Friction and Wear of Asbestos-Free Brake Friction Materials

The results of tribological studies of various asbestos-free brake friction materials from leading manufacturers are presented. Two main aspects of the effect of the thermal conditions on the friction and wear characteristics of the selected materials are established: a change in the physical and mechanical properties at a low thermal load of the friction contact and changes due to various structural transformations and mechanochemical processes of the surface layers at a high thermal load of the friction contact. It is shown that high-temperature friction of frictional asbestos-free polymeric materials proceeds in a multistage mode, accompanied by pyrolysis of volatile products, binder destruction, degradation of the reinforcing element, and carbonization of the friction surface, which are constant factors. The materials under study are capable of forming a frictional transfer film on the counterbody friction surface in the form of a monolithic layer or separate transferred fragments oriented along the sliding direction. The developed materials form a film on the counterbody surface at relatively high temperatures, in the region of maximum friction values. It is established that the mechanism of high-temperature destruction of the surface layers of asbestos-free brake friction materials is characterized by the accumulation of damage in the subsurface layer and the wear process is most fully explained by fatigue peeling.