Jamming of 3D prolate granular materials
Abstract
We have found that the ability of long thin rods to jam into a solid-like state in response to a local
perturbation depends upon both the particle aspect ratio and the container size. The dynamic phase
diagram in this parameter space reveals a broad transition region separating granular stick-slip and
solid-like behavior. In this transition region the pile displays both solid and stick-slip behavior. We
measure the force on a small object pulled through the pile, and find the fluctuation spectra to have
power law tails with an exponent characteristic of the region. The exponent varies from = −2
in the stick-slip region to = −1 in the solid region. These values reflect the different origins —
granular rearrangements vs. dry friction — of the fluctuations. Finally, the packing fraction shows
only a slight dependence on container size, but depends on aspect ratio in a manner predicted by a
mean field theory and implies an aspect-ratio independent contact number of hci = 5.25 ± 0.03.