Study on braking tribological behaviors of brake shoe material under the wet condition

• The braking frictional behavior was evaluated under the wet condition.
• The braking friction coefficient has a close relationship with the braking velocity.
• The water leads to partial high pressure point in cracks and serious pitting damage.
• The stability of friction coefficient under wet condition is worse.

The objective of this study is to investigate the influence of water on tribological braking behavior of brake shoe material using a sub-scale frictional braking machine. The results indicate that the friction coefficient of braking interface has a close relationship with the braking velocity and the pressure under the wet condition. The friction coefficient shows a reduction by 30% compared with the dry condition at low braking speed. With an increase in braking velocity, more water is thrown off from the braking interface. This makes the water film becomes thinner and the surfaces becomes closer, which results in more contact and more wear. Therefore, more friction heat is produced and more water is evaporated, which makes the water film thinner and the interface more similar to the dry. The water sealed up in the cracks leads to partial high pressure point on the surface resulting in serious pitting damage of brake shoe. Both the stability of friction coefficient and the wear loss under wet condition are worse than those under dry condition.