Inserting 3d file with STEP extension is asking for geometry thickness

heleno_martins

Hello, I'm a new Mecway user. I'm inserting some 3D files and it's asking for profile thickness, could you help me? I've seen examples where thickness oppression is not requested.

It ultimately gives an error result like :Error: Invalid stiffness for element 1.

Victor

That means the material is used by shell elements. It looks like you have a surface mesh instead of a volume mesh. That can happen either by setting the Surface mesh option in Meshing parameters or if the mesher failed to make the volume mesh and left only the surface mesh (unlikely here since it has quad faces which aren't available for volume meshes).

heleno_martins

Hello, I will attach the file STEP so you can evaluate. But I believe it is due to the thickness of the plate and the radius is the thickness of the plate, it is creating a line that perhaps is preventing the solid mesh from being created.

Victor

You're right that those small radii cause it trouble. I got a solid mesh with the default meshing parameters. However, the small radius leads to a lot of badly shaped elements which you probably encountered.

Ways to correct that:

Turn off Fit midside nodes to geometry. Easy but you lose the detail of the radius so it depends if you're interested in the stress there or the overall deflection.

Increase Min. number of elements per curve. 2 and 3 didn't work here.

Put a surface refinement on the inside radii. This removes most of them but produces a huge mesh over a million nodes at 0.8 mm Maximum element size.

Use the Gmsh mesher which is generally more robust but I didn't have much luck here.

For thin-walled prismatic shapes like this, you can get a higher quality and much lower node count mesh (hex-dominant instead of tet) by using Mesh tools -> Extrude from a surface mesh of one end. Delete the remaining surface mesh afterwards. Or possibly just model the cross-section shape alone in CAD then extrude it in Mecway.



Or use shell elements which is the usual way for thin-walled materials. Ideally, you'd model the midplane in CAD and do a surface mesh on that, but you could also use one of the surfaces of what you have and set Shell offset in Element properties to bring the midplane in the correct distance.

heleno_martins

Your suggestion to use shell elements for thin walls would be more practical.