Finite width of quasistatic shear bands

Ea, Jagla

doi:10.1103/physreve.78.026105

Cited by 8 publications

(16 citation statements)

References 18 publications

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“…The first exponent is in agreement with the results of Jagla [32] obtained for the stationary zone width. Thus, in our model the functional form of the curve describing the evolution of the shear zone width in scaled variables is independent of the length factor.…”

Section: B Model Resultssupporting

confidence: 91%

“…This is a self-organized process: the rearrangement along the yielding path (corresponding to the minimal force) modifies the potential, which is then used to determine the location of the next plastic event. The above mentioned fundamental features of nonlocality and self-organization can also be found in other models: e.g., the models of elastic [32], kinetic elasto-plastic [14,33], and shear transformation zone [34] theory.…”

Section: A Description Of the Fluctuating Band Modelmentioning

confidence: 96%

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Evolution of shear zones in granular materials

et al. 2014

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The evolution of wide shear zones or shear bands was investigated experimentally and numerically for quasistatic dry granular flows in split bottom shear cells. We compare the behavior of materials consisting of beads, irregular grains, such as sand, and elongated particles. Shearing an initially random sample, the zone width was found to significantly decrease in the first stage of the process. The characteristic shear strain associated with this decrease is about unity and it is systematically increasing with shape anisotropy, i.e., when the grain shape changes from spherical to irregular (e.g., sand) and becomes elongated (pegs). The strongly decreasing tendency of the zone width is followed by a slight increase which is more pronounced for rodlike particles than for grains with smaller shape anisotropy (beads or irregular particles). The evolution of the zone width is connected to shear-induced packing density change and for nonspherical particles it also involves grain reorientation effects. The final zone width is significantly smaller for irregular grains than for spherical beads.

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Section: B Model Resultssupporting

confidence: 91%

Section: A Description Of the Fluctuating Band Modelmentioning

confidence: 96%

Evolution of shear zones in granular materials

et al. 2014

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“…The velocity field is well approximated by an errorfunction [11,12,[22][23][24] with a width considerably increasing from bottom to top (free surface) [19,[24][25][26]. The width of the shear-band is considerably larger than only a few particle diameters, as reported in many other systems.…”

Section: Discussion Of the Present Approachmentioning

confidence: 55%

The critical-state yield stress (termination locus) of adhesive powders from a single numerical experiment

Luding¹,

Alonso‐Marroquín

2011

Granular Matter

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Dry granular materials in a split-bottom ring shear cell geometry show wide shear bands under slow, quasistatic, large deformation. This system is studied in the presence of contact adhesion, using the discrete element method (DEM). Several continuum fields like the density, the deformation gradient and the stress tensor are computed locally and are analyzed with the goal to formulate objective constitutive relations for the flow behavior of cohesive powders. From a single simulation only, by applying time-and (local) space-averaging, and focusing on the regions of the system that experienced considerable deformations, the critical-state yield stress (termination locus) can be obtained. It is close to linear, for non-cohesive granular materials, and nonlinear with peculiar pressure dependence, for adhesive powdersdue to the nonlinear dependence of the contact adhesion on the confining forces. The contact model is simplified and possibly will need refinements and additional effects in order to resemble realistic powders. However, the promising method of how to obtain a critical-state yield stress from a single numerical test of one material is generally applicable and waits for calibration and validation.

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“…Extending the variational principle -To explain the broad shearbands in the split-bottom geometry, a random or randomly varying local material failure strength [14,21] was invoked. The main extension extends the minimal dissipation model by combining the variational principle with a self organized random potential as follows.…”

Section: Flows In the Split-bottom Geometry: Theorymentioning

confidence: 99%

Granular flows in split-bottom geometries

Dijksman

Hecke

2010

Soft Matter

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There is a simple and general experimental protocol to generate slow granular flows that exhibit wide shear zones, qualitatively different from the narrow shear bands that are usually observed in granular materials . The essence is to drive the granular medium not from the sidewalls, but to split the bottom of the container that supports the grains in two parts and slide these parts past each other. Here we review the main features of granular flows in such split-bottom geometries. PACS numbers: 45.70.Mg, 47.57.Gc, 83.50.Ax, Granular media exhibit a complex mixture of solid and fluid-like behavior, often hard to predict or capture in models. Perhaps the most striking feature of granular flows is their tendency to localize in narrow shear bands [1]. A decent model of grain flows should be able to capture, and preferably, predict this type of behavior, but at present there is no general approach which, for given geometry, driving strength and grain properties, predicts the ensuing flow fields.In recent years, much progress has been made for fast flows, such as avalanche flows down an incline, where large flowing zones form. Microscopically, momentum exchange then takes place by a mixture of collisions and enduring contacts. This allows the definition of a dimensionless parameter I, the inertial number, which characterizes the local "rapidity" of the flow. A local relation between stresses, strain-rates and I then successfully captures many aspects of these rapid granular flows [2][3][4].In contrast, the situation for slow flows, such as those made by slowly shearing the boundaries of a container containing grains, is still wide open. The averaged stresses and flow profiles become essentially independent of the flow rate, so that constitutive relations based on relating stresses and strain rates are unlikely to capture the full physics. In this regime, shear banding is generally very strong, with shear bands having a typical thickness of five to ten grain diameters. These shear bands often localize near the moving boundary. For a recent review, see [1]. Experimental handles for probing this shear localization appears to be limited, since shear banding appears so robust. For example, granular flows in Couette cells always show the formation of a narrow shear band near the inner cylinder, irrespective of dimensionality, driving rate, or details of the geometry [5].In this regime of slow flows, the inertial number I tends to zero and momentum transfer is dominated by enduring contacts. Soil mechanics is then a natural starting point to describe these flows, and both rate independence and shear banding are consistent with a Mohr-Coulomb picture where the friction laws acting at the grain scale are translated to the stresses acting at coarse-grained level. The idea is that when the ratio of shear to normal stresses is below the yielding threshold, grains remain quiescent, while in slowly flowing regions the shear stresses will be given by a (lower) dynamical yield stress. This way of thinking readily captures the maxi...

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Finite width of quasistatic shear bands

Cited by 8 publications

References 18 publications

Evolution of shear zones in granular materials

Evolution of shear zones in granular materials

The critical-state yield stress (termination locus) of adhesive powders from a single numerical experiment

Granular flows in split-bottom geometries

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