As we discussed in Chapter 1, engineers design millions of products and services that
we use in our everyday lives: products such as cars, computers, aircrafts, clothing, toys,
home appliances, surgical equipment, heating and cooling equipment, health care
devices, tools and machines that make various products, and so on. Engineers also
design and supervise the construction of buildings, dams, highways, power plants,
and mass transit systems.
As design engineers, whether you are designing a machine part, a toy, a frame
for a car, or a structure, the selection of material is an important design decision.
There are a number of factors that engineers consider when selecting a material for
a specific application. For example, they consider properties of material such as den-
sity, ultimate strength, flexibility, machinability, durability, thermal expansion,
electrical and thermal conductivity, and resistance to corrosion. They also consider
the cost of the material and how easily it can be repaired. Engineers are always
searching for ways to use advanced materials to make products lighter and stronger
for different applications.
In this chapter, we will look more closely at materials that are commonly used
in various engineering applications. We will also discuss some of the basic physical
characteristics of materials that are considered in design. We will examine solid
materials such as metals and their alloys, plastics, glass, wood, and those that solid-
ify over time, such as concrete. We will also investigate in more detail basic fluids,
such as air and water, that not only are needed to sustain life but also play impor-
tant roles in engineering. Did you ever stop to think about the important role that
air plays in food processing, driving power tools, or in your car’s tire to provide a cush-
iony ride? You may not think of water as an engineering material either, but we not
only need water to live, we also need water to generate electricity in steam and hydro-
electric power plants, and we use high-pressurized water, which functions like a
saw, to cut materials.
17.1 Material Selection
Design engineers, when faced with selecting materials for their products, often ask questions
such as: How strong will the material be when subjected to an expected load? Would it fail, and
if not, how safely would the material carry the load? How would the material behave if its tem-
perature were changed? Would the material remain as strong as it would under normal condi-
tions if its temperature is increased? How much would it expand when its temperature is
increased? How heavy and flexible is the material? What are its energy-absorbing properties?
Would the material corrode? How would it react in the presence of some chemicals? How
expensive is the material? Would it dissipate heat effectively? Would the material act as a con-
ductor or as an insulator to the flow of electricity?17.1 Material Selection 553
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