Wide shear zones and the spot model: Implications from the split-bottom geometry

The spot model has been developed by Bazant and co-workers to describe quasistatic granular flows. It assumes that granular flow is caused by the opposing flow of so-called spots of excess free volume, with spots moving along the slip lines of Mohr-Coulomb plasticity. The model is two-dimensional an...

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Bibliographic Details
Published in:The European physical journal. E, Soft matter and biological physics Soft matter and biological physics, 2009-01, Vol.28 (1), p.73-78
Main Authors: Woldhuis, E., Tighe, B. P., van Saarloos, W.
Format: Article
Language:English
Subjects:
Biological and Medical Physics
Biophysics
Chemistry
Colloidal state and disperse state
Complex Fluids and Microfluidics
Complex Systems
Cross-disciplinary physics: materials science
rheology
Exact sciences and technology
General and physical chemistry
Granular solids
Material form
Nanotechnology
Physical and chemical studies. Granulometry. Electrokinetic phenomena
Physics
Physics and Astronomy
Polymer Sciences
Regular Article
Rheology
Soft and Granular Matter
Surfaces and Interfaces
Thin Films
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Summary:The spot model has been developed by Bazant and co-workers to describe quasistatic granular flows. It assumes that granular flow is caused by the opposing flow of so-called spots of excess free volume, with spots moving along the slip lines of Mohr-Coulomb plasticity. The model is two-dimensional and has been successfully applied to a number of different geometries. In this paper we investigate whether the spot model in its simplest form can describe the wide shear zones observed in experiments and simulations of a Couette cell with split bottom. We give a general argument that is independent of the particular description of the stresses, but which shows that the present formulation of the spot model in which diffusion and drift terms are postulated to balance on length scales of order of the spot diameter, i.e. of order 3-5 grain diameters, is difficult to reconcile with the observed wide shear zones. We also discuss the implications for the spot model of co-axiality of the stress and strain rate tensors found in these wide shear flows, and point to possible extensions of the model that might allow one to account for the existence of wide shear zones.
ISSN:1292-8941
1292-895X
DOI:10.1140/epje/i2008-10418-0