A brake is one of the most important safety and performance components of a high-speed train and the final guarantee toensure it soperation safety. A high-speed train brake consists of one or a few brake discs, and each brake disc is associated with a number of friction blocks that take various geometric shapes (such as circle and hexagon). Under relatively low-speed braking conditions, the friction contact interface between a brake disc and friction blocksmay lead to unstable stick-slip vibration of a brake system. During actual braking, the dynamic characteristics of stick-slip vibration of abrake system is affected by the structural parameters of the system and the characteristics of the frictional contact interface. However, the study on the influence of the configuration, shape and orientation of these friction blocks on stick-slip vibration in a brake system is not adequate. Therefore, in order to discover the effect of the installation direction of a hexagonal friction block of a high-speed train brake on the stick-slip vibration of the block, tribological tests under different installation directions are carried out on a self-designed multi-mode high-speed train braking performance simulation test bench, combined with modal analysis and wear simulation in finite element analysis. The relationship between the installation direction of the friction block and interface contact behaviour, interface friction and wear, and stick-slip vibration was established.
The comprehensive test and simulation results showed that the installation direction of the friction block significantly affected the contact pressure distribution and wear state of the interface, resulting in different stick-slip vibration phenomena in the system. Among them, the hexagonal friction block system installed at 30° angle produced the lowest amplitude of stick-slip vibration, the shortest period of stick-slipmotion, the highest frequency of stick-slip vibration, the disk-block interface contact state was most even, and the surface wear severity was the least. The stick-slip vibration could induce noise, but the intensity was low. The installation direction of the friction block would affect the frequency and intensity of the stick-slip vibration, but it did not change the attribute that the stick-slip vibration was a kind of low-frequency vibration. The finite element simulation frequency was approximately equal to the measured vibration frequency. Modal analysis showed that the stick-slip vibration was contributed to mostly by the first mode of the brake structure, and the installation direction would affect the mode of the structure, and led to different interface contact states and dynamic behaviours. In addition, the wear simulation analysis also showed that the installation direction of the hexagonal friction block would significantly affect the contact states of the friction interface, so that the contact area, contact stress distribution and wear level all varied with the direction and thereby affect the stick-slip vibration characteristics of different friction systems.
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