Failure analysis of a diesel engine gear-shaft

A failure investigation has been conducted on a diesel-engine gear-shaft used in a truck, which is made from 45# steel. The crack initiated from the root transition region between the cylinder and the platform of the gear-shaft, and propagated toward the direction with an angle of 45° to the axial direction first, then toward the direction normal to the axial direction. Multiply-origin fatigue fracture is the dominant failure mechanism. The oil hole on the cylinder of the gear-shaft was stopped up by the overlong bolt to lead to the absence of oil lubrication between the cylinder surface and the internal circle surface of the gear so that the friction force between them increased, which is mainly responsible for the failure of the gear-shaft. The absence of the induction-hardened layer in the root transition region between the cylinder and the platform of the fixed plate of the gear-shaft makes the fatigue strength decrease in this region. The fatigue crack initiated and propagated in this region easily under the abnormal stress.