Divergence near 0

[Talanel-Elin]

Hello!
I find that the values i obtain with this code match my references quite closely deeper into the structure, but diverge significantly near the top.
Additionally, i find a smaller value directly at 0 under the pressure than the pressure itself, for example for 100 Psi i only measure 91.94 PSI directly under the force circle (x, z = 0). Intuitively i would have supposed that these two values should be identical.

Do you have an idea why, apart from different integration methods etc, my values might diverge from the reference higher up in the structure?
Why is the stress not more or less equivqlent to the applied pressure directly under the center of said pressure?

Thank you for your work,
best regards

[Talanel-Elin]

Well, FredDuharts previous issue solves my problem at exactly zero, sadly it does not fix the divergence from my reference numbers at shallow measurement points...

[Talanel-Elin]

Also, i get extremely strange phenomena when testing directly under the disk going outward...

when i input a radius of 12.5 cm for the disk, and i measure only at x=12, i get
Stress_Z:
[[0.62396388]]

however when i measure at x = [12, 12.1, 12.2, 12.3, 12.4, 12.5, 12.6] i get a different value for 12 and weird values for those points:
Stress_Z:
[[0.4121571 0.3939893 0.37570382 0.3573469 0.33896499 0.32060456 0.30231189]]

is the model simply not meant for close to the surface? how does the measurement point influence the result? integration points problem? it does converge further down the structure as i stated before.