Aging and self-organization of shear bands in granular materials

We introduce a simple lattice model for the formation and evolution of shee r bands in granular media. We study this model by numerical simulations and find that due to the localization of the shear band and the consequent inh omogeneous aging of the material, the average density shows very unusual sy stem-size-dependent features. We find qualitatively similar features on stu dying the same model on a hierarchical lattice for which we are able to der ive several analytical results. (C) 1999 Elsevier Science B.V. All rights r eserved.