Jamming and shear for granular materials

This paper describes a series of experiments which have explored systems of frictional disks that have been prepared near jamming and then subjected to shear strain. A key observation is that below a density (described by packing fraction, ) of about J ≃ 0.84, it is possible to prepare stress-free states, and then by applying shear, traverse states that are fragile (highly anisotropic), shear jammed, and then increasingly isotropic. The anisotropy of these states is a dominante feature in the shear jamming process, which differs from the Liu-Nagel scenario. The evolution of these states suggests that an activated process in the context of a force (or stress) ensemble characterizes the stress evolution during cyclic strain