Nontrivial plasticity of a shear-jammed granular system*

We report shear experiments on a layer of photo-elastic disks in which shear is applied through basal friction with 21 independently controllable concentric rings below the granular layer in a Couette geometry. The rings rotate at different rates to make the local shear strain uniform inside the system. By applying this uniform shear in small steps, we create an ensemble of static shear jammed (SJ) configurations with different packing fractions (\phi) below the isotropic jamming packing fraction (\phi_J). We find that the average size and radial profile of plastic deformations between steps vary with packing fraction. A transition at \phi_c<\phi_J is observed. When \phi>\phi_c, the plastic deformation is localized to a narrow shear band close to the inner boundary of the shear cell. When \phi<\phi_c, the plastic deformation is spread through the entire system. We report power-law dependence of deformation amplitude on packing fraction close to \phi_c. We also find similar behavior for non-uniform applied shears.