yade-users team mailing list archive

[Bruno Chareyre <bruno.chareyre@xxxxxxxxxxx>]

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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--
_______________
Bruno Chareyre
Associate Professor
Grenoble INP
Lab. 3SR
BP 53 - 38041, Grenoble cedex 9 - France
Tél : 33 4 56 52 86 21
Fax : 33 4 76 82 70 43
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