A series of tests for low cycle fatigue were conducted for the notched specimens of Mod.9Cr-1Mo ferrite steel under nonproportional loading. The crack initiation life was measured by the direct-current(DC) potential difference method. The effects of the notched radius and strain path on crack initiation life were discussed. The test results show that the ratio of the crack initiation life to the fatigue life is related to the strain path and notched radius. ANSYS software was used for simulation

while the von Mises yield criterion

multlinear kinematic hardening rule

and uniaxial cyclic stress-strain curve were employed to indicate the material elastic-plastic behavior. The simulation results show that the stress concentration at the notched root occurs significantly for any strain paths. It is obvious that the maximum equivalent stress lies in the notched root. But the stress decreases with the increase of distance. For different notched radiuses

the changing trend of the stress gradient with the distance to the notched root differs with the strain paths. Smith-Watson-Topper (SWT) model was used to predict the fatigue life based on the simulation results. The better prediction results are gained for the larger notched radius and most results are in a factor-2 scatter band. But for smaller notched radius

the predictions are conservative.