Bolt Mesh Matching with Layered Thin Solid Mesh

[bryan_mcnatt]

Is there a way to fix this or force this situation to work as desired?  Parts are to be meshed as layers of thin elements.  Assembly is mostly welded but there are some welded sub-assemblies that are bolted to other parts or welded sub-assemblies.  I cannot get the surface meshes on most of the solid-meshed parts to match up with the head & nut spokes of the bolt meshes.

[bryan_mcnatt]

I may have my own answer now.  I selected the construction vertices at the ends of the radial bolt spokes and used them to create refinement points.  I set the refinement radius to just less than the thickness of the part and I set the mesh size to the thickness of the part (which was smaller than the existing mesh size prior to refinement, so maybe the key there is to just ensure that you're refining smaller than what you have currently, which is really the obvious intent anyway with refinement).

I then remeshed the entire assembly and the spokes are now properly matched with the surface nodes.

If there are other ways or if this approach has pitfalls I haven't found yet, please reply.  Otherwise, I'll move on and will update this thread if needed.

[bryan_mcnatt]

UPDATE

Above approach does not work all the time.  Still searching for solution.

[John_Holtz · Accepted solution]

Hi Bryan,

The reason that it does not work is because of the way the layered thin solid mesh works. It meshes the surface of the solid, takes one of the faces and deletes the other faces, and extrudes the face to create the solid. (The actual details may be a little different, but that is the general principle.)

So if the construction vertices created for the bolt are not on the side that gets extruded, the mesh between the bolt and solid will not match up. Here are some random ideas. (I have not tried any of these, so you might want to try a subset of your full model or create a small test model.)

1. Bolts can be created that do not have the "spokes" and construction vertices. It just has the radial lines from the bolt shank to the edge of the hole. I wonder if this type of bolt would match better?
2. Create the same construction vertices on the "bottom" as on the top. Then, regardless of which side the software chooses to extrude, the mesh will match the bolt spokes.
3. You may have noticed that different parts that are meshed as thin layers do not have matching meshes. So you must be using smart bonding or the Nastran solver to connect the adjacent parts. In this case, you could add "washer" parts to the model and mesh them as a normal solid. That way, the construction vertices for the bolt would create mesh points on the washer, and the smart bonding would connect the washer to the layer mesh part.

[bryan_mcnatt]

Thanks John.  I will try all three ideas to see what I like best.  Your third option may be the best all-round since the CAD I get usually has flat washers anyway.  Instead of suppressing them and placing bolts without washers, I could leave them and add the bolts as you suggest.  My reluctance had been the small mesh of such washers driving mesh/solve times but we'll see.  I'll bet they don't hurt much, especially since I don't care about the mesh/stress in the washers (they can be quite coarse I bet).