yade-users team mailing list archive

[Nguyen Hien <question226254@xxxxxxxxxxxxxxxxxxxxx>]

New question #226254 on Yade:
https://answers.launchpad.net/yade/+question/226254

Hello,
First, my system's info
Ubuntu 11.1
Yade-daily 3+3496+44

I'm modeling a triaxial test of a cube of 10000 particles, using the strain rate method with 3 values of confinement stress: 100 kPa, 200 kPa and 300 kPa.
Based on the example file for the triaxial test on gibhub, I use different values of confinement stress for two processes: the isotropic compression and the deviatoric loading.
For the isotropic compression state, I use internalCompression=True.
What I want to archive: in order to have a reliable curve of deviatoric loading - axial deformation
I realize that when I make those two stresses different, the behavior of the specimen at the very beginning of the deviatoric loading process is not stable: the deviatoric stress, it's not starting from zero (since the confinement stress is suddenly go up like we defined in the code). For example, if I use the 80 kPa for the isotropic compression, next for the deviatoric loading, I use 100 kPa as the confinement stress on the radical axes and a strain rate of 0.1 on the vertical axe. The first moment as I start the deviatoric loading, the deviatoric load (q=sigma1-sigma3) is not equal to zero but about 20kPa not 0 (since the confinement stress go from 80 kPa to 100 kPa) but the deformation epsilon is alreary started to change and being recorded. For the confinement stress of 300 kPa, it's eventually more painful.

So I propose two questions:
1. Should we really use a low value of confinement stress for the isotropic compression state, or we can use the same as the deviatoric state's, even 300 kPa?
2. (A little specific) If no, which value is best for the isotropic conpression process, and how to avoid the unstable effect in the first steps of the deviatoric loading process?

Thanks in advance

Here is the unstable phenomenon curve I got with the code (notice the red circle that I use to mark the problem): http://i.imgur.com/vY2aASP.gif
The excel file of the result from whice the above image is created from: http://www.mediafire.com/view/?llclbl1ls8tocky
And don't forget the code:  http://pastebin.com/sQXmmeU5

One of the resolution I'm considering is the way I extract the result: I draw the curve since the deformation begins to change. But I'm not sure.

-- 
You received this question notification because you are a member of
yade-users, which is an answer contact for Yade.