Source of low friction in fragmenting granular shear flow

We report laboratory experiments and numerical simulations thereof which show similar reductions in frictional resistance when fragmentation occurs in dry comminut- ing granular shear flow, in the absence of any mechanism for reducing friction except that of grain comminution. These results, together with the ubiquitous occurrence of comminution in association with low-friction geological phenomena, suggest that fragmentation is both a sufficient and a necessary condition for low friction in granular shear. In the numerical simulations a low damping factor was required to generate realistic results. This indicates that most of the fracture surface energy utilised in comminution is recycled to the system as free energy, in agreement with experimental data.