Force Statistics and Correlations in Dense Granular Packings

TL;DR

This paper investigates the statistical properties and correlations of contact forces and pressures in dense granular packings, revealing non-random correlations and analyzing measurement errors related to pressure estimation.

Contribution

It provides new insights into force correlations and pressure measurement accuracy in dense granular media, with experimental proposals for further understanding.

Findings

Non-random force correlations extend over 10-15 particle diameters.

Pressure measurement errors depend on the number of contacts considered.

Pressure distributions vary with the size of the pressure cell.

Abstract

In dense, static, polydisperse granular media under isotropic pressure, the probability density and the correlations of particle-wall contact forces are studied. Furthermore, the probability density functions of the populations of pressures measured with different sized circular pressure cells is examined. The questions answered are: (i) What is the number of contacts that has to be considered so that the measured pressure lies within a certain error margin from its expectation value? (ii) What is the statistics of the pressure probability density as function of the size of the pressure cell? Astonishing non-random correlations between contact forces are evidenced, which range at least 10 to 15 particle diameter. Finally, an experiment is proposed to tackle and better understand this issue.