Effect of Hard Particle Grit Size on Friction Coefficients and Embedment of Automotive Braking

Abstract

The effect of hard particle grit size on friction coefficients and particle embedment of braking system was investigated using a model brake test rig. Silica sand grit sizes ranging from 180 - 355 µm were used in drag and stop mode braking application and results were compared to the tests without the grit particles in order to determine the changes in friction coefficient (CoF) and the percentage ofparticle embedment. Sliding speeds of 4 m/s, 8 m/s, 10 m/s and 12 m/s at constant pressures of 0.6 MPa, 0.8 MPa and 1 MPa were applied during the tests. Results showed that the presence of hard particles and grit size has significant effect on the CoF values. The values of CoF tend to reduce when grit particles are present. However, CoF values increase with sliding speed and applied pressure. Weardebris and particle embedment of silica sand was analyzed using SEM and optical microscopy after the test. Particle embedment (PE) of 1- 2 % of the pad area was observed. Fragmentation of hard particle has occurred only at high applied pressures. Also correlation between PE and CoF values was found to be slightly an inverse relationship as small reduction of CoF values with higher percentageof PE was determined.