I'm having difficulty simulating the deflection of a thin disk. The actual phenomenon has a nonlinear relationship with edge displacement and looks like this,

I'm using a 5 degree slice of the disk with a symmetry constraint with fixed constraint on the inner diameter. OD = 24.4mm, load line diameter of interest is actually 23mm, ID = 10mm, thickness = 0.150mm, modulus of elasticy = 210 GPa. I made the mesh 3 elements thick, I've done 5 but it didn't seem to matter. I'm running the study as nonlinear as well. The force-deflection is completely linear though and doesn't match experimental at all.

Am I overlooking something? This should have some kind of geometric nonlinearity that increases stiffness correct?

Any help would be appreciated,

Thank you

Could the fixed rotations on the symmetry planes be throwing off the results of the simulation?