Good evening. I am modeling a simple three-point bending test of a sandwich structure. I started with modeling the whole assembly including facesheet and core as solid elements (C3D8R). This runs without any problems.
Then i wanted to simplify the model with using shell elements. When i model the assembly with shell elements and defining the thicknesses by mid-surface everything worked. But this does not replicate the solid model. So i want to define the surface sections as bottom or top faces. This is where the trouble begins and the simulation does not converge already after 5%. The part is constraint on both sides with Z-Symmetry. If i run the simulation with only one side constrained it also works.

Anyone any idea what is so special about the shell elemets when they are defined in a different way than by mid-surface?

I am running Abaqus 2020, implicit solver, NLGeom=on, isotropic elastic-plastic hardening.