The notch (i.e., stress concentration) and defect are important factors influencing the conventional fatigue behavior of metallic materials. What is the influence of notches and defects on the dwell fatigue mechanism and fatigue life? In this paper, the effects of notches and defects on the dwell fatigue behavior of the Ti-6Al-4V ELI alloy used in deep-sea submersibles are investigated under the load control mode. It is shown that the dwell fatigue is insensitive to the defect size (190–438 μm) compared to the conventional fatigue. For notched specimens, they all present fatigue failure mode under dwell fatigue testing, and the dwell fatigue life is higher than that of the smooth specimen at the same local maximum stress. The dwell of the maximum stress has no influence on the fatigue life and failure mechanism for notched specimens. Moreover, the facet feature is observed in the crack initiation region for both the conventional and dwell fatigue of notched specimens. Electron backscatter diffraction observation indicates that the feature of the fine line markings on the facet in the image by scanning electron microscope is due to the steps on the fracture surface of the α grain.

中文翻译：

---

缺口和缺陷对深海潜水器用Ti-6Al-4V ELI合金停留疲劳机理和疲劳寿命的影响

缺口（即应力集中）和缺陷是影响金属材料常规疲劳行为的重要因素。缺口和缺陷对驻留疲劳机理和疲劳寿命有什么影响？本文在载荷控制模式下研究了缺口和缺陷对深海潜水器用Ti-6Al-4V ELI合金的驻留疲劳行为的影响。结果表明，与传统疲劳相比，驻留疲劳对缺陷尺寸（190-438 μm）不敏感。对于缺口试样，在保压疲劳试验中均呈现疲劳失效模式，在相同的局部最大应力下，保压疲劳寿命高于光滑试样。最大应力的驻留对缺口试样的疲劳寿命和失效机理没有影响。而且，对于缺口试样的常规疲劳和驻留疲劳，在裂纹萌生区域都观察到了刻面特征。电子背散射衍射观察表明，扫描电镜图像中刻面细线标记的特征是由于α晶粒断面的台阶。