Study on mechanism of radial long cracks propagation on sliding surface of wheel brake discs

Abstract

A long radial crack with a length of more than 60 mm was observed near the bolt hole of the brake disc of high-speed railway vehicles. It is necessary to study its causes and propagation mechanism. In this study, the gradient change of grain size was studied by microscopic observation of the brake disc after service. Through a variety of tensile tests, a relationship describing the gradient distribution of mechanical properties of materials was established. The radial crack propagation at the bolt hole of the friction surface was analyzed by using the extended finite element model (XFEM). The final crack lengths at the initial speeds of 250 km/h and 350 km/h are 32 mm and 43 mm, respectively. The reduction of material strength on the sliding surface and the stress concentration near the bolt hole make the crack propagate rapidly. The crack length increases with the decrease of residual strength. Cracks may continue to expand to the core through fatigue propagation, eventually leading to fatigue failure. It is proposed that the hot spot area around the bolt hole should be the key area for checking cracks during operation and maintenance.