AN INVESTIGATION OF FRICTION AND WEAR MECHANISMS OF CARBON-CARBON COMPOSITES IN NITROGEN AND AIR AT ELEVATED-TEMPERATURES

This paper presents the general results of an investigation of the fri ction and wear of a carbon-carbon (C/C) composite material in dry nitr ogen and ambient air using a constant speed type of test apparatus. Wi th brake applications in mind, much of the work has been carried out a t experimental conditions that allow the temperature of the specimen t o reach 700 degrees C by frictional heating. The steady-state coeffici ent of friction in dry nitrogen is high (0.35-0.5) because nitrogen do es not have any lubricative effect on C/C composites. In ambient air, however, C/C composites undergo an abrupt transition from a low-fricti on regime (mu = 0.1-0.2) to a high-friction regime (mu = 0.25-0.5) at 150-200 degrees C. The friction in ambient air is generally lower than that in dry nitrogen at elevated temperatures, which suggests that ox ygen in air could have a limited lubricative effect on C/C composites. The existence of temperature-dependent friction and wear regimes in a mbient air implies that the performance of brakes made with C/C compos ites is markedly affected by the thermal properties of the composites, the humidity content in the atmosphere, and operating conditions that can influence the operational temperature of these brakes. Copyright (C) 1996 Elsevier Science Ltd