Cambridge University Press 978-0-521-64684-0 - Fractography: Observing, Measuring and Interpreting Fracture Surface Topography Derek Hull Frontmatter More information Fractography: observing, measuring and interpreting fracture structure topography Fracture surfaces are produced by breaking a solid. The appearance of the surface, particu­ larly the topography, depends on the type of material-for example, metal, polymer, ceramic, biomaterial, composite, rock, etc. - and on the conditions under which it was broken, for example, stress (tensile, shear, creep, fatigue, impact), temperature, environment (air, water, oil, acid), etc. This book describes ways of studying the surface topography using a wide range of techniques, and the interpretation of the topographical features in terms of the microstruc­ ture of the material and the way it was tested. The level of interest and depth of understanding and interpretation in fractography vary from discipline to discipline. For that reason, the material in the book is presented at different levels and in a number of different ways. Each chapter opens with a feature image and an introduction highlighting important aspects treated in that chapter. Each chapter is copiously illustrated with line figures and half-tone images, accompanied by detailed captions describ­ ing the techniques used in obtaining the images. The main text is also supplemented by foot­ notes, which give additional technical details and the sources of information. Fractography has numerous applications in a wide range of materials, and is particularly relevant in materials science and to inter-disciplinary subjects involving materials science, including physics, chemistry, engineering, biomimetics, earth sciences, biology and archaeol­ ogy. This book provides the basis for an understanding of deformation and fracture in all solids, for interpreting fracture surface topography, and for design of clear and unambiguous experiments involving many aspects of fracture in a wide range of solids. It will be used by senior undergraduates, graduate students, researchers, industrial scientists and engineers and failure investigation engineers. DEREK HULL has had a distinguished academic career in the Universities of Liverpool and Cambridge. His early research was carried out in the University of Wales, Cardiff, at the Atomic Energy Research Establishment, Harwell, and at Oxford University. He has held a number of Visiting Professorships and is a Fellow of the Royal Society and a Fellow of the Royal Academy of Engineering. He has consulted widely for government and industrial com­ panies around the world. His two previous books on Dislocations and Composite Materials have been published in new editions with joint authors and are used extensively in undergrad­ uate university courses in many countries. They have been translated into many languages. The present book draws on his research interests and benefits from the work of many of his research students and colleagues in a wide range of materials. He is Emeritus Goldsmiths' Professor of the University of Cambridge and his current affiliations are as Distinguished Research Fellow in the Department of Materials Science and Metallurgy, University of Cambridge and Senior Fellow, Department of Materials Science and Engineering, University of Liverpool, where he is continuing his research in fracture phenomena. © in this web service Cambridge University Press www.cambridge.org Cambridge University Press 978-0-521-64684-0 - Fractography: Observing, Measuring and Interpreting Fracture Surface Topography Derek Hull Frontmatter More information © in this web service Cambridge University Press www.cambridge.org Cambridge University Press 978-0-521-64684-0 - Fractography: Observing, Measuring and Interpreting Fracture Surface Topography Derek Hull Frontmatter More information Fractography observing, measuring and interpreting fracture surface topography DEREK HULL CAMBRIDGE UNIVERSITY PRESS © in this web service Cambridge University Press www.cambridge.org Cambridge University Press 978-0-521-64684-0 - Fractography: Observing, Measuring and Interpreting Fracture Surface Topography Derek Hull Frontmatter More information cambridge university press Cambridge, New York, Melbourne, Madrid, Cape Town, Singapore, São Paulo, Delhi, Dubai, Tokyo, Mexico City Cambridge University Press The Edinburgh Building, Cambridge cb2 8ru, UK Published in the United States of America by Cambridge University Press, New York www.cambridge.org Information on this title: www.cambridge.org/9780521646840 © Derek Hull 1999 This publication is in copyright. Subject to statutory exception and to the provisions of relevant collective licensing agreements, no reproduction of any part may take place without the written permission of Cambridge University Press. First published 1999 A catalogue record for this publication is available from the British Library Library of Congress Cataloguing in Publication Data Hull, Derek. Fractography: observing, measuring, and interpreting fracture surface topography / Derek Hull. p. cm. Includes bibliographical references and index. ISBN 0 521 64082 2-ISBN 0 521 64684 7 (pbk.) 1. Surfaces (Technology) - Analysis. 2. Fractography. 3. Microstructure. 4. Fracture mechanics. I. Title. TA418.7.H85 1999 62.1’126-dc21 98-40657 CIP isbn 978-0-521-64082-4 Hardback isbn 978-0-521-64684-0 Paperback Cambridge University Press has no responsibility for the persistence or accuracy of URLs for external or third-party internet websites referred to in this publication, and does not guarantee that any content on such websites is, or will remain, accurate or appropriate. Information regarding prices, travel timetables, and other factual information given in this work is correct at the time of first printing but Cambridge University Press does not guarantee the accuracy of such information thereafter. © in this web service Cambridge University Press www.cambridge.org Cambridge University Press 978-0-521-64684-0 - Fractography: Observing, Measuring and Interpreting Fracture Surface Topography Derek Hull Frontmatter More information to Pauline © in this web service Cambridge University Press www.cambridge.org Cambridge University Press 978-0-521-64684-0 - Fractography: Observing, Measuring and Interpreting Fracture Surface Topography Derek Hull Frontmatter More information © in this web service Cambridge University Press www.cambridge.org Cambridge University Press 978-0-521-64684-0 - Fractography: Observing, Measuring and Interpreting Fracture Surface Topography Derek Hull Frontmatter More information Contents Preface xiii Acknowledgements xvi 1 Introduction to the concepts used in the observation, measurement and interpretation of fracture surface topography 1 1.1 Aspects of seeing 1.2 Some scaling issues 6 1.2.1 General 6 1.2.2 Fractal geometry 10 1.2.3 Microstructural dimensions and stress fields 12 1.3 What is a crack? 14 1.4 The origin of cracks 17 1.4.1 Introduction 17 1.4.2 Nucleation of cracks by deformation 18 1.4.3 Other aspects of crack nucleation 21 1.5 Mechanics and micro-mechanics of cracks 23 1.5.1 Introduction 23 1.5.2 Stress fields around an elliptical hole and a crack 25 1.5.3 Critical condition for crack propagation: Griffith and Irwin 28 1.5.4 Other topics 32 2 Observing, describing and measuring fracture surface topography: some basics using Ketton stone as an example 35 2.1 An approach to appreciating 3-D topography 35 2.2 A brief look at the past 37 2.3 What is Ketton stone? 42 2.4 Hooke's observations 44 2.5 Light microscopy 45 2.5.1 The naked eye 45 2.5.2 General 46 2.5.3 Resolution and depth of field 47 2.5.4 Geometrical considerations 50 2.5.5 Illumination 51 2.6 Optical sections and quantitative descriptions of topographical detail 52 vii © in this web service Cambridge University Press www.cambridge.org Cambridge University Press 978-0-521-64684-0 - Fractography: Observing, Measuring and Interpreting Fracture Surface Topography Derek Hull Frontmatter More information viii Contents 2.7 Confocal scanning light microscopy 56 2.8 Scanning electron microscopy 58 2.8.1 General 58 2.8.2 Images produced by secondary and back-scattered electrons 59 2.8.3 Resolution, magnification and depth of field 62 2.8.4 Geometrical considerations 62 2.9 SEM and Ketton stone 64 2.10 Other experimental procedures for investigating fracture surfaces 68 3 Tilting cracks 69 3.1 Evolution of smoothly curving cracks with double curvature 69 3.2 Modes of loading 74 3.3 The geometrical constraint 76 3.3.1 Definitions of tilt and twist 76 3.3.2 Growth of cracks to form smooth surfaces 79 3.3.3 Experimental observation of crack expansion 80 3.4 Growth or evolution of a crack under mixed 1111 conditions 81 3.5 Cracks round bends 87 4 River line patterns 91 4.1 Topographical features of river line patterns 91 4.2 Development of river line patterns on crystalline cleavage facets 94 4.2.1 Steps formed by cracks intersecting screw dislocations 94 4.2.2 Increasing step height in crystalline solids 102 4.3 River patterns in amorphous brittle solids: Sommer's experiment 103 4.3.1 Sommer's experiment 104 4.4 Measurement of surface topography using interference light microscopy 109 4.5 Examples of river lines in a variety of solids 113 4.6 Nucleation of river line steps 117 4.7 Separation at the steps 118 5 Mirror, mist and hackle: surface roughness, crack velocity and dynamic stress intensity 121 5.1 The meaning of 'mirror', 'mist' and 'hackle' 121 5.2 Surface topography from the measurement of roughness profiles