Fatigue crack propagation behavior under superimposed loading histories with several mean stress conditions is highlighted.Numerical simulation of fatigue crack propagation based on an advanced fracture mechanics approach using the RPG (Re-tensile Plastic zone Generating) stress criterion for fatigue crack propagation is improved to enable the extraction of the effective loading history for fatigue crack propagation. The parameter, which is based on the plastic hysteresis consuming in the vicinity of a crack tip,is applied to extract the effective loading for fatigue crack propagation and implemented into the numerical simulation code of fatigue crack propagation. Fatigue crack propagation tests under various superimposed loading conditions, which contain several constants and variable mean stress, are performed and comparison of fatigue crack propagation histories obtained from the improved numerical simulations with the measurements is performed. These comparisons show the validity of the proposed procedure for extracting the effective loading history from the superimposed loading histories with different frequencies. Subsequently, practical fatigue strength evaluation based on the linear cumulative fatigue damage parameter were conducted to investigate the tendency of fatigue damage value affected by mean stresses.
