Root causes analysis of differential pinion shaft assembly failure in WRX class car

The purpose of this paper is to present a case of fatigue damaging of the attacking roller of the WRC class car. Fatigue fractures are a very essential source of cognitive and usable information about the cause of damage of various engineering components. Microfractography allows extending considerations about the main mechanism of initiation and growth of fatigue cracks. The presented research procedure allowed establishing the root cause analysis of the premature fatigue failure of the pinion shaft.

The specimen for metallographic investigation was extracted from failures pinion shaft. According to the light microscopy and scanning electron microscopy (SEM) study, the detailed observations of microstructure were performed. Fracture surface of pinion shaft and teeth were examined using SEM. The presence of the extraordinary mechanical notch was found as a potential failure root cause.

The potential cause of premature failure pinion shaft assembly has been found. The microstructural causes were excluded due to correctly performed heat treatment. The main reason of failure was improper mechanical machining of the pinion shaft due to large mechanical notch.

A detailed metallographic expertise route is presented. The usefulness of fractographic analysis is confirmed in case of the failure analysis of premature pinion shaft. The root cause was found and the concluding remarks are included in this paper.