The engine of a car is mounted on four shear bolts designed to fail in shear in

Question

The engine of a car is mounted on four shear bolts designed to fail in shear in a front-end collision, detaching the engine from the car, if the deceleration exceeds 10 g. Assume that all four bolts carry the same load. The mass of the engine is 80 kg. Because of space limitations, the maximum diameter of each shear bolt cannot exceed 5 mm. Calculate the constraint on the yield strength ?y of the material of the shear bolt, assuming that the shear strength is ?y/2 and that the mounting is done in such a way that the shear can take place without friction.

Explanation / Answer

In case of a collision, force applied due to deceleration

F = 80*10g = 800g

Now,

shear stress applied on one bolt = F/4A = 800*9.81/4*3.14*.005^2 = 2.3 * 10^7 N/m^2

This is the shear strength of the bolt

yield strength >= 2.3 * 10^7 * 2 = 4.6 * 10^7 N/m^2

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