Failure Analysis of a Fractured Wrench Socket

Failure of a 13/16 in. wrench socket while hand tightening a socket was investigated using hardness test, optical microscopy, scanning electron microscopy, and energy dispersive spectroscopy techniques. Hardness and microstructure of the fractured socket are compared with those of other original (unfailed) wrench sockets from other manufacturers. Wrench material is a low carbon steel, and socket was manufactured in a powder metallurgy (PM) process. Results of this analysis indicate that non-uniform socket wall thickness, poor socket geometric design featuring sharp corners forming stress raisers, and poor sintering step in the PM process leaving unsintered particles were causes of the socket failure. The presence of the inclusions containing contaminants such as S and Al on the socket fracture surface may have played a role in this failure.