Influence of Running-In on the Friction Coefficient of C/C Composite Materials for Aircraft Brakes

This work describes experimental studies on the effect of running-in on the tribological properties of friction carbon–carbon (C/C) composite materials used in the production of disc brakes on Russian airplanes. Three groups of friction material were selected for the study, differing in the reinforcement of the pec matrix. The first and second groups’ samples were made of Termar brand carbon composite on the basis of discrete graphitized fiber and different from each other in the length of filaments in the finished material. The third group of samples was made of a composite based on carbonized fiber. The friction coefficient was determined on a tribometer according to a scheme in which the contact pin was on the disc at room temperature (23°C) by a method of a two-factor planned experiment in the range of normal pressures 2—22 MPa and sliding velocities 0.03—0.30 m/s. The study of the third body on the friction path was carried out by Raman spectroscopy using an exciting green laser with a wavelength of 532 nm. The results obtained in this work show that the running-in of the studied C/C materials leads to an increase in the friction coefficient. This is due to the appearance of a third body on the friction track, which is a thin layer of wear particles. By Raman spectroscopy it was show that the third body mainly contains carbon fibers. This work demonstrates the prospects for improving the C/C friction properties by increasing the tribological properties of carbon fibers used in the manufacture of composites.