A unit is rated for exposure to 20 gs However it fails a tes

A unit is rated for exposure to 20 g\'s. However, it fails a test with a maximum input acceleration of 10 g\'s. Tests show the unit was constructed properly and the calculations for the 20 g rating were correct. Explain possible root causes for the failure.

Solution

Root Causes for the given condition are:-

1) Wrong material selection for surface of unit. g-force produces a weight increasing effect which is transmitted through object by interior mechanical stresses. g-force acceleration experienced by an object results in surface contact stresses. In this case if the material used on the surface of the unit has a toughness less that what is required to withstand given g-force the unit is likely to fail below rated g\'s.

2) Stress Concentration due to cracks or notches .If the material selection is right and all other calculations are done correctly yet if the surface of the unit has cracks this can result in localised stress concentration at crack tips under g-force and cause fracture and ultimately complete failure of the unit below its rated capacity can take place. This phenomenon is mainly due to the fact that crack tips or notches provide minimum resistance path as a result these areas are prone to failures below rated loads.