Failure Analysis of a Locomotive Engine Oil Pump Shaft

In this study, the fracture of a locomotive engine oil pump shaft is investigated. According to the reports, all oil pump shafts of this type fail in short periods of time due to the fracture at a location on the shaft which is in contact with a pinion. Stress analysis showed that the shaft bears torsion and cyclic bending stresses in the fracture site. The fracture surface observations revealed that the cracks are generated from the surface, and fatigue fracture occurs due to the cyclic bending stresses. According to the laboratorial analysis, the shaft is a surface-hardened lowalloy steel. The lack of suitable pre-heat treatment and surface hardening and the roughness created by the slippage between the shaft and the pinion are concluded to be responsible for the failure of the oil pump shaft.