DEM Simulation of Macro and Micro-Scale Behavior of Granular Materials during Loading and Unloading

Abstract

The present paper aims at comparing the simulated stress-strain behavior of granular materials quantitatively with the experiment and exploring the evolution of the micro-scale behaviors during loading and unloading using the discrete element method (DEM). A numerical sample consisting of 9826 randomly generated spheres similar to the experiment was prepared. The numerically prepared isotropic sample was subjected to loading and unloading under strain controlled condition. It is noticed that the simulated stress-strain behavior agrees well with the experimental stress-strain behavior during loading and unloading. The evolution of micro-scale parameters is studied by varying the maximum applied strain. The evolution pattern of coordination number and slip coordination number depends on the maximum applied strain during loading and unloading. Slip coordination number evolves differently during loading from coordination number, but it evolves in a similar manner during unloading. The ratio of strong contacts to all contacts increases abruptly on reversal of loading, which is opposite to what is observed for coordination number and slip coordination number. The deviatoric fabric considering strong contacts mimics the deviatoric stress regardless of the values of maximum applied strain during loading and unloading. Fabric ratio can be linearly correlated to the stress ratio during loading and unloading regardless of the values of maximum applied strain when the contact normal vectors only at strong contacts are considered.