Friction and Vibration of Brake Friction Materials Reinforced with Chopped Glass Fibers

Friction, wear, and friction-induced vibration of brake friction material reinforced with chopped glass fibers were investigated using a Krauss-type tribometer and a one-fifth-scale brake dynamometer. The friction tests were carried out using friction material specimens based on an experimental formulation slid against gray iron disks. The glass fibers increased the surface hardness and contact stiffness of the friction material but decreased compressibility, friction level, and fade resistance. Wear resistance slightly improved with glass fibers at moderate temperatures, whereas it decreased at temperatures beyond the glass transition temperature of the binder resin. Friction oscillation during sliding changed its mode from stick–slip to harmonic oscillation as the velocity increases and was followed by smooth sliding at higher velocities beyond a critical value. Friction-induced vibrations occurred over a wider velocity range when the friction material contained chopped glass fibers, indicating higher propensity of brake-induced noise. Surface analysis after friction tests revealed that contact stiffness of the friction material surface increased due to promoted contact plateaus fostered by the chopped glass fiber bundles.