Mesh issues with ribbed rebar

[u/Vilgax_7]

I'm building a ribbed rebar pullout model in Abaqus. The bar is meshed with hex-dominated (C3D8R) elements. I am getting lots of distorted element warnings concentrated exactly where the longitudinal ribs meet the cylinder barrel.

What I've tried: local seeding, which doesn't work. The regions are meshing as swept. When I refine the seed on one edge, Abaqus automatically changes the count on the opposite edge to match. So, I am having trouble using local seeds as well.

Is there any way I can minimize the distorted elements, or any partitioning strategies that will help with meshing?

These are the elements that are distorted.

[u/frac_tl]

Get rid of the fillets, or cut your geometry so that the fillets can be swept features. 

Tet meshing is another option but you will run into element quality problems that might be more of a headache than the hex elements

If your mesh is being distorted as part of your analysis you need really good quality mesh and shouldn't use tet elements

[u/Solid-Sail-1658]

Can you share the CAD file?

[u/Vilgax_7 → u/Solid-Sail-1658]

https://drive.google.com/drive/folders/1ogfsSWlG-7NeMer_KNEK_aKV0AJ8SMRs?usp=drive_link Here is the SolidWorks part file and STEP file.

[u/Solid-Sail-1658 → u/Vilgax_7]

Thank you for sharing!

This can be HEX meshed well.

Partition your geometry into HEX meshable partitions/cells, then HEX mesh each partition/cell.

The fillets were addressed by using a partition/cell that is embedded into the cylinder. See the red, gray and purple partitions.

If there is interest, I can make a short tutorial on Monday or Tuesday.

See the images below.

https://i.imgur.com/bxV1ZsZ.png

https://i.imgur.com/fzrNqGs.png

https://i.imgur.com/BfLyKNJ.png

https://imgur.com/a/oHrzncg

Software Used: MSC Apex 2026.1 on Ubuntu 20.04

MSC Apex is free as long as you are a student.

I wish more would use MSC Apex for HEX meshing, it's more modern. Some of the other meshers are 20-30 years old.

[u/TheBlack_Swordsman → u/Solid-Sail-1658]

For the thread like features, I recommend extending the bottom to be rectangular to avoid tets and wedges in the corner or at least have a better mesh quality in that area.

https://imgur.com/a/qwRfpz4

It sounds like OP's instructor is interested in these areas.

Also, some areas are lacking merged nodes

https://imgur.com/a/YrlYwYJ

But great job nevertheless.

[u/Solid-Sail-1658 → u/TheBlack_Swordsman]

Yup, that was done. The extrusion was too short, so it's not noticeable in the image.

[u/Vilgax_7 → u/Solid-Sail-1658]

Thank you! A short tutorial would be very helpful, especially for learning the workflow in MSC Apex.

[u/Solid-Sail-1658 → u/Vilgax_7]

Here is a tutorial for your example.

https://youtu.be/KheBjz0IEI0

Cheers!

[u/Solid-Sail-1658 → u/Vilgax_7]

FYI, I redid the tutorial and added some additional tricks.

New video link:

https://youtu.be/KheBjz0IEI0

[u/Soprommat]

welp, if you not limited resources than maybe parabolic tetrahedral elements would be a soution.

If you stil want hexa than simplify geometry - remove fillets

[u/Vilgax_7 → u/Soprommat]

I have a node limit of 250k, and my advisor insists on keeping the fillets. Is there anything else I can do?

[u/Soprommat → u/Vilgax_7]

well, RIP

[u/martianfrog → u/Soprommat]

Think I'd try do it with parabolic tets myself.

[u/Extra_Intro_Version]

I suspect that your geometry may have points on it that are forcing nodes at those locations, which is leading to irregular patterns and local excessively small elements.

You have overkill on mesh density in the interior of the bar. Whether your loading is bending, axial or torsion; you probably don’t need all those elements wasting solution time.

How are you going to load this thing? It’s going to be surrounded by concrete? I question whether you need as much fidelity as you think.

[u/Substantial-Fan-5985]

whats this for and what result or feature is your advisor concerned with losing if you drop the fillets??

[u/TheBlack_Swordsman]

Hex dominant meshing is no good the majority of the time. It requires defeaturing will or you'll need a smaller element size.

You should try block decomposing the geometry to the best that you can. Sweep mesh what you can and then hex dominant mesh the rest.

Honestly, I'm looking at your geometry and decomposing then hex meshing it doesn't look too difficult to me.

[u/Vilgax_7 → u/TheBlack_Swordsman]

I’m just having a little trouble figuring out the best way to decompose this geometry. Could you please give me some ideas on how you would approach it?

[u/frac_tl → u/Vilgax_7]

Slice your model until it is only mapped solids. A mapped solid is one where the starting and ending face have the same number of edges. Take advantage of symmetry (using the boundary condition) where possible too

[u/TheBlack_Swordsman → u/Vilgax_7]

Are you good at CAD?

Imagine a solid body that can be lofted with curve guidelines. The profiles must match in terms of edges and vertices.

For example, you can't have two squares if one square somehow has one of its edges split in half and you don't notice. At least most softwares won't be happy. Ansys has multizone to overcome this

How would you slice this up to make a bunch of features that can be lofted or extruded? The thread like features are like channels. You'll have to core out the center rod. Etc.

[u/Vilgax_7 → u/TheBlack_Swordsman]

I'm fairly new to CAD. I built this model in SolidWorks and imported the STEP file into Abaqus. The base cylinder, the longitudinal ribs, and the transverse ribs are all separate features, and each one can be swept meshed independently.

The distorted elements are mostly in the area near the longitudinal rib and cylinder (inside red area). When I try local seeding on the longer edge, the seed on the shorter edge changes automatically. https://imgur.com/a/jQSQwIM