A damage-oriented track evaluation method based on measured bogie frame dynamic stress

Track condition significantly influences the fatigue performance of metro bogie frames and constitutes a critical external factor in their structural durability. However, existing approaches to track evaluation rely primarily on track geometry measurements or axle box acceleration data and seldom establish a direct relationship with the fatigue state of the bogie frame. This study proposes a damage-oriented track evaluation framework grounded in bogie frame fatigue safety to address this limitation. Using field test datasets, we identified fatigue-critical locations through detailed structural inspection and statistical analysis of segmental fatigue damage. We then developed a combined fatigue damage index to characterize the overall fatigue response of the bogie frame. Building on this, we introduced a track comprehensive excitation index (TCEI) that integrates equivalent track curvature, track structure index, and mean operating speed. The weighting coefficients of these parameters were determined using a vehicle-track coupled dynamic model. The results demonstrate that the track curvature and structure predominantly govern fatigue excitation, whereas the operating speed exerts a comparatively minor influence. Furthermore, we observed a clear positive monotonic correlation between TCEI and the combined fatigue damage. Based on fatigue damage exceedance probabilities, we established corresponding track evaluation thresholds. Overall, the proposed framework provides a practical and reliable tool for identifying track sections associated with elevated fatigue risk in metro bogie frames.