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
processes. 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, economical, 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 beginning 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 materials 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 selection 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 in Fig. 2–15. Each vertical line represents the range of values of E for a particular material. Only some of the materials are labeled. Now, more material information can be displayed if the x axis represents another material property, say density.
Mechanical Engineering
McGraw−Hill Primis
ISBN: 0−390−76487−6
Text:
Shigley’s Mechanical Engineering Design,
Eighth Edition
Budynas−Nisbett
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