Question about beam calculation with calculix

About the development of the FEM module/workbench.

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bernd
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Re: Question about beam calculation with calculix

Post by bernd » Thu Jan 09, 2020 4:55 pm

But this would mean all 1D stress results we present ATM are just rubbish. Am I right?

Only the expanded 3D ones are useful.
fandaL
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Re: Question about beam calculation with calculix

Post by fandaL » Thu Jan 09, 2020 6:20 pm

Yes, if the beam is loaded in bending.
But if you change element type e.g. to truss T3D3 which does not transfer bending moments, I would expect stresses to be correct. (it will behave like a cable)

In 2D elements analogous situation is for membrane elements.
ickby
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Re: Question about beam calculation with calculix

Post by ickby » Fri Jan 10, 2020 10:46 am

I intuitively assumed the beam is calculated with the profile I specify, and the 3d option is only for visualization purposes. So like a normal hand calculation calculix calculates bending moments etc. from the beam, and deflections and stresses than from those moments and the profile. If this option uses different elements it is not very clear, and maybe should be made more obvious.
But this would mean all 1D stress results we present ATM are just rubbish. Am I right?
Only the expanded 3D ones are useful.
Yes, at least for the FC presentation where one assumes a beam element with a given profile, e.g. rectangle, the 1D results are not what is expected by the user and IMHO wrong.
thschrader
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Re: Question about beam calculation with calculix

Post by thschrader » Fri Jan 10, 2020 2:07 pm

bernd wrote:
Thu Jan 09, 2020 4:55 pm
Only the expanded 3D ones are useful.
Yes, deflection line / sigma-x-stress (along arrow left pic) seems ok.
The model "error" at the fixing (no tangent zero) as I said above does not occur when using
FC0.19 instead of FC0.18. Sorry...
Now done with
OS: Windows 10 (10.0)
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.19.19181 (Git)
Build type: Release
Branch: master
Hash: 2504247d65271b937dd5f033a0efff9c0d7bf375
Python version: 3.6.8
Qt version: 5.12.1
Coin version: 4.0.0a
OCC version: 7.3.0
Locale: German/Germany (de_DE)
stress_sigmaXX.JPG
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bernd
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Re: Question about beam calculation with calculix

Post by bernd » Fri Jan 10, 2020 7:49 pm

Are you sure it is a FreeCAD difference between 0.18 and 0.19? AFAIK I did not change anything in this regard.

Since you are on Windows and on Windows ccx is bundled with FreeCAD it could be FreeCAD 0.18 just uses an older ccx. Try to use the same ccx binary from 0.18 and 0.19 (set in FEM prefs) and see if you get the expected results with 0.18 too.
thschrader
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Re: Question about beam calculation with calculix

Post by thschrader » Sat Jan 11, 2020 11:22 am

bernd wrote:
Fri Jan 10, 2020 7:49 pm
... just uses an older ccx.
Yep. Now done with a very "old" FC0.17 version. Just for the protocol...
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bernd
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Re: Question about beam calculation with calculix

Post by bernd » Sat Jan 11, 2020 12:39 pm

which ccx version did you use to get 0.365 mm?
thschrader
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Re: Question about beam calculation with calculix

Post by thschrader » Sat Jan 11, 2020 2:18 pm

bernd wrote:
Sat Jan 11, 2020 12:39 pm
which ccx version did you use to get 0.365 mm?
No ccx. I just opened the beam-file from ickby, activated the FEM-wb and
displayed the results. No FEM-run. 0,44 mm are from recalculating.
How can I find out the ccx version? I see this:
FC_bin.JPG
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fandaL
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Re: Question about beam calculation with calculix

Post by fandaL » Sat Jan 11, 2020 3:00 pm

thschrader wrote:
Sat Jan 11, 2020 2:18 pm
How can I find out the ccx version?
When you click to run CalculiX from FreeCAD, there is a log window which contains version information.
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bernd
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Re: Question about beam calculation with calculix

Post by bernd » Sat Jan 11, 2020 4:28 pm

if you use the task panel version info should be printed inside task panel.
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