Particle scale anisotropy controls bulk properties in sheared granular materials
Data files
Aug 07, 2025 version files 106.58 MB
-
figure2.zip
9.47 KB
-
figure3.zip
2.84 KB
-
figure4.zip
30.90 KB
-
rawdata.zip
106.53 MB
-
README.md
7.23 KB
Abstract
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.
Dataset DOI: 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 $<fnor(theta)/f0*$, *the average normal force within the angle bin, normalized by the total average normal force f_0.
Ftan(theta).txt contains the data associated with the tangential force distribution at different strain steps. Columns correspond to [angle, tangential 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 $<ftan(theta)/f0*$, *the average tangential force within the angle bin, normalized by the total average normal force f_0.
File: figure3.zip
Description: This folder contains the data corresponding to figure 3 of the paper.
figure3.txt has columns that correspond to the following:
-strain: shear strain, the independent variable
-z (without rattlers): the average coordination number for load bearing particles at the given strain step
-std(zwor): the standard deviation of the previous mean
-z(with rattlers): the average coordination number for all particles at the given strain step
-std(zwr): the standard deviation of the previous mean
-f_0: the average normal force on a load bearing particle at the given strain step
-std(f_0): standard deviation in the normal force
-theta_contact: the principle angle for the contact probability distribution, i.e. main direction of contacts, in radians
-std(theta_contact): the standard deviation in principle angle for the contact probability distribution, i.e. main direction of contacts, in radians
-theta_normal: the principle angle for the normal force distribution, i.e. main direction of strongest normal forces, in radians
-std(theta_contact): the standard deviation in principle angle for the normal force distribution, i.e. main direction of strongest normal forces, in radians
-a: the magnitude of anisotropy for the contacts probability distribution, averaged over the strain step.
-std(a): standard deviation of the magnitude of anisotropy for the contacts, averaged over the strain step.
-an: the magnitude of anisotropy for the normal force distribution, averaged over the strain step.
-std(a_n): standard deviation of the magnitude of anisotropy for the normal force distribution, averaged over the strain step.
-a_t: the magnitude of anisotropy for the tangential force distribution, averaged over the strain step.
-std(a_t): standard deviation of the magnitude of anisotropy for the tangential force distribution, averaged over the strain step.
File: figure4.zip
Description: This folder contains the two files required to recreate figure 4 in the text. bulkcalculation.txt contains data that corresponds to the bulk measures like the stress tensor. SFFanisotropy contains the relevant parameters for the particle scale comparison.
bulkcalculation.txt has the following columns:
strain: shear strain step
mu: calculated from equation 2 in the paper
sigma_rr: the radial-radial component of the stress tensor in Pa m
sigma_rtheta: the radial-theta component of the stress tensor in Pa m
sigma_thetatheta: the radial-theta component of the stress tensor in Pa m
sigma_thetar: the radial-theta component of the stress tensor in Pa m
SFFanisotropy contains the following columns
strain: shear strain step
a: the magnitude of anisotropy for the contacts probability distribution, averaged over the strain step.
-std(a): standard deviation of the magnitude of anisotropy for the contacts, averaged over the strain step.
-a_n: the magnitude of anisotropy for the normal force distribution, averaged over the strain step.
-std(a_n): standard deviation of the magnitude of anisotropy for the normal force distribution, averaged over the strain step.
-a_t: the magnitude of anisotropy for the tangential force distribution, averaged over the strain step.
-std(a_t): standard deviation of the magnitude of anisotropy for the tangential force distribution, averaged over the strain step.
-f0 nu z / pi d*:* the prefactor calculated in equation 5. Units of Pa m
Particle positions and force network were found using the Photoelastic Grain Solver analysis code. This code is available at https://github.com/photoelasticity