Thank you for your tip of the vertex BC, it gave me some realistic results:
Load: Heat flux and free convection in addition with earth gravity BC: Remote displacement on the vertex in the middle + displacement of sheet locked in z-direction due to the gravity.
To achieve the "potato chip" deformation, how should I definie an initial load? I tried it with a point load on the vertex in the middle, same result as above. Or do you mean with the step controls?
I want to depict the real experiment as close as possible. Heating pad on top of the sheetmetal which lays unclamped (free) on the floor -> therefore I guess there will be no "potato chip" deformation. Just an in-plane deformation as shown above.