An experimental assessment of displacement fluctuations in a 2D granular material subjected to shear

TL;DR

This study experimentally investigates displacement fluctuations in a 2D granular material under shear, revealing a characteristic length scale of about ten times the particle size using digital image correlation.

Contribution

It applies and extends the Radjai and Roux framework to experimental data, identifying a minimum length scale in displacement fluctuations.

Findings

Displacement fluctuations are spatially organized.

A minimum length scale of ~10 particle sizes is observed.

Digital Image Correlation effectively measures fluctuations.

Abstract

In a granular material, a macroscopically homogeneous deformation does not correspond to a homogeneous displacement field when looking at the individual grains. The deviation of a grain displacement from the value dictated by the continuum field (referred to as fluctuation) is likely to hold valuable information about the characteristic length(s) involved in grains' rearrangement, which is the principal mechanism of irreversible deformation for granular materials. This paper shows a selection of results from a series of shear tests on a 2D analogue granular material. We have followed the route opened by the pioneering work of Radja\"i and Roux (2002), and used the same framework to analyze our experimental data on displacement fluctuations. Digital Image Correlation has been used to measure and characterize the displacement fluctuations. The analysis of their spatial organization reveals the emergence of a minimum length scale that is in the order of 10 times the mean particle size.