Effect of small defect on the flaking strength of rolling bearings (Part 1: FEM analyses of stress intensity factor KII under rolling contact)

Abstract

It has been shown that rolling contact fatigue (RCF) test using specimen having a small drilled hole is a useful method for evaluating the effect of small defect on flaking strength of steels. In this study, RCF tests of rolling bearings having a small drilled hole were carried out. The flaking failure was considered as a problem of shear-mode fatigue crack emanating from the small defect. As a first step to quantify the crack-growth threshold on the basis of fracture mechanics, mode II stress intensity factor range, ΔK_II, of a ring-shaped crack emanated around the edge of a drilled hole under the passing of a rolling element was analyzed by using finite element method. And then, the obtained values were correlated with the ΔK_II values of penny-shaped cracks in an infinite body under uniform shear through the intermediary of a correlation factor, f_drill. The stress intensity factor of the ring-shaped crack was uniformly correlated with that of the penny-shaped crack by the single factor f_drill irrespective of hole diameter, d, depth of hole edge, h’, and maximum contact pressure, q_max, within the ranges: d = 0.05 ~ 0.2 mm, h’ = 0.05 ~ 0.345 mm and q_max = 2.0 ~ 3.0 GPa. The obtained results will be applied for the quantification of RCF test results shown in the subsequent paper.