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Force chains resulting from a computer simulation of weight transmission through an SSI granular system.
Source publication
The transmission of forces through a disordered granular system is studied by means of a geometrical-topological approach that reduces the granular packing into a set of layers. This layered structure constitutes the skeleton through which the force chains set up. Given the granular packing, and the region where the force is applied, such a skeleto...
Citations
... Using a photoelastic test, Behringer et al. carried out the experiments on a granular system consisting of photoelastic polymer disks subjected to shear and compression loading, calculated the probability distributions of normal and tangential force chains, and found that the probability distributions had exponential decay [9,10]. Aste et al. used a geometrical-topological approach to investigate the transmission of force chains in a disordered granular system with two different sizes of photoelastic discs [11]. Sanfratello et al. [12] analyzed the length distribution of force chains in 2D granular assemblies of the photoelastic disks under pure shear and isotropical compression. ...
Three digital specimens of asphalt mixtures (AC-13, SMA-13 and OGFC-13) were reconstructed to conduct a virtual simple performance test using the discrete element method. The distribution characteristics of force chains were investigated by a statistical method. The results indicate that it is reasonable and feasible to analyze the mesoscopic responses of asphalt mixtures using digital models. The probability distribution of the normal force chains varies with loading time and the variation laws are consistent at four loading times. And the probability distribution of the shear force chains decays exponentially. Besides, the maximum probability distributions of the normal and shear force chains decrease with increasing timestep. OGFC-13 has the maximum probability distributions of the normal and shear force chains, which are 0.34186 and 0.55884, respectively. The proportions of the “strong” force chains decrease over the loading time, and AC-13 has a maximum proportion of 49.41% for the three asphalt mixtures at four loading times. In addition, the angle distributions of the force chain are mainly near 90°, and the average ratio of the normal contact force to the mean normal contact force increases with increasing loading time at 90°. Finally, the angle distribution proportions in the first and second quadrants are much greater than those in the third and fourth quadrants.
Graphic abstract
... Their long-time motion may be modeled as vertically isotropic and constant diffusion. Short-time dynamics show that creeping grains are caged, and indicate that their motion is likely induced by long-range transmission of forces through the granular contact network 46,47 . This may be why creep motion is independent of shear rate, at least for the range of Shields stresses examined here. ...
River bed-load transport is a kind of dense granular flow, and such flows are known to segregate grains. While gravel-river beds typically have an "armoured" layer of coarse grains on the surface, which acts to protect finer particles underneath from erosion, the contribution of granular physics to riverbed armouring has not yet been investigated. Here we examine these connections in a laboratory river with bimodal sediment size, by tracking the motion of particles from the surface to deep inside the bed, and find that armour develops by two distinct mechanisms. Bed-load transport in the near-surface layer drives rapid, shear rate-dependent advective segregation. Creeping grains beneath the bed-load layer give rise to slow but persistent diffusion-dominated segregation. We verify these findings with a continuum phenomenological model and discrete element method simulations. Our experiments suggest that some riverbed armouring may be due to granular segregation from below-rather than fluid-driven sorting from above-while also providing new insights on the mechanics of segregation that are relevant to a wide range of granular flows.
... En el caso de un material granular, este está conformado por un conjunto de elementos discretos macroscópicos altamente disipativos (granos), a través de los cuales, el esfuerzo no se distribuye de manera uniforme sobre las paredes del contenedor. Esto se debe, a que la interacción grano-grano rompe la simetría impuesta por la gravedad[2], dando origen a la formación de cadenas de fuerza no isótropas, que convierten parte del esfuerzo axial en esfuerzo radial[3].INGENIERÍA Y CIENCIAS APLICADAS: MODELOS MATEMÁTICOS Y COMPUTACIONALES E. Dávila, J. Del Río, M. Cerrolaza, R. Chacón (Editores) © 2014 SVMNI Todos los derechos reservados ...
Presentamos resultados experimentales sobre el comportamiento de un material granular contenido en un silo el cual es descargado por gravedad. Se midió la fuerza de fricción cinética que ejercen los granos sobre la pared del silo durante la descarga, utilizando granos de diferentes tamaños y densidad material. Mostramos que esta fuerza de fricción cinética puede ser modelada haciendo una extensión de la teoría de Janssen para el caso de un silo estático. De los resultados obtenidos, encontramos que el cociente entre el esfuerzo radial y axial sobre las paredes del silo, depende de la densidad aparente y tamaño de los granos, lo cual es contrario a lo establecido para el caso estático, donde el cociente es constante.
... Through experimental investigations, the correlation between granular temperature has been developed as a function of forcing in a periodically forced bed of granular media (Zivkovic et al., 2009) while some studies have theoretically investigated shocks in granular gases (Serna and Marquina, 2005;Du and Kamath, 2009). Force transmission features in granular layers have been investigated using a combination of photoelasticity and theoretical modeling (Aste et al., 2002) while sound propagation attributes have been studied over a range of forcing frequencies through transmitted amplitude and phase (Liu and Nagel, 1994). With respect to mechanical behavior, anisotropy in granular media has been observed to arise from variations in contact distribution, shape of particles and the non-linear contact law (Cambou et al., 2004), but there is less evidence of anisotropy in solitary wave propagation in 2D or 3D granular media. ...
The impact-induced wave propagation in a model granular material composed of closely packed linearly elastic spherical particles interacting through Hertzian contact is investigated numerically using a specially adapted molecular dynamics framework. Of particular interest is the effect of the stiffness and density mismatch between main and interstitial beads on the anisotropic nature and speed of propagation of the primary compressive wave generated by a localized impact event in an extended square-packed granular medium. Two propagation regimes are observed in the numerical simulations: the first one described by a solitary wave pattern emanating from the point of impact, and the other characterized by a directional propagation of the impact energy in the principal directions of the pack. A simple model is proposed to describe the bounds between these two propagation regimes in the parametric space defined by the mass and stiffness ratios between main and interstitial particles. Maps of the normalized maximum compressive force and wave speed are presented to quantify the anisotropy of the wave propagation response.
With the continuous development of marine operations, the intermittent faults caused by the external salt fog environment threaten the safety of ship operations seriously. Among them, the intermittent fault of electrical connectors presents the major problem faced by ships. This article analyzed the mechanism of the intermittent fault of the electrical connector under salt-spray corrosion with and without vibration. In the meantime, the designs and vibration experiment of the electrical connector with corrosion degradation were carried out. In conclusion, the intermittent fault of the electrical connector is the main fault problem faced by ships.
We study fire-ant columns, an active version of passive granular columns, and find that, despite the inherent activity of the ants and their natural tendency to rearrange, the ants develop force-chain structures that help support the weight of the column. Hence, the apparent mass at the bottom of the column saturates with added mass in a Janssen-like fashion, reminiscent of what is seen in passive-grain columns in wide containers. Activity-induced rearrangements within the column, however, lead to changes in the force-chain structure that slightly reduce the supportive nature of the force-chains over time and to fluctuations in the pressure at the bottom of the column that scale like the law of large numbers. We capture the experimental results in simulations that include not only friction with the walls, but also a fluctuating force that introduces activity and that effectively affects the force-chain structure of the ant collective.
Packed structures are an essential part of nuclear reactors, food, chemical, transport, and process industries. Since the safety and quality of products in the packed structures is of high priority, identifying critical failure spots in packed structures is of utmost importance. The present study aims to identify critical spots in the hexagonally packed structures under mechanical loads in the presence of defects. The role of defects in the formation of force networks is also investigated in this work. The granular mechanics approach is used to analyze the analogous force pattern formation in packed structures. Discrete element method (DEM) is used to simulate the particle interaction in the granular assembly. The hexagonal packing, in X-Y plane, is created by stacking the horizontal contacting particle chains in X-direction, and thus creating inclined contact chains in the Y-direction. Hexagonal packings display two stable force network formations corresponding to compression along X and Y-direction. The effect of point defect and stacking fault on the force network is investigated. The presence of point defect is shown to induce high force concentration near the defect zone. When the assembly is compressed along X-direction, force redistribution at the defect zone increases the force levels in inclined force chains. When the assembly is compressed along Y-direction, the point defect induces zones with lesser force levels. Further, the study explores various levels of force zones induced in the system. The effect of the presence of multiple point defects in the system is analyzed further. The distance between two point defects and their loading direction induces a different set of force chains. Stacking fault is found to induce strong vertical force chains at the defect zone, unlike point defect. However, multiple stacking faults affect only the horizontal force chains near the defect zone. The present study highlights the formation of critical spots as well as lower force zones and also provides useful insights to design efficient packing structures.
Graphical Abstract
Titanium diboride (TiB2) is a granular material with good electrical conductivity. Its electrical resistance changes significantly under the action of force. Therefore, it can be used as a variable resistor in the power field. In order to achieve this goal, TiB2 particles with a diameter of 30 μm are selected. Through experiments, the resistance of a granular system under a different material height, a different cylinder diameter, and a different force is measured. The relationship between resistance and force is analyzed. Based on the force chain network, a model of the resistance network of the granular system under constant force is established. The effect of cylinder diameter and material height on electrical resistance can be described by this model. The experimental results show the accuracy of the model. The research results of this paper can provide a basis for the application of granular material in the field of power equipment.
Chains dynamics, specially when repulsive interactions come at play, remains an unsolved problem of polymer physics, although understanding this dynamics could improve our knowledge about crucial phenomena at the cellular level. For instance, the transport of RNA across the nuclear pore or the injection of viral DNA plasmid by bacteriophages into a bacteria. Alas, studying repulsive polymers in confined geometries is as experimentally difficult as it is biologically relevant. In spite of recent advances in ≪ nanorheology ≫, from the Brownian motion of local probes, or in com- puter simulation, designing experiments matching the biological parameters is near impossible. All this leads to unchallenged theoretical tools. Even the straightforward problem of polymer translocation remains lively debated. As a way out of this impasse, we propose to use granular chain as a macroscopic equivalent of a polymer. First we were interested in the internal structure of a stack of granular chains at rest and we rationalized it with polymer analogy. Then we added energy in our experimental system via mechanical excitations which appears to be analogous to the equilibration with a thermal bath. Finally we studied the dynamics of chains in specific confined geometries and compared it to both molecular dynamics simulation and theoretical tools.
The careful experiments run by several scientists have shown that the stress transmission in granular matter is a complex problem that embodies mainly the development of strong inhomogeneities and the polarization of the grain contacts. So that some theories based on the statistical mechanics have been proposed to solve some simple problems. In this paper, the principle of the biased mean value is used to determine each separable variable of the stress function. This simplifi es the Burmister's problem, to the point that only second-order transfer matrices are needed to describe the continuity conditions of the vertical displacement and stress at the interface between two consecutive layers. The imposition of the boundary conditions to the overall system not only completes the required number of equations needed to fi nd all the constants of integration but also provides a differential equation for the horizontal plane, much simpler than the Lagrange's equation for plates. Stresses, displacements and strains at any point are determined by means of hyperbolic functions of each layer thickness; for a load uniformly distributed over a circular area and over an arbitrary area as well. The values so calculated fi t well the Boussinesq's solution and the Burmister's rigorous results for small values of the coeffi cients of layer interaction, as befi ts a granular material.
