Revealing of Factors of Increased Wear of Friction Carbon-Carbon Materials in Aircraft Taxi Brakes

The study compared properties of carbon-carbon composites for aircraft brakes manufacturing. Composites based on various graphitized and carbonized fibers, coal, tar pitch and pyrocarbon matrices were considered. Friction tests were carried out on full-size brake discs (3-disk stand) and on model samples (testing machine UTM-2168). A significant wear increase of composites based on pyrocarbon matrix was found during taxi braking in the temperature range of 50—250 °C. Wear of composites based on coal tar pitch matrix did not depend on the temperature of friction surface. It was found, that the “third body” of composites based on pyrocarbon has a coarse, rough structure with distinct individual abrasive particles; its hardness is more than twice as high as hardness of “third body” of composites based on pitch matrix. The size distribution of pores for composites based on different matrices is given, the difference in the quantity and size of structural defects is illustrated. The variation in wear of materials during taxi braking is explained. The increase of anisotropy degree of the pitch matrix, provided the decrease of wear of the material. The wear was measured during taxi braking of specimens with a hybrid matrix having a different ratio of coal tar pitch and pyrocarbon components. Carbon-carbon composites containing 45 percent or more of the pitch component in matrix have stable reduced wear during taxi braking, regardless of the reinforcement scheme. The possibility of reducing wear during taxi braking of composites on pyrocompacted matrices by modifying the matrix with pitch is shown.

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