Fretting fatigue damage and crack propagation of shot-peening dovetail joints assisted with the U-Net model

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.