Rearrangements in a two-dimensional packing of disks

Abstract

Several aspects of the dynamics of a granular two-dimensional (2D) packing of disks slowly tilted until the system loses stability and an avalanche takes place are discussed. The evolution of the system, constructed with monodisperse disks placed on a thin cell, is studied by image analysis. As in the 3D case (packing of spheres), the system undergoes several rearrangements of different magnitude before the avalanche takes place. For thick systems, not only are small rearrangements detected but also displacements of large clusters of disks are observed in the bulk and on the free surface of the packing. In particular, characteristic angles and the avalanche mass were determined for samples of different heights. On thick systems, velocity fields of large rearrangements are presented and changes in the internal structure of the packing produced by these rearrangements are analyzed. It is found that the main effects of rearrangements is to increase the disorder of the system. Also, as the disorder of the system increases its stability threshold decreases.

Avalanches of grains with inhomogeneous distribution of inner mass

“…We remark, in addition, that even for piles of axisymmetric particles, i.e., two-dimensional stacks of homogeneous and isotropic cylinders, not much work has previously been done regarding their stability [5,6,13].…”

“…The mechanical stability of granular piles has been the subject of numerous studies, both experimental and theoretical [1][2][3][4][5][6][7][8][9][10][11][12], and it has been found to depend on various factors: the number of grains, packing fraction, history, boundary conditions, and cohesion, particularly due to humidity. Also, the maximum slope that the pile can exhibit depends on the shape of the grains, on the physical properties of their surface (for instance on the roughness), and on the distribution of their size [13][14][15][16][17].…”

“…Grains with a radial symmetry have a tendency to organize in crystals characterized by an ordered contact network as well as an ordered positional array of the center of mass of the particles. It has been observed that such ordered and compact arrays of grains are more stable than disordered ones [6]. The formation of crystals can be avoided by the use of nonspherical grains.…”

Compacity influence in reorganization of two dimensional granular packings: Numerical model

“…In two dimensional systems two types of packings were analyzed: disordered and hexagonally ordered. It was relevant to notice the absence of rearrangements in ordered systems [7]. This behavior might be due to the fact that ordered packings have less available empty space for the disks to move, which suggest the packing fraction or compacity C, is of great importance in the origin of these reorganization events.…”

“…We have experimentally studied granular packing stability. In particular, we have exhaustively studied stability and dynamics in three dimensional systems of spheres [3][4][5][6] and two dimensional packing of disks [7,8].…”