simple shear test with PBCs

Asked by Chiara Modenese on 2011-10-19

Hi,

I see that the class PeriTriaxController is not suitable to run simple shear test, for instance. Would it be possible to create a similar general class, where each component of the velocity gradient can be controlled independently? Or do you think that this could be done directly in python using the available functions which compute stresses and so on? Any hint?

Thanks, Chiara

Question information

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Solved by:
Bruno Chareyre
Solved:
2011-10-19
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2011-10-19
Last reply:
2011-10-19
Jan Stránský (honzik) said : #1

Hi Chiara,

for this purposes there is Peri3dController, so you can try to use it on
simple shear. See scripts/tests/peri3dController_shear.py for an example.
Good luck
Jan

2011/10/19 Chiara Modenese <email address hidden>

> New question #175211 on Yade:
> https://answers.launchpad.net/yade/+question/175211
>
> Hi,
>
> I see that the class PeriTriaxController is not suitable to run simple
> shear test, for instance. Would it be possible to create a similar general
> class, where each component of the velocity gradient can be controlled
> independently? Or do you think that this could be done directly in python
> using the available functions which compute stresses and so on? Any hint?
>
> Thanks, Chiara
>
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Yes, thanks. Actually I knew about this option but I asked anyway because I
would like to keep the test as simple as possible. Your code is definitely
more complex. I would like to keep the same way we control stresses and
strains in PeriTx but for a more general case...

2011/10/19 Jan Stránský <email address hidden>

> Your question #175211 on Yade changed:
> https://answers.launchpad.net/yade/+question/175211
>
> Status: Open => Answered
>
> Jan Stránský proposed the following answer:
> Hi Chiara,
>
> for this purposes there is Peri3dController, so you can try to use it on
> simple shear. See scripts/tests/peri3dController_shear.py for an example.
> Good luck
> Jan
>
> 2011/10/19 Chiara Modenese <email address hidden>
>
> > New question #175211 on Yade:
> > https://answers.launchpad.net/yade/+question/175211
> >
> > Hi,
> >
> > I see that the class PeriTriaxController is not suitable to run simple
> > shear test, for instance. Would it be possible to create a similar
> general
> > class, where each component of the velocity gradient can be controlled
> > independently? Or do you think that this could be done directly in python
> > using the available functions which compute stresses and so on? Any hint?
> >
> > Thanks, Chiara
> >
> > --
> > You received this question notification because you are a member of
> > yade-users, which is an answer contact for Yade.
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> > Mailing list: https://launchpad.net/~yade-users
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>
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What is wrong with PeriTriaxController?
The only thing it will not do is imposing shear stress. But for classical simple shear, i.e. imposed s11,s22,s33 and shear rate it should be ok.
See periodic-simple-shear.py

Jan Stránský (honzik) said : #4

Or transform the simple shear stress into principal stress values, that are
always normal and then there should be no problem running it on
PeriTriaxController as there is no real shear stress..
Jan

2011/10/19 Chareyre <email address hidden>

> Question #175211 on Yade changed:
> https://answers.launchpad.net/yade/+question/175211
>
> Status: Open => Answered
>
> Chareyre proposed the following answer:
> What is wrong with PeriTriaxController?
> The only thing it will not do is imposing shear stress. But for classical
> simple shear, i.e. imposed s11,s22,s33 and shear rate it should be ok.
> See periodic-simple-shear.py
>
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> You received this question notification because you are a member of
> yade-users, which is an answer contact for Yade.
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On 19 October 2011 11:20, Chareyre <email address hidden>wrote:

> Your question #175211 on Yade changed:
> https://answers.launchpad.net/yade/+question/175211
>
> Status: Open => Answered
>
> Chareyre proposed the following answer:
> What is wrong with PeriTriaxController?
>
Oh sorry, it is possible to do the simple shear test with the PeriTx. I was
confused but the fact that I needed no lateral extension (like eodometric
conditions) and at the same time constant vertical stress plus imposed shear
stress (this is how I would run a simple shear test). But it is all
possible. The only external thing to do is to set the value of velGrad for
the shear. Thanks for hints, Chiara

> The only thing it will not do is imposing shear stress. But for classical
> simple shear, i.e. imposed s11,s22,s33 and shear rate it should be ok.
> See periodic-simple-shear.py
>
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Thanks Chareyre, that solved my question.

Jan, it will not work. In simple shear, there is a continuous rotation of principal axis during the loading. You can't do that by simply rotating the initial problem.

Chiara, no, imposing shear stress is not possible, shear stress will be a result. It would not be a good type of control anyway. We don't impose stress but strain rate in axial compression, for the same reason (post-peak behaviour).
I guess you get it already, but if you want oedometer-type conditions, then you have to change a little the boundary conditions of the script. For now all three sigma_kk are imposed.

On 19 October 2011 15:41, Chareyre <email address hidden>wrote:

> Your question #175211 on Yade changed:
> https://answers.launchpad.net/yade/+question/175211
>
> Chareyre posted a new comment:
> Jan, it will not work. In simple shear, there is a continuous rotation
> of principal axis during the loading. You can't do that by simply
> rotating the initial problem.
>
> Chiara, no, imposing shear stress is not possible, shear stress will be a
> result. It would not be a good type of control anyway. We don't impose
> stress but strain rate in axial compression, for the same reason (post-peak
> behaviour).
>
Of course! Sorry I meant precisely that (I said that velGrad should be set
from outside PeriTx).

I guess you get it already, but if you want oedometer-type conditions, then
> you have to change a little the boundary conditions of the script. For now
> all three sigma_kk are imposed.
>
Yep, got it thanks :-)

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