Aircraft Brakes By The C / C Composite Friction Wear Behavior Research

C/C composites is the latest aircraft friction material and their friction and wear properties are very important. Friction and wear properties of C/C composites from different techniques were studied and effects of braking speeds and pressures were also analyzed. In order to inquire into the worn mechanisms, the morphology and structure of worn surfaces and wear debris were examined through using optical microscopy, scanning electron microscopy , X-ray diffraction, laser Raman micro-spectroscopy.1) Friction and wear properties of C/C composites with different pyrolytic carbon microstructure were studied . It showed that C/C composites mainly with rough laminar (RL) pyrolytic carbon have small uniform wear debris and the most stable friction and wear properties, which can maintain at high braking speeds and pressure and the linear wear is under 2 u m/plate.time, owing to the highest degrees of graphitization and thermal conductivities . C/C composites mainly with smooth laminar (SL) pyrolytic carbon have unstable properties of friction and wear owing to lower graphitization degrees and thermal conductivities. C/C composites impregnated only by pitch have the highest wear rates and the linear wear is up to 27.33 u m/plate.time.2) The friction and wear properties of C/C composites under different braking speeds and pressures were studied. The results showed: at braking speed of lOm/s there is a peak in coefficient-of-friction-speed curves when the braking pressure is kept at 60N/cm , and wear rates increased with braking speed and the weight loss increased largely at higher braking speeds owing to oxidation, especially to C/C composites with low conductivities; with the increase of braking pressure the coefficient of friction decreased lightly but the weight loss increased, especially to C/C composites with low conductivities.3) For the first time, Graphitization degree of worn surfaces under different braking speeds and pressure was studied by using Raman spectroscopy and X-ray diffraction . Graphitization degrees of worn surfaces decreased with braking speeds and pressure at low energy braking; but it increased to C/C composites with low thermal conductivities and decreased to the one with high thermal properties at the braking speed of 28m/s; it increased with braking pressure at high braking energies to C/C composites with either high or low thermal conductivities, which was caused by stress assisting graphitization. The increase of graphitization degree is helpful to lower friction coefficient.4 ) The wear mechanism of C/C composites in braking have been inquired , they were abrasion, delamination of part of the friction film, oxidation wear and adhesion wear.