The fatigue crack initiation at twin boundary (TB) and the life prediction of IN718 alloys in the high cycle fatigue (HCF) regime and very high cycle fatigue (VHCF) regime were investigated through crystal plasticity finite element (CPFE) simulations and experiments. The fatigue damage parameter, considering the evolution of geometrically necessary dislocation (GND) density, slip and back stress, known as the back-stress-based stored energy density in this study, G_ba, was proposed to precisely characterize the plastic strain distribution and localization, which in turn was engaged in locating fatigue crack initiation site and predicting the fatigue life. The element analysis around TB and the CPFE simulations indicated the coupling of slip activation parallel to the TB and the absence of primarily strengthening phase (γ'') on the both side near the TB was responsible for crack initiation. To predict fatigue life, the varying pattern of the G_ba at fracture with fatigue life was studied based on the experimental results in the HCF and VHCF regimes, and the life prediction method was obtained accordingly. Finally, the fatigue life evaluations of the IN718 alloy at three load ratios (R = −0.1, 0.1, and 0.5) were conducted and results showed that the life estimates were basically within ±3 scatted bands.

通过晶体塑性有限元 (CPFE) 模拟和实验，研究了 IN718 合金在高周疲劳 (HCF) 状态和超高周疲劳 (VHCF) 状态下的双晶界 (TB) 疲劳裂纹萌生和寿命预测。考虑到几何必要位错 (GND) 密度、滑移和背应力的演变的疲劳损伤参数，在本研究中称为基于背应力的存储能量密度，G _ba, 提出了精确表征塑性应变分布和局部化的特征，进而用于定位疲劳裂纹萌生部位和预测疲劳寿命。TB 周围的元素分析和 CPFE 模拟表明平行于 TB 的滑移激活耦合以及 TB 附近两侧缺少主要强化相 (γ'') 是裂纹萌生的原因。为了预测疲劳寿命，根据HCF和VHCF状态下的实验结果，研究了断裂处G _ba随疲劳寿命的变化模式，并据此得出了寿命预测方法。最后，IN718合金在三种载荷比下的疲劳寿命评价（R = −0.1、0.1 和 0.5) 进行了计算，结果显示寿命估计值基本在 ±3 个散点带内。