Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session B09: Nonlinear Response of Complex Granular Materials IIFocus Recordings Available
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Sponsoring Units: GSNP DSOFT DFD Chair: Ishan Srivastava, Lawrence Berkeley National Laboratory Room: McCormick Place W-180 |
Monday, March 14, 2022 11:30AM - 11:42AM |
B09.00001: Numerical study of shear-history memory in slowly compressed granular media made of soft, frictional grains Donald Candela
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Monday, March 14, 2022 11:42AM - 11:54AM |
B09.00002: Quantifying Rearrangement Statistics, Correlations, and Contributions to Macroscopic Strain in 3D Granular Materials Using X-ray Measurements Ryan C Hurley, Chongpu Zhai, Eric B Herbold, Stephen Hall, Nahuel Albayrak, Jonas Engqvist, Jonathan Wright, Marta Majkut Local rearrangements are an essential ingredient of the quasi-static and dynamic deformation of granular materials. Various models have been proposed for relating local particle rearrangements to macroscopic plasticity in granular materials. All such models rely on assumptions regarding rearrangement strain, frequency, stress relaxation, and contributions to macroscopic deformation. Here, we examine in-situ X-ray measurements of particle-resolved structure and stress in quasi-statically deforming granular materials in various geometries to study the statistics of rearrangements, their length scales, their correlations with structure and stress, and their contribution to macroscopic strain. We first define distinct rearrangement measures that quantify local strain, non-affine motion, and relative rotation. We show that rearrangements defined by each of these measures have length scales of about three particle diameters. We use particle-resolved structure and stress measurements to examine the coupling between rearrangement measures, for instance between local volumetric and shear strain and between non-affine motion and relative particle rotation. We examine correlations between rearrangement magnitude and local stress and porosity preceding rearrangements, showing that, at the length scale of local rearrangements, structure plays at least as important of a role as stress. Finally, we study how local regions exhibiting large rearrangements contribute to macroscopic strain. Our results provide insight into the features and statistics of rearrangements in quasi-statically deforming granular media. |
Monday, March 14, 2022 11:54AM - 12:06PM |
B09.00003: Force chains in 3D granular media Wei Li, Ruben Juanes Under the action of external forces, particles in granular materials form a complex network of contacts—these force chains transmit the external load through the medium. Understanding the emergence of these force chains and their spatial structure constitutes a fundamental goal of granular mechanics. For decades, our understanding of force chains has been derived from 2D experiments, using quasi-2D photoelastic particles with various shapes. Here, we introduce a new experimental technique, which integrates photoelasticimetry into tomography, to observe the evolution of 3D force chains under isotropic compression, triaxial shear and rotary shear. Our experimental study unveils the astonishing 3D nested, parallel and helical force chain patterns in the granular medium under isotropic, triaxial shear and rotary shear conditions, respectively. We also show the length and orientation statistics of the force chains are closely correlated to the 3D loading conditions. |
Monday, March 14, 2022 12:06PM - 12:42PM |
B09.00004: Stickiness in granular and related soft solids Invited Speaker: Brian P Tighe Repulsive soft spheres are a widely studied computer model for grains, pastes, and emulsions, especially in the context of the jamming transition. However, laboratory models such as wet sand, capillary suspensions, and surfactant-stabilized oil droplets, all possess some degree of interparticle attraction. Therefore, understanding the role of “stickiness” in the soft sphere model is necessary in order to translate results from simulations to the lab. |
Monday, March 14, 2022 12:42PM - 12:54PM |
B09.00005: Strongly protocol-dependent jamming of frictional cohesive grains Robert S Hoy, Kai Nan Using molecular dynamics simulations, we examine how the structure of marginally jammed systems of grains with varying degrees of friction and cohesion depends on the protocol with which these systems are prepared. We compare results for systems with four types of intergrain interactions: (1) no friction or cohesion, (2) friction but no cohesion, (3) cohesion but no friction, and (4) both cohesion and friction. The final packing fractions (φJ) of systems prepared by beginning with a dilute state and then ramping the pressure (to a fixed, small Pfinal) range from ~.64 for system (1) to ~.35 for system (4). Critically, while these φJ are almost independent of the pressure ramp rate RP for systems (1-3), φJ in system (4) decreases substantially with decreasing RP . We show that this effect arises from friction slowing down the rearrangement dynamics of weakly-cohesively-bound clusters that form prior to jamming, which in turn leads to the formation of stable voids in the final jammed solids whose size increases with decreasing RP. |
Monday, March 14, 2022 12:54PM - 1:06PM Withdrawn |
B09.00006: Sheared, not shaken: contact numbers are history dependent Matthias Schroeter, Sagar Chaudhary Granular media gain mechanical stability by the contacts between individual particles. Predicting the average number of contacts per particle as a function of shape, volume fraction, and friction coefficient has been an important test case for the various theoretical approaches. At present, experimental data for tapped sphere packings is in good agreement with the mean field type approach of Song et al. (2008). Here we present measurements of sphere packing prepared by gyratory shear, a method which avoids the formation of shear bands. We find that the number of contacts as a function of volume fraction does depend strongly on the way the packing was prepared. |
Monday, March 14, 2022 1:06PM - 1:18PM |
B09.00007: Ultra-stable shear jammed granular material Yiqiu Zhao, Yuchen Zhao, Dong Wang, Hu Zheng, Bulbul Chakraborty, Joshua Socolar We report experiments that demostrate the existence of unexpected, nearly elastic states in a shear-jammed granular material. These ``ultra-stable'' states are formed by applying low-amplitude, quasistatic cyclic shear to an initially shear-jammed system. After a transient relaxation, all the particle positions and inter-particle contact forces remain unchanged after each complete shear cycle for thousands of cycles. We perform experiments on a layer of plastic discs, using photoelasticimetry to measure all inter-particle vector forces. For a given strain amplitude, the ultra-stable states are formed from shear-jammed states prepared by a sufficiently large initial shear strain. The ultra-stable states display different mechanical behavior than the conventional shear jammed states, being nearly elastic and resisting shear reversal up to a finite yield strain. |
Monday, March 14, 2022 1:18PM - 1:30PM |
B09.00008: Large-scale granular packings of power-law-distributed polydisperse spheres Joseph Monti, Joel Clemmer, Ishan Srivastava, Leo Silbert, Jeremy Lechman, Gary S Grest Discrete element simulations of granular packings of size-dispersed spheres with largest-to-smallest diameter ratios >10 have remained elusive. Previous numerical studies of power-law-distributed particles have typically been constrained to work with relatively narrow spans of particle sizes, limiting the correspondence between simulation results and real-world granular materials of geophysical and industrial relevance. We employ a newly developed neighbor binning algorithm, implemented in LAMMPS, to efficiently generate multi-million particle granular packings of power-law-distributed spheres with largest-to-smallest diameter ratios of 50 and larger. By varying the exponent of the underlying power-law size distribution, along with interparticle coefficients of friction, our simulations reveal striking insights into the structure and properties of packings of both frictionless and frictional particles. Our work underscores the importance of balancing the relative abundance of large-large and small-small particle contacts to optimize packing properties. We contextualize our results with simulations of monodispersed packings and bidispersed packings with comparable size disparities. |
Monday, March 14, 2022 1:30PM - 1:42PM |
B09.00009: Influence of friction on the dynamics of sheared granular materials Qinghao Mao, Yujie Wang, Walter Kob The presence of friction is one of the most important aspects of granular materials. Although the influence of friction on the static properties of the jammed state has been studied well, much less is known about the friction-dependence of the dynamics. Using particle-based computer simulations, we probe how friction influences the relaxation dynamics of frictional particles that undergo oscillatory shear in 2d. We find that increasing friction gives rise to a liquid-solid-liquid transition in the translational mean squared displacement and at the same time a diffusion-ballistics-diffusion transition in the rotational dynamics. We show that these reentrant transitions can be rationalized with two competing mechanisms: i) Slowing down of the dynamics because of an increasing coupling between the translational degrees of freedom with the rotational ones and ii) Acceleration of the dynamics because of the emergence of domains that move collectively due to high friction. |
Monday, March 14, 2022 1:42PM - 1:54PM |
B09.00010: Haptic detection of obstacles in granular media Shivam Chopra, Drago Vasile, Michael T Tolley, Nick G Gravish Navigation and obstacle detection within granular media (GM) is challenging because vision and acoustic localization methods are hindered by the granular material. In this work, we explore a strategy for detecting obstacles in GM by measuring the changes in reaction force experienced by intruders as they move near an obstacle. We first performed experiments with a rotating beam instrumented with a torque sensor at the base to measure the change in forces experienced by the beam as a function of object proximity. We tested this for five different configurations of the obstacle with respect to the beam rotation plane, and we systematically varied the obstacle distance from the rotation axis from 0 to 14 cm. We observed that when the object disrupts the upward flow of GM pushed by the beam a large change in force is observed. However, objects below or normal to the rotation plane did not result in a detectable force change. To understand this, we measured the quasi-2D flow fields through particle image velocimetry. We demonstrated the feasibility of obstacle detection in GM using an appendage-driven robot instrumented with force sensors on its limbs. Our results advance the understanding of obstacle localization in GM with many applications in robotics. |
Monday, March 14, 2022 1:54PM - 2:06PM |
B09.00011: Electrostatic Interactions between Rough Dielectric Particles: Implications for the Lunar Dust Problem Matt Gorman, Rui Ni We present the results of a study investigating the electrostatic interactions between rough particles. A Boundary Element Method has been implemented to calculate the distribution of surface charge on rough non-spherical particles and the resulting electrostatic force and potential energy. The local surface curvature can significantly modify the local charge distribution and alter the particle-particle interactions. To provide statistical parameterization of this interaction, we systematically study the electrostatic force between a pair of generic rough particles with different roughness feature sizes and relative orientations. This framework will potentially help to understand the complex interplay between roughness and electrostatic interactions for both highly jagged and charged lunar regolith particles and the irregular biomass particles that are triboelectrically charged in gasification process. |
Monday, March 14, 2022 2:06PM - 2:18PM |
B09.00012: Robotic Folding of Sheets with a Mechanics-based Approach Mohammad Khalid Jawed, Dezhong Tong We report a mechanics-based approach for automatic folding of elastic sheets, e.g., rectangular towel. When manipulating deformable objects, robots must account for the deformation, which is often large and geometrically nonlinear. Challenges arise because the manipulation scheme should depend on the intrinsic properties (e.g., material and geometry) of the manipulated objects and environmental parameters (e.g., friction). We demonstrate that incorporating the mechanics of materials can improve the performance of robotic manipulation. A seemingly simple problem of folding a flexible sheet (e.g., a rectangular towel) into multiple layers is studied. A numerical simulation tool based on discrete differential geometry is used to model the folding process. We analyze the folding process with the numerical tool to compute the optimal trajectory of the robotic manipulator that is robust against friction of the surface and jittering of the manipulator. Simple energy scaling shows that a single parameter - the gravito-bending length – governs the folding process. The trajectories are implemented on a collaborative robot. Our experiments show that, even without any feedback control, the robot can fold sheets made of different materials into multiple layers. Compared with a mechanics-agnostic approach, the improvement in performance is demonstrated. |
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