structural composite materials (#05287g) f.c. …€¦ · chapter 11 machining and assembly 307...

StructuralCompositeMaterials

F.C. Campbell

ASM International®

Materials Park, Ohio 44073-0002www.asminternational.org

Structural Composite Materials (#05287G) F.C. Campbell

Copyright © 2010, ASM International® All rights reserved. www.asminternational.org

Copyright © 2010by

ASM International®

All rights reserved

No part of this book may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the writ-ten permission of the copyright owner.

First printing, November 2010

Great care is taken in the compilation and production of this book, but it should be made clear that NO WARRANTIES, EXPRESS OR IMPLIED, INCLUDING, WITHOUT LIMITATION, WAR-RANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, ARE GIVEN IN CONNECTION WITH THIS PUBLICATION. Although this information is believed to be accurate by ASM, ASM cannot guarantee that favorable results will be obtained from the use of this publication alone. This publication is intended for use by persons having technical skill, at their sole discretion and risk. Since the conditions of product or material use are outside of ASM’s control, ASM assumes no liability or obligation in connection with any use of this information. No claim of any kind, whether as to products or information in this publication, and whether or not based on negligence, shall be greater in amount than the purchase price of this product or publica-tion in respect of which damages are claimed. THE REMEDY HEREBY PROVIDED SHALL BE THE EXCLUSIVE AND SOLE REMEDY OF BUYER, AND IN NO EVENT SHALL EITHER PARTY BE LIABLE FOR SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES WHETHER OR NOT CAUSED BY OR RESULTING FROM THE NEGLIGENCE OF SUCH PARTY. As with any material, evaluation of the material under end-use conditions prior to speci-fication is essential. Therefore, specific testing under actual conditions is recommended.

Nothing contained in this book shall be construed as a grant of any right of manufacture, sale, use, or reproduction, in connection with any method, process, apparatus, product, composition, or system, whether or not covered by letters patent, copyright, or trademark, and nothing contained in this book shall be construed as a defense against any alleged infringement of letters patent, copyright, or trademark, or as a defense against liability for such infringement.

Comments, criticisms, and suggestions are invited, and should be forwarded to ASM International.

Prepared under the direction of the ASM International Technical Book Committee (2009–2010), Michael J. Pfeifer, Chair.

ASM International staff who worked on this project include Scott Henry, Senior Manager, Content Development & Publishing; Steven R. Lampman, Content Developer; Eileen De Guire, Senior Content Developer; Ed Kubel, Technical Editor; Ann Britton, Editorial Assistant; Bonnie Sanders, Manager of Production; Madrid Tramble, Senior Production Coordinator; Diane Whitelaw, Pro-duction Coordinator; and Patricia Conti, Production Coordinator.

Library of Congress Control Number: 2010937090 ISBN-13: 978-1-61503-037-8

ISBN-10: 0-61503-037-9SAN: 204-7586

ASM International®

Materials Park, OH 44073-0002www.asminternational.org

Printed in the United States of America



This book is dedicated to my youngest granddaughter, Matilda, who is so little yet is so brave and strong.



Contents

Preface xiAbout the Author xv

Chapter 1 Introduction to Composite Materials 11.1 Isotropic, Anisotropic, and Orthotropic Materials 41.2 Laminates 71.3 Fundamental Property Relationships 81.4 Composites versus Metallics 101.5 Advantages and Disadvantages of Composite Materials 141.6 Applications 18

Chapter 2 Fibers and Reinforcements 312.1 Fiber Terminology 312.2 Strength of Fibers 322.3 Glass Fibers 332.4 Aramid Fibers 392.5 Ultra-High Molecular Weight Polyethylene Fibers 412.6 Carbon and Graphite Fibers 422.7 Woven Fabrics 492.8 Reinforced Mats 522.9 Chopped Fibers 522.10 Prepreg Manufacturing 52

Chapter 3 Matrix Resin Systems 633.1 Thermosets 643.2 Polyester Resins 653.3 Epoxy Resins 673.4 Bismaleimide Resins 703.5 Cyanate Ester Resins 713.6 Polyimide Resins 723.7 Phenolic Resins 743.8 Toughened Thermosets 753.9 Thermoplastics 81

3.9.1 Thermoplastic Composite Matrices 823.9.2 Thermoplastic Composite Product Forms 87

3.10 Quality Control Methods 903.10.1 Chemical Testing 913.10.2 Rheological Testing 923.10.3 Thermal Analysis 943.10.4 Glass Transition Temperature 97

3.11 Summary 99



vi / Contents

Chapter 4 Fabrication Tooling 1014.1 General Considerations 1014.2 Thermal Management 1044.3 Tool Fabrication 111

Chapter 5 Thermoset Composite Fabrication Processes 1195.0 Lay-up Processes 1195.1 Wet Lay-Up 1195.2 Prepreg Lay-Up 122

5.2.1 Manual Lay-Up 1235.2.2 Flat Ply Collation and Vacuum Forming 1245.2.3 Roll or Tape Wrapping 1255.2.4 Automated Methods 1255.2.5 Vacuum Bagging 1315.2.6 Curing 133

5.3 Low-Temperature Curing/Vacuum Bag Systems 1375.4 Filament Winding 1415.5 Liquid Molding 146

5.5.1 Preform Technology 1485.5.2 Resin Injection 1625.5.3 Priform Process 1645.5.4 RTM Curing 1665.5.5 RTM Tooling 1675.5.6 RTM Defects 1705.5.7 Vacuum-Assisted Resin Transfer Molding 172

5.6 Resin Film Infusion 1745.7 Pultrusion 175

Chapter 6 Thermoplastic Composite Fabrication Processes 1836.1 Thermoplastic Consolidation 1836.2 Thermoforming 1866.3 Thermoplastic Joining 192

Chapter 7 Processing Science of Polymer Matrix Composites 2017.1 Kinetics 2027.2 Viscosity 2067.3 Heat Transfer 2077.4 Resin Flow 209

7.4.1 Hydrostatic Resin Pressure Studies 2147.4.2 Resin Flow Modeling 217

7.5 Voids and Porosity 2197.5.1 Condensation-Curing Systems 226

7.6 Residual Curing Stresses 2267.7 Cure Monitoring Techniques 232

Chapter 8 Adhesive Bonding 2358.1 Theory of Adhesion 2358.2 Surface Preparation 235

8.2.1 Composite Surface Preparation 2378.2.2 Aluminum Surface Preparation 2398.2.3 Titanium Surface Preparation 2428.2.4 Aluminum and Titanium Primers 243

8.3 Epoxy Adhesives 2448.3.1 Two-Part Room-Temperature Curing Epoxy Liquid and Paste

Adhesives 2458.3.2 Epoxy Film Adhesives 247



Contents / vii

8.4 Bonding Procedures 2488.4.1 Prekitting of Adherends 2498.4.2 Prefit Evaluation 2498.4.3 Adhesive Application 2508.4.4 Bondline Thickness Control 2518.4.5 Bonding 252

Chapter 9 Sandwich and Integral Cocured Structure 2559.1 Sandwich Structure 2559.2 Honeycomb Core Sandwich Structure 255

9.2.1 Honeycomb Processing 2649.2.2 Cocured Honeycomb Assemblies 267

9.3 Foam Cores 2719.3.1 Syntactic Core 272

9.4 Integrally Cocured Unitized Structure 273

Chapter 10 Discontinuous-Fiber Composites 28510.1 Fiber Length and Orientation 28510.2 Discontinuous-Fiber Composite Mechanics 28710.3 Fabrication Methods 28910.4 Spray-Up 28910.5 Compression Molding 290

10.5.1 Thermoset Compression Molding 29010.5.2 Thermoplastic Compression Molding 295

10.6 Structural Reaction Injection Molding 296 10.7 Injection Molding 297

10.7.1 Thermoplastic Injection Molding 29810.7.2 Thermoset Injection Molding 304

Chapter 11 Machining and Assembly 30711.1 Trimming and Machining Operations 30711.2 General Assembly Considerations 30911.3 Hole Preparation 311

11.3.1 Manual Drilling 31111.3.2 Power Feed Drilling 31411.3.3 Automated Drilling 31511.3.4 Drill Bit Geometries 31611.3.5 Reaming 31711.3.6 Countersinking 317

11.4 Fastener Selection and Installation 31811.4.1 Special Considerations for Composite Joints 32011.4.2 Solid Rivets 32211.4.3 Pin and Collar Fasteners 32311.4.4 Bolts and Nuts 32311.4.5 Blind Fasteners 32611.4.6 Interference-Fit Fasteners 328

11.5 Sealing and Painting 329

Chapter 12 Nondestructive Inspection 33312.1 Visual Inspection 33312.2 Ultrasonic Inspection 33512.3 Portable Equipment 34112.4 Radiographic Inspection 34212.5 Thermographic Inspection 345



viii / Contents

Chapter 13 Mechanical Property Test Methods 35113.1 Specimen Preparation 35113.2 Flexure Testing 35213.3 Tension Testing 35313.4 Compression Testing 35413.5 Shear Testing 35613.6 Open-Hole Tension and Compression 35713.7 Bolt Bearing Strength 35813.8 Flatwise Tension Test 36113.9 Compression Strength After Impact 36113.10 Fracture Toughness Testing 36213.11 Adhesive Shear Testing 36413.12 Adhesive Peel Testing 36413.13 Honeycomb Flatwise Tension 36713.14 Environmental Conditioning 36713.15 Data Analysis 369

Chapter 14 Composite Mechanical Properties 37314.1 Glass Fiber Composites 37414.2 Aramid Fiber Composites 37614.3 Carbon Fiber Composites 37914.4 Fatigue 38314.5 Delaminations and Impact Resistance 38814.6 Effects of Defects 393

14.6.1 Voids and Porosity 39314.6.2 Fiber Distortion 39714.6.3 Fastener Hole Defects 398

Chapter 15 Environmental Degradation 40115.1 Moisture Absorption 40115.2 Fluids 41115.3 Ultraviolet Radiation and Erosion 41115.4 Lightning Strikes 41215.5 Thermo-Oxidative Stability 41515.6 Heat Damage 41615.7 Flammability 417

Chapter 16 Structural Analysis 42116.1 Lamina or Ply Fundamentals 42116.2 Stress-Strain Relationships for a Single Ply Loaded Parallel to the

Material Axes (θ = 0° or 90°) 42516.3 Stress-Strain Relationships for a Single Ply Loaded Off-Axis to the

Material Axes (θ ≠ 0° or 90°) 42716.4 Laminates and Laminate Notations 42916.5 Laminate Analysis—Classical Lamination Theory 43016.6 Interlaminar Free-Edge Stresses 43916.7 Failure Theories 44016.8 Concluding Remarks 446

Chapter 17 Structural Joints—Bolted and Bonded 44917.1 Mechanically Fastened Joints 44917.2 Mechanically Fastened Joint Analysis 45017.3 Single-Hole Bolted Composite Joints 45517.4 Multirow Bolted Composite Joints 45917.5 Adhesive Bonding 463



Contents / ix

17.6 Bonded Joint Design 46417.7 Adhesive Shear Stress-Strain 46617.8 Bonded Joint Design Considerations 47517.9 Stepped-Lap Adhesively Bonded Joints 47917.10 Bonded-Bolted Joints 481

Chapter 18 Design and Certification Considerations 48918.1 Material Selection 48918.2 Fiber Selection 49018.3 Product Form Selection 491

18.3.1 Discontinuous-Fiber Product Forms 49218.3.2 Continuous-Fiber Product Forms 493

18.4 Matrix Selection 49418.5 Fabrication Process Selection 496

18.5.1 Discontinuous-Fiber Processes 49618.5.2 Continuous-Fiber Processes 497

18.6 Trade Studies 49818.7 Building Block Approach 49918.8 Design Allowables 50118.9 Design Guidelines 50318.10 Damage Tolerance Considerations 50818.11 Environmental Sensitivity Considerations 512

Chapter 19 Repair 51719.1 Fill Repairs 51719.2 Injection Repairs 51719.3 Bolted Repairs 52019.4 Bonded Repairs 52319.5 Metallic Details and Metal-Bonded Assemblies 533

Chapter 20 Metal Matrix Composites 53720.1 Aluminum Matrix Composites 54020.2 Discontinuous Composite Processing Methods 54220.3 Stir Casting 54220.4 Slurry Casting—Compocasting 54420.5 Liquid Metal Infiltration 545

20.5.1 Squeeze Casting 54520.5.2 Pressure Infiltration Casting 54520.5.3 Pressureless Infiltration 546

20.6 Spray Deposition 54620.7 Powder Metallurgy Methods 54820.8 Secondary Processing of Discontinuous MMCs 54920.9 Continuous-Fiber Aluminum MMCs 55020.10 Continuous-Fiber Reinforced Titanium Matrix Composites 55420.11 Continuous-Fiber TMC Processing Methods 55720.12 TMC Consolidation Procedures 56020.13 Secondary Fabrication of TMCs 56220.14 Particle-Reinforced TMCs 56620.15 Fiber Metal Laminates 567

Chapter 21 Ceramic Matrix Composites 57321.1 Reinforcements 57521.2 Matrix Materials 57821.3 Interfacial Coatings 58021.4 Fiber Architectures 580



x / Contents

21.5 Fabrication Methods 58121.6 Powder Processing 58121.7 Slurry Infiltration and Consolidation 58321.8 Polymer Infiltration and Pyrolysis (PIP) 584

21.8.1 Space Shuttle C-C Process 58521.8.2 Conventional PIP Processes 58721.8.3 Sol-Gel Infiltration 588

21.9 Chemical Vapor Infiltration (CVI) 58921.10 Directed Metal Oxidation (DMO) 59221.11 Liquid Silicon Infiltration (LSI) 594

Appendix A Metric Conversion Factors 597Index 599



Preface

Composite materials are pervasive throughout our world and include both natural and man-made composites. For example, in nature, wood is a composite consisting of wood fibers (cellulose) bound together by a matrix of lignin. Composite materials have been used by mankind for thousands of years; many of the sun-dried mud brick buildings of the earliest known civilization in Mesopotamia at Sumer were reinforced with straw as early as 4900 b.c. However, with the advent of high-strength man-made fibers and the tremendous advances in polymer chemistry during the twentieth century, in many in-stances composite materials now can be made that offer advantages comparable to those of competing materials. The advantages of these advanced composites are many, includ-ing lighter weight, the ability to tailor composites for optimum strength and stiffness, improved fatigue life, corrosion resistance, and, with good design practice, reduced assembly costs due to fewer detail parts and fasteners. The specific strength (strength/density) and specific modulus (modulus/density) of high-strength fiber-reinforced com-posites, especially those with carbon fibers, are higher than those of comparable metal alloys. This translates into greater weight savings, resulting in improved performance, greater payloads, longer ranges (for vehicles), and fuel savings.

This book is intended primarily for technical personnel who want to learn more about modern composite materials. It would be useful to designers, structural engineers, ma-terials and process engineers, manufacturing engineers, and production personnel in-volved with composites.

The book deals with all aspects of advanced composite materials: what they are, where they are used, how they are made, their properties, how they are designed and analyzed, and how they perform in service. It covers continuous- and discontinuous- fiber composites fabricated from polymer, metal, and ceramic matrices, with an empha-sis on continuous-fiber polymer matrix composites. The book covers composite materi-als at the introductory to intermediate level. Throughout the book, practical aspects are emphasized more than theory. Because I spent 38 years in the industry, the information covers the current state-of-the-art in composite materials.

The book starts with an overview of composite materials (Chapter 1) and how highly anisotropic composites differ from isotropic materials, such as metals. Some of the important advantages and disadvantages of composites are discussed. Chapter 1 wraps up with some of the applications for advanced composites. Chapter 2 examines the reinforcements and their product forms, with an emphasis on glass, aramid, and carbon fibers. Chapter 3 covers the main thermosetting and thermoplastic resin sys-tems. Thermoset resin systems include polyesters, vinyl esters, epoxies, bisma-leimides, cynate esters, polyimides, and phenolics. Thermoplastic composite matrices include polyetheretherketone, polyetherketoneketone, polyetherimide, and polypro-pylene. The principles of thermoset resin toughening are also presented, along with an introduction to the physiochemical tests that are used to characterize resins and cured laminates.



xii / Preface

Chapters 4 through 11 describe the progression of composite fabrication steps. Chap-ter 4 covers the basics of cure tools. This is followed by a discussion of thermoset com-posite fabrication processes (Chapter 5). Important thermoset lay-up methods include wet lay-up, prepreg lay-up, automated tape laying, fiber placement, filament winding, and pultrusion. Vacuum bagging in preparation for cure is also discussed, along with the cure processes for both addition and condensation curing thermosets. Thermoset liquid molding covers preforming technology (weaving, knitting, stitching, and braiding) fol-lowed by the major liquid molding processes, namely, resin transfer molding, resin film infusion, and vacuum-assisted resin transfer molding.

In Chapter 6, thermoplastic composite consolidation is covered, along with the differ-ent methods of thermoforming thermoplastics. Finally, the joining processes that are unique to thermoplastic composites are discussed. After these processing fundamentals are fully described, Chapter 7 deals with some of the detailed processing issues unique to thermoset and thermoplastic composites. The concept of cure modeling is introduced along with the importance of both lay-up and cure variables, hydrostatic resin pressure, chemical composition, resin and prepreg, debulking, and caul plates. Residual cure stresses and exothermic reactions are also covered, followed by a brief description of in-process cure monitoring.

Adhesive bonding, sandwich, and integrally cocured structures are introduced in Chapters 8 and 9. The basics of adhesive bonding are covered, along with its advantages and disadvantages. The importance of joint design, surface preparation, and bonding procedures is discussed, along with honeycomb bonded assemblies, foam bonded as-semblies, and integrally cocured assemblies. Large, one-piece composite airframe struc-tures have demonstrated the potential for impressive reductions in part counts and as-sembly costs.

The properties and fabrication technology for discontinuous-fiber polymer matrix composites are addressed in Chapter 10, with an emphasis on spray-up, compression molding, structural reaction injection molding, and injection molding.

Assembly (Chapter 11) can represent a significant portion of the total manufacturing cost, as much as 50 percent of the total delivered cost. In this chapter, the emphasis is on mechanical joining, including the hole preparation procedures and fasteners used for structural assembly. Sealing and painting are also briefly discussed.

Chapters 12 through 15 cover the test methods and properties for composite materials. Important nondestructive test methods (Chapter 12) include visual, ultrasonics, radio-graphic, and thermographic inspection methods. Mechanical property test methods (Chapter 13) include tests for both composite materials and adhesive systems. In Chap-ter 14, the strength and stiffness for both discontinuous and continuous reinforced com-posites are compared. Chapter 15 covers the important topic of environmental degrada-tion, including moisture absorption, fluids exposure, ultraviolet radiation and erosion, lightning strikes, thermo-oxidative behavior, heat damage, and flammability.

Chapters 16 through 19 cover the analysis, design, and repair of composites. Struc-tural analysis (Chapter 16) starts with analysis at the lamina, or ply, level and then uses classical lamination theory to illustrate the analysis methods for more complex lami-nates. The concept of interlaminar free edge stresses is introduced. Four failure theo-ries are discussed: the maximum stress criterion, the maximum strain criterion, the Azzi-Tsai-Hill maximum work theory, and the Tsai-Wu failure criterion. The impor-tant topic of analysis of composite joints, both bolted and bonded, is covered in Chap-ter 17. Chapter 18 deals with composite design and certification considerations, includ-ing materials and process selection, design trade studies, the building block approach to certification, design allowables, and design guidelines. Considerations for handling damage tolerance and environmental issues are also discussed. Repair of composites (Chapter 19) includes fill repairs, injection repairs, bolted repairs, and bonded repairs.

Metal matrix composites (Chapter 20) offer a number of advantages compared to their base metals, such as higher specific strengths and moduli, higher elevated-temperature resistance, lower coefficients of thermal expansion, and, in some cases, better wear re-



Preface / xiii

sistance. On the downside, they are more expensive than their base metals and have lower toughness. Because of their high costs, commercial applications for metal matrix composites are limited. As with metal matrix composites, there are few commercial ap-plications for ceramic matrix composites (Chapter 21), also because of their high costs, as well as concerns for reliability. Carbon-carbon composites have been used in aero-space applications for thermal protection systems. However, metal and ceramic matrix composites remain an important material class, because they are considered enablers for future hypersonic flight vehicles.

The reader is cautioned that the data presented in this book are not design allow-ables. The reader should consult approved design manuals for statistically derived design allowables.

I would like to acknowledge the help and guidance of Ann Britton, Eileen De Guire, Steve Lampman, and Madrid Tramble, ASM International, and the staff at ASM for their valuable contributions. I would also like to thank my wife, Betty, for her continuing support.

F.C. CampbellSt. Louis, Missouri

July 2010



About the Author

F.C. Campbell’s 38-year career at The Boeing Company (retired 2007) was closely divided equally between engineering and manufacturing. He worked in the engineering laboratories, manufacturing research and development, as well as engineering on four production aircraft programs, and in production operations. At the time of his retire-ment, he was a Senior Technical Fellow in the field of structural materials and manufac-turing technology. He is knowledgeable about a large number of materials, fabrication, and assembly processes for airframe structural materials. Previously, he was director of manufacturing process improvement (1995–2000), and from 1987–1995, he was direc-tor of manufacturing research engineering. Earlier in his career, he worked in materials and process development with responsibility for composite related research and devel-opment programs. He has also worked on the F-15, F/A-18, AV-8B, and C-17 aircraft programs, conducted manufacturing research on composite and metallic materials, and worked as a laboratory engineer doing process development on both metal matrix and organic matrix composite materials.



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