Shearing of frictional sphere packings

Abstract

Submitted to the themed issue on granular and jammed materials. We measure shear stress in packings of glass spheres by pulling a thin metal plate vertically through a bed of volume fractions φ, which is set (before the plate is pulled) to be in the range 0.575 to 0.628. The yield stress increases exponentially with φ with a change in slope at φ ≈ 0.594. An analysis of the shear stress fluctuations provides a measure of the shear modulus divided by shear zone width; this measure also exhibits distinct regimes above and below φ ≈ 0.594. The yield stress and the rescaled shear modulus are velocity independent over 4 decades. 1