Multi-Slip Formulation for Modeling Localization in Granular Materials

Abstract

This paper presents a higher order gradient multi-slip formulation to model the effect of inhomogeneous deformation in granular materials. In most current formulations, the flow stress in the plastic constitutive equation is modified with a higher order gradient term of the effective plastic strain as a means of modeling the effect of inhomogeneous deformation. Granular material consists of discrete particles and associated voids. Therefore, a higher order gradient constitutive model must explicitly account for its gradients in terms of the heterogeneous granular microstructure. The effect microstructure is accounted for by considering the mobilized friction coefficient in the model to be a function of a higher gradient porosity distribution. The double-slip version of the model has been implemented in a standard finite element code and used to simulate biaxial shear tests on dry sand. The effect of the two new formulations and the current formulations using effective plastic strain on the prediction of strain localization are examined.