Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session E56: In the memory of Bob Behringer: Statistical and Nonlinear Physics |
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Sponsoring Units: GSNP GSOFT Chair: Daniel Lathrop, University of Maryland, College Park Room: BCEC 255 |
Tuesday, March 5, 2019 8:00AM - 8:12AM |
E56.00001: Emergence of a crystalline phase in sheared granular matter Harry Swinney, Charles Radin, Frank Rietz, Matthias Schroeter One-half century ago a classic experiment by G.D. Scott (Nature 188, 908, 1960) showed that pouring steel balls into a rigid container filled the volume to an upper limit volume fraction of 0.64, which is well below the volume fraction 0.74 filled by spheres in a hexagonal close-packed (HCP) or face-centered cubic (FCC) lattice. Subsequent experiments confirmed a ``random closed-packed" (RCP) volume fraction of about 0.64. However, the physics of the RCP limit has remained a mystery. We have conducted an experiment on a cubical box filled with 49400 precision glass spheres under weak shear imposed by a small slow angular oscillation of two opposite sidewalls. A phase transition occurred at a volume fraction of 0.645, from a disordered to an ordered state, consisting of crystallites of mixed FCC and HCP symmetry that coexist with the amorphous bulk. The transition is initiated by homogeneous nucleation. In the shearing process small crystallites with about ten or fewer spheres dissolve, while larger crystallites grow (doi.org/10.1103/PhysRevLett.120.055701, JSP doi.org/10.1007/s10955-018-2144-4). |
Tuesday, March 5, 2019 8:12AM - 8:24AM |
E56.00002: Jamming by shear in a dilating granular system Meimei Wang, Dong Wang, Joshua Socolar, Hu Zheng, Robert P Behringer Jamming can occur in frictional granular materials undergoing shear at a fixed packing fraction, φ, for φ within a range of packing fractions below the isotropic jamming point, and the amount of strain required to induce jamming, γ, increases with decreasing φ. We are interested in how the shear jamming process is affected if the system is dilating as it is sheared. We conduct experiments to shear a 2D granular system while continuously increasing the system volume. Below a certain dilation rate, the system is still able to jam at packing fraction, φ_{c}, smaller than the initial φ. We measure γ for different dilation rates and initial packing fractions by monitoring the coordination number of non-rattlers and the system pressure. We find that γ is the same as the γ required to jam a system with fixed packing fraction φ_{c} via pure shear. |
Tuesday, March 5, 2019 8:24AM - 8:36AM |
E56.00003: System Size Dependence in Shear Jamming of 2D Frictional Grains Dong Wang, Hu Zheng, Jonathan Bares, Robert P Behringer Shear jamming (SJ) occurs for frictional granular materials with packing fractions (Φ) in a finite range below the isotropic jamming point, when the material is subject to a sufficiently large shear strain, γ_{SJ}, starting from a force-free state. Here we report experimental studies on the system size dependence for a quasi-2D frictional system composed of bidisperse photoelastic disks. The number of particles in the system ranges from 60 to 3000 by varying particle diameters while maintaining the number and size ratio between big and small disks the same. We observe that γ_{SJ }increases with system size at the same Φ for systems with less than 1000 particles, reminiscent of a recent simulation work (Baity-Jesi et al., J. Stat. Phys. 167, 735 (2017)). However, such a dependence is much weaker comparing systems with 1000 and 3000 particles. Our results imply that SJ still exists in frictional granular materials in the thermodynamic limit. |
Tuesday, March 5, 2019 8:36AM - 8:48AM |
E56.00004: Granular jamming transition: induced by shearing and compressing Hu Zheng, Dong Wang, Yiqiu Zhao, Robert P Behringer Jamming of a granular system can be achieved by either isotropically increasing the packing fraction (isotropic jamming) or applying pure shear over a range of packing fractions below the isotropic jamming point (shear jamming). We experimentally study jammed configurations obtained by isotropic biaxial compression or pure shear in a quasi-2D granular system composed of photoelastic disks. A density matching method is applied to avoid basal friction. The fabric anisotropy and stress anisotropy are clearly different in the two cases. However, studies of the scaling behavior near the jamming transition reveal that, as the transition is approached, the scaling exponent of the pressure is the same for the isotropic jamming and shear jamming cases. |
Tuesday, March 5, 2019 8:48AM - 9:00AM |
E56.00005: Experimental observation of shear jamming in 3D granular materials David Z Chen, Ryan Kozlowski, Robert P Behringer Frictional granular media can shear jam over a range of packing fractions below the isotropic jamming packing fraction. We experimentally study shear jamming in 3D by applying cyclic shear at fixed volume for a granular packing submerged in a density-matched solution; the effects of gravity are minimized in this environment, preventing compaction by grain weight. We observe signatures of shear jamming in the macroscopic pressure signal with a variety of packing fractions and shear amplitudes over many (on the order of 100) shear cycles. We report on analysis of particle positions (tracked via refractive index matched scanning [1]) from cycle to cycle that show correlations between microscopic rearrangements and changes in peak pressure across cycles. |
Tuesday, March 5, 2019 9:00AM - 9:12AM |
E56.00006: Nontrivial plasticity of a shear-jammed granular system Yiqiu Zhao, Jonathan Bares, Hu Zheng, Aghil Abed Zadeh, Joshua Socolar, Robert P Behringer We report shear experiments on a layer of photo-elastic disks in which shear is applied through basal friction with 21 independently controllable concentric rings below the granular layer in a Couette geometry. The rings rotate at different rates to make the local shear strain uniform inside the system. By applying this uniform shear in small steps, we create an ensemble of static shear jammed (SJ) configurations with different packing fractions (\phi) below the isotropic jamming packing fraction (\phi_J). We find that the average size and radial profile of plastic deformations between steps vary with packing fraction. A transition at \phi_c<\phi_J is observed. When \phi>\phi_c, the plastic deformation is localized to a narrow shear band close to the inner boundary of the shear cell. When \phi<\phi_c, the plastic deformation is spread through the entire system. We report power-law dependence of deformation amplitude on packing fraction close to \phi_c. We also find similar behavior for non-uniform applied shears. |
Tuesday, March 5, 2019 9:12AM - 9:24AM |
E56.00007: Experiments on jamming with oil droplets instead of photoelastic disks Eric Weeks, Yonglun Jiang, Carlos S Orellana, Xia Hong We use quasi-two-dimensional emulsions as experimental models to study the flow of jammed materials. Our emulsions are oil droplets in water and are compressed between two parallel glass plates so that the droplets are deformed into pancake-like disks. We use microscopy to observe these droplets as they flow. From the deformed outlines of the droplets, we can measure all of the inter-droplet forces to within 10%. In this talk I'll present some of the experiments we've done that were directly inspired by Behringer group experiments, and also briefly mention some recent results on flowing samples. |
Tuesday, March 5, 2019 9:24AM - 9:36AM |
E56.00008: Dynamic Measurements of Normal and Tangential Coefficients of Restitution for an Inelastic Billiard Jeffrey Olafsen, Kai Yang Driven granular media dissipate a large amount of energy in their particle-particle and particle-boundary interactions. As such, our understanding of the fundamental dynamics in these systems is complicated by the velocity-dependent nature of the coefficient of restitution. Even how a driven granular flow jams necessitates a better understanding of the details of this dissipative mechanism. Very sophisticated experiments have sought to better understand and characterize the velocity dependence of the coefficient of restitution by attempting to constrain and control aspects of the collisions. A careful and in-depth analysis for an inelastic billiard moving within a confining boundary allows the velocity-dependence to be measured as the dynamics freely evolve over multiple collisions in the driven system. The shape of the geometry can be varied to tease out details of the dynamics as well as the differences between the normal and tangential coefficients of restitution. The large amount of data generated in this experiment allows the contributions from both the normal and tangential velocity components in the particle-boundary interactions to be examined. Two derivative experiments, one for particle-boundary and the other for particle-particle collisions will also be discussed. |
Tuesday, March 5, 2019 9:36AM - 9:48AM |
E56.00009: Nontrivial power-law scaling of impact forces into granular materials Nasser Krizou, Abe Clark When an intruder strikes a granular material, the grains exert a force which decelerates and stops the intruder. Existing ballistic models can successfully describe much of the intruder-material interaction using a macroscopic force law, but these models often fail near the moment of impact. Here, we show results from experiments and numerical simulations, focusing on microscopic intruder-grain interactions during the early stages of impact. We record high-speed videos of intruders (of varying size and density) impacting assemblies of photoelastic disks, and we quantify both the intruder dynamics and the forces in the material. We show nontrivial power law scaling of peak forces during the initial transient phase of the impact into granular materials. Experiments and simulations indicate that this scaling is insensitive to many system details, such as friction, grain stiffness, and whether grain-grain interactions are linear (Hookean) or nonlinear (Hertzian). We also find important similarities to impact forces in dense suspensions, suggesting that our results may be generic for impacts into many kinds of soft, deformable materials. |
Tuesday, March 5, 2019 9:48AM - 10:00AM |
E56.00010: Experimental seismicity and avalanches in sheared granular media Aghil Abed Zadeh, Jonathan Bares, Joshua Socolar, Robert P Behringer We report on experiments investigating the dynamics of a 2D granular medium, consisting of a vertical layer of photo-elastic disks sheared by a slider that is pulled by a spring. The motion of the slider proceeds through a sequence of discrete events, analogues to seismic shocks, in which elastic energy stored in the spring is rapidly released. We measure the statistics of several properties of the individual events: the energy loss in the spring, the duration of the movement, and the temporal profile of the slider motion. We also study certain conditional probabilities and the statistics of mainshock-aftershock sequences. At low driving rates, we observe crackling with Omori-Utsu, Bath, and waiting time laws similar to those observed in seismic dynamics. At higher driving rates, where the sequence of events shows strong periodicity, we observe scaling laws and asymmetrical event shapes that are clearly distinguishable from those in the crackling regime. |
Tuesday, March 5, 2019 10:00AM - 10:12AM |
E56.00011: Dynamics of a grain-scale intruder in a granular system with and without basal friction Ryan Kozlowski, David Z Chen, Hu Zheng, Joshua Socolar, Lou Kondic, Karen Daniels, Robert P Behringer When a granular medium is sheared by a spring-driven mechanism, the system can exhibit stick-slip dynamics: The grains form a rigid solid as the spring loads (stick event) which plastically deforms when the spring load exceeds the yield stress of the stable configuration (slip event). We experimentally investigate the dynamics of a single grain-scale intruder driven by a spring through a 2D annular bed of photoelastic disks. We vary the grain packing fraction, the interparticle friction, and the basal friction between grains and the table surface, and we measure the azimuthal force on the intruder. For grains resting on a dry surface, where basal friction is present, the system undergoes aperiodic stick-slip motion; when the grains are floating on a fluid and basal friction is negligible, the intruder flows unimpeded through the medium but occasionally clogs. These qualitative behaviors do not seem to depend on packing fraction and interparticle friction coefficient. We report on measurements of the intruder force and speed distributions as well as particle displacements. |
Tuesday, March 5, 2019 10:12AM - 10:24AM |
E56.00012: Tears of wine and shock dynamics Yonatan Dukler, Andrea Bertozzi, Andreas Muench, Hangjie Ji We revisit the classical problem of "tears of wine" and discuss the role of the geometry of the wine glass in regards to the formation of tears. Transport of a thin liquid up the side of the glass is instigated by a Marangoni stress due to a combination of thermal gradient and surface tension gradient. This effect is balanced by both normal and tangential components of gravity. When gravity effects are non-negible the possibility of undercompressive shocks enters the picture. We discuss this implications of compressive versus undercompressive shocks for film morphologies and compare with prior experiments on the tears of wine problem and experiments on thermally driven films. |
Tuesday, March 5, 2019 10:24AM - 10:36AM |
E56.00013: Vibration can enhance stick-slip behavior for granular friction Jacqueline Krim, Robert P Behringer, Abe Clark We experimentally study the frictional behavior of a two-dimensional slider [1] pulled slowly over a granular substrate comprised of photoelastic disks while being vibrated at frequencies ranging from 0 to 30 Hz in a direction parallel to sliding. Measurements are performed at constant peak acceleration amplitude, which results in constant average friction levels, but varying frictional behaviors. Surprisingly, we find that stick-slip behavior, where stress slowly builds up and is released in intermittent slips, is enhanced as the frequency of vibration is increased. Our results suggest that increasing the frequency of vibration may help to combine many smaller rearrangements into fewer, but larger, avalanche-like slips. We also examine the manner in which the self-affine character of the force curves evolves with frequency, and find additional support for this interpretation. |
Tuesday, March 5, 2019 10:36AM - 10:48AM |
E56.00014: Nonlocal rheology of a dense granular flow in annular shear experiments Karen Daniels, Zhu Tang, Theodore Anthony Brzinski, Michael Shearer The flow of dense granular materials at low inertial numbers cannot be fully characterized by local rheological models; several nonlocal rheologies have recently been developed to address these shortcomings. To test the efficacy of these models across different particle shapes, packing fractions and shear rates, we perform experiments in a quasi-2D annular shear cell using photoelastic particles. The apparatus is designed to measure both the stress ratio μ and the inertial number through the use of a torque sensor, laser-cut leaf springs, and particle-tracking. We observe that across several different packing fractions and rotation rates, a single set of model parameters is able to capture the full range of data collected once we account for frictional drag with the bottom plate. While the model's local parameter is always approximately unity, the nonlocal parameter varies sensitively on both the particle shape and material. Our measurements confirm the prediction that there is a growing lengthscale at a finite value μ_{s}, associated with a frictional yield criterion. Finally, we newly identify the physical mechanism behind this transition at μ_{s} by observing that it corresponds to a drop in the susceptibility to force chain fluctuations. |
Tuesday, March 5, 2019 10:48AM - 11:00AM |
E56.00015: Non-local effects in intermediate granular avalanching flows Nathalie Vriend, Amalia L Thomas, Karen Daniels In this work we showed that photoelastic analysis allows the quantification of rheologies in an intermediate chute flow. We characterize stresses and velocities in a flow layer with regions below and above the yield ratio mu_s. We compare our experimental results with a nonlocal rheology. Preliminary results show that the timescale over which the force chains decorrelate is strongly associated with the inverse of the fluidity, a viscosity-like quantity. This provides a physical interpretation of its particle-scale origins. |
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