共查询到20条相似文献,搜索用时 15 毫秒
1.
N. Fraysse H. Thomé L. Petit 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(4):615-619
Humidity is well-known to significantly affect the mechanical properties, static as well as dynamic, of granular materials.
We present the method of humidification of granular media from an under-saturated vapor that we designed in order to experimentally
quantify such moisture-induced effects under accurately-controlled humidity conditions. We report the quantitative measurements
of the maximum angle of stability of a pile made of small glass beads, as a function of the relative vapor pressure, up to
close to saturation. The results obtained with liquids differing in their wetting properties on glass, namely water and heptane,
are presented. It is shown that the wetting properties of the liquid on the grains have a strong influence on the cohesion
of the non-saturated granular medium.
Received 26 October 1998 and Received in final form 30 March 1999 相似文献
2.
Oger L Ammi M Valance A Beladjine D 《The European physical journal. E, Soft matter》2005,17(4):467-476
We performed numerical simulations of one-bead collision on the surface of a static granular medium. The simulations have been done for two- and three-dimensional packings of beads. The effect of the incident bead velocity, the shot angle, the mechanical parameters and the packing structure are analyzed for ordered and disordered 2D packings and only disordered 3D packings. The 2D results are in good agreement with experimental available data. The 3D simulations give good preliminaries results about the shock-wave propagation through the stacking and provides new insights in the ejection process (“splash function”). 相似文献
3.
We study how the aggregate statistical properties for density fluctuations in granular aggregates scale with the sample size and how such a scaling is associated with the correlations between grains. Correlations are studied both between grain positions and between Vorono? cell volumes, showing distinct behaviors and properties. A non-linear scaling in the aggregate volume fluctuations as function of the sample size is discovered and the connection between such anomalous scaling and correlations is explained. It emerges that volume fluctuations might be described by means of a single universal equation for all samples at all cluster sizes. 相似文献
4.
In horizontally shaken granular material different types of pattern formation have been reported. We want to deal with the
convection instability which has been observed in experiments and which recently has been investigated numerically. Using
two dimensional molecular dynamics we show that the convection pattern depends crucially on the inelastic properties of the
material. The concept of restitution coefficient provides arguments for the change of the behaviour with varying inelasticity.
Received 3 March 1999 相似文献
5.
The response of a granular material during a stop-and-go
shear experiment is investigated using an annular shear cell and
silicagel powders of different particle sizes. The experimental
results are examined on the basis of the Dieterich-Rice-Ruina
model for solid friction. In addition to making this analogy
with solid friction, we describe a new instability that is
observed when restarting shear, where the powder bed is found to
slip and compact for short hold times but only dilates for long
hold times. The minimum hold time to restore a non-slip
behaviour has been investigated for different size particles and
normal loadings. The observed dependencies show analogies
between this behaviour and the sliding rearrangements seen above
the stick-slip threshold. 相似文献
6.
V. Buchholtz J.A. Freund T. Pöschel 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,16(1):169-182
We investigate autogenous fragmentation of dry granular material in rotating cylinders using two-dimensional molecular dynamics.
By evaluation of spatial force distributions achieved numerically for various rotation velocities we argue that comminution
occurs mainly due to the existence of force chains. A statistical analysis of these force chains explains the spatial distribution
of comminution efficiency in ball mills as measured experimentally by Rothkegel [1] and Rolf [2]. For animated sequences of
our simulations see http://summa.physik.hu-berlin.de/kies/mill/bm.html
Received 19 January 2000 相似文献
7.
Topin V Delenne JY Radjai F Brendel L Mabille F 《The European physical journal. E, Soft matter》2007,23(4):413-429
Cemented granular materials (CGMs) consist of densely packed solid particles and a pore-filling solid matrix sticking to the
particles. We use a sub-particle lattice discretization method to investigate the particle-scale origins of strength and failure
properties of CGMs. We show that jamming of the particles leads to highly inhomogeneous stress fields. The stress probability
density functions are increasingly wider for a decreasing matrix volume fraction, the stresses being more and more concentrated
in the interparticle contact zones with an exponential distribution as in cohesionless granular media. Under uniaxial loading,
pronounced asymmetry can occur between tension and compression both in strength and in the initial stiffness as a result of
the presence of bare contacts (with no matrix interposed) between the particles. Damage growth is analyzed by considering
the evolution of stiffness degradation and the number of broken bonds in the particle phase. A brutal degradation appears
in tension as a consequence of brittle fracture in contrast to the more progressive nature of damage growth in compression.
We also carry out a detailed parametric study in order to assess the combined influence of the matrix volume fraction and
particle-matrix adherence. Three regimes of crack propagation can be distinguished corresponding to no particle damage, particle
abrasion and particle fragmentation, respectively. We find that particle damage scales well with the relative toughness of
the particle-matrix interface with respect to the particle toughness. This relative toughness is a function of both matrix
volume fraction and particle-matrix adherence and it appears therefore to be the unique control parameter governing transition
from soft to hard behavior. 相似文献
8.
P. Boltenhagen 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(1):75-78
We have studied the maximal angle of stability of a granular packing confined between two walls. The effect of the walls is
to increase the angle dramatically. The decay of the angle with the distance between the walls is exponential with a characteristic
length which is a function of the beads diameter. The effect of the roughness of the walls has been also studied.
Received 1 April 1999 相似文献
9.
J.-M. Hertzsch 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,18(3):459-466
A cellular model for the compaction of granular material is described. It takes into account horizontal redistribution as
well as vertical transfer of particles. Parameters are the width of the horizontal redistribution and the settling probability.
Numerical simulations of the behaviour of a granular column in a container are shown as an example, and the evolution of some
characteristic features over time has been followed for some typical configurations. Experimental results for the time evolution
of the density can be reproduced for a settling probability proportional to the unoccupied spaces for particles in the lower
cells.
Received 3 March 2000 and Received in final form 21 July 2000 相似文献
10.
Chaoming Song 《Physica A》2010,389(21):4497-455
We introduce a “Hamiltonian”-like function, called the volume function, indispensable to describe the ensemble of jammed matter such as granular materials and emulsions from a geometrical point of view. The volume function represents the available volume of each particle in the jammed systems. At the microscopic level, we show that the volume function is the Voronoi volume associated to each particle and in turn we provide an analytical formula for the Voronoi volume in terms of the contact network, valid for any dimension. We then develop a statistical theory for the probability distribution of the volumes in 3d to calculate an average volume function coarse-grained at a mesoscopic level. The salient result is the discovery of a mesoscopic volume function inversely proportional to the coordination number. Our analysis is the first step toward the calculation of macroscopic observables and equations of state using the statistical mechanics of jammed matter, when supplemented by the condition of mechanical equilibrium of jamming that properly defines jammed matter at the ensemble level. 相似文献
11.
This paper presents techniques and algorithms to compute microstructure properties of irregular-shaped granulate assemblies utilizing 3D images. The techniques are capable of extracting microstructure properties of particles such as centeroid, particle size distribution, shape indices (i.e., sphericiy and angularity), number of contacts (i.e., distribution of coordination numbers), contact network, packing efficiency, distribution of local void ratio and radial distribution function. Such properties are critical parameters for micromechanical-based numerical models to capture micro- and macromechanical behavior of geomaterials. X-ray microtomography was used to reconstruct high-resolution 3D image of a natural sand system to represent granular materials. Microstructure properties of the sand system were computed and compared with properties of a computer-simulated image of periodic random spheres. Findings indicate that the use of simplified systems of idealized spheres to model micro- and macromechanical behavior of granular systems can lead to inaccurate results due to the differences in the microstructure between both systems. Methods presented in this paper enabled capturing a more realistic microstructure that can be incorporated in micromechanical models to better simulate, understand, or explain macroscale behavior of granular materials based on their actual microstructure. 相似文献
12.
Gilberto M. Kremer 《Physica A》2010,389(19):4018-4025
The aim of this work is to analyze the entropy, entropy flux and entropy rate of granular materials within the frameworks of the Boltzmann equation and continuum thermodynamics. It is shown that the entropy inequality for a granular gas that follows from the Boltzmann equation differs from the one of a simple fluid due to the presence of a term which can be identified as the entropy density rate. From the knowledge of a non-equilibrium distribution function-valid for processes closed to equilibrium-it is obtained that the entropy density rate is proportional to the internal energy density rate divided by the temperature, while the entropy flux is equal to the heat flux vector divided by the temperature. A thermodynamic theory of a granular material is also developed whose objective is the determination of the basic fields of mass density, momentum density and internal energy density. The constitutive laws are restricted by the principle of material frame indifference and by the entropy principle. Through the exploitation of the entropy principle with Lagrange multipliers, it is shown that the results obtained from the kinetic theory for granular gases concerning the entropy density rate and entropy flux are valid in general for processes close to equilibrium of granular materials, where linearized constitutive equations hold. 相似文献
13.
Ribière P Richard P Philippe P Bideau D Delannay R 《The European physical journal. E, Soft matter》2007,22(3):249-253
When submitted to gentle mechanical taps a granular packing
slowly compacts until it reaches a stationary state that depends
on the tap characteristics. The properties of such stationary states are
experimentally investigated. The influence of the initial state, taps properties and tapping protocol are studied. The compactivity
of the packings is determinated. Our results strongly support the idea that the stationary states are genuine thermodynamic
states. 相似文献
14.
The compaction of granular packings or soils is a collective process which for higher densities becomes increasingly slower
reaching glassy behaviour. We present a study of this problem from various points of view, in particular we will represent
the evolving force network that percolates through the system by an inverse fiber rupture model.
Received 15 March 2002 and Received in final form 29 July 2002 相似文献
15.
Ribière P Richard P Bideau D Delannay R 《The European physical journal. E, Soft matter》2005,16(4):415-420
We report on experiments to measure the temporal and spatial evolution of packing arrangements of anisotropic and weakly confined granular material, using high-resolution -ray adsorption. In these experiments, the particle configurations start from an initially disordered, low-packing-fraction state and under vertical solicitations evolve to a dense state. We find that the packing fraction evolution is slowed by the grain anisotropy but, as for spherically shaped grains, can be well fitted by a stretched exponential. For a given type of grains, the characteristic times of relaxation and of convection are found to be of the same order of magnitude. On the contrary, compaction mechanisms in the media strongly depend on the grain anisotropy. 相似文献
16.
N.V. Brilliantov T. Pöschel 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(2):299-301
We show that two basic mechanical processes, the collision of particles and rolling motion of a sphere on a plane, are intimately
related. According to our recent findings, the restitution coefficient for colliding spherical particles , which characterizes the energy loss upon collision, is directly related to the rolling friction coefficient for a viscous sphere on a hard plane. We quantify both coefficients in terms of material constants which allows to determine
either of them provided the other is known. This relation between the coefficients may give rise to a novel experimental technique
to determine alternatively the coefficient of restitution or the coefficient of rolling friction.
Received 5 May 1999 相似文献
17.
This paper deals with the quasi-static regime of deformation of granular matter. It investigates the size of the Representative
Elementary Volume (REV), which is the minimum packing size above which the macroscopic mechanical behaviour of granular materials
can be defined from averaging. The first part uses typical results from recent literature and finds that the minimum REV contains
in general 10 grains; this result holds true either for most experiments or for Discrete Element Method (DEM) simulation.
This appears to be quite small. However, the second part gives a counterexample, which has been found when investigating uniaxial
compression of glass spheres which exhibit stick-slip; we show in this case that the minimum REV becomes 107 grains. This makes the system not computable by DEM. Moreover, similarity between the Richter law of seism and the exponential
statistics of stick-slip is stressed.
Received 8 March 2002 and Received in final form 12 July 2002 相似文献
18.
19.
Magneto-vibratory separation of glass and bronze granular mixtures immersed in a paramagnetic liquid
López-Alcaraz P Catherall AT Hill RJ Leaper MC Swift MR King PJ 《The European physical journal. E, Soft matter》2007,24(2):145-156
A fluid-immersed granular mixture may spontaneously separate when subjected to vertical vibration, separation occurring when
the ratio of particle inertia to fluid drag is sufficiently different between the component species of the mixture. Here,
we describe how fluid-driven separation is influenced by magneto-Archimedes buoyancy, the additional buoyancy force experienced
by a body immersed in a paramagnetic fluid when a strong inhomogeneous magnetic field is applied. In our experiments glass
and bronze mixtures immersed in paramagnetic aqueous solutions of MnCl2 have been subjected to sinusoidal vertical vibration. In the absence of a magnetic field the separation is similar to that
observed when the interstitial fluid is water. However, at modest applied magnetic fields, magneto-Archimedes buoyancy may
balance the inertia/fluid-drag separation mechanism, or it may dominate the separation process. We identify the vibratory
and magnetic conditions for four granular configurations, each having distinctive granular convection. Abrupt transitions
between these states occur at well-defined values of the magnetic and vibrational parameters. In order to gain insight into
the dynamics of the separation process we use computer simulations based on solutions of the Navier-Stokes' equations. The
simulations reproduce the experimental results revealing the important role of convection and gap formation in the stability
of the different states. 相似文献
20.
We present a hydrodynamic theoretical model for “Brazil nut” size segregation in granular materials. We give analytical solutions for the rise velocity of a large intruder particle immersed in a medium of monodisperse fluidized small particles. We propose a new mechanism for this particle size-segregation due to buoyant forces caused by density variations which come from differences in the local “granular temperature”. The mobility of the particles is modified by the energy dissipation due to inelastic collisions and this leads to a different behavior from what one would expect for an elastic system. Using our model we can explain the size ratio dependence of the upward velocity. 相似文献