Circular fixed membrane with initial stress

Hello,

I'm trying to simulate the bending of a circular fixed membrane. The membrane is prestressed with ca. 50MPa. I've found out how to apply the prestress in Code-Aster by first creating a field (CREA_CHAMP) with the given prestress in X- and Y-direction, then applying uit with ETAT_INIT in STAT_NON_LINE and then using it in a second STAT_NON_LINE with ETAT_INIT and EVOL_NOLI. A pressure of 1Pa will be applied on the lower surface of the membrane, which is called 'Pressure' in the *.comm-file and mesh-file. The simulation runs and it shows me a result but in my opinion the result isn't right due to the fact that I have an analytical formula to calculate the bending of a circular fixed prestressed membrane. The result of the analytical calculation is about 3 nm and the result of the simulation is about 430 nm (with the finest mesh I could use without getting a JEVEUX-error for more RAM), which differs with a factor over 129. In Paravis the stress at the beginning can be illustrated with 50MPa.
The mesh is created with GMSH. I've tried to refine the mesh and with finer mesh, the bending increases and there is no point of convergence.


I'm thankful for any help,

Hanna