Hydraulic torque wrench adapter failure analysis

Flaw appearance, crack occurrence and consequential failures are of serious concern in any mechanical design process. Once failed, parts can be analyzed in order to determine the causes of failures. Therefore, failure analysis proves to be a valuable tool in design improvement. This research deals with a failure of hydraulic torque wrench square drive adapter. It is a 1.5” size adapter capable of handling 15500 Nm torque. There has been a considerable number of identical failures so an attempt was made to determine the causes. Failure analysis was performed using experimental and numerical approach. Visual examination revealed the location and path of the fracture, while optical microscopy was used to inspect microstructure of the fractured surface and reveal possible inclusions. Detailed scanning electron microscopy (SEM) examination at suitable magnifications was employed to characterize fine microstructure of the fractured surface and reveal flaws that served as crack initiation points. Chemical composition of the material was determined using optical emission spectrometer with glow discharge source (GDS) sample stimulation. Maximum tensile strength of the material was derived from the performed hardness test results. Further research employs finite element (FE) analysis to determine stress levels of a failed 1.5” square drive adapter. These results are compared with FE stress analysis of a 2.5” adapter capable of handling the same torque. Excessive stress concentration is noticed at a crack initiation point of a smaller adapter leading to conclusion that the dimensions of the adapter need to be reconsidered in order to avoid future failures.