Abstract: In the process of train braking, the phenomenon of metal mosaic will occur in the tread braking and disc braking, which will cause damage to the wheel tread and surface of the brake disc, thus bringing potential safety hazards to the vehicle operation. In order to study the formation and behavior of metal mosaic, the metal mosaic produced by two friction pairs of low friction composite brake shoe and wheel, P/M brake pad and brake disc were selected for macroscopic and microscopic morphology observation, material physical and mechanical properties test and material composition content analysis. At the same time, the micro scale structure model of disc brake is established by ABAQUS to study the scuffing and wearing process of hard abrasive particles on the brake disc surface. The results show that the metal mosaic comes from the wheel and the brake disc. Braking at different speeds has little effect on the plastic strain and maximum contact stress of the brake disc material, but higher speed aggravates the material deformation and changes the plastic work into a large amount of temperature. When there is cold welding condition between the friction pairs, the external hard abrasive particles are easy to melt on the surface of the brake shoe or the brake disc and become the starting point of the metal mosaic, which is affected by the extrusion cutting action and grows up continuously, affecting the working performance of the wheel tread and the brake disc.

Key words: train brake, tread braking, disc braking, metal mosaic, test analysis