THE RELATIONSHIP BETWEEN SURFACE QUALITY AND THE RUNNING-IN CHARACTER OF CARBON-CARBON COMPOSITE (CCC) AIRCRAFT BRAKES

The surface quality effect on the friction and wear properties and the running in characteristics of the carbon carbon composite (CCC) aircraft braking disks was investigated. Because the peaks of asperities on the mating surfaces mutually penetrate as the surfaces move tangentially relative to each other, plastic elastic deformation occurs in the surface layer. The surface friction film depends on the depth of the deformed layer and the quantity of the wear particles. The latter depends on the surface roughness of the CCC disks. The surface morphology, roughness, and profiles of the machined and worn surfaces are measured with a Talysurf 4, and studied using SEM. Running in deforms the machined surface roughness Ra (arithmetic mean deviation of the profile, which can be directly read from the profilometer or surface analyzer) to a deformed Ra. Running in is optimal when the machined surface roughness is slightly greater than deformed surface roughness after running in, and the optimal value of the machined surface roughness in this study is 12.5?μm. The properties of the surface layer of a material depend significantly on the cutting process. A correct machining method should produce a high precision surface with little undulation but a large roughness may shorten the running in time and decrease the number of running in braking cycles.