A METHOD TO BUILDING PROBABILISTIC S-N CURVES FOR MULTIPLE FALIURE MODES IN VERY HIGH CYCLE FATIGUE

Very high cycle fatigue (VHCF) tests were carried out by using the carburized CrMn steel. By observing the fracture surface, three different failure modes were distinguished, namely the surface-crack induced failure mode and the inclusion induced failure mode under HCF (5×10⁴<N<10⁷) and VHCF (N>10⁷) conditions. The S-N curves were assumed for each failure mode in the present study. Based on the mixed Weibull distribution, the Basquin S-N curve and the three-parameter S-N curve, the probabilistic S-N (P-S-N) curves were established for three different failure modes respectively, and a method for constructing the P-S-N curve associated with multiple failure modes was developed. In comparison with experimental data, the fatigue life predicted by the P-S-N curve with 99% survival probability is acceptable at VHCF regime.