Polymer Composites for Civil and Structural Engineering

Transcription

1 Polymer Composites for Civil and Structural Engineering

2 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.

3 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 ISBN (ebook) DOI / 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 Printed on permanent acid-free text paper, manufactured in accordance with the proposed ANSI/NISO Z X and ANSI Z

4 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

5 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.

6 Contents 1 Introduction 1 References 10 2 Characterization and mechanism of fibre matrix materials Introduction Mechanism of reinforcement of fibre reinforced polymers Fibres Matrix Interface Geometrical aspects Properties of fibres, matrices and composites, elastic properties of continuous unidirectional laminae Longitudinal stiffness Transverse stiffness Stress and strain distribution around fibre ends of discontinuous fibres Elastic properties of short fibre composite materials Polymeric materials Thermoplastic polymers Thermosetting polymers Foamed polymers Elastomers The major thermoplastic resins The major thermosetting resins Fibres Glass fibres Carbon fibres Aramid fibres Synthetic fibres Prestressing fibres Mechanical properties of polymers Creep deformation and rupture Time dependent behaviour: long-term tests Experimental techniques to determine creep properties Mechanical properties of fibres Mechanical properties of structural composites Stress-strain relationship for fibre/polymer materials The deformation characteristics of composites Fatigue in composite materials Matrix cracking Delamination Fibre breakage and interface debonding Fatigue behaviour 59 References 61 3 Laminate theory: macro analysis of composite laminates Introduction Isotropic lamina Elastic properties of a randomly oriented fibre lamina 64

7 viii CONTENTS 3.3 Orthotropic lamina Orthotropic lamina: arbitrary orientation Properties of laminates Stress within individual laminae Yield strength of polymers Strength theories of unidirectional laminae Longitudinal tensile strength Transverse tensile strength Longitudinal compressive strength Shear strength Strength and failure criteria of orthotropic laminates not loaded in the principal directions Maximum stress theory of fracture Maximum strain theory of fracture Interaction theory (Tsai-Hill failure criterion) Grant-Sanders method Characteristics of laminated composites Laminated composite beam behaviour Laminated composite plate behaviour Design of composites 94 References 94 4 Measurements of engineering properties of fibre reinforced polymers Introduction Uniaxial tension Tension test procedure Compressive tests In-plane shear tests The uniaxial tensile test on a symmetric ± 45 coupon Off-axis test Rail shear test Torsional shear of a thin-walled tube Flexural tests Interlaminar shear tests The three-point load interlaminar shear test Iosipescu shear specimen Impact behaviour Impact test techniques for composite materials Observations on the impact tests Non-destructive testing techniques 107 References Processing techniques: thermoplastic polymers, thermosetting and thermoplastic composites Introduction 111 PART PART Processing methods for the manufacture of reinforced thermosetting polymers Open mould techniques Closed mould techniques Processing methods for the manufacture of unreinforced thermoplastic polymer items Profile products

8 CONTENTS Film-blowing polymer sheet Blow moulding Co-extrusion Highly orientated grid sheets 5.4 Processing methods for the manufacture of reinforced thermoplastic composites Film stacking process 5.5 Manufacturing faults Porosity Prepreg gaps and fibre alignment Prepreg joints Resin micro-cracks Resin shrinkage References ix End-use performance properties of structural polymer composites Introduction 128 PART Specification and quality control Thermal properties Chemical resistance properties Effects of chemicals on polymers Natural weathering of polymers Sound insulation Ligh t transmission property Abrasion resistance PART Durability The fibre behaviour of polymers Reaction to fire: test on materials Fire resistance: test on structures Smoke generation characteristics Method of imparting flame retardancy to GRP Repair of composite materials Types of repair Bonded repairs Bolted repairs Techniques for modelling and analysis of composite repairs PART References End-use performance properties of geosynthetics Introduction The utilization of geotextile reinforcement Geotextile characteristics Strength characteristics Durability Effects of oxidation Effects of hydrolysis Effects of external chemicals

9 X CONTENTS 7 Low density rigid foam materials, sandwich construction and design methods Introduction Rigid plastic foams Phenolic foam Rigid polyurethane foam Expanded PVC foam Urea formaldehyde Uses and manufacturing processes of polymer foams Mechanical testing of rigid polymer foams Compressive strengths Flatwise tension test Shear test Sandwich laminates: beams Shear stress in the core Thin face sandwich beams Thick face sandwich beams Characteristic behaviour of a sandwich beam Buckling of sandwich struts with thin faces Buckling of sandwich struts with thick faces Wrinkling instability offaces of sandwich struts with cores of finite thickness Buckling of sandwich panels Buckling of thin face sandwich panels Buckling of thick face sandwich panels Bending of simply supported panels with uniform transverse load 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 Bonding and bolting composites Introduction Adhesive bonded joints Modes of failure Tubular lap joints J ointing closed section members Theoretical solutions to bonded joints Single lap joint: elastic analyses Double lap joint: linear classical theory Single and double lap joint: non-linear analysis Adhesive stress-strain characteristics Physical considerations during the bonding operations In-service properties of adhesives Surface preparation Flaws in adhesive bonds Adherend thermal mismatch Mechanical joints Introduction The failure modes The influence of various parameters on the failure mechanisms of bolted composites The geometric factors Fibre orientation, resin type and method of manufacture Bolt fit Clamping force 212 References 213

10 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