Left-right asymmetry in granular contact force networks
Abstract Book of the XXIII IUPAP International Conference on Statistical Physics, Genova, Italy, (9-13 July 2007)Abstract
Granular media as well as other amorphous materials show a peculiar mechanical behavior including the possibility of exhibiting jammed configurations that can eventually yield under shear stress. Several recent experimental and theoretical investigations address this question and relate jamming and yielding to structural changes in contact force networks. Here we study the scalar arching model (SAM) proposed for a jammed pile of grains under gravity, where force chains are formed through simple rules for weight transmission and slip between neighbor particles in a tilted square lattice. Borrowing concepts and techniques from percolation theory, we investigate the topological properties of the contact force network in this model and we find clear evidence of a second order phase transition. The transition is related to the break of symmetry in the number of particles slipping right or left inside the pile. Furthermore, this transition is also accompanied by a sharp peak in the width of the distribution characterizing the asymmetry in the number of force chains directed either to the right or to the left of the granular pile. We finally discuss the scaling properties of several quantities of interest and establish connections between the topology of the contact force network and the weight at the bottom of the pile.