Dissipation in granular materials
For two simple setups it is discussed, how dissipative grain-grain interactions give rise to unexpected properties on large scales. In the first example, a spherical particle rolling along a rough surface experiences an effective viscous friction on large time scales. It is due to temporal correlations among collisions with incomplete normal restitution. The second example is a sheared granular packing. There, spatial correlations among nonsliding and sliding contacts with Coulomb friction suggest that the deviatoric stress, although responsible for the dissipation, is localized on bonds that are nonsliding and hence nondissipative. 1 Introduction Granular media (like sand) are classical many particle systems with dissipative interactions (for a recent review see [Jager et. al. 1996]). In the absence of external driving the kinetic energy of the grains decreases in each collision due to the irreversible transfer of energy into the internal degrees of freedom of the grains.
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