Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session B43: Avalanches in Granular and Other Particle-based Materials IIFocus
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Sponsoring Units: GSNP GSOFT Chair: Bob Behringer, Duke University Room: 346 |
Monday, March 14, 2016 11:15AM - 11:51AM |
B43.00001: Global and local avalanches in cohesive and non cohesive granular material: crackling and seismicity Invited Speaker: Jonathan Bares Commonly, granular materials yield or flow if sufficiently large stress is applied, leading to avalanche-like behavior. For experimentally wedge split cohesive granular material and sheared 2D and 3D grains, we seek to understand the dynamics of these burst of activity from the local to the global scale. Whether the system rearranges locally like in the case of a fracture front propagating in a cohesive material or in the whole system like in the case of sheared granular medium, similar free scale statistics are observed for the intensity of the rearrangements. We present first an experimental setup that allows growing well-controlled tensile cracks in brittle heterogeneous solids of tunable microstructure. Also, force networks and displacement fields are measured both on two and three-dimensional sheared material for cyclically sheared photoelastic and hydrogel particles. Avalanches, their size, location and duration are extracted at the global scale from the rapid variation of the stored energy whereas at the local scale they are measured form the energy drop, displacement and acoustic activity. Statistics of those different quantities are computed and correlated to test their intrinsic entanglement and analyze their universal dynamics. [Preview Abstract] |
Monday, March 14, 2016 11:51AM - 12:03PM |
B43.00002: Experimental Avalanches in a Rotating Drum. Aline Hubard, Corey O'Hern, Mark Shattuck We address the question of universality in granular avalanches and the system size effects on it. We set up an experiment made from a quasi-two-dimensional rotating drum half-filled with a monolayer of stainless-steel spheres. We measure the size of the avalanches created by the increased gravitational stress on the pile as we quasi-statically rotate the drum. We find two kinds of avalanches determined by the drum size. The size and duration distributions of the avalanches that do not span the whole system follow a power law and the avalanche shapes are self-similar and nearly parabolic.~ The distributions of the avalanches that span the whole system are limited by the maximal amount of potential energy stored in the system at the moment of the avalanche. [Preview Abstract] |
Monday, March 14, 2016 12:03PM - 12:15PM |
B43.00003: Stability of Granular Packings Jammed under Gravity: Avalanches and Unjamming Carl Merrigan, Sumit Birwa, Shubha Tewari, Bulbul Chakraborty Granular avalanches indicate the sudden destabilization of a jammed state due to a perturbation. We propose that the perturbation needed depends on the entire force network of the jammed configuration. Some networks are stable, while others are fragile, leading to the unpredictability of avalanches. To test this claim, we simulated an ensemble of jammed states in a hopper using LAMMPS. These simulations were motivated by experiments with vibrated hoppers where the unjamming times followed power-law distributions\footnote{Lozano, C., Zuriguel, I., Garcimartín, A. (2015). Stability of clogging arches in a silo submitted to vertical vibrations. Physical Review E, 91(6), 062203.}. We compare the force networks for these simulated states with respect to their overall stability. The states are classified by how long they remain stable when subject to continuous vibrations. We characterize the force networks through both their real space geometry and representations in the associated force-tile space \footnote{Sarkar, S., Bi, D., Zhang, J., Behringer, R. P., Chakraborty, B. (2013). Origin of rigidity in dry granular solids. Physical review letters, 111(6), 068301.}, extending this tool to jammed states with body forces. [Preview Abstract] |
Monday, March 14, 2016 12:15PM - 12:27PM |
B43.00004: Structure of jammed configurations and their relation to unjamming times Sumit Kumar Birwa, Carl Merrigan, Bulbul Chakraborty, Shubha Tewari The distribution of the times for the cessation of flow of grains falling under gravity in a vertical hopper is known to be exponential. Recent experiments have shown, however, that the time lapse between avalanches follows a power-law distribution when the hopper is unjammed using periodic vertical vibrations\footnote{I. Zuriguel et al., Scientific reports 4, 7324 (2014).}. The reasons for this distribution of the unjamming times, which indicates the time needed for an applied continuous perturbation to induce another avalanche, are not well understood. We report on a numerical simulation of granular hopper flow using LAMMPS\footnote{http://lammps.sandia.gov/} in which we seek to understand the origin and scope of this behavior. We find that cessation of flow is related to the formation of a stable arch that spans the system. However, the actual structure of the jammed configuration varies and is closely related to the unjamming time. We find that the symmetry of the arches is an important parameter in determining the strength of the jammed configurations. Using different force thresholds, we have characterized the contact networks around the arches which provides stability to the packed structure and analyzed the strength of various jammed configurations. [Preview Abstract] |
Monday, March 14, 2016 12:27PM - 12:39PM |
B43.00005: Intermittent Flow of Granular Matter in an Annular Geometry Ted Brzinski, Karen E. Daniels Granular solids can be subjected to a finite stress below which the response is elastic. Above this yield stress, however, the material fails catastrophically, undergoing a rapid plastic deformation. In the case of a monotonically increasing stress the material exhibits a characteristic stick-slip response. We investigate the statistics of this intermittent failure in an annular shear geometry, driven with a linear-ramp torque in order to generate the stick-slip behavior. The apparatus is designed to allow visual access to particle trajectories and inter-particle forces (through the use of photoelastic materials). Additionally, twelve piezoelectric sensors at the outer wall measure acoustic emissions due to the plastic deformation of the material. We vary volume fraction, and use both fixed and deformable boundaries. We measure how the distribution of slip size and duration are related to the bulk properties of the packing, and compare to systems with similar governing statistics. [Preview Abstract] |
Monday, March 14, 2016 12:39PM - 12:51PM |
B43.00006: Effect of interstitial fluid on event-size distribution for granular hoppers. Juha Koivisto, Douglas Durian The discharge of granular hoppers is avalanche-like in that flow proceeds until probabilistically interrupted by the formation of a stable arch over the hole. The average event size appears to diverge at a critical hole size, thus defining a putative clogging transition. However, we now believe that instead it grows exponentially as a power of the hole diameter, so in fact all hoppers are susceptible to clogging\footnote{C.C. Thomas et al., Phys. Rev. Lett. 114, 178001 (2015).}. To investigate the influence of grain dynamics on arch formation, we conducted a series of experiments where the event size distribution was measured for grains in a system that was totally submerged in water. We find that the distribution is exponential, just as for dry non-cohesive grains in air. However, for a given hole the number of grains in the average event decreases roughly with a factor of two, and the critical hole size increases by 10\%. Thus, submerged hoppers are more susceptible to clogging and dynamics play a role. In air, the ``effective temperature" set by rms grain speed helps to prevent arch formation. [Preview Abstract] |
Monday, March 14, 2016 12:51PM - 1:03PM |
B43.00007: Non-local rheology for dense granular flows in avalanches Adrien Izzet, Eric Clement, Bruno Andreotti A local constitutive relation was proposed to describe dense granular flows (GDR MiDi, EPJE 2004). It provides a rather good prediction of the flowing regime but does not foresee the existence of a “creep regime” as observed by Komatsu et al. (PRL 2001). In the context of a 2D shear cell, a relaxation length for the velocity profile was measured (Bouzid et al., PRL 2013) which confirmed the existence of a flow below the standard Coulomb yield threshold. A correction for the local rheology was proposed. To test further this non-local constitutive relation, we built an inclined narrow channel within which we monitor the flow from the side. We managed to observe the “creep regime” over five orders of magnitude in velocity and fit the velocity profiles in the depth with an asymptotic solution of the non-local equation. However, the boundary condition at the free surface needs to be selected in order to calibrate the non-local rheology over the whole range of stresses in the system. In this perspective, we complement the experimental results with 2D simulations of hard and frictional discs on an inclined plane in which we introduce a surface friction force proportional to the effective pressure in the granular. We analyze these results in the light of the non-local rheology. [Preview Abstract] |
Monday, March 14, 2016 1:03PM - 1:15PM |
B43.00008: Jamming and chaotic dynamics in different granular systems Homayoon Maghsoodi, Erik Luijten Although common in nature and industry, the jamming transition has long eluded a concrete, mechanistic explanation. Recently, Banigan \textit{et al.} (Nat. Phys. \textbf{9}, 288--292, 2013) proposed a method for characterizing this transition in a granular system in terms of the system's chaotic properties, as quantified by the largest Lyapunov exponent. They demonstrated that in a two-dimensional shear cell the jamming transition coincides with the bulk density at which the system's largest Lyapunov exponent changes sign, indicating a transition between chaotic and non-chaotic regimes. To examine the applicability of this observation to realistic granular systems, we study a model that includes frictional forces within an expanded phase space. Furthermore, we test the generality of the relation between chaos and jamming by investigating the relationship between jamming and the chaotic properties of several other granular systems, notably sheared systems (Howell, D., Behringer R. P., Veje C., Phys. Rev. Lett. \textbf{82}, 5241--5244, 1999) and systems with a free boundary. Finally, we quantify correlations between the largest Lyapunov vector and collective rearrangements of the system to demonstrate the predictive capabilities enabled by adopting this perspective of jamming. [Preview Abstract] |
Monday, March 14, 2016 1:15PM - 1:27PM |
B43.00009: 3D imaging of particle-scale rotational motion in cyclically driven granular flows Matt Harrington, Dylan Powers, Eric Cooper, Wolfgang Losert Recent experimental advances have enabled three-dimensional (3D) imaging of motion, structure, and failure within granular systems. 3D imaging allows researchers to directly characterize bulk behaviors that arise from particle- and meso-scale features. For instance, segregation of a bidisperse system of spheres under cyclic shear can originate from microscopic irreversibilities and the development of convective secondary flows. Rotational motion and frictional rotational coupling, meanwhile, have been less explored in such experimental 3D systems, especially under cyclic forcing. In particular, relative amounts of sliding and/or rolling between pairs of contacting grains could influence the reversibility of both trajectories, in terms of both position and orientation. In this work, we apply the Refractive Index Matched Scanning technique to a granular system that is cyclically driven and measure both translational and rotational motion of individual grains. We relate measured rotational motion to resulting shear bands and convective flows, further indicating the degree to which pairs and neighborhoods of grains collectively rotate. [Preview Abstract] |
Monday, March 14, 2016 1:27PM - 1:39PM |
B43.00010: Characterizing local forces and rearrangements inside a gravity-driven granular flow Emma Thackray, Kerstin Nordstrom While the gravity-driven flow of a granular material in a silo geometry can be modeled by the Beverloo equation, the mesoscale-level particle rearrangements and interactions that drive this flow are not well-understood. We have constructed a quasi-two-dimensional system of bidisperse, millimeter-scale disks with photoelastic properties that make force networks within the material visible. The system is contained in an acrylic box with an adjustable bottom opening. We can approach the clogging transition by adjusting this opening and by adding external forcing to the top of the flowing pile. By placing the system between cross-polarizers, we can obtain high-speed video of this system during flow, and extract intensity signals that can be used to identify and quantify localized, otherwise indeterminate forces. We can simultaneously track individual particle motions, which can be used to identify shear transformation zones in the system. We are therefore able to correlate local forces with rearrangements within the system, and characterize the evolution of this interplay on the approach to the clogging transition. [Preview Abstract] |
Monday, March 14, 2016 1:39PM - 1:51PM |
B43.00011: Dynamic structural network evolution in compressed granular systems. Lia Papadopoulos, James Puckett, Karen Daniels, Danielle Bassett The heterogeneous dynamic behavior of granular packings under shear or compression is not well-understood. In this study, we use novel techniques from network science to investigate the structural evolution that occurs in compressed granular systems. Specifically, we treat particles as network nodes, and pressure-dependent forces between particles as layer-specific network edges. Then, we use a generalization of community detection methods to multilayer networks, and develop quantitative measures that characterize changes in the architecture of the force network as a function of pressure. We observe that branchlike domains reminiscent of force chains evolve differentially as pressure is applied: topological characteristics of these domains at rest predict their coalescence or dispersion under pressure. Our methods allow us to study the dynamics of mesoscale structure in granular systems, and provide a direct way to compare data from systems under different external conditions or with different physical makeup. [Preview Abstract] |
Monday, March 14, 2016 1:51PM - 2:03PM |
B43.00012: Self organization and shear-jamming in magnetic photoelastic particles Meredith Cox, Dong Wang, Jonathan Bares, Bob Behringer Many experimental studies of simple particles in granular systems have been conducted, but the behavior of complex particles in such systems has not been addressed. There has been a growing interest in functionalized microparticles, and the study of these complex particles may reveal interesting analogues between micro- and macroparticles. We perform experiments to investigate magnetic particles in a 2D granular material close to the jamming transition. We incrementally compress and shear photoelastic particles containing magnets and image the interparticle forces in each compression using a photoelastic technique. To track the orientation of individual particles, we draw UV-visible bars on each particle and image each compression of the system under ultraviolet light. We repeat the experimental procedure using varying ratios of magnetic to nonmagnetic particles from 0\% magnetic to 100\% magnetic. By using custom software to resolve particle deformations, we extract particle contact and pressure. [Preview Abstract] |
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