Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session S17: Avalanches and Rearrangements during Shear |
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Chair: Karen Daniels, North Carolina State University Room: 402 |
Thursday, March 6, 2014 8:00AM - 8:12AM |
S17.00001: Slip avalanches in granular systems under shear Dmitry Denisov, Karin Dahmen, Peter Schall We study the evolution of slowly sheared granular systems deforming via discrete strain bursts (slips). The granular sample consisting of 10$^{\mathrm{5}}$ hard spheres (mm-size) is subjected to applied shear and studied with the combination of two techniques -- precise stress-strain measurements and laser sheet imaging. Fluctuations in the stress-strain profile correspond to internal slip avalanches leading abrupt reconstructions in the system due to the shear. The magnitude of the fluctuations is taken as the size of the avalanche events. The power-law distribution of the slip sizes signifies the existence of the dynamically critical state in granular samples under the shear. Laser sheet imaging allows us to visualize each individual slip event, estimate its spatial distribution together with local strain change and connect it to the global fluctuation in the stress-strain curve. Such unique combination of the techniques and analysis lead us to comprehensive understanding of slip avalanches. [Preview Abstract] |
Thursday, March 6, 2014 8:12AM - 8:24AM |
S17.00002: On the stability of amorphous solid Jie Lin, Alaa Saade, Edan Lerner, Alberto Rosso, Matthieu Wyart The plasticity of amorphous material occurs via local plastic rearrangements, shear transformation zones(STZ). The elastic coupling between STZs can generate large-scale avalanches of plastic events. We study the stability condition of amorphous solid toward extensive avalanches. We argue that stability is controlled by the distribution $P(x)$ of the local stress increase $x$ that would lead to an instability. In particular stability requres that $P(x)\sim x^{\theta}$ where $\theta$ satisfies a lower bound. To investigate this, we use a elasto-plastic model based on two ingredients: local plastic events above microscopic stress, and the non-local elastic stress release generated by these plastic events. For a class of models of lond range interaction, $\theta$ is found to lie near saturation. For quadrupole interaction, the model yields $\theta\approx 0.6$ in 2D, and $\theta\approx 0.4$ in 3D. [Preview Abstract] |
Thursday, March 6, 2014 8:24AM - 8:36AM |
S17.00003: Laboratory Earthquakes: Granular Friction and Scaling Robert Ecke, Drew Geller, Sergiy Gerashchenko, Scott Backhaus Geological processes drive shear motion between tectonic plates over 10-100 km. The rupture gap, of order meters, contains granular matter - fault gouge - produced by the grinding motion of the plates over millennia. The complex behavior of natural earthquakes and the difficulty in making {\it in situ} measurements, has led to laboratory experiments that allow more control. We describe a laboratory experiment to model the physics of earthquakes that involves the interaction of continuum and granular behavior around a fault. Two photo-elastic plates confine about 3000 bi-disperse rods in a gap with a length-to-width ratio 50. The plates are held rigidly along their outer edges with one held fixed while the other is driven at constant speed at strain rates of $10^{-5}$/s. We measure strains from the motions of small spheres on the plate surface, stresses from plate photo-elastic response, and granular motion using particle tracking. We determine the dependence of the friction and the moment distribution of the system on the normal force. The moment distribution scales with a power law close to -1.5. There is an increasing probability for large events with a non-random recurrence time at higher normal force. [Preview Abstract] |
Thursday, March 6, 2014 8:36AM - 8:48AM |
S17.00004: Stress avalanches in sheared granular materials Somayeh Farhadi, Karin Dahmen Granular systems, subject to external shear stress, deform plastically at the yield point, where stress is released in the form of avalanches. The sizes(strength) of stress avalanches show a broad range in magnitude and demonstrate scaling properties. Here, we perform MD simulation to study stress avalanches of granular materials. The systems are dense packings of both 2D and 3D Hertzian spheres (close to their jamming points). Both micro-structure of failure as well as global stress are measured throughout gradual shear steps. Finally, we compare mean-field predictions of an existing model of failure, with our simulation data. [Preview Abstract] |
Thursday, March 6, 2014 8:48AM - 9:00AM |
S17.00005: Record-Breaking Avalanches in Nonlinear Threshold Systems Robert Shcherbakov Record-breaking avalanches generated by the dynamics of several driven non-linear threshold models are studied. Such systems are characterized by intermittent behaviour, where slow build-up of energy is punctuated by an abrupt release of energy through avalanche events which usually follow scale invariant statistics. From the simulations of these systems it is possible to extract sequences of record-breaking avalanches, where each subsequent record-breaking event is larger in magnitude than all previous events. In the present work, several cellular automata are analyzed among them the sandpile model, Manna model, Olami-Feder-Christensen (OFC) model, and the forest-fire model to investigate the record-breaking statistics of model avalanches which exhibit temporal and spatial correlations (Shcherbakov et al., PRE 87, 2013, 052811). Several statistical measures of record-breaking events are derived analytically and confirmed through numerical simulations. It is found that the statistics of record-breaking avalanches for the above cellular automata exhibit behaviour different from that observed for i.i.d. random variables which in turn can be used to characterize complex their spatio-temporal dynamics. The most pronounced deviations are observed in the case of the OFC model. [Preview Abstract] |
Thursday, March 6, 2014 9:00AM - 9:12AM |
S17.00006: Scaling Analysis And Tuning Parameters For Avalanches On A Slowly-Driven Conical Bead Pile Susan Lehman, Lilianna Christman, Paroma Palchoudhuri, D.T. Jacobs We report the results of our investigation of the dynamic behavior of a 3D conical beadpile composed of 3~mm steel beads. Beads are added to the pile by dropping them onto the apex one at a time; avalanches are measured through changes in pile mass. We have previously shown that the avalanche size distribution generally follows a power law relation for beads dropped onto the pile apex from a low drop height; for higher drop heights or beads dropped over a larger region, the distribution deviates from a power law due to a reduction in the number of larger avalanches. We are now tuning the critical behavior of the system through the addition of cohesion from a uniform magnetic field, and we find an increase in the probability of very large avalanches and decreases in the mid-size avalanches. Similar distributions have been observed previously by other researchers in conical piles of sand, suggesting a possibility that cohesion may have been a factor. All our distributions without cohesion show universality by collapsing onto a common curve in a scaling analysis; so far no scaling has been found in the system with cohesion. The distribution of the time between avalanche events of various size has also been analyzed and shown to depend on both drop height and cohesion strength. [Preview Abstract] |
Thursday, March 6, 2014 9:12AM - 9:24AM |
S17.00007: Unexplained voltage signals from granular materials Troy Shinbrot, Karen Daniels, Chris Marone, Theo Tsiu Powders and grains exhibit unpredictable jamming-to-flow transitions that manifest themselves on geophysical scales in catastrophic slip events such as landslides and earthquakes, and on laboratory/industrial scales in profound processing difficulties. Over the past few years, insight into these transitions has been provided by new evidence that slip events may accompanied, or even preceded, by electrical effects. In this talk, we describe three independent experiments using organic powders, polymeric disks, and glass particles, all of which generate unexplained voltage signals. [Preview Abstract] |
Thursday, March 6, 2014 9:24AM - 9:36AM |
S17.00008: Listening to Anticracks in Laboratory Earthquakes under the True Triaxial 3D Remote Stress Field H.O. Ghaffari, M.H.B. Nasseri, R. Paul Young A real deformation in the earth produces 3D stress as well as displacements on polymodal fault sets. Here we present the results of the multi-stationary acoustic waveforms from the orthorhombic faulting patterns in sandstone under 3D-polyaxial stress fields. Based on the analysis of over 104 rupture fronts and using the functional acoustic network theory, we show that generally waveforms from true triaxial tests carry shorter rapid slip phase (8-10 $\mu$s), implying the controlling role of the intermediate remote-stress field on mesoscopic faulting which is explained with inducing irregular micro-cracking. Furthermore, we extract failure criterion in network's phase space per each occurred failure of heterogeneity/asperity, confirming the macroscale failure measures in true triaxial tests. Our results suggest that boundary conditions can drastically change the regime of ruptures in laboratory earthquakes by inducing a sort of anti-crack like ruptures. [Preview Abstract] |
Thursday, March 6, 2014 9:36AM - 9:48AM |
S17.00009: Unjamming and jamming transitions of granular avalanches Jie Zhang, Ziwei Wang Study of the jamming transitions of granular materials has become an active field of research in recent years. A closely related inverse process is the unjamming transition, where granular systems may suddenly lose rigidity and start to flow freely. Understanding such a process is of crucial implication towards the understanding of natural disasters such as snow avalanches, landslides and earthquakes. Recent work by Banigan and colleagues (Nature Physics 2013) has provided a new perspective in the study of unjamming and jamming transitions by applying nonlinear dynamical methods. To test their proposition experimentally, we have designed a rotating drum filled with bidisperse photo-elastic disks to create particle avalanches. In unjamming transition, Lyapunov vector and velocity fields are indeed strongly correlated in spatial domain, whereas in jamming transition no such a strong correlation is observed. The Lyapunov exponents are positive in unjamming transition and negative in jamming transition. In addition, the total stress variation, kinetic energy, and non-affine motion of particles all show strong correlations in the time domain during avalanches. Their spatial correlations have also been analyzed. [Preview Abstract] |
Thursday, March 6, 2014 9:48AM - 10:00AM |
S17.00010: Correlations in Particle Displacements and Plastic Deformation in Sheared Amorphous Solids Mark O. Robbins, K. Michael Salerno We present results from molecular-dynamics simulations of model disordered solids under quasi-static, steady-state shear in two and three dimensions. Plastic deformation occurs through intermittent ``avalanches'' of local rearrangements. As in other slowly-driven systems from magnets to geologic faults, avalanches exhibit critical scaling behavior. Particle motion during avalanche events leads to local yielding and plastic strain. Local strain statistics for individual avalanche events will be discussed. Over many avalanche events long-range spatial correlations form in the particle displacement and strain fields. These correlations are seen most visibly in the power spectra of local measures of particle motion, S(q). One result of these correlations is system-size dependent effective particle ``diffusion,'' with particle mean-square displacement that is linear in the applied strain. Results for three different particle damping regimes will be compared. Results from two and three dimensions will also be presented and compared. [Preview Abstract] |
Thursday, March 6, 2014 10:00AM - 10:12AM |
S17.00011: Structure and deformation in compressed disordered packings Jennifer Rieser, Wenbin Li, Ju Li, Jerry Gollub, Douglas Durian How the local structural configuration influences large-scale deformation in disordered materials is not known. We explore this relationship in two-dimensional disordered granular packings under uniaxial compression. The two-dimensionality of the system allows for direct observation of all particle dynamics during the compression of a pillar. The grains can be cohesive, with an attraction governed by tunable capillary forces that are induced through an interstitial fluid. Topological quantities derived from a generalized Voronoi diagram as well as the resulting triangulation are used to characterize local structure within the packing. Dynamics are characterized by local deformations to the triangulation as well as the local non-affine motion. We investigate correlations between these structural and dynamical measures, and we observe that holes tend to develop in regions of high strain. [Preview Abstract] |
Thursday, March 6, 2014 10:12AM - 10:24AM |
S17.00012: Shear deformations in foam: will it T1? Merlijn van Deen, Vera Janssen, Alexander Siemens, Martin van Hecke When dry foams are sheared, energy is dissipated in localized, plastic, T1 events, where particles swap neighbors. In wet foams, the picture is different. We have experimentally probed rearrangements in wet packings of bubbles in a bi-axial shear cell. We show that the volume fractions at which T1's dominate is limited, and show the rich behavior that ensues closer to the jamming transition. [Preview Abstract] |
Thursday, March 6, 2014 10:24AM - 10:36AM |
S17.00013: Avalanches of Rearrangements in 2D Emulsion Hopper Flow Xia Hong, Kenneth Desmond, Dandan Chen, Eric Weeks We conduct experiments with a quasi-two-dimensional binary emulsion flowing through a hopper. Our samples are oil-in-water emulsions confined between two close-spaced parallel plates, so that the droplets are deformed into pancake shapes. In this system, there is only viscous friction and no static friction between droplets. By imaging the droplets during flow, we observed T1 events, which are topological rearrangement events when droplets exchange neighbors. Avalanche like flow behavior has been found by controlling the flow velocity and area fraction. We study the statistics of rearrangements as a function of the control parameters and observe a fairly smooth transition from avalanche-dominated flow to continuous flow. [Preview Abstract] |
Thursday, March 6, 2014 10:36AM - 10:48AM |
S17.00014: Structural perturbations in granular beds due to shear-flow-driven, fluvial erosion Julia Salevan, Mark Shattuck, Corey O'Hern, Nicholas Ouellette The complex interactions between granular media and flowing fluid play a principal role in shaping landscapes via erosion. Despite a large body of work in granular materials and in large scale topographical changes of granular beds due to fluid flow, the detailed physical mechanisms that underlie the coupling between hydrodynamic shear and internal rearrangement remain poorly understood. To address these questions, we perform experimental studies of shear flow across granular beds and monitor changes in the structural properties of the granular packing. We pay particular attention to the extent of perturbations of the packing as a function of depth within the bed and examine the effects of varied fluid flow regimes and time scales on bed rearrangements. [Preview Abstract] |
Thursday, March 6, 2014 10:48AM - 11:00AM |
S17.00015: Synthesis and Mechanical Response of Colloidal Micropillars Daniel Strickland, Lei Zhang, Yun-Ru Huang, Daeyeon Lee, Daniel Gianola We present a new approach for studying the uniaxial compressive behavior of colloidal micropillars as a function of structural order/disorder, pillar and colloid dimension, and interparticle interaction. By varying the polydispersity of the particles, ordered packing may be promoted or suppressed, leading to the formation of crystalline or amorphous pillars. Pillars composed of nanometer scale particles develop cracks during drying, while pillars composed of micron scale particles dry crack-free. We subject the pillars, with diameters ranging from 300$\mu $m to 1mm, to uniaxial compression experiments using a custom-built micromechanical testing apparatus. In pillars with pre-existing cracks, compression activates the macroscopic defects, leading to fracture and stochastic mechanical response as a result of the flaw distribution. Pillars that dry crack-free fail by shear bands that develop near the punch face. While macroscopically identical, pillar-to-pillar mechanical response varies significantly. We rationalize the difference in behavior as a result of varying structure and environmental conditions. Specifically, the level of atmospheric humidity significantly affects particle-particle cohesion and friction, resulting in dramatically different mechanical response. We discuss the results in the context of underlying particle rearrangements leading to mesoscopic shear localization and examine comparisons with atomic disordered systems such as metallic glasses. [Preview Abstract] |
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