Loading-dependent microscale measures control bulk properties in granular material: an experimental test of the Stress-Force-Fabric relation

The bulk behaviour of granular materials is tied to its mesoscale and particle-scale features: strength properties arise from the buildup of various anisotropic structures at the particle-scale induced by grain connectivity, force transmission, and frictional mobilization. More fundamentally, these anisotropic structures work collectively to define features like the bulk friction coefficient and the stress tensor at the macroscale and can be explained by the Stress-Force-Fabric (SFF) relationship stemming from the microscale arrangement of the forces and fabric. Although the SFF relation has been extensively verified by discrete numerical simulations, a laboratory realization has remained elusive due to the challenge of measuring both normal and frictional contact forces. In this study, we analyze experiments performed on a photoelastic granular system under four different loading conditions: uniaxial compression, isotropic compression,  pure shear, and annular shear. During these ..., Photoelastic granular images were taken using colour images and analysed using the PhotoElastic Grain Solver algorithm to determing the particle positions and contact forces. Four distinct loading histories are recorded, packings in a rectangular chamber are subject to pure shear, isotropic compression and uniaxial compression, where particles in an annular chamber are annular shear. Each loading history has a number of datasets, in which are the particle positions, adjacency matrix and in the case of the rectangular chambers are the valid images. See README for a further description, , # Loading-dependent microscale measures control bulk properties in granular material: an experimental test of the Stress-Force-Fabric relation

Dataset DOI: [10.5061/dryad.mcvdnck95](10.5061/dryad.mcvdnck95)

## Description of the data and file structure

This repository contains three folders corresponding to the data (at different stages of processing) for three cartesian loading schemes for photoelastic particles on an airtable.

### Files and variables

#### 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 figure2 of the paper.

**Ec(theta).txt** columns correspond:

-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.

**Fn...,

颗粒材料的宏观力学行为与其细观及颗粒尺度特征紧密关联：其强度特性源于颗粒接触连通性、力传递与摩擦活化所诱导的颗粒尺度各向异性结构的形成。从根本上讲，这些各向异性结构共同决定了宏观尺度下的体积摩擦系数与应力张量等特征，而这可通过源于力与组构微观排布的应力-力-组构（Stress-Force-Fabric, SFF）关系加以阐释。尽管SFF关系已通过离散数值模拟得到广泛验证，但由于难以同时测量法向与切向接触力，实验室实现该关系的验证始终颇具挑战。本研究针对光弹性颗粒系统开展了四种不同加载条件下的实验：单轴压缩、等静压缩、纯剪切与环形剪切。实验过程中……通过彩色成像采集光弹性颗粒图像，并采用光弹性颗粒求解器（PhotoElastic Grain Solver）算法分析图像以获取颗粒位置与接触力。本次实验共记录了四种独立的加载历程：矩形仓内的颗粒填充体分别经历纯剪切、等静压缩与单轴压缩，而环形仓内的颗粒则承受环形剪切。每种加载历程均包含多组数据集，涵盖颗粒位置、邻接矩阵，对于矩形仓的实验还包含有效成像数据。详细说明请参见README文件。
# 载荷依赖的微观尺度调控颗粒材料宏观特性：应力-力-组构关系的实验验证

数据集DOI：[10.5061/dryad.mcvdnck95](10.5061/dryad.mcvdnck95)

## 数据与文件结构说明

本仓库包含三个文件夹，对应气浮平台上光弹性颗粒的三种笛卡尔坐标加载方案的不同处理阶段数据。

### 文件与变量

#### 文件：figure2.zip
**描述：** 该文件夹内的数据包含三个文件，分别对应论文图2中绘制的接触力、法向力与切向力的角度分布。
**Ec(theta).txt** 各列含义如下：
-angle：与正文中定义的θ对应的角度，单位为弧度
-eps = 0.xx：列标签代表测量该分布时的应变步长
首列之后的各列对应接触概率密度$E^c( heta)$。
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