Fade behaviour of copper-based brake pad during cyclic emergency braking at high speed and overload condition

• Published in: Wear 2019-06, Vol.428-429, p.10-23
• Main Authors: Zhang, Peng, Zhang, Lin, Fu, Kangxi, Wu, Peifang, Cao, Jingwu, Shijia, Cairang, Qu, Xuanhui
• Format: Article
• Language: English
• Subjects: Brakes; Braking; Braking systems; Coefficient of friction; Copper; Crack propagation; Cu-based brake pad; Damage accumulation; Emergencies; Emergency braking; Fade behaviour; Fatigue cracks; Fatigue failure; Fracture mechanics; Friction; Friction coefficient; Friction layer; Friction reduction; Friction resistance; High speed rail; High temperature; Softening; Solid lubricants; Surface layers
• ISSN: 0043-1648; 1873-2577
• DOI: 10.1016/j.wear.2019.01.126

In order to simulate the fade behaviour of friction between copper-based brake pads and brake disc during emergency braking of high-speed railway train, accelerated fade experiments were performed by executing cyclic emergency braking under high braking speeds and overload conditions. The fade behaviour and its relationship with variations in the microstructure and composition of the friction layer were investigated in detail. The results showed that continuous emergency braking resulted in the formation of fatigue cracks in the friction layer, and the high temperature led to the softening and flow of copper-rich phase existing in the surface layer. Those promoted the formation of friction layer composed of copper-rich phase and iron-rich phase alternately. The softening copper-rich phase was the primary cause of the fading friction coefficient, serving as a solid lubricant to reduce the clamping force on hard particles and in turn reduce the friction resistance. Moreover, the accumulated damage and rapid transfer of the friction layer on the friction surface weakened the brake pad tolerance and caused the friction coefficient to fade more rapidly. •The changing relationship of instantaneous friction coefficient and temperature during braking is exhibited.•The relation between the variation of friction layer and the friction coefficient is explained in detail.•The main factor that induces the fade behaviour of copper-base brake pads is elucidated.