Wear and environmental aspects of composite materials for automotive braking industry

Braking is accompanied with the release of a variety of particulates. More than 230 million vehicles are on the roads and over 16 million new vehicles are sold in the USA each year [1]. Brake linings are complex composites typically formulated of more than 10 constituents, and more than 3000 different materials were used in different brands [2]. Use of asbestos has been suppressed because of health implications [3], however, it is not clear what impact the currently used materials have. In this research, the collected wear debris as well as the friction layers were analyzed. The adopted SAE J2430 friction test is frequently used in the USA for evaluating the performance of brakes. Combination of light and electron microscopy supported by energy dispersive microanalysis, grazing angle X-ray diffraction, and atomic force microscopy allow successful analysis of released matter. It was shown that nanoparticles of newly formed materials are being released during wear process and it is suggested to initiate additional research addressing possible impact of these species on the environment. The released amounts of CO2 can be correlated with wear of brake lining materials.