Perspective: Mechanics of randomly packed filaments -- the `bird nest' as meta-material

TL;DR

This paper explores the mechanics of randomly packed filament systems, like bird nests, linking their bulk and local behaviors and highlighting their elastoplastic responses, with implications for designing disordered meta-materials.

Contribution

It introduces a perspective connecting the mechanics of packed filaments with granular physics, emphasizing the elastoplastic behavior and potential applications of such disordered systems.

Findings

Robust packing statistics across systems

Unusual elastoplastic response to compression

Link between bulk and local behavior of packed filaments

Abstract

Systems of randomly packed, macroscopic elements, from jammed spherical grains to tangled long filaments, represent a broad class of disordered meta-materials with a wide range of applications and manifestations in nature. A `bird nest' presents itself at an interface between hard round grains described by granular physics to long soft filaments, the center of textile material science. All of these randomly packed systems exhibit forms of self assembly, evident through their robust packing statistics, and a common, unusual elastoplastic response to oedometric compression. In reviewing packing statistics, mechanical response characterization and consideration of boundary effects, we present a perspective that attempts to establish a link between the bulk and local behaviour of a pile of sand and a wad of cotton, demonstrating the nest's relationship with each. Finally, potential directions for impactful applications are outlined.