Abstract
Powders or cohesive granular materials are widely handled in industries. However, our understanding of the rheology of these materials is limited. Here, we provide a comprehensive analysis of the rheology of a cohesive granular medium, sheared in a normal-stress-imposed plane shear cell over a wide range of shear rate, employing numerical simulations. At high imposed shear rates, the flow is homogeneous, and the rheology is well described by the existing scaling laws, involving the inertial number and the effective cohesion number [S. Mandalet al., Insights into the Rheology of Cohesive Granular Media, Proc. Natl. Acad. Sci. U.S.A. 117, 8366 (2020)]. However, at low imposed shear rates, the flow is inhomogeneous, exhibiting the coexistence of flowing and nonflowing regions in the material, popularly known as shear banding. We thoroughly analyze the crucial features of this shear-banded flow regime and discuss striking similarities between the shear banding for granular media and other complex fluids. We reveal that the occurrence of shear banding is related to the existence of a nonmonotonic intrinsic rheological curve and that increasing adhesion increases the nonmonotonicity and the tendency toward shear localization. A simple theoretical model based on a nonlocal rheological model coupled with a nonmonotonic flow curve is proposed and is shown to successfully reproduce all the key features of the shear banding observed in the numerical simulations. The results have important implications for the handling of powders in industries.
Highlights
Many industrial processes handle powders or cohesive granular media and are confronted with flow and jamming problems in production lines
In our previous study [13] involving the flow down a rough inclined plane, we have shown that this description of the rheology of cohesive granular media is incomplete
We have numerically investigated the rheology of a model cohesive, frictional granular medium, in which a short-range interparticle adhesive force is active when two particles overlap
Summary
Many industrial processes handle powders or cohesive granular media and are confronted with flow and jamming problems in production lines. Some studies [4,43,44] observed static regions in cohesionless or cohesive granular materials flowing in configurations like wide-gap cylindrical or split bottom Couette shear cells and reported this phenomenon as SB. This phenomenon is nothing but a usual solid-liquid coexistence [15], caused by the presence of heterogeneous shear stress profiles and a yield criterion. The model parameters used in (b) (a) the simulations are normal spring constant kn=ðσezxztdÞ 1⁄4 2 × 105, tangential springpcffioffiffiffinffiffisffiffitffiaffiffint kt 1⁄4 2=7kn, and quality factor Q 1⁄4 0.94 (Q 1⁄4 kn=m=γn is a function of the restitution coefficient in the cohesionless case [13]; the higher the Q, the lesser the inelastic dissipation), sliding friction coefficient μp 1⁄4 0.5, and various adhesion Nc=ðσezxztd2Þ from 0(cohesionless) to 17.1
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