An improved macro–micro-two-scale model to predict high-cycle fatigue life under variable amplitude loading

This study is based on continuum damage mechanics and constructs an improved macro–micro-two-scale model to predict the fatigue life of engineering metallic materials subjected to variable amplitude loading. To account quantitatively for the fatigue damage retarding effect of higher load on lower ones in a loading sequence, the cyclic plastic response curve of microscopic weak inclusion is independently designed. Meanwhile, an improved two-scale fatigue damage model in rate form is proposed by introducing a new exponent function acted on the equivalent plastic strain term in the model for taking account of fatigue mean stress effect under variable amplitude loading. The parameters of the two-scale fatigue damage model are identified through an inverse approach based on fatigue test results under constant amplitude loading. The predictive accuracy of the proposed model is validated by fatigue test data of Al 2024-T3 standard coupon and plate with a hole under different variable amplitude loading.