Effect of normal stress and shear velocity on dynamic friction between a rubber block and hard surface

Rubber friction at high velocity is important for a variety of applications, ranging from the design of tires to brakes. The present study investigates experimentally the dynamic friction stress between a rubber block and a smooth glass surface at varying normal stress and shear velocity. It is observed that dynamic stress increases with sliding velocity until it reaches a maximum value. It is then that steady friction decreases as the shear velocity continues to increase. The most significant result is that maximum dynamic stress and corresponding sliding velocity increase with normal stress. Coulomb’s law of friction was also used to determine both adhesive friction and the coefficient of friction as a function of shear velocity. Furthermore, the dynamic friction data were optimized using the friction model proposed in the literature for developing scaling laws related to rubber friction. The results are discussed in light of the surface morphology of the rubber surfaces obtained from scanning electron microscopy (SEM), chemical composition using energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), as well as surface roughness, before and after the friction test. This study emphasized that a tire should also be designed for peak friction at higher velocities against skidding or sliding of the vehicle.