I'm trying to simulate a triaxial test (compression) on a cubic sample surrounded by 6 mesh faces. Only the top face will move in (-ve) z direction to compress sample while the other 5 faces are stationary. I want to draw the stress-strain curve for this sample to get the yield and ultimate stresses. My problem is that during compression the stress is only increasing and never decrease. I think this is because the lateral deformation for the sample in the other two directions (x,y) is not allowed.
Is there any way to insert a wall that allow this lateral deformation? or am I simulating this test in a wrong way?