Optimization of Particle Distribution in Al-SiC Metal-Matrix Composite (MMC) Brake Rotors

This paper presents a study of Al-SiCp metal matrix composite (MMC) brake rotors based on microscopic characterization, macroscopic thermomechanical tests and two-scale finite element analyses (FEA) aiming at rotor optimization. The objective is to achieve lower thermal stress of the rotor in working condition. The MMC microstructure and composition is confirmed under SEM, which also provides the micron-scale FEA geometry. Homogenized composite properties from micron-scale FEA is used to inform cm-scale FEA simulation of the realistic braking events. The simulated stress and temperature profiles in the brake rotor are compared against braking dyno tests to calibrate the FEA model, as well as quantifying the coefficient of friction (COF) evolution during the braking process. The dyno tests reveal that COF decreases with increasing sliding speed at temperatures ranging from 18 °C to approximately 350 °C. At a given sliding speed less than 50 mph, COF first increases and then decreases with increasing temperature, before reaching the brake fade limit of 350 °C. The FEA-based parametric study indicates that the peak macroscopic thermal stress in a braking event could be reduced by 31.8% with the optimized SiC distribution. The key to the minimization of in-brake thermal stress is found to be the accurate engineering of spatial distribution gradient of SiC particles in the transition Region linking the surface-under-friction and the hub Region around the bearing.