ABSTRACT
The viscous behavior of bulk solids shear flow is known since Bagnold 1954. K. Hutter and H. Hwang have shown (Hwang 1994), that the velocitydependent behavior of the general constitutive stress deviator can be derived from a rate-dependent functional, where the dynamic extension is represented by an additional term which includes the deformation tensor coupled with a viscous parameter.Thus, the equation (1) can be written in the following form by separating T˚ in a static part T˚s and a dynamic part T˚v
The velocity-dependent dynamic material tensor Gijkl is a description of a non-Newtonian fluid. A densitydependent viscous parameter µ is used, see Böhrnsen (2002). With a decrease of the density during the discharge, especially near to the orifice, a decrease of the viscosity takes place. A increase of the density causes a increase of viscosity. So, a loose sample has a low viscosity.
