Accurate estimation of multiaxial fatigue life plays a critical role in maintaining the structural integrity and operational reliability of mechanical components subjected to complex loading conditions. Under non-proportional loading, fatigue life tends to decrease significantly due to the emergence of additional damage mechanisms, such as dislocation accumulation, cyclic hardening, and accelerated propagation of micro-cracks. This study conducts a systematic investigation into the primary factors that influence fatigue behavior under non-proportional loading conditions. A novel damage factor is proposed, which quantifies the additional strengthening effects caused by complex stress and strain interactions. Based on this factor, a new prediction model is developed through the combination of critical plane theory and an energy-based framework. This model captures the influence of non-proportional strengthening on fatigue strength with improved accuracy. Experimental validation is carried out using En8, TC4, and Al7050-T7451 materials under tension and torsion loading conditions. Comparative analysis with three conventional models shows that the proposed method improves the accuracy of predictions and offers a dependable approach for practical engineering applications.
Wang et al. (Mon,) studied this question.
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