FEM BUG HELP?

About the development of the FEM module/workbench.

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xsuper9988
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Re: FEM BUG HELP?

Post by xsuper9988 »

UR_ wrote: Mon Jun 07, 2021 4:45 pm Unfortunately you ignored some advise :shock:

- Refinement not done
- Defeaturing not done
Screenshot 002.png
Screenshot 003.png


if you choose 2nd order elements and there are high curvature geometries (fillets),
you should set Second Order Linear to True
Screenshot 004.png


Screenshot 001.png


Before continuing, please update to latest https://github.com/FreeCAD/FreeCAD-Bund ... kly-builds


_FEM_still_no_BUG_TEST2_mesh_cleared.FCStd
Thank you very much!
I finally finish it!
But it doesn’t seem to support two materials yet, right?
user1234
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Re: FEM BUG HELP?

Post by user1234 »

Hello!
Should work with CompSolids (https://wiki.freecadweb.org/Part_BooleanFragments). Never used it myself, but some remarks:

- if you want calculate the whole beam like in the first video, do it not plane on plane, because when you mesh it, the whole surface is "welded" which is not in real life and the FEM result is also invalid. Make a gap in it and make a welding seam (rectangle) in it, where you weld it.

- also if you want calculate the whole support and all is steel, a CompSolid makes no sense because the elastic modulus and the poisson ratio are mostly the same (at least this is my opinion, special usecase not included). The plane on plane error above have more effect (for the large beam in the video).

- C45 (or C45E or C45U) are bad beam materials, because they are bad for welding (except you weld it with Xuper, but i would use Xuper680S, at least use that for Carbon Steel, i do not know if your name is intended).

Greetings
user1234
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bernd
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Re: FEM BUG HELP?

Post by bernd »

xsuper9988 wrote: Tue Jun 08, 2021 6:57 am But it doesn’t seem to support two materials yet, right?
FEM_Shear_of_a_Composite_Block and the examples in FEM examples GUI
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xsuper9988
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Re: FEM BUG HELP?

Post by xsuper9988 »

bernd wrote: Tue Jun 08, 2021 11:56 am
xsuper9988 wrote: Tue Jun 08, 2021 6:57 am But it doesn’t seem to support two materials yet, right?
FEM_Shear_of_a_Composite_Block and the examples in FEM examples GUI
Thank you
I will study it
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xsuper9988
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Re: FEM BUG HELP?

Post by xsuper9988 »

user1234 wrote: Tue Jun 08, 2021 9:31 am Hello!
Should work with CompSolids (https://wiki.freecadweb.org/Part_BooleanFragments). Never used it myself, but some remarks:

- if you want calculate the whole beam like in the first video, do it not plane on plane, because when you mesh it, the whole surface is "welded" which is not in real life and the FEM result is also invalid. Make a gap in it and make a welding seam (rectangle) in it, where you weld it.

- also if you want calculate the whole support and all is steel, a CompSolid makes no sense because the elastic modulus and the poisson ratio are mostly the same (at least this is my opinion, special usecase not included). The plane on plane error above have more effect (for the large beam in the video).

- C45 (or C45E or C45U) are bad beam materials, because they are bad for welding (except you weld it with Xuper, but i would use Xuper680S, at least use that for Carbon Steel, i do not know if your name is intended).

Greetings
user1234
1.
Yes it's not all welded
Welding is only a small part of my plan
Most of them are positioning holes and lock screws

2.
I'm not sure if it is C45
Just cheap iron
But I will add granite epoxy

3.
xsuper9988 just a ID...haha

4.
Because I want to DIY a CNC
So I think about how to analyze the structure
The above are just some simple tests
I found that using FREECAD's "Assembly" to design
Seems to be in trouble on FEM
In addition, I have added Linear Rail to do FEM testing
There are still many errors

I found a machine STEP link
How to do FEM structure analysis for machine STEP files like this?


https://grabcad.com/library/diy-cnc-mac ... id=8980056
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bernd
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Re: FEM BUG HELP?

Post by bernd »

xsuper9988 wrote: Wed Jun 09, 2021 12:59 pm How to do FEM structure analysis for machine STEP files like this?

https://grabcad.com/library/diy-cnc-mac ... id=8980056
Depends on which of the dozens of parts you would like to analyze?
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xsuper9988
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Re: FEM BUG HELP?

Post by xsuper9988 »

bernd wrote: Wed Jun 09, 2021 1:18 pm
xsuper9988 wrote: Wed Jun 09, 2021 12:59 pm How to do FEM structure analysis for machine STEP files like this?

https://grabcad.com/library/diy-cnc-mac ... id=8980056
Depends on which of the dozens of parts you would like to analyze?
That's right
I am doing a simple example
Contains dual materials
I'll ask questions later
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