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研究DD3镍基单晶合金在高温多轴非对称循环载荷下的低周疲劳特性,对比分析试样的应力应变响应和试验参数与疲劳寿命的关系,发现材料的循环硬化、软化特性与温度、加载相位角、应变加载路径有关;低周疲劳试验的轴向应变范围对疲劳破坏的贡献较大,切向应变范围的贡献较小;在轴向非对称循环载荷作用下,不同取向的试样均表现出应力松弛和非弹性应变累积现象,存在应力弱化损伤。引入与疲劳寿命呈指数函数关系的参量F表征材料在高温非对称循环载荷下产生的应力弱化损伤,结合von Mises等效应变范围、单晶应力三轴性因子和晶体取向函数构造循环塑性应变能作为疲劳损伤参量,建立疲劳寿命预测模型,利用低周疲劳试验数据进行多元线性回归分析,表明模型与试验寿命具有很好的相关性。
The low-cycle fatigue behavior of DD3 nickel-base single crystal alloy under multi-axial asymmetric cyclic loading under high temperature was studied. The stress-strain response and the relationship between test parameters and fatigue life were analyzed. The results show that the cyclic hardening, softening properties and temperature, Loading phase angle and strain loading path. The axial strain range of low-cycle fatigue test contributes more to fatigue failure and the contribution of tangential strain range is smaller. Under the axial asymmetric cyclic loading, the specimens with different orientations All showed the phenomenon of stress relaxation and inelastic strain accumulation, and the existence of stress-induced damage. The parameter F, which expresses the exponential function of fatigue life, is introduced to characterize the stress-induced weakening damage of the material under asymmetric cyclic loading under high temperature. The cyclic plastic strain energy is constructed according to the von Mises equivalent strain range, the single crystal stress triaxiality and the crystal orientation function As fatigue damage parameters, fatigue life prediction model was established, and multiple linear regression analysis using low cycle fatigue test data showed that the model has a good correlation with test life.