Non-monotonic constitutive curves and shear banding in dry and wet granular flows

TL;DR

This study uses particle simulations to explore how dry and wet granular materials respond to shear, revealing non-monotonic behaviors and shear banding phenomena under different conditions, with implications for understanding granular flow dynamics.

Contribution

It provides a comprehensive simulation-based analysis of shear rheology in granular matter, highlighting the distinct effects of fixed pressure and fixed volume protocols on constitutive curves and shear banding.

Findings

Non-monotonic constitutive curves are shear thinning at fixed pressure.

Non-monotonic constitutive curves are shear thickening at fixed volume.

Presence of volume fraction signature under fixed pressure predicts non-monotonicity.

Abstract

We use particle simulations to map comprehensively the shear rheology of dry and wet granular matter comprising particles of finite stiffness, in both fixed pressure and fixed volume protocols. At fixed pressure we find non-monotonic constitutive curves that are shear thinning, whereas at fixed volume we find non-monotonic constitutive curves that are shear thickening. We show that the presence of one non-monotonicity does not imply the other. Instead, there exists a signature in the volume fraction measured under fixed pressure that, when present, ensures non-monotonic constitutive curves at fixed volume. In the context of dry granular flow we show that gradient and vorticity bands arise under fixed pressure and volume respectively, as implied by the constitutive curves. For wet systems our results are consistent with a recent experimental observation of shear thinning at fixed pressure. We furthermore predict discontinuous shear thickening in the absence of critical load friction.