Elastic granular flows of ellipsoidal particles

Granular flow rheology can be divided into two global regimes: the elastic, which is dominated by force chains, and the inertial, which is nearly free of force chains. As the propensity of a material to form force chains should be strongly influenced by particle shape, this paper is an attempt to assess the effects of shape on flow regime transitions through computer simulations of shear flow of ellipsoidal particles. On one hand, the results show that at a given concentration, ellipsoidal particles generate smaller quasistatic stress than spheres, likely a result of their ability to form denser packings. But at the same time, large aspect ratio ellipsoids more readily form force chains and demonstrate elastic behavior at smaller concentrations than spheres. This is shown to be due to a tradeoff between a shear-induced particle alignment that tends to minimize the interference of the particles and the shear flow, and the particle surface friction, which works to rotate the particles into the flow. (c) 2011 American Institute of Physics. [doi:10.1063/1.3546037]