Failure Investigation of a Diesel Engine Gear-Shaft

A diesel engine gear-shaft used in a truck fractured in service. Fracture occurred at the root fillet region of the upper groove and the platform. The fracto-graphic study shows that the failure of the gear-shaft was initiated by fatigue. The small fillet radius of the upper groove provided a stress concentration level in root fillet region and created the conditions responsible for the fracture of the gear-shaft. Absence of the induction-hardening layer on the surfaces of the cylinder and the platform led to further problems at the root fillet region in terms of operation of the gear-shaft. Both the geometry of the gear-shaft and incorrect induction-hardening process are responsible for the failure of the gear-shaft.