Angle of repose and angle of marginal stability: molecular dynamics of granular particles

AbstracL We present an implemenlalion of realistic static friction in molecular dynamics (MD) simulations of granular particles. In our model, to break contact between two particles, one has to apply a Bnile amount of force, determined by the Coulomb criterion. Using a Wo.dimmsional model, we show that piles generated by avalanches have a @e angle of repose 8, (finite slopes). Furthermore, these piles are stable under tilting by an angle smaller lhan a non-zero tilting angle h, showing that 8 R is different from the angle of marginal stability Oms. which is the maximum angle of stable piles. These measured angles are compared to a theorelical approximation. We also measure 8Ms by continuously adding particles on the top of a stable pile.