I modelled prony series data using some of the shear test data I have.

After having the prony series term I used them in one of my simulations.

I just applied a load of 1Mpa and then in the next step fixed the test specimen.

Ran a coupled temperature displacement step with 3600 seconds step time but could not see any stress relaxation in the results.

could not understand why this is happening.

Even ran the simulation for 360000 secs means 100 hours but still no stress relaxation.

Used two terms prony series.

Can someone help me understand what could be the reason for the same.

My prony series parameters looks like the following 

*Viscoelastic, time=PRONY
0.249,0.249,334191.0683
0.016,0.016,98.359613