Local fluctuations and spatial correlations in granular flows under constant-volume quasistatic shear

Abstract

We investigate the local fluctuations in dense granular media subjected to athermal, quasistatic shearing, based on three-dimensional discrete element method simulations. By shearing granular assemblies of different polydispersities under constant-volume constraint, we quantify the characteristics of local structures (in terms of local volume and local anisotropy) and local deformation (using local shear strain and nonaffine displacement). The distribution of the local volume in a granular medium is found unchanged during the entire shearing process, which indicates a constant temperaturelike compactivity for the material. The compactivity is not, however, equilibrated among different particle groups in a polydisperse assembly. The local structures of a disordered granular assembly are inherently anisotropic. The fluctuations in local anisotropy can be well captured by a gamma or mixed-gamma distribution function, which is also unchanged during the shear. The local anisotropic orientation evolves towards the coaxial direction of the stress anisotropy with shear. The deformation characteristics of a jammed granular medium have their origins in the structural amorphousness. The local shear strain field depicts clear shear transformation zones which act as plasticity carriers. The spatial correlation of the local shear strains exhibits a fourfold pattern which is stronger in the stress deviatoric planes than in the stress isotropic plane. The fluctuations of nonaffine displacement suggest an isotropic granular temperature and an isotropic spatial correlation independent of the stress state. Both the local strain and the nonaffine displacement exhibit a power-law decayed distribution with a long-range correlation. We further modify the shear-transformation-zone theory to predict the pressure-dependent constitutive behavior of a sheared granular material and compare its prediction with our simulation data.

Microscopic Origin of Nonlocal Rheology in Dense Granular Materials

“…Note also that the two modes of elementary rearrangements observed in our simulations (Fig. 2) are strongly reminiscent of the concepts of shear-transformation zones [29][30][31][32] or plastic events [14,33]. Our results provide further direct evidence of these mechanisms, as well as a quantitative link between these micromechanical processes and the macroscopic behavior of the material.…”

“…The robustness of the proposed constitutive law was checked in simple shear for different system sizes and geometries. Further work will be required to investigate the extension of our results to more general 3D strain fields [31].…”

Voronoi cell analysis: The shapes of particle systems

“…This approach has been used to examine local volume fluctuations [69][70][71][72] and dynamic jamming fronts. 73 The use of Voronoi cell faces to identify neighboring particles 74 and the examination of Voronoi cell anisotropy 75,76 have also proven fruitful in the study of granular media and other amorphous systems.…”

Numerical Investigation of Triaxial Shear Behaviors of Cemented Sands with Different Sampling Conditions Using Discrete Element Method

“…As shown in Table 1, the particle density was set as 2650 kg/m 3 , the same as that of Ottawa 20-30 sand. A linear contact model was assigned between the sand particles for its simplicity, following the practice in Guo and Zhao [36]. Therefore, the interparticle contact stiffness was linearized using Equation (1), which was based on the Hertz-Mindlin theory and derived by Li et al [26].…”

“…Materials 2022, 15, x FOR PEER REVIEW 3 of 14 particles for its simplicity, following the practice in Guo and Zhao [36]. Therefore, the interparticle contact stiffness was linearized using Equation (1), which was based on the Hertz-Mindlin theory and derived by Li et al [26].…”