Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session V16: Packing and Jamming of Granular MaterialsFocus Live

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Sponsoring Units: GSNP DSOFT Chair: Jeremy Lechman, Sandia National Laboratories 
Thursday, March 18, 2021 3:00PM  3:36PM Live 
V16.00001: Quantifying Local Rearrangements in Granular Media Using Xray Tomography, Diffraction, and Machine Learning Invited Speaker: Ryan Hurley Granular materials deform macroscopically via local slip and coordinated particle rearrangement events at the microscale. Discrete and continuum numerical models have been employed in the engineering and physics communities to capture the effects of individual particle rearrangements on the macroscopic plasticity of granular and related materials. For instance, glassy rheology models and shear transformation zone theories have been used to capture the aggregated effects of local individual rearrangement events and their interactions in colloids, metallic glasses, and granular media. A major challenge remains the quantitative validation and calibration of these models using insitu 3D experimental data. 
Thursday, March 18, 2021 3:36PM  3:48PM Live 
V16.00002: Modeling loading and fragmentation in compacted granular systems Joel Clemmer, Dan Bolintineanu, Jeremy Lechman Hard particle jamming in the limit of zero pressure is well studied in granular physics, but many applications are far from this limit. As pressure increases, rearrangement is no longer the only mechanism for densification as grains will deform and eventually fracture. The breakdown of granular matter, or comminution, produces irregular shapes and sizes and affects macroscopic properties including rheology. We explore the compaction of brittle granular systems using bonded discrete element simulations. Each grain is composed of many smaller, fundamental particles which are connected by a network of breakable bonds. This allows grains to crack and fragment. During loading, we monitor both the evolution of macroscopic properties (e.g. stress and porosity) as well as the evolution of grain size distributions. We explore how compaction depends on strain rate and material properties. Finally, the pressure at which single grains fail is identified and compared to theory. 
Thursday, March 18, 2021 3:48PM  4:00PM Live 
V16.00003: Effect of pins on force distributions in frictionless jammed systems Celia Parts, Andy Zhang, Sean Ridout, Katharina VollmayrLee, Brian Utter, Amy Graves, Cacey Bester Important properties related to systems capable of jamming  such as the jamming threshold and contact force distributions  have been wellstudied for a broad range of experimental systems and theoretical models. By introducing lattices of fixed pins of negligible size into two dimensional bidisperse systems with purely repulsive harmonic interactions, we provide a tuning parameter to systematically modify these properties. We find that these pin lattices in square, triangular, and random configurations can significantly alter the force distribution of the system near the jamming transition. For instance, there is an increasing prevalence of very weak contacts with increasing pin lattice density, and we examine “bucklers”, particles with d+1 contacts, to understand this behavior. Additionally, the presence of pins shifts the tail of the force distribution from exponential decay to a distribution with “fat tails”. We also examine the bond angle distributions which accompany these trends. 
Thursday, March 18, 2021 4:00PM  4:12PM Live 
V16.00004: Meanfield predictions of scaling prefactors match lowdimensional jammed packings James Sartor, Sean Ridout, Eric Corwin Many results from the mean field theory of glasses and jamming are found to be accurate at low dimensions. While the exponents of scaling power laws between pressure, excess packing fraction, and number of excess contacts are expected to be exact at and above the upper critical dimension of 2, the prefactors to such power laws are not. We present measurements of these prefactors in dimensions 210 and show that they do closely follow mean field predictions, suggesting a deeper connection. To explain these findings, we present an exact, first principles derivation for the relation between pressure and excess packing fraction that does not invoke the mean field. These results suggest that mean field theories of critical phenomena may compute more above the upper critical dimension than has been previously appreciated. 
Thursday, March 18, 2021 4:12PM  4:24PM Live 
V16.00005: Energy landscape approach to understanding systems beyond jamming Amruthesh Thirumalaiswamy, Robert Riggleman, John Crocker The dynamics and structure of systems beyond the glass and jamming transition have been of interest for a long time. The slow dynamics and complexity of these systems has restricted the ability to simulate them using conventional methods, particularly at low temperatures or high volume fractions. The properties of the low energy states are of particular importance to answering many fundamental questions surrounding the glass transition. In this study, we use an energy landscape based approach to probe the existence of such inherent structure athermal energies and provide an algorithm to explore the energy landscape The algorithm is inspired by metadynamics, and proceeds as a high dimensional basin filling algorithm that allows us to explore the energy landscape of a model softsphere foam system. We demonstrate the ability of the algorithm to reach low energies while revealing interesting characteristics about the nature of the landscape. We study how connected metabasins are organized relative to a starting energy minimum and their orientations relative to each other. Finally, we compare our method with conventionally used swap Monte Carlo that allows us to equilibrate glassy systems at lower temperatures by accessing lower energy portions of the energy landscape. 
Thursday, March 18, 2021 4:24PM  4:36PM Live 
V16.00006: Effect of chain stiffness on athermal polymer jamming and phase behaviour Daniel Martinez Fernandez, Miguel Herranz, Katerina Foteinopoulou, Nikos Ch. Karayiannis, Manuel Laso Through Monte Carlo simulations [1], we study the behavior of athermal, linear semiflexible polymers of tangent hard spheres at progressively increased concentrations. Stiffness is controlled by a tunable potential for the bending angles whose intensity dictates rigidity. We analyze how packing density, chain length and stiffness affect the maximally random jammed (MRJ) state [2,3] compared to the fully flexible model. In parallel, we employ a structural descriptor [4], based on crystallographic symmetry operations, to quantify local structure and the emerging degree of randomness. We discuss how backbone flexibility affects the established short and longrange structure of polymer chains in the vicinity of the MRJ state. 
Thursday, March 18, 2021 4:36PM  4:48PM Live 
V16.00007: Percolation in metalinsulator composites of disordered jammed spherocylindrical nanoparticles Shiva P Pokhrel, Brendon Waters, ZhiFeng Huang, Boris Nadgorny While classical percolation is well understood, percolation effects in random jammed structures are much less explored. Here we investigate both experimentally and theoretically the electrical percolation in a binary system of disordered jammed spherocylinders. Experimentally we determine the percolation threshold and conductivity critical exponent for composites of conducting (CrO_{2}) and insulating (Cr_{2}O_{3}) nanoparticles that are geometrically identical. Simulations and modeling are implemented through a combination of the mechanical contraction method and a variant of random walk (de Gennes ant) approach, in which charge diffusion is correlated with the system conductivity via the NernstEinstein equation. The percolation threshold and critical exponents are identified through finite size scaling and are in good agreement with the experimental results. Interestingly, the calculated percolation threshold for spherocylinders with an aspect ratio of 6.5, p_{c}= 0.312 ± 0.002, is very close (within numerical errors) to the one found in two other distinct systems of disordered jammed spheres and simple cubic lattice, an intriguing and surprising result. We also explored tunneling percolation in a system of CrO_{2} nanoparticles with variable thickness of insulating Cr_{2}O_{3} shell barriers. 
Thursday, March 18, 2021 4:48PM  5:00PM Not Participating 
V16.00008: Characterizing the structure of a compression of hard sphere systems up to jamming Timothy Middlemas, Salvatore Torquato Via computer simulations, we generate threedimensional hardsphere systems as a function of packing fraction by compressing initial liquidstate configurations up to their ending jammed states, which depend on the rate of compression. We study these metastable branches for a broad range of compression rates. Of particular interest is the characterization of the degree of order via order metrics as well as relaxation times along each of these trajectories. Specifically, we compare trajectories obtained by relaxing snapshots along the various metastable branches to thermalized snapshots taken along the equilibrium crystal branch. We expect that this work will help clarify the various kinematic features of the jamming process, and assist in the development of jamming algorithms based on the underlying dynamics of the densification procedure. 
Thursday, March 18, 2021 5:00PM  5:12PM Live 
V16.00009: Jamming and percolation of dimers in restrictedvalence random sequential adsorption Alexandre Furlan, Diogo Carlos dos Santos, Robert M. Ziff, Ronald Dickman Restrictedvalence random sequential adsorption is studied in its pure, disordered and oriented versions on the square and triangular lattices. For the simplest case (pure on the square lattice) we prove the absence of percolation for maximum valence V_{max}=2. In other cases, Monte Carlo simulations are used to investigate the percolation threshold, universality class, and jamming limit. Our results reveal a continuous transition for the majority of the cases studied. The percolation threshold is computed through finitesize scaling analysis of seven properties; its value increases with the average valency. Scaling plots and datacollapse analyses show that the transition belongs to the standard percolation universality class even in disordered cases. 
Thursday, March 18, 2021 5:12PM  5:24PM Live 
V16.00010: Nonlinear acoustic resonance and waveinduced softening in dense granular matter through flow heterogeneities Charles Lieou, Jerome Laurent, Paul A Johnson, Xiaoping Jia We report a series of experiments on the softening and compaction of a dense granular pack through traveling acoustic pressure and shear waves. Softening is manifested by a reduction the travelingwave speed, as the amplitude of the disturbance increases beyond some threshold. We explain these seemingly contradictory observations using a theoretical model, based on shear transformation zones (STZs), that directly attributes these observations to dynamical heterogeneities and slipping contacts in the granular pack. Softening is accounted for by the increase of the fraction of STZs or slipping contacts as a function of increasing strain amplitude, while compaction is explained by an Isinglike correlation between STZs in the subyield regime. In so doing, we demonstrate the fundamental connection between nonaffine granular rearrangements, mesoscopic glassy dynamics, jamming and unjamming, and matterwave interactions. 
Thursday, March 18, 2021 5:24PM  5:36PM Live 
V16.00011: Vibrational Spectrum of Granular Packings with Random Matrices Onuttom Narayan, Harsh Mathur It has previously been proposed that the vibrational spectrum of a jammed solid can be approximately obtained via random matrix theory. We observe that random matrix theory cannot explain the mean density of states but it should be able to predict universal properties of the spectrum including the correlations of the density of states. Consistent with this expectation we demonstrate good agreement between dynamical numerical simulations of granular bead packs and the analytic predictions of the Laguerre orthogonal ensemble of random matrix theory. At the same time there is clear disagreement with the predictions of the Gaussian orthogonal ensemble which establishes the Laguerre ensemble as the correct random matrix description of the jammed vibrational spectrum. We also construct a random lattice model which is a physically motivated variant on the random matrix theory. Numerical calculations reveal that this model is able to explain the mean density of states while also retaining the correct correlations obtained from the Laguerre orthogonal ensemble. We propose that the random lattice model can therefore be applied to understand not only the spectrum but more general properties of bead packs including the spatial structure of modes both at the jamming point and far from it. 
Thursday, March 18, 2021 5:36PM  5:48PM Live 
V16.00012: Brazil nut effect controlled by vibration velocity Mika Umehara, Ko Okumura When grains of different sizes are vibrated, the largest particle rises and separates. This Braizl nut effect has been studied for a long time. However, there has been no consensus on what parameters (eg., frequency, acceleration, velocity of vibration) characterize this phenomenon. However, recent studies [12] have shown the convection velocity can be governed only by the vibration velocity when continuous vibrations were applied. Recently, we have conducted an experiment using small particles and a large disk in a pseudotwodimensional cell and found the rising motion is always governed by the vibration velocity when continuous vibrations were given [3]. Here, we further confirm the BN effect is controlled by vibration velocity even under discontinuous vibration [4]. We find that the BN effect under discontinuous vibration is divided into two regimes and the final convection regime is clearly governed by vibration velocity. This suggests the segregation due to convection can be universally controlled by the vibration velocity. 
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