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 stren gth and plasticity of a material is a mechanical property parameter sensiti ve to the fatigue damage process. The reduction of the static toughness in the fatigue damage process indicates the progressive exhaustion of the abil ity to absorb energy inherent in the material due to fatigue damage evoluti on, which is associated directly with the irreversible process of energy di ssipation of fatigue failure. Based on the exhaustion of the static toughne ss and dissipation of the plastic strain energy during fatigue failure, a d amage variable that is consistent with the fatigue damage mechanism, sensit ive to the fatigue damage process and can be measured with a simple experim ental procedure is defined in this paper. A corresponding fatigue damage ev olution equation is derived by connecting the damage variable with the stat ic toughness exhaustion during fatigue, which is further examined in both t heory and experiment. A fatigue damage accumulation formula that has the ca pacity of predicting the load sequencing effect correctly and can be applie d very conveniently in engineering practice is further deduced by using equ ivalent-loading postulate. A comparison of experimental data with the predi ctions shows excellent agreement for two-stage cyclic tests. (C) 2001 Elsev ier Science Ltd. All rights reserved.