Strength degradation law of metallic material under fatigue loading

The residual strength is one of the important properties of materials, and it is the basis for predicting fatigue life. It is known that the residual strength is a monotonically decreasing function of the number of loading cycles, and the degradation of the strength is caused by the damage development. The degradation rule of 35CrMo steel is studied based on the development of the damage in the material under cyclic loading and a model to describe the degradation of tensile residual strength of 35CrMo steel is presented. Large amounts of experimental data have been employed to support this model and the comparison between prediction and experiment demonstrates that this model has better capacity of predicting the degradation of tensile residual strength. Three parameter Weibull function is considered applicable to the distributions of the residual strength after different cycle numbers. However, the parameters of the Weibull distribution are different after different cycle numbers, that is, the parameters of the Weibull distribution changes with cycle numbers. With the cycle numbers increasing, the distribution of residual strength is changing.