The influence of material build up around artificial defects on rolling contact fatigue life and failure mechanism

This paper reports the results obtained in tests conducted to evaluate the evolution of wear tracks and artificial defects under rolling contact fatigue (RCF) loading and its effect on RCF life. The experiments were conducted on specimens of different materials commonly used in rolling bearings and gears. The artificial defects were introduced with the rounded tip of a Rockwell-C type indenter, with a diameter of ∼120 μm. The evolution of the micro-roughness profiles was followed, in the rolling and transversal directions, for both, artificial defect and wear track. The RCF lives of the samples were correlated with the build up height. Furthermore, the RCF lives of three variants of the SAE 52100 steel with artificial defects were compared to those obtained for the same variants where the build ups had been machined off. In the later case, the lives were observed to increased by a factor close to two; while the spall appearance remained unchanged indicating a similar failure mechanism. These results give room to question the precision and validity of finite element models, when analyzing artificial defects without proper accounting for the build up, i.e. surface roughness, and subsequent life theories formulated to match the numerical results. This paper also deals with the influence of artificial defects (when used to accelerate tests) on the life reduction factor for different materials, which was observed to be dependent on the material hardness.