(Solution Manual) Accompany the Science and Engineering of Materials

Askeland,Wright, 7

Engineering

Solution Manual

7th Edition

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Solution Manual for Accompany the Science and Engineering of Materials, The downloadable file consists of 460 pages, and the total size of the file is 10.01 MB. Purchase now only for highly discounted price.

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AN INSTRUCTOR ’S SOLUTIONS MANUAL TO ACCOMPANY THE SCIENCE AND ENGINEERING OF MATERIALS SEVENTH EDITION DONALD R. ASKELAND WENDELIN J. WRIGHT Printed in the United States of America Print Number: 01 Print Year: 2015 © 2016, 2011 Cengage Learning WCN: 01-100-101 ALL RIGHTS RESERVED. No part of this work covered b y the copyright herein may be reproduced, transmitted, st ored, or used in any form or by any means graphic, electroni c, or mechanical, including but not limited to photocopyi ng, recording, scanning, digitizing, taping, Web distri bution, information networks, or information storage and re trieval systems, except as permitted under Section 107 or 1 08 of the 1976 United States Copyright Act, without the prior written permission of the publisher except as may be permit ted by the license terms below. For product information and technology assistance, contact us at Cengage Learning Academic Resource Center, 1-800-423-0563 . For permission to use material from this text or pr oduct, submit all requests online at www.cengage.com/permissions . Further permissions questions can be emailed to permissionrequest@cengage.com . ISBN : 978-1-305-07678-5 Cengage Learning 20 Channel Center Street Boston, MA 02210 USA Cengage Learning is a leading provider of customize d learning solutions with office locations around the globe, including Singapore, the United Kingdom, Australia, Mexico, Brazil, and Japan. Locate your local office at: international.cengage.com/region . Cengage Learning products are represented in Canada by Nelson Education, Ltd. For your course and learning solutions, visit www.cengage.com/engineering . Purchase any of our products at your local college store or at our preferred online store www.cengagebrain.com . NOTE: UNDER NO CIRCUMSTANCES MAY THIS MATERIAL OR A NY PORTION THEREOF BE SOLD, LICENSED, AUCTIONED, OR OTHERWISE REDISTRIBUTED EXCEPT AS MAY BE PERMITT ED BY THE LICENSE TERMS HEREIN. 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INSTRUCTOR 'S SOLUTIONS MANUAL TO ACCOMPANY The Science and Engineering of Materials Seventh Edition DONALD R. ASKELAND University of Missouri —Rolla, Emeritus WENDELIN J. WRIGHT Bucknell University Contents Chapter 1 ......................................... ................................................... .............................................. 1 Chapter 2 ......................................... ................................................... ............................................ 13 Chapter 3 ......................................... ................................................... ............................................ 25 Chapter 4 ......................................... ................................................... ............................................ 77 Chapter 5 ......................................... ................................................... ............................................ 97 Chapter 6 ......................................... ................................................... .......................................... 121 Chapter 7 ......................................... ................................................... .......................................... 153 Chapter 8 ......................................... ................................................... .......................................... 173 Chapter 9 ......................................... ................................................... .......................................... 197 Chapter 10 ........................................ ................................................... ......................................... 225 Chapter 11 ........................................ ................................................... ......................................... 251 Chapter 12 ........................................ ................................................... ......................................... 271 Chapter 13 ........................................ ................................................... ......................................... 293 Chapter 14 ........................................ ................................................... ......................................... 313 Chapter 15 ........................................ ................................................... ......................................... 325 Chapter 16 ........................................ ................................................... ......................................... 335 Chapter 17 ........................................ ................................................... ......................................... 349 Chapter 18 ........................................ ................................................... ......................................... 375 Chapter 19 ........................................ ................................................... ......................................... 385 Chapter 20 ........................................ ................................................... ......................................... 403 Chapter 21 ........................................ ................................................... ......................................... 415 Chapter 22 ........................................ ................................................... ......................................... 431 Chapter 23 ........................................ ................................................... ......................................... 443 1 © 2016 Cengage Learning. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Chapter 1: Introduction to Materials Science and En gineering 1-1 Define materials science and engineering (MSE). Solution: Materials science and engineering (MSE) is an inter disciplinary field that studies and manipulates the composition and structure of materi als across length scales to control materials properties through synthesis and processi ng. 1-2 What is the importance of the engineering tetrahedr on for materials engineers? Solution: Structure, properties and performance all depend on the route in which a material is processed. We cannot predict the end properties for a material until we have specified a process to produce the component. Using the same ma terial, but changing the way it is processed will result in different structure, prope rties and performance of that material. This is applicable to all material systems. 1-3 Define the following terms: (a) composition; (b) structure; (c) synthesis; (d) processing; and (e) microstructure. Solution: (a) The chemical make-up of a material. (b) The arrangement of atoms, seen at different lev els of detail. (c) How materials are made from naturally occurring or man-made chemicals. (d) How materials are shaped into useful components . (e) The structure of an object at the microscopic s cale. 1-4 Explain the difference between the terms materials science and materials engineering. Solution: Materials scientists work on understanding underlyi ng relationships between the synthesis and processing, structure, and properties of materials. Materials engineers focus on how to translate or transform materials in to useful devices or structures. 2 © 2016 Cengage Learning. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 1-5 The myriad materials in the world primarily fall in to four basic categories; what are they? What are materials called that have one or mo re different types of material fabricated into one component? Give one example. Solution: Metals, polymers and ceramics. The addition of one or more of these to a single system is called a composite. An example of a composite m aterial is fiberglass. 1-6 What are some of the materials and mechanical prope rties of metals and alloys? Solution: Metals and alloys have good electrical and thermal conductivity, high strength, ductility and formability, and high stiffness. 1-7 What is a ceramic, and what are some of the propert ies that you expect from a ceramic? Solution: Ceramics tend to have very high compressive strengt hs, but behave in a brittle (glass- like) manner. They have very high melting temperatu res. Poor thermal conductivity and electrical conductivity make ceramics behave as an insulator instead of a conductor. 1-8 Make comparisons between thermoplastics and thermos etting polymers (a) on the basis of mechanical characteristics upon heating, and (b) according to possible molecular structures. Solution: Thermoplastics tend to soften with elevated tempera ture exposure with gradually decreasing viscosity. Thermosetting polymers do not soften with elevated temperature exposure; instead they will remain hard and will de grade, possibly charring with prolonged exposure. Thermoplastics consist of long chain molecular arra ngements of covalently bonded carbon atoms with various side groups. Thermosettin g polymers tend to be a complex 3- D arrangement usually deviating from the clearly de fined long-chain molecular arrangement. 1-9 Give three examples of composites that can be fabri cated. Solution: Metal matrix composites (MMC) – A metal matrix rein forced with a ceramic material in the form of particles, whiskers or fibers. Example: Cobalt alloy reinforced with tungsten- carbide particulates. Polymer matrix composites (PMC) – A polymer matrix reinforced with a ceramic material in the form of whiskers or fibers. Example : Kevlar or fiberglass. 3 © 2016 Cengage Learning. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Ceramic matrix composites (CMC) – A ceramic matrix reinforced with ceramic or metallic material in the form of whiskers or fibers . Example: Carbon fibers in an alumina (Al 2O3) matrix. 1-10 For each of the following classes of materials, giv e two specific examples that are a regular part of your life: (a) metals; (b) ceramics; (c) polymers; and (d) semiconductors. Specify the object that each material is found in a nd explain why the material is used in each specific application. Hint: One example answer for part (a) would be that aluminum is a metal used in the base of some pots a nd pans for even heat distribution. It is also a lightweight metal that makes it useful in kitchen cookware. Note that in this partial answer to part (a), a specific metal is des cribed for a specific application. Solution: (a) Aluminum was described in the problem statement . Stainless steel is used for flatware. It is easily formed and has good corrosio n resistance, strength, and hardness. (b) Two specific examples of polymers are polystyre ne and polytetrafluoroethylene also known as Teflon. Styrofoam is polystyrene rigid foa m insulation that is used for cups that keep hot drinks warm. Teflon is used as a coat ing on the inside of kitchen cookware such as frying pans because it prevents food from s ticking to the pan while cooking. (c) Two examples of semiconductors are silicon dope d with phosphorus ( n–type) and silicon doped with boron ( p–type). Both types of impurities convert silicon fr om a poor into a useful conductor. Both n and p–type semiconductors are contained in the semiconductor device called a diode, so that at the junction between both types, current is able to flow. A diode blocks current in one direction while allowing current flow in the other direction. A device that uses bat teries, e.g. a remote control or a calculator, often contains a diode that protects th e device if the batteries are inserted backward. The diode blocks the current from leaving the battery if it is reversed, protecting the sensitive electronics in the device. Another semiconductor is the compound semiconductor Al xGa 1-xAs, which is used in lasers. (d) Ceramics are compounds that contain metallic an d nonmetallic elements. Two specific examples are tungsten carbide and magnesia . Tungsten carbide is often bonded with cobalt and/or nickel. Tungsten carbide is used mainly in tips for metal cutting tools (knives can be made with this) because of its good wear resistant characteristics. Magnesia is a heat resistant ceramic that is used i n liners for ovens. Magnesia can resist high temperatures but is susceptible to thermal str ess cracking. 4 © 2016 Cengage Learning. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 1-11 Describe the enabling materials property of each of the following and why it is so: (a) steel for I-beams in skyscrapers; (b) a cobalt chrome molybdenum alloy for hip implan ts; (c) polycarbonate for eyeglass lenses; and (d) bronze for artistic castings. Solution: (a) Steel for I-beams in skyscrapers must be strong in order to bear large mechanical loads. (b) A cobalt chrome molybdenum alloy for hip implan ts must be biocompatible, meaning that it must not degrade when inserted into the body nor be toxic or otherwise dangerous. (c) Polycarbonate for eyeglass lenses must be trans parent and impact-resistant. (d) Bronze can be melted and poured into molds to b e shaped. It is also fairly corrosion resistant (which is important for outdoor sculpture s). Over long periods of time when subjected to an outdoor environment, bronze will de velop an oxide known as a patina. The patina protects the bronze from further corrosi on. 1-12 Describe the enabling materials property of each of the following and why it is so: (a) aluminum for airplane bodies; (b) polyurethane for teeth aligners (invisible brac es); (c) steel for the ball bearings in a bicycle’s whee l hub; (d) polyethylene terephthalate for water bottles; a nd (e) glass for wine bottles. Solution: (a) Aluminum has a high strength to weight ratio. T hus it has the strength needed to withstand the forces imposed on an airframe, but ke eps the weight of the airplane low compared to other metals. The lighter the airplane body, the less force it takes to lift the plane into the air. This results in less fuel being used and a reduction in operating costs. Aluminum also has good corrosion resistance. (b) Polyurethane for teeth aligners must be highly formable and transparent. Since teeth aligners are worn during the day, a transparent mat erial is desirable to make them less conspicuous. A unique set of teeth aligners must be produced for each individual, and so the polyurethane must be easily molded. Computer so ftware is used to produce computer models of a person’s teeth during various stages of the correction process. A rapid prototyping tool is used to create physical m odels of the person’s teeth at each stage. A sheet of polyurethane is then heated and f ormed onto the models to produce the teeth aligners. 5 © 2016 Cengage Learning. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. (c) Ball bearings in a bicycle’s wheel hub reduce f riction between metal surfaces. Therefore, steel is used because it has high streng th and hardness. (d) Polyethylene terephthalate is easily formed by a blow molding process and is recyclable, critical properties for mass-produced w ater bottles. (e) Glass has high chemical resistance; thus, glass bottles are used to preserve the taste of the wine contained in them. 1-13 What properties should an engineer consider for a t otal knee replacement of a deteriorated knee joint with an artificial prosthes is when selecting the materials for this application? Solution: Properties that should be considered are those rela ting to strength (fatigue, tensile and compressive) since the knee sustains static, dynami c and cyclic loads. Hardness will promote wear resistance. Modulus of elasticity simi lar to that of the human bone otherwise other problems will occur. Chemical stabi lity in regards to corrosion resistance and cellular toxicity to prevent negativ e reactions to the material selected. The material needs to have the ability to bond with the residual bone material and have longevity in order to avoid frequent replacement. 1-14 Write one paragraph about why single-crystal silico n is currently the material of choice for microelectronics applications. Write a second p aragraph about potential alternatives to single-crystal silicon for solar cell applicatio ns. Provide a list of the references or websites that you used. You must use at least three references. Solution: Answers will vary. 1-15 Coiled springs should be very strong and stiff. Sil icon nitride (Si 3N4) is a strong, stiff material. Would you select this material for a spri ng? Explain. Solution: Springs are intended to resist high elastic forces, where only the atomic bonds are stretched when the force is applied. The silicon ni tride 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 ens ure that the spring will not fail catastrophically. We also would like to be sure tha t all springs will perform satisfactorily. Ceramic materials such as silicon nitride have virt ually no ductility, poor impact properties, and often are difficult to manufacture without introducing at least some small flaws that cause failure even for relatively low forces. The silicon nitride is NOT recommended. 6 © 2016 Cengage Learning. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 1-16 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 a re the important properties that the material in the indicator must possess? Solution: Bimetallic materials are produced by bonding two ma terials having different coefficients of thermal expansion to one another, forming a lami nar composite. When the temperature changes, one of the materials will expa nd or contract more than the other material. This difference in expansion or contracti on causes the bimetallic material to change shape; if the original shape is that of a co il, then the device will coil or uncoil, depending on the direction of the temperature chang e. In order for the material to perform well, the two materials must have very diff erent coefficients of thermal expansion and should have high enough moduli of ela sticity so that no permanent deformation of the material occurs. 1-17 What is the purpose of the classification for funct ional materials? Solution: It specifically categorizes the types of materials used with specific applications. For instance, aerospace materials use lightweight mater ials such as aluminum alloys or carbon-composites for flight applications instead o f using heavy materials such as stainless steel. 1-18 Explain the difference between crystalline and amor phous materials. Give an example of each that you use in your daily life. Solution: Crystalline materials have long-range order arrange ment of its atoms while amorphous materials have short-range order. One example of a crystalline material is metal and an example of an amorphous material is glass. 1-19 If you were given a material and were asked to dete rmine whether it is crystalline or amorphous, how would you determine it? Solution: Crystalline materials can be delineated from amorph ous materials using diffraction techniques. Crystalline materials will produce diff raction patterns while amorphous materials will not. 1-20 List six materials performance problems that may le ad to failure of components. Solution: Excessive deformation (overload), fracture, wear, c orrosion, fatigue and creep. 7 © 2016 Cengage Learning. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 1-21 Steel 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 t his coated, or galvanized, steel? What precautions should be considered in producing this product? How will the recyclability of the product be affected? Solution: The zinc provides corrosion resistance to the iron in two ways. If the iron is completely coated with zinc, the zinc provides a barrier betwe en the iron and the surrounding environment, therefore protecting the underlying ir on. 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 23). To be effective, the zinc should bond well to the iron so that it does not permit reactions to oc cur 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 oxid ation 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 o f the zinc dust. 1-22 The relationship between structure and materials pr operties can be influenced by the service conditions (environmental conditions). Name two engineering disasters that have had tragic results and why they happened. Solution: Answers will vary. Two sample answers: The Titanic sank when it hit an iceberg. Hull plate and rivets of the ship were made of the strongest material to use at that time, but at room temperature. The material failed due to its anisotropy and temperature sensitivity f or when it was exposed to the frigid waters during its voyage, behaved like glass (britt le). The Space Shuttle Challenger tragic flight when the rocket boosters exploded due to the solid rocket booster (SRB) O-ring failure. The free zing temperatures of that morning had the O-rings behave like glass and the vibrations du ring lift-off cracked the O-rings and the boosters exploded. 1-23 What is the difference between physical and mechani cal properties? List three examples for each one. Solution: Physical properties are the properties of a materia l as it is found in nature such as density, thermal conductivity, electrical conductiv ity, luster, color, corrosion resistance, oxidation resistance, coefficient of thermal expans ion (CTE) and magnetic permeability. Mechanical properties are properties that can be te sted for such as strength (fatigue, impact, tensile, yield), ductility, stiffness, cree p rupture, toughness and hardness. 8 © 2016 Cengage Learning. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 1-24 The type of jet engine used on most large commercia l aircraft is called a turbofan jet engine because it has a large wheel at the front of the engine that propels air rearward. Most of this air bypasses the engine, but bypass ai r significantly increases thrust and efficiency of these engines. Some engine manufactur ers are now using carbon fiber- epoxy composites rather than traditional aluminum b lades. (a) What materials properties do you think an engin eer must consider when selecting a material for this application? Be as specific as po ssible. (b) What benefits do you think carbon fiber epoxy c omposites have compared to aluminum alloys? What limitations or possible downs ides could there be to using a carbon fiber epoxy composite? Solution: (a) Properties that should be considered include th e following: Tensile strength, impact toughness, fracture toughness, modulus of elasticit y and resistance to ultraviolet radiation, which is a deteriorative property for po lymers. (b) Potential benefits include significant weight r eduction and greater stiffness over aluminum. The downsides include increase cost and m ost likely lower fracture toughness. 1-25 You are an engineer working for a manufacturer of l and-based gas turbines. These turbines are similar to jet engines, but they are u sed on land to provide power for electricity generation and gas compression pipeline applications. Suppose that you would like to apply a ceramic-based thermal barrier coating to the turbine blades in the first-stage turbine to increase the operating tempe rature and efficiency of the engine. (a) What difficulties might engineers experience in trying to design a ceramic coating that will be applied to a super alloy metal blade? (b) What properties should be taken into considerat ion when choosing a suitable ceramic material for a coating? Be as thorough as p ossible. Solution: (a) Difficulties include a suitable method to apply and bond the ceramic to the metal blades. Coefficients of thermal expansion (CTE) for metals and ceramics differ greatly which would result in spallation of the ceramic coa ting. (b) Properties to be considered should be coefficie nt of thermal expansion (CTE), thermal conductivity, specific heat, melting temper ature, impact toughness and deteriorative properties. 1-26 We would like to produce a transparent canopy for a n aircraft. If we were to use a traditional window glass canopy, rocks or birds mig ht cause it to shatter. Design a material that would minimize damage or at least kee p the canopy from breaking into pieces. 9 © 2016 Cengage Learning. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Solution: We might sandwich a thin sheet of a transparent pol ymer between two layers of the glass. This approach, used for windshields of autom obiles, 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, “gl assy” polymer material such as polycarbonate. Some polymers have reasonably good i mpact properties and may resist failure. The polymers can also be toughened to resi st impact by introducing tiny globules of a rubber, or elastomer, into the polyme r; these globules improve the energy- absorbing ability of the composite polymer, while b eing too small to interfere with the optical properties of the material. 1-27 You would like to design an aircraft that can be fl own by human power nonstop for a distance of 30 km. What types of material propertie s would you recommend? What materials might be appropriate? Solution: Such an aircraft must possess enough strength and s tiffness to resist its own weight, the weight of the human “power source,” and any aerodyn amic forces imposed on it. On the other hand, it must be as light as possible to ensure that the human can generate enough work to operate the aircraft. Composite mate rials, particularly those based on a polymer matrix, might comprise the bulk of the airc raft. The polymers have a light weight (with densities of less than half that of al uminum) and can be strengthened by introducing strong, stiff fibers made of glass, car bon, or other polymers. Composites, having the strength and stiffness of steel, but wit h only a fraction of the weight, can be produced in this manner. 1-28 You would like to place a three-foot diameter micro satellite into orbit. The satellite will contain delicate electronic equipment that will sen d and receive radio signals from earth. Design the outer shell within which the elec tronic equipment is contained. What properties will be required, and what kind of mater ials might be considered? Solution: The shell of the microsatellite must satisfy severa l criteria. The material should have a low density, minimizing the satellite weight so tha t it can be lifted economically into its orbit; the material must be strong, hard, and impac t resistant in order to ensure that any “space dust” that might strike the satellite do es not penetrate and damage the electronic equipment; the material must be transpar ent to the radio signals that provide communication between the satellite and earth; and the material must provide some thermal insulation to ensure that solar heating doe s not damage the electronics. One approach might be to use a composite shell of s everal materials. The outside surface might be a very thin reflective metal coati ng that would help reflect solar heat. 10 © 2016 Cengage Learning. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. The main body of the shell might be a light weight fiber-reinforced composite that would provide impact resistance (preventing penetra tion by dust particles) but would be transparent to radio signals. 1-29 What properties should the head of a carpenter’s ha mmer possess? How would you manufacture a hammer head? Solution: The head for a carpenter’s hammer is produced by fo rging, 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. These por tions must also possess some impact resistance, particularly so that chips do no t flake off the striking face and cause injuries. 1-30 You would like to select a material for the electri cal contacts in an electrical switching device that opens and closes frequently and forcefu lly. What properties should the contact material possess? What type of material mig ht you recommend? Would Al 2O3 be a good choice? Explain. Solution: The material must have a high electrical conductivi ty to ensure that no electrical heating or arcing occurs when the switch is closed. High pu rity (and therefore very soft) metals such as copper, aluminum, silver, or gold provide t he high conductivity. The device must also have good wear resistance, requiring that the material be hard. Most hard, wear resistant materials have poor electrical conductivi ty. One solution to this problem is to produce a partic ulate composite material composed of hard ceramic particles embedded in a continuous matrix of the electrical conductor. For example, silicon carbide particles could be int roduced into pure aluminum; the silicon carbide particles provide wear resistance w hile aluminum provides conductivity. Other examples of these materials are described in Chapter 17. Al 2O3 by itself would not be a good choice—alumina is a ceramic material and is an electrical insulator; however, alumina particles di spersed into a copper matrix might provide wear resistance to the composite. 1-31 Aluminum has a density of 2.7 g/cm 3. Suppose you would like to produce a composite material based on aluminum having a density of 1.5 g/cm 3. Design a material that would have this density. Would introducing beads of polye thylene, with a density of 0.95 g/cm 3, into the aluminum be a likely possibility? Explai n. 11 © 2016 Cengage Learning. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. Solution: In order to produce an aluminum-matrix composite ma terial with a density of 1.5 g/cm 3, we would need to select a material having a density considerably less than 1.5 g/cm 3. While polyethylene’s density would make it a possib ility, the polyethylene has a very low melting point compared to aluminum; this would make it very difficult to introduce the polyethylene into a solid aluminum matrix—proce sses such as casting or powder metallurgy would destroy the polyethylene. Therefor e 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 alumin um, a hollow bead will have a very low density. The glass also has a high melting temp erature and could be introduced into liquid aluminum for processing as a casting. 1-32 You would like to be able to identify different mat erials without resorting to chemical analysis or lengthy testing procedures. Describe so me possible testing and sorting techniques you might be able to use based on the ph ysical properties of materials. Solution: Some typical methods might include: measuring the d ensity of the material (may help in separating metal groups such as aluminum, copper, s teel, magnesium, etc.), determining the electrical conductivity of the mate rial (may help in separating ceramics and polymers from metallic alloys), measuring the h ardness of the material (perhaps even just using a file), and determining whether th e material is magnetic or nonmagnetic (may help separate iron from other meta llic alloys). 1-33 You would like to be able to physically separate di fferent materials in a scrap recycling plant. Describe some possible methods that might be used to separate materials such as polymers, aluminum alloys, and steels from one anot her. Solution: 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 n ear that of water; the specific gravity of aluminum alloys is around 2.7; that of s teels is between 7.5 and 8. Electrical conductivity measurements could be used—polymers ar e insulators while aluminum has a particularly high electrical conductivity. 1-34 Some pistons for automobile engines might be produc ed from a composite material containing small, hard silicon carbide particles in an aluminum 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?