Finite Element Simulations on Failure Behaviors of Granular Materials with Microstructures Using a Micromechanics-Based Cosserat Elastoplastic Model

This paper presents a micromechanics-based Cosserat continuum model for microstructured granular materials. By utilizing this model, the macroscopic constitutive parameters of granular materials with different microstructures are expressed as sums of microstructural information. The microstructures under consideration can be classified into three categories: a medium-dense microstructure, a dense microstructure consisting of one-sized particles, and a dense microstructure consisting of two-sized particles. Subsequently, the Cosserat elastoplastic model, along with its finite element formulation, is derived using the extended Drucker-Prager yield criteria. To investigate failure behaviors, numerical simulations of granular materials with different microstructures are conducted using the ABAQUS User Element (UEL) interface. It demonstrates the capacity of the proposed model to simulate the phenomena of strain-softening and strain localization. The study investigates the influence of microscopic parameters, including contact stiffness parameters and characteristic length, on the failure behaviors of granular materials with microstructures. Additionally, the study examines the mesh independence of the presented model and establishes its relationship with the characteristic length. A comparison is made between finite element simulations and discrete element simulations for a medium-dense microstructure, revealing a good agreement in results during the elastic stage. Some macroscopic parameters describing plasticity are shown to be partially related to microscopic factors such as confining pressure and size of the representative volume element.