yade-users team mailing list archive
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About your questions: replies below
nejib hadda a écrit :
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 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 :
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 ?
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