Strain fluctuations and elastic moduli in disordered solids

TL;DR

This paper demonstrates that common video-microscopy methods for estimating elastic moduli in disordered solids do not accurately reflect the true elastic properties, combining theory, experiments, and simulations.

Contribution

It provides a theoretical and empirical critique of existing methods for inferring elastic moduli from particle displacements in disordered solids.

Findings

Video-microscopy techniques do not reliably measure true elastic moduli.

Assumption of Boltzmann distribution for affine deformation components is invalid.

The inferred moduli do not correspond to actual elastic properties.

Abstract

Recently there has been a surge in interest in using video-microscopy techniques to infer the local mechanical properties of disordered solids. One common approach is to minimize the difference between particle vibrational displacements in a local coarse-graining volume and the displacements that would result from a best-fit affine deformation. Effective moduli are then be inferred under the assumption that the components of this best-fit affine deformation tensor have a Boltzmann distribution. In this paper, we combine theoretical arguments with experimental and simulation data to demonstrate that the above does not reveal information about the true elastic moduli of jammed packings and colloidal glasses.