# Role of gravity or confining pressure and contact stiffness in granular rheology

Abhinendra Singh, Vanessa Magnanimo, Kuniyasu Saitoh, Stefan Luding

30 Citations (Scopus)

### Abstract

The steady-state shear rheology of granular materials is investigated in slow quasistatic and inertial flows. The effect of gravity (thus the local pressure) and the often-neglected contact stiffness are the focus of this study. A series of particle simulations are performed on a weakly frictional granular assembly in a split-bottom geometry considering various magnitudes of gravity and contact stiffnesses. While traditionally the inertial number, i.e., the ratio of stress to strain-rate time scales, is used to describe the flow rheology, we report that a second dimensionless number, the ratio of softness and stress time scales, must also be included to characterize the bulk flow behavior. For slow, quasistatic flows, the density increases while the effective (macroscopic) friction decreases with increase in either particle softness or local pressure. This trend is added to the $\mu (I)$ rheology and can be traced back to the anisotropy in the contact network, displaying a linear correlation between the effective friction coefficient and deviatoric fabric in the steady state. When the external rotation rate is increased towards the inertial regime, for a given gravity field and contact stiffness, the effective friction increases faster than linearly with the deviatoric fabric.
Original language English 043028 20 New journal of physics 17 https://doi.org/10.1088/1367-2630/17/4/043028 Published - 2015

### Fingerprint

rheology
confining
stiffness
gravitation
softness
friction
dimensionless numbers
granular materials
coefficient of friction
strain rate
assembly
shear
trends
anisotropy
geometry
simulation

• METIS-312765
• IR-95650

### Cite this

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title = "Role of gravity or confining pressure and contact stiffness in granular rheology",
abstract = "The steady-state shear rheology of granular materials is investigated in slow quasistatic and inertial flows. The effect of gravity (thus the local pressure) and the often-neglected contact stiffness are the focus of this study. A series of particle simulations are performed on a weakly frictional granular assembly in a split-bottom geometry considering various magnitudes of gravity and contact stiffnesses. While traditionally the inertial number, i.e., the ratio of stress to strain-rate time scales, is used to describe the flow rheology, we report that a second dimensionless number, the ratio of softness and stress time scales, must also be included to characterize the bulk flow behavior. For slow, quasistatic flows, the density increases while the effective (macroscopic) friction decreases with increase in either particle softness or local pressure. This trend is added to the $\mu (I)$ rheology and can be traced back to the anisotropy in the contact network, displaying a linear correlation between the effective friction coefficient and deviatoric fabric in the steady state. When the external rotation rate is increased towards the inertial regime, for a given gravity field and contact stiffness, the effective friction increases faster than linearly with the deviatoric fabric.",
keywords = "METIS-312765, IR-95650",
author = "Abhinendra Singh and Vanessa Magnanimo and Kuniyasu Saitoh and Stefan Luding",
note = "Open access",
year = "2015",
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language = "English",
volume = "17",
journal = "New journal of physics",
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Role of gravity or confining pressure and contact stiffness in granular rheology. / Singh, Abhinendra; Magnanimo, Vanessa ; Saitoh, Kuniyasu; Luding, Stefan .

In: New journal of physics, Vol. 17, 043028, 2015.

TY - JOUR

T1 - Role of gravity or confining pressure and contact stiffness in granular rheology

AU - Singh, Abhinendra

AU - Magnanimo, Vanessa

AU - Saitoh, Kuniyasu

AU - Luding, Stefan

N1 - Open access

PY - 2015

Y1 - 2015

N2 - The steady-state shear rheology of granular materials is investigated in slow quasistatic and inertial flows. The effect of gravity (thus the local pressure) and the often-neglected contact stiffness are the focus of this study. A series of particle simulations are performed on a weakly frictional granular assembly in a split-bottom geometry considering various magnitudes of gravity and contact stiffnesses. While traditionally the inertial number, i.e., the ratio of stress to strain-rate time scales, is used to describe the flow rheology, we report that a second dimensionless number, the ratio of softness and stress time scales, must also be included to characterize the bulk flow behavior. For slow, quasistatic flows, the density increases while the effective (macroscopic) friction decreases with increase in either particle softness or local pressure. This trend is added to the $\mu (I)$ rheology and can be traced back to the anisotropy in the contact network, displaying a linear correlation between the effective friction coefficient and deviatoric fabric in the steady state. When the external rotation rate is increased towards the inertial regime, for a given gravity field and contact stiffness, the effective friction increases faster than linearly with the deviatoric fabric.

AB - The steady-state shear rheology of granular materials is investigated in slow quasistatic and inertial flows. The effect of gravity (thus the local pressure) and the often-neglected contact stiffness are the focus of this study. A series of particle simulations are performed on a weakly frictional granular assembly in a split-bottom geometry considering various magnitudes of gravity and contact stiffnesses. While traditionally the inertial number, i.e., the ratio of stress to strain-rate time scales, is used to describe the flow rheology, we report that a second dimensionless number, the ratio of softness and stress time scales, must also be included to characterize the bulk flow behavior. For slow, quasistatic flows, the density increases while the effective (macroscopic) friction decreases with increase in either particle softness or local pressure. This trend is added to the $\mu (I)$ rheology and can be traced back to the anisotropy in the contact network, displaying a linear correlation between the effective friction coefficient and deviatoric fabric in the steady state. When the external rotation rate is increased towards the inertial regime, for a given gravity field and contact stiffness, the effective friction increases faster than linearly with the deviatoric fabric.

KW - METIS-312765

KW - IR-95650

U2 - 10.1088/1367-2630/17/4/043028

DO - 10.1088/1367-2630/17/4/043028

M3 - Article

VL - 17

JO - New journal of physics

JF - New journal of physics

SN - 1367-2630

M1 - 043028

ER -