Shape effect on dynamical properties of granular materials*

We have investigated the effect of shape on dynamical and rheological properties of granular materials through Couette shear and cyclic isotropic compression experiments. We track the evolution of our systems by measuring the mean velocity local density, orientational order, and local stress. This set of experiments which were performed on systems of bidisperse disks and identical ellipses at exactly same conditions, reveals striking differences between the dynamics of disks and ellipses. In particular we observe a very slow relaxation in various dynamical quantities for systems of ellipses. We also demonstrate that the strain history of the system (i.e. shear vs. compression) highly impacts the aging process.