Quantitative assessment of the initial damage state of a structure and fatigue life prediction on this basis, especially when it is sensitive to manufacturing quality, is crucial for both engineering application and material science. Traditional solutions based on fracture or damage mechanics either require precise constitutive relationships and cumbersome physical mechanism models or simply ignore the initial damage state. This study developed a novel equivalent initial flaw size (EIFS) quantitative evaluation method for film cooling holes in Nickel-based single crystal superalloy turbine blades to address the strong correlation between the initial damage in and fatigue life of the material. The temperature and stress field differences at the edges of holes with different inclination angles were simulated using a solid-liquid-gas three-phase level-set model and considered to represent the same initial damage. Next, the coupled damage–fracture mechanics model was used to achieve equivalent crack insertion, crack propagation, and fatigue life prediction based on the EIFS. The results indicate that this method can provide a highly robust EIFS distribution interval and that the crack geometry correction factor and EIFS distribution range are weakly correlated with the loading conditions (with an error within 2 %). The EIFS-based fatigue life predictions demonstrated a notable degree of accuracy, with the majority of the predicted and experimental fatigue lives falling within a three-fold dispersion band and all predictions remaining confined within a five-fold dispersion band of the actual lifetime. These results represent a substantial advancement in accuracy compared to traditional damage mechanics predictions. Therefore, this study provides a powerful approach for evaluating the fatigue life of turbine blades considering the initial damage state and can be widely applied to guide drilling process optimization and blade fatigue analysis.

中文翻译：

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不同倾斜气膜冷却孔镍基单晶高温合金的疲劳寿命估算：初始损伤量化和损伤断裂力学模型耦合

结构初始损伤状态的定量评估以及在此基础上的疲劳寿命预测，尤其是在对制造质量敏感的情况下，对于工程应用和材料科学都至关重要。基于断裂或损伤力学的传统解决方案要么需要精确的本构关系和繁琐的物理机制模型，要么干脆忽略初始损伤状态。本研究开发了一种新颖的镍基单晶高温合金涡轮叶片气膜冷却孔的等效初始缺陷尺寸（EIFS）定量评估方法，以解决材料的初始损伤与疲劳寿命之间的强相关性。采用固-液-气三相水平集模型模拟了不同倾角孔边缘的温度和应力场差异，并认为代表了相同的初始损伤。接下来，使用损伤-断裂耦合力学模型实现基于EIFS的等效裂纹插入、裂纹扩展和疲劳寿命预测。结果表明，该方法可以提供高度鲁棒的EIFS分布区间，并且裂纹几何修正因子和EIFS分布范围与加载条件的相关性较弱（误差在2%以内）。基于 EIFS 的疲劳寿命预测表现出显着的准确性，大多数预测和实验疲劳寿命都落在三倍色散带内，所有预测仍然限制在实际寿命的五倍色散带内。与传统损伤力学预测相比，这些结果代表了准确性的显着进步。因此，本研究为考虑初始损伤状态的涡轮叶片疲劳寿命评估提供了有力的方法，可广泛应用于指导钻井工艺优化和叶片疲劳分析。