Effect of Heat Treatment on Crack Propagation and Performance of Disk Brake with Cross Drilled Holes

A vehicle disk brake, which has cross drilled hole patterns on a frictional surface for improving cooling and braking performance, has propensity to cause crack problem under the harsh braking condition. In this study, the finite element analysis by using ABAQUS was adopted to investigate a cause of crack occurrence by the thermo-mechanical phenomenon around drilled hole patterns. As a remedy of the crack generation, the disk brake rotor with stress relieving and ferritic nitrocarburizing was prepared and tested on brake dynamometer in harsh condition. The test result was examined in terms of pad wear, the braking torque variation, the braking temperature changes, the crack initiation timing, and the crack propagation speed. As a test result, the disk after heat treatment showed 3.61 % higher average braking temperature than the disk without heat treatments, to suggest decreased heat dissipation performance, however, it also showed 14 % lower pad wear amount, and 0.1 % smaller braking torque variance than the disk without heat treatments, to stand for improved contact characteristics. Also, the heat treated brake rotor showed 51.3 % lower crack propagation rate which is considered as proper countermeasure of the fracture phenomenon at the edge of cross drilled hole.