Effects of Loading Modes on Fatigue Limit Estimation in Terms of Rotating Bending Fatigue and Rate Process Theory

In this study, the influence of loading modes on the fatigue limit estimation of low-to-medium-carbon steels was modeled in terms of the rate process theory proposed by Guennec et al. The axial loading model established in terms of the rate process theory has been shown to be effective for axial loading fatigue, but its applicability to rotating bending fatigue is uncertain. Therefore, low- and medium-carbon steels were tested for rotating bending fatigue, and the fatigue limits obtained were compared with those estimated by the axial loading model established in terms of the rate process theory. However, since the model could not be applied, we propose a new model in which the material parameters of an estimation equation established in terms of the rate process theory are expressed based on Vickers hardness, which was introduced to improve the usability of the model. It was found that there was a discrepancy between the axial load fatigue limit and the rotating bending fatigue limit due to the effect of the loading mode. To solve this discrepancy, the stress index was introduced into the model. The proposed model provides a method for estimating the frequency-dependent fatigue limits for different loading modes.