Macroscopic material properties from quasi-static, microscopic   simulations of a two-dimensional shear-cell
  One of the essential questions in the area of granular matter is, how to obtain macroscopic tensorial quantities like stress and strain from ``microscopic'' quantities like the contact forces in a granular assembly. Different averaging strategies are introduced, tested, and used to obtain volume fractions, coordination numbers, and fabric properties. We derive anew the non-trivial relation for the stress tensor that allows a straightforward calculation of the mean stress from discrete element simulations and comment on the applicability. Furthermore, we derive the ``elastic'' (reversible) mean displacement gradient, based on a best-fit hypothesis. Finally, different combinations of the tensorial quantities are used to compute some material properties.   The bulk modulus, i.e. the stiffness of the granulate, is a linear function of the trace of the fabric tensor which itself is proportional to the density and the coordination number. The fabric, the stress and the strain tensors are {\em not} co-linear so that a more refined analysis than a classical elasticity theory is required. 
Marc L\"atzel (1), Stefan Luding (1), and Hans J. Herrmann (2)   ((1)ICA1, Stuttgart, Germany (2) PMMH ESPCI, Paris, France)