| The study of a dense granular system concerns both the dynamic (i.e. force configurations) and kinematic (i.e. particle displacements) behaviors. To explore these two issues, a shearing experiment was performed using a simple shearing apparatus on a dense 2D granular system made of frictional photo-elastic particles. The platform base and boundaries of this apparatus are carefully designed to eliminate the inhomogeneity caused by the boundaries during shearing. Upon increasing shear strain (ε) by small quasi-static steps, photos were taken with and without a polariscope to capture the force configuration changes and particle displacements respectively. Image analysis showed that systems sheared from isotropic unjammed states jam upon shear, while systems sheared from isotropic jammed states stay jammed. Additionally, after the system jams, it enters a strain-hardening regime where the system pressure (P), shear stress (τ), and mean contact number (Z) grow upon increasing ε until τ reaches its peak value. Then the system enters a strain-softening regime, where both P and Z become saturated, and τ begins to decrease. In the meantime, particle-tracking analysis found no obvious shear band during shearing. This suggests that the formation of a shear band might be caused by the inhomogeneity of boundary conditions. |
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