The fatigue limit of bearing steels – Part II: Characterization for life rating standards

The dynamic load ratings and life rating standard for rolling bearings, ISO 281:2007, makes use of a fatigue limit stress of hardened bearing steels as a parameter in the estimation of the fatigue life of rolling bearings. Part I of this paper series presented an analytical-probabilistic model that provides a unified prediction of fatigue strength corresponding to various fatigue regimes including the very high cycle fatigue (VHCF) regime. Based on the fatigue model, Monte Carlo simulation of rotating bending and push–pull tests of bearing steels indicates the existence of a horizontal asymptote in the S–N curve in excess of 1012 cycles, which corresponds to the fatigue limit. Prediction of fatigue limit associated with certain reliability can be realized using the developed model and methodology. In the present paper (Part II of the paper series), the application of a fatigue limit stress in the standard fatigue load ratings of rolling bearings is described. The up-to-date interpretations and standard definition of the fatigue limit stress are discussed in relation to the very long stress cycling. The recent developments and results in the area of VHCF testing of hardened AISI 52100, SUJ2, 100Cr6 bearing steels are also reviewed. The fatigue limits predicted using the model from Part I, are compared with the VHCF data of bearing steels available from both the in-house tests and those in the literature. Good correlation is observed between the fatigue limit model and the experimental results. Plotting the experimental data on top of the predicted fatigue limit shows that the S–N data approaches asymptotically the predicted fatigue limit in the VHCF regime. It is found that the predicted fatigue limits and the VHCF testing data correlate well with the fatigue limit value set in the ISO 281:2007 standard for life rating of rolling bearings.