A Micromechanics-Based Modeling the Simple Shear Behaviors of Granular Materials

Abstract

For granular materials, their principal directions of stress and inelastic strain rate may become non-coaxial (non-coincident) when subjected to non-proportional loading, e.g., to the simple shear deformation. Non-coaxiality, as an important aspect of anisotropy of granular materials, may also produce significant effects on other plastic behaviors, such as dilatancy of materials. A micromechanics-based framework is developed to model the proportional behaviors. The back stress defined in the classical plasticity is interpreted as contribution of fabric anisotropy and its evolution can be quantified with the deviation of principal direction of stress rate from that of stress. A standard isotropic-hardening model has been modified to be a mixed (isotropic/kinematic) hardening one. As an assessment for validity of the proposed non-coaxial model, this study uses this model to examine the non-coaxial behaviors of the simple shear deformation. It has been found that fabric anisotropy plays significant roles on non-coaxiality as well as dilatancy of granular materials. The degree of non-coaxiality strongly depends on fabric anisotropy under simple shear. Due to fabric anisotropy, both dilatancy also becomes less. All predictions are of agreement with the measured from a series of simple shear tests.