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The present study addresses the tribological behavior of polyester composites reinforced with a natural fiber (sisal), a synthetic fiber (glass) and their combination (glass/sisal hybrid). The composites were obtained by compression molding with an overall fiber content of 20 or 40 vol%. The composites were rubbed against a steel counterface using a tribometer. Pure sisal composite exhibited superior wear resistance, mainly due to the formation of a concise tribofilm. It also showed the lowest coefficient of friction (CoF) because of the lubricating action of the water present in the natural fiber. Pure glass composite showed the lowest wear resistance due to the strong abrasive effect of the glass fibers. The increase in fiber content lead to an increase in CoF and its effect on wear was complex and discussed throughout the article.

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Brake friction materials (BFMs) are designed to have low wear rate under different conditions of contact pressure, temperature, and sliding velocity. The conditions to ensure a low wear rate (i.e., a moderate wear regime) between the disc and the BFM are not well established. The present article aims to enhance the comprehension about the wear regimes for BFMs. For this purpose, a commercial BFM was slid against a gray cast iron rotor (disc). Tests were performed under different sliding velocities and with both increasing and decreasing steps of pressure levels. Tribofilm formed on the disc's surface and BFM's wear were monitored during the tests. It was possible to conclude that the previous condition of the surface of the disc, with respect to the presence or absence of tribofilm, affects the required conditions for the transition in the wear regime. The removal of tribofilm on the surface of the disc was affected by high contact pressures and high sliding velocities. Those conditions led to a severe wear regime with a destruction of contact plateaus and an increase in friction and BFM's wear.

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