 (Figure 2-3) 582 co-reactants 62-65 (Table 3-1) 73 159-161 582 crosslinking 28 31 48-49 57-65 (Figure 3-6. Table 3-1) 91-104 (Figures 4-10 to 4-15. ) melting 25 (Figure 2-5) molecule 19-20 (Figure 2-1) oligomer 19 78 466 508 590 pendant attachment 33 591 processing viscosity 51 592 secondary bond 25 381 593-594 solidification 25 temperature (Tg) 26 274 thermoset polyesters 48-51 unsaturated polyesters 48-51 (Figure 3-1) polyol 142 592 polyphenylene sulfide (PPS) 172 (Figure 6-4) polysulfone (PSU) 172-173 (Figure 6-4) polytetrafluoroethylene (PTFE) 174 polyurethanes 142-146 (Figure 5-15) 356 365 polyvinyl alcohol 385 positive-type mold closure 408 592 post-curing 75 104 457 592 post-processing 366-370 pot life 65 102-103 429 592 CrossCheckTM device 111-112 for filament winding resins 441-442 for pultrusion resins 456 monitoring 111-112 of prepregs 103 potting 67 592 powder coating 466 (Figure 19-1) powder metallurgy 192 Predator 568-569 571 This page has been reformatted by Knovel to provide easier navigation. .Index Terms Links polymerization (Cont. . Table 16-3) 592 preform compression molding 412-415 premix 68 592 pre-polymer 20 592 prepreg 14 103 109-111 159 253-255 473 592 compression molding 413 582 curing 399 583 drape 255 584 epoxy 103 109-111 390-395 (Figures 14-1 to 14-3) filament winding 442-443 585-586 lay-up 390-395 (Figures 14-1 to 14-3) 455 (Figure 18-2) 588-589 properties 255 tack 255 tow 473 592 596 unidirectional tape 254 597 winding 442-443 press capacity 408 pressure intensifier 397 592 primary damage 481 process design 519-520 process flow 517-518 (Figure 21-1) process simulation 518-519 processing viscosity 51 592 ProcessSimulator® 519 production flow 135 (Figure 5-11) ® ProModel 519 promoters 65-66 74 101 376 592 This page has been reformatted by Knovel to provide easier navigation.Index Terms Links preform 258-260 425-428 (Figures 16-4 16-5. 8-3) 251-252 shear 280-281 (Figures 10-8. 8-3) 251-252 flexural 280-281 (Figure 10-8) 586 gel coat 377-378 586 glass fiber 206-207 (Tables 8-2. 8-21) 242-243 276-279 (Figures 10-5 to 10-7) 304-305 312 316 335 (Figure 11-19) 337 595 This page has been reformatted by Knovel to provide easier navigation. 8-11) impact toughness 281-283 laminate 318 (Table 11-1) mechanical 275-276 (Table 10-1. metals 333-340 (Figures 11-18 to 11-24) control 50-51 377-378 dicyclopentadiene (DCPD) 153 584 electrical 39 engineering thermoplastics 165 (Table 6-3) 168 (Table. 8-3) graphite fiber 212-218 (Table 8-4. . Figures 8-10.Index Terms Links properties. bismaleimide 140 carbon/graphite fibers 212 carbon matrix materials 136-137 (Table 5-3) 581 composites vs. 10-9) silicone 146-148 tensile 215 (Figure 8-10) 222 (Figure 8-15) 235 (Figure. 6-4) epoxy 104-109 (Table 4-5) fiber 199-200 (Table 8-1) 206-207 (Tables 8-2. Figure 10-5) metal matrix composites 188-191 (Table 7-2) molding compound 412 (Table 15-1) 590 optical 39 optimization 70-76 polyimide 139 polyurethane 144-146 prepreg 255 reinforcement 199-200 (Table 8-1) 206-207 (Tables. 8-2. Index Terms Links properties. 10-2. .) thermal 35-37 215-217 (Figure 8-11) 287-289 (Table. (Cont. Figure 10-14) thermoset polyesters 105 (Table 4-5) unsaturated polyesters 105 (Table 4-5) viscosity 70 597 propylene glycol 56 80 (Table 3-3) 592 prosthesis 550 (Figure 23-1) prototype 533 pseudo-isotropic structure 307 592 pultruded beam 459-460 (Figure 18-3) pultruded part analysis 460-461 pultrusion 153 453-461 (Figures 18-1 to 18-3) 473-474 pyrolysis 135 592 Q QS 9000 267-268 quality 265-306 benchmarking 270 capability analysis 268 cause-and-effect diagram 270 correlation plot 268-269 (Figure 10-1) design of experiments (DOE) 268-269 documentation/certification 267 failure mode and effects analysis (FMEA) 270 foreign manufacturing 521-522 (Table 21-1) function deployment 270 308 histograms 268-269 (Figure 10-2) history 265-266 improvement 270-271 inspection 298-303 ISO 9000 267-268 588 kaizen 272 lean manufacturing 272 This page has been reformatted by Knovel to provide easier navigation. ) management 272 open molding 386 Pareto chart 268 270 (Figure 10-3) principles 266-272 (Figures 10-1 to 10-3) QS 9000 267-268 six sigma 270 space structures 555 statistical process control 268 299 system integration 271-272 Taguchi loss function 271 testing 272-306 (Figures 10-4 to 10-16. Tables 10-1 to 10-4) total quality management (TQM) 271 quartz 205 592 quasi-isotropic laminate 314 quench 73 592 questions 17 (chapter 1) 46 (chapter 2) 82 (chapter 3) 113 (chapter 4) 156 (chapter 5) 176 (chapter 6) 194 (chapter 7) 242 (chapter 8) 263 (chapter 9) 305 (chapter 10) 347 (chapter 11) 373 (chapter 12) 387 (chapter 13) 406 (chapter 14) 416 (chapter 15) 435 (chapter 16) 451 (chapter 17) 461 (chapter 18) 480 (chapter 19) 504 (chapter 20) 523 (chapter 21) 540 (chapter 22) 577 (chapter 23) R radar cross-sections 8 (Table 1-3) ® Radel 173 radiant panel test 294 radiation 556 radiography 301 592 rapid curing 154 This page has been reformatted by Knovel to provide easier navigation. .Index Terms Links quality (Cont. Index Terms Links Raven 570 raw material testing 272-273 rayon 208 592 reaction injection molding (RIM) 420 465 (Table 19-1) reactive diluent 61 63 (Table 3-1) 505 592 reciprocating knife 391 recycling 516 reduced emissions 76-78 505-509 reinforced vs. . Table 8-1) fiber-matrix interactions 230-239 (Figures 8-18 to 8-25) filament 204-205 (Figure 8-4) 245-247 (Figure 9-1. non-reinforced materials 17-18 (Table 1-7) reinforcement 1-5 (Table 1-2) 197-243 592 alumina 228 and curing 73 aramid 218-226 (Figures 8-12 to 8-16. Table 8-4) 581 comprehensive stitching 257 582 damage effects 481 485 487 diamond 193 directed fiber preforming 259 fiber characteristics 197-203 (Figures 8-1 to 8-3. Table 9-1) 585 filament winding 440-441 585 hybrid 260-261 (Figure 9-6) 587 knitted fabric 251-252 (Figure 9-4) 588 lay-up molding 379-380 long fiber 166 464 This page has been reformatted by Knovel to provide easier navigation. Table 8-5) 580 aspect ratio 197 246 580 basalt 228 boron 226-228 (Figure 8-17) braided 256 261-262 580 carbon/graphite 207-218 (Figures 8-5 to 8-11. Table 16-3) 454-455 592 prepreg 14 103 109-111 159 253-255 390-395 (Figures 14-1 to 14-3) 473 592 properties 199-200 (Table 8-1) 206-207 (Tables 8-2. 8-3) 595 stitched laminates 256-257 strand 245-247 (Figure 9-1. Figures 8-2.Index Terms Links reinforcement (Cont. Table 9-1) 593 shapes 184 (Figure 7-1) silicon carbide 226-228 (Figure 8-17) size 198 (Figure 8-1) specialty 228 spinning 245 594 staple fiber 246 440 595 stiffness 199-203 (Table 8-1. Figures 8-2. .) manufacture 203-205 (Figure 8-4) mat 252-253 (Figure 9-5) milled fibers 261 357 589-590 monofilaments 245 590 nitrides 228 non-woven fabrics (mat) 252-253 (Figure 9-5) out time 254 591 particle 261 preform 258-260 425-428 (Figures 16-4. 8-3) 206 (Table 8-2) three-dimensional laminates 257-258 319-320 This page has been reformatted by Knovel to provide easier navigation. Table 9-1) 595 strength 199-203 (Table 8-1. 16-5. 8-3) 251-252 role of 5 (Table 1-2) roving 245-247 (Figure 9-1. Index Terms Links reinforcement (Cont. . Table 9-1) 597 z-fiber construction 267 598 release agent 148 385 515 592 release film 395 592-593 remotely guided vehicle (RGV) 573 remotely piloted vehicle (RPV) 573 repair 495-504 (Figures 20-6 to 20-9) resin 19-21 53 55 593 bath 456 characteristics for resin infusion 427 429-430 (Table 16-5) curing 28 48 63 65-66 70-76 (Figures 3-8. 9-3) woven roving 252 597 yarn 245-247 (Figure 9-1. Table 9-1) 473 592 596 unidirectional tape 254 597 veil 252 378 597 whiskers 163 184 246 261 597 woven fabric 247-250 (Figures 9-2.) tow 208 245-247 (Figure 9-1. 3-9) 398-399 457 583 dam 398 damage tolerant 484-486 defined 19-21 593 filament winding 441-442 585-586 film infusion 421 423 (Figure 16-2) 593 freeze/stallout 426 593 -hardener ratio 112 This page has been reformatted by Knovel to provide easier navigation. ) impregnation 135 455-457 587 injection 456-457 lay-up molding 379 melt-processible 170 589 migration 477 (Figure 19-6) neat 142 163 290 (Table 10-3) 379 590 one-step 124 590 ratio 112-113 reduced emissions 76-78 505-509 shrinkage 69 104 silicones 146-151 (Figure 5-16) 365 515 starving 398 593 storage 513-514 523 toughened 43-44 (Table 2-3) 484-486 transfer molding 153 417 420 422 425 433-435 (Table 16-7. Figure 16-6) 593 two step 125 597 viscosity 31 (Figure 2-6) 41-43 410 464 597 resin infusion technologies 417-436 (Figures 16-1 to 16-6. Tables 16-1 to 16-7) 593 advantages 417 419(Table 16-1) centrifugal casting 153 432 581 comparison to other processes 421 (Table 16-2) 435 (Figure 16-6) core materials 429-431 (Table 16-6) disadvantages 419 (Table 16-1) equipment 424-425 expansion RTM 423-424 This page has been reformatted by Knovel to provide easier navigation.Index Terms Links resin (Cont. . .) fiber wash 422 585 flow media materials 429-431 (Table 16-6) molds 425 part design 431-432 preform 425-428 (Figures 16-4. Figure 16-6) 593 rubber-assisted RTM 423 SCRIMPTM 421 424 (Figure 16-3) TM SPRINT 423 structural reaction injection molding (SRIM) 153 420 thermal expansion RTM 423 thermoplastic composites 472 vacuum-assisted injection 420 vacuum infusion processing 421-423 (Table 16-2) 433-434 (Table 16-7) resistance to gases 38 resistance to solvents and water 37 155-156 356 resole (phenolic) 124 593 ripening 70 593 roll forming 478 roll wrapping 400-401 (Figure 14-6) 451 593 rolling drum peel test 281-282 (Figure 10-10) room-temperature vulcanization (RTV) 101 593 roving 245-247 (Figure 9-1. Table 9-1) 593 rubber 147 This page has been reformatted by Knovel to provide easier navigation.Index Terms Links resin infusion technologies (Cont.16-5. Table 16-3) 592 reaction injection molding (RIM) 420 465 (Table 19-1) resin characteristics 427 429-430 (Table 16-5) resin film infusion (RFI) 421 423 (Figure 16-2) 593 resin freeze/stallout 426 593 resin transfer molding (RTM) 153 417 420 422 425 433-435 (Table 16-7. Index Terms Links rubber-assisted RTM 423 Rule of Mixtures 315-317 runners 469 593 ® Ryton 173 S sacrificial skirt 488 (Figure 20-3) sag point 474 593 sanding 367 sandwich structures 349-374 (Figures 12-1 to 12-11. Table 12-1) 593 components 350 (Figure 12-1) construction 370-372 (Figure 12-10) core material 353-357 (Table 12-1. costs 350-352 (Figures 12-2. Figure 12-4) 373 core thickness 351 (Figure 12-2) double composite 350 584 edges 358 (Figure 12-5) 398 failure modes 355 (Figure 12-4) manufacture 357-358 (Figure 12-5) milled fibers 261 357 589-590 performance vs. . 12-3) use conditions 356-357 z-direction stiffeners 357-359 satin weave 249-250 (Figure 9-3) 593 saturated diacid 53-54 (Figure 3-3) sawing 367 scarf 593 scarf joint 364 (Figure 12-8) scarf repair 497-498 (Figure 20-6) 503-504 scratch 490 (Figure 20-4) TM SCRIMP 421 424 (Figure 16-3) sea of electrons 180 593 sealant 396 593 seamless molding paste 385 593 secondary bond 25 381 593-594 This page has been reformatted by Knovel to provide easier navigation. Table 15-1) 594 shelf life 65 102-103 111-112 594 short beam shear test 235-236 (Figure 8-22) 281 shower/tub units 386-387 shrinkage 69 104 silane 146 silicon 146 silicon carbide fibers 226-228 (Figure 8-17) siliconates 148 silicones 146-151 (Figure 5-16) 365 515 silkworm silk fiber 229 simulation 484 (Figure 20-1) 516-521 (Figure 21-1) This page has been reformatted by Knovel to provide easier navigation.10-9) shearography 301-302 594 shear-out failure 360-361 (Figure 12-7) sheet molding compound 68-69 (Figure 3-7) 408-412 (Figures 15-1 15-2.Index Terms Links Seeman’s composite resin infusion molding process (SCRIMPTM) 421 424 (Figure 16-3) selective stitching 257 594 self-healing composites 501-503 (Figure 20-9) selvage 248 (Figure 9-2) 594 semi-automated cutting 393 (Figure 14-2) semi-crystalline polymer 36 (Figure 2-8) 172 181 594 sensors/actuators 494 service life testing 291-292 S-glass 205 594 Shadow 569-570 shape memory alloys 494 shape memory polymer 444 594 shear. . force 276 (Figure 10-5) modulus 316 336 (Figure 11-20) strength 105-106 339 (Figure 11-23) testing 280-281 (Figures 10-8. Table 5-1) 356 365 591 This page has been reformatted by Knovel to provide easier navigation. Table 5-2) cyanate esters 140-142 (Figure 5-14) dicyclopentadiene (DCPD) 57 151-153 (Figure 5-17) 584 phenolics 122-130 (Figures 5-6 to 5-9. 23-2) specialized monomer additives 56-57 80 (Table 3-4) specially orthotropic laminate 325 specialty fibers 228 specialty thermosets 115-157 bismaleimide (BMI) 139-140 (Figure 5-13) carbon matrix 130-136 (Figures 5-10. .Index Terms Links single-lap joint 364 (Figure 12-8) sintering 170 187 588 594 six sigma 270 sizing 230 239 310 (Figure 11-2) 594 ski construction 372-373 (Figure 12-11) smart structures 329 491-495 594 smoke 109 128 (Figure 5-8) smoke chamber test 294 Society for the Advancement of Materials and Process Engineering (SAMPE) 266 513 577 Society of Manufacturing Engineers (SME) 513 Society of the Plastics Industry (SPI) 266 solidification 25 Solvay 170 173 solvent 62-65 (Table 3-1) 73 99 108 159-161 solvent effects 37-38 289-291 (Table 10-3. 5-11. Figure 10-15) 356 solvent resistance 108 155-156 space structures 553-559 (Tables 23-1. Figures 8-2.Index Terms Links specialty thermosets (Cont. Figures 8-2.) polyimides 136-139 (Figure 5-12) polyurethanes 142-146 (Figure 5-15) 356 365 silicones 146-151 (Figure 5-16) 365 515 vinyl esters 115-122 (Figures 5-1 to 5-5) 505 597 specific modulus 594 specific stiffness 190 (Figure 7-2) 199-203 (Table 8-1. 8-3) 289 (Figure 10-14) 594 Spectra® 218 562 Spectrum civilian aircraft 565-566 (Figure 23-4) spider silk fiber 229 spin casting 594 spinneret 219 594 spinning 245 594 sports products 549-550 spray-up 594 spray-up molding 153 381-383 (Figure 13-2) 455 (Figure 18-2) 594 TM SPRINT 423 sprue 469 594 stabilization 131 208-210 (Figure 8-6) 594-595 staining agents 38 staple fibers 246 440 595 Starship 450 statistical process control 268 299 stealth technology 8 (Table 1-3) steel rule blanking 391 595 stepped-lap joint 364 (Figure 12-8) This page has been reformatted by Knovel to provide easier navigation. 8-3) 594 specific strength 190 (Figure 7-2) 199-203 (Table 8-1. . Table 9-1) 595 strategic decisions 530-531 595 strategic mapping 595 strength 106 199-203 (Table 8-1. 8-3) 279 315-316 325 (Figure 11-9) 332-333 (Figures 11-16. adaptive 329 anisotropic 307 580 aramid fiber 218-226 (Figures 8-12 to 8-16. 11-4) 321 595 stress-coupled activated damping (SCAD) 287 stretch forming 474 595 Strongwell 459 structural decisions 530 595 structural reaction injection molding (SRIM) 153 420 structural repair 495-504 (Figures 20-6 to 20-9) structure. Table 8-5) 580 bismaleimide (BMI) 139-140 (Figure 5-13) constructions 370-372 (Figure 12-10) core material 353-357 (Table 12-1.Index Terms Links stepped repair 497-498 (Figure 20-7) 595 steric interaction 131 595 stiffness 106 199-203 (Table 8-1. Figure 12-4) damping 285-287 327-329 (Figure 11-13) 356 583 dicyclopentadiene (DCPD) 152 (Figure 5-17) 584 double composite 350 584 This page has been reformatted by Knovel to provide easier navigation. Figures 8-2. . 11-17) 595 stitched fabric 595 stitched laminates 256-257 stoichiometric ratio 97 595 straight-lap joint 359-360 (Figure 12-6) strain 278 595 strands 245-247 (Figure 9-1. Figures 8-2. 8-3) 206 (Table 8-2) Stress 278 311-313 (Figures 11-3. Tables 4-1. 4-2) graphite fiber 208-213 (Figures 8-6 to 8-9) health monitoring 329 isotropic 307 588 laminate sizing 310 (Figure 11-2) lay-up 259 344 (Figure 11-27) 380 421 (Table 16-2) 435 (Figure 16-6) 455 (Figure 18-2) 588-589 lay-up notation 321-324 (Figure 11-7. 11-17) 595 vibration 327-329 (Figure 11-13) 356 597 styrene 73 emissions 76-78 505-509 government regulation 509-513 hazardous air pollutant 506 508 587 other monomer substitution 508 reactive diluent 61 63 (Table 3-1) 505 592 reducing content 506-509 suppressants 509 This page has been reformatted by Knovel to provide easier navigation. Table 11-2) milled fibers 261 357 589-590 non-isotropic 307 orthogonal 590 orthotropic 307 590 polyimide 138 polyurethanes 142-144 (Figure 5-15) pseudo-isotropic 307 592 sandwich 349-374 (Figures 12-1 to 12-11. (Cont.Index Terms Links structure. Table 12-1) 593 silicones 146 smart 329 491-495 594 stiffness 332-333 (Figures 11-16.) epoxy 85-91 (Figures 4-1 to 4-9. . . force 276 (Figure 10-5) modulus 215 (Figure 8-10) 335 (Figure 11-19) properties 595 property testing 276-279 (Figure 10-5 to 10-7) 304-305 strength 215 (Figure 8-10) 222 (Figure 8-15) 242-243 316 337 (Figure 11-21) stresses 312 tension failure 361 (Figure 12-7) terephthalic acid (tere) 55 595 testing. accelerated 291 (Figure 10-15) active damping 287 aero-elasticity 287 aging/service life 291-292 Barcol hardness 274 This page has been reformatted by Knovel to provide easier navigation.Index Terms Links Suppliers of Advanced Composite Materials Association (SACMA) 266 suppressants 509 surface agent 42-43 surface free energy 233-234 (Figure 8-19) 595 surface tension 233 595 surfactant 43 595 symmetric laminate 323-325 (Figure 11-8) 342 (Figure 11-25) system simulation 519 T tack 255 tack test 274 595 Taguchi loss function 271 tap test 491 595 tape-laying machine 394 (Figure 14-3) ® Teflon 171 174 556 Ten Cate Advance Composites 174 tensile. Index Terms Links testing. Figure 10-16) flexural properties 280-281 (Figure 10-8) 586 glass transition temperature (Tg) 274 586 horizontal burn 298 impact/toughness properties 281-283 587 internal damping 285 Iosipescu (v-notch) 281 Izod 166 282-283 (Figure 10-11) laminate 353 355-356 (Figure 12-4) limiting oxygen index (LOI) 297 (Figure 10-16) mechanical 275-287 (Figures 10-5 to 10-13. . Table 10-1) micro-indentation 237 589 microwave 302 This page has been reformatted by Knovel to provide easier navigation. Figure 10-14) 582 compression after impact 582 cone calorimeter 294 constrained layer damping 287 core material 353 355-356 (Figure 12-4) creep 283-285 (Figure 10-12) 583 curing 274-275 583 damping 286-287 583 dart drop impact 583 differential scanning calorimetry (DSC) 274 584 drape 274 584 dynamic mechanical analysis (DMA) 275 eddy current 302 584 elastic deformation 278 584 elongation 278 584 embedded single filament 236-237 (Figure 8-23) falling dart 282 fatigue 285-286 (Figure 10-13) 585 fiber pullout test 234-235 (Figure 8-20) flammability 292-298 (Table 10-4. (Cont.) burst 279 581 carbon matrix materials 131-133 (Table 5-2) Charpy 282-283 (Figure 10-11) coefficient of thermal expansion (CTE) 288-289 (Table 10-2. Index Terms Links testing. Figure 10-14) thermo-gravimetric analysis (TGA) 275 thermo-mechanical analysis (TMA) 275 time-temperature transposition 292 596 traverse tensile 235 (Figure 8-21) ultrasonic 299-300 597 vertical burn 297-298 vibration 286-287 597 This page has been reformatted by Knovel to provide easier navigation. Figure 10-15) space structures 555 stiffness 279 595 strain 278 595 strategy 272 stress 278 595 stress-coupled activated damping (SCAD) 287 tack 274 595 tap 491 595 tensile properties 276-279 (Figure 10-5 to 10-7) 595 thermal 287-289 (Table 10-2. 10-9) short beam shear 235-236 (Figure 8-22) 281 smoke chamber 294 solvent effects 289-291 (Table 10-3. . (Cont.) modulus 279 590 moisture effects 289-291 (Table 10-3. Figure 10-15) nondestructive 298-303 488-489 (Table 20-1) 590 open-hole 279 484 (Figure 20-1) 590 peel 281 (Figure 10-9) permanent set 283 591 properties 272 quality 272-306 (Figures 10-4 to 10-16. Tables 10-1. to 10-4) radiant panel 294 raw material 272-273 rolling drum peel 281-282 (Figure 10-10) service life 291-292 shear properties 280-281 (Figures 10-8. Figure 10-14) thermofolding 476-477 (Figure 19-5) 596 thermoforming 479 thermography 301 596 thermo-gravimetric analysis (TGA) 275 thermo-mechanical analysis (TMA) 275 thermoplastic 8 27-31 (Figure 2-6) 160 463-480 (Figures 19-1 to 19-6. Tables 6-1 to 6-3) advanced 164 advanced thermoset 161-162 (Table 6-1) advantages 463 co-mingling 466 582 compression molding 474 582 co-weaving 466 (Figure 19-1) 583 cure 159-161 463-480 (Figures 19-1 to 19-6. . Table 19-1) 596 thermoplastic composites 159-177 (Figures 6-1 to 6-5. (Cont.) viscosity 273 (Figure 10-4) 597 v-notch 281 void content 275 Young’s modulus 279 597 tetrabromophthalic anhydride 55 595 tetra-functional epoxy 89 (Figure 4-5) tetraglycidyldiaminodiphenylmethane (TGDDM) 89 (Figure 4-5) tetraglycidylmethylenedianiline (TGMDA) 89 (Figure 4-5) Texaco 226 textile fibers 595-596 thermal. Table 19-1) 583 disadvantages 463 This page has been reformatted by Knovel to provide easier navigation. 11-4 Figure 11-25) testing 287-289 (Table 10-2. expansion RTM 423 properties 35-37 215-217 (Figure 8-11) stability 107-108 130-131 stresses 340-342 (Tables 11-3.Index Terms Links testing. 8-2. Table 19-1) pultrusion 473-474 resin viscosity 464 roll forming 478 sag point 474 593 short fiber 467-470 (Figures 19-2. 19-3) This page has been reformatted by Knovel to provide easier navigation. 8-3) 585 filament winding 399-400 437-452 (Figures 17-1 to 17-3) 472-473 585-586 film stacking 466 (Figure 19-1) flexible die forming 475-476 586 flow forming 474-475 586 high-performance 161-164 (Tables 6-1.) engineering 7-10 (Tables 1-4. . Figure 6-1) 584-585 engineering thermoset 161-162 (Table 6-1) 375-388 (Figures 13-1 to 13-3) extrusion 467-468 (Figure 19-2) fiberglass reinforced plastics 161 203 206-207 (Tables. 6-2) 168-176 (Figures 6-2 to 6-5) 375-388 (Figures 13-1 to 13-3) hydroforming 475 587 incremental forming 476-477 587 injection molding 465 (Table 19-1) 468-470 (Figure 19-3) lightweight ladder 478 molding 471-472 474-478 (Figures 19-4 to 19-6) neat resins 163 590 oligomers 466 590 open molding 375-388 (Figures 13-1 to 13-3) 471-472 474-478 (Figures 19-4 to 19-6) powder coating 466 (Figure 19-1) prepreg tow 473 592 processing 463-480 (Figures 19-1 to 19-6. 1-5) 161-168 (Tables 6-3 6-4.Index Terms Links thermoplastic composites (Cont. . thermosets 176 transition molding 477-478 596 wet-out 464-467 (Table 19-1. 2-6) 176 596 thermoset engineering composites 596 thermoset polyesters 47-83 596 additives 56-57 69 72 (Figure 3-9) 76 80 (Table 3-4) 579 adipic acid 55 579 alkyd 50 67 579 bisphenol A 56 80 (Table 3-3) 580 chlorendic acid 55 581 cis isomer 52 581 crosslinking 57-65 (Figure 3-6. Figure 19-1) 597 thermoplastic polyimides 169-171 (Figure 6-2) thermoset 8 27-31 (Figures 2-5. Table 3-1) 583 curing 65-66 72 (Figure 3-9) 78-79 583 diacid 49 51-55 (Figures 3-2.) stretch forming 474 595 thermofolding 476-477 (Figure 19-5) 596 thermoforming 479 toughness vs. 3-3) 79 (Table 3-2) 583 dicyclopentadiene (DCPD) 57 151-153 (Figure 5-17) 584 diethylene glycol 56 80 (Table 3-3) 584 diluent 61-65 (Table 3-1) 73 99 108 159-161 505 esters 50 585 This page has been reformatted by Knovel to provide easier navigation.Index Terms Links thermoplastic composites (Cont. Index Terms Links thermoset polyesters (Cont.) ethylene glycol 55 80 (Table 3-3) 585 fumaric acid 52 586 glycol 49 55-56 (Figure 3-4) 80 (Table 3-3) 587 maleic acid 52 589 maleic anhydride 52 589 molding compounds 66-70 159 408-412 (Figure 15-2. . Table 15-1) 590 monomers 49 376 590 neopentyl glycol 56 80 (Table 3-3) 590 polymerization 48-51 592 pot life 65 592 properties 105 (Table 4-5) propylene glycol 56 80 (Table 3-3) 592 recipes 81 (Table 3-5) shelf life 65 594 smoke 128 (Figure 5-8) solvent 62 terephthalic acid (tere) 55 595 tetrabromophthalic anhydride 55 595 trans-isomer 52 596 TM THERM-X process 151 Thinner 70 596 thixotrope 43 70 596 three-dimensional laminates 257-258 319-320 time-temperature transposition 292 596 tooling 110-111 383-386 (Figure 13-3) 401-404 (Table 14-1) ® Torlon 170 This page has been reformatted by Knovel to provide easier navigation. .Index Terms Links torque tube 341-345 (Figures 11-26. Table 9-1) 473 592 596 transformation toughening 183 596 trans-isomer 52 596 transition molding 477-478 596 trans-laminar reinforced composite 267 596 transportation products 543-545 transverse direction 248 596 transverse modulus 316 trapped rubber molding 150 400 596 traverse tensile test 235 (Figure 8-21) triaxial weaving 251 (Figure 9-4) 596 tri-functional epoxy 89 (Figure 4-4) truck component 414-415 tub/shower units 386-387 tube rolling 400-401 (Figure 14-6) 596 TWA 575 twill weave 249-250 (Figure 9-3) 597 This page has been reformatted by Knovel to provide easier navigation. 11-27) torsional force 276 (Figure 10-5) total quality management (TQM) 271 toughened epoxy 92 (Figure 4-10) 106-107 596 toughened resin 43-44 (Table 2-3) 484-486 toughener 596 toughening agent 40 596 toughness 40 281 596 ceramic matrix composites 183-184 epoxy 106-107 equilibrium 281 585 impact 281 587 testing 281-283 vinyl esters 122 tow 208 245-247 (Figure 9-1. Index Terms Links two-step resin 125 597 U Udel® 172 ® Ultem 170 174 ultra-high-molecular-weight polyethylene (UHMWPE) fibers 223-226 597 ultrasonic testing 299-300 597 ultrasonic vibratory cutting 391 597 ultraviolet (UV) 597 inhibitors 39 588 597 light 74 108-109 290 597 resistance 39 108-109 290 597 uncrosslinked polymer 181 uncured reactants 99 Underwriters Laboratory (UL) 266 unidirectional tape 254 597 United Technology 226 University of Florida 570 University of Illinois Urbana-Champaign 501 unmanned combat air system (UCAV) 571 unmanned vehicles 567-573 (Figure 23-5) unsaturated diacid 51-55 (Figure 3-2) unsaturated polyesters 47-83 (Figure 3-5) 597 additives 56-57 69 72 (Figure 3-9) 76 80 (Table 3-4) 505 579 adipic acid 55 579 alkyd 50 67 579 bisphenol A 56 80 (Table 3-3) 580 chlorendic acid 55 581 This page has been reformatted by Knovel to provide easier navigation. . 3-3) 79 (Table 3-2) 583 dicyclopentadiene (DCPD) 57 151-153 (Figure 5-17) 584 diethylene glycol 56 80 (Table 3-3) 584 diluent 62 esters 50 585 ethylene glycol 55 80 (Table 3-3) fumaric acid 52 586 glycol 49 55-56 (Figure 3-4) 80 (Table 3-3) 587 maleic acid 52 589 maleic anhydride 52 589 molding compounds 67-70 159 590 monomers 49 590 neopentyl glycol 56 80 (Table 3-3) 590 polymerization 48-51 (Figure 3-1) 592 pot life 65 592 properties 105 (Table 4-5) propylene glycol 56 80 (Table 3-3) 592 recipes 81 (Table 3-5) shelf life 65 594 smoke 128 (Figure 5-8) solvent 62 terephthalic acid (tere) 55 595 tetrabromophthalic anhydride 55 595 trans-isomer 52 596 This page has been reformatted by Knovel to provide easier navigation.Index Terms Links unsaturated polyesters (Cont. .) cis isomer 52 581 crosslinking 57-65 (Figure 3-6. Table 3-1) 583 curing 65-66 72 (Figure 3-9) 78-79 583 diacid 49 51-55 (Figures 3-2. 14-5) vacuum infusion processing 421-423 (Table 16-2) 433-434 (Table 16-7) Value Jet 174-175 Van der Waals bond 212-213 ® Vectra 173 226 veil 252 378 597 vertical burn test 297-298 Verton 465 ® Vespel 170 vibration 286-287 327-329 (Figure 11-13) 356 597 vinyl esters 115-122 (Figures 5-1 to 5-5) 505 597 viscoelastic behavior 328 (Figure 11-13) viscosity 31 (Figure 2-6) 41-43 597 control 42-43 epoxy 100 gel permeation chromatography 51 586 molding compounds 410-411 (Figure 15-2) of common materials 429 (Table 16-4) optimization 70 processing 51 resin 31 (Figure 2-6) 41-43 410 464 597 This page has been reformatted by Knovel to provide easier navigation. Department of Defense 572 use conditions 356-357 V vacuum-assisted injection molding 420 vacuum bag 150 397-398 (Figure 14-5) 597 vacuum bagging 395-398 (Figures 14-4.S. .Index Terms Links unsaturation 51 597 Urban Challenge 572 U. absorption 108 120-121 (Figure 5-5) 356 and curing 75 effects 37-38 155-156 356 waterjet cutting 368-369 wax/film 75 395 weaves 249-251 (Figures 9-3. 9-4) 597 weft 248 597 weft knitting 251 (Figure 9-4) weld line 469-470 (Figure 19-3) 597 wet-out 41-42 45 100 380-381 383 442 464-467 (Table 19-1.Index Terms Links viscosity (Cont. Figure 19-1) 597 whiskers 163 184 246 261 597 winding patterns 438-439 (Figure 17-2) 447-448 (Figure 17-3) This page has been reformatted by Knovel to provide easier navigation.) testing 273 (Figure 10-4) thinner 70 596 thixotrope 43 70 596 visual inspection 302-303 v-notch testing 281 void content 275 395 void volume ratio 316 volatiles 100 W Warp 597 warp clock 322 (Figure 11-7) warp direction 247 (Figure 9-2) waste disposal 516 water. . . M. Kellogg Company 7 wood fiber 229 woof 248 597 work of adhesion 233 597 woven fabric 247-250 (Figures 9-2.Index Terms Links W. 9-3) woven roving 252 597 Wright brothers 564 573-575 X Xydar® 173 Y yarn 245-247 (Figure 9-1. Table 9-1) 597 Young’s modulus 279 597 Z z-direction stiffeners 357-359 z-fiber construction 267 598 This page has been reformatted by Knovel to provide easier navigation.