Colin Thornton

An examination of shear bands by discrete particle simulations

Abstract: Strain localisation and shear band formation is frequently observed during the handling and flow of dense phase particulate materials. Shear bands also develop adjacent to wall boundaries, e.g. during discharge from silos. However, a complete understanding of how shear bands form and what happens inside shear bands is still lacking. In order to addresses this problem, simulations have been carried out to examine the detailed physics/micromechanical processes that occur at the grain scale associated with the initiation and development of shear bands.

Results from simulations of pure shear tests (in both a periodic cell and with a wall-bounded specimen) and simple shear tests are reported. It is demonstrated that strain localisation is the result of buckling of the strong force chains and this creates strong discontinuities in the fluctuating velocity field. This leads to the development of shear bands and it is shown that the inclination of such bands depend on the boundary conditions. Attention is also given to particle rotations and non-coaxiality of stress and strain-rate directions. From examining the results of simple shear simulations the complete stress tensor and dilation inside a shear band is calculated and the corresponding flow rule is identified.