低周循环应力-应变关系和损伤

引入硬化状态变量表征微结构变化对材料循环变形行为的影响，提出应变控制下材料的循环应力一应变关系，由此导出的疲劳损伤演变方程与材料的损伤和硬化状态有关，考虑加载历史的影响。其结果可以为分析多级疲劳加载时，损伤演变过程和剩余寿命估算提供新的思路。

RELATIONSHIP OF CYCLIC STRESS-STRAIN AND DAMAGE FOR LOW-CYCLE FATIGUE

Micro-structure of material keeps on changing during fatigue. It causes cyclic deformation behavior varying, i.e. material turns into hardening. In order to express the hardening effect on material deformation properties, a new internal variable, "hardening variable", is introduced into the cyclic stress-strain equation. It takes the hardening state as well as the damage state into account and can describe the cyclic hardening and softening behavior which can be seen during fatigue. The fatigue damage constitutive equation is obtained. This equation shows that fatigue damage evolution under conditions of two or multi-level fatigue loading depends not only on the existing damage state but also on the hardening state. In this case, the remaining life is affected by the damage state as well as the hardening states caused by loading history.