A fastener bolt for the engine on a supersonic jet aircraft has a crosssectional area of 2.0 cm 2 and a length of 4.0 cm. The bolt part must be able withstand a tensile force of 10 × 104 N, and as a factor of safety this tensile force can produce a stress of no more than 50 percent of the tensile yield stress in the bolt. For sufficient resistance to fracture this critical bolt must have at least 15 percent strain to fracture. Because weight is critical for this jet aircraft design the maximum weight possible for this bolt is 40 g. The bolt is subject to temperatures up to 400°C (752°F).
To minimize the possibility of high temperature plastic strain the selected material should not be subject to more than 1/3 of its melting temperature. Of the materials covered in this chapter what would be the best material to select? Because this is a supersonic jet aircraft high priced materials can be utilized.
Ceramics are eliminated from consideration because they should not be used in a design with any significant tensile forces. The weight requirement could limit the selection of the material. The maximum density (?) for the part is calculated from the maximum weight divided by the volume of the part.
There are no magnesium or aluminum alloy or any polymer that have this yield strength. There are several titanium alloys with the required yield strength, but only the alloy Ti-8Al-1Mo-1V has 17 percent strain to failure exceeding the required 15 percent.
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