The effects of the friction block shape on the tribological and dynamical behaviours of high-speed train brakes

Abstract

Drag brake experiments using hexagonal, pentagonal, and circular friction blocks are conducted using a self-designed small-scale brake dynamometer to investigate the influence of the friction block shape on the tribological and dynamical behaviours of high-speed train brakes. A four-degree-of-freedom model that considers the interface contact behaviour is established to investigate the influence of the contact stiffness at the friction interface on the stability and vibration characteristics of the braking system. The experimental results show that the surface of the hexagonal friction block is slightly worn, and the contact plateaus is relatively uniform in size, whereas the pentagonal and circular friction blocks show visible ploughing and exfoliation and a significant proportion of large contact plateaus. Accordingly, the hexagonal friction block produces considerably less friction-induced vibration and noise than the pentagonal block and the circular block. Moreover, analysis of the vibration characteristics of the friction system indicates that the interface of the hexagonal friction block is mainly subjected to normal impact, whereas the interfaces of the other two blocks exhibit significantly more ploughing and shearing action in the tangential direction. In general, higher contact stiffness results in stronger friction-induced vibration, thereby enhancing the instability of the friction system. In this work, it is found that the friction block shape has a significant effect on the contact pressure distribution. The hexagonal friction block exhibits a more uniform distribution of contact pressure than the pentagonal and circular friction blocks, resulting in the lowest contact stiffness, as well as the least wear, vibration, and noise.