A stress-based method to predict lifetime under multiaxial fatigue loadings

This paper extends to low/medium-cycle fatigue a stress-based method recently proposed by the same authors for high-cycle multiaxial fatigue assessments. By considering the plane of maximum shear stress amplitude coincident with the microcrack initiation plane, the method requires the calculation both of the maximum shear stress amplitude and the maximum normal stress relative to the same plane. Multiaxial fatigue life estimates are made by means of bi-parametric modified Wohler curves, which take into account the mean stress effect, the influence of the out-of-phase angle and the presence of notches by using a generalization to multiaxial fatigue of the fatigue strength reduction factor K-f. Approximately 700 experimental data taken from the literature are used to demonstrate that the method is a useful tool to summarize fatigue strength data of both smooth and notched components, subjected to either in-phase or out-of-phase loads. Finally, a simple practical rule for the calculation of the multiaxial fatigue strength reduction factor is proposed.