SECOND EDITION 'A' AN INTRODUCTION TO THEIF; PROPERTIES & APPLICATIONS Michael F Ashby. David R H Jones Engineering Materials 1 An lntroduction to their Properties and Applications Other titles of interest Ashby Ashby and Jones Brydson Charles and Crane Crawford Hull and Bacon Jones Neale Shreir et al. Smallman and Bishop Smith Materials Selection in Mechanical Design Engineering Materials 2 Plastics Materials, 6th Edition Selection and Use of Engineering Materials, 2nd Edition Plastics Engineering, 2nd Edition Introduction to Dislocations, 3rd Edition Engineering Materials 3 Tribology Handbook, 2nd Edition Corrosion, 3rd Edition Metals and Materials The Language of Rubber Engineering Materials 1 An Introduction to their Properties and Applications Second Edition by Michael F. Ashby and David R. H. Jones Department of Engineering, University of Cambridge, UK UTTERWORTH EINEMANN OXFORD AMSTERDAM BOSTON LONDON NEW YORK PARIS SAN DIEGO SAN FRANCISCO SINGAPORE SYDNEY TOKYO Butterworth-Heinemann An imprint of Elsevier Science Linacre House, Jordan Hill, Oxford OX2 8DP 225 Wildwood Avenue, Wobum, MA 01801-2041 First published 1980 Second edition 1996 Reprinted 1997, 1998 (twice), 2000,2001,2002 0 1980, 1996, Michael F. Ashby and David R. H. Jones. All rights reserved. The right of Author name to be identified as the author of this work has been asserted in accordance with the Copyright, Designs and Patents Act 1988 No part of this publication may be reproduced in any material form (including photocopying or storing in any medium by electronic means and whether or not transiently or incidentall to some other use of this publication) without the written permission of the copyright holder except in accordance with the provisions of the Copyright, Designs and Patents Act 1988 or under the terms of a licence issued by the Copyright Licensing Agency Ltd, 90 Tottenham Court Road, London, England WIT 4LP. Applications for the copyright holder’s written permission to reproduce any part of this publication should be addressed to the publishers British Library Cataloguing in Publication Data Ashby, Michael E Engineering materials. 1. an introduction to their properties and applications. - 2nd. ed. 1. Materials 2. Mechanics I. Title 11. Jones, David R. H. (David Rayner Hunkin), 1945-620.1’1 ISBN 0 7506 3081 7 Library of Congress Cataloguing in Publication Data Ashby, Michael E Engineering materials. 1. an introduction to their properties and applicationsby Michael F. Ashby and David R. H. Jones - 2nd. ed. p. cm. Rev.ed of Engineering materials. 1980. Includes bibliographical references and index. ISBN 0 7506 3081 7 1. Materials. I. Jones, David R. H. (David Rayner Hunkin), 1945 11. Ashby, M.F. Engineering materials III. Title TA403.A69 96-1677 620.1’1-dc20 CIP For information on all Butterworth-Heinemann publications visit our website at www.bh.com Typeset by Genesis Typesetting, Rochester, Kent Printed and bound in Great Britain by MFG Books Ltd, Bodmin, Comwall General introduction 1. Engineering Materials and their Properties examples of structures and devices showing how we select the right material for the job 3 A. Price and availability 2. The Price and Availability of Materials 15 what governs the prices of engineering materials, how long will supplies last, and how can we make the most of the resources that we have? B. The elastic moduli 3. The Elastic Moduli 27 stress and strain; Hooke’s Law; measuring Young’s modulus; data for design 4. Bonding Between Atoms 36 the types of bonds that hold materials together; why some bonds are stiff and others floppy 5. Packing of Atoms in Solids 45 how atoms are packed in crystals - crystal structures, plane (Miller) indices, direction indices; how atoms are packed in polymers, ceramics and glasses 6. The Physical Basis of Young’s Modulus 58 how the modulus is governed by bond stiffness and atomic packing; the glass transition temperature in rubbers; designing stiff materials - man-made composites 7. Case Studies of Modulus-limited Design 66 the mirror for a big telescope; a stiff beam of minimum weight; a stiff beam of minimum cost vi Contents C. Yield strength, tensile strength, hardness and ductility 8. The Yield Strength, Tensile Strength, Hardness and Ductility definitions, stress-strain curves (true and nominal), testing methods, data 9. Dislocations and Yielding in Crystals the ideal strength; dislocations (screw and edge) and how they move to give plastic flow 10. Strengthening Methods and Plasticity of Polycrystals solid solution hardening; precipitate and dispersion strengthening; work-hardening; yield in polycrystals 11. Continuum Aspects of Plastic Flow the shear yield strength; plastic instability; the formability of metals and polymers 12. Case Studies in Yield-limited Design materials for springs; a pressure vessel of minimum weight; a pressure vessel of minimum cost; how metals are rolled into sheet D. Fast fracture, toughness and fatigue where the energy comes from for catastrophic crack growth; the condition for fast fracture; data for toughness and fracture toughness 13. Fast Fracture and Toughness 14. Micromechanisms of Fast Fracture ductile tearing, cleavage; composites, alloys - and why structures are more likely to fail in the winter 15. Fatigue Failure fatigue testing, Basquin’s Law, Coffin-Manson Law; crack growth rates for pre-cracked materials; mechanisms of fatigue 16. Case Studies in Fast Fracture and Fatigue Failure fast fracture of an ammonia tank; how to stop a pressure vessel blowing up; is cracked cast iron safe? E. Creep deformation and fracture high-temperature behaviour of materials; creep testing and creep curves; consequences of creep; creep damage and creep fracture 17. Creep and Creep Fracture 77 93 104 111 119 131 140 146 155 169 Contents vii 18. Kinetic Theory of Diffusion 1 79 Arrhenius's Law; Fick's first law derived from statistical mechanics of thermally activated atoms; how diffusion takes place in solids 19. Mechanisms of Creep, and Creep-resistant Materials 187 metals and ceramics - dislocation creep, diffusion creep; creep in polymers; designing creep-resistant materials 20. The Turbine Blade - A Case Study in Creep-limited Design 197 requirements of a turbine-blade material; nickel-based super-alloys, blade cooling; a new generation of materials? - metal-matrix composites, ceramics, cost effectiveness F. Oxidation and corrosion 21. Oxidation of Materials the driving force for oxidation; rates of oxidation, mechanisms of oxidation; data 22. Case Studies in Dry Oxidation making stainless alloys; protecting turbine blades 23. Wet Corrosion of Materials voltages as driving forces; rates of corrosion; why selective attack is especially dangerous 24. Case Studies in Wet Corrosion how to protect an underground pipeline; materials for a light-weight factory roof; how to make motor-car exhausts last longer G. Friction, abrasion and wear 25. Friction and Wear surfaces in contact; how the laws of friction are explained by the asperity-contact model; coefficients of friction; lubrication; the adhesive and abrasive wear of materials 26. Case Studies in Friction and Wear the design of a journal bearing; materials for skis and sledge runners; 'non-skid' tyres 211 219 225 232 241 250 viii Contents Final case study 27. Materials and Energy in Car Design the selection and economics of materials for automobiles Appendix 1 Examples Appendix 2 Aids and Demonstrations Appendix 3 Symbols and Formulae 261 273 290 297 Index 303 General introduction To the student Innovation in engineering often means the clever use of a new material - new to a particular application, but not necessarily (although sometimes) new in the sense of ‘recently developed’. Plastic paper clips and ceramic turbine-blades both represent attempts to do better with polymers and ceramics what had previously been done well with metals. And engineering disasters are frequently caused by the misuse of materials. When the plastic tea-spoon buckles as you stir your tea, and when a fleet of aircraft is grounded because cracks have appeared in the tailplane, it is because the engineer who designed them used the wrong materials or did not understand the properties of those used. So it is vital that the professional engineer should know how to select materials which best fit the demands of the design - economic and aesthetic demands, as well as demands of strength and durability. The designer must understand the properties of materials, and their limitations. This book gives a broad introduction to these properties and limitations. It cannot make you a materials expert, but it can teach you how to make a sensible choice of material, how to avoid the mistakes that have led to embarrassment or tragedy in the past, and where to turn for further, more detailed, help. You will notice from the Contents list that the chapters are arranged in groups, each group describing a particular class of properties: the elastic modulus; the fracture toughness; resistance to corrosion; and so forth. Each such group of chapters starts by defining the property, describing how it is measured, and giving a table of data that we use to solve problems involving the selection and use of materials. We then move on to the basic science that underlies each property, and show how we can use this fundamental knowledge to design materials with better properties. Each group ends with a chapter of case studies in which the basic understanding and the data for each property are applied to practical engineering problems involving materials. Each chapter has a list of books for further reuding, ranked so that the more elementary come first. At the end of the book you will find sets of examples; each example is meant to consolidate or develop a particular point covered in the text. Try to do the examples that derive from a particular chapter whilesthis is still fresh in your mind. In this way you will gain confidence that you are on top of the subject. No engineer attempts to learn or remember tables or lists of data for material properties. But you should try to remember the broad orders-of-magnitude of these quantities. All grocers know that ’a kg of apples is about 10 apples’ - they still weigh them, but their knowledge prevents them making silly mistakes which might cost them money. In the same way, an engineer should know that ’most elastic moduli lie between 1 and lo3 GN m-2; and are around 102GN mW2 for metals’ - in any real design you need an accurate value, which you can get from suppliers’ specifications; but an order-of- [...]... aspects of this choice, returning in later chapters to a discussion of the other properties Further reading J E Gordon, The New Science of Strong Materials, or Why You Don‘t Fall Through the Floor, Penguin Books, London, 1976, (an excellent general introduction to materials) K E Easterling, Tomorrow’s Materials, Institute of Materials, London, 1987, (an entertaining introduction focussing on the use of high-tech... engineering: gold for microcircuits, platinum for catalysts, sapphire for bearings, diamond for cutting tools They range in price from UE50,OOO (US$75,000)to well over UKElOOm (US$150m) per tonne As an example of how price and availability affect the choice of material for a particular job, consider how the materials used for building bridges in Cambridge have changed over the centuries As our photograph... GFRP has good appearance and, unlike steel or wood, does not rust or become eaten away by Terido worm The mast is made from aluminium alloy, which is lighter for a given strength than wood; advanced masts are now being made by reinforcing the alloy with carbon or boron fibres (man-made composites) The sails, formerly of the natural material cotton, are now made from the polymers nylon, Terylene or... properties mechanical properties Surface properties ease of manufacture, fabrication, Y Aesthetic propertiesappearance, texture, feel Fig 1.7 How the properties of engineering materials affect the way in which products are designed Engineering materials and their properties 11 tonne It is in this sector of the market that the competition between materials is most intense, and the greatest scope for... How are we going to cope with the shortages of engineering materials in the future? One way obviously is by Material-efficient design Many current designs use far more material than is necessary, or use potentially scarce materials where the more plentiful would serve Often, for example, it is a surface property (e.g low friction, or high corrosion resistance) which is wanted; then a thin surface film... The cost of energy enters here The extraction of materials requires energy (Table 2.4) As a material becomes scarcer - copper is a good example - it must be extracted from leaner and leaner ores This expends more and more energy, per tonne of copper metal produced, in the operations of mining, crushing and concentrating the ore; and these energy costs rapidly become prohibitive The rising energy content... and a good designer must be aware of these changes, and continually on the look out for opportunities to substitute one material for another Further reading P E Chapman and E Roberts, Metal Resources and Energy, Butterworths, London, 1983 A H Cottrell, Environmental Economics, Edward Arnold, 1977 T Danvent (ed.), World Resources - Engineering Solutions, Inst Civil Engineers, London, 1976 E G Kovach... and energy) of extracting and transporting the ore or feedstock and processing it to give the engineering material Inflation and increased energy costs obviously drive the price up; so, too, does the necessity to extract materials, like copper, from increasingly lean ores; the leaner the ore, the more machinery and energy are required to crush the rock containing it, and to concentrate it to the level... thin skin of rubber might be useful because its friction coefficient is high, making it easy to grip Traditionally, of course, tool handles were made of another natural, polymer - wood - and, if you measure importance by the volume consumed per year, wood is still by far the most important polymer available to the engineer Wood has been replaced by PMMA Engineering materials and their properties 5 because... fracture toughness But the metal must also resist fatigue (due to rapidly fluctuating loads), surface wear (from striking everything from water droplets to large birds) and corrosion (important when taking off over the sea because salt spray enters the engine) Finally, density is extremely important for obvious reasons: the heavier the engine, the less the pay-load the plane can carry In an effort to reduce . Corrosion how to protect an underground pipeline; materials for a light-weight factory roof; how to make motor-car exhausts last longer G. Friction, abrasion and wear 25. Friction and Wear surfaces. No engineer attempts to learn or remember tables or lists of data for material properties. But you should try to remember the broad orders-of-magnitude of these quantities. All grocers. (GFRP); the much more expensive carbon-fibre reinforced polymers (CFRP); and the still more expensive boron-fibre reinforced alloys (BFRP). The range of composites is a large and growing