Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session G01: Non-Equilibrium and Transient Mechanics of Granular and Soft Materials IFocus
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Sponsoring Units: GSNP DSOFT DFD Chair: Ishan Srivastava, Lawrence Berkeley National Laboratory Room: Room 124 |
Tuesday, March 7, 2023 11:30AM - 11:42AM Author not Attending |
G01.00001: Average outpouring velocity and flow rate of grains discharged from a tilted quasi-2D silo Ryan H Kozlowski, Jon C Luketich, Elijah Oshatz, Douglas J Durian, Luis A Pugnaloni The flow of granular materials through constricted openings is important in many natural and industrial processes. These complex flows – featuring dense, dissipative flow in the bulk but low-dissipation, low density outpouring in the vicinity of the orifice – have long been characterized empirically by the Beverloo rule and, recently, modeled successfully using energy balance [J. R. Darias, et. al., Phys. Rev. E 101, 052905 (2020)]. The dependence of flow rate on the silo's angle with respect to gravity, however, is not captured by current models. We experimentally investigate the role of tilt angle in this work using a quasi-2D monolayer of grains in a silo. We measure mass flow rate, the average exit velocities of grains, and the packing fraction along the orifice with varying tilt angles. We propose a model that describes our results (and findings with 3D systems [H. G. Sheldon and D. J. Durian, Granul. Matter 12, 579 (2010)]) by considering the dependence of outpouring speed and angle with respect to the orifice angle and, importantly, the angle of stagnant zones adjacent to the orifice. We conclude by posing questions about possible extensions of our model in order to describe spatial variations of exit velocity and density along the orifice. |
Tuesday, March 7, 2023 11:42AM - 11:54AM |
G01.00002: Properties of 3D arches in a clogged hopper of soft deformable particles. Rahul Pandare, Corey S O'Hern, Eric R Weeks, Mark D Shattuck We study arches that form during clogging in a 3D system of soft hydrogel particles (bulk modulus 10-30 kPa) in water flowing through a square cross-section tube with a circular outlet. The particles are dyed with a fluorescent dye and a laser sheet is used to locate the particles in 3D when the system clogs. The tube's dimensions are 7.62 cm x 7.62 cm x 25.4 cm. The mean particle diameter is 1.46 cm. We vary the total number of particles from 80-125 and the diameter of the outlet from 2-3.5 cm. We measure the clogging probability, and the 3D particle positions in the clog to identify 3D arches. We find that the number of particles in the clogged arch depends on the width of the orifice and the number of particles. |
Tuesday, March 7, 2023 11:54AM - 12:06PM |
G01.00003: Deformation of a soft, acoustically-bound granular solid under applied stress Nina M Brown, Bryan VanSaders, Heinrich M Jaeger Mesoscale particles can be levitated in an ultrasonic standing wave, in which acoustic scattering produces attractive interparticle forces that cause these particles to self-assemble into quasi-two-dimensional rafts. Previously, indirect methods have been used to investigate mechanical properties of this cohesive granular material by modeling a stochastically rotating raft as a liquid droplet.[1] This material, however, can also be viewed as a soft, semicrystalline solid. By using custom probes to carefully modify the acoustic field near a sample, we perform micromechanical tests on this material, such as tensile testing. We observe millimeter-sized rafts deform under applied stresses of just tens of Pa. We measure forces on the μN scale with a thin cantilever and can examine elastic and plastic deformation at the scale of individual particles. Prior work on this athermal system has found that the material's properties can depend significantly on sample size.[1] This implies that the binding potential exhibits many-body effects, a phenomenon which is investigated here through direct mechanical testing. |
Tuesday, March 7, 2023 12:06PM - 12:42PM |
G01.00004: Stress and velocity fluctuations to probe the rheology of photoelastic granular avalanches Invited Speaker: Nathalie M Vriend Granular fluidity has been central to the development of non-local constitutive equations, which are necessary for characterizing non-local effects observed in experimental granular flow data. However, validation of these equations has been largely computational, due to challenges in conducting precise laboratory experiments. In this presentation, we are introducing our photoelastic avalanche experiment, which does not only produce intriguing visuals, but also reveal the internal stress state of our 2D granular avalanches. We explore the role of velocity and stress fluctuations on the rheology of granular avalanches, and show that they could form a predictor of the stability of the internal state of a granular packing. |
Tuesday, March 7, 2023 12:42PM - 12:54PM |
G01.00005: Visualizing force chains in clogged silos Benjamin McMillan, Alban Sauret, Nathalie M Vriend Despite the importance of clogging of particles in a multitude of industrial processes and natural systems, our understanding of why and how materials clog is relatively poor. Specifically, we consider clogging by the formation of stable arches at silo openings; our insight into the precursors and mitigation measures of these clogs is currently limited. By performing experiments using photoelastic techniques on particles in a hopper setup, we are able to analyse clogging events of two-dimensional dry granular materials. The distribution of forces is precisely monitored at the silo output and surrounding areas, allowing us to witness what occurs before, during, and after clogging. With high temporal and spatial resolution, we quantitatively investigate patterns in the force network that precede clogging events and see how the residual forces impact the probability of subsequent clogs. This development in our understanding of the role of force networks in clogging could enable us to predict more effectively when clogs will occur. |
Tuesday, March 7, 2023 12:54PM - 1:06PM |
G01.00006: Granular flow near shear jamming Joel T Clemmer, Ishan Srivastava, Gary S Grest, Jeremy B Lechman Dense granular materials flow when driven above a critical shear stress. Near this limit, the system deforms at a near-quasistatic strain rate and the flow profile exhibits spatial inhomogeneities. Flow is characterized by intermittent bursts of particle rearrangement and finite-sized systems are prone to find a jammed state and arrest right above the critical shear stress. We use a discrete element model of frictional grains to explore this limit using a combination of stress and strain-rate controls. By tracking the spatial-temporal rearrangement of grains and the approach to arrest, we characterize how these behaviors depend on the size of the system. |
Tuesday, March 7, 2023 1:06PM - 1:18PM |
G01.00007: Discontinuous rigidity transition associated with shear jamming in granular simulations Srikanth Sastry, varghese babu, H. A Vinutha, Dapeng Bi The rigidity transition associated with isotropic and shear jamming have in the past been investigated through the analysis of constraints. Whereas the transition is discontinuous for isotropic jamming, with the sudden percolation of a rigid contact network when the isostatic condition is crossed, previous work has suggested that the transition is more continuous in the case of shear jamming of frictional grain assemblies. To understand better this apparent difference, we investigate the rigidity transition associated with shear jamming in frictional, as well as frictionless disk packings [1,2] in the quasi-static regime and at low shear rates. We find that while the transition appears continuous for finite shear rates, it is sharper for lower shear rates, and with quasi-static shearing the transition is discontinuous with an instantaneous emergence of a system spanning rigid cluster at the transition. We also show that the same picture holds for frictionless shear jamming at high densities under quasi-static shearing. Thus, our results suggest that the rigidity transition associated with shear jamming in both frictional and frictionless packings is discontinuous, and therefore similar to the transition for isotropic jamming. |
Tuesday, March 7, 2023 1:18PM - 1:30PM |
G01.00008: Frictional weakening of vibrated granular flows Abe Clark, Emily Brodsky, Stephanie E Taylor, John Nasrin We computationally study the frictional properties of sheared granular media subjected to harmonic vibration applied at the boundary. Such vibrations are thought to play an important role in weakening flows, yet the independent effects of amplitude, frequency, and pressure on the process have remained unclear. Based on a dimensional analysis and DEM simulations, we show that weakening requires that the absolute amplitude of the displacement is sufficiently large relative to the grain size in addition to sufficiently high acceleration. The analysis in terms of normalized amplitude, frequency and pressure combined provides a basis for predicting flows in more complex geometries subjected to arbitrary external vibration. |
Tuesday, March 7, 2023 1:30PM - 1:42PM |
G01.00009: Rheology of dense granular binary mixtures Joseph M Monti, Andrew Santos, Joel T Clemmer, Ishan Srivastava, Gary S Grest, Jeremy B Lechman Dry flow of monodisperse granular systems has enjoyed a rich history of investigation, but the rheological properties of binary mixtures with strong size dispersity are still poorly understood. Here, we perform discrete element modeling simulations with frictionless inter-particle interactions to study dry granular flow of binary mixtures under simple shear in the small inertial number regime. Spherical particles with particle size ratios of up to 16 are considered. We compute the shear stress ratio during steady flow as a function of the particle size ratio and fraction of small particles, and compare our results with identically parametrized monodisperse granular flows. Intriguing variations in the rheology for systematic variations in particle size ratios and small particle volume fractions are examined from microstructural analysis of the coordination number, volume fraction, and the stress partitioning between particles of separate size classes. |
Tuesday, March 7, 2023 1:42PM - 1:54PM |
G01.00010: Changing granular flows and impact dynamics with negative Poisson's ratio grains Daan Haver Granular materials are known to have the unique property of being able to act both as a solid when jammed and as a liquid when unjammed. Due to dilation, it is generally difficult to unjam a jammed packing by applying simple shear. Here, we introduce a negative Poisson's ratio to all the individual grains. A packing of auxetic grains is observed to locally generate some freedom to move and reduce the occurrence of force chains upon compaction due to their radial size reduction. This size reduction leads to a sharp decrease in yield stress when sheared and distinctive unclogging behaviour when obstructed in a hopper configuration. When impacted by a circular object, part of the kinetic energy is shown to be absorbed and returned elastically, causing the packing to heal inflicted damage. |
Tuesday, March 7, 2023 1:54PM - 2:06PM |
G01.00011: Discrete Element and Continuum Modeling of Secondary Flows in Dense Granular Materials Ishan Srivastava, Eunji Yoo, Ann S Almgren, John B Bell We investigate secondary flows in the flow of dense granular materials across several geometries such as flows through non-axisymmetric channels. Using discrete element method simulations, we demonstrate the existence of weak secondary vortical flows in a direction perpendicular to the primary flow in such geometries. We explain the existence of these secondary flows based on a second-order rheological model that incorporates viscometric functions such as the normal stress differences. We implement the frame-invariant rheological model in an incompressible continuum flow solver and demonstrate good agreement between the predictions of velocity and stress fields by the continuum solver and the corresponding coarse-grained fields obtained from simulations using the discrete element method. |
Tuesday, March 7, 2023 2:06PM - 2:18PM |
G01.00012: Understanding the Acoustics of Marine Sediments using Granular Mechanics Andrew J Swartz, Abe Clark, So Bing Phua, Derek Olson Understanding and predicting the acoustic behavior of water-saturated marine sediments (e.g., on the ocean floor) represents a fundamental technology issue for underwater sensing, navigation, and communication. Large collections of data collected from experiments and field measurements show a clear dependence on frequency for both the attenuation coefficient and acoustic wave speed. Existing theories can be fit to these data, but only by invoking multiple physical mechanisms involving parameter values that cannot be measured in situ. Here we focus on losses due to an inelastic component of normal compression at grain-grain contacts. This mechanism, although well established in granular mechanics, is not included in the existing models of sediment acoustics. Using theoretical analysis and DEM simulations, we show that this granular mechanics perspective, where forces are transmitted along lossy force chains, may be able to explain salient features of the acoustic properties of marine sediments |
Tuesday, March 7, 2023 2:18PM - 2:30PM |
G01.00013: Erosion by the unsteady motion of a disk close to a granular bed Joanne Steiner, Cyprien Morize, Ivan Delbende, Alban Sauret, Philippe Gondret Flatfish, such as flounders, bury themselves in the sand to hide from predators. They are able to hide very quickly : with a few oscillations of their fins close to the seabed, they suspend sand, which then falls onto their body. This study aims at better understanding this natural behaviour by simplifying it in the laboratory. To do so, a rigid disk of diameter D replicates the behaviour of the flatfish : the disk can oscillate at a frequency f and an amplitude L/2 at a minimum distance h0 from a flat granular bed. |
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