  Monodisperse packings of dry, air-fluidized granular media typically exist
between volume fractions from $\Phi$= 0.585 to 0.64. We demonstrate that the
dynamics of granular drag are sensitive to volume fraction $\Phi$ and their
exists a transition in the drag force and material deformation from smooth to
oscillatory at a critical volume fraction $\Phi_{c}=0.605$. By dragging a
submerged steel plate (3.81 cm width, 6.98 cm depth) through $300 \mu m$ glass
beads prepared at volume fractions between 0.585 to 0.635 we find that below
$\Phi_{c}$ the media deformation is smooth and non-localized while above
$\Phi_{c}$ media fails along distinct shear bands. At high $\Phi$ the
generation of these shear bands is periodic resulting in the ripples on the
surface. Work funded by The Burroughs Wellcome Fund and the Army Research Lab
MAST CTA
