Effect of fiber-types on the braking performances of carbon/carbon composites

The braking performance of carbon/carbon composites prepared from carbonized oxidized polyacrylonitrile fiber (OPF) and from carbon fiber (CF) felts were investigated using a friction performance tester to simulate the normal landing and rejected take-off conditions of an aircraft. The microstructures, worn surfaces and hardness of the composites were characterized by Raman spectrometry, scanning electron microscope and nanoindentation. Results showed that the OPF-derived composites have stable friction coefficients, friction curves and acceptable wear loss at two braking levels, while the friction coefficients of the CF-derived composites present a relatively obvious performance degradation. An increase in braking energy not only reduces the friction coefficient of both composites, but also significantly increases their wear. Due to the higher hardness of CFs that makes them harder to deform and crush, their debris may experience rolling friction and abrade the friction film, resulting in a lower friction coefficient and a higher wear loss, especially under rejected take-off conditions. However, outstanding braking performance is obtained for the OPF-derived composites under both braking conditions, because the softer fibers in the matrix and the loose OPF debris are easier to crush and to form beneficial friction films.