The effect of metal fibers on the friction performance of automotive brake friction materials

This study investigates the effect of different metallic fibers upon friction and wear performance of various brake friction couples. Based on a simple experimental formulation, friction materials with different metal fibers (Cu, steel, or Al) were fabricated and then evaluated using a small-scale friction tester. Two different counter disks (gray cast iron and aluminum metal matrix composite (Al-MMC)) were employed for friction tests. The friction tests were carried out at two different temperature ranges: ambient and elevated temperatures. Results from ambient temperature tests revealed that the friction materials with Cu fibers showed a pronounced negative μ–ν (friction coefficient versus sliding velocity) relation when the friction material was rubbed against gray cast iron disks, implying that stick–slip may occur at low speeds. The negative μ–ν relation was not observed when the friction material with Cu fibers was rubbed against the Al-MMC counter surface. On the other hand, elevated temperature tests showed that the friction material with Cu fibers exhibited better fade resistance than the others. The test results also showed that the friction material with steel fibers was not compatible with Al-MMC disks due to severe material transfer and erratic friction behavior during sliding at elevated temperatures.