Effect of local equivalent stress on fatigue life prediction of carburized Cr-Ni alloy steel based on evaluation of maximum crack sizes

The fatigue assessment methods considering surface strengthening process were proposed through experimental investigation of fatigue properties of carburized Cr-Ni alloy under stress ratios of 0 and 0.3. Interior-failure is caused by continuous debondings of refined grains due to stress concentration around interior-inclusion, while surface-failure is caused by grain dislocation slip around surface-inclusion. In view of the effect of local equivalent stress (residual stress, mean stress and stress concentration around the inclusion), the PRx-S-N curves of carburized Cr-Ni alloy steel were constructed based on the prediction of crack characteristic sizes by Generalized Extreme Values (GEV) and Generalized Pareto (GP) distributions under different cumulative probabilities, and the comparison shows that GP distribution can predict the fatigue strength better than GEV distribution. The fatigue life prediction models can be established by GP distribution for surface and interior failures, and the predicted results are in good agreement with the experimental results.