CiteULike: dchen's force

Spatial force correlations in granular shear flow. I. Numerical evidence

Gregg Lois — 2008-06-10T23:40:05-00:00

Physical Review E (Statistical, Nonlinear, and Soft Matter Physics), Vol. 76, No. 2. (2007)

We investigate the emergence of correlations in granular shear flow. By increasing the density of a simulated granular flow, we observe a transition from a dilute regime, where interactions are dominated by binary collisions, to a dense regime characterized by large force networks and collective motions. With increasing density, interacting grains tend to form networks of simultaneous contacts due to the dissipative nature of collisions. We quantify the size of these networks by measuring two-point force correlations and find dramatic changes in the statistics of contact forces as the size of the networks increases.

Shape of impact craters in granular media

Simon de Vet — 2008-06-10T20:36:31-00:00

Physical Review E (Statistical, Nonlinear, and Soft Matter Physics), Vol. 76, No. 4. (2007)

We present the results of experiments studying the shape of craters formed by the normal impact of a solid spherical projectile into a deep noncohesive granular bed at low energies. The resultant impact crater surfaces are accurately digitized using laser profilometry, allowing for the detailed investigation of the crater shape. We find that these impact craters are very nearly hyperbolic in profile. Crater radii and depths are dependent on impact energy, as well as the projectile density and size. The precise crater shape is a function of the crater aspect ratio. While the dimensions of the crater are highly dependent on the impact energy, we show that the energy required to excavate the crater is only a tiny fraction (0.1%–0.5%) of the kinetic energy of the projectile.

Effects of friction and disorder on the quasistatic response of granular solids to a localized force

C Goldenberg — 2008-06-08T23:44:30-00:00

Physical Review E (Statistical, Nonlinear, and Soft Matter Physics), Vol. 77, No. 4. (2008)

The response to a localized force provides a sensitive test for models of stress transmission in granular solids. Elasto-plastic models, traditionally used by engineers, have been challenged by theories and experiments that suggest a wavelike (hyperbolic) propagation of the stress, as opposed to the elliptic equations of static elasticity. Simulations of two-dimensional granular systems subject to a localized external force have been employed to examine the nature of stress transmission in these systems as a function of the magnitude of this force, the frictional parameters, and degree of disorder. The results indicate that in large systems (as considered by engineers) the response is close to that predicted by isotropic elasticity, whereas for small systems (or strongly forced ones) it is strongly anisotropic. In the latter case the applied force induces changes in the contact network accompanied by frictional sliding and gives rise to hyperboliclike stress propagation. The larger the static friction, the more extended the range of forces for which the response is elastic, and the smaller the anisotropy. Increase in the degree of polydispersity (in the studied range, up to 25%) decreases the range of elastic response. This paper is an extension of a previously published Letter [C. Goldenberg and I. Goldhirsch, Nature (London) 435, 188 (2005)].

Force Distributions in Dense Two-Dimensional Granular Systems

Farhang Radjai — 2008-01-23T15:01:26-00:00

Physical Review Letters, Vol. 77, No. 2. (July 1996), 274.

Relying on contact dynamics simulations; we study the statistical distribution of contact forces inside a confined packing of circular rigid disks with solid friction. We find the following: (1) The number of normal and tangential forces lower than their respective mean value decays as a power law. (2) The number of normal and tangential forces higher than their respective mean value decays exponentially. (3) The ratio of friction to normal force is uniformly distributed and is uncorrelated with normal force. (4) When normalized with respect to their mean values; these distributions are independent of sample size and particle size distribution.

Jamming and Fluctuations in Granular Drag

I Albert — 2007-09-27T03:46:04-00:00

Physical Review Letters, Vol. 84, No. 22. (29 May 2000), 5122.

We investigate the dynamic evolution of jamming in granular media through fluctuations in the granular drag force. The successive collapse and formation of jammed states give a stick-slip nature to the fluctuations which is independent of the contact surface between the grains and the dragged object; thus implying that the stress-induced collapse is nucleated in the bulk of the granular sample. We also find that while the fluctuations are periodic at small depths; they become “stepped” at large depths; a transition which we interpret as a consequence of the long-range nature of the force chains.

Statistical Mechanics of Stress Transmission in Disordered Granular Arrays

SF Edwards — 2008-04-28T13:46:02-00:00

Physical Review Letters, Vol. 82, No. 26. (28 June 1999), 5397.

Stress Fluctuations in a 2D Granular Couette Experiment: A Continuous Transition

Daniel Howell — 2008-04-27T00:21:13-00:00

Physical Review Letters, Vol. 82, No. 26. (28 June 1999), 5241.

Measuring the distribution of interdroplet forces in a compressed emulsion system

Jasna Brujic — 2008-04-27T00:12:13-00:00

Physica A: Statistical Mechanics and its Applications, Vol. 327, No. 3-4. (15 September 2003), pp. 201-212.

The micromechanics of a variety of systems experiencing a structural arrest due to their high density could be unified by a thermodynamic framework governing their approach to [`]jammed' configurations. The mechanism of supporting an applied stress through the microstructure of these highly packed materials is important in inferring the features responsible for the inhomo- geneous stress transmission and testing the universality for all jammed matter. In this paper, we present a novel method for measuring the force distribution within the bulk of a compressed emulsion system using confocal microscopy and explain our results with a simple theoretical model and computer simulations. We obtain an exponential distribution at large forces and a small peak at small forces, in agreement with previous experimental and simulation data for other particulate systems.

Force distributions in three-dimensional granular assemblies: Effects of packing order and interparticle friction

Daniel Blair — 2008-04-27T00:03:02-00:00

Physical Review E, Vol. 63, No. 4. (27 March 2001), 041304.

Force distributions in three-dimensional compressible granular packs

Michael Erikson — 2008-04-27T00:01:52-00:00

Physical Review E, Vol. 66, No. 4. (14 October 2002), 040301.

Footprints in Sand: The Response of a Granular Material to Local Perturbations

Junfei Geng — 2008-04-27T00:00:46-00:00

Physical Review Letters, Vol. 87, No. 3. (2 July 2001), 035506.

Foam Mechanics at the Bubble Scale

DJ Durian — 2007-09-27T03:41:32-00:00

Physical Review Letters, Vol. 75, No. 26. (25 December 1995), 4780.

By focusing on entire bubbles rather than films or vertices; a simple model is proposed for the deformation and flow of foam in which dimensionality; polydispersity; and liquid content can easily be varied. Simulation results are presented for the linear elastic properties as a function of bubble volume fraction; showing a melting transition where the static shear modulus vanishes and the relaxation time scale peaks. Results are also presented for shear stress versus strain rate; showing intermittent flow via avalanchelike topological rearrangements and Bingham-plastic behavior.

Granular matter A tale of tails

Martin van Hecke — 2005-06-23T02:21:28-00:00

Nature, Vol. 435, No. 7045. (22 June 2005), pp. 1041-1042.

Statistics of the contact network in frictional and frictionless granular packings

Leonardo Silbert — 2008-01-01T22:14:34-00:00

Physical Review E, Vol. 66, No. 6. (10 December 2002), 061303.

Simulated granular packings with different particle friction coefficient μ are examined. The distribution of the particle-particle and particle-wall normal and tangential contact forces P ( f ) are computed and compared with existing experimental data. Here f ≡ F / F ̅ is the contact force F normalized by the average value F ̅ . P ( f ) exhibits exponential-like decay at large forces; a plateau/peak near f =1; with additional features at forces smaller than the average that depend on μ. Additional information beyond the one-point force distribution functions is provided in the form of the force-force spatial distribution function and the contact point radial distribution function. These quantities indicate that correlations between forces are only weakly dependent on friction and decay rapidly beyond approximately three particle diameters. Distributions of particle-particle contact angles show that the contact network is not isotropic and only weakly dependent on friction. High force-bearing structures; or force chains; do not play a dominant role in these three-dimensional; unloaded packings.

Force Fluctuations in Bead Packs

Liu — 2008-01-23T15:01:10-00:00

Science, Vol. 269, No. 5223. (28 July 1995), pp. 513-515.

Experimental observations and numerical simulations of the large force inhomogeneities present in stationary bead packs are presented. Forces much larger than the mean occurred but were exponentially rare. An exactly soluble model reproduced many aspects of the experiments and simulations. In this model, the fluctuations in the force distribution arise because of variations in the contact angles and the constraints imposed by the force balance on each bead in the pile. 10.1126/science.269.5223.513

Force distribution in a granular medium

Daniel Mueth — 2008-04-26T22:59:22-00:00

Physical Review E, Vol. 57, No. 3. (1 March 1998), 3164.

3D bulk measurements of the force distribution in a compressed emulsion system

Jasna — 2008-04-26T22:58:14-00:00

Bimodal Character of Stress Transmission in Granular Packings

Farhang Radjai — 2008-04-26T22:55:58-00:00

Physical Review Letters, Vol. 80, No. 1. (5 January 1998), 61.

Green's function measurements of force transmission in 2D granular materials

Junfei Geng — 2008-03-28T13:14:35-00:00

Physica D: Nonlinear Phenomena, Vol. 182, No. 3-4. (15 August 2003), pp. 274-303.

We describe experiments that probe the response to a point force of 2D granular systems under a variety of conditions. Using photoelastic particles to determine forces at the grain scale, we obtain ensembles of responses for the following particle types, packing geometries and conditions: monodisperse ordered hexagonal packings of disks, bidisperse packings of disks with different amounts of disorder, disks packed in a regular rectangular lattice with different frictional properties, packings of pentagonal particles, systems with forces applied at an arbitrary angle at the surface, and systems prepared with shear deformation, hence with texture or anisotropy. We experimentally show that disorder, packing structure, friction and texture significantly affect the average force response in granular systems. For packings with weak disorder, the mean forces propagate primarily along lattice directions. The width of the response along these preferred directions grows with depth, increasingly so as the disorder of the system grows. Also, as the disorder increases, the two propagation directions of the mean force merge into a single direction. The response function for the mean force in the most strongly disordered system is quantitatively consistent with an elastic description for forces applied nearly normally to a surface, but this description is not as good for non-normal applied forces. These observations are consistent with recent predictions of Bouchaud et al. [Eur. Phys. J. E 4 (2001) 451] and Socolar et al. [Eur. Phys. J. E 7 (2002) 353] and with the anisotropic elasticity models of Goldenberg and Goldhirsch [Phys. Rev. Lett. 89 (2002) 084302]. At this time, it is not possible to distinguish between these two models. The data do not support a diffusive picture, as in the q-model, and they are in conflict with data by Da Silva and Rajchenbach [Nature 406 (2000) 708] that indicate a parabolic response for a system consisting of cuboidal blocks. We also explore the spatial properties of force chains in an anisotropic textured system created by a nearly uniform shear. This system is characterized by stress chains that are strongly oriented along an angle of 45[degree sign], corresponding to the compressive direction of the shear deformation. In this case, the spatial correlation function for force has a range of only one particle size in the direction transverse to the chains, and varies as a power law in the direction of the chains, with an exponent of -0.81. The response to forces is the strongest along the direction of the force chains, as expected. Forces applied in other directions are effectively refocused towards the strong force chain direction.

Universal anisotropy in force networks under shear

Srdjan Ostojic — 2008-04-26T22:42:46-00:00

Physical Review E (Statistical, Nonlinear, and Soft Matter Physics), Vol. 75, No. 3. (2007)

Scaling properties of patterns formed by large contact forces are studied as a function of the applied shear stress, in two-dimensional static packings generated from the force network ensemble. An anisotropic finite-size-scaling analysis shows that the applied shear does not affect the universal scaling properties of these patterns, but simply induces different length scales in the principal directions of the macroscopic stress tensor. The ratio of these length scales quantifies the anisotropy of the force networks, and is found not to depend on the details of the underlying contact network, in contrast with other properties such as the yield stress.

Sheared Force Networks: Anisotropies, Yielding, and Geometry

Jacco Snoeijer — 2008-04-26T22:37:46-00:00

Physical Review Letters, Vol. 96, No. 9. (2006)

A scenario for the yielding of granular matter is presented by considering the ensemble of force networks for a given contact network and applied shear stress . As is increased, the probability distribution of contact forces becomes highly anisotropic, the difference between average contact forces along minor and major axes grows, and the allowed networks span a shrinking subspace of all force networks. Eventually, contacts start to break, and at the maximal shear stress the packing becomes effectively isostatic. The size of the allowed subspace exhibits simple scaling properties, which lead to a prediction for the yield stress for packings of an arbitrary contact number.

Measurements of the yield stress in frictionless granular systems

Ning Xu — 2008-04-26T22:36:05-00:00

Physical Review E (Statistical, Nonlinear, and Soft Matter Physics), Vol. 73, No. 6. (2006)

We perform extensive molecular dynamics simulations of two-dimensional frictionless granular materials to determine whether these systems can be characterized by a single static yield shear stress. We consider boundary-driven planar shear at constant volume and either constant shear force or constant shear velocity. Under steady flow conditions, these two ensembles give similar results for the average shear stress versus shear velocity. However, near jamming it is possible that the shear stress required to initiate shear flow can differ substantially from the shear stress required to maintain flow. We perform several measurements of the shear stress near the initiation and cessation of flow. At fixed shear velocity, we measure the average shear stress yv in the limit of zero shear velocity. At fixed shear force, we measure the minimum shear stress yf required to maintain steady flow at long times. We find that in finite-size systems yf>yv, which implies that there is a jump discontinuity in the shear velocity from zero to a finite value when these systems begin flowing at constant shear force. However, our simulations suggest that the difference yf–yv, and thus the discontinuity in the shear velocity, tend to zero in the infinite-system-size limit. Thus, our results imply that in the large-system limit, frictionless granular systems can be characterized by a single static yield shear stress. We also monitor the short-time response of these systems to applied shear and show that the packing fraction of the system and shape of the velocity profile can strongly influence whether or not the shear stress at short times overshoots the long-time average value.

Granular micro-structure and avalanche precursors

Lydie Staron — 2006-08-01T00:34:06-00:00

J. Stat. Mech., Vol. 2006, No. 07. (July 2006), P07014.

Force, relative-displacement, and work networks in granular materials subjected to quasistatic deformation

NP Kruyt — 2008-04-26T22:31:19-00:00

Physical Review E (Statistical, Nonlinear, and Soft Matter Physics), Vol. 75, No. 5. (2007)

To describe the heterogeneous nature of stress transmission in granular materials, the concept of the “strong” network consisting of contacts with large normal forces has been proposed by Radjaï et al. [Phys. Rev. Lett. 80, 61 (1998)]. The shear stress is mainly determined by this strong network. The dual viewpoint is adopted here, by not only considering the forces at contacts, but also the deformation. It is shown that the strain increments are determined by the tangential component of the relative displacements at the contacts. A “mobile” network consisting of contacts with large tangential relative displacements is defined that primarily accounts for the strain increments. The investigation of the relation between the strong and the mobile networks shows that these networks are largely unrelated. An alternative network is defined that consists of contacts at which the contribution to the work input is large. It is found that this work input occurs primarily through the tangential forces and tangential relative displacements.

Bounds on the shear load of cohesionless granular matter

Wouter Ellenbroek — 2007-01-30T17:40:14-00:00

J. Stat. Mech., Vol. 2007, No. 01. (January 2007), P01023.

Shear-Induced Stress Relaxation in a Two-Dimensional Wet Foam

John Lauridsen — 2008-04-26T22:16:37-00:00

Physical Review Letters, Vol. 89, No. 9. (2002), 098303.

Packing of Compressible Granular Materials

Hernán Makse — 2008-01-23T15:02:23-00:00

Physical Review Letters, Vol. 84, No. 18. (1 May 2000), 4160.

3D computer simulations and experiments are employed to study random packings of compressible spherical grains under external confining stress. In the rigid ball limit; we find a continuous transition in which the stress vanishes as (φ-φ c ) β ; where φ is the (solid phase) volume density. The value of φ c depends on whether the grains interact via only normal forces (giving rise to random close packings) or by a combination of normal and friction generated transverse forces (producing random loose packings). In both cases; near the transition; the system's response is controlled by localized force chains.

Jamming, Force Chains, and Fragile Matter

ME Cates — 2008-04-26T21:58:44-00:00

Physical Review Letters, Vol. 81, No. 9. (1998), 1841.

Contact force measurements and stress-induced anisotropy in granular materials

TS Majmudar — 2005-06-23T02:21:24-00:00

Nature, Vol. 435, No. 7045., pp. 1079-1082.

Measurement of Forces Inside a Three-Dimensional Pile of Frictionless Droplets

J Zhou — 2008-01-01T22:04:40-00:00

Science, Vol. 312, No. 5780. (16 June 2006), pp. 1631-1633.

We present systematic and detailed measurements of interparticle contact forces inside three-dimensional piles of frictionless liquid droplets. We measured long-range chainlike correlations of the directions and magnitudes of large forces, thereby establishing the presence of force chains in three dimensions. Our correlation definition provides a chain persistence length of 10 mean droplet diameters, decreasing as load is applied to the pile. We also measured the angles between contacts and showed that the chainlike arrangement arises from the balance of forces. Moreover, we found that piles whose height was comparable to the chain persistence length exhibited substantially greater strain hardening than did tall piles, which we attributed to the force chains. Together, the results establish a connection between the microscopic force network and the elastic response of meso- or macroscopic granular piles. The conclusions drawn here should be relevant in jammed systems generally, including concentrated emulsions and piles of sand or other heavy particles. 10.1126/science.1125151

Force Distributions near Jamming and Glass Transitions

Corey O'Hern — 2007-05-18T10:36:37-00:00

Physical Review Letters, Vol. 86, No. 1. (1 January 2001), 111.

We calculate the distribution of interparticle normal forces P ( F ) near the glass and jamming transitions in model supercooled liquids and foams; respectively. P ( F ) develops a peak that appears near the glass or jamming transitions; whose height increases with decreasing temperature; decreasing shear stress and increasing packing density. A similar shape of P ( F ) was observed in experiments on static granular packings. We propose that the appearance of this peak signals the development of a yield stress. The sensitivity of the peak to temperature; shear stress; and density lends credence to the recently proposed generalized jamming phase diagram.

Effect of Particle Shape on the Stress Dip Under a Sandpile

I Zuriguel — 2008-03-19T17:13:57-00:00

Physical Review Letters, Vol. 98, No. 2. (2007)

The results of an experimental investigation into the effects of particle shape on the stress dip formed under a 2D sandpile is reported. We find good agreement with previous results of a small dip for mixtures of disks poured from a localized source. The new finding is that the dip is significantly enhanced when elliptical particles are used. We attribute the amplification of the effect to orientational ordering induced by the shape of the grains which removes the degeneracy of circular particles.