Failure analysis of inner wall of X-10 brake discs for urban rail vehicles

Abstract

Some X-10 type brake discs for urban rail vehicles were examined by fluorescent magnetic particle inspection test, and the magnetic trace accumulation was observed at the root of the connecting claw of the brake discs. In this work, the causes of failure for the brake discs are analyzed and discussed. The chemical composition, metallographic structure, and mechanical property of the failure samples were characterized by means of X-ray energy dispersive spectrometry, metallographic microscope, scanning electron microscopy, and an electronic universal material-testing machine. At the same time, the stress and crack propagation states were analyzed by numerical simulation, braking dynamic and fatigue tests, respectively. Based on the fracture mechanics theory, the residual fatigue life was also predicted. The failure reason of the inner wall of brake disc was that the fatigue crack occurred at the root of the connecting claw of the brake disc body, and the crack source was taken from graphite sheets exposed on the surface of the grey cast iron matrix. The results of the numerical simulation showed that the larger thermal stress acted on the graphite sheets at the root of the connecting claw, and promoted the crack to expand along the path of the graphite sheets. The results of the braking force and fatigue tests showed that there was stability propagation of the crack. Finally, some suggestions and prevention for brake discs are provided.