[sfepy] Young's modulus from average nodal stress

Dear all,

I'm observing something suspicious in a simulation that I wanted to share with you. I appreciate if you could help me out with it please: I'm simulating a 2D plate which is fixed in one end and I'm displacing the other end mimicking a uniaxial test. Now, when I average the nodal stress and divide by strain, I got a Young's modulus that shows 5% difference comparing with initial input E. So, is there any plausible explanation for it or there is something I'm missing in my simulation ? I tried different types of mesh, mesh size, mesh refinement, different integration order but all ended up into same observation.

Best, Ali