Dislocation, Vortex and Couple Stress In The Formation of Shear Bands Under Trap-Door Problems

Abstract

A study is made on the characteristics of the shear banding formation of granular materials under a trap-door problem based on the framework of both granular and continuum approaches. An assembly of dry sand is initially modeled by using the DEM simulation considering the rolling friction, instead of the physical experiments, and an ensemble of realizations for the trap-door problem is generated to address the behavior of grain particles. Dislocation lines are newly defined to observe what happens to the movement of grains during the deformation process. It is revealed from careful observations that within a very short period of time, the distribution of dislocation lines is concentrated in a zone, which may be called a ‘sliding zone’ for both active and passive modes. In the vicinity of this zone, some vortices whose diameter is 10 to 20 times the grain particle appear and disappear during the shear banding. An analysis based on the micropolar theory incorporated into the viscoplastic model is also performed to explain the deformational behavior of grain assemblies from another point of view. The numerical results are then discussed.