在680和850℃下对DD3镍基单晶合金进行多轴非比例加载低周疲劳试验,结果表明等效应变范围△ε_e、试验温度、等效应力范围△σ_e对单晶合金的低周疲劳寿命有显著影响。基于能量耗散理论,引入参量k表征多轴非比例加载对疲劳寿命的影响,构造循环塑性应变能作为损伤参量,建立镍基单晶合金低周疲劳寿命预测模型。参量k与循环寿命之间呈幂函数关系。根据镍基单晶合金的微观尺度结构特征.建立γ/γ′双相单胞有限元模型,进行多轴非比例循环加载应力应变数值模拟。根据宏观有限元模型和γ/γ′双相单胞微观有限元模型的计算结果,以及镍基单晶合金680和850℃低周疲劳试验数据,对疲劳寿命模型进行多元线性回归分析,结果表明微观单胞有限元模型的分析精度比宏观有限元模型显著提高,两种温度下的试验数据分别落在1.6倍和2.0倍偏差分布带内。
Low cycle fatigue tests of the single crystal nickel-based superalloy DD3 were conducted under multiaxial non-proportional loading at 680 and 850℃respectively.The results show that some factors affect low cycle fatigue life significantly.Based on energy dissipation theory,a low cycle fatigue life prediction model for the single crystal superalloy was proposed by using cyclic plasticity strain energy as a parameter.According to the micro structure feature,aγ/γ＇ two-phase unit cell finite element model was established,and its cyclic stress-strain was simulated.Calculation results of the macro and the micro finite element model,and low cycle fatigue test data at 680 and 850℃were applied to fit the low cycle fatigue life model by multiple linear regression analysis.The results show that the accuracy of the unit cell model is better than that of the macro model significantly,and all test data of two kinds of temperatures fall into the factor of 1.6 and 2.0 scatter band,respectively.
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