you can see two my test of a tank (only the inferior part) where I have 0.96 bar of pression.
Why have I very different results in those test?
NB: I start from a 3D design from inventor and I chaked my values when I use plates.ù
In the first two images, the ribs are not bonded to the main body. You can see this from the displacements where there is a noticeable difference in their colour contours. If the parts are bonded together, their displacements will be equal at the connecting node and you will get something like your third image.
Bonded contact will only happen when the nodes of the two parts share a position. This will occur if the CAD geometry is touching one another when it is meshed, where Sim Mech will create nodes that are the same for each of the contacting surfaces. If the nodes are apart, then Sim Mech would not create any contact and they are free to separate or penetrate each other.
When you midplane mesh, your 3D geometry gets compacted to form a surface at its mid thickness. Hence, what was once connected 3D geometry, now becomes disconnected plates. And there you have your problem.
I suggest you do one of these:
1. Use 3D elements instead of plate elements. Turn on midside nodes if you have small element count across the thickness.
2. Go back to CAD, modify your solid object and turn it to surfaces, perform offsets and make sure the surfaces are in contact, bring it to Sim Mech, mesh as plate/shell.