Numerical and Experimental Investigation of Yielding for Cohesive Dry Powder

We study the effect of particle cohesion on the steady state shear strength of a granular material. For cohesive powders, the steady state shear loci (termination loci) from DEM simulations are nonlinear with a peculiar pressure dependence due to the non-linear increase of contact adhesion with pressure in the contact model. Physical experiments are carried out on fine limestone powder in the direct shear box to validate the interesting non-linearity in the material behavior, as detected by the simulations and to provide a basis for calibration of DEM. In order to enhance the reproducibility, the standard test procedure from Jenike shear tester is ameliorated for the direct shear tester. Finally, the difference between the yield (transition from static to flow) and the steady state shear stress (required to maintain shear motion) will be addressed.