Discussion Forum

Hello,

I'm trying to simulate what the stress distribution is in a silicon nitride square membrane when it is under tension. We know from experiments that when a membrane is under tension, the center will rearrange its molecules slightly to release some of this energy. So one would image a Gaussian-like distribution, where the edges are most under stress. I'm trying to mimic this experiment in COMSOL.

The nodes that I use are (besides the standard ones from the structural mechanics module):
-Initial Stress and Strain:
Where I put 0.9[GPa] of pressure in the in-plane directions. (the first two diagonals in the tensor)
-Fixed Boundaries:
All four boundaries are fixed.

And the study I use is stationary, where I have tried both with and without geometric non-linearity. I have also tried this using the membrane module.

The problem is that when I press compute, I get a uniform stress distribution. This clearly does not make sense, but I think it's an issue of me not understanding which nodes I should apply for COMSOL to understand what I'm trying to calculate. Could anyone tell me what I should change in the boundary conditions? I attached the file so anyone can tinker with it.

Kind regards,
Martijn