Nonlocal orientational distribution of contact forces in granular samples containing elongated particles

In this paper we introduce the branch tensor as an internal variable able to account for the structural anisotropy of a granular sample. The distribution of averaged contact forces is assumed to depend not only on the macroscopic stress and the local orientation, but also on the value of the fabric tensor. In contrast to previous work, including the fabric tensor has the crucial advantage that accounts for all relative positions between interacting particles, through the average value of the branch tensor. Based on a classical representation result, we propose an identification procedure that uses information obtained from both isotropic and anisotropic configurations.