Effect of Filling Materials into Friction Block on Brake Performance of High-Speed Train Brake Pad

The brake pad, as one of the key components in the brake system of the high-speed train, is a vital link in the brake process, playing a significant part in determining the safe operation of the fast-running high-speed train. However, the brake pad will be excessively and eccentrically worn after a long time of service due to the uneven pressure acting on it, which may greatly reduce the brake torque and thereby make the train operation unreliable. In addition, friction-induced vibration and noise (FIVN) generated during the brake process generally relating to the poor wear situation at the brake interface can be extremely annoying. Therefore, for the sake of safe operations of the high-speed train, it’s of great significance to comprehensively study the tribological behaviors at the brake interface, so as to find effective ways to improve wear and FIVN performance of the brake pad. In practical settings, the brake pad of a high-speed train consists of multiple friction blocks. For enhanced heat dissipation and pressure welding process, perforated structure is introduced in the friction block. However, the effective contact area is inevitably reduced because of the existence of the hole. If appropriate filling materials are filled into the hole, on the one hand, the contact area is compensated, on the other hand, the role of wear debris at the brake interface influencing the surface wear, thermal distribution and FIVN characteristics may be understood through comparing the tribological behaviors of the perforated block and those of the blocks filled with different additive materials. This can provide guidance to choose proper fillers that can make the friction block behave better in terms of interfacial tribology behavior. Given this, in this study, perforated friction blocks of high-speed train brake pad respectively filled with powder metallurgy, cooper, graphite and cast iron in the central hole were employed on a small-scaled braking dynamometer to conduct tribological tests. Complex eigenvalue analysis and contact stress analysis were performed on finite element software. The effect of different additive fillers on the brake tribological behavior was investigated, and the relationship between the wear situation, thermal distribution, and FIVN at the brake interface was discussed. The results showed that the additive materials had no visible effect on the interfacial friction coefficient and the unstable vibration frequency and mode However, the tribological behaviors in terms of wear behavior, thermal distribution and FIVN characteristics at the brake interface were significantly affected by the fillers. The noise of the braking system increased after the filling of powder metallurgy material, which may be due to the reduced wear trapping performance of the powder metallurgy filled block, consequently the wear behavior was worsened and the FIVN of the brake system was intensified. The noise of the braking system was reduced after filling cooper, graphite and cast iron. However, the worn surface of the copper filled block showed obvious material accumulation phenomenon. In addition, significant thermal concentration was observed on the brake interface when the friction block was filled with graphite. For the cast iron filler case, the number of large contact plateaus were significantly reduced, which lowered the contact stiffness and improved the wear situation and thermal distribution of the brake interface, and the FIVN of brake system was greatly reduced. The wear behaviors caused by the additive fillers were the key factors affecting the FIVN and the interfacial thermal distribution. Filling proper additive materials into the friction block contributed to reduce the FIVN and improve the interfacial wear behavior and thermal distribution.