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[Jan Stránský <question691913@xxxxxxxxxxxxxxxxxxxxx>]

Question #691913 on Yade changed:
https://answers.launchpad.net/yade/+question/691913

Jan Stránský proposed the following answer:
Hello,

> by using O.cell.velgrad, all the particles of the assembly are
assigned a velocity based on their position with reference to the cell.

roughly.
(by default) velocity of particles is composed of this "macroscopic" or "homogeneous" term ("a velocity based on their position with reference to the cell") and their own interactions with real and "periodic" members.

> in a ... cylinder torsion shear tests on sands, the deformation may
not be linear, right?

yes, it may be non-linear. That's why I asked for more information about
the experiment.

> Is it still reasonable to consider periodic simple shear scenario in
replicating the element stresses of a torsional shear experiment?

as usually, it depends on many factors :-)
- what is the dimension of periodic cell compared to the specimen?
- Is the axial dimension fixed, or is the specimen free to dilate in axial direction?*
- what are the "trnasverse boundary conditions"?*
- periodicity also forces strain localization (shear bands) to be periodic. Is it a problem or not? 
- ...

* in "true simple shear", all "normal" dimensions of the cell are fixed,
only the shear is applied. Depending on the experiment, it may not
correspond to reality and some adjustment may be needed (e.g. zero
strain in one direction but zero stress in a perpendicular direction).

cheers
Jan

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