In Comparison of In-Service Surface Defects and Prefabricated Notches of High-Speed Train Axles

Surface defects such as scratches and impacts on high-speed train axles are often conservatively treated in fatigue design and maintenance standards. This study investigates the fatigue behavior of full-scale axles with circumferential V-shaped notches introduced to simulate such surface damage. Three rounds of fatigue testing were conducted up to 2 × 10⁷ cycles, with notch depths ranging from 0.538 mm to 1.760 mm and corresponding stress concentration factors (SCFs) up to 5.49. Despite the sharp geometries and elevated local stresses (up to 1082.8 MPa), no fatigue cracks were observed at any of the notched sites. Statistical analyses of in-service defects further revealed that real scratches and impacts typically exhibit lower depths and curvatures than the prefabricated notches. These findings highlight the exceptional fatigue resistance of the axle material and suggest that current overhaul limits for allowable surface defect depths may be overly conservative. The results provide an experimental foundation for refining defect tolerance criteria and support future adoption of geometry- and curvature-based inspection strategies.