Failure mechanism analysis on railway wheel shaft of power locomotive

In this paper, the premature failure of the railway wheel shaft of power locomotive operated three million kilometres in China was investigated. Series of macroscopic and microscopic analysis was conducted to identify the damage degree and failure mechanism of the axle thoroughly, and the root causes of the unexpected failure were fully obtained. The results showed that the different extent damage (fretting damage, fatigue crack and corrosion) occurred in the interference fit of the wheel seats, gear seats and bearing seats without any material defect. In particular, plentiful cracks distributed on the wheel seat were sprouted in the subsurface and exhibited multi-source characteristics, which were fretting fatigue failure caused by interference fit under alternating loads of rotation and bending. The main reason of fatigue crack initiation is that there were numerous tangle and a pile-up of dislocations in the sub-surface of wheel seat position, which resulted in stress concentration at the grain boundary and phase boundary, and when it exceeded the strength limit of the material, the micro-crack would initiate and propagate. Therefore, to reduce the stress concentration at the wheel seat portion, the structure of the axle need to be further optimized, and the surface be strengthened also crucial for resisting the fretting damage.