Jamming of Two-Dimensional Systems of Polygonal Grains

Significant progress has been made in experimental studies of the jamming transition of systems of circular grains. However, grains are rarely circular in real world granular materials. Shape adds complexity to the system-scale behavior of granular systems, which we explore in jamming experiments. We biaxially compress two-dimensional packings of photoelastic polygonal grains, allowing us to visualize internal stresses as the packing shifts to a jammed state. To systematically study the effect of grain shape, regular polygons of varying numbers of sides are used in our experiments. We then measure the contact number evolution and critical packing fraction at jamming, comparing systems of polygons to that of disks. We also explore the influence of features, such as face-face contacts, in connection with the jamming transition.