Comparative FE-studies of interface behavior of granular Cosserat materials under constant pressure and constant volume conditions (original) (raw)
2021, Archives of Mechanics
This article shows the outcomes of a systematic series of finite element (FE) calculations relevant to the shear behavior of a particulate-continuum interface system under different normal boundary conditions. In this respect, shearing of a thin and long granular Cosserat layer in the vicinity of a rigid moving wall with varied surface roughness values is analyzed under constant normal pressure and constant volume conditions. The material behavior is defined with a special elasto-plastic Cosserat model, taking into account micro-rotation, micro-curvature, couple stress, and mean particle size. The interaction between the layer of boundary particles and the surface roughness of the adjoining bottom wall is modeled by the rotation resistance of particles along the wall surface. Herein, the coupled effects of normal confining constraints imposed on the layer and the surface roughness of the bottom wall, are considered on the response of granular material under shearing. The influences ...
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A frictional Cosserat model for the slow shearing of granular materials
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A rigid-plastic Cosserat model for slow frictional flow of granular materials, proposed by us in an earlier paper, has been used to analyse plane and cylindrical Couette flow. In this model, the hydrodynamic fields of a classical continuum are supplemented by the couple stress and the intrinsic angular velocity fields. The balance of angular momentum, which is satisfied implicitly in a classical continuum, must be enforced in a Cosserat continuum. As a result, the stress tensor could be asymmetric, and the angular velocity of a material point may differ from half the local vorticity. An important consequence of treating the granular medium as a Cosserat continuum is that it incorporates a material length scale in the model, which is absent in frictional models based on a classical continuum. Further, the Cosserat model allows determination of the velocity fields uniquely in viscometric flows, in contrast to classical frictional models. Experiments on viscometric flows of dense, slowly deforming granular materials indicate that shear is confined to a narrow region, usually a few grain diameters thick, while the remaining material is largely undeformed. This feature is captured by the present model, and the velocity profile predicted for cylindrical Couette flow is in good agreement with reported data. When the walls of the Couette cell are smoother than the granular material, the model predicts that the shear layer thickness is independent of the Couette gap H when the latter is large compared to the grain diameter dp. When the walls are of the same roughness as the granular material, the model predicts that the shear layer thickness varies as (H/dp)1/3 (in the limit H/dp [dbl greater-than sign] 1) for plane shear under gravity and cylindrical Couette flow.
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