Multiaxial fatigue life prediction under complex cyclic loading

Multiaxial fatigue in structural components of aircraft engines is one of the critical challenges limiting the improvement of engine reliability and structural integrity. The presence of non-zero mean stress and non-proportional multiaxial cyclic loading further complicates the fatigue life assessment. To accurately predict the life under complex multiaxial cyclic loading, the peak, valley, and mean points of the loading path are first defined. Based on this, a definition of the multiaxial stress ratio is proposed. Subsequently, the Walker correction method for uniaxial fatigue with non-zero mean stress is extended to multiaxial fatigue using the proposed multiaxial stress ratio. In conjunction with existing multiaxial fatigue models, a multiaxial fatigue life model suitable for non-zero mean cyclic loading is developed. To address the characteristics of non-proportional loading paths under non-zero mean loading conditions, a method for characterizing non-proportional paths under non-zero mean loading is proposed, which further extends the applicability of the non-zero mean cyclic loading multiaxial fatigue model. Finally, experimental data on non-zero mean, non-proportional path multiaxial fatigue for three materials are used to validate the proposed model. The results show that, without introducing additional parameters, most predicted life values fall within a scatter band of 3^±1 times the experimental data, and the prediction accuracy surpasses that of three commonly used models. This demonstrates that the proposed model can accurately capture the influence of non-zero mean loading and non-proportional paths on multiaxial fatigue life.