Jamming Transition In Non-Spherical Particle Systems: Pentagons Versus Disks

We investigate the jamming transition in a quasi-2D granular material composed of regular pentagons or disks subjected to quasistatic uniaxial compression. We report six major findings based on experiments with monodisperse photoelastic particles with static friction coefficient μ≈1. (1) For both pentagons and disks, the onset of rigidity occurs when the average coordination number of non-rattlers, Znr, reaches 3, and the dependence of Znr on the packing fraction ϕ changes again when Znr reaches 4. (2) Though the packing fractions ϕc1 and ϕc2 at these transitions differ from run to run, for both shapes the data from all runs with different initial configurations collapses when plotted as a function of the non-rattler fraction. (3) The averaged values of ϕc1 and ϕc2 for pentagons are around 1% smaller than those for disks. (4) Both jammed pentagons and disks show Gamma distribution of the Voronoi cell area with same parameters. (5) The jammed pentagons have similar translational order for particle centers but slightly less orientational order for contacting pairs compared to jammed disks. (6) For jammed pentagons, the angle between edges at a face-to-vertex contact point shows a uniform distribution and the size of a cluster connected by face-to-face contacts shows a power-law distribution

Jamming Transition In Non-Spherical Particle Systems: Pentagons Versus Disks

We investigate the jamming transition in a quasi-2D granular material composed of regular pentagons or disks subjected to quasistatic uniaxial compression. We report six major findings based on experiments with monodisperse photoelastic particles with static friction coefficient μ≈1. (1) For both pentagons and disks, the onset of rigidity occurs when the average coordination number of non-rattlers, Znr, reaches 3, and the dependence of Znr on the packing fraction ϕ changes again when Znr reaches 4. (2) Though the packing fractions ϕc1 and ϕc2 at these transitions differ from run to run, for both shapes the data from all runs with different initial configurations collapses when plotted as a function of the non-rattler fraction. (3) The averaged values of ϕc1 and ϕc2 for pentagons are around 1% smaller than those for disks. (4) Both jammed pentagons and disks show Gamma distribution of the Voronoi cell area with same parameters. (5) The jammed pentagons have similar translational order for particle centers but slightly less orientational order for contacting pairs compared to jammed disks. (6) For jammed pentagons, the angle between edges at a face-to-vertex contact point shows a uniform distribution and the size of a cluster connected by face-to-face contacts shows a power-law distribution

Packings of 3D stars: stability and structure

© 2016, Springer-Verlag Berlin Heidelberg.We describe a series of experiments involving the creation of cylindrical packings of star-shaped particles, and an exploration of the stability of these packings. The stars cover a broad range of arm sizes and frictional properties. We carried out three different kinds of experiments, all of which involve columns that are prepared by raining star particles one-by-one into hollow cylinders. As an additional part of the protocol, we sometimes vibrated the column before removing the confining cylinder. We rate stability in terms of r, the ratio of the mass of particles that fall off a pile when it collapsed, to the total particle mass. The first experiment involved the intrinsic stability of the column when the confining cylinder was removed. The second kind of experiment involved adding a uniform load to the top of the column, and then determining the collapse properties. A third experiment involved testing stability to tipping of the piles. We find a stability diagram relating the pile height, h, versus pile diameter, (Formula presented.) , where the stable and unstable regimes are separated by a boundary that is roughly a power-law in h versus (Formula presented.) with an exponent that is less than unity. Increasing vibration and friction, particularly the latter, both tend to stabilize piles, while increasing particle size can destabilize the system under certain conditions

Conceptualización, léxico y gramática: los principios de traducibilidad y sinonimia

Ministerio de Ciencia e Innovación del Gobierno de España

Iberoamerican Reviews

Reseñas iberoamericanasIberoamerican Review

Statistical organization of acoustic events induced by the slow propagation of a single crack in a heterogeneous solid

International audienceIn heterogeneous materials under slowly increasing compressive loading, damaging processes are sometimes erratic, with random sudden cascades of microcracking events spanning a variety of sizes. Such so-called crackling dynamics [1] are e.g. revealed by the acoustic emission accompanying the compressive failure of porous materials or, at much larger scale the seismic activity going along with earthquakes (see [2] for review). In both cases, statistical analyses have revealed complex time-energy organization in mainshock-aftershock sequences obeying a range of robust empirical scaling laws [3] (Gutenberg-Richter and Omori-Utsu being the most well-known) that help carry out seismic hazard analysis and damage mitigation. These laws are usually conjectured to betray the collective dynamics of microcrack nucleation.The experiments presented at CFRAC were designed to unravel to which extent such a seismic-like time energy organization for acoustic events (AE) hold in the much simpler situation of a single propagating. Such cracks were slowly driven in artificial rocks under tension [4] and the statistical organization of the so produced acoustic events was characterized. This organization shares some similarities with that observed in compressive or shear fracture and, at much larger scales, in earthquakes. Some specific features however emerges and, as will be discussed at CFRAC, constraint the seismic laws and their interrelations