care and repair of advanced composite

CARE AND REPAIR OF

ADVANCED COMPOSITES

SECOND EDITION

Also of interest from SAE:

Design of Durable, Repairable, andMaintainable Aircraft Composites

(Order No. AE-27)

For more information or to order a book, contact SAE at400 Commonwealth Drive, Warrendale, PA 15096-0001;

phone (724) 776-4970; fax (724) 776-0790;e-mail [email protected];

website http://store.sae.org.

CARE AND REPAIR OF

ADVANCED COMPOSITES

SECOND EDITION

Keith B. ArmstrongL. Graham BevanWilliam F. Cole II

Warrendale, Pa.

All rights reserved. No part of this publication 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 prior written permission of SAE.

For permission and licensing requests, contact:SAE Permissions400 Commonwealth DriveWarrendale, PA 15096-0001 USAE-mail: [email protected]: 724-772-4028Fax: 724-772-4891

Library of Congress Cataloging-in-Publication DataArmstrong, Keith B.

Care and repair of advanced composites / Keith B. Armstrong, L.Graham Bevan, William F. Cole II.--2nd ed.

p. cm.Includes bibliographical references and index.ISBN 0-7680-1062-41. Composite materials--Repairing. 2. Composite materials--

Bonding. 3. Airplanes--Materials. 4. Airframes--Maintenance and repair.I. Bevan, L. Graham. II. Cole, William F. III. Title.

TA418.9.C6A76 2005620.1'18'0288--dc22 2004065362

Cover photos (from top to bottom): Airbus A.340-600, Boeing 777, Airbus A.380, B-2 StealthBomber, and Lockheed-Martin Joint Strike Fighter.

SAE400 Commonwealth DriveWarrendale, PA 15096-0001 USAE-mail: [email protected]: 877-606-7323 (inside USA and Canada)

724-776-4970 (outside USA)Fax: 724-776-1615

Copyright © 2005 SAE InternationalISBN 0-7680-1062-4SAE Order No. R-336Printed in the United States of America.

The information contained herein is believed by the authors to be the best available at the timeof printing, but it is given without acceptance of liability, whether expressed or implied, for lossor damage attributable to reliance thereon. Users of this book should make their own assess-ments of its contents for their own conditions of use, and by reference to original manufactur-ers' repair documentation.

This book is dedicated to the members of the original International Air Transport Association(IATA) Task Force (1988–1991) set up to standardize composite repairs, for which the firstauthor acted as chairman, and to the members of the various Task Groups of the CommercialAircraft Composite Repair Committee (CACRC) and especially the Training Task Groupand its chairmen over several years: first Ed Herman of McDonnell-Douglas (now partof Boeing), followed by Rick Barrett of Continental Airlines, and then by Ralph Edwardsof Northwest Airlines. Work from the Design, NDI, and Repair Techniques Task Groups isincluded in this book and is gratefully acknowledged. We particularly wish to record thegreat debt we all owe to Henk Lodewijk of KLM. When the IATA Task Force completed itswork and produced IATA Document DOC:GEN:3043, it made several recommendations.Henk had the vision and enthusiasm to persuade three committees (ATA, IATA, and SAE)to combine to form the CACRC and to implement the recommendations of the IATA TaskForce. This book is one of the many products of that vision.

ACKNOWLEDGMENTS

The first author especially wishes to thank E.I. Du Pont de Nemours and Company for sup-port for attendance at the early Training Task Group Meetings of the Commercial AircraftComposite Repair Committee (CACRC) through the good offices and personal interest ofDr. Rene Pinzelli of its Geneva office and Ginger Gupton of Wilmington. Ginger is nowworking with her husband, Jim Gardiner, at his company, the Consolidated Yacht Corpora-tion in Miami. More recently, support from the Defence Evaluation and Research Agency(DERA), Farnborough (U.K.) (now the Defence Science and Technology Laboratory afterJuly 1, 2001), and British Aerospace Systems and Equipment Ltd. (now Chelton RadomesLtd.) allowed attendance at later meetings. Without their interest and support, neither thisbook nor the Composites and Metal Bonding Glossary (SAE AIR 4844) would have beenpossible.

Our thanks also are extended to Mike Hoke of Abaris Training Inc. for many of the diagramsand to Matt Waterson of Aerobond (U.K.) for the forms in Chapter 12. Dave Bunt of BritishAirways (BA) kindly reviewed the book and made many helpful comments. Ian Fidler ofBA supplied some diagrams. The first author also would like to thank BA for the 24 yearsof experience on which this book is based. Many companies have contributed photographsand diagrams, and we have individually acknowledged them.

Our thanks are extended to Chris Mekern for scanning and improving some of the drawingsand to Bert Groenewoud for arranging the text around them. The support of KLM by givingthem the time to do this is greatly appreciated. Because of a burglary at his home, Chris losthis computer and the disks for most of the work he had done; therefore, the majority of thescanning had to be redone by our local printer, Chris Bond, at very short notice.

We should also thank Philip Griggs, Ralph Edwards, and Patricia Morrison for their time inreviewing the book and in making valuable comments before the first edition was preparedfor printing.

Special thanks are due to Graham Bevan (now a co-author of this second edition) of Airbus(U.K.) Ltd. for reviewing the final product, helping to correct many small errors in the firstedition, and providing useful additions to make this second edition better than the original.Our combined thanks to Graham's Airbus (U.K.) Ltd. colleagues in the Customer Support,Test Laboratories, Materials & Processes, and Composite Wing departments at Airbus(U.K.) Ltd., Filton, for assistance and encouragement with our revisions. Graham wouldalso like to thank the management at Airbus (U.K.) Ltd. for its permission to enable him toco-author this book.

Finally, thanks are due to Bill Cole (another co-author of this second edition) for writingan additional new chapter (Chapter 17) to extend the scope of the book for repair designengineers.

TABLE OF CONTENTS

Foreword........ xxiii

Preface to the Second Edition xxv

Preface to the First Edition xxvii

Chapter 1 Introduction to Composites and Care of Composite Parts 11.1 Definition of Composites ........11.2 History of Composite Materials............... ......................21.3 Advantages and Disadvantages of Composites. .......................2

1.3.1 Advantages of Composites... .....21.3.2 Disadvantages of Composites............................. ...31.3.3 Advantages of Thermoset Resin Composites .........31.3.4 Disadvantages of Thermoset Resin Composites...........41.3.5 Advantages of Thermoplastic Resin Composites.........41.3.6 Disadvantages of Thermoplastic Resin Composites.....5

1.4 Applications of Composites to Modern Aircraft, Yachts,Cars, and Trains ...51.4.1 Early Aircraft Structures 51.4.2 Modern Aircraft Structures and Other

Applications ....61.5 Care of Composite Parts 7

1.5.1 Sources of Damage to Composite Parts 101.5.1.1 Physical or Chemical Damage...................101.5.1.2 Deterioration in Normal Service ...........12

1.5.2 Avoidance of Damage and Reduction ofDeterioration in Service ..........13

1.6 References........ ........16

Chapter 2 Materials ......172.1 Fiber Reinforcement... .....................................17

2.1.1 Comparison of Some High-Performance Fibersand Common Metals 17

2.1.2 Glass Fiber 192.1.2.1 Glass Manufacture... ........222.1.2.2 Glass Fiber Manufacture.. .....23

2.1.3 Carbon Fibers...... 252.1.3.1 Carbon Fiber Manufacture .252.1.3.2 Future Development ........................252.1.3.3 Further Details of Carbon

and Graphite Fibers......... .....262.1.4 Aramid Fibers 32

ix

CARE AND REPAIR OF ADVANCED COMPOSITES

2.1.5 Boron Fibers..... 342.1.6 Other New Fibers 34

2.2 Forms of Reinforcement ......372.2.1 Tapes... ..............372.2.2 Fabrics 38

2.2.2.1 Woven Fabric Weave Styles........ .382.2.2.2 Effect of Weave Style 422.2.2.3 Noncrimp Fabrics..... 432.2.2.4 Nonwoven Randomly Oriented Mats.... 432.2.2.5 Fiber and Fabric Glossary ...45

2.3 Fiber Sizing and Finish ...472.3.1 Glass Fiber Finishes ...472.3.2 Carbon Fiber Finishes ............502.3.3 Aramid Fiber Finishes 512.3.4 Sizing and Finish for New Types of Fibers

and Fabrics ...522.4 Matrix (Resin) Systems..... 52

2.4.1 Thermoplastic Resins ..522.4.2 Thermosetting Resins 532.4.3 Properties Required of Matrix Resins and

Adhesives 572.4.3.1 Physical and Chemical Properties 572.4.3.2 Mechanical Properties 592.4.3.3 Epoxy-Based Matrix Resins and

Adhesives for Aerospace Use. ...............592.4.4 Epoxy and Phenolic Pre-Pregs and Film

Adhesives—Curing Stages 612.4.5 Mixing and Mix Ratios for Epoxy Wet Resins 63

2.4.5.1 Weighing ....632.4.5.2 Mixing ........642.4.5.3 Definitions Related to Mixing and

Application. .....652.4.6 Polyester Resins ...66

2.5 Adhesives................... .. ....662.5.1 Liquid and Paste Adhesives ...662.5.2 Foaming Adhesives 682.5.3 Film Adhesives 692.5.4 Glue-Line Thickness Control .....712.5.5 In-Service Effects on Resin Systems ...........76

2.6 Core Materials.. ...762.6.1 Wood................. 792.6.2 Foam Core Materials.. ............80

2.6.2.1 Material Types 802.6.2.2 Foam Density 812.6.2.3 Advantages and Disadvantages ...81

2.6.3 Honeycomb Core Materials ............82

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TABLE OF CONTENTS

2.6.3.1 Honeycomb Material Types ......852.6.3.2 Cell Shapes 882.6.3.3 Honeycomb Densities and Cell Sizes ....88

2.6.4 Fluted Core ...902.6.5 Syntactic Core 90

2.7 Syntactic Foams and Potting Compounds... 902.7.1 Filler Materials for Potting Compounds, Resin

Systems, and Adhesives 922.7.2 Other Fillers 93

2.8 Protective Coatings ......932.8.1 Sealants 93

2.8.1.1 Old-Generation Thiokol Sealants. 962.8.1.2 New-Generation Polythioether

Sealants. 962.8.1.3 Silicone Sealants 972.8.1.4 Viton Rubber Sealants 98

2.8.2 Primers...... ...982.8.3 Finishes 992.8.4 Conductive Coatings 1012.8.5 Erosion-Resistant Coatings.. 1022.8.6 Other Protective Coatings 103

2.9 References 1042.10 Bibliography 106

Chapter 3 Handling and Storage 1073.1 Shipping and Receiving ...1073.2 Temperature Requirements 1073.3 Storage Practices 108

3.3.1 Temperature Requirements ..1083.3.1.1 Dry Fabrics 1083.3.1.2 Storage of Pre-Preg, Film, and Paste

Adhesives, Potting Compounds, andPrimers 108

3.3.1.3 Storage of Sealants for Aircraft Use 1093.3.1.4 Storage of Consumable Items for

Composite and Bonded MetalRepairs.... 110

3.3.2 Cleanliness and Damage Prevention 1103.3.3 Moisture Damage Prevention.............. 1123.3.4 Identification ..............1133.3.5 Release Notes and Approved Certificates 114

3.4 Shelf Life/Out Time 1163.5 Kitting.. .....1173.6 Recertification 1183.7 Care of Materials in the Hangar or Workshop 118

xi


Chapter 4 Manufacturing Techniques 1214.1 Filament Winding 1214.2 Lay-Up Methods for Fabrics and Tapes.. ......123

4.2.1 Hand Lay-Up (Wet and Pre-Preg Laminating).........1234.2.2 Automated Lay-Up 124

4.3 Pultrusion 1254.4 Resin Transfer Molding..... .......1264.5 Injection Molding... ....1284.6 Tow Placement... ..1304.7 Press Molding .................1304.8 Vacuum Bonding 1314.9 Autoclave Bonding. 1314.10 Oven Curing .......1354.11 References ...1364.12 Other Useful Reading......... 136

Chapter 5 Original Design Criteria.. .....1375.1 Principal, Primary, and Secondary Structures 137

5.1.1 Sources of Damage to Composite AirframeComponents 141

5.1.2 Consequences of Failure 1425.2 Types of Composite Structures 142

5.2.1 Monolithic Laminated Structures (SolidLaminates).............. 142

5.2.2 Sandwich Structures ..........1435.3 Ply Orientation ...149

5.3.1 Warp Clock. ........1495.3.2 Balance and Symmetry 1525.3.3 Nesting and Stacking .............153

5.4 Core Orientation ....1545.5 Operational Environment.. ....155

5.5.1 Temperature ...1555.5.2 Humidity. .......1565.5.3 Contaminants 1565.5.4 Erosion...... ....... ....1565.5.5 Thermal Stresses 1585.5.6 Hygrothermal Effects. ....1585.5.7 Fire Resistance ......158

5.6 Electrical Requirements ..1595.6.1 Galvanic Corrosion .............1595.6.2 Electromagnetic Interference..... 1635.6.3 Electrostatic Discharge 1635.6.4 Lightning Strike Energy Dispersion................... ..1645.6.5 Radar Transmissivity.. ...165

5.7 Mechanical Requirements.. 1665.7.1 Tensile and Flexural Strength ..166

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TABLE OF CONTENTS

5.7.2 Stiffness.............. ....1675.7.3 Fatigue .....1675.7.4 Impact Resistance (Damage Tolerance) 1695.7.5 Creep..... 170

5.8 Attachments/Joints 1715.8.1 Bonded Joints ..............1725.8.2 Mechanically Fastened/Riveted Joints 175

5.9 Other Design Requirements 1765.9.1 Aerodynamic Smoothness ..1765.9.2 Weight and Balance 177

5.10 References 177

Chapter 6 Safety and Environment ......1816.1 Introduction.. 1816.2 Workshop Conditions for Good Bonding ..............1846.3 Respirable Fibers and Dust .....186

6.3.1 Fiberglass 1866.3.2 Carbon and Graphite Fibers 1876.3.3 Aramid Fibers 1876.3.4 Sanding Dust ........187

6.4 Fumes and Vapors 1886.4.1 Resin Fumes 1886.4.2 Solvent Vapors ....1896.4.3 Sealant Vapors. 1906.4.4 Coatings 1906.4.5 Fuel... ..........1906.4.6 Acid Fumes and Splash 1906.4.7 Exposure Limits ...191

6.5 Skin Contact 1926.5.1 Fibers in Contact with the Skin 1926.5.2 Resins in Contact with the Skin ........................1926.5.3 Solvents in Contact with the Skin.... 1936.5.4 Selection of Suitable Gloves. 1936.5.5 Skin Creams for Personal Protection 194

6.6 Material Safety Data Sheets 1956.7 Exothermic Reactions .....1956.8 Waste Disposal ......1966.9 Safety Procedures 197

6.9.1 Emergency Action First-Aid Procedures 1976.9.2 General Safety Procedures. 1976.9.3 Personal Safety Precautions .....1986.9.4 Dermatitis 199

6.10 Action in the Event of a Chemical Spillage 2016.11 Explosion Risk 2026.12 Static Discharge and Fire Prevention ........202

6.12.1 Static Discharge Prevention.... ....202

xiii


6.12.2 Fire Prevention 2036.13 Safety Requirements for Electrical Appliances 2046.14 ISO Environmental Management Standards 2056.15 References 2066.16 Bibliography ...207

Chapter 7 Damage and Repair Assessment..... 2097.1 Visual Inspection 2107.2 Tap Test .2137.3 Ultrasonic Inspection ...2157.4 X-Ray Methods 2207.5 Eddy Current Inspection 2217.6 Thermography... .2227.7 Bond Testers 2237.8 Moisture Meters .2247.9 Interferometry/Shearography 2267.10 Damage Types 2267.11 Sources of Mechanical Damage... ..................2327.12 Damage Mapping 2337.13 Assessment of Damage Significance ........2337.14 References.. 239

Chapter 8 Source Documents ........2418.1 Revision Systems 2418.2 Effectivity 2428.3 Drawing Numbering Systems .......2428.4 Internal Documents ....2458.5 Material and Process Specifications ...........................2458.6 Original Equipment Manufacturer Documents 2478.7 Regulatory Documents. ..2488.8 Air Transport Association of America ATA 100 System............2498.9 Aircraft Maintenance Manual 2498.10 Component Maintenance Manual 2498.11 Overhaul Manual 2508.12 Illustrated Parts Catalog ......2508.13 Structural Repair Manual..... 2518.14 Engine Manual 252

Chapter 9 Structural Repair Manual (SRM) Repair Method Selection....... 2539.1 Component Identification ....2539.2 Damage Classification 254

9.2.1 Damage Terminology .2549.2.2 Critical Areas 2559.2.3 Allowable/Negligible Damage 2559.2.4 Repairable Damage ...2569.2.5 Overhaul or Replace 256

xiv

TABLE OF CONTENTS

9.2.6 Other Considerations..... 2579.3 Repair Methods 258

9.3.1 Speedtape 2599.3.2 Resin Sealing 2599.3.3 Potted Repairs 2599.3.4 Bolted Doublers (Metal Plates) and

Bonded Doublers (Composite Patches) 2599.3.5 Pre-Cured Doublers Versus Co-Cured Doublers 2609.3.6 Room-Temperature Wet Lay-Up ...2619.3.7 Elevated-Temperature Wet Lay-Up 2629.3.8 Pre-Preg Repairs 2629.3.9 Scarfed and Stepped Lap Repairs 2639.3.10 Composite Repairs to Metals ....265

9.4 References.. .266

Chapter 10 Repair Techniques.... 26710.1 Preparation. ...267

10.1.1 Paint Removal..... 27010.1.2 Disbonding Methods 270

10.1.2.1 Disbonding Adhesively BondedMetal Parts ...............270

10.1.2.2 Disbonding Composite Parts 27410.1.3 Damage Removal.... ..274

10.1.3.1 Damage Removal from Metal Parts ...27410.1.3.2 Removal of Skin and Doubler

Material 27610.1.3.3 Damage Removal from Composite

Parts .......27710.1.3.4 Removal of Core Material 27710.1.3.5 Removal of Surface Corrosion 278

10.1.4 Moisture and Contamination Removal ...............27910.1.5 Surface Preparation of Composites—Repair

Sanding and Ply Determination 28010.1.5.1 Abrading 28110.1.5.2 Taper Sanding/Scarfing 28110.1.5.3 Step Sanding and Cutting ...282

10.1.6 Water Break Test 28410.1.7 Metallic Surface Preparation ...285

10.2 Typical Repairs .28510.2.1 Edge Band Repairs.... 28510.2.2 Repair of Damage to Core and One Skin 28610.2.3 Repair of Damage to Core and Both Skins ..28610.2.4 Hybrid Repairs 28610.2.5 Blind Repairs 29110.2.6 Injected Repairs 29110.2.7 Solid Laminate Repairs.... ....295

xv


10.2.8 Potted Repairs ....29610.2.9 Metal-to-Metal Bonding 29610.2.10 Plastic Welding (Solvent or Heat)... 296

10.3 Adhesive Usage 29710.4 Bagging Materials, Release Films, Release Fabrics, Peel

Plies, Breather Cloths, Bleeder Cloths, Bleed-Out Fabrics,and Application Techniques 29710.4.1 Terminology 29810.4.2 Selection Criteria 30110.4.3 Surface Versus Envelope Bagging 30210.4.4 Pleating 30410.4.5 Bagging Sequence 30410.4.6 Vacuum Requirements and Principles... ...304

10.4.6.1 Vacuum Bonding 30510.4.6.2 Application of Vacuum Pressure to

Plates and Assemblies UsingNonperforated Honeycomb 306

10.4.6.3 Practical Techniques to EnsureAdequate Applied Vacuum Pressure toParts Under Repair ..........310

10.4.7 Caul Plate and Dam Usage.. 31410.4 8 Vertical Bleed Method 31610.4.9 Squeeze-Out (Edge Bleed-Out) Method........... ...31610.4.10 Zero-Bleed Method 31710.4.11 Ply Compaction and Debulking ...31810.4.12 Debagging Precautions and Typical Problems.... 318

10.5 Curing Stages and Temperatures—Heating Techniques 31910.5.1 Curing Stage Definitions .............31910.5.2 Low-Temperature Cure 32010.5.3 Elevated-Temperature Cure 32010.5.4 Direct Versus Indirect Heating .......32110.5.5 Ramp Rates and Soak Cycles 32110.5.6 Temperature Control and Monitoring ..32110.5.7 Thermocouple Placement 32310.5.8 Temperature Control Problems 32410.5.9 Hot Bonder and Heater Blanket Usage 32410.5.10 Heat Sinks ..32710.5.11 Thermocouples... 32810.5.12 Distortion of Parts During Heating or Cooling ....329

10.6 Post-Repair Inspection 33010.7 Surface Restoration 33310.8 References 335

Chapter 11 Mechanical Fastening Systems 33711.1 Introduction 33711.2 Fastener Types .338

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TABLE OF CONTENTS

11.2.1 Fastener Standards 33911.2.2 Fastener Compatibility 33911.2.3 Rivets. ...340

11.2.3.1 Solid Rivets 34011.2.3.2 Blind Rivets...... .....34111.2.3.3 Hollow End Rivets ......................343

11.3 Screws, Nuts, and Bolts ..............34311.3.1 Specialty Fasteners (Special Bolts) 34311.3.2 Lockbolts ........34611.3.3 Hex Drive Bolts 35011.3.4 Specialty Blind Bolts .....350

11.4 Spacers, Bolt Inserts, and Grommets 35311.5 Hole Preparation ......................357

11.5.1 Drilling ....35711.5.2 Hole Sizes and Tolerances 36011.5.3 Edge Distance and Fastener Pitch .....36111.5.4 Hole Protection ..361

11.6 Fastener Installation and Removal .........................36211.6.1 Fastener Installation ....36211.6.2 Fastener Removal..... ......371

11.7 Fastener Substitution... 37211.8 Bonded Fasteners ...37211.9 Composite Fasteners 37411.10 References.... ..375

Chapter 12 Documentation ...37712.1 Process Control Documents.... 377

12.1.1 Cure Chart/Data Strip 37712.1.2 Routine and Nonroutine Work Documents 378

12.1.2.1 Routine Work Documents 37812.1.2.2 Nonroutine Work Documents.. .391

12.1.3 Nondestructive and Destructive Inspection Data......39212.1.4 Coupon Test Results....................................... 39212.1.5 Clean-Room Temperature and Humidity ...........39212.1.6 Return to Service/Log Book Sign-Offs.... 392

12.2 Calibration Records ........................39312.3 Material Control Records... 39512.4 Component Documentation 39612.5 Training Records..... 397

Chapter 13 Shop Equipment and Hand Tools....... ..39913.1 Hand Tools and Techniques............. ............399

13.1.1 Drills 39913.1.2 High-Speed Grinders. .....40113.1.3 Cutting Utensils 40413.1.4 Hand Routers...... 405

xvii


13.1.5 Orbital Sanders ..40613.1.6 Cast Cutter (Oscillating Saw) ..............40713.1.7 Painting Equipment 40813.1.8 Resin Applicators..... 408

13.2 Shop Equipment........ 40813.2.1 Bandsaws .....40813.2.2 Air Compressors ..........409

13.3 Heating Devices 41113.4 Measuring Devices 41213.5 Health and Safety Equipment.. 41413.6 References 416

Chapter 14 Tooling and Mold Making ...41714.1 Introduction 41714.2 Caul Plate and Dam Fabrication 41814.3 Splash Mold Making.... 42014.4 Release Agents/Films....... .......42014.5 Simple Room-Temperature Tooling 42114.6 Room-Temperature Curing Pre-Preg Tooling ....422

14.6.1 Lay-Up 42314.6.2 Debulk Procedure. 42414.6.3 Final Bagging Procedure 42514.6.4 Autoclave Cure ...42514.6.5 Time Limits 42614.6.6 Step Post-Curing Procedure After Room-

Temperature or Low-Temperature Initial Cure 42614.6.7 Support Structures.... ..42714.6.8 Initial Release Priming of New Composite

Tools ... ..42914.6.9 Developments in Low-Temperature Curing

Materials 43014.7 References 430

Chapter 15 Metal Bonding ..........43115.1 Introduction.......... 431

15.1.1 History and Requirements 43115.1.1.1 Metal Bonding......... ..........................43315.1.1.2 Epoxy Adhesives............ ..43515.1.1.3 Requirements for Adhesives... .............435

15.1.2 Principles of Adhesion ....43615.1.2.1 Adhesion Theory ....................43615.1.2.2 Environmental Durability..... .........43915.1.2.3 Temperature Effects ...........44015.1.2.4 Humidity Effects .....................441

15.1.3 Advantages and Disadvantages of MetalBonding. 441

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TABLE OF CONTENTS

15.2 Surface Preparation Methods 44215.2.1 Abrasive Cleaning 44415.2.2 Pasa-Jell 44415.2.3 Hydrofluoric Acid Etching 44615.2.4 Grit Blast/Silane. 44815.2.5 Alodine or Alochrom 1200 ........44815.2.6 Boeing Boegel EPII Sol-Gel Process ........45015.2.7 FPL Etch. ......45015.2.8 Chromic Acid Anodizing 45115.2.9 Phosphoric Acid Anodizing ........451

15.2.9.1 Phosphoric Acid Containment System(PACS) ....452

15.2.9.2 Phosphoric Acid Non-Tank Anodizing(PANTA) 452

15.2.10 Metadalic/Sifco Selective Plating (U.K.) Ltd 45715.2.11 Ciba Laser Pretreatment ..45715.2.12 Other Surface Preparations 457

15.3 Primers 45815.3.1 Reasons for Using Primers 45815.3.2 Primer Types 45915.3.3 Application of Primers..... 45915.3.4 Curing/Drying...... ....46115.3.5 Thickness Verification 461

15.4 Handling Primers 46215.5 References 46315.6 Bibliography 464

Chapter 16 Design Guide for Composite Parts .........46516.1 Introduction 46516.2 Analysis of Reports Received 46516.3 Other Required Design Features Not Mentioned in the

Analyzed Reports 49016.4 References ...494

Chapter 17 Repair Design 49517.1 General Repair Design 495

17.1.1 Introduction to Repair Design 49517.1.2 Laminate Loading..... ......495

17.1.2.1 Tension and Compression Loadsand Strains 495

17.1.2.2 Shear Stress and Strain 49717.1.2.3 Poisson's Ratio 498

17.1.3. Repair Philosophy and Design Requirements ..50017.1.3.1 Certification Load Capacity 50017.1.3.2 Repair Categorization ..505

17.2 Laminate Repair Design 507

xix


17.2.1 Introduction to Laminate Repair Design 50717.2.2 Laminate Repair Design Considerations 507

17.2.2.1 Stiffness ..........50717.2.2.2 Strength ....51017.2.2.3 Stability 51117.2.2.4 Environmental Effects and Protection 511

17.2.2.4.1 Operational and GlassTransition Temperatures(Tg) 511

17.2.2.4.2 Lightning and ElectrostaticProtection 512

17.2.2.5 Other Repair Design Considerations 52017.2.2.6 Laminate Repair Recommendations 521

17.2.3 Laminate Analysis Techniques for RepairDesign 52217.2.3.1 Introduction to Simplified Analysis

Techniques 52217.2.3.2 Elastic Modulus (E) Analysis 52417.2.3.3 Strength (F) Analysis 52917.2.3.4 Poisson's Ratio (ν0) Analysis 53117.2.3.5 In-Plane Shear Modulus (G) 534

17.2.4 In-Plane Shear Strength (τ) 53517.3 Core Repair Design 540

17.3.1 Function and Loading of Core in SandwichConstruction 540

17.3.2 Core Material, Density, and Cell Size 54417.3.3 Core Repair Design Recommendations 544

17.4 Bonded Joint Repair Design 54517.4.1 Introduction to Bonded Joints 54517.4.2 Types of Bonded Joints ....54517.4.3 Failure Modes of Bonded Joints ........54717.4.4 Adhesive Behavior in Bonded Joints. 549

17.4.4.1 Adhesive Shear Stress and Strain ....54917.4.4.2 Elastic and Plastic Adhesive

Behavior 55117.4.4.3 Temperature and Moisture Effects 56017.4.4.4 Joint Adherend Effects—Stiffness

Imbalance and Thermal Mismatch.... .56317.4.4.5 Recommended Joint Overlaps and

Simplistic Analysis 56817.4.5 Adhesive Peel Stress and Displacement 57017.4.6 Durability—Fatigue, Creep, and Environmental

Effects 58117.4.7 Bonded Joint Repair Considerations 58217.4.8 Bonded Joint Repair Design Recommendations 583

17.5 Mechanically Fastened Joints 584

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TABLE OF CONTENTS

17.5.1 Introduction to Mechanically Fastened Joints 58417.5.2 Fastened Laminate Failure Modes .........58517.5.3 Fastener Failure Modes 58817.5.4 Open-Hole Stress Concentrations—Composites

Versus Metals 58817.5.5 Loading of Mechanically Fastened Joints 58817.5.6 Loaded Fastener Holes.... 59217.5.7 Fastener Load Distribution and Joint Geometry 59417.5.8 Lay-Up Orientation for Fastened Joints ........59617.5.9 Pad-Ups and Hybrid Material Application 59717.5.10 Fatigue of Fastened Composite Joints 60017.5.11 Effects of Gaps and Shims 60117.5.12 Fastener Selection 60117.5.13 Mechanically Fastened Repairs in Sandwich

Panels 60417.5.14 Fastened Joint Repair Recommendations .608

17.6 References 60917.7 Bibliography... ..612

Additional Information 613

Index 617

About the Authors 637

xxi

FOREWORD

This book is a detailed work of reference, drawing from many industry sources around theworld. It is a comprehensive, in-depth look at the principal materials and processes involvedin manufacturing, inspecting, and repairing advanced composite aircraft structures. It shouldalso be useful to those working with composites in non-aerospace industries.

This book becomes even more valuable considering the background of the authors. Dr. KeithArmstrong is extremely well respected for his many years of experience and leadership inadvanced composite aircraft structures. He was involved in the development of carbon fiber/Nomex® honeycomb floor panels for the VC-10 airliner with Graham Bevan of Rolls-RoyceComposite Materials and now with Airbus (U.K.) Ltd. These were the first carbon fibercomposites to fly on commercial aircraft. Almost all flooring used in commercial aircrafttoday meets specifications that have evolved from these early composite structures. Dr.Armstrong developed many new methods in the infancy of the industry during his 24years with British Airways. He led the effort to standardize composite repair as chairman ofthe International Air Transport Association (IATA) Composite Repair Task Force from 1988to 1991. He continues to be a key player in the effort to improve composites education viahis ongoing participation in the Training Task Group of the SAE/IATA/ATA CommercialAircraft Composite Repair Committee (CACRC). As part of this work, he compiled a glos-sary of terms, published by SAE as AIR 4844 Composites and Metal Bonding Glossary.

Dr. Armstrong possesses a unique combination of theoretical and practical knowledge. Heearned an M.Sc. (1978) and a Ph.D. (1991) in Adhesion Science and Technology from TheCity University in London, England. He also has spent many years performing simple butvaluable hands-on experiments, such as wedge testing of composite and aluminum alloysamples after years of immersion in water. These have now been published and are listedas references in this book.

This second edition is co-authored by L. Graham Bevan and William F. Cole II. Dr. Arm-strong and Mr. Bevan have worked together on lightweight floor panels and other projectsfor more than 30 years. Mr. Bevan has worked in or has been associated with the aircraftindustry for most of his working life. His involvement with composites started in 1969 whenhe joined Rolls-Royce Composite Materials, from the then British Aircraft Corporation. Hehas maintained this involvement with composites without a break during the past 35 years.Mr. Bevan currently works in Customer Support at Airbus (U.K.) Ltd. and is involved incomposite repairs on all Airbus aircraft. He is a past member of the Airbus Composite RepairTask Force and a past member of the Repair Techniques Task Group of the CACRC.

Bill Cole, now Director of Engineering at AAR Corporation, has done an exceptional jobas chairman of the Analytical Repair Techniques Task Group of the CACRC. Rick Barrett,co-author of the first edition has, unfortunately, left the aerospace industry. His leadershiphelped to establish the syllabus for this book while he was chairman of the CACRC Train-ing Task Group from 1992 to 1994. He also contributed valuable practical experience ofhands-on repair work.

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This book will become a standard by which future efforts are judged. All of us in thisevolving field owe the authors of this book a debt of gratitude, not only for this work butalso Dr. Armstrong's many fundamental contributions to composites technology, GrahamBevan's 35 years of dedication to this subject, Bill Cole's extremely valuable mathematicalability, and Rick Barrett's ideas and enthusiasm that made this project possible.

Mike Hoke, PresidentAbaris Training Inc.

Reno, Nevada

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PREFACE TO THE SECOND EDITION

This second edition has been prepared to make improvements and additions to keep thebook up to date. At the same time, the opportunity has been taken to correct some minorerrors in the first edition. Some diagrams have been improved, some have been deleted,and others have been added.

At the present time, it is quite a challenge to keep pace with takeovers, amalgamations,and company name changes. These have been included up to the point of submission forprinting, but in the future, there may be more.

A few new nondestructive inspection (NDI) methods have been added, together with somenew fasteners for composite materials and one new method for the surface preparation ofmetals prior to adhesive bonding. A number of water-based primers have been included,and a few new books and papers have been added to the references.

It has been encouraging to receive favorable comments on the first edition from the practicalpeople who carry out repairs and say they have found it a very readable volume.

This second edition has been co-authored by Graham Bevan of Airbus (U.K.) Ltd. andWilliam F. Cole II of AAR Corporation, as Rick Barrett (who co-authored the first edition)is no longer working in the aerospace industry. Graham has been involved with compos-ites almost all his working life and is a recognized expert in this field. He has made usefulimprovements to this second edition. Bill Cole, chairman of the Analytical Repair Tech-niques Task Group of the Commercial Aircraft Composite Repair Committee (CACRC),has produced a new chapter on repair design (Chapter 17) for this second edition, and wehope it will be particularly helpful.

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PREFACE TO THE FIRST EDITION

This book is intended to meet the background information needs of composite repair techni-cians who repair aircraft composite components and structures for return to airline service. Itsupplements the practical work required to achieve the necessary level of skill in performingthese repairs. The syllabus was developed by the Training Task Group and approved bythe Commercial Aircraft Composite Repair Committee (CACRC). It has been publishedby the Society of Automotive Engineers (SAE) as SAE AIR 4938 Composite and BondedStructure Technician/Specialist Training Document and covers materials, handling andstorage, design aspects, damage assessment, repair techniques, manufacturers' documents,fastening systems, tools and equipment, health and safety aspects, and care of compositeparts. Chapter 15 covers metal bonding, partly because some composite parts include metalreinforcements and fittings and partly because the term "composite" is sometimes used tomean any combination of two or more materials such as a skin and honeycomb core, forexample. Repair design engineers should also find the book useful.

This book is designed primarily for aerospace use, but these notes have been compiled forall composite repair technicians, regardless of the type of vehicle or component they haveto repair. Although some of the materials used may be either different from, or less strictlyregulated than, those used in the aerospace industries, we hope that this book will be usefulto the marine, automobile, railway, wind power generation, and sporting goods industriesand others using composite components. The general principles involved are very similarfor all composite materials, regardless of their end use.

A book of this size and topic range cannot cover any subject in great detail; therefore, moreextensive references should be studied when necessary. For detailed specific repair proce-dures, the Original Equipment Manufacturers' (OEMs') Structural Repair Manuals (SRMs),Overhaul Manuals (OHMs), etc., should be used. SAE (CACRC) produced AerospaceRecommended Practices (ARPs) will be included in these manuals as alternative means ofcompliance as opportunity arises during normal amendment procedures and as these ARPsbecome available.

Metal bonding has been covered in Chapter 15 because there are occasions when metal partsare bonded to composites, and the design guide in Chapter 16 documents experience andshows where small design improvements could extend the service lifetimes of compositeparts. The support of SAE for all of the CACRC work is greatly appreciated. This bookhas been written to meet the CACRC syllabus, and it has been reviewed by some CACRCmembers. The book has not been approved by the CACRC; therefore, the views expressedare those of the authors and do not necessarily reflect the opinions of the committee as awhole or of the organizations that sponsor the committee.

The purpose of training is to improve performance and to provide leadership for others. Wehope that the following thoughts will inspire further effort.

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"Education expands the boundaries of our known ignorance faster than it expands theboundaries of our knowledge."

If we wish to be good leaders, we have a vast amount of study and research to do.

As an old poem states,

1. He that knows and knows that he knows is wise, follow him,

2. He that knows not and knows he knows not is willing to learn, teach him,

3. He that knows not and knows not that he knows not is a fool, shun him.

Let us all try to become at least "Type 2" and strive to reach "Type 1."

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