  Two dimensional simulations of non-cohesive granular matter in a biaxial
shear tester are discussed. The effect of particle elasticity on the mechanical
behavior is investigated using two complementary distinct element methods
(DEM): Soft particle molecular dynamics simulations (Particle Flow Code, PFC)
for elastic particles and contact dynamics simulations (CD) for the limit of
perfectly rigid particles. As soon as the system dilates to form shear bands,
it relaxes the elastic strains so that one finds the same stresses for rigid
respectively elastic particles in steady state ow. The principal stresses in
steady state ow are determined. They are proportional to each other, giving
rise to an effective macroscopic friction coefficient which is about 10 %
smaller than the microscopic friction coefficient between the grains.
