Experimental study of rolling-sliding transition and friction coefficients of particles

The rolling-sliding friction is important to the dynamics of granular materials on micro and macro scales. In the granular flow dynamics, the sliding friction has been investigated well, but the mechanism of rolling friction is paid less attention before. The rolling friction is influenced by many factors, and there is no unified theory to describe the rolling friction. The experiment for friction coefficients under the influences of normal loads, roughness of contact surfaces, particle shapes has been carried out; and the transition mechanism of the rolling-sliding friction is studied. It is shown that the particle performs sliding when the particle shape is quite irregular and the contact surface is too smooth; otherwise, the particle performs rolling. Moreover, the sliding friction coefficient and rolling friction coefficient are measured under various particle shapes and surface roughnesses.