This research analyzes the very-high-cycle-fatigue behavior of TC4 titanium alloy through fatigue tests at R = −1, −0.3, and 0.1. The results show that the S-N curves are all bilinear and exhibit three failure modes as surface slip failure, surface cleavage failure and interior cleavage failure. Transmission electron microscopy analysis reveals the dislocation structure in interior cleavage failure and suggests that the deformation mechanism of faceting cracking involves both anti-phase boundary shearing and stacking fault shearing mechanisms. It concludes that interior failure results from cleavage fracture of α grains due to dislocation slip. Based on the stress intensity factor of the maximum defect, a slip-cleavage competitive failure model was developed by considering factors such as control volume, defect size, external loading, and grain content, with good predictive results. Additionally, on the basis of the failure mechanism and crack propagation rate model, considering the coupled effects of crack tip blunting, stress ratio, Vickers hardness, and material fracture toughness on crack propagation, the crack propagation life prediction model is constructed. The life prediction model is further modified to be more conservative and accurate in predicting life by consideration the maximum defect size, providing important theoretical support and practical guidance for engineering applications.

中文翻译：

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TC4钛合金的极高周疲劳行为：基于位错特性的刻面开裂机理和寿命预测


本研究通过在 R = -1、-0.3 和 0.1 下的疲劳测试来分析 TC4 钛合金的极高周疲劳行为。结果表明：S-N 曲线均为双线性曲线，表现出表面滑移破坏、表面解理破坏和内部解理破坏 3 种破坏模式。透射电子显微镜分析揭示了内部解理破坏中的位错结构，并表明刻面开裂的变形机制包括反相边界剪切和堆叠断层剪切机制。它得出的结论是，内部破坏是由于位错滑移导致α晶粒的解理断裂引起的。基于最大缺陷的应力强度因子，考虑控制体积、缺陷大小、外部载荷和晶粒含量等因素，建立了滑移解理竞争失效模型，预测结果较好。此外，在破坏机理和裂纹扩展速率模型的基础上，考虑裂纹尖端钝化、应力比、维氏硬度和材料断裂韧性对裂纹扩展的耦合影响，构建了裂纹扩展寿命预测模型。通过考虑最大缺陷尺寸，进一步修改了寿命预测模型，使其在预测寿命时更加保守和准确，为工程应用提供了重要的理论支持和实践指导。