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Materials 61
2–21 Materials Selection

As stated earlier, the selection of a material for a machine part or structural member is
one of the most important decisions the designer is called on to make. Up to this point
in this chapter we have discussed many important material physical properties, various
characteristics of typical engineering materials, and various material production pro-
cesses. The actual selection of a material for a particular design application can be an
easy one, say, based on previous applications (1020 steel is always a good candidate
because of its many positive attributes), or the selection process can be as involved and
daunting as any design problem with the evaluation of the many material physical, eco-
nomical, and processing parameters. There are systematic and optimizing approaches
to material selection. Here, for illustration, we will only look at how to approach some
material properties. One basic technique is to list all the important material properties
associated with the design, e.g., strength, stiffness, and cost. This can be prioritized by
using a weighting measure depending on what properties are more important than
others. Next, for each property, list all available materials and rank them in order begin-
ning with the best material; e.g., for strength, high-strength steel such as 4340 steel
should be near the top of the list. For completeness of available materials, this might
require a large source of material data. Once the lists are formed, select a manageable
amount of materials from the top of each list. From each reduced list select the materi-
als that are contained within every list for further review. The materials in the reduced
lists can be graded within the list and then weighted according to the importance of
each property.
M. F. Ashby has developed a powerful systematic method using materials selec-
tion charts. 16 This method has also been implemented in a software package called
CES Edupack. 17 The charts display data of various properties for the families and
classes of materials listed in Table 2–4. For example, considering material stiffness
properties, a simple bar chart plotting Young’s modulus E on the y axis is shown

Table 2–4 Family Classes Short Name
Material Families and Metals Aluminum alloys Al alloys
Classes (the metals and alloys of Copper alloys Cu alloys
engineering) Lead alloys Lead alloys
Magnesium alloys Mg alloys
Nickel alloys Ni alloys
Carbon steels Steels
Stainless steels Stainless steels
Tin alloys Tin alloys
Titanium alloys Ti alloys
Tungsten alloys W alloys
Lead alloys Pb alloys
Zinc alloys Zn alloys

(continued)

16 M. F. Ashby, Materials Selection in Mechanical Design, 3rd ed., Elsevier Butterworth-Heinemann,
Oxford, 2005.
17 Produced by Granta Design Limited. See www.grantadesign.com.