Polymer Composites for Civil and Structural Engineering

Polymer Composites for Civil and Structural Engineering

Polymer Composites for Civil and Structural Engineering by L. HOLLAWAY Professor Composite Structures Research Unit Department of Civil Engineering University of Surrey rm SPRINGER-SCIENCE+BUSINESS MEDIA, B.V.

First edition 1993 Springer Science+Business Media Dordrecht 1993 Origina1ly published by Chapman & Hall in 1993 Softcover reprint ofthe hardcover Ist edition 1993 Typeset in 10/12 pt Times New Roman by Thomson Press (India) Ltd., New Delhi ISBN 978-94-010-4946-7 ISBN 978-94-011-2136-1 (ebook) DOI 10.1007/978-94-011-2136-1 Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted under the UK Copyright Designs and Patents Act, 1988, this publication may not be reproduced, stored, or transmitted, in any form or by any means, without the prior permission in writing ofthe publishers, or in the case of reprographic reproduction only in accordance with the terms of the licences issued by the Copyright Licensing Agency in the UK, or in accordance with the terms of licences issued by the appropriate Reproduction Rights Organization outside the UK. Enquiries concerning reproduction outside the terms stated here should be sent to the publishers at the Glasgow address printed on this page. The publisher makes no representation, express or implied, with regard to the accuracy of the information contained in this book and cannot accept any legal responsibility or liability for any errors or omissions that may be made. A catalogue record for this book is available from the British Library Library of Congress Cataloging-in-Publication data available @J Printed on permanent acid-free text paper, manufactured in accordance with the proposed ANSI/NISO Z 39.48-199X and ANSI Z 39.48-1984

Preface Synthetic polymers and fibre reinforced polymer composite systems have become increasingly important to the civil and structural engineer over the last decade and now have a wide range of applications in a variety of engineering fields. A large percentage of all fibre reinforced products are made from unsaturated polyester resins reinforced with glass fibre. However, epoxy and toughened epoxy resins and the high technology thermoplastic polymers, together with the carbon and aramid fibres, are playing an ever more important role in structural engineering, particularly in the aerospace industry, but increasingly in the construction field, and this trend is likely to continue, as chapter 1 convincingly demonstrates. Polymer composites have unique advantages over more conventional materials and these advantages can be enhanced by correct design technology; the engineer has the opportunity to design the composite material and the structural system simultaneously. An attempt has been made to combine, within one book, information on the various composite systems currently in use in construction, together with fabrication processes, mechanical and physical properties of the matrices, fibres and composites, analytical and experimental testing and design techniques and jointing methods. The section on failure theories is a generic presentation in that structural composites generally consist of various multi-ply laminates which will fail when subjected to a sufficiently large load. It will be realized that the failure of composites is complicated because of the many different ways in which structural systems can collapse. Therefore, this section can serve only as a guide to the prediction of structural integrity. The aims of this book, therefore, are to provide a simple guide to the principal aspects of the theory and use of composites in construction. It is directed at consulting engineers and designers of polymer composites in the mechanical and civil engineering industries, but will also serve as a reference source for advanced undergraduates and postgraduates studying materials, and material scientists interested in the utilization of composites in engineering. I would like to express my appreciation to those of my past and present postgraduate students and research assistants at the University of Surrey who have directly and indirectly encouraged and helped me to produce this book. I am particularly indebted to Professor B. Grieveson, Consultant to

VI PREFACE the Department of Civil Engineering, with whom I have had many hours of technical discussion and who read the draft of the book and made many valuable suggestions. Finally I would like to thank my wife, Pat, for her help, patience and encouragement. L.H.

Contents 1 Introduction 1 References 10 2 Characterization and mechanism of fibre matrix materials 12 2.1 Introduction 12 2.2 Mechanism of reinforcement of fibre reinforced polymers 12 2.2.1 Fibres 13 2.2.2 Matrix 13 2.2.3 Interface 13 2.3 Geometrical aspects 14 2.4 Properties of fibres, matrices and composites, elastic properties of continuous unidirectional laminae 18 2.4.1 Longitudinal stiffness 18 2.4.2 Transverse stiffness 19 2.5 Stress and strain distribution around fibre ends of discontinuous fibres 21 2.6 Elastic properties of short fibre composite materials 23 2.7 Polymeric materials 24 2.7.1 Thermoplastic polymers 25 2.7.2 Thermosetting polymers 25 2.7.3 Foamed polymers 26 2.7.4 Elastomers 26 2.7.5 The major thermoplastic resins 27 2.7.6 The major thermosetting resins 27 2.8 Fibres 28 2.8.1 Glass fibres 29 2.8.2 Carbon fibres 31 2.8.3 Aramid fibres 33 2.8.4 Synthetic fibres 34 2.8.5 Prestressing fibres 36 2.9 Mechanical properties of polymers 38 2.9.1 Creep deformation and rupture 40 2.9.2 Time dependent behaviour: long-term tests 43 2.9.3 Experimental techniques to determine creep properties 47 2.10 Mechanical properties of fibres 48 2.11 Mechanical properties of structural composites 50 2.12 Stress-strain relationship for fibre/polymer materials 54 2.13 The deformation characteristics of composites 55 2.14 Fatigue in composite materials 56 2.14.1 Matrix cracking 57 2.14.2 Delamination 57 2.14.3 Fibre breakage and interface debonding 58 2.14.4 Fatigue behaviour 59 References 61 3 Laminate theory: macro analysis of composite laminates 63 3.1 Introduction 63 3.2 Isotropic lamina 64 3.2.1 Elastic properties of a randomly oriented fibre lamina 64

viii CONTENTS 3.3 Orthotropic lamina 65 3.3.1 Orthotropic lamina: arbitrary orientation 66 3.4 Properties of laminates 69 3.4.1 Stress within individual laminae 71 3.5 Yield strength of polymers 74 3.6 Strength theories of unidirectional laminae 75 3.6.1 Longitudinal tensile strength 75 3.6.2 Transverse tensile strength 76 3.6.3 Longitudinal compressive strength 77 3.6.4 Shear strength 79 3.7 Strength and failure criteria of orthotropic laminates not loaded in the principal directions 80 3.7.1 Maximum stress theory of fracture 80 3.7.2 Maximum strain theory of fracture 82 3.7.3 Interaction theory (Tsai-Hill failure criterion) 82 3.7.4 Grant-Sanders method 86 3.8 Characteristics of laminated composites 86 3.8.1 Laminated composite beam behaviour 87 3.8.2 Laminated composite plate behaviour 89 3.9 Design of composites 94 References 94 4 Measurements of engineering properties of fibre reinforced polymers 96 4.1 Introduction 96 4.2 Uniaxial tension 96 4.2.1 Tension test procedure 97 4.3 Compressive tests 99 4.4 In-plane shear tests 100 4.4.1 The uniaxial tensile test on a symmetric ± 45 coupon 100 4.4.2 Off-axis test 100 4.4.3 Rail shear test 101 4.4.4 Torsional shear of a thin-walled tube 102 4.5 Flexural tests 103 4.6 Interlaminar shear tests 103 4.6.1 The three-point load interlaminar shear test 103 4.6.2 Iosipescu shear specimen 104 4.7 Impact behaviour 105 4.7.1 Impact test techniques for composite materials 105 4.7.2 Observations on the impact tests 107 4.8 Non-destructive testing techniques 107 References 109 5 Processing techniques: thermoplastic polymers, thermosetting and thermoplastic composites 111 5.1 Introduction 111 PART 1 5.2 PART 2 5.3 Processing methods for the manufacture of reinforced thermosetting polymers 5.2.1 Open mould techniques 5.2.2 Closed mould techniques Processing methods for the manufacture of unreinforced thermoplastic polymer items 5.3.1 Profile products 111 113 116 121 122

CONTENTS 5.3.2 Film-blowing polymer sheet 5.3.3 Blow moulding 5.3.4 Co-extrusion 5.3.5 Highly orientated grid sheets 5.4 Processing methods for the manufacture of reinforced thermoplastic composites 5.4.1 Film stacking process 5.5 Manufacturing faults 5.5.1 Porosity 5.5.2 Prepreg gaps and fibre alignment 5.5.3 Prepreg joints 5.5.4 Resin micro-cracks 5.5.5 Resin shrinkage References ix 122 122 123 124 124 125 125 126 126 126 126 127 127 6 End-use performance properties of structural polymer composites 128 6.1 Introduction 128 PART 1 6.2 6.3 6.4 6.5 6.6 6.7 Specification and quality control Thermal properties Chemical resistance properties 6.4.1 Effects of chemicals on polymers 6.4.2 Natural weathering of polymers Sound insulation Ligh t transmission property Abrasion resistance 128 130 131 132 133 135 136 136 PART 2 6.8 6.9 6.10 Durability The fibre behaviour of polymers 6.9.1 Reaction to fire: test on materials 6.9.2 Fire resistance: test on structures 6.9.3 Smoke generation characteristics 6.9.4 Method of imparting flame retardancy to GRP Repair of composite materials 6.10.1 Types of repair 6.10.2 Bonded repairs 6.10.3 Bolted repairs 6.10.4 Techniques for modelling and analysis of composite repairs 137 139 140 141 144 145 146 146 148 149 149 PART 3 6.11 References End-use performance properties of geosynthetics 6.11.1 Introduction 6.11.2 The utilization of geotextile reinforcement 6.11.3 Geotextile characteristics 6.11.4 Strength characteristics 6.11.5 Durability 6.11.6 Effects of oxidation 6.11. 7 Effects of hydrolysis 6.11.8 Effects of external chemicals 149 149 151 151 151 154 154 154 155 155

X CONTENTS 7 Low density rigid foam materials, sandwich construction and design methods 157 7.1 Introduction 157 7.2 Rigid plastic foams 157 7.3 Phenolic foam 158 7.4 Rigid polyurethane foam 160 7.5 Expanded PVC foam 161 7.6 Urea formaldehyde 162 7.7 Uses and manufacturing processes of polymer foams 162 7.8 Mechanical testing of rigid polymer foams 164 7.8.1 Compressive strengths 165 7.8.2 Flatwise tension test 166 7.8.3 Shear test 168 7.9 Sandwich laminates: beams 168 7.9.1 Shear stress in the core 170 7.9.2 Thin face sandwich beams 172 7.9.3 Thick face sandwich beams 174 7.9.4 Characteristic behaviour of a sandwich beam 174 7.10 Buckling of sandwich struts with thin faces 176 7.11 Buckling of sandwich struts with thick faces 177 7.12 Wrinkling instability offaces of sandwich struts with cores of finite thickness 178 7.13 Buckling of sandwich panels 179 7.13.1 Buckling of thin face sandwich panels 179 7.13.2 Buckling of thick face sandwich panels 181 7.14 Bending of simply supported panels with uniform transverse load 182 7.15 Simply supported sandwich panels with edge load and uniform transverse load 184 i16 Summary: a guide for design of sandwich beams and struts and panels with edge loads 184 Appendix 185 References 186 8 Bonding and bolting composites 187 8.1 Introduction 187 8.2 Adhesive bonded joints 187 8.3 Modes of failure 190 8.4 Tubular lap joints 195 8.4.1 J ointing closed section members 195 8.5 Theoretical solutions to bonded joints 198 8.5.1 Single lap joint: elastic analyses 198 8.5.2 Double lap joint: linear classical theory 200 8.5.3 Single and double lap joint: non-linear analysis 200 8.6 Adhesive stress-strain characteristics 201 8.7 Physical considerations during the bonding operations 204 8.7.1 In-service properties of adhesives 204 8.7.2 Surface preparation 204 8.8 Flaws in adhesive bonds 205 8.8.1 Adherend thermal mismatch 205 8.9 Mechanical joints 206 8.9.1 Introduction 206 8.9.2 The failure modes 207 8.10 The influence of various parameters on the failure mechanisms of bolted composites 210 8.10.1 The geometric factors 210 8.10.2 Fibre orientation, resin type and method of manufacture 211 8.10.3 Bolt fit 212 8.10.4 Clamping force 212 References 213

CONTENTS 9 Numerical examples for fibre-matrix composites 9.1 Introduction 9.2 Axial tensile forces in composite systems 9.3 Buckling of members under axial compression forces 9.4 Bending moment on a composite beam example 9.5 Sandwich beam construction References Glossary Appendix: ASTM specifications Index xi 215 215 215 229 233 236 244 246 251 255