Effect of void ratio on stress relaxation response 1

[saja11]

I have to analyze the stress relaxation response (reaction force as a function of time) of a poroelastic,isotropic material (cartilage) that is compressed to 5% of its thickness in unconfined compression. Young modulus is 0.5 Mpa, poisson's ratio as 0.15 and permeability as 1e-8. Nlgeom is off.
I have to see response while changing void ratio from 4 (original) to 9 and 1.333. I have defined void ratio(originally 4) in Predefined field and 0 value in material properties ( under permeability tab). However, after changing void ratio to 9 or 1.333 in predefined field tab, the stress relaxation response is not changing.Can someone suggest what I can do to see accurate response after changing void ratio values?

 

[FEA way]

Can you say more about this model - what is its geometry, how is it constrained and loaded ? In material properties window you define permeability as a function of void ratio.

 

[saja11]

Thanks for your reply.
It is 3-D cylindrical model of cartilage. For boundary conditions:
Lateral expansion is allowed
Fix rotation of geometry
Free fluid flow from the tissue allowed (por=0 on outer most surfaces).
5% Compression of tissue’s thickness
I have attached images of geometry and void ratio tabs. I am changing void ration as 9 or 1.333 in predefined field tab.