ENGINEERED INTERFACES IN FIBER REINFORCED COMPOSITESJANG-KYO KIM & Y I U docx

ENGINEERED

INTERFACES IN

FIBER REINFORCED

COMPOSITES

JANG-KYO KIM & YIU-WING MA1

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ENGINEERED

INTERFACES IN

FIBER REINFORCED

COMPOSITES

ENGINEERED

INTERFACES IN

FIBER REINFORCED

COMPOSITES

Jang-Kyo Kim

Department of Mechanical Engineering

Hong Kong University of Science and Technology

Clear Water Bay, Hong Kong

Yiu-Wing Mai

Centre for Advanced Materials Technology and

Department of Mechanical & Mechatronic Engineering

University of Sydney, NSW 2006, Australia

1998

ELSEVIER

Amsterdam Lausanne * New York * Oxford - Shannon * Singapore Tokyo

ELSEVIER SCIENCE Ltd

The Boulevard, Langford Lane

Kidlington, Oxford OX5 IGB, U.K.

Library of Congress Cataloging-in-Publica~on Data

Kim, Jang-Kyo.

Engineered interfaces in fiber reinforced composites / Jang-Kyo

Kim and Yiu-Wing, Mai. -- 1st ed.

p. cm.

Includes index.

ISBN 0-08-042695-6 (hardcover)

1. Fibrous composites. I. Mai, Y. W., 1946- . 11. Title.

TA418.9.C6K55 1998

620,1'18--DC21 97- 5 2002

CIP

First edition 1998

ISBN 0-08-042695-6

0 1998 Elsevier Science Ltd

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, electrostatic, magnetic tape, mechanical

photocopying, recording or otherwise, without permission in writing from the publishers.

Q The paper used in this publication meets the requirements of ANSUNIS0 239.48-1992

(Permanence of Paper).

Printed in The Netherlands

It is a pleasure to write the foreword to this book. This work emphasizes for the first

time in one volume how interfaces in fibrous composites can be defined, measured,

improved and optimized. Many practitioners of composites technology will find in

this book the information they have been seeking to match fiber and matrix at the

interface, thereby obtaining the best mix of properties in the final application.

Composites engineering is a relatively young field in which the test methods and

measurement techniques are not yet fully developed. Even more important, the ideas

linking the properties of composites to the interface structure are still emerging. This

book not only reviews the historic and pragmatic methods for studying composites;

but it also presents the most recent theories and fundamental tests of interface

properties. This allows the reader to find the true framework of theory to fit his/her

observations.

The fact that two brittle materials can be brought together to give a tough product

is the proof that interfaces are critical to composite properties. However, the

complexities of this process depend on the raw materials, on the surface chemistry of

the components, on the fabrication procedures, on the chemistry of hardening, and

on the damage and corrosion sustained in use. A wide view of material science,

chemistry, mechanics, process engineering and applications experience is necessary

to focus successfully on the role of the interface. The authors have demonstrated

such a global view in this volume.

I have known Professor Mai for over 20 years. He is a foremost authority on

fracture mechanics of composite materials, having studied polymer composites,

cement, ceramic and natural composite systems, in the US, Britain, Australia and

Hong Kong. In particular, he has made memorable contributions to the

understanding of cracks and to the crack-inhibiting effects seen in fibrous

composites. He has previously coauthored two books on fracture. Professor Kim

originally worked in the composites industry and has returned during the past 10

years to study interface mechanisms more closely. He is currently working in the

Hong Kong University of Science & Technology.

In summary, the topic of engineered interfaces in composites is an important one,

critical to the advance of the composites industry. Many practitioners from a range

of disciplines are seeking the information which can be found in this book. The

authors display the wide experience and theoretical knowledge necessary to provide

a critical view of the subject. I strongly recommend this volume to the composite

expert and student alike.

Kevin Kendall

Keele University, UK

May 1997

V

PREFACE

The study and application of composite materials are a truly interdisciplinary

endeavor that has been enriched by contributions from chemistry, physics, materials

scicncc, mcchanics and manufacturing cnginecring. The undcrstanding of thc

interface (or interphase) in composites is the central point of this interdisciplinary

effort. From the early development of composite materials of various nature, the

optimization of the interface has been of major importance. While there are many

reference books available on composite materials, few of them deal specifically with

the science and mechanics of the interface of fiber reinforced composites. Further,

many recent advances devoted solely to research in composite interfaces are

scattered in different published literature and have yet to be assembled in a readily

accessible form. To this end this book is an attempt to bring together recent

developments in the field, both from the materials science and mechanics

perspective, in a single convenient volume.

The central theme of this book is tailoring the interface properties to optimize the

mechanical performance and structural integrity of composites with enhanced

strength/stiffness and fracture toughness (or specific fracture resistance). It deals

mainly with interfaces in advanced composites made from high performance fibers,

such as glass, carbon, aramid, ultrahigh modulus polyethylene and some inorganic

(e.g. B/W, A1203, Sic) fibers, and matrix materials encompassing polymers, metals/

alloys and ceramics. The book is intended to provide a comprehensive treatment of

composite interfaces in such a way that it should be of interest to materials scientists,

technologists and practising engineers, as well as graduate students and their

supervisors in advanced composites. We hope that this book will also serve as a

valuable source of reference to all those involved in the design and research of

composite interfaces.

The book contains eight chapters of discussions on microstructure-property

relationships with underlying fundamental mechanics principles. In Chapter 1, an

introduction is given to the nature and definition of interfaces in fiber reinforced

composites. Chapter 2 is devoted to the mechanisms of adhesion which are specific

to each fiber-matrix system, and the physico-chemical characterization of the

interface with regard to the origin of adhesion. The experimental techniques that

have been developed to assess the fiber-matrix interface bond quality on a

microscopic scale are presented in Chapter 3, along with the techniques of

measuring interlaminar/intralaminar strengths and fracture toughness using bulk

composite laminates. The applicability and limitations associated with loading

geometry and interpretation of test data are compared. Chapter 4 presents

comprehensive theoretical analyses based on shear-lag models of' the single fiber

composite tests, with particular emphasis being placed on the interface debond

vii

...

VI11 Preface

process and the nature of the fiber-matrix interface bonding. Chapter 5 is devoted to

reviewing current techniques of fiber surface treatments which have been devised to

improve the bond strength and the fiber-matrix compatibility/stability during the

manufacturing processes of composites. The microfailure mechanisms and their

associated theories of fracture toughness of composites are discussed in Chapter 6.

The role of the interface and its effects on the mechanical performance of fiber

composites are addressed from several viewpoints. Recent research efforts to

augment the transverse and interlaminar fracture toughness by means of controlled

interfaces are presented in Chapters 7 and 8. Three concepts of engineered interfaces

are put forward to explain the results obtained from fiber coatings. Among those

with special interest from the composite designer’s perspective are the effects of

residual stresses arising from differential shrinkage between the composite

constituents, tough matrix materials, interleaves as delamination arresters and

three-dimensional fiber preforms.

We are grateful for assistance from many sources in the preparation of this book.

We acknowledge the invaluable contributions of many individuals with whom we

had the privilege and delight to work together: in particular the past and present

colleagues at the University of Sydney and the Hong Kong University of Science &

Technology, including C.A. Baillie, F. Castino, B. Cotterell, K.A. Dransfield, S.L.

Gao, Y.C. Gao, M.I. Hakeem, B.J. Kennedy, M.G. Lau, L.M. Leung, H.Y. Liu, R.

Lord, I.M. Low, S.V. Lu, D.B. Mackay, L. Ye and L.M. Zhou. The generous

financial support provided by many organizations, most notably the Australian

Research Council and the Hong Kong Research Grant Council, for performing the

research recorded in this book is greatly appreciated. Thanks are also due to all

those who have allowed us to reproduce photographs and diagrams from their

published work and to their publishers for the permission to use them.

Special thanks are also due to our technical writer Dr. Virginia Unkefer of the

Hong Kong University of Science & Technology for her help without which this

book would never have eventuated. Finally, we can never thank sufficiently our

family members, Hyang and Jong-Rin Kim, and Louisa Mai, for their patience and

understanding of our pressure to undertake and complete such a time-consuming

task.

Jang-Kyo Kim

Clear Water Bay, Hong Kong

May 1997

Yiu- Wing Mai

Sydney, Australia

May 1997

CONTENTS

Foreword v

Preface vii

Chapter 1.

Chapter 2.

2.1.

2.2.

2.2.1.

2.2.2.

2.2.3.

2.2.4.

2.2.5.

2.2.6.

2.3.1.

2.3.2.

2.3.3.

2.3.4.

2.3.5.

2.3.6.

2.3.7.

2.3.8.

2.3.9.

2.3.10.

2.3.1 1.

2.3.

Chapter 3.

3.1.

3.2.

Introduction 1

References 4

Characterization of Interface Properties 5

Introduction 5

Theories of Adhesion and Types of Bonding 5

Adsorption and Wetting 7

Interdiffusion 12

Electrostatic Attraction 13

Chemical Bonding 14

Reaction Bonding 14

Mechanical Bonding 16

Physico-chemical Characterization of Interfaces

Introduction 17

Infrared (IR) and Fourier Transform Infrared (FTIR)

Spectroscopy 18

Laser Raman Spectroscopy 21

X-Ray Photoelectron Spectroscopy (XPS) 24

Auger Electron Spectroscopy (AES) 26

Secondary Ion Mass Spectroscopy (SIMS) 29

Ion Scattering Spectroscopy (ISS) 30

Solid State Nuclear Magnetic Resonance (NMR) Spectroscopy

Wide-Angle X-Ray Scattering (WAXS) 32

Small-Angle Light Scattering (SALS) and Small-Angle X-ray Scattering

(SAXS) 33

Measurement of Contact Angle 34

References 38

1 7

3 1

Measurements of Interface/Interlaminar Properties 43

Introduction 43

The Mechanical Properties of Fiber-Matrix Interfaces 44

ix

X

3.2.1.

3.2.2.

3.2.3.

3.2.4.

3.2.5.

3.2.6.

3.2.7.

3.3.1.

3.3.2.

3.3.3.

3.3.4.

3.3.5.

3.3.6.

3.3.7.

3.3.8.

3.4.1.

3.4.2.

3.4.3.

3.4.4.

3.3.

3.4.

Contents

Introduction 44

Single Fiber Compression Test 44

Fiber Fragmentation Test 45

Fiber Pull-out Test 5 1

Microindentation (or Fiber Push-out) Test

Slice Compression Test 58

Comparison of Microcomposite Tests and Experimental Data

Interlaminar/Intralaminar Properties 61

Introduction 61

Short Beam Shear Test 62

Iosipescu Shear Test 66

[ f 45"Is Tensile Test 69

[ lo"] Off-axis Tensile Test 70

Rail Shear Test 71

In-plane Lap-shear Test 72

Transverse Tensile Test 72

Interlaminar Fracture Toughness 74

Delamination 74

Mode 1 Interlaminar Fracture Tests (IFT) 76

Mode I1 Interlaminar Fracture Tests

Mode I Edge Delamination Tests

References 85

56

59

81

83

Chapter 4. Micromechanics of Stress Transfer Across the Interface 93

4.1.

4.2.

4.2.1.

4.2.2.

4.2.3.

4.2.4.

4.3.1.

4.3.2.

4.3.3.

4.3.4.

4.3.5.

4.3.6.

4.3 7.

4.4.1.

4.4.2.

4.4.3.

4.5.1.

4.3.

4.4.

4.5.

Introduction 93

Fiber Fragmentation Test 94

Introduction 94

Early Shear-Lag Models 97

An Improved Model based on a Fracture Mechanics Approach

An Improved Model based on a Shear Strength Criterion 110

Fiber Pull-Out Test 125

Introduction 125

Solutions for Stress Distributions 128

Interface Debond Criterion and Partial Debond Stress

Instability of Debond Process 135

Characterization of Interface Properties 138

Multiple Fiber Composite Model 139

Two-way Debonding Phenomenon 147

Fiber Push-out 150

Solutions for Stress Distributions 150

Debond Criterion and Debond Stresses

Comparisons between Fiber Pull-out and Fiber Push-out

Cyclic Loading in Fiber Pull-out and Fiber Push-out

Introduction 156

101

131

152

154

156

Contents xi

4.5.2. Relative Displacements and Degradation Function 157

4.5.3. Degradation of Interface Frictional Properties 161

References 164

Chapter 5. Surface Treatments of Fibers and Effects on Composite Properties 171

5.1.

5.2.

5.2.1.

5.2.2.

5.3.1.

5.3.2.

5.4.1.

5.4.2.

5.5.1.

5.5.2.

5.5.3.

5.5.4.

5.5.5.

5.5.6.

5.3.

5.4.

5.5.

Introduction 17 1

Glass Fibers and Silane Coupling Agents

Structure and Properties of Glass Fibers

Silane Treatments of Glass Fibers 174

Carbon Fibers 183

Structure and Properties of Carbon Fibers

Surface Treatments of Carbon Fibers 186

Polymeric Fibers 196

Aramid Fibers 196

Ultrahigh Modulus Polyethylene (UHMPE) Fibers 201

Inorganic Fibers 205

Introduction 205

Selection of Coating Materials and Coating Techniques 206

Carbon Fibers 210

Boron Fibers 214

Silicon Carbide (Sic) Fibers 216

Alumina (A1,OJ Fibers 223

References 228

172

172

183

Chapter 6. Interface Mechanics and Fracture Toughness Theories 239

6.1.

6.1.1.

6.1.2.

6.1.3.

6.1.4.

6.1.5.

6.1.6.

6.1.7.

6.2.

6.2.1.

6.2.2.

6.2.3.

6.2.4.

6.3.1.

6.3.2.

6.3.

6.4.

Interface-related Fracture Toughness Theories 239

Introduction 239

Fiber-Matrix Interface Debonding in Mode I1 Shear 242

Post-debond Friction 243

Stress Redistribution 243

Fiber Pull-out 243

Total Fracture Toughness Theories 245

Fracture of Ductile Fibers and Ductile Matrices 247

Toughness Theories for Short and Randomly Oriented Fiber

Composites 247

Introduction 247

Fiber Pull-out Dominant Fracture Mechanisms 248

Matrix Dominant Fracture Mechanisms 250

Total Fracture Toughness Theory 252

Fracture Toughness Maps 254

Continuous Fiber Composites 255

Short Fiber Composites 255

Crack-Interface Interactions 257

xii Contents

6.4.1. Tensile Debonding Phenomenon 257

6.4.2. Transverse Cracking versus Longitudinal Splitting 260

6.4.3. Crack Growth Resistance (R-curve) Behavior

in Transverse Fracture 268

References 273

Chapter 7. Improvement of Transverse Fracture Toughness

with Interface Control 279

7.1.

7.2.

7.2.1.

7.2.2.

7.2.3.

7.3.

7.3.1.

7.3.2.

7.4.

7.5.

7.5.1.

7.5.2.

Introduction 279

Fiber Coating and Intermittent Bonding Concept - Experimental

Studies 281

Intermittent Bonding Concept 282

Fiber Coating for Improved Energy Absorption Capability

Fiber Coating Techniques 293

Theoretical Studies of Interphase and Three Engineered

Interphase Concepts 295

Theoretical Studies of Interphase 296

Engineered Interface Concepts with Fiber Coating 300

Control of Laminar Interfaces-Delamination Promoters 306

Residual Stresses 308

Origin of Residual Stresses 308

Control of Residual Stresses 3 15

References 320

285

Chapter 8. Improvement of Interlaminar Fracture Toughness

with Interface Control 329

8.1.

8.2.

8.2.1.

8.2.2.

8.2.3.

8.3.

8.3.1.

8.3.2.

8.4.1.

8.4.2.

8.4.3.

8.4.

Introduction 329

Effects of Matrix Materials on Interlaminar Fracture Resistance 330

Introduction 330

Correlations between Matrix Properties and Composite Interlaminar

Properties 332

Impact Resistance and Tolerance of Fiber Composites with Tough

Matrices 339

Delamination Resisters 342

Mechanics of Free-edge Delamination 342

Interleaving Techniques 345

Three-dimensional Textile Composites Concept 35 1

Introduction 351

Improvement of Interlaminar Fracture Toughness

Impact Response of Stitched Composites 357

References 360

354