Propagation trends of cracks situated in bogie frames based on a rigid-flexible coupled vehicle dynamic model

The bogie frame of high-speed electric multiple units in China is subjected to more complex fatigue loads, significantly increasing the risk of fracture. However, current research lacks a comprehensive dynamic model that accounts for the presence of cracks in the flexible bogie frame within a rigid-flexible coupled vehicle system. To address this gap, this study develops a novel rigid-flexible coupled vehicle dynamic model to investigate the fracture behaviour of bogie frames with cracks. The motion equations of the vehicle model, incorporating crack effects, are firstly derived and validated for accuracy and effectiveness. Numerical results reveal that Mode-II fracture mode primarily governs crack propagation at all critical positions studied. It is observed that during vehicle operation, the maximum dynamic energy release rate generally increases with crack size, with the peak value shifting to different points along the crack front. Among the three critical positions examined, when a single crack is present, the crack at the curved area of the top cover plate exhibits a higher likelihood of propagation. In scenarios where two cracks are present, the crack located at the gearbox suspender seat is more prone to propagation.