Shear-induced pressure localization in granular materials of nonspherical particles.

When a granular material composed of elongated grains is sheared in a split-bottom shear cell, a pressure difference develops within the material. This pressure difference depends on the interparticle friction, which affects shear localization and particle alignment. At high friction, alignment is confined to a narrow shear band, leading to localized increases in packing density and pressure. At low friction, the particles align over a wider region, leading to a nearly uniform packing density and pressure throughout the material. In contrast, assemblies of spherical particles exhibit a uniform packing density and pressure, independent of the friction coefficient. Elongated grains behave similarly to the Weissenberg effect in non-Newtonian fluids, where the normal stress differences are associated with pressure variations, in contrast to the nearly uniform pressure field observed for spherical particles.