A review and analysis of granular shear experiments under low effective stress conditions

Cheng, Xiaohui; Xiao, Shize; Cao, Alex Sixie; Hou, Meiying

doi:10.1007/s10035-019-0955-x

Cited by 7 publications

(2 citation statements)

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“…It was recently extended to include friction, softness and cohesion [2,12,13,69,70,[73][74][75], but it does not have a fully tensorial form [76,77], and doubts about its well-posed-ness are still discussed [78][79][80]. Modern experimental techniques [25,71,81,82], also with focus on low confining stress [83], shed new light on classical works on the response to local perturbations [84], jamming and un-jamming [23,[84][85][86][87], in particular by shear [10,49,60,65,[88][89][90], and transient fabric/micro-structure evolution [31,49,55,[91][92][93][94]. One of the classical experimental techniques involves photoelastic materials that allow to visualize stress [95][96][97], as complemented by a huge amount of particle simulations, e.g., see Ref.…”

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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Section: A Brief History Of Granular Researchmentioning

confidence: 99%

Un-jamming due to energetic instability: statics to dynamics

2021

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“…This behavior is not captured by the rate-dependent Bingham model nor by rate-independent critical state soil mechanics models. Moreover, the underlying mechanism is not yet known, and the pressure sensitive characteristics of such transient flows is yet to be investigated 21 , 22 .…”

Section: Introductionmentioning

confidence: 99%

A unified constitutive model for pressure sensitive shear flow transitions in moderate dense granular materials

Cheng

Xiao

Cao

et al. 2021

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Granular shear flows exhibit complex transitional regimes that are dramatically affected by the pressure level and shear stress state. New advances in granular shear tests at low pressure have enlightened the understanding of the two granular shear flow transitions: between quasi-static and moderate shear flows, and between steady-state and transient shear flows. However, a unified constitutive model to describe these two transitions is yet to develop. In this work, a simplified and unified model is proposed based on innovative triaxial shear flow tests, using two dimensionless physical variables. Model results validated against experimental data suggest that the shear flow transition between a quasi-static to a moderate Isotach type flow state is highly pressure-dependent. At extremely low pressure, the granular viscosity becomes the primary mechanism, suppressing the quasi-static mechanism even under “quasi-static” shear rates. In transient to steady state granular flow transitions, a mobilized shear stress ratio or mobilized friction coefficient between zero and the critical state ratio for consolidated granular packings is taken into consideration. This is coupled with the mechanism of granular viscosity. These findings have not been discussed before and are of great relevance to granular mechanics as well as space and earthquake engineering.

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