Interrelationship among wear, debris, and friction-induced stick-slip vibration at high-speed train brake interfaces in humid environments

During the friction braking process of high-speed trains, the strong friction between the brake discs and brake pads can cause significant wear on the pads, resulting in a large amount of wear debris that participates in the friction at the braking interface. Particularly in humid environments, the strong friction can induce significant friction-induced stick–slip vibrations (FISSV). Additionally, the humid environment promotes oxidation reactions, leading to the formation of harder wear debris that induces abrasive wear. Both abrasive wear and the impacts of FISSV can cause damage to the braking interface, posing significant challenges to the operational safety of the pads. Therefore, in humid operating environments, it is essential to fully consider the interactions among wear, debris, and vibrations at the braking interface of high-speed trains. However, the relationships among these three factors have not been clearly understood. To address this issue, we designed smooth and grooved discs and conducted simulated tests of FISSV in a humid environment to investigate the damage mechanisms of wear debris and FISSV on the braking interface in such conditions. The results indicate that under humid environments, the wear debris generated at the interface is difficult to compact due to the action of water films, and its oxidation reaction is accelerated. These combined effects hinder the formation of large-area contact plateaus, resulting in lower interface stiffness and inducing high-frequency FISSV. Furthermore, the abrasive wear caused by high-hardness oxidized debris and the impact effects of FISSV further damage contact plateaus, generating more debris. This forms a vicious cycle of interface wear-debris generation-intensified FISSV-aggravated wear. By designing grooves to collect debris, the amount of free-flowing debris at the friction interface is effectively reduced, allowing the load to be borne mainly by the disc and the pad matrix. This forms higher-stiffness contact, significantly suppresses FISSV intensity, alters the wear mechanism, breaks the abrasive wear-dominated vicious cycle, and demonstrates the role of controlling debris behavior in improving the tribological performance of brake interfaces in humid environments.