Analytical and experimental investigation of the static friction regime for rubber-rigid ball contact

The static friction regime is of great importance for systems requiring accurate positioning. The parameters of the static friction regime in terms of static friction force and limiting displacement before gross sliding are investigated for a rubber ball/metal flat configuration. Single-asperity friction measurements carried out on a Nano-Tribometer revealed that the static friction parameters depend on various parameters such as normal load (pressure), geometry (radius of the ball) and velocity. The coefficient of static friction decreases significantly by increasing the normal load, while the preliminary displacement increases. Smaller radii of the ball determine a smaller static friction force but a greater limiting displacement. Tests that were run at higher velocities resulted in a decrease of the coefficient of static friction as well as of the limiting displacement. The experimental results show a good agreement with those calculated with the developed static friction model for a load-controlled case, in which the viscoelastic behaviour of rubber has been modelled by a mechanical model.