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Shell vs Solid element

Shell vs Solid element

Shell vs Solid element

(OP)
Hi together!:)
I have got a really fundamental problem and I would be very very grateful if someone could help me here :)

I am trying to explain the reasons for the deviations of my simplified model. It's a simple rectuangular body similar to a beam with fixed constraints on one end and a load on the other end. (L=100mm,b=40mm,t=3mm or 20mm, F=1N)
With this model I want to explain the deviations between the shell-element and the volume-element approach. I am using CQUAD8/4 and CHEXA8.
I already tried to read myself into the Reissner-Mindlin theory, FEM theory and documents concerning locking but somehow I am still lacking the basics I think.
Why are there deviations between these both approaches. Of course, both use different assumptions for the solving of the differential equations.

Volume-elements can deform in each direction under load but shell-elements can't change their dimension in the thickness direction, am I right? They can only deform in x and y direction (when z is the normal direction). Can this be one reason for the different displacement? Are there more important and essential differences in their assumptions? The shell element is a reduced volume model with assummptions which have to be considered. (Thickness has to be small compared to the other dimensions etc.)
What else could be reason for the differences in y-displacement of the two element categories?

The Locking phenomenon can occur also in both shell and volume element modelling, right? I read somewhere that shear locking is the main occurence when using shell elements. I can also see that the displacement is changing, when I'm moving from one volume element per thickness to 4-5 elements per thickness. Is it also possible that the locking phenonemon plays a role in the deviations of displacements?

I can bring the displacements closer to each other when I am setting the poisson ratio of the volume-meshed material to 0. This is because the deformation of the volume-elements is getting closer to the shell-element deformation. Is this correct?

Thank you a lot!

Regards
Benny


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