DISSIPATION IN GRANULAR-MATERIALS

For two simple set-ups, we discuss how dissipative grain-grain interac tions give rise to unexpected properties on large scales. In the first example, a spherical particle rolling along a rough surface experienc es an effective viscous friction on large time scales. It is due to te mporal correlations among collisions with incomplete normal restitutio n. The second example is a sheared granular packing. There, spatial co rrelations among non-sliding and sliding contacts with Coulomb frictio n suggest that the deviatoric stress, although responsible for the dis sipation, is localized on bonds that are non-sliding and hence nondiss ipative.