Fatigue–ratcheting damage assessment of steel samples under asymmetric multiaxial stress cycles

•Fatigue–ratcheting damage was assessed under multiaxial histories in steel samples.•Damage parameter involving both fatigue and ratcheting were defined through the upper and lower curves.•Ratcheting damage parameter was defined in consistent with energy-based fatigue damage model.•A weight factor partitioned overall damage to damages due to fatigue and ratcheting.•The predicted lives well agreed with those of experimentally obtained values.

The present study develops a model to assess fatigue–ratcheting damage in 1025 and 42CrMo steel samples undergoing various biaxial and multiaxial loading histories. Damage indices in fatigue and ratcheting phenomena were respectively defined by the upper and lower curves at which the upper curve is constructed under fully reversed multiaxial fatigue cycles by means of an earlier developed critical plane-energy model by the author. The lower curve is developed on the basis of an energy-based ratcheting model in consistent with fatigue damage model to merely present damage values due to ratcheting phenomenon. Equations developed to address overall damage due to fatigue and ratcheting hold both axial and shear stress and strain components for data falling between the upper and the lower bounds. Weight factor ξ is used to partition the overall damage to damage values due to fatigue and ratcheting. The predicted life values based on the overall damage and the upper and lower damage bounds well agreed with those of experimentally obtained for steel samples under biaxial and multiaxial loading histories.