复杂应力状态镍基单晶合金低周疲劳损伤模型

Multiaxial Low Cyclic Fatigue Damage Model for Single Crystal Nickel-Based Superalloy

根据连续介质损伤力学理论,采用应变能释放率作为热力学广义力描述正交异性材料的疲劳损伤过程,引入取向函数考虑镍基单晶合金晶体取向对疲劳损伤的非线性影响,提出了一个各向异性疲劳损伤模型。应用多元线性回归分析方法,拟合疲劳试验数据可确定模型参数。从应变能释放率的应变空间表达式出发,导出了含有3个弹性常数的单晶合金应变三轴性因子,它既反映了材料性能的晶体取向相关性,又反映了正应力和剪应力的相互作用,并可退化为各向同性材料的应变三轴性因子。利用该模型对CMSX-2镍基单晶合金在应力控制对称循环拉-扭载荷作用下的低周疲劳寿命进行预测,预测值与试验值吻合的相当好,试验所得数据均落在2.2倍偏差的分布带内。

According to the continuum damage mechanics theory, being known as a thermodynamics generalized force, a strain energy release ratio is employed in describing fatigue damage course of orthotropic materials. The nonlinear effect of crystal orientation of single crystal Nickel-based superalloys on fatigue damage is taken into account by introducing an orientation function. An anisotropic fatigue damage model is proposed, the coefficients appearing in the model can be obtained by fitting fatigue test data with multi-analysis of linear regression. The strain triaxiality factor for single crystal superalloys containing three elastic constants was deduced, where the correlation of crystalloid orientation of material performance as well as mutual action between tension stress are manifested. The correlation coincides with experiments well while the model is used to predict the stress controlled low cycle fatigue life of single crystal Nickel-based superalloy CMSX-2 under fully-reversed tension-torsion loads, and the all data fall into the factor of 2.2 scatter band.