FEM Stress values are not showing

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Prakash
Posts: 6
Joined: Wed Feb 20, 2019 6:37 am

FEM Stress values are not showing

Postby Prakash » Sun May 16, 2021 5:32 am

Hi All

i'm trying to do static analysis (with force and fixed constraint on sides)
in Previous version of FreeCAD i could see Stress Values along with displacement in CCX_Results
but now i see only displacement, Stress is always zero on all the faces (tried with different materials, but no effect on result)
although i can see min and max values for Stress in CCX_Result but in color gradient its zero on entire model

Since attachment file size limit is 1mb, FreeCAD file can be found here
Is it something to do with latest version of FreeCAD or FEM solver settings?

Freecad Version: 0.19
Revision Number: 24291 (Git)

Thanks for your time.
with warm regards,
Prakash
UR_
Posts: 1326
Joined: Tue Jan 03, 2017 8:42 pm

Re: FEM Stress values are not showing

Postby UR_ » Wed May 19, 2021 3:59 am

FEM solver needs a mesh satisfying some quality standards to get a valid solution.

Tetrahedrons should have a maximum aspect ratio of 2.

That means if you consider a profile thickness of 2 mm, mesh element size should not exceed 4 mm.

Furthermore model defeaturing is a major task in your workflow and shouldn't be skipped.

All these tiny arc has to be removed before engaging a mesher.

Screenshot 007.png
Screenshot 007.png (16.75 KiB) Viewed 566 times

This gives using gmsh_4.8.4:

Screenshot 002.png
Screenshot 002.png (91.14 KiB) Viewed 566 times

========================== Dump contents of mesh ==========================
1) Total number of nodes: 488861
2) Total number of edges: 15066
3) Total number of faces: 160078
4) Total number of polygons: 0
5) Total number of volumes: 248750
6) Total number of polyhedrons: 0

7) Total number of linear edges: 0
8) Total number of linear faces: 0
9) Total number of linear volumes: 0

10) Total number of quadratic edges: 15066
11) Total number of quadratic faces: 160078
11.1) Number of quadratic triangles: 160078
11.2) Number of quadratic quadrangles: 0
12) Total number of quadratic volumes: 248750
12.1) Number of quadratic hexahedrons: 0
12.2) Number of quadratic tetrahedrons: 248750
12.3) Number of quadratic prisms: 0
12.4) Number of quadratic pyramids: 0
===========================================================================



Solving with ccx_2.17_PARDISO.dhondt.exe gives:

Screenshot 006.png
Screenshot 006.png (43.12 KiB) Viewed 566 times
Screenshot 004.png
Screenshot 004.png (396.33 KiB) Viewed 566 times
Screenshot 005.png
Screenshot 005.png (230.77 KiB) Viewed 566 times

used versions:
gmsh 4.8.4
ccx_2.17_PARDISO.dhondt.exe

OS: Windows 10 (10.0)
Word size of FreeCAD: 64-bit
Version: 0.20.24893 (Git)
Build type: Release
Branch: master
Hash: 03855f793feaceeb4385c02f6520f3e1b6429c93
Python version: 3.9.4
Qt version: 5.12.9
Coin version: 4.0.0
OCC version: 7.5.2
Locale: German/Germany (de_DE)
UR_
Posts: 1326
Joined: Tue Jan 03, 2017 8:42 pm

Re: FEM Stress values are not showing

Postby UR_ » Wed May 19, 2021 4:05 am

files:
(mesh and result object stripped)

Profile_stripped.FCStd
(105.69 KiB) Downloaded 16 times
profil.dxf
(46.53 KiB) Downloaded 14 times
Prakash
Posts: 6
Joined: Wed Feb 20, 2019 6:37 am

Re: FEM Stress values are not showing

Postby Prakash » Wed May 19, 2021 10:31 am

Thanks for Detailed Answer.

Did you manually removed all those tiny arcs(fillets) or can we do it by macro(python)
There is an option (Decimation) in Mesh Design Workbench..but this option removed large faces instead of flattening the fillets.

Thanks Again

with warm regards,
Prakash
User avatar
Kunda1
Posts: 10518
Joined: Thu Jan 05, 2017 9:03 pm

Re: FEM Stress values are not showing

Postby Kunda1 » Wed May 19, 2021 12:50 pm

Prakash, please mark a thread [Solved] by prepending it to the title of the first post of this thread. Thanks :D
Alone you go faster. Together we go farther
Please mark thread [Solved]
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UR_
Posts: 1326
Joined: Tue Jan 03, 2017 8:42 pm

Re: FEM Stress values are not showing

Postby UR_ » Wed May 19, 2021 2:26 pm

Prakash wrote: Wed May 19, 2021 10:31 am Did you manually removed all those tiny arcs ...
Yes, I used QCAD working on exported dxf file.

If you prefer working on extruded solid, please have a look at:

https://wiki.freecadweb.org/Part_Defeaturing