Continuum limit of amorphous elastic bodies (II): Response to a point source

TL;DR

This study investigates how two-dimensional amorphous elastic bodies respond to point forces, revealing significant local fluctuations near the source that average out at larger distances, aligning with classical elasticity predictions beyond a certain length scale.

Contribution

It provides a detailed analysis of stress and displacement fluctuations in amorphous solids, identifying a self-averaging length scale and examining local rigidity variations.

Findings

Stress fluctuations decay exponentially with distance from the source.

Classical elasticity applies beyond approximately 30 interatomic distances.

Displacement correlations indicate domains of varying rigidity without a clear characteristic length.

Abstract

The linear response of two-dimensional amorphous elastic bodies to an external delta force is determined in analogy with recent experiments on granular aggregates. For the generated forces, stress and displacement fields, we find strong relative fluctuations of order one close to the source, which, however, average out readily to the classical predictions of isotropic continuum elasticity. The stress fluctuations decay (essentially) exponentially with distance from the source. Only beyond a surprisingly large distance, $b \approx 30$ interatomic distances, self-averaging dominates, and the quenched disorder becomes irrelevant for the response of an individual configuration. We argue that this self-averaging length $b$ sets also the lower wavelength bound for the applicability of classical eigenfrequency calculations.Particular attention is paid to the displacements of the source, allowing a direct measurement of the local rigidity. The algebraic correlations of these displacements demonstrate the existence of domains of slightly different rigidity without, however, revealing a characteristic length scale, at least not for the system sizes we are able to probe.