Nonlocal Rheology of Grannular Flows

EXECUTIVE SUMMARY

depends on both the particle shape and material.

while the local rheological parameter is largely independent of particle-shape, the nonlocal parameter

from material properties such as the coefficient of friction or elastic modulus. We observe that

shape of the interparticle contacts (rounded vs. angular) is an important control on s, separate

with three different elastic moduli, and small range of particle sizes. We have observed that the

parameters, using particles of three different shapes (circles, ellipses, and pentagons), materials

We have successfully performed experiments to test how the particle properties affect the model

observing that it corresponds to a drop in the susceptibility to force chain fluctuations.

yield criterion. Finally, we newly identify the physical mechanism behind this transition at s by

the prediction that there is growing lengthscale at a finite value s, associated with a frictional

collected once we account for frictional drag with the bottom plate. Our measurements confirm

successfully find that a single set of model parameters is able to capture the full range of data

We obtain (I) curves for several different packing fractions and rotation rates, and

and the inertial number I through the use of a torque sensor, laser-cut leaf springs, and particle tracking.

The apparatus is designed to measure both the stress ratio (the ratio of shear to normal stress)

photoelastic particles.

quasi-2D annular shear cell with a fixed outer wall and a rotating inner wall, including using

different packing fractions, shear rates, and particle properties, we performed experiments in a

model [gradient model, Bouzid et al. 2013]. To validate the efficacy of these two models across

nonlocal theory [cooperative model, Kamrin and Koval 2012], and added a comparison to a second

Through the three years of this project, we have have conducted laboratory testing of one

to macroscale behaviors.

to bulk data for a particular flow geometry and particles, we aim to connect grain-scale parameters

of granular materials, independent of the flow geometry. Rather than using empirical relations fit

and thereby provides an improved understanding of how particle properties control the rheology

best describe such flows. Therefore, there is a need for experimental data which tests these theories,

aside adhesion, which is more challenging still). It is an open question what constitutive equations

predicts its rheological response as a function of particle size, shape, and friction (even leaving

Currently, there is no first-principles, general theory of intermediate dry granular flow that