Gmsh applied on threaded fastener inside a threaded hole produces warnings

About the development of the FEM module/workbench.

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thschrader
Posts: 2129
Joined: Sat May 20, 2017 12:06 pm
Location: Germany

Re: Gmsh applied on threaded fastener inside a threaded hole produces warnings

Postby thschrader » Sun May 02, 2021 3:45 pm

Hi and welcome to the Forum!
Sorry for late reply...
It seems that the geometry itself has errors.
GMSH gives back distortion errors, Netgen produces only 2D-faces,
mesh-analysis has errors. In reality there is a gap between the bolt/hole.
What is your goal? Contact analysis?
netgen_bolt.JPG
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netgen_mesh.JPG
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misharsta
Posts: 11
Joined: Tue Apr 27, 2021 3:47 am

Re: Gmsh applied on threaded fastener inside a threaded hole produces warnings

Postby misharsta » Wed May 05, 2021 11:59 am

Thank you so much Thschrader. I sincerely appreciate your response. My goal is to conduct an FEA but I'm not able to progress because of these errors. What I posted is only a simpler version of my project but it illustrates it just fine. My real project is a dental implant screw in a dental jaw.

I noticed that gmsh produces errors even with any standard fastner from the Freecad Fastener workbench.

After you showed me where my problem is, my next question is how do I go about solving it. I tried using Meshlab to fix the mesh but I honestly could figure out what exactly need to be corrected 8n the mesh. Honestly speaking, even if I figured that out, I would still need to be guided in order to be able to fix it.

I'd appreciate any tutorial videos to help me diagnose exactly what's wrong with my mesh and how to go about fixing it.

Best regards
Salman Mishari
RatonLaveur
Posts: 977
Joined: Wed Mar 27, 2019 10:45 am

Re: Gmsh applied on threaded fastener inside a threaded hole produces warnings

Postby RatonLaveur » Wed May 05, 2021 4:48 pm

From what i understand of your problem it's not a meshing error. It's a geometry error. The gap between the threaded hole and threaded screw is already a problem in itself. It might be of use to redesign the problem in a simpler way and not using the fastener directly to check other functionalities. Then gradually complexify to achieve your full case.
thschrader
Posts: 2129
Joined: Sat May 20, 2017 12:06 pm
Location: Germany

Re: Gmsh applied on threaded fastener inside a threaded hole produces warnings

Postby thschrader » Wed May 05, 2021 7:35 pm

RatonLaveur wrote: Wed May 05, 2021 4:48 pm ...
It's a geometry error.
...
Yes Sir.
I tried extreme mesh refinement up to 800000 cells for the screw.
With gmsh. Netgen wont work. This problem looks easy... Aaah
Maybe a 2D approach?
I am drowning in work, I will try a new run at the weekend.

BTW:
Do you know the film "The Marathon Man". For the dentists...
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misharsta
Posts: 11
Joined: Tue Apr 27, 2021 3:47 am

Re: Gmsh applied on threaded fastener inside a threaded hole produces warnings

Postby misharsta » Wed May 05, 2021 10:56 pm

I tried the screw alone with no hole . Gmsh still produces errors although the screw is a standard fastener selected from the Fastener workbench. The following are some of the errors I got.

[01:35:41 Gmsh had warnings ...
01:35:41 Warning : 4 elements remain invalid in surface 20
Warning : 12 elements remain invalid in surface 21
Warning : 4 elements remain invalid in surface 22

I see you're suggesting a 2D approach. The thing is that my project is more sophisticated that this. I'm posting a simple version of the problem to illustrate my point to the forum more directly and with minimum confusion.

I'm honestly not to sure how to progress further in this project.

Attached is a copy of the FCStd of the fastener alone with no hole in case someone wants an inside look.
Attachments
FEA Fastner only.FCStd
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