The Solid to Fluid Transition of a Granular Flow in a Powder Rheometer

We study the transition from solid-like to fluid-like behavior of a granular material in a powder rheometer using sand and glass beads. The yielding stress and the volume fraction change before reaching the steady state; the free surface also changes its shape. A burping sound can be heard as the shear stress increases due to the change in the free surface and the pressure increasing. Based on the minimum stress ratio, the flow transits through the inertial region to the quasi-static region. A continuum model to determine the inertial region and quasi-static region inside the bulk is given. From the model, we specify the boundary between inertial zone and quasi-static zone. By this model, we estimate how the strain rate corresponds to the dilatant behavior locally.