Anisotropic particles strengthen granular pillars under compression

Abstract

We probe the effects of particle shape on the global and local behavior of a two-dimensional granular pillar, acting as a proxy for a disordered solid, under uniaxial compression. This geometry allows for direct measurement of global material response, as well as tracking of all individual particle trajectories. In general, drawing connections between local structure and local dynamics can be challenging in amorphous materials due to lower precision of atomic positions, so this study aims to elucidate such connections. We vary local interactions by using three different particle shapes: discrete circular grains (monomers), pairs of grains bonded together (dimers), and groups of three bonded in a triangle (trimers). We find that dimers substantially strengthen the pillar and the degree of this effect is determined by orientational order in the initial condition. In addition, while the three particle shapes form void regions at distinct rates, we find that anisotropies in the local amorphous structure remain robust through the definition of a metric that quantifies packing anisotropy. Finally, we highlight connections between local deformation rates and local structure.

Densest versus jammed packings of bent-core trimers

“…The dependence of granular materials' macroscopic properties on the shape of the grains composing them has attracted great interest over the past decade [5,6,11,20,50,53]. The results presented in this paper suggest that bent-core trimers are a model granular system in which both φ J and the local ordering of jammed states can be tuned by varying a single particle-shape parameter (θ 0 ).…”

“…The results presented in this paper suggest that bent-core trimers are a model granular system in which both φ J and the local ordering of jammed states can be tuned by varying a single particle-shape parameter (θ 0 ). Moreover, they should be relatively easy to synthesize using readily available techniques [18][19][20]. Future work will examine how jammed bent-core trimer systems' mechanical and acoustic properties depend on θ 0 .…”

“…Tangent-sphere trimers have R = 1; smaller values of R lead to overlap. While the first colloidal dimers and trimers had R < 1 [13][14][15], "colloidomers" with R 1 have recently been synthesized [16,17], and granular trimers with R 1 can be produced using readily available techniques such as spark welding, adhesive bonding or 3D printing [18][19][20]. Here we will focus primarily on the tangent-sphere case because it allows for straightforward identification of the densest packings and comparison to the very extensive literature on monodisperse hard spheres.…”

Machine learning characterization of structural defects in amorphous packings of dimers and ellipses

“…Our experimental system is a two-dimensional granular pillar driven by uniaxial compression, using an apparatus previously described in Refs. [23,24,44,[47][48][49]]. The granular system consists of bidisperse rods that stand upright on a table-top acrylic substrate.…”

“…The monomers and dimers used in this study are the same as those described in Ref. [44]. Monomers are acetal (Delrin) rods with large and small diameters of 0.25 in.…”