Mesoscale Investigation of Fine Grain Contribution to Contact Stress in Granular Materials

Abstract

Fine grains play an important role in mechanical properties of granular materials as they control how plastic strain may develop, which has a noticeable impact on mechanical stability. In this work, we use numerical simulations based on a discrete element method (DEM) to analyze the stress contribution of fine grains to the total stress. Different from usual DEM simulations, the analysis is conducted directly at the mesoscopic scale by considering an idealized grain assembly. The results show how fine grains get progressively jammed and increasingly participate in stress transmission. Fine contribution to contact stress is shown to be nonisotropic. The principal anisotropy direction coincides with the principal direction of contraction and the anisotropy ratio (i.e., the ratio between the largest and the smallest eigenvalues of the fine stress) is shown to be limited (σmax/σmin≃2). By performing strain controlled directional analyses, an analytical model is proposed to account for the stress contribution of fine grains along various loading paths. Its simple form will help to enrich advanced micromechanically-based constitutive formulations and better account for the constitutive behavior of widely graded granular materials.