THIRD EDITION NORTH AMERICAN Materials EDITION ENGINEERING, SCIENCE, PROCESSING AND DESIGN Michael Ashby, Hugh Shercliff and David Cebon Materials: engineering, science, properties, and design 3e Solution manual Chapter 1: Exercises with worked solutions Exercise E1.1 Use a search engine such as Google to research the history and uses of one of the following materials: . Tin . Glass . Cement . Titanium . Carbon fiber Present the result as a short report of about 100 - 200 words (roughly half a page). Specimen answer: Tin. Tin (symbol Sn), a silver-white metal, has a long history. It was traded in the civilizations of the Mediterranean as early as 1500 BC (the Old Testament of the Christian bible contains many references to it). Its importance at that time lay in its ability to harden copper to give bronze (copper containing about 10% tin), the key material for weapons, tools and statuary of the Bronze age (1500 BC – 500 BC). Today tin is still used to make bronze, for solders and as a corrosion resistant coating on steel sheet (“tin plate” ) for food and drink containers – a “tinnie”, to an Australian, is a can of beer. Plate glass is made by floating molten glass on a bed of liquid tin (the Pilkington process). Thin deposits of tin compounds on glass give transparent, electrically conducting coatings used for frost-free windshields and for panel lighting. Exercise E1.2 What is meant by the design-limiting properties of a material in a given application? Answer. A design-limiting property in a given application is one that limits the performance of the application. To meet a required level of performance, the design-limiting properties must meet or exceed target values. Exercise E1.3 There have been many attempts to manufacture and market plastic bicycles. All have been too flexible. Which design-limiting property is insufficiently large? Answer. Flexibility is lack of stiffness. The stiffness of a structure depends on its shape and size, and on the value of Young’s modulus E of the material of which it is made. In design for stiffness E is a design-limiting property. In bicycle design the values of E offered by plastics are insufficiently large. However if the plastic is reinforced with carbon or glass fiber the stiffness can be increased to a useful level – high performance bicycles are made of carbon-reinforced plastic. Exercise E1.4 What, in your judgment, are the design-limiting properties for the material for the blade of a knife that will be used to gut fish? Answer. Hardness (to give a wear resistant, sharp edge); ability to be shaped to a blade; resistance to corrosion in fresh and salt water; stiffness (meaning modulus) to ensure that the thin blade does not bend or buckle during use. Exercise E1.5 What, in your judgment, are the design-limiting properties for the material of an oven glove? Answer. Flexibility (to allow weaving or shaping, and motion in use); low thermal conductivity (to insulate); maximum operating temperature > 200C (high oven setting); and ability to be washed, meaning tolerance of water. Exercise E1.6 What, in your judgment, are the design-limiting properties for the material of an electric lamp filament? Answer. The filament must be a good electrical conductor; maximum operating temperature > 2000oC (or a temperature of that order); ductility to enable it to be drawn to fine wire. Exercise E1.7 A material is needed for a tube to carry fuel from the fuel tank to the carburetor of a motor- powered mower. The design requires that the tube be flexible, and that the fuel be visible. List what you think would be the design-limiting properties. Answer. Flexible (meaning low modulus E ); transparency (to allow fuel to be visible); very good resistance to organic solvents (gasoline and oil); ability to be formed into tube. Exercise E1.8 A material is required as the magnet for a magnetic soap holder. Soap is mildly alkaline. List what you would judge to be the design-limiting properties. Answer. Ferromagnetic; very good resistance to fresh water and mild alkali. Exercise E1.9 The cases in which most CDs are sold have an irritating way of cracking and breaking. Which design-limiting property has been neglected in selecting the material of which they are made? Answer. Fracture toughness Exercise E1.10 List three applications that, in your judgment, need high stiffness and low weight. Think of things that must be light (as they are moved, perhaps rapidly) but must not be too 'bendy'. Possible answers. Racing bicycle frames; aircraft wing spars; car wheels; sports equipment; precision machine tools; radio-telescope dishes; high-speed printing presses. Exercise E1.11 List three applications that, in your judgment, need optical quality glass. Think of products that rely on distortion-free imaging. Possible answers. Binoculars; cameras; contact lenses; microscopes; telescopes; fiber-optic cables. Exercise E1.12 List three applications that you think would require high thermal conductivity. Think of things that you have to get heat into or out of. Possible answers. Cooking utensils; heat exchangers (car radiators, air-conditioning units); heat sinks (like those that conduct the heat from the processor in your PC); thermal sensors and thermally activated safety equipment. Exercise E1.13 List three applications that you think would require low thermal expansion. Think of things that you that will lose accuracy or won’t work if they distort. Possible answers. Optical benches; precision watches; gyroscopes such as those in inertial guidance systems; precision equipment generally. Materials: engineering, science, properties, and design 3e Solution manual Chapter 2. Exercises with worked solutions Exercise E2.1 Material properties from experience. List the six main classes of engineering materials. Use your own experience to rank them approximately: (a) by stiffness (modulus, E ). A sheet of a material that has a high modulus is hard to bend when in the form of sheet. A sheet of material with a low modulus is floppy. (b) by thermal conductivity ( ). Materials with high conductivity feel cold when you pick them up on a cold day. Materials with low conductivity may not feel warm, but they don’t freeze your hands. Answer. The main classes of engineering materials are ceramics, glasses, metals, polymers, elastomers and hybrids that include composites, foams and natural materials. (a) Metals, ceramics and glasses and composites are stiff; polymers, elastomers and foams are less stiff. (b) Metals are cold to touch - they conduct heat well; polymers, many hybrids (like wood and foams) have low thermal conductivity. Exercise E2.2 Classification (1). A good classification looks simple – think, for instance, of the periodic table of the elements. Creating it in the first place, however, is another matter. This chapter introduced two classification schemes that work, meaning that every member of the scheme has a unique place in it, and any new member can be inserted into its proper position without disrupting the whole. Try one for yourself. Here are some scenarios. Make sure that each level of the hierarchy properly contains all those below it. There may be more than one way to do this, but one is usually better than the others. Test it by thinking how you would use it to find the information you want. How many different ways can two sheets of paper be attached to each other, temporarily or permanently? Classify these, using ‘Mechanism of joining’ as the top level of the classification. Then try to develop the next level, based on your observations of the ways in which sheets of paper are joined. Possible answer Adhesives Water based Solvent based Staples Steel Brass Paper clips Metal Plastic Sewing Natural fibers Man-made fibers Exercise E2.3 Classification (2). In how many ways can wood be treated to change its surface appearance? Classify these, using the generic finishing technique as the top level of the classification. Then try to develop the next level, based on your observations of the ways in which wood products are finished. Possible answer Varnish Clear Tinted Paint Water-based Solvent based Polish Wax Spray Dye, stain Natural, Synthetic Texture Sanded, sand-blasted Weathered. Exercise E2.4 Classification (3). You run a bike shop that stocks bikes of many types (children’s bikes, street bikes, mountain bikes, racing bikes, folding bikes etc), prices and sizes. You need a classification system to allow customers to look up your bikes on the internet. How would you do it? Possible answer. Bicycles Racing Steel 24 inch Alloy 26 inch 28 inch Titanium Carbon fiber Mountain Street Folding Children’s etc Exercise E2.5 Classification (4). You are asked to organize the inventory of fasteners in your company. There are several types (snap, screw, bolt, rivet) and within each, a range of materials and sizes. Devise a classification scheme to store information about them. Possible answer Fasteners Bolts Steel 4 mm Stainless 5 mm 6 mm etc Brass High tensile Rivets Screws Snap etc Exercise E2.6 Shaping. What is meant by a shaping process? Look around you and ask yourself how the things you see were shaped. Answer. A shaping process takes a raw material and gives it shape (eg casting or molding), or modifies the shape of an already shaped component (eg machining or grinding). Exercise E2.7 Joining. Almost all products involve several parts that are joined. Examine products immediately around you and list the joining methods used to assemble them. Answer. Find examples of joining by: adhesives, fasteners, snap-fits and welding. Exercise E2.8 Surface treatment. How many different surface treatment processes can you think of, based on your own experience? List them and annotate the list with the materials to which they are typically applied.