This study systematically examines the fretting fatigue behavior of Ti-6Al-4 V dovetail joints with and without shot-peening (SP) treatment, focusing on crack initiation, propagation mechanisms, and SP-induced microstructural modifications. An innovative four-camera in situ observation system was developed to track real-time crack evolution at four critical locations of the dovetail tenon. Integrated with deep learning-based U-Net models for crack segmentation and length quantification, the effects of SP treatment on fretting fatigue life, crack propagation rates, and surface damage were analyzed under varying loads (26–40 kN). The results demonstrate that SP treatment significantly enhances overall fretting fatigue life at low and medium loads (26–34 kN) by delaying crack initiation and early propagation through compressive residual stresses (CRS) and strain hardening, achieving maximum life enhancement of 186.19 % at 26 kN, while proving ineffective in suppressing long-crack growth under cyclic stress superposition. At 40 kN, SP exhibits detrimental effects due to accelerated CRS relaxation and stress concentration induced by surface roughness. Although the initiation life remains superior to untreated specimens, the overall fretting fatigue life decreases due to accelerated crack propagation rates. These findings highlight the dual role of SP in fretting fatigue resistance, emphasizing the necessity of load-dependent optimization strategies for aerospace applications.

中文翻译：

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U-Net 模型辅助喷丸处理燕尾榫接头的微动疲劳损伤和裂纹扩展

本研究系统地研究了 Ti-6Al-4 V 燕尾榫接头在喷丸处理和不喷丸处理下的微动疲劳行为，重点关注裂纹萌生、扩展机制和 SP 诱导的微观结构修饰。开发了一种创新的四摄像头原位观察系统，用于跟踪燕尾榫四个关键位置的实时裂纹演变。与基于深度学习的 U-Net 模型集成，用于裂纹分割和长度量化，分析了 SP 处理对不同载荷 （26–40 kN） 下微动疲劳寿命、裂纹扩展速率和表面损伤的影响。结果表明，SP 处理通过压缩残余应力 （CRS） 和应变硬化延迟裂纹萌生和早期扩展，显著提高了中低载荷 （26–34 kN） 下的整体微动疲劳寿命，在 26 kN 时实现了 186.19% 的最大寿命延长，同时证明在循环应力叠加下抑制长裂纹扩展无效。在 40 kN 时，由于表面粗糙度引起的加速 CRS 弛豫和应力集中，SP 表现出不利影响。尽管起动寿命仍然优于未处理的试样，但由于裂纹扩展速率加快，整体微动疲劳寿命会缩短。这些发现强调了 SP 在抗微动疲劳性中的双重作用，强调了航空航天应用负载相关优化策略的必要性。