Behavior of Sheared Granular Materials at Micro-Scale during the Cyclic Loading

Abstract

The aim of this paper is to explore the evolution of different micro-scale quantities during the cyclic loading using the discrete element method (DEM) for a granulate system such as sand. The numerical samples comprising of 9826 spheres were generated and consolidated isotropically using the periodic boundaries. These numerical samples were subjected to the cyclic loading for different maximum applied strains. The simulated stress-strain behavior was validated with the experiment and found an excellent agreement between them during loading and unloading. The evolutions of different micro-scale quantities were investigated in detail considering the variation of the maximum applied strain and the density of sample. It is noted that the evolution of the coordination number and the slip coordination number is a function of the maximum applied strain and the density of sample during the cyclic loading. The change of the slip coordination number is larger at the end of unloading than that at end of loading during the cyclic loading regardless of the values of the maximum applied strain and the density of sample. The ratio of strong contacts to all the contacts increases abruptly when the load is reversed, which is opposite to what is observed for the coordination number and the slip coordination number. The deviatoric fabric computed by the fabric tensor considering the strong contacts mimics the deviatoric stress irrespective of the values of the maximum applied strain and the density of sample during the cyclic loading. Moreover, a linear correlation between the macro and micro quantities exists regardless of the variation of the maximum applied strains or the variation of the density of the sample during the cyclic loading. The slopes of the lines of these correlations are almost same.

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