A New Approach Towards Life Prediction of Case Hardened Bearing Steels Subjected to Rolling Contact Fatigue

TLDR: In this paper, an experimental methodology was proposed to measure the location and magnitude of cyclically evolving elastoplastic von Mises stresses in terms of micro-hardness numbers.

Abstract: The failure of a bearing-raceway assembly is governed by the spatial distribution of subsurface stresses at the vicinity of a bearing-raceway contact and the evolution of these stresses during rolling contact fatigue (RCF) loading. In this paper, we propose an experimental methodology that allows one to accurately measure the location and magnitude of the cyclically evolving elastoplastic von Mises stresses in terms of microhardness numbers. An M50NiL steel rod is subjected to RCF by three silicon nitride (Si3N4) balls for over several hundred million cycles at 5.5 GPa contact stress level. Microindentation hardness measurements within the subsurface RCF-affected regions of the rod revealed significant material hardening. A mechanistic methodology to construct a stress-life (S-N) diagram for RCF loading is proposed. S-N diagrams are constructed based on maximum von Mises stress amplitude and volume average von Mises stress amplitude. The effects of elastic modulus and yield strength gradient on stress fields are also considered in this analysis. Comparison of S-N diagrams based on both stress amplitudes indicates that the maximum von Mises stress amplitude overpredicts the fatigue strength of material in S-N diagrams. The experimental results obtained by following this methodology can help construct material hardening models for RCF, which may lead to an improved estimate of bearing fatigue life.