Evaluation of multiaxial fatigue criteria under irregular loading

A series of fatigue tests were conducted on SNCM630 steel under irregular axial–torsional loading. Additional hardening in most non-proportional path tests is found to be insignificant for this material. Fatigue parameters proposed by Wang et al. (WB), Smith et al. (SWT), Fatemi et al. (FS), Chen et al. (CXH), Pan et al. (PHC) and Varvani-Farahani (VF) were evaluated using test data. Rainflow cycle counting and the Miner–Palmgren damage rule were applied. The FS parameter gives good life estimates, and the WB parameter is found to be somewhat conservative for some non-proportional loading conditions. The energy-based parameters PHC and VF give satisfactory life predictions when the maximum damage plane is used for the critical plane.