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 Y01: Mechanics of Granular Materials |
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Sponsoring Units: GSNP DSOFT DFD Chair: Joseph Monti, Sandia National Laboratories Room: Room 124 |
Friday, March 10, 2023 8:00AM - 8:12AM |
Y01.00001: Using Good Vibrations: Melting and Controlled Shear Jamming of Dense Granular Suspensions Chloé Garat Flows of suspensions can be blocked when the suspended particles are densely packed. This makes their formulation and their transport challenging in the industry. Our work focus on the impact of vibrations on the behavior of dense granular suspensions prepared at volume fraction above their jamming volume fraction, but below the particle assembly random close packing. Vibrations are shown to have a strong effect on their rheological properties and to tune their transition from solid-like to liquid-like behavior. We study suspensions of rough silica particles in a Newtonian fluid. In the absence of vibrations, they have a solid-like behavior: they flow only above a yield stress. Particles are confined by the liquid interface and the yield stress is of frictional origin. When vibrations are applied, the yield stress vanishes to give rise to a liquid-like pseudo-Newtonian behavior at low shear rate. Using shear-reversal experiments, we show that these liquid-like vibrated suspensions of frictional particles behave like nonvibrated suspensions of frictionless particles. As the shear rate is increased, we observe a shear thickening of the vibrated suspensions, eventually leading to shearjamming: the yield stress behavior is recovered and vibrations have no more impact. We show that this shear thickening can be tuned by changing the vibration energy injected into the system. We finally propose a physical picture based on the competition between contact opening by vibration and contact formation by shear to account for these behaviors. In the framework of the Wyart and Cates (2014) model, vibrations can be seen as introducing a thermal-like repulsive force, yielding a critical stress proportional to the vibration stress introduced by Hanotin et al. (2015). |
Friday, March 10, 2023 8:12AM - 8:24AM |
Y01.00002: The collapse of a granular raft under bi-axial compression Ranit Mukherjee, Benjamin Druecke, Xiang Cheng, Sungyon Lee Granular particles can self-assemble on a liquid interface via capillary attraction, even if they are denser than either liquid. Here, we show two distinct failure modes of granular rafts without a free periphery when they are subjected to a quasi-static bi-axial compression. For smaller particles, the rafts fail by expulsion of individual particles from the interface, whereas the failure is via collective creasing of the entire interface for larger particles. We performed systematic experiments with different particle wettability, diameter, liquid density, and surface tension and mapped a phase diagram of raft failure modes. We found that the creasing can be suppressed by either increasing the density difference between the liquids or decreasing the interfacial tension. This latter observation is counter-intuitive since the weight of the rafts in our system is balanced by the hydrostatic pressure due to liquid displacement rather than interfacial tension. A transient failure mode, intermediate to creasing and single-particle expulsion, is also observed during gradual addition of surfactant in the heavier liquid. Taken together, our study provides new insights on the unusual dynamics of fluid interfaces laden with a monolayer of granular particles. |
Friday, March 10, 2023 8:24AM - 8:36AM |
Y01.00003: Particle induced lubrication during the flow of a granular material Ravindra S Ghodake, Ashish V Orpe, Pankaj Doshi We have studied the flow behavior of a granular material by coating the surface of individual particles in the material with very tiny, frictionless, lubricant particles. Gravity driven flow of such lubricant coated granular material was initiated on an inclined chute for different concentrations of the lubricant employed. Experiments were performed for a fixed particle size and constant inclination and inlet gate opening of the chute while varying the lubricant concentration (weight ratio of $10^{-5}$ to $10^{-3}$). The measured volumetric flow rate was observed to exhibit a non-monotonic behavior with increasing lubricant concentration. The flow rate initially increased for small enough lubricant concentration and subsequently decreased at much larger lubricant concentration. The increase in flow rate was attributed to the reduced inter-particle friction while the decrease resulted due to damping of the inter-particle collisions caused by excessive coating of the lubricant thereby reducing the inter-particle momentum transfer. We conjecture that the non-monotonicity arises from the relative dominance between inter-particle friction and collision which is altered with respect to lubricant concentration employed. The overall observed behavior suggests an alternative, yet simple, method to characterize the effect of inter-particle interactions on the granular flow behavior. |
Friday, March 10, 2023 8:36AM - 8:48AM |
Y01.00004: The odd weight of grains: Anomalous Janssen effect in narrow granular columns Ramon Planet, Caleb J Anderson, Iker Zamorano, Bernat Argelich, Alberto Fernandez-Nieves Granular matter exhibits unusual mechanical properties. For instance, when filling a cylindrical column with grains the weight measured at the bottom of the column does not scales linearly with the added mass, but asymptotically saturates towards a constant "apparent" weight. This observation is the well-known Janssen effect, and the "lost weight" is supported by frictional forces between the grains and the column wall. Here, we present an experimental study addressing the mechanical behavior of static granular packings confined within a narrow vertical column: by reproducing the classical experiment designed by Janssen in 1895 but using narrower columns, we observe a reverse Janssen effect whereby the fraction of the weight supported by the base overcomes one. |
Friday, March 10, 2023 8:48AM - 9:00AM |
Y01.00005: Simulating soft granular silo flow in varying gravity Abigail Tadlock, Kerstin Nordstrom We present results of LAMMPS Molecular Dynamics simulations of 2D gravity-driven flows of ~30,000 soft uniform spheres through a vertical silo. We vary the gravitational field (g), elastic modulus of the particles (E), and silo outlet diameter (D) and measure the effects on mass flow rate, flow profiles, and microscale metrics such as granular temperature, looking in particular at the approach to clogging. We find a dimensionless combination of g, E, particle density ρ, and particle diameter pd rescales the data for some measurements. We find the Beverloo equation describes the bulk flow many trials, but fails at extreme conditions. We also observe interesting pressure waves in the system. |
Friday, March 10, 2023 9:00AM - 9:12AM Author not Attending |
Y01.00006: Granular Rod Flows Leo E Silbert, Imane Bahji Motion down a frictional, inclined plane is a classic example presented in first year physics classes, yet the concept serves as a standard method to study the flow of granular materials. A parameter of interest remains the inclination angle at which a flowing system comes to rest, also known as the angle of repose, or the friction angle. For a block on an incline, the angle of repose is related to the static friction coefficient that can be readily derived. However, for more industrially relevant situations and materials, both particle shape and friction properties affect the angle of repose. Sometimes these relations follow standard reasoning: for example, the angle of reponse for monodisperse spheres of larger surface friction lies at circa 20o, whereas smoother particles stop flowing at much lower angles. While for particles with aspect ratios different from unity, the angle of repose will typically increase, as is the case of granular rods. Here we explore how the properties of a granular rod, namely it's aspect ratio and surface roughness, influence the angle of reponse for systems of varying size, flowing down an inclined plane, using the discrete element method, that is fully accessible to students at any level. |
Friday, March 10, 2023 9:12AM - 9:24AM |
Y01.00007: The astonishing behavior of non-convex grains in granular shear experiments Ralf Stannarius, Mahdieh Mohammadi, Ahmed Ashour, Dmitry Puzyrev, Torsten Trittel Granular material composed of regular tetrapods and hexapods is exposed to continuous shear in a split-bottom shear cell. We observe the generation of a secondary convective flow which is astonishingly opposite to that previously observed with cylinders and ellipsoids. The convective flow drags the particles at the surface towards the rotation center, where it is pulled downward, leaving a dimple in the center. The details of this phenomenon are extremely sensitive to the particle geometry and the height of the granular bed. We propose a hypothesis that explains this behavior qualitatively. |
Friday, March 10, 2023 9:24AM - 9:36AM |
Y01.00008: Rotation and translation dynamics in a granular gas of rough spheres in microgravity Kirsten Harth, Torsten Trittel, Dmitry Puzyrev, Ralf Stannarius Granular gases are dilute ensembles of grains, interacting only in rare collision events, where energy is dissipated. Their collective dynamics have been studied analytically and numerically in numerous publications. One striking scenario is granular cooling, the decay of kinetic energy from an initially agitated state, originally modeled by P. Haff in1983 [1]. Experimental proof of the scaling laws was achieved only recently in 3D ensembles in microgravity [2,3]. It revealed striking quantitative disagreement with theory and previous simulations. One question concerns the role of particle rotations. For rods, rotaions around the short axis can be easily excited without friction, and those have been evaluated [2]. The purely frictionally or contact asymmetry excited rotation of spheres has previously not been addressed, for technical reasons. This is the |
Friday, March 10, 2023 9:36AM - 9:48AM |
Y01.00009: Granular shear jamming with fixed pinning sites Brian Utter, Diana Phommavanh, Christopher Mastandrea, Cacey S Bester, Katharina Vollmayr-Lee, Amy L Graves The rheology of granular media is characterized in part by shear jamming, in which shearing of collections of individual grains under confinement leads to a transition from fluid-like to solid-like behavior. Such systems are driven by the boundaries and exhibit anisotropic force networks and history-dependent behavior. Here we experimentally investigate planar shear of an athermal, granular system with small pins inserted within the shearing zone which act as fixed obstacles within the bulk. We use photoelastic grains to visualize the stress networks and particle tracking to characterize particle locations and kinematics. We characterize the mean flow and stress response when small numbers of pinning sites are present in the system. We find that these pins can act as additional supports to stabilize the stress network and enhance anisotropy based on their arrangement. Such experiments represent a step to exploring the effects of pinning lattices which may offer a route to tunable granular rheology. |
Friday, March 10, 2023 9:48AM - 10:00AM |
Y01.00010: Local and global measures of the shear modulus of jammed packings Weiwei Jin, Shiyun Zhang, Jerry Zhang, Mark D Shattuck, Corey S O'Hern When the shape of the bounding box is controlled to generate jammed particle packings using isotropic compression, they can be stabilized with positive, as well as negative shear moduli. We carry out computational studies of jammed disk packings using isotropic compression, while fixing the shape of the bounding box under periodic boundary conditions. We first measure the ensemble-averaged shear modulus, <Gtot> = <G+ − |G−|> as a function of the pressure p, where G+ and |G–| are the contributions from configurations with positive and negative shear moduli, respectively. We show that <G+> and <|G−|> obey different scaling relations with pressure above and below pN2∼1, where N is the system size. For pN2 < 1, <|G−|> ∼ p and <G+> − G0 ∼ p0.7. In contrast, for pN2 > 1, both <G+> and <|G−|> ∼ p1/2. We calculate the probability distribution of shear moduli P(Gtot), and show that it varies from a gamma distribution with shape parameter k = 1/2 for pN2 « 1 to a left-skewed Gaussian distribution for pN2 » 1. We also investigated the local shear moduli of the jammed packings, where the local strain is determined by the strain tensor of Delaunay triangles constructed from the disk centers. We show that the spatial correlations of the local shear moduli decrease with decreasing pressure. In addition, the local shear moduli can be negative even when Gtot > 0. We further show that it is unnecessary to remove jammed configurations with negative shear moduli from the ensemble to obtain a correspondence between an ensemble average and a spatial average in large systems. |
Friday, March 10, 2023 10:00AM - 10:12AM |
Y01.00011: Statistics Predict Random Circle Packing David Meer, Eric R Weeks The densest amorphous packing of rigid particles is known as random close packing (RCP). If you pack with a mixture of circle sizes, you can attain highly dense packing fractions. Mixtures of different sized circles are described by the probability distribution function (PDF) of circle radii. Previous results from our lab in 3D packing find the polydispersity and skewness of the underlying PDF determine the packing fractions of spheres. We find analogous results in 2D, that there is some function of polydispersity and skewness that determines the RCP packing fraction. In addition, 2D packings can spontaneously pack hexagonally, which requires introducing an additional PDF-dependent parameter to predict such non-random behavior. In this talk, we present the general formula for the density of random packed circles from their PDFs, and the theoretical underpinnings of the formula. |
Friday, March 10, 2023 10:12AM - 10:24AM |
Y01.00012: Sailing Leidenfrost droplets on superheated granular layer Binh T Nguyen, Tuan A Tran, Dongdong Liu, Vu N Nguyen A droplet deposited on a superheated granular layer may sail away from the deposited position. We characterize the sailing motion for a wide range of particle sizes and liquid properties. We provide a theoretical model to explain the sailing motion based on instability of pressure distribution at the bottom of the droplet and experimental verification of the model. |
Friday, March 10, 2023 10:24AM - 10:36AM |
Y01.00013: In-Situ Measurements of Stress Fluctuations and Kinematics in Triaxial Tests Ryan C Hurley, Ghassan Shahin, Ye Tian, Edward Ando, Øyvind Torgersrud, Eleni Stavropoulou, Andrew King A triaxial test on a granular material is a classical “elemental” test in geomechanics. Geomechanics researchers have increasingly acknowledged that these tests are not elemental, but in fact boundary value problems accompanied by complex grain-scale behaviors including localization and breakage. With the goal of elucidating these complex grain-scale behaviors and their connection to macroscale plasticity, we recently developed a novel triaxial compression apparatus. Our apparatus permits in-situ grain-resolved x-ray tomography for grain structure and breakage and 3D x-ray diffraction for grain stress tensors. The apparatus can uniquely be used to study sand samples as small as 1 mm diameter by 2 mm tall (containing about 1000 grains of Ottawa sand) and as large as 15 mm diameter by 30 mm tall (containing over 50000 grains of Ottawa sand). Here, we report uses of this apparatus at laboratory and synchrotron x-ray facilities to study the micromechanics of sand undergoing large strains (>30% in shear bands, 15% axially). Samples contain over 30000 sand grains, with shear bands engaging approximately 10000 grains – the largest known experiments to-date with in-situ x-ray tomography and 3D x-ray diffraction measurements. We report grain-resolved kinematics and, most importantly, stress and force fluctuations in and out of shear bands. Our results address important questions in geomechanics, such as principal stress rotations in shear bands, and important questions in granular physics, such as the nature of kinematic, stress, and force fluctuations in shear flows. |
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