Rate process analysis of the loading frequency effect on the fatigue endurance of low carbon steel

Due to the bcc microstructure of a-phase ferrite, low carbon steels highlight a significant effect of the strain rate on its mechanical properties, such as yield stress. Indeed, at a constant temperature, the higher the strain rate is, the higher the uniaxial yield stress becomes. Some studies also pointed out similar trend for the fatigue strength of low carbon steels in high cycle fatigue regime. An influence of the loading frequency on the dislocation arrangement of observed fatigued specimens has also been reported. Nevertheless, strain rate effect on the fatigue strength of low carbon steels has not been discussed from a viewpoint of rate process yet. Referring to this point, an analytical model based on the activation energy of dislocations was proposed to evaluate the fatigue endurance of low carbon steels. Accepting five typical data sets actually obtained by fatigue tests, analytical results based on the present model were compared with the experimental data. Thus, it was found that the analytical results are in good agreement with the experimental results. In addition, this work also includes a discussion on the activation energy of the dislocation related to the present model. Activation volume of the dislocations thus calculated showed good agreement with corresponding experimental data available in the literature. © 2019 Society of Materials Science Japan. All rights reserved.