Multiaxial fatigue of a titanium alloy under complex loading with asymmetric paths

Multiaxial fatigue under complex asymmetric loading paths has gained significant attention because it better represents the actual loading conditions of engineering components. However, research on this topic remains limited. In this study, a definition of the multiaxial fatigue stress ratio is proposed by identifying the peak and valley points of complex loading paths. Subsequently, the Walker mean stress correction method is extended for application to multiaxial fatigue. By incorporating mean stress correction into an existing symmetric model, an improved asymmetric multiaxial fatigue model is developed without introducing additional fitting parameters. To validate the proposed model, 50 fatigue tests were conducted on TC4 alloy using 12 distinct loading paths with varying mean stresses and phase angles. The results show that the model accurately captures damage differences across various asymmetric loading paths. Most predicted fatigue lives fall within the 3^±1 scatter band of the experimental data. The reliable prediction performance demonstrates that the proposed model can be effectively applied to multiaxial fatigue life prediction under asymmetric loading in engineering structures.