Effect of pressure in the transition between moderate and severe wear regimes in brake friction materials

The transition in wear regime is a tribological phenomenon observed in many materials, where a sudden change in wear regime (from moderate to severe) occurs when operating parameters (e.g. pressure or sliding velocity) are changed. However, this phenomenon is rarely explored in brake friction materials (BFMs). Severe wear regime for BFMs results in an increase in cost and leads to environmental issues due to the high amount of loss in material. This work aims to study the transition in BFM applying different levels of pressure, where a BFM was rubbed against a gray cast iron disc in a tribometer. The tribofilm deposited on the disc surface and the area ratio of contact plateaus of BFMs were analyzed. The coefficient of friction (COF) and the BFM's wear were also measured. The wear regime changed from moderate to severe at a limit pressure of 90 bar. At the severe wear regime, a sudden increase in the COF was observed, and the wear of the BFM was approximately 13 times higher than in the moderate wear regime. It was also seen a removal of the tribofilm deposited on the disc's surface and a reduction of contact plateaus over the BFM's surface.