large deformation - shear test

Asked by Chiara Modenese on 2011-10-31

Hi,

how do we account for large deformations while using the periodic boundary in a simple shear test?

Thanks, Chiara

Question information

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Yade Edit question
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Solved by:
Bruno Chareyre
Solved:
2011-11-03
Last query:
2011-11-03
Last reply:
2011-11-02

On 31 October 2011 18:01, Chareyre <email address hidden>wrote:

> Your question #176964 on Yade changed:
> https://answers.launchpad.net/yade/+question/176964
>
> Status: Open => Answered
>
> Chareyre proposed the following answer:
> What do you mean exactly Chiara?
>
Maybe am wrong but say that you want to shear the periodic cell (at
constant volume or constant stress). In large deformation there are second
order terms to consider in the definition of strain tensor. How do we
account for those terms?

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Actually, the strain tensor is simply not defined (only the diagonal term is).
Had it to be defined, then we would have to choose between various large strain formalisms, but why would we do that?
The only thing you have is the transformation matrix, and I think that most authors are using it to define the shear amplitude.
If you shear along (x,y), then O.cell.tsrf(x,y) will give you the displacement/height value.

On 2 November 2011 12:55, Chareyre <email address hidden>wrote:

> Your question #176964 on Yade changed:
> https://answers.launchpad.net/yade/+question/176964
>
> Status: Open => Answered
>
> Chareyre proposed the following answer:
> Actually, the strain tensor is simply not defined (only the diagonal term
> is).
> Had it to be defined, then we would have to choose between various large
> strain formalisms, but why would we do that?
> The only thing you have is the transformation matrix, and I think that
> most authors are using it to define the shear amplitude.
> If you shear along (x,y), then O.cell.tsrf(x,y) will give you the
> displacement/height value.

Yes it is what am doing, I was just wondering if when I set
velGrad[0,2]=toSomething am really shearing at a constant rate considering
that we are in large deformation... Is it so then? Thanks, Chiara

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> If you still need help, you can reply to this email or go to the
> following page to enter your feedback:
> https://answers.launchpad.net/yade/+question/176964
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> You received this question notification because you asked the question.
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Yes, velGrad[0,2] is really the shear rate. So, if velGrad[0,2] is constant then the shear rate is constant.

Thanks Chareyre, that solved my question.