Friction and Hertzian contact in granular glass

We study the jamming process arising in granular systems subjected to decreasing external vibration, which has features similar to the cooling of glass-forming liquids. We modify the friction between grains and observe that jamming occurs 'more easily' for grains with higher surface roughness. To understand the observed behavior we present a detailed analysis of the elastic and tribological phenomena at the length scale of the grains in contact and provide a qualitative model, where the Hertzian nonlinear elastic contact between grains plays a relevant role.