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Discrete element modelling of material non-coaxiality in simple shear flows

Ai, Jun; Langston, Paul A.; Yu, Hai-Sui

Authors

Jun Ai

Paul A. Langston

Hai-Sui Yu



Abstract

We investigate the quasi-static simple shear flow of a two-dimensional assembly of cohesionless particles using discrete element method (DEM) simulations. We focus on the unsteady flow regime where the solid would experience significant evolution of stresses, mobilised shear strength and dilation. We construct the DEM model using a discretised-wall confined granular cell where the apparent boundary is allowed to dilate or contract synchronously with the confined solid. A rather uniform simple shear field is achieved across the whole assembly, which benefits rheological studies in generalising constitutive laws for continuum methods. We examine two aspects of the simple shear behaviour: macroscopic stress and strain rate evolution, particularly the non-coaxiality between the principal directions of the two; and micromechanics such as evolution of fabric. For an initially anisotropic specimen sheared under constant normal pressure, the direction of principal stress rotates towards that of the principal strain rate, gradually reducing the degree of non-coaxiality from about 45° to fluctuating around 0°. The rate in approaching coaxiality is slower in samples with larger initial porosity, stress ratio and mean stress. Generally, a faster rate in approaching coaxiality in simple shear is observed in a more dilatant sample, which often shows a larger degree of mobilised fabric anisotropy, suggesting the possible important role of instantaneous internal friction angle. The evolution of principal fabric direction resembles that of the principal stress direction.

Citation

Ai, J., Langston, P. A., & Yu, H. (2014). Discrete element modelling of material non-coaxiality in simple shear flows. International Journal for Numerical and Analytical Methods in Geomechanics, 38(6), 615-635. https://doi.org/10.1002/nag.2230

Journal Article Type Article
Acceptance Date Aug 15, 2013
Online Publication Date Oct 4, 2013
Publication Date Apr 25, 2014
Deposit Date Apr 24, 2014
Publicly Available Date Apr 24, 2014
Journal International Journal for Numerical and Analytical Methods in Geomechanics
Print ISSN 0363-9061
Electronic ISSN 0363-9061
Publisher Wiley
Peer Reviewed Peer Reviewed
Volume 38
Issue 6
Pages 615-635
DOI https://doi.org/10.1002/nag.2230
Keywords Simple shear, Non-coaxiality, Discrete element modelling
Public URL http://eprints.nottingham.ac.uk/id/eprint/2403
Publisher URL https://onlinelibrary.wiley.com/doi/full/10.1002/nag.2230
Copyright Statement Copyright information regarding this work can be found at the following address: http://creativecommons.org/licenses/by/4.0

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Publisher Licence URL
http://creativecommons.org/licenses/by/3.0/





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