On the crack path of rolling contact fatigue cracks in a railway wheel steel

The objective of the present paper is to give some preliminary results obtained in the frame of a more wide investigation on the rolling contact fatigue (RCF) behavior of a railway wheel steel. The effect of different test parameters on the RCF fatigue strength of the railway wheel steel was evaluated. RCF tests were conducted using two cylindrical contact specimens under different Po/k ratio (where Po is the maximum Hertzian pressure, k is the yield stress in shear of the material), under dry contact conditions or with water lubrication, and at varying slip ratio. In the present study crack initiation location and crack growth direction were carefully investigated; microscopic examination showed that the cracks were initiated at the surface, propagated obliquely in the depth direction and then occasionally branched into two directions. Usually multiple cracks are initiated, at the rolling contact surface, caused by the accumulation of shear deformation due to repeated rolling–sliding contact loading. Subsequent crack growth has been found to occur along specific sloped directions. The influence of Po/k ratio, dry or wet contact, and slip ratio on crack slope angle to the radial direction and the depths at which slope changes occur has been investigated. Observed crack slopes and slope change position have been discussed according to crack path prediction criteria in the literature.