Question 5.CS.3C: Automobile Scissors-Jack Failure Analysis Problem Determine ...
Automobile Scissors-Jack Failure Analysis
Problem Determine safety factors at critical points in a scissors jack.
Given The stresses are known from Case Study 3B on p. 214. The design load is 2 000 lb total or 1 000 lb per side. The width of the links is 1.032 in and their thickness is 0.15 in. The screw is a 1/2-13 UNC thread with root dia = 0.406 in. The material of all parts is ductile steel with E = 30 Mpsi and S_{y} = 60 kpsi.
Assumptions The most likely failure points are the links as columns, the holes in bearing where the pins insert, the connecting pins in shear, the gear teeth in bending, and the screw in tension. There are two sets of links, one set on each side, Assume the two sides share the load equally. The jack is typically used for very few cycles over its lifetime so a static analysis is appropriate.
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