Failure investigation of a spline half-shaft in a loader rickshaw differential system

Abstract Large number of pre-mature failure cases of spline half-shafts of loader automobile rickshaws were encountered by an industry in Lahore, Pakistan. Unexpected fracture of the spline-region of half-shafts were reported shortly after the shafts were put to service. This paper presents the findings of a systematic investigation that was carried out to find the root cause of the failure. Visual inspection, mechanical characterization, microstructural analysis, and chemical composition analysis were used to study the failure. It was revealed that the failure was torsional fatigue fracture in nature, with crack initiating from one of the machining marks present near the spline-root. Main cause of failure was found to be stress concentration at machine marks present on the surface, especially the ones closer to spline-roots, resulting in crack initiation. Moreover, other factors like presence of manganese sulfide (MnS) inclusions and improper material had also contributed towards crack propagation and final fracture.