A surface crack growth model considering load sequence effects and application to damage tolerance evaluation of railway bogie frames

This study developed a surface crack growth model that accounts for load sequence effects under variable amplitude loading. This was achieved using a three-dimensional crack growth analysis model that integrates the strip-yield model and the K-Analogy method. Fatigue crack growth (FCG) tests were performed on surface-cracked steel plates under various variable amplitude loadings to calibrate and validate the strip-yield model. The results demonstrate that the developed model exhibits superior predictive accuracy in estimating surface crack growth life under variable amplitude loading compared to the conventional NASGRO equation. As an application case for the damage tolerance evaluation of railway bogie frames, the developed model was then utilized to evaluate the residual life of a metro bogie frame’s gearbox suspension seat featuring a surface crack under a 12-level spectrum loading, resulting in a predicted operational distance of 430 × 10³ km for a descending-order load sequence. Stochastic analysis was conducted to explore the impact of load sequence effects and load spectrum expansion on the FCG life of bogie frames. Findings indicated that load sequence effects significantly influence FCG life predictions, with FCG life following a normal distribution. Contrary to traditional assumptions, descending-order load sequences may lead to non-conservative FCG life estimates. Additionally, load spectrum expansion increases the median FCG life and alters the scatter characteristics of life predictions. The developed model supports damage tolerance design, maintenance optimization, and the design of fatigue test spectra for railway components.