A new approach to low-cycle fatigue damage based on exhaustion of static toughness and dissipation of cyclic plastic strain energy during fatigue

Experimental results show that the static toughness synthesizing both strength and plasticity of a material is a mechanical property parameter sensitive to the fatigue damage process. The reduction of the static toughness in the fatigue damage process indicates the progressive exhaustion of the ability to absorb energy inherent in the material due to fatigue damage evolution, which is associated directly with the irreversible process of energy dissipation of fatigue failure. Based on the exhaustion of the static toughness and dissipation of the plastic strain energy during fatigue failure, a damage variable that is consistent with the fatigue damage mechanism, sensitive to the fatigue damage process and can be measured with a simple experimental procedure is defined in this paper. A corresponding fatigue damage evolution equation is derived by connecting the damage variable with the static toughness exhaustion during fatigue, which is further examined in both theory and experiment. A fatigue damage accumulation formula that has the capacity of predicting the load sequencing effect correctly and can be applied very conveniently in engineering practice is further deduced by using equivalent-loading postulate. A comparison of experimental data with the predictions shows excellent agreement for two-stage cyclic tests.