Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session B15: Mechanics of Granular Materials 
Hide Abstracts 
Sponsoring Units: GSNP GSOFT Chair: Shubha Tewari, University of Massachusetts Amherst Room: 274 
Monday, March 13, 2017 11:15AM  11:27AM 
B15.00001: Energy dissipation in sheared wet granular systems L Kondic, L Kovalcinova, S Karmakar, M Schaber, AL Hippler, M Scheel, M DiMichiel, S Herminghaus, M Brinkmann, R Seemann We carry out experiments and targeted simulations to analyze energy dissipation in sheared dry and wet granular systems. We consider the regime such that the wetness leads to the formation of capillary bridges, that are in the experiments visualized in 3D by in situ Xray tomography in ESRF (Grenoble, France). The main focus is on unraveling the energy loss mechanisms, in particular regarding the role of friction, inelasticity of the particle collisions, and capillary bridges. We will show that, both in the experiments and simulations, the main source of energy loss depends strongly on the applied pressure. The simulations provide additional insight regarding the transition between different energy loss mechanisms, and allow for gaining further insight into the role that cohesive forces play in sheared granular systems. [Preview Abstract] 
(Author Not Attending)

B15.00002: Lowresistive penetration in granular media Baptiste Darbois Texier, Alejandro Ibarra, Fransisco Melo The quasistatic immersion of an intruder into a granular assembly requires a force that is several orders of magnitude larger than necessary in fluids under similar conditions. This occurs as a result of the progressive formation of a network composed of force chains, which simultaneously increase in size with intruder penetration. The present work shows that the resisting force for the immersion of an intruder into a granular material can be reduced by an order of magnitude with mechanical vibrations of small amplitude (A = 10 $\mu$m) and low frequency (f = 50200 Hz). The effect of the vibrations characteristics and the intruder geometry on the drop of the resistive force were inspected experimentally. Thanks to flow visualizations, it has been shown that vibrations induce a local convection into the granular media leading to the modification of the network of force chains. Moreover, scaling arguments are developed in order to rationalize our observations and to predict under which circumstances the resistive force is reduced. Finally, the use of such a phenomenon in the animal kingdom and the technological world will be discussed. [Preview Abstract] 
Monday, March 13, 2017 11:39AM  11:51AM 
B15.00003: Granular fingering instability: A first attempt to access the most unstable mode Chico Rocha, Nico Gray, Chris Johnson Mixtures of grains of different sizes tend to segregate as they avalanche downslope, with large particles rising to the near surface regions which move faster. As a result, large particles tend to be preferentially transported to flow front where they can accumulate by being overrun and resegregated to the surface. If the large particles are also more frictional, the flow becomes unstable and breaksup in a series of fingers: the socalled granular fingering instability. This instability is observed in a wide variety of systems, from geophysical mass flows, such as pyroclastic flows, to smallscale experiments relevant to industry. Key features of the fingering pattern are predicted by a particlesize segregation model, coupled with a depthaveraged avalanche model, in which a viscous term play a vitally important role in making the equations wellposed. We carry out a detailed numerical stability analysis to investigate what sets the wavelength of the fingers. [Preview Abstract] 
Monday, March 13, 2017 11:51AM  12:03PM 
B15.00004: An experimental investigation of the force network ensemble Jonathan Kollmer, Karen Daniels In granular packings, the particle positions alone are insufficient to determine the force network that carries the load on that packing. While this has been studied numerically, there have been few experiments to examine this question in real, frictional materials. We present an experiment in which a horizontal quasi2D granular system with a fixed neighbor network is cyclically compressed and decompressed over many cycles, allowing the system to explore different force configurations. We characterize several statistical properties of the packing, including the probability density function of contact forces, and compare them with predictions from the force network ensemble theory. [Preview Abstract] 
Monday, March 13, 2017 12:03PM  12:15PM 
B15.00005: Granular avalanches due to nonlinear acoustic waves Julien Leopoldes, Arnaud Tourin, Xiaoping Jia We investigate how unjamming of granular media by shear is modified by transmitted ultrasound. We show that, above a critical wave amplitude, the soundmatter interaction is irreversible. Moreover, the wave velocity (elastic modulus) decreases because of the strong modification of the force network, as shown by the correlation function of the multiply scattered Coda waves\footnote{ X. Jia, T. Brunet and J. Laurent. Phys. Rev. E 84, 020301(R) (2011)}. Then, we illustrate the consequences of such a softening with some experiments where a granular layer brought to an inclination below the angle of avalanche $\theta_m$ is destabilized by acoustic waves. Such avalanches are triggered at small sound amplitudes, close to the metastable state, and occur because of the decreased friction between the particles\footnote{J. L\'{e}opold\`{e}s, G. Conrad and X. Jia , Phys. Rev. Lett. 110, 248301 (2013)} \footnote{J. L\'{e}opold\`{e}s, A. Mangeney, A. Tourin and X. Jia, to be submitted}. Wellbelow $\theta_m$, the resulting dynamics is slow and the creeplike flow depends on the amplitude of the acoustic waves. This dependance is no longer observed close to $\theta_m$ where the flow is inertial. Our results provide insights on how mechanical noise affects the rheology of granulars. [Preview Abstract] 
Monday, March 13, 2017 12:15PM  12:27PM 
B15.00006: Arch Structure Dynamics in a 2d Vibrated Granular Hopper: Mapping to a Continuous Time Random Walk Process. Carl Merrigan, Bulbul Chakraborty, Sumit Birwa, Shubha Tewari Granular particles driven through a narrow opening can be blocked by the spontaneous formation of clogging arches. Experiments using controlled vibrations have found that the arch breaking times follow power law tails with exponents that can be tuned by changing the vibration strength or the opening size. In this talk, I will describe a mapping of the arch dynamics to a continuous time random walk model that can explain the occurrence of these continuously varying power law exponents. We have carried out molecular dynamics simulations of the arch breaking that produce distributions consistent with power laws cutoff by exponential tails at long times. Time series of the opening angles describing the arch shape resemble time series for continuous time random walks. Mean squared displacement analysis of these time series reveal results qualitatively similar to those expected for subdiffusive continuous time random walks. Hence, I will argue that the main mechanism for arch failure is the cooperative, stochastic evolution of the arch shape through a series of distinct, stable configurations until the first unsustainable configuration is reached. We are working towards achieving a precise quantitative implementation of this mapping. [Preview Abstract] 
Monday, March 13, 2017 12:27PM  12:39PM 
B15.00007: Granular flow in a twodimensional silo in the clogging regime Kiwing To Clogging is an annoying phenomenon that takes place when materials flow through a bottle neck, e.g. grains flowing out of a silo with small outlet. To initiate flow after clogging, one has to break the arch that stops the flow at the outlet. This can be done by oscillating the outlet of the silo. Here we present experimental data of the flow rate of monodisperse metal spheres through a twodimensional silo with outlet size slightly larger than the diameter of the beads. When the outlet is oscillating at amplitude $a$ and angular frequency $\omega$, we find that the flow rate $Q$ at different $a$ and $\omega$ can be collapsed to a single curve $Q(v)$ when plotted against the speed of oscillation $v=a\omega$. [Preview Abstract] 
Monday, March 13, 2017 12:39PM  12:51PM 
B15.00008: Effects of wall friction on flow in a quasi2D hopper Neil Shah, Sumit Birwa, Brenda CarballoRamirez, Mollie Pleau, Nalini Easwar, Shubha Tewari Our experiments on the gravitydriven flow of spherical particles in a vertical hopper examine how the flow rate varies with opening size and wall friction. We report here on a model simulation using LAMMPS of the experimental geometry, a quasi2D hopper. Keeping interparticle friction fixed, the coefficient of friction at the walls is varied from 0.0 to 0.9 for a range of opening sizes. Our simulations find a steady rate of flow at each wall friction and outlet size. The Janssen effect attributes the constant rate of flow of a granular column to the column height independence of the pressure at the base, since the weight of the grains is borne in part by friction at the walls. However, we observe a constant flow regime even in the absence of wall friction, suggesting that wall friction may not be a necessary condition for pressure saturation. The observed velocities of particles near the opening are used to extrapolate their starting positions had they been in free fall. In contrast to scaling predictions, our data suggest that the height of this ‘freefall arch’ does not vary with opening size for higher frictional coefficients. We analyze the velocity traces of particles to see the range over which contact interactions remain collisional as they approach the hopper outlet. [Preview Abstract] 
Monday, March 13, 2017 12:51PM  1:03PM 
B15.00009: Clogging of soft particles in 2D hoppers Haoran Wang, Eric Weeks We study the flow of soft hydrogel particles out of a quasitwo dimensional hopper. The hopper chamber is set thin enough for all the particles to stay in one plane without overlapping with each other. We examine the probability of a clog forming as the particles flow out, as a function of the size of the hopper exit. We find that clogging of these soft particles requires the hopper exit to be quite small, only slightly larger than the particle diameter. Also, we investigate how the clogging probability changes as we reduce the influence of gravity (by tilting the hopper chamber away from vertical). [Preview Abstract] 
Monday, March 13, 2017 1:03PM  1:15PM 
B15.00010: Universality of granular shock fronts Yasin Karim, Eric Corwin We experimentally study quasi 2d dilute granular flow around asymmetrical intruders. By directly measuring the grain flow field around various shapes we extract the functional form of the granular shock front. We demonstrate the universality of the shock front shape and its invariance with respect to intruder shape. The shock fronts are described by inverted catenaries whose centers and peaks are sensitive to obstacle symmetry. The consequent shift of the catenary results in dramatic changes in lift force on the intruder which we also measure. We model this lift by accounting for contributions from 1) weight of trapped beads between the shock front and the intruder, 2) collisions from freely falling grains and 3) reaction force from grains being ejected from the trapped region. [Preview Abstract] 
Monday, March 13, 2017 1:15PM  1:27PM 
B15.00011: Study of an athermal quasi static plastic deformation in a 2D granular material Jie Zhang, Jie Zheng In crystalline materials, the plasticity has been well understood in terms of dynamics of dislocation, i.e. flow defects in the crystals where the flow defects can be directly visualized under a microscope. In a contrast, the plasticity in amorphous materials, i.e. glass, is still poorly understood due to the disordered nature of the materials. In this talk, I will discuss the recent results we have obtained in our ongoing research of the plasticity of a 2D glass in the athermal quasi static limit where the 2D glass is made of bidisperse granular disks with very low friction. Starting from a densely packed homogeneous and isotropic initial state, we apply pure shear deformation to the system. For a sufficiently small strain, the response of the system is linear and elastic like; when the strain is large enough, the plasticity of the system gradually develops and eventually the shear bands are fully developed. In this study, we are particularly interested in how to relate the local plastic deformation to the macroscopic response of the system and also in the development of the shear bands. [Preview Abstract] 
Monday, March 13, 2017 1:27PM  1:39PM 
B15.00012: Significantly reduced size separation of mixing cohesive highlybidisperse particles under gravity. GuoJie Jason Gao Mixing particles of various sizes, ranging from several microns to hundreds of millimeters, is a widely used strategy to achieve supercompact packings in the industry. However, it is wellknown that separation of sizes between particles occurs if a system is cohesionless and subject to external disturbance such as shearing and shaking. Presumably, interparticle cohesive interactions, for example, attractive van der Waals forces can prevent size separation. However, a thorough analysis in this regard is still lacking. Using molecular dynamics simulation, we investigate a system of a 2D box containing highlybidisperse circular particles with a dispersity of 10 under gravity. There is cohesive interaction between particles of different dispersities, while particles of the same dispersity are mutually repulsive. We systematically change the range of the cohesive interaction and detect if size separation happens when the system is recursively subject to quasistatic shear deformation. Our results show that even a very short range of interparticle cohesion (1{\%} of the average diameter of small and large particles) can effectively prevent size separation. Besides, we increase the number of small particles while keeping that of large particles fixed. We observe large particles can steadily acquire more small cohesive neighbors as the system gradually loses its flowability. [Preview Abstract] 
Monday, March 13, 2017 1:39PM  1:51PM 
B15.00013: Trapping solitary waves as localized modes in granular chains with soft grains Michelle Przedborski, Thad Harroun, Surajit Sen Granular chains have numerous applications, from shock absorption and vibration reduction, to detecting buried objects, to energy localization. As energy is transferred between grains they deform slightly, and the contact potential arising from the elastic deformation of grains is given by the nonlinear Hertz law. The discrete nature of these systems in combination with the nonlinear contact interaction between grains leads to complex collective behavior. I will discuss the dynamics of granular chains and, in particular, I will show how solitary wave propagation in these systems is affected by grain softness, and how introducing inertial mismatches affects the reflection of solitary waves at boundaries. I will further show how initial solitary wave energy can be trapped into localized modes with predictable frequencies in chains with soft central grains. [Preview Abstract] 
Monday, March 13, 2017 1:51PM  2:03PM 
B15.00014: Understanding GrainScale Mechanisms in Dynamic Compaction of Granular Materials Michael Homel, Eric Herbold, Darren Pagan, Jonathan Lind, Ryan Hurly, Ryan Crum, Minta Akin Xray analysis of granular materials has produced detailed images of grainscale deformation and failure during highrate compaction. These experimental results guide the development of continuum constitutive models for granular materials, providing a connection between micromechanical behavior and bulk material response. To interpret the results it is necessary to distinguish between observed phenomena that are intrinsic physical properties of the granular material, and those that are merely artifacts of the test geometry or loading conditions. We perform detailed mesoscale simulations of the experiments, using our recently developed damagefield gradient partitioning approach for simulating fracture and frictional contact in the material point method (MPM). With this approach we have demonstrated a capability to produce meshindependent predictions of particle size distributions in simulations of comminution of brittle materials. Implications on continuum constitutive model development are discussed. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DEAC5207NA27344 and was supported by LLNL Laboratory Directed R{\&}D Program (tracking no. 16ERD010). [Preview Abstract] 
Monday, March 13, 2017 2:03PM  2:15PM 
B15.00015: Clogging transition of bidisperse disks driven through a periodic lattice of obstacles. Hong Nguyen, Charles Reichhardt, Cynthia Jane Reichhardt We numerically examine the clogging transition for binary disks flowing through a twodimensional periodic obstacle array. We show that clogging is a probabilistic event that occurs~when the mobile disks become trapped in dense connected clusters, producing~a transition from a homogeneous flowing state to a heterogeneous or phase separated jammed state. The probability for clogging to occur for a fixed time interval increases with increasing disk packing or decreasing obstacle spacing. For driving forces applied at different angles with respect to the symmetry axis of the obstacle array, we show that certain directions exhibit a higher clogging susceptibility. We also observe a filtration effect in which one species becomes completely trapped while the other species continues to flow. [Preview Abstract] 
Follow Us 
Engage
Become an APS Member 
My APS
Renew Membership 
Information for 
About APSThe American Physical Society (APS) is a nonprofit membership organization working to advance the knowledge of physics. 
© 2020 American Physical Society
 All rights reserved  Terms of Use
 Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 207403844
(301) 2093200
Editorial Office
1 Research Road, Ridge, NY 119612701
(631) 5914000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 200452001
(202) 6628700