Kinematic Model of Transient Shape-Induced Anisotropy in Dense Granular Flow

Nadler, Ben; Guillard, François; Einav, Itai

doi:10.1103/physrevlett.120.198003

Cited by 25 publications

(26 citation statements)

References 30 publications

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“…The flow radiographs (see Fig. 2 and Supplementary Movie 1 ) offer one explanation, showing that the barley particles have a tendency to align their major axis with the primary flow direction, which is supported by recent models 32 . This means that the effective contact friction between grains is actually between their minor axes (2.1 mm), resulting in enhanced overall flowability compared to glass beads.…”

Section: Discussionsupporting

confidence: 68%

“…Studying shape effects in granular flow has been historically challenging, largely due to the difficulties in characterising experimental results and conducting DEM simulations for verification (unlike for spherical particles, as used for validation here). However, recent kinematic models 32 provide a simple analytical framework, and Fourier-based image analysis of high-speed X-rays have been used to give experimental fabric measurements of particle size, shape, and alignment 24 . Although these have currently only been applied in a 2D, beam-averaged sense, it may be possible to relate the energy spectrums obtained from the Fourier analysis to PDFs of the relevant fields, allowing similar 3D reconstructions to the velocity field.…”

Section: Discussionmentioning

confidence: 99%

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X-ray rheography uncovers planar granular flows despite non-planar walls

Baker¹,

Guillard²,

Marks³

et al. 2018

Nat Commun

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Extremely useful techniques exist to observe the interior of deforming opaque materials, but these methods either require that the sample is replaced with a model material or that the motion is stopped intermittently. For example, X-ray computed tomography cannot measure the continuous flow of materials due to the significant scanning time required for density reconstruction. Here we resolve this technological gap with an alternative X-ray method that does not require such tomographs. Instead our approach uses correlation analysis of successive high-speed radiographs from just three directions to directly reconstruct three-dimensional velocities. When demonstrated on a steady granular system, we discover a compressible flow field that has planar streamlines despite curved confining boundaries, in surprising contrast to Newtonian fluids. More generally, our new X-ray technique can be applied using synchronous source/detector pairs to investigate transient phenomena in various soft matter such as biological tissues, geomaterials and foams.

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Section: Discussionsupporting

confidence: 68%

Section: Discussionmentioning

confidence: 99%

X-ray rheography uncovers planar granular flows despite non-planar walls

Baker¹,

Guillard²,

Marks³

et al. 2018

Nat Commun

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“…In this context, a challenge that has not yet been fully explored is the non-isotropic connotation of particle shapes, in that any departure from a spherical geometry involves the incorporation of directional properties, which can in turn impact all aspects of the macroscale response. Recent work in this context offers guidance on how to describe the granular fabric in light of shape descriptors [64], as well as to incorporate it into CBM frameworks [65]. The unification of these research ideas should therefore provide a promising avenue for material optimization, design and manufacturing.…”

Section: Discussionmentioning

confidence: 99%

The mechanics of brittle granular materials with coevolving grain size and shape

Buscarnera

Einav

2021

Proc. R. Soc. A.

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The influence of particle shape on the mechanics of sand is widely recognized, especially in mineral processing and geomechanics. However, most existing continuum theories for engineering applications do not encompass the morphology of the grains and its evolution during comminution. Similarly, the relatively few engineering models accounting for grain-scale processes tend to idealize particles as spheres, with their diameters considered as the primary and sole geometric descriptor. This paper inspires a new generation of constitutive laws for crushable granular continua with arbitrary, yet evolving, particle morphology. We explore the idea of introducing multiple grain shape descriptors into Continuum Breakage Mechanics (CBM), a theory originally designed to track changes in particle size distributions during confined comminution. We incorporate the influence of these descriptors on the elastic strain energy potential and treat them as dissipative state variables. In analogy with the original CBM, and in light of evidence from extreme fragmentation in nature, the evolution of the additional shape descriptors is postulated to converge towards an attractor. Comparisons with laboratory experiments, discrete element analyses and particle-scale fracture models illustrate the encouraging performance of the theory. The theory provides insights into the feedback among particle shape, compressive yielding and inelastic deformation in crushable granular continua. These results inspire new questions that should guide future research into crushable granular systems using particle-scale imaging and computations.

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“…[98] and references therein. One important success of granular research was to bring solid-like and flowing behavior of granular matter together, e.g., in a continuum theory with fluidity [18,47,48,99], and to understand anisotropy [70,91,93,94], also shape induced [100,101], as well as involving the rotational degrees of freedom and micro-polar models [2,[102][103][104][105][106], not to forget wet particle systems [3,4], for which a thermodynamically consistent theory [21,107] and numerical solutions [108] were recently proposed.…”

Section: A Brief History Of Granular Researchmentioning

confidence: 99%

Un-jamming due to energetic instability: statics to dynamics

2021

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Jamming/un-jamming, the transition between solid- and fluid-like behavior in granular matter, is an ubiquitous phenomenon in need of a sound understanding. As argued here, in addition to the usual un-jamming by vanishing pressure due to a decrease of density, there is also yield (plastic rearrangements and un-jamming that occur) if, e.g., for given pressure, the shear stress becomes too large. Similar to the van der Waals transition between vapor and water, or the critical current in superconductors, we believe that one mechanism causing yield is by the loss of the energy’s convexity (causing irreversible re-arrangements of the micro-structure, either locally or globally). We focus on this mechanism in the context of granular solid hydrodynamics (GSH), generalized for very soft materials, i.e., large elastic deformations, employing it in an over-simplified (bottom-up) fashion by setting as many parameters as possible to constant. Also, we complemented/completed GSH by using various insights/observations from particle simulations and calibrating some of the theoretical parameters—both continuum and particle points of view are reviewed in the context of the research developments during the last few years. Any other energy-based elastic-plastic theory that is properly calibrated (top-down), by experimental or numerical data, would describe granular solids. But only if it would cover granular gas, fluid, and solid states simultaneously (as GSH does) could it follow the system transitions and evolution through all states into un-jammed, possibly dynamic/collisional states—and back to elastically stable ones. We show how the un-jamming dynamics starts off, unfolds, develops, and ends. We follow the system through various deformation modes: transitions, yielding, un-jamming and jamming, both analytically and numerically and bring together the material point continuum model with particle simulations, quantitatively. Graphic abstract

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Kinematic Model of Transient Shape-Induced Anisotropy in Dense Granular Flow

Cited by 25 publications

References 30 publications

X-ray rheography uncovers planar granular flows despite non-planar walls

X-ray rheography uncovers planar granular flows despite non-planar walls

The mechanics of brittle granular materials with coevolving grain size and shape

Un-jamming due to energetic instability: statics to dynamics

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