Modeling of Bifurcation and Post-Bifurcation Response of Granular Materials: Insights From Discrete Element Modeling

Abstract

A softening elastoplasticity model for sand has been constructed and its mathematical derivations are described in this paper. The proposed model is based on the concept of a non-associated elastoplastic material description. The model first was coupled with a strain hardening plasticity model, as developed by Gutierrez 2010 [1], for granular soil before the bifurcation point. The softening elastoplasticity model then develops a tangential stiffness matrix which plays a crucial role in describing the softening behavior. The smeared shear band model proposed by Pietruszczak and Mroz 1981 [2] is employed in this model to incorporate a characteristic length dimension (i.e. shear band thickness). The objectivity of the constitutive model has been established from the form-invariance principal. The plastic module in terms of stress and strain-increments is provided for simulating stress and strain-controlled biaxial tests. The results of a study of RF-Huston sand and of DEM simulation served as a basis for evaluating the capabilities of the model. The results indicate that, the softening elastoplasticity model accurately depicts the trends observed in the experimental data of RF-Hostun and the DEM sand simulation.