Shear jamming and flow with novel shear profiles*

Bi et al. have shown that, if sheared, a granular material can jam
even if its packing fraction (φ) is lower than the critical
isotropic jamming point φ_J. They have introduced a new critical
packing fraction value φ_S such that for φ_S<φ<φ_J the
system jams if sheared. Nevertheless, the nature of φ_S remains
poorly understood because of the experimental complexity to access
high strain without shear banding. We present a novel experimental
setup that overcomes this difficulty. The setup is a 2D periodic shear
apparatus made of 21 independent, aligned and mirrored glass
rings. Each ring moves independently, which permits us to impose any
desired shear profile. The circular geometry allows access to any
strain value. The forces between grains are measured using reflective
photoelasticity. We capture shear jammed states based on the isostatic
condition, and measure the value of φ_S for different kinds of
shear flows. In addition, by studying the steady state flow under
different packing fractions and different kinds of shear driving, we
investigate how the appearance of the shear jammed states changes the
flow from the driving profile.