The Science and Engineering of Materials The Science and Engineering of Materials Third 8.1. edition 8olutions manual Donald R. Askeland Prepared by Gregory Lea Adaptation by Paul Porgess, Steve Horne and Howard Taylor luni SPRINGER-SCIENCE+BUSINESS MEDIA, B.V. First edition 1996 © 1996 Springer Science+Business Media Dordrecht Originally published by Chapman & Hall in 1996 ISBN 978-0-412-72610-1 ISBN 978-1-4613-0443-2 (eBook) DOI 10.1007/978-1-4613-0443-2 Apart from any fair deal ing 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 of the 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 conceming reproduction outside the terms stated here should be sent to the publishers at the London 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 8 Printed on acid-free text paper, manufactured in accordance with ANSIINISO Z39.48-1992 and ANSIINISO Z39.48-1984 (Permanence of Paper). CONTENTS Solutions to Practice Problems 1. Introduction to Materials....... .................... 1 2. Atomic Structure... ........ ....... .................. 5 3. Atomic Arrangement .................................. 11 4. Imperfections in the Atomic Arrangement............. 28 5. Atom Movement in Materials .......................... 39 6. Mechanical Testing and Properties ................... 49 7. Strain Hardening and Annealing ...................... 67 8. Principles of Solidification Strengthening and Processing ........................ 75 9. Solid Solution Strengthening and Phase Equilibrium................................... 86 10. Dispersion Strengthening by Solidification. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 96 11. Dispersion Strengthening by Phase Transformation and Heat Treatment ............. 105 12. Ferrous Alloys ...................................... 116 13. Nonferrous Alloys.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 130 14. Ceramic Materials ................................... 139 15. Polymers............................................ 153 16. Composite Materials ................................. 170 17. Construction Materials .............................. 184 18. Electrical Behavior of Materials .................... 187 19. Magnetic Behavior of Materials ...................... 202 20. Optical Behavior of Materials ....................... 208 21. Thermal Properties of Materials ..................... 217 22. Corrosion and Wear .................................. 224 23. Failure - Origin, Detection and Prevention............ . . . . . . . . . . . . . . . . . . . . . . . . .. 234 Suggested Solutions to Design Problems Suggested Solutions ..................................... 246 Sample Homework, Study Guides, Quizzes Example Set 1........................................... 309 Example Set 2 ........................................... 356 VI Chapter 1 Introduction to Materials 1.1 Iron is often coated with a thin layer of zinc if it is to be used outside. What characteristics do you think the zinc provides to this coated, or galvanized, steel? What precautions should be considered in producing this product? How will the recyclability of the product be affected? The zinc provides corrosion resistance to the iron in two ways. If the iron is completely coated with zinc, the zinc provides a barrier between the iron and the surrounding environment, therefore protecting the underlying iron. If the zinc coating is scratched to expose the iron, the zinc continues to protect the iron because the zinc corrodes preferentially to the iron (see Chapter 22). To be effective, the zinc should bond well to the iron so that it does not permit reactions to occur at the interface with the iron and so that the zinc remains intact during any forming of the galvanized material. When the material is recycled, the zinc will be lost by oxidation and vaporization, often producing a "zinc dust" that may pose an environmental hazard. Special equipment may be required to collect and either recycle or dispose of the zinc dust. 1.2 We would like to produce a transparent canopy for an aircraft. If we were to use a ceramic (that is, traditional window glass) canopy, rocks or birds might cause it to shatter. Design a material that would minimize damage or at least keep the canopy from breaking into pieces. We might sandwich a thin sheet of a transparent polymer between two layers of the glass. This approach, used for windshields of automobiles, will prevent the "safety" glass from completely disintegrating when it fails, with the polymer holding the broken pieces of glass together until the canopy can be replaced. Another approach might be to use a transparent, "glassy" polymer mate rial such as polycarbonate. Some polymers have reasonably good impact properties and may resist failure. The polymers can also be toughened to resist impact by introducing tiny globules of a rubber, or elastomer, into the polymer; these globules improve the energy-absorbing ability of the composite polymer, while being too small to interfere with the optical properties of the material. 1.3 Coiled springs ought to be very strong and stiff. Si3N4 is a strong, stiff material. Would you select this material for a spring? Explain. Springs are intended to resist high elastic forces, where only the atomic bonds are stretched when the force is applied. The silicon nitride would satisfy this requirement. However, we would like to also have good resistance to impact and at least some ductility (in case the spring is overloaded) to assure that the spring will not fail catas trophically. We also would like to be sure that all springs will perform satisfactorily. Ceramic materials such as silicon nitride have virtually no ductility, poor impact properties, and often are difficult to manufacture without introducing at least some small flaws that cause to fail even for relatively low forces. The silicon nitride is NOT recommended. 1 1.4 Temperature indicators are sometimes produced from a coiled metal strip that uncoils a specific amount when the temperature increases. How does this work; from what kind of material would the indicator be made; and what are the important properties that the material in the indicator must possess? Bimetallic materials are produced by bonding two materials having dif ferent coefficients of thermal expansion to one another, forming a laminar composite. When the temperature changes, one of the materials will expand or contract more than the other material. This difference in expansion or contraction causes the bimetallic material to change shape; if the original shape is that of a coil, then the device will coil or uncoil, depending on the direction of the temperature change. In order for the material to perform well, the two materials must have very different coefficients of thermal expansion and should have high enough modulus of elasticity so that no permanent deformation of the material occurs. 1.S You would like to design an aircraft that can be flown by human power nonstop for a distance of 30 km. What types of material properties would you recommend? What materials might be appropriate? Such an aircraft must possess enough strength and stiffness to resist its own weight, the weight of the human "power source", and any aerody namic forces imposed on it. On the other hand, it must be as light as possible to assure that the human can generate enough work to operate the aircraft. Composite materials, particularly those based on a polymer matrix, might comprise the bulk of the aircraft. The polymers have a light weight (with densities of less than half that of aluminium) and can be strengthened by introducing strong, stiff fibres made of glass, carbon, or other polymers. Composites having the strength and stiffness of steel, but with only a fraction of the weight, can be produced in this manner. 1.6 You would like to place a three-foot diameter microsatellite into orbit. The satellite will contain delicate electronic equipment that will send and receive radio signals from earth. Design the outer shell within which the electronic equipment is contained. What properties will be required and what kind of materials might be considered? The shell of the microsatellite must satisfy several criteria. The material should have a low density, minimizing the satellite weight so that it can be lifted economically into its orbit; the material must be strong, hard, and impact resistant in order to assure that any "space dust" that might strike the satellite does not penetrate and damage the electronic equipment; the material must be transparent to the radio signals that provide communication between the satellite and earth; and the material must provide some thermal insulation to assure that solar heating does not damage the electronics. One approach might be to use a composite shell of several materials. The outside surface might be a very thin reflective metal coating that would help reflect solar heat. The main body of the shell might be a light weight fibre-reinforced composite that would provide impact resistance (preventing penetration by dust particles) but would be transparent to radio signals. 1.7 What properties should the head of a carpenter's hammer possess? How would you manufacture a hammer head? 2 The head for a carpenter's hammer is produced by forging, a metal working process; a simple steel shape is heated and formed in several steps while hot into the required shape. The head is then heat treated to produce the required mechanical and physical properties. The striking face and claws of the hammer should be hard -- the metal should not dent or deform when driving or removing nails. Yet these portions must also possess some impact resistance, particularly so that chips do not flake off the striking face and cause injuries. 1.8 The hull of the space shuttle consists of ceramic tiles bonded to an aluminium skin. Discuss the design requirements of the shuttle hull that led to the use of this combination of materials. What problems in producing the hull might the designers and manufacturers have faced? The space shuttle experiences extreme temperatures during re-entry into earth's atmosphere; consequently a thermal protection system must be used to prevent damage to the structure of the shuttle (not to mention its contents!). The skin must therefore be composed of a material that has an exceptionally low thermal conductivity. The material must be capable of being firmly attached to the skin of the shuttle and to be easily repaired when damage occurs. The tiles used on the space shuttle are composed of silica fibres bonded together to produce a very low density ceramic. The thermal conductivity is so low that a person can hold on to one side of the tile while the opposite surface is red hot. The tiles are attached to the shuttle skin using a rubbery polymer that helps assure that the forces do not break the tile loose, which would then expose the underlying skin to high temperatures. 1.9 You would like to select a material for the electrical contacts in an electrical switching device which opens and closes frequently and force fully. What properties should the contact material possess? What type of material might you recommend? Would Al 0 be a good choice? Explain. 2 3 The material must have a high electrical conductivity to assure that no electrical heating or arcing occurs when the switch is closed. High purity (and therefore very soft) metals such as copper, aluminium, sil ver or gold provide the high conductivity. However the device must also have good wear resistance, requiring that the material be hard. Most hard, wear resistant materials have poor electrical conductivity. One solution to this problem is to produce a particulate composite material composed of hard ceramic particles embedded in a continuous matrix of the electrical conductor. For example, silicon carbide par ticles could be introduced into pure aluminium; the silicon carbide par ticles provide wear resistance while aluminium provides conductivity. Other examples of these materials are described in Chapter 16. A1 0 by itself would not be a good choice -- alumina is a ceramic 2 3 material and is an electrical insulator. However alumina particles dispersed into a copper matrix might provide wear resistance to the composite. 1.10 Aluminium has a density of 2.7 Mg.m-3• Suppose you would like to produce a composite material based on aluminium having a density of 1.5 Mg.m-3 • Design a material that would have this density. Would introducing beads of polyethylene, with a density of 0.95 Mg.m-3, into the aluminium be a likely possibility? Explain. 3 In order to produce an aluminium-matrix composite material with a den sity of 1.5 Mg.m-3, we would need to select a material having a density considerably less than 1.5 Mg.m-3• While polyethylene's density would make it a possibility, the polyethylene has a very low melting point compared to aluminium; this would make it very difficult to introduce the polyethylene into a solid aluminium matrix -- processes such as casting or powder metallurgy would destroy the polyethylene. Therefore polyethylene would NOT be a likely possibility. One approach, however, might be to introduce hollow glass beads. Although ceramic glasses have densities comparable to that of aluminium, a hollow bead will have a very low density. The glass also has a high melting temperature and could be introduced into liquid aluminium for processing as a casting. 1.11 You would like to be able to identify different materials without resorting to chemical analysis or lengthy testing procedures. Describe some possible testing and sorting techniques you might be able to use based on the physical properties of materials. Some typical methods might include: measuring the density of the mate rial (may help in separating metal groups such as aluminium, copper, steel, magnesium, etc.), determining the electrical conductivity of the material (may help in separating ceramics and polymers from metallic alloys), measuring the hardness of the material (perhaps even just using a file), and determining whether the material is magnetic or nonmagnetic (may help separate iron from other metallic alloys) . 1.12 You would like to be able to physically separate different materials in a scrap recycling plant. Describe some possible methods that might be used to separate materials such as polymers, aluminium alloys, and steels from one another. Steels can be magnetically separated from the other materials; steel (or carbon-containing iron alloys) are ferromagnetic and will be attracted by magnets. Density differences could be used -- polymers have a density near that of water; the specific gravity of aluminium alloys is around 2.7; that of steels is between 7.5 and 8. Electrical conductivity measurements could be used -- polymers are insulators, aluminium has a particularly high electrical conductivity. 1.13 Some pistons for automobile engines might be produced from a composite material containing small, hard silicon carbide particles in an aluminium alloy matrix. Explain what benefits each material in the composite may provide to the overall part. What problems might the different properties of the two materials cause in producing the part? Aluminium provides good heat transfer due to its high thermal conducti vity. It has good ductility and toughness, reasonably good strength, and is easy to cast and process. The silicon carbide, a ceramic, is hard and strong, providing good wear resistance, and also has a high melting temperature. It provides good strength to the aluminium, even at elevated temperatures. However there may be problems producing the material -- for example, the silicon carbide may not be uniformly distributed in the aluminium matrix if the pistons are produced by casting. We need to assure good bonding between the particles and the aluminium -- the surface chemistry must therefore be understood. Differences in expansion and contraction with temperature changes may cause debonding and even cracking in the composite. 4