Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session N29: Granular Packing and Impacting |
Hide Abstracts |
Sponsoring Units: GSNP Chair: Eric Corwin, University of Oregon Room: 337 |
Wednesday, March 20, 2013 11:15AM - 11:27AM |
N29.00001: A Dynamically Based Study of Percolation through Spaces between Polyhedral Grains Donald Priour Many porous materials in nature are made up of grains in the form of non-spherical crystallites. Depending on the density of the grains, such systems may admit the flow of fluid through the spaces between the grains on a macroscopic scale (percolation for sufficiently sparsely spaced grains) or prevent fluid flow (percolation is blocked if the grain concentration is high enough that voids between grains are not contiguous). To provide a more realistic treatment of percolation through granular media, we examine systems comprised of randomly placed angular impermeable inclusions (e.g. disks, tetrahedrons, cubes, and octahedrons), and we give a rigorous continuum treatment to the geometry of the grains and the spaces between them. To extrapolate to the bulk limit in the context of a finite-size scaling analysis, we examine multiple systems of different sizes, where disorder averaging mitigates statistical fluctuations unrelated to bulk properties. An order parameter based on root mean square (RMS) excursion of dynamical trajectories is calculated in the context of a large-scale Monte Carlo simulation and used to evaluate the critical concentration $\rho_{c}$ of grains. In addition, critical exponents such as $\nu$ for the correlation length $\xi$ are determined. [Preview Abstract] |
Wednesday, March 20, 2013 11:27AM - 11:39AM |
N29.00002: Simulation of current-activated pressure-assisted densification Dietrich Wolf, Sebastian Angst, Gabi Schierning Cohesive particles usually form very porous agglomerates. They support loads up to a consolidation pressure, which increases with decreasing particle size. Compaction of nano-powders can therefore be very costly and time consuming. If the particles are electrically conducting, which is the case e.g. for novel nano-structured thermoelectric materials, the technique of current-activated pressure-assisted densification (CAPAD) turns out to have many advantages. Electrical power deposited locally as Joule heat lowers the consolidation pressure such that particles fill nearby pores. This process leads to fast, scalable densification without much coarsening. Simulations are presented which address the influence of correlations on density and conductivity [1]. They also take thermal conductivity and Peltier coefficient into account [2].\\[4pt] [1] S. Hartner et al. in: Nanoparticles from the Gasphase - Formation, Structure, Properties. A. Lorke, M. Winterer, R. Schmechel, Ch. Schulz (eds.) (Springer, Berlin 2012) pp. 231 - 270.\\[0pt] [2] A. Becker et al., Appl. Phys. Lett. 101, 013113 (2012). [Preview Abstract] |
Wednesday, March 20, 2013 11:39AM - 11:51AM |
N29.00003: Fully ordered to disordered granular sphere packings with random deposition Arshad Kudrolli, Andreea Panaitescu Granular packings are typically obtained by pouring grains into a container in a gravitational field as when sugar is poured into a jar, or grains into a silo. We deconstruct this method and study the impact on packing by simply varying the pour rate and energy of particles dropped randomly but spatially uniformly in a large container whose substrate can act as a template. We find that fully disordered packings are observed when large number of particles are added all at once but an ordered fcc crystal is observed when particles are added sequentially at random locations and allowed to come to rest before adding the next layer. By scanning the packings obtained by 3D X-ray tomography, we identify the positions of all the particles and the growth of order and defects. We present an analysis of the structures formed and compare and contrast it with packings obtained using other protocols including by cyclic shear [1]. [1]: ``Nucleation and Crystal Growth in Sheared Granular Sphere Packings," Andreea Panaitescu, K. Anki Reddy, and Arshad Kudrolli, Phys. Rev. Lett. 108, 108001 (2012). [Preview Abstract] |
Wednesday, March 20, 2013 11:51AM - 12:03PM |
N29.00004: Comparison between bridges and force-chains in granular packings Ling Zhang, Shuxiao Cai, Zunpeng Hu, Jie Zhang In dense granular materials, there exist chain-like force networks from which we can obtain much information on the mechanical properties of packings. But it is extremely difficult to characterize these structures, especially in 3D packings. Mehta and her coauthors have proposed theoretically that bridge-like structures can form because of spatial inhomogeneity and large fluctuations, and they conjecture that these mesoscopic geometric structures play the role of force-chains (Mehta et. al. 2004, Pugnaloni et. al. 2001). Some statistical features of bridges have been observed in a recent paper by Mattew C. Jenkins et al (Jenkins et. al. 2011). Despite the success, the lack of independent force network information makes the justification of Mehta et al.'s theoretical conjecture inconclusive. In this study, we focus on the comparison of bridges and force-chains in two different granular packing using photo-elastic granular particles. We have found no clear evidence that there exists a one-to-one mapping between bridges and force-chains. Nonetheless, for systems of different force chain structures, it does seem to show some differences in the respective bridge structures. This seems to suggest that some connection may exist between bridges and force-chains. [Preview Abstract] |
Wednesday, March 20, 2013 12:03PM - 12:15PM |
N29.00005: Novel spiral-like columnar packings of hard spheres from sequential deposition - a route to new architecture in the scientific world Ho-Kei Chan Recent work [Physical Review E 84, 050302(R) (2011)] shows that the densest columnar packings of identical hard spheres inside a cylinder can be constructed from a sequential deposition of such spheres onto a specially designed template at the cylinder base, if the cylinder-to-sphere diameter ratio D is within [1,2.7013]. In this talk, I will present some novel, non-densest spiral-like structures as discovered from the same deposition algorithm, and will elaborate on how we can manipulate a columnar structure by changing its underlying template. [Preview Abstract] |
Wednesday, March 20, 2013 12:15PM - 12:27PM |
N29.00006: Cavity method for jammed disordered packings of hard particles at mean-field level Lin Bo, Romain Mari, Chaoming Song, Hernan Makse We apply the cavity method at mean-field level to investigate the problem of random close packings of hard particles. We derive the Belief Propagation equations describing this force/torque balance problem to solve the force distribution and suggest an estimation of the coordination number of the jammed packing. We compare the numerical results with approximate analytical solutions and show the dependence of coordination numbers on particle shapes. The method can be applied to spherical frictionless and frictional particles as well as non-spherical particles to obtain the jamming properties and study the appearance of isostaticity. [Preview Abstract] |
Wednesday, March 20, 2013 12:27PM - 12:39PM |
N29.00007: Detection of Multidimensional Structures in Granular Materials Danielle Bassett, Karen Daniels, Eli Owens, Mason A. Porter, M. Lisa Manning Granular media display features across a range of spatial scales, from the particle scale to the force-chain scale and the bulk scale. In contrast to particulate and continuum models, network representations facilitate the simultaneous examination of microscopic, mesoscopic, and macroscopic features. We treat granular materials as spatially embedded networks in which the nodes (particles) are connected by weighted edges obtained from contact forces. Using community detection techniques, we identify local 2D geographic domains composed of particles that exert strong forces on one another. We subsequently develop and apply a novel spatial null model constrained by the contact network to extract chain-like structures reminiscent of force chains. We demonstrate that most of these chain-like structures are located close to the center of mass of the 2D geographic domains. However, a minority are located towards the edge of the 2D geographic domains, potentially forming points of instability in granular media. We explore the robustness of these detection techniques to algorithmic degeneracies, to simulation versus experimental data, and to varying pressure states. [Preview Abstract] |
Wednesday, March 20, 2013 12:39PM - 12:51PM |
N29.00008: Compaction of frictional octahedra N. Nirmal Thyagu, Max Neudecker, Stephan Herminghaus, Matthias Schroeter We perform experiments with frictional polypropylene octahedra to study the packing properties. Starting with the loose packing, compaction of octahedra is done by two types of forcing -- a) tapping and b) shearing. The compaction gives rise to crystallization of octahedra due to heterogenous nucleation from the walls. We obtain the X-ray tomograms of the packing configurations as a function of packing fraction. From the contact geometries we obtain results for the packings such as - pair correlation function, distance to isostaticity, and spatial {\&} angular correlation functions. We contrast these results with a similar study on the simplest platonic solid, the tetrahedron\footnote{Jammed frictional tetrahedra are hyperstatic, M. Neudecker, S. Ulrich, S. Herminghaus, M. Schr\"{o}ter. (arXiv:1202.6272v2)} and the sphere. [Preview Abstract] |
Wednesday, March 20, 2013 12:51PM - 1:03PM |
N29.00009: Revealing the structure of a granular medium through acoustic measurements Ramon Planet Latorre, S\'ebastien Lherminier, Gilles Simon, Loic Vanel, Osvanny Ramos An array of acoustic sensors records the sound that has travelled across a bi-dimensional granular medium, consisting of photoelastic discs, which are confined between two transparent plates and arranged into different crystalline or disordered structures. The system is compressed along one direction (either force-controlled or displacement-controlled) and can be sheared in the direction perpendicular to the applied force; while the acoustic signals are generated through a well-controlled and local mechanical excitation. The results show power-law regimes in the force vs. sound speed relation, with exponents that are sensitive to the structure of the packing. Small structural changes are also detectable which, in principle, can be used to predict large avalanches during the slow shearing of the system. [Preview Abstract] |
Wednesday, March 20, 2013 1:03PM - 1:15PM |
N29.00010: The vanishing Janssen effect in a confined 2D granular system compressed by friction Yasin Karim, Eric Corwin As described by H.A. Janssen in 1895, the pressure in a granular packing saturates above a certain filling height, determined by the particle-particle and particle-wall interactions. This effect has been studied extensively for 2D and 3D confined granular packs compressed by gravity. However, many industrially relevant processes involve the horizontal transport of granular materials by conveyor belts. In such a case gravity becomes irrelevant and the system is driven by frictional forces. We study horizontal 2D confined granular packs on a conveyor belt as they are driven into a stationary barrier. We measure the relationship between pressure and filling height and, surprisingly, find no saturation of pressure. Instead, we observe a linear relationship between pressure and filling height irrespective of the particle-wall coefficient of friction demonstrating that the Janssen effect is not relevant for such systems. However, we can recover a Janssen-like saturation if we replace the straight confining walls with a sawtooth pattern on the scale of the particle size. This allows for a mechanical transfer of load onto the walls and can be interpreted in terms of an effective mechanical ``friction.'' [Preview Abstract] |
Wednesday, March 20, 2013 1:15PM - 1:27PM |
N29.00011: From Kepler to Ulam: searching for the optimal packing in the space of object shapes Romain Mari, Adrian Baule, Lin Bo, Maximilien Danisch, Hernan Makse The quest for the best packing of particles has been guided by two notorious conjectures. Kepler stated that the optimal sphere packing is the face-centered-cubic lattice, while Ulam conjectured that all convex shapes pack better than spheres. While the former was proved by Hales, there is yet no theoretical framework to predict the density of non-spherical particles. Here, we present a formalism to describe packings of objects of arbitrary shape in random configurations by reducing the particle interactions to simple sets of points, and lines. The framework predicts the optimum packing fraction of a large class of shapes as an analytical continuation from the spherical point, thus paving the way for a proof of Ulam's conjecture. In particular, the formalism predicts that spherocylinders pack better than both spheres and dimers. Ellipsoids and tetrahedra can be studied, highlighting the universality 1of the framework to search for optimal packings. [Preview Abstract] |
Wednesday, March 20, 2013 1:27PM - 1:39PM |
N29.00012: Forces on Intruders in Granular Media Ibar de la Cruz We measure the forces acting on intruders moving in different directions in a granular medium consisting of mono-disperse spherical glass beads. We present the dependence of the drag force on the intruder's geometry and surface roughness, bead size, dragging speed and immersion depth. We present a model that considers not only the wedge dragged by the intruder but also the pile created as the intruder moves through the granular material to calculate the drag force. We compare our experimental and analytical results. [Preview Abstract] |
Wednesday, March 20, 2013 1:39PM - 1:51PM |
N29.00013: Granular Dynamics during Impact Kerstin Nordstrom, Emily Lim, Matt Harrington, Wolfgang Losert In this work, we study the impact of a projectile onto a bed of 3 mm grains immersed in an index-matched fluid. Using a laser sheet scanning technique, a high speed camera, and particle tracking, we can measure the trajectory of each grain throughout an impact event. We characterize the bulk and microscopic dynamics within the granular material as a function of initial sample preparation, specifically applying a uniaxial prestrain to the sample. We find that small changes in sample preparation lead to drastic departures from the universal depth scaling seen in previous studies of shallow granular impacts. By examining the nonaffine motion within the system, we propose the effect is due to different loading and buckling of force chains within the system. [Preview Abstract] |
Wednesday, March 20, 2013 1:51PM - 2:03PM |
N29.00014: What is the granular response to a high-speed impact? Abram Clark, Lou Kondic, Robert Behringer Although many studies of impact on a granular material exist, the connections between the local granular response, the microscopic processes which dissipate kinetic energy, and the intruder dynamics are unclear, largely due to experimental difficulties in obtaining very fast data at the grain scale. We use high-speed imaging (40 kHz) of an intruder striking a quasi-2D system of photoelastic disks, yielding both the intruder dynamics and the force response of individual grains. The frame rates are fast enough to resolve rich acoustic activity on the particle scale. For long time scales, the intruder dynamics are consistent with previously used empirical force laws. However, for short time scales, we observe very large fluctuations in the deceleration, which we connect to the intermittent acoustic activity beneath the intruder as it moves. We show that these intense, intermittent acoustic pulses, which travel much faster than the intruder along networks of grains, are the primary microscopic mechanism of energy loss. These pulses carry energy away into the medium, and they decay roughly exponentially with distance. We examine the statistics of these fluctuations in order to better understand their origin and behavior. [Preview Abstract] |
Wednesday, March 20, 2013 2:03PM - 2:15PM |
N29.00015: The Jamming transition in photoelastic disks: local perturbations versus diverging responses Corentin Coulais, Antoine Seguin, Olivier Dauchot We investigate the spatial response of the contact network to local perturbations in experiments on horizontal packings of bidisperse photo-elastic soft disks close to jamming. First, an intruder is pulled at constant force through the packing: while the overall contact number remains unchanged, the contact network geometry drastically changes and develops a strong asymmetry between the front and the back of the intruder. Second, an intruder is inflated inside the packing leading to a global increase of the contact number. While particle rearrangements become increasingly large as the unjamming transition is approached, there are only few contact changes in the packing. We discuss these results in the light of a recent work [1] on fluctuations where a similar link between dynamical heterogeneities and contact fluctuation has been reported. \\[4pt] [1] C. Coulais, R. P. Behringer, and O. Dauchot, arXiv eprint: 1202.5687 (2012). [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700