Fatigue life prediction for titanium alloy under multiaxial very high and low cycle combined thermo-mechanical loading

The investigation found that von Mises equivalent stress used to calculate multiaxial fatigue damage cannot reflect the contribution of shear stress to damage in the very high cycle regime, as well as the influence of shear-to-axial ratio on the damage behavior of titanium alloy is revealed under multiaxial very high cycle loading. Based on the damage mechanism, a method was proposed to equivalently convert multiaxial stresses into uniaxial form in the very high cycle regime, and the experimental verification results under different shear-to-axial ratios showed that almost all of the fatigue life prediction errors are within a factor of 2.5. Moreover, the coupled effects of multiaxial low-cycle fatigue loading, multiaxial very high-cycle fatigue loading, and temperature loading will transform the crack propagation mode into one that is co-dominated by fatigue and creep. According to the damage mechanism, an interactive damage model was proposed, and a brand-new life prediction method was developed by combining the proposed equivalent method, the multiaxial fatigue damage model and creep damage model. The experimental verification results under multiaxial very high and low cycle combined thermo-mechanical fatigue loading show that all prediction errors are within a factor of 2.5.