Force constraint Direction by vector in .inp file?

About the development of the FEM module/workbench.

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bernd
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Re: Force constraint Direction by vector in .inp file?

Postby bernd » Sun Jul 02, 2017 7:25 pm

I do not use the contact at all. What is the difference between this contact and the contact implemented in FreeCAD FEM?
UR_
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Re: Force constraint Direction by vector in .inp file?

Postby UR_ » Sun Jul 02, 2017 9:17 pm

Hello bernd,

in simple words:
  • implemented contact pair is only for pushing face against face. It prevents only from intrusion, but not against lifting and sliding
  • tie contact locally "bonds" adjacent faces together like bolts, rivlets or spot welding.
Therefore, but not only, it's a simplified model to check stress in such customized steel connectors.

steel connector.jpg
steel connector.jpg (8.54 KiB) Viewed 857 times

For further information, please have a look at:
(page 467)
http://www.dhondt.de/ccx_2.12.pdf

Hope you like it :roll:
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bernd
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Re: Force constraint Direction by vector in .inp file?

Postby bernd » Mon Jul 03, 2017 8:52 pm

Got it! YEAH I really it :D issue #3114
eggy
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Re: Force constraint Direction by vector in .inp file?

Postby eggy » Fri Jul 21, 2017 10:35 pm

Thank you both, bernd and UR_!

I have been away for a while, but this works for me. I wanted to model the hands gripping the bar as an area input area to apply the force vector, and bernd's suggestion worked.

And, now a great new tool in contact constraints! Thanks!!

Eggy
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bernd
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Re: Force constraint Direction by vector in .inp file?

Postby bernd » Sat Jul 22, 2017 7:04 am

hands gripping bars sounds interesting, what are you going to model? We happily like to see some cool pics! :D
bernd
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Re: Force constraint Direction by vector in .inp file?

Postby bernd » Tue Aug 15, 2017 5:36 am

UR_ wrote:
Sun Jul 02, 2017 7:17 pm
i think eggy is talking about such a feature, which calculix calls a "tied contact"
(e.g. bonding two faces together, even if there is a gap in between)

Below you can find an example containing two not connected plates (gap 0,1 mm).
...
And this is result view: (color range mapped 0 to 50 MPa)
TieContactVanMises.png
Works great here too. Updated the example to FreeCAD 0.17.11789

TiedSurfaceStripped_2.FCStd
(23.95 KiB) Downloaded 60 times



screen.jpg
screen.jpg (158.01 KiB) Viewed 748 times
sebobi
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Re: Force constraint Direction by vector in .inp file?

Postby sebobi » Tue Aug 04, 2020 10:17 am

eggy wrote:
Sat Jun 24, 2017 3:56 pm
I need to place a Direction on the force constraint on my model. It is placed on the inside of the cylindrical face. I want to choose a Direction that does not match any face or edge in my model.
Is it possible to edit the .inp file (is that where I would find the Direction?) or other file to put in a vector?
[...]

Eggy
Hello,

here maybe some solution without support-geometry for general load vector:

1) possibility for defining general loadvector, if edges or faces in global x,y,z-direction are available:
-> Define 3 single forces in the FEM-modul on the identical face(s) you want. First force is pointing only in global x, 2nd only in y and last only in z-direction. Then give them the desired x,y,z-compents of your special force vector (every forces gets only one global force component).

2) regarding input file (inp):
Is the manipulation of the direction of the forces at nodes in the input file (.inp) a correct approach? The force values stay unaffected. Is afterwords the single force at every node correct regarding the global force distribution of the load regarding the new direction?
The structure of the inputfile for force looks like this for me: nodenumber,direction,forcevalue

For example changing the given Y-Direction = 2 to Z-Direction = 3?

Original-FreeCAD inp-File (Y=2):
...
*CLOAD
** FemConstraintForce
** node loads on shape: Part__Feature:Face5
1,2,0.0000000000000E+00
2,2,0.0000000000000E+00
...


Manipulated inp-File (Z=3):
...
*CLOAD
** FemConstraintForce
** node loads on shape: Part__Feature:Face5
1,3,0.0000000000000E+00
2,3,0.0000000000000E+00
...


Point 2) would be helpfull if for example only one face in x-direction is available. The force in y- and z-direction could then be generated with a manipulated inp-file.
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bernd
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Re: Force constraint Direction by vector in .inp file?

Postby bernd » Tue Aug 04, 2020 12:00 pm

the fastest way to create any force direction you like is just, adding a edge to your FreeCAD file and use this one. See one of the contact examples provided with FreeCAD FEM 0.19