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Structural Adhesive Joints in Engineering PDF

316 Pages·1984·8.78 MB·English
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Structural Adhesive Joints in Engineering Structural Adhesive Joints in Engineering ROBERT D. ADAMS BSc (Eng.) (Lond.), PhD(Cantab.), ACGI, C Eng., FIMechE, FInstP Reader in Mechanical Engineering, University of Bristol, UK and WILLIAM C. WAKE MSc, PhD, DSc(Lond.), FRSC, FPRI, Hon.DSc (The City University) Hon. Fellow, The City University, London, UK ELSEVIER APPLIED SCIENCE PUBLISHERS LONDON and NEW YORK ELSEVIER APPLIED SCIENCE PUBLISHERS LID Crown House, Linton Road, Barking, Essex IGll 8JU, England Sole Distributor in the USA and Canada ELSEVIER SCIENCE PUBLISHING CO., INe. 52 Vanderbilt Avenue, New York, NY 10017, USA British Ubrary Cataloguing in Publication Data Adams, R. D. Structural adhesive joints in engineering. 1. Adhesive joints 1. Title II. Wake, William C. 624.1'89'9 TA492.A3 ISBN-13 :978-94-0 10 -8977-7 e-ISBN-13 :978-94-009-5616-2 DOI: 10.1007/978-94-009-5616-2 WITH 30 TABLES AND 125 ILLUSTRATIONS © ELSEVIER APPLIED SCIENCE PUBLISHERS LID 1984 Reprinted 1986 Softcover reprint ofthe hardcover 1st edition 1984 Special regulations for readers in the USA This publication has been registered with the Copyright Clearance Center Ine. (CCC), Salem, Massaehusetts. Information ean be obtained from the CCC about conditions under which photoeopies of parts of this publieation may be made in the USA. All other copyright questions, incIuding photo- copying outside of the USA, should be referred to the publisher. All rights reserved. No part of this publieation may be reprodueed, 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 the publisher. Preface The intention of this book is that it should contain everything an engineer needs to know to be able to design and produce adhesively bonded joints which are required to carry significant loads. The advan tages and disadvantages of bonding are given, together with a sufficient understanding of the necessary mechanics and chemistry to enable the designer to make a sound engineering judgement in any particular case. The stresses in joints are discussed extensively so that the engineer can get sufficient philosophy or feel for them, or can delve more deeply into the mathematics to obtain quantitative solutions even with elasto plastic behaviour. A critical description is given of standard methods of testing adhesives, both destructively and non-destructively. The essen tial chemistry of adhesives and the importance of surface preparation are described and guidance is given for adhesive selection by me ans of check lists. For many applications, there will not be a unique adhesive which alone is suitable, and factors such as cost, convenience, produc tion considerations or familiarity may be decisive. A list of applications is given as examples. The authors wish to increase the confidence of engineers using adhesive bonding in load-bearing applications by the information and experience presented. With increasing experience of adhesives en gineering, design will become more elegant as weH as more fitted to its products. R. D. ADAMS W.C.WAKE Acknowledgements Acknowledgements are necessarily and gladly made by the authors for help, advice and criticism to Dr J. A. Harris of Bristol University, Dr A. J. Kinloch of the Ministry of Defence (PERME), Waltham Abbey, and Dr P. Poole of the Royal Aircraft Establishment, Farnborough. Former colleagues and students have contributed in the past to the work on which this book is largely based, in particular Drs N. A. Peppiatt, J. Coppendale and A. D. Crocombe. The publisher joins with the authors in thanking those individuals and Journals listed below for permission to use diagrams and photo graphs which have either appeared elsewhere or are modifications of published material: Adhäsion (Berlin) for Figs 99-101, 110 and 111 from papers by the late Prof. Dr-Ing. A. Matting. K. W. Allen and J. Adhesion for Figs 107 and 108. Dr W. Althof and Metall (Berlin) for Figs 116, 119 and 120. Dr H. A. Burgman and J. Appl. Polym. Sei. for Fig. 118. Dr J. Cotter and J. Adhesion for Fig. 115. Prof. Dr-Ing. F. Eichhorn and Adhäsion for Fig. 114. Engineering Sciences Data Unit Publication, ESDU 79016 for Fig. 33. Dr L. J. Hart-Smith for Figs 32, 34-36 and the Douglas Aircraft Co., for Figs 37 and 38. The Institution of Civil Engineers for Figs 54 and 56. J. Adhesion for Figs 27-30, 69 and 87. J. Strain Anal. for Figs 10, 13-23 and 63-68. Dr H. Schonhorn and J. Appl. Polym. Sei. for Fig. 92. Dr M. E. R. Shanahan and The City University for Fig. 98. Dr B. Wargotz and J. Adhesion for Fig. 102. Figures 1 and 124 are Crown Copyright and Fig. 109 is based on data supplied by the Royal Aircraft Establishment, Farnborough. vi Contents Preface v Acknowledgements . vi Chapter 1. INTRODUCrION 1 Joint Configurations: Lap-shear Joints, Butt Joints, Fillets. Metals and Other Constructional Materials. The Decision to Use Adhesive Bonding. The Balance of Advantages and Disadvantages Chapter 2. THE NATURE AND MAGNITUDE OF STRESSES IN ADHESIVE JOINTS 14 Introduction: Reality, Methods of Mathematical Analysis. The Single Lap Joint: Linear Elastic Analysis, Volkersen's Analysis, The Analysis of Go- land and Reissner, Effect of Bending in a Double-lap Joint, Volkersen's Second Theory, Later Work. The Single-lap Joint-End Effects: Reduction of Stress Concentrations. The Single-Iap Joint-Elasto-plastic Analysis. The Effect of Adherend Shape-Scarfed, Bevelled and Stepped Adherends. Composite Ma- terialls. Tubular Joints. Butt Joints. The Use of Joints in Design: Lap Joints, Tubular Joints, T -joints, Corner Joints, Butt Joints, Stiffeners, Doublers, Assembly Chapter 3. STANDARD MECHANICAL TEST PROCE- DURES .................. 115 Destructive Testing: Tests with Thin Sheet Adherends, Tests for Properties of Adhesives. Non- vii viii CONTENrS destructive Testing: Nature of Defects, Tests Carried Out Before Bonding, Post-bonding and In-service Testing Chapter 4. THE GENERAL PROPERTIES OF POLY MERIC ADHESIVES . . . . . 143 Polymer Structures: Unsaturation. Mixed Adhesives. Properties and Temperature: The Glass Transition Temperature, Decomposition Temperature, Melting Temperature, The Deformation of Adhesive Poly mers by Stress, Viscoelasticity, The Modulus of an Adhesive, Poisson's Ratio, Strength Properties of Adhesive Polymers, Yie1ding Stresses of Polymers, Failure Modes After Yie1ding, Creep, Failure without Yielding-Brittle Fracture, Crazing, Coefficient of Thermal Expansion, Resistance to Deterioration Chapter 5. FACTORS INFLUENCING THE CHOICE OF ADHESIVE .............. 175 Interaction with Substrate. Structural Adhesives for Metals: Check-list for Structural Metal Adhesives Used at Temperatures up to 70°C, The Advantage of Supported Filmic Adhesives (Tapes'), Unsupported Films, Liquids and Pastes, Infiuence of Metal of Adherend, High Temperature Metal-Metal Adhe- sion. Structural Adhesives for Wood: Check-list for the Use of Structural Wood Adhesives. Structural Adhesives for Mixed Constructions: Metal-Wood Structures, Metal-reinforced Plastics Structures. Choice of Adhesives for Semi-structural Use: Check- list for Adhesives for Semi-structural Use Chapter 6. SURFACE PREPARATION 218 Metals. Wood. Concrete. Glass or Carbon-fibre Reinforced Plastics. Shot, Sand or Grit Blasting. Solvent Degreasing or Wiping. Chemical Etching: Aluminium, Ferrous Metals, Titanium, Other Metals. Priming Layers: Primers as Coupling Agents Chapter 7. SERVICE LIFE 237 The Creep of Adhesive Joints. Time-to-failure (Under Static Loading). Cyc1es-to-failure: Influence CONTENTS IX of Temperature, Infl.uence of Test Frequency, In f1.uence of Amplitude, Infl.uence of Moisture. Effects of Temperature Change on Joint Strength. Service Life as Indicated by Climatic Exposure Trials Chapter 8. APPLICAT IONS 271 Aircraft, Anchorages. Bridges. Carriages. Cars. Decking. Furniture. Glass Reinforced Plastics. Heli copters. He1icopter Blades. Hovercraft. Lamp Posts. Magnets. PABST. Rollers. Segmental Construction. Ski Constructions. Telephone Kiosks. Yachts Reterences . 283 Appendix: Standard American and UK Specijications tor Adhesion Tests. . . . . . . . . . . . . . 293 Author Index 299 Subject Index 303 Chapter 1 Introduction An engineer designs or builds machines and structures. This book is about the design and building of structures using a particular method of construction chosen from the several, diverse methods available. Structures built from metallic components can have these components assembled by bolting, riveting or other forms of mechanical fastening, by welding, by the related processes of brazing or soldering, or an organic adhesive can be used to bond the components to each other. One of the few remaining alternatives is to machine the structure from a solid block as astatue is sculpted from a monolith. Training and experience combine to teach the engineer to marry design and method of assembly when considering the various me ans of mechanical fasten ing, distinguishing them not only from each other but also from the alternatives of welding or brazing. His training is less able to cope with the use of adhesives, with essential choices between the many types available and with the design approach appropriate to structures assembled with them. Subsequent chapters of this book have been written to assist the training of engineers in this extension of their expertise, to give practising engineers an aide-memoire of design criteria with adhesive properties and as a bonus, to help the adhesives technologist in assessing the needs of the engineering industry. Apart from structural uses, adhesives are used for surfacing either by the adhesives material itself providing the finished surface or by its use for attaching ceramic tiles or brick slips. They are also used as sealants for curtain walls and for sealing the seams of liquid containers from the small tin can to the integral fuel tanks of large aircraft. Neither the surfacing nor the sealing use of adhesives will feature, other than trivially, in these pages. Also excluded is the use of adhesives sub- 1 2 STRUCTURAL ADHESIVE JOINTS IN ENGINEERING stances as aggregate binders in 'resin concretes', which may be re garded as structural material in their own right and have been recently discussed in the context of adhesion (Hewlett and Shaw, 1977). Glass and carbon fibre reinforced plastics are important structural materials, the strength of which depends on the performance of the polymer matrix as an adhesive but, once again, it is the material rather than its manufacture which is the concern of the structural engineer. Fastening or bonding structural components made of GRP or CFRP is a focus of attention and features in Chapters 3 and 5-8. This brief catalogue of inclusions and exclusions may be briefly summed up by stating that the engineer, in building structures, is concerned about the transmission and accommodation of stresses. This book discusses the behaviour of adhesives, and joints made with them, when stresses of significant magnitude are imposed, and how such joints are best made. JOINT CONFIGURATIONS Joint design is dependent upon the nature of the materials to be joined as weIl as on the method of joining. The first cast iran bridge, at Ironbridge, Salop, was made by casting massive half-arches and as sembling the structure with mortise and tenon joints, with fit-on parts and tapered pegs. This mode of construction was the only one known to the designer, a mode used for timber structures. The only conces sion to the new structural material was in the use of large scale, single piece, curved members. Rolled bars of T - and L-sections did not become available until after the Napoleonic wars and the first I-beams, for light loading only, were made in Paris in 1847 (Hamilton, 1958). Heavy I-beams only became available in 1860 after the invention of mild steel. Fastening was originally by slotting a circular cylinder, cast as an integral part of the beam, over a cylindrical column, cast with a retaining lip, but fish plates and bolting were introduced at an early stage. The design of joints in wooden structures similarly underwent changes through the centuries when structural iron became available. Mortised joints, at best half the strength of the wooden tie-beams transmitting a puH, were avoided in large structures. In the eighteenth century iron work was introduced, and forged straps secured by gib and cotter, enabled loads to be suspended via wooden tie bars (Hamil ton, 1958). Tie bars were also lengthened by various designs of scarfed joints secured with fish plates and bolts. These impravements in joint

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The intention of this book is that it should contain everything an engineer needs to know to be able to design and produce adhesively bonded joints which are required to carry significant loads. The advan­ tages and disadvantages of bonding are given, together with a sufficient understanding of the
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