Dear PeterĀ 

Thanks for your answer. I will try to explain the context of the simulation.

I think that for correctly simulate a membrane it is needed to turn off the bending stiffness because it is suppose that the stress is constant along the thickness and in the specific case that I want to simulate the thickness is very small compared with the other dimensions of the membrane. However, if I try this i.e. keyopt(1)=1, the deformation is equal to zero if I apply a pressure perpendicular to the membrane so I suppose that the most correct approach is try to keep the default value of keyopt(1)=0 but I am not sure.

I pretend to validate an analytical expression described in literature (image in annex) for the maximum stress and the deflection in the center of the membrane.

In the analyze setting, in the stabilization only appears off, constant and reduce. What is suppose I select?

In annex are also the mesh and the loads.

Thanks for all.