asdeasoft.net

Dear STKOteam,

I'm simulating the loading and unloading behavior of a cell with PIMY constitutive.
When the load is applied in the elastic stage, the vertical compressive strain of soil is -0.0263158.
Then the plastic activation of the soil is carried out, and the vertical strain of the soil changes abruptly to -0.0331689.
In the next stage, all applied loads are unloaded, and the vertical strain after unloading is -0.000149026.
The residual strain is only 0.5% of the maximum vertical strain.
Why is there so little involvement?

Looking forward to your reply!

Try this model (slightly changed).
Between the loading and unloading of vertical stress, I added an imposed shear displacement. The vertical stress behavior shows this (export e11 vs s11):
Note that the first linear branch is linear because of the elastic assumption. In the second stage, you switch to plastic, and the shear modulus reduces in the plastic stage according to the stress state (and so does the E modulus here). However, for the equilibrium with your vertical load which is constant, the vertical stress should remain constant. This is suddenly jumps to a higher vertical strain (it seems a plastic plateau but it's not... simply because the E modulus suddenly changes when switched to plastic) The real plastic behavior of this material happens for shear deformation (the stage I added in between):
Note that this material in 2D has a strange way to output results: strain vector has 3 components, to the E12 is the shear strain.
Stress has 5 components (s11, s22, s33, s12, nr... see the OpenSees doc). It's strange so STKO does not recognize it as a plain strain vector. So if you want the 4th component in STKO you have to select sigma23