Probing non-affine expansion with light scattering

TL;DR

This paper introduces a novel optical method to experimentally detect and quantify nonaffine deformation in disordered materials under elastic stress, overcoming previous measurement challenges.

Contribution

The authors develop a phase compensation technique using wavelength tuning to measure nonaffinity in amorphous materials, validated with a glass frit sample.

Findings

Confirmed nonaffinity occurs in the elastic regime.

Achieved complete reversibility of deformation in experiments.

Estimated the magnitude and correlation domain of nonaffine displacements.

Abstract

In disordered materials under mechanical stress, the produced deformation can deviate from the affine one already in the elastic regime. The nonaffine contribution was observed and characterized in numerical simulations for various systems. However, low amplitude of nonaffinity and its local character makes the experimental study challenging. We present a novel method on the based on a phase compensation of the wave scattered from a dilated amorphous material using fine wavelength tuning of the optical probe beam. Using a glass frit as a sample, we provide complete reversibility of the material deformation which enables to confirm the occurrence of nonaffinity in the elastic regime. We develop a model for the coupled effect of the thermal expansion/contraction of the material and the dilatation of the incident wavelength which allows us to estimate the magnitude of the nonaffine displacement and the spatial extent of its correlation domain.