Force results plot not "smooth"

[engrjaydee]

Hello everyone! Thank you very much for accepting me here in the PrePoMax forum. This is my first post here. With that, I have a question regarding the force results in PrePoMax/CalculiX.

In the above, I modeled a simple 100 mm x 200 mm x 6 m long cantilever beam made of steel. One end is fixed, that end is in the picture. All meshes are C3D20 with max size of 25 mm. A uniform load of 10 kN/m (applied as a surface traction of 10 x 6 = 60 kN at the top surface of the beam) is applied; self-weight is also applied. Nonlinear geometry and material is turned on.

The picture shows the vertical shear distribution F3 at the fixed end. Coming from Ansys, I anticipate that the contour plots are smooth, but here, there are negative values (blue) at the mesh corners and positive values (red) at the mesh interior, which is weird to me. I am guessing that this has something to do with mesh integration points and how values are interpolated at the nodes.

I would like to ask if there is a way (e.g. options in PrePoMax or keywords in CalculiX) that I can use to smoothen out these results?

Thank you very much.

[FEAnalyst]

You can find an explanation on the CalculiX forum here: Singular post process view on reaction force results with C3D10 solid element - CalculiX (official versions are on www.calculix.de, the official GitHub repository is at https://github.com/Dhondtguido/CalculiX).

[engrjaydee]

Thank you for this link, exactly what I needed.

From what I understand from this link, the picture I posted is a natural result of how C3D10 and C3D20 elements work in CalculiX (and Abaqus) for force reactions. Also, (discrete) force reactions at a node are not meaningful (and not always accurate) in a continuum mechanics problem; but getting their resultant at a region is meaningful (and accurate).

[FEAnalyst]

Yes, the FORC (RF) contour plots are rarely used. If you want to check the reaction forces, you should request history output with Totals = Only.