A lumped-parameter model for stick–slip vibration in train brake systems considering hexagonal friction block sizes

This study introduces a lumped-parameter dynamic model considering the geometric characteristics of friction blocks to elucidate the stick–slip vibration in high-speed train brake systems. Taking hexagonal friction blocks in train brake pads as an example, the model integrates their geometric and uneven contact pressure characteristics. A multiscale modeling approach combining fractal contact theory and discrete Iwan model was proposed to describe contact behavior, and a Switch model was employed to simulate stick–slip friction. The variations in stick–slip responses of hexagonal friction blocks of different sizes were analyzed by inputting derived equivalent parameters into the dynamic model. The model was validated using a high-speed train brake simulation test bench, with tests conducted for various friction block sizes. Theoretical and experimental results showed good agreement, confirming the effectiveness of the model. The findings indicate that friction block geometry significantly influences the stick–slip vibration. Larger blocks with increased contact area and mass, improve pressure distribution, increase equivalent contact stiffness, and enhance elastic recovery from minor deformations, thereby reducing nonlinear effects and resulting in a smoother sliding process that mitigates stick–slip vibration. The model provides insights into friction-induced vibration mechanisms and aids in optimizing brake pad design in brake systems.