Dense granular flows: Structure and microscopic origins of internal friction

Abstract

By means of three-dimensional Contact Dynamics simulations, we investigate the microstructural properties of sheared granular packings by varying systematically the inertial number I from the quasi-static to the collisional regime. A detailed analysis of the connectivity of the particles reveals that the transition between the regimes is correlated to profound changes of the nature of the contact network. In particular, we show that the increase of internal friction angle with inertial number is mainly a consequence of contact anisotropy. As the inertial number increases, the role of force chains decreases and that of friction mobilization increases as long as percolating force chains are present in the system. A detailed analysis of the spatial correlations of floating particles, i.e., particles without bearing contacts, reveals the occurrence of “fluidized” volumes in the dense flow regime, which increase in size and coalesce at the approach of the collisional regime.