T Matthey and J P Hansen

Friction in a dense two-dimensional granular material is studied by molecular dynamics simulations. Initially the particles are ordered in a triangular lattice where the top layer feels a constant vertical pressure and horizontal velocity field. The dynamics of the material at low velocities is found to be characterized by avalanche-type motion during short time intervals followed by long stationary periods of internal stress buildup. At low external pressures, the time-averaged shear stress is found to be nearly constant for low values of the normal pressure and proportional to the load for higher pressures.