3D Simulation of 2D Geometries

Model setup
1

I believe I have correctly re-written an Abaqus UEL into a format usable for CalculiX (User Element Troubleshooting), and now I am trying to verify it works as intended in comparison to analytical solutions. Unfortunately, these analytical solutions are all 2D, which makes the setup more challenging because CalculiX is strictly 3D and the two 2D approximations (plane stress and plane strain) have different assumptions.

I will note that the user element is fully 3D (at Guido’s suggestion), and therefore I don’t think utilizing the “2D” elements is an appropriate solution.

Has anyone worked to replicate plane stress and plane strain assumptions in CalculiX without using the “2D” elements? If so, how did you accomplish this? Or would other users disagree with my assertion above and think I need to just replicate the SPC’s mentioned in ccx 2.23 sections 6.2.22 (CPS8 plane stress elements) and 6.2.26 (CPE8 plane strain elements)?

P.S. For context, the user element is a cohesive element. Therefore, there is a single row of (user) cohesive elements in the middle of the geometry, whereas the rest of the geometry is filled with continuum elements.

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Yes.Take a look at this thread. Plane Stress Problem - #31 by Disla

Z-unrestrained 3D solid element is not the same as a Plane Stress Solution.

The problem is that it was achieved playing with the material properties which in your case I’m not sure you can.

3

Check this post: Inquiry Regarding 2D Finite Element Analysis in FEBio - FEBio Forum

And this thread: https://www.eng-tips.com/threads/2d-problems-in-3d.499698/

Usually, this should suffice:

  • plane stress: no Z restraint on entire surfaces (can constrain e.g. a single vertex)
  • plane strain: block normal displacement in the Z direction for both surfaces (front/back)
  • axisymmetric: block normal displacements on the surfaces of the revolved segment or use cyclic symmetry

Possibly, use a single layer of hex/wedge elements.

However, there can be some exceptions (e.g. if you want to ensure zero stress in the thickness direction for plane stress case, but be careful about Poisson’s effect and ensure loading only in plane) and CalculiX already expands 2D models to 3D internally.