Discrete element modeling of first shear strain gradient effects on mechanical behaviors in granular materials

Abstract

The effects of strain gradient on the mechanical behavior of granular materials have attracted attention from many researchers. In this paper, the effects of the first shear strain gradient in granular materials are focused on. Granular assemblies with various particle radii and porosities are built through a two-dimensional discrete element method (2D-DEM) simulations. The results indicate that the macro shear stress is insensitive to the first shear strain gradient at low strains, but is indeed affected at high strains; the third order stress conjugated with the first shear strain gradient is sensitive to the first shear strain gradient in all deformation cases; the third order work done by the third order stress and the ratio of it versus the total work are affected by the first shear strain gradient; the evolutions of the invariants of the third order stresses present severe change of the local relative vertical displacement of particles, which lead to localization occurrence. Based on DEM simulations, it is found that only the effect consideration of the first shear strain gradient on the macro shear stress is not sufficient, whereas the effect on work should also be taken into account and the third order work as a part of strain energy cannot be ignored, which is falsely classified as a portion of the accumulated energy dissipated by frictional sliding.