Multiscale Investigation on Fatigue Crack Growth and Remaining Useful Life of Bogie Frame Materials Under Service-Induced Damage
This study quantifies the degradation of fatigue crack growth (FCG) resistance in high-speed train bogie frame materials after long-term service. Full-scale frame fatigue tests, multiaxial FCG experiments, and finite element simulations were integrated to determine equivalent crack loading conditions. Digital image correlation captured surface displacement fields for stress intensity factor calculation. Comparative testing of as-welded (AW) and base metal (BM) regions before and after service revealed substantial reductions in remaining useful life: 70.54% for AW and 22.31% for BM. Crack-tip strain responses increased by more than twofold in AW and 1.44 times in BM after service, indicating diminished crack growth resistance. Microscopic fracture surface analysis showed more secondary cracks, unstable crack paths, and blurred fatigue striations in post-service materials, particularly in the AW region. Phased array ultrasonic testing detected no macroscopic defects, yet microstructural deterioration was evident. These findings establish a quantitative link between service-induced damage and fatigue performance degradation, supporting region-specific residual life assessment strategies for bogie frames. The experimental protocol, grounded in actual service loading spectra, improves the accuracy of remaining useful life prediction and provides a reliable basis for maintenance decision-making in high-speed rail operations.