I am trying to model a stress relaxation experiment in ABAQUS. I am using cartilage material in the test and for modeling that I am using the soil analysis. The displacement of the indenter for each step is a ramp rising at constant velocity for t0 seconds and then constant over some prescribed time period. In order to do that, I defined two steps. One where the cartilage plug is being loaded, for which I set a velocity type boundary condition at the top surface, and a the second step where I remove this BC to fix the position of the top surface and let the plug relax. When I plot the results it I don't see any relaxation. The second step shows constant stress (S22) - it's just looks like a ramp. I tried increasing the permeability just to see if it had any effect. However, it seems that the problem has nothing to do with the material properties, but with the way I am modeling the condition. This may be very trivial but I am just beginning to learn ABAQUS and appreciate any thoughts on this.
I can post my input file if needed.