Quantitative Evaluation of the Flaking Strength of Rolling Bearings with Small Defects: (Part 1: FEM Analyses of the Stress Intensity Factor, KII, under Rolling Contact)

Abstract

It has been demonstrated that the rolling contact fatigue (RCF) test, using a specimen with a small drilled hole, is a useful means of evaluating the influence of a minor defect on the flaking strength of steels. In this study, RCF tests were conducted on rolling bearings with small drilled holes. Flaking failure was determined to be caused by the shear-mode fatigue cracks that emanated from the small defects. As a first step to quantifying the crack-growth threshold according to fracture mechanics principles, using the finite element method (FEM), it was necessary to analyze the Mode II stress intensity factor (SIF) range, ΔKII, of a ring-shaped crack, as emanated around the edge of a drilled hole after the passage of a rolling element. Subsequently, the derived values were correlated with the ΔKII values of penny-shaped cracks in an infinite body under uniform shear via a correlation factor, fdrill. The SIF of the ring-shaped crack was also uniformly correlated with that of the penny-shaped crack, using the single factor, fdrill, irrespective of the hole diameter, d, the depth of the hole-edge, h′, and the maximum contact pressure, qmax, within the following ranges: d = 0.05 ~ 0.2 mm, h′ = 0.05 ~ 0.345 mm and qmax = 2.0 ~ 3.0 GPa. The obtained results were later applied towards the quantification of the RCF test results, as detailed in Part 2 of the report on this research.