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Register a new userJamming transition in non-spherical particle systems: pentagons vs. disks
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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 $muapprox 1$. (1) For both pentagons and disks, the onset of rigidity occurs when the average coordination number of non-rattlers, $Z_{nr}$ , reaches 3, and the dependence of $Z_{nr}$ on the packing fraction $phi$ changes again when $Z_{nr}$ reaches 4. (2) Though the packing fractions $phi_{c1}$ and $phi_{c2}$ 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 $phi_{c1}$ and $phi_{c2}$ 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 comparing 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.
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The jamming scenario of disordered media, formulated about 10 years ago, has in recent years been advanced by analyzing model systems of granular media. This has led to various new concepts that are increasingly being explored in in a variety of systems. This chapter contains an introductory review of these recent developments and provides an outlook on their applicability to different physical systems and on future directions. The first part of the paper is devoted to an overview of the findings for model systems of frictionless spheres, focussing on the excess of low-frequency modes as the jamming point is approached. Particular attention is paid to a discussion of the cross-over frequency and length scales that govern this approach. We then discuss the effects of particle asphericity and static friction, the applicability to bubble models for wet foams in which the friction is dynamic, the dynamical arrest in colloids, and the implications for molecular glasses.
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Granulation is a ubiquitous process crucial for many products ranging from food and care products to pharmaceuticals. Granulation is the process in which a powder is mixed with a small amount of liquid (binder) to form solid agglomerates surrounded by air. By contrast, at low solid volume fractions {phi}, the mixing of solid and liquid produces suspensions. At intermediate {phi}, either granules or dense suspensions are produced, depending on the applied stress. We address the question of how and when high shear mixing can lead to the formation of jammed, non-flowing granules as {phi} is varied. In particular, we measure the shear rheology of a model system - a suspension of glass beads with an average diameter of $sim$ 7 {mu}m - at solid volume fractions {phi} $gtrsim$ 0.40. We show that recent insights into the role of inter-particle friction in suspension rheology allow us to use flow data to predict some of the boundaries between different types of granulation as {phi} increases from $sim$ 0.4 towards and beyond the maximum packing point of random close packing.
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