Résumé
A packing of rigid frictional particles can be found in an infinite number of different metastable fabricstates with different levels of connectivity, anisotropy, packing fraction, local order, and long-range order. Itseems therefore extraordinary that such a multi-state material is able to exhibit well-defined reproduciblebehavior under external loading. We discuss this point in the light of particle dynamics simulations, whichprovide access to the details of microstructure. We show that the fabric states involve a subtle interplaybetween force balance and steric exclusions. We demonstrate the crucial role of both disorder and stericexclusions in driving the granular microstructure towards steady fabric states that underlie the plasticbehavior of granular materials. We also discuss the effects of friction, particle shape, and boundaryconditions in this respect.