Hi Luc Scholtès (and Luc Sibille, read that too)
I think the problem had been introduced with these lines in TTController :
- max_vel1=3 * width /(depth+width+depth)*max_vel;
- max_vel2=3 * height /(depth+width+depth)*max_vel;
- max_vel3 =3 * depth /(depth+width+depth)*max_vel;
Now (r2066) replaced by :
+ max_vel1=3 * width /(height+width+depth)*max_vel;
+ max_vel2=3 * height /(height+width+depth)*max_vel;
+ max_vel3 =3 * depth /(height+width+depth)*max_vel;
I didn't check the result yet. Tell me if that's better.
Bruno
luc scholtes a écrit :
Hi all,
(Bruno, you probably have an idea about this)
A remark for those who are interested in doing triaxial loadings on
samples with height/width ratio different from 1. Here is the test I did:
1 - take 2 samples, one with a ratio equal to 1 (a cube typically) and
another with a ratio equal to 2.
2 - give them exactly the same micro properties (it appears to me that
it is more interesting with a high E(Yade Young
Modulus)/confiningPressure ratio)
3 - from an initial dense state (say that you have already created a
dense sample with the compaction procedure of the triaxial state),
apply them an hydrostatic loading in order to reach a higher confining
pressure, with a sufficiently small wall velocity to avoid inertial
effects (setting the maxVel parameters small enough)
4 - plot the evolution of the 3 principal stresses as a function of 1
one the 3 principal strains (the corresponding strain rates are equal
according to the servo-controlled controlller) for both of the 2 samples.
-> see the attached figure for the results
As you can see, in the case of the cube, the 3 principal stresses
evolve in an identical way with the deformation, which is a good news,
but, unfortunately, for the sample with a ratio heigh/width = 2, we
can see that it is not the case at all. The stresses reach the desired
confining pressure, but there is a kind of a delay between the axial
stress (S2) and the radial ones (S1,S3) that occurs during the
loading: the axial stress increase more rapidly than the 2 others...
This leads to less deformation in the axial direction than in the
radial ones to reach the desired confining pressure.
I tried with several velocities and with very low damping values
(wallDamping=0, damping(NewtonIntegrator)=0.05), and I always get the
same result. The sample is supposed to be isotropic and homogeneous in
regards to contact forces and orientations distribution.
One of my experienced colleague though about relaxation effects that
should occur in the sample, creating this delay between the axial and
the radial responses of the system.
If you have any advice....
Cheers
Luc
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