DOI: 10.5061/dryad.m905qfvds
title: Particle scale anisotropy controls bulk properties in sheared granular materials

description: The bulk dynamics of dense granular materials arise through a combination
 of particle-scale and mesoscale effects. Theoretical and numerical studies
 have shown that collective effects are created by particle-scale
 anisotropic structures such as grain connectivity, force transmission, and
 frictional mobilization, all of which influence bulk properties like bulk
 friction and the stress tensor through the Stress-Force-Fabric (SFF)
 relationship. To date, establishing the relevance of these effects to
 laboratory systems has remained elusive due to the challenge of measuring
 both normal and frictional contact forces at the particle scale. In this
 study, we perform experiments on a sheared photoelastic granular system in
 a quasi-2D annular cell. During these experiments, we measure particle
 locations, contacts, and normal and frictional force vectors during
 loading. We reconstruct the angular distributions of the contact and force
 vectors, and extract the corresponding emergent anisotropies for each of
 these metrics. Finally, we show for the first time in an experimental
 system that the SFF relation quantitatively predicts the relationship
 between particle scale anisotropies, the stress tensor components, and the
 bulk friction coefficient, capturing even transient behaviors — closing
 the gap between experimental measurements and prior theoretical and
 numerical models. These datasets contain the particle position
 information, force network information, as well as the data from the three
 data-containing figures in the paper relating bulk stress information to
 the particle scale anisotropies.
description: # Particle scale anisotropy controls bulk properties in sheared granular
 materials Dataset DOI: [10.5061/dryad.m905qfvds](10.5061/dryad.m905qfvds)
 ## Description of the data and file structure This repository contains
 four folders corresponding to the data (at different stages of processing)
 of a full rotation of the shear on an annular shear cell. ### Files and
 variables #### File: rawdata.zip **Description:** The data in this folder
 contains 3 files named as centers_tracked.txt, Adjacency_list.txt, and
 annulusgeometry.txt **centers_tracked.txt:** This file contains the
 particle position information and radius. The columns are: [frame,
 particleID, x, y, r, edge] *frame:* image number corresponding to a strain
 step *particleID:* individual id of one particle that should persist from
 frame to frame x: x position of particle, in pixels y: y position of
 particle, in pixels r*:* radius of particle, in pixels edge*:* boolean
 edge flag, 0 not near an edge, -1 near the inner boundary, 1 near the
 outer boundary **Adjacency_list.txt:** This file contains the force
 connection/network information in the form of an adjacency matrix. The
 columns are [frame, id1, id2, tangential force, normal force.]
 *frame:* image number corresponding to a strain step id1*:* individual id
 of one particle in contact with particle id2 id2*:* individual id of one
 particle in contact with particle id1 tangential force: in Newtons normal
 force: in Newtons **annulusgeometry.txt:** contains information on the
 geometry of the annular shear cell needed for independent analysis. It
 contains:\ -Center of the annulus, in pixels. -The inner and outer radius
 of the annulus in pixels. -The conversion from pixels to meters.  -The
 frame rate of taking images in seconds -The rotation rate of the inner
 wheel in rad/picture. #### File: figure2.zip **Description:** The data in
 this folder contains three files corresponding to the angular
 distributions of the contact, normal forces and tangential forces that are
 plotted in figure 2 of the paper. **Ec(theta).txt** contains the data
 associated with the contact distribution at different strain steps.
 Columns correspond to [angle, contact probability density at the given
 strain step] -angle: angle corresponding to \theta as defined in the text.
 Units radians -eps* =* 0.xx : column labels indicate the strain step at
 which each distribution is measured columns beyond the first angle column
 corresponds to $E^c(\theta)$, the contact probability density.
 **Fnor(theta).txt**: contains the data associated with the normal force
 distribution at different strain steps. Columns correspond to [angle,
 normal force values at the given strain step] -angle: angle corresponding
 to \theta as defined in the text. Units radians -eps* =* 0.xx : column
 labels indicate the strain step at which each distribution is measured
 columns beyond the first angle column corresponds to
 $