Influence of thermal properties on friction performance of carbon composites

Three different needled felt C/C composites containing from 5 to 25% fiber oriented normal to the friction surface (z-fiber) were evaluated and tested for friction performance. A laboratory dynamometer was used to simulate cold taxi, hot taxi and normal landing braking events utilizing a single stator and rotor pair. Temperatures measured near the friction surface were lowest for highest thermal diffusivity material demonstrating the effectiveness of z-fiber content at reducing friction surface temperature. Low friction coefficient (similar to0.12) under cold taxi conditions increased by a factor of two under hot taxi conditions due to water-desorption transitions. Composites with high diffusivity needed greater braking power to experience transition relative to lower diffusivity materials. Higher braking power was needed to produce a transition under higher humidity conditions. Highest z-fiber content discs showed the lowest wear rate which was attributed to higher in-plane shear strength. The wear rate was highest under hot taxi conditions and it was concluded that mechanisms other than oxidation loss were primarily responsible for the wear rate of the C/C composites tested in this study. The C/C composite surfaces had a polished appearance suggesting that the removal of nano-scale particles occurs from the friction process. (C) 2001 Elsevier Science Ltd. All rights reserved.