Stresses in smooth flows of dense granular media

Abstract

<p>The form of the stress tensor is investigated in smooth, dense granular flows which<br>are generated in split-bottom shear geometries. We find that, within a fluctuation fluidized spatial<br>region, the form of the stress tensor is directly dictated by the flow field: The stress and strain-rate<br>tensors are co-linear. The effective friction, defined as the ratio between shear and normal stresses<br>acting on a shearing plane, is found not to be constant but to vary throughout the flowing zone.<br>This variation cannot be explained by inertial effects, but appears to be set by the local geometry<br>of the flow field. This is in agreement with a recent prediction, but in contrast with most models<br>for slow grain flows, and points to there being a subtle mechanism that selects the flow profiles.<br></p>