Friction & wear characteristics of pitch & poly-acrylonitrile based carbon-carbon composites in air and nitrogen environment under aircraft taxi conditions

Abstract

In this investigation, a disc brake test rig was designed and developed to evaluate the friction and wear characteristics of pitch and poly-acrylonitrile based carbon-carbon composites subjected to different aircraft taxi energy fluxes and temperatures in air and nitrogen environment. The test rig was operated in drag configuration at a constant speed, and it was found that temperature of the disc, humidity of the surrounding environment, the supplied energy flux as well as the type of the composite play a critical role in determining whether coefficient of friction lies in the normal wear regime (<=0.2) or dusting wear regime (>=0.3). Results from these tests were compared with existing results in literature and a good agreement was found. Additionally, to quantify wear at different specimen temperatures and taxi energy fluxes, controlled tests were performed using an external thermal chamber, reaching temperatures up to 550 °C. It was found out that temperature and energy flux had a significant influence on friction and wear behavior depending on the type of composite and operating environment. Furthermore, optical and scanning electron microscopy were conducted to analyze the wear mechanisms. Matrix and interface cracking along with fiber breakage were observed from tests in air environment, whereas in nitrogen environment, particulate and layered debris played a prominent role.