Force Transmission in Cohesive Granular Media

F. Radjai, V. Topin, V. Richefeu, C. Voivret, J.-Y. Delenne, E. Azéma et S. El Youssouf (2010), , pp. 240-260, in Mathematical Modeling and Physical Instances of granular Flows (AIP, Melville), édité par J. D. Goddard, J. T. Jenkins et P. Giovine, ISBN 978-0-7354-0772-5.

We use numerical simulations to investigate force and stress transmission in cohesive granular media covering a wide class of materials encountered in nature and industrial processing. We consider both liquid bridges and solid bridges between particles. The liquid bridges will be treated by implementing a capillary force law within a debonding distance between particles and simulated by the Discrete Element Method (DEM). The solid bridges or more generally the binding matrix is treated by means of the Lattice Element Method (LEM) based on a lattice-type discretization of the particles and matrix. Our data indicate that the exponential fall-off of strong compressive forces is a generic feature of both cohesive and noncohesive granular media. Interestingly, the tensile forces exhibit a similar decreasing exponential distribution, suggesting that this form basically reflects granular disorder. This is consistent with the finding that not only the contact forces but also the stress components in the bulk of the particles and matrix, accessible from LEM simulations, show a exponential fall-off. We also find that the distribution of weak compressive forces is sensitive to packing anisotropy, particle shape and particle size distribution. In the case of wet packings, we analyze the self-equilibrated forces induced by liquid bonds and show that the positive and negative particle pressures form a bi-percolating structure.