← Back to team overview

yade-users team mailing list archive

Re: triaxialtest


First, please reply to the yade-users mailing list and not to me. Your questions may be usefull for others, and others can help you much better than me!

About your questions: replies below

nejib hadda a écrit :
Hi Luc,
I have noticed it thanks to your last mail, but still there are some
questions that I'm not sure about the answer and it would be great if
you clarify things to me :

1-  Is the default triaxialtest response with lateral move of the walls
corresponds to the triaxial test with axial load. Elsewhere, what shall
I do?

I am not sure to very well understand your question... do you mean: how to impose stress paths different of the axisymmetric triaxial compression?

2-  in theory q = sigma11-sigma33, but on Yade it is in fact
sigma22-sigma33. (triaxialtest, triaxialtestwater)

Yes by default with TriaxialCompressionEngine the axial direction is the direction 22, but if you sample is isotropic the compression direction should influence the result (and if you want to add gravity, you add gravity in the direction you want to, direction 22 for instance). Actually sigma11 may be a little bit different of sigma33 so you can compute q = sigma22 - (sigma11+sigma33)/2.

3-  Why does Yade go on with calculations until epsilon22 is equal to
50% which does not corresponds to small deformations hypothesis.

You can change this value of 50% in the xml, so you stop the simulation when you want, it is just a default value. Strains computed in the TriaxialStressController are logarithmic strains, thus they should be valid for large displacements. Have a look in the archive of the mailing list, I think there is questions / answers about that.



Le jeudi 10 décembre 2009 à 14:17 +0100, Luc Sibille a écrit :
Hi Nejib,

In the TriaxialCompressionEngine, I think there is a booleen that you can swith from 1 to 0 to stop the computation when the compaction is finished. I don't remember the name of the booleen, but it should be something like "AutoCompressionActivation".

About the stress deviator q: generally speaking, during the compaction phase Yade tries to reach the same stress value for the three space direction. During the compaction, sigma_1, sigma_2 et sigma_3 may be a little bit different, thus you can compute a non vanishing q value (negative or positive), but q value should be very small (and it is not really a problem).
Does it solve your problem?


nejib hadda a écrit :
I don't see how to seperate these two phases on yade.
In fact what I want to do is to compact my specimen before launching the
calculus so that I get the density I wish to have.
But here, yade do both phases simultaniously, and the phase at which q
takes negatives values is the phase of compaction which corresponds to
the first ietrations.

Le mardi 08 décembre 2009 à 17:55 +0100, Luc Sibille a écrit :
For which phase have you got negative q values? The compaction phase, the deviatoric phase, ... ?

Hadda Nejib a écrit :
I don’t know if it is common in YADE to have negative values for the deviatoric stress q in both triaxial test and triaxial test water for the first iterations (numerical problem) until the specimen is stabilized. I have also always had this sudden fall in the value of sigma22 after some iterations at the beginning of my simulations.

Shall I take the initial value of sigmaisocompactation near to value of the confining pressure to avoid such problem ?


Mailing list: https://launchpad.net/~yade-users
Post to     : yade-users@xxxxxxxxxxxxxxxxxxx
Unsubscribe : https://launchpad.net/~yade-users
More help   : https://help.launchpad.net/ListHelp

Luc Sibille

Université de Nantes - Laboratoire GeM UMR CNRS

IUT de Saint Nazaire
58, rue Michel-Ange - BP 420
44606 Saint-Nazaire Cedex, France

Tel: +33 (0)2 40 17 81 78