FreeCAD FEM moment of inertia & axial torsion

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blubee
Posts: 31
Joined: Sun Jun 18, 2017 5:04 pm

FreeCAD FEM moment of inertia & axial torsion

Postby blubee » Mon Aug 21, 2017 2:08 am

I am trying to model the force of a motor on a central pipe [hexagon and cylindrical] along with some disks.

I would like to see how many pascals it would take for any of the parts to reach failure. I am using standard medium carbon steel, I've attached two files they both have a gmsh with a max size of 1.00000000 mm so it might be a bit slow to open.

I'd like to see what's the maximum radial torsion I could apply to a gear connected to the shaft at the three different sections. I would also like to see how I can do the same for the hexagon hole in the inner disk as well as the six holes that would hold more stabilizing pins going horizontally.

Actually the files are too large to attach with the gmsh and analysis. I'll add the files without gmsh and analysis.

Would anyone be able to guide me through applying a rotational torsion to the pipe to see where they will break?
pipe.jpeg
pipe.jpeg (304.29 KiB) Viewed 988 times
disk.jpeg
disk.jpeg (375.57 KiB) Viewed 988 times
OS: Ubuntu 17.04
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.17.11827 (Git)
Build type: None
Branch: master
Hash: ca4488f4387f761df47322038585b23cb5a1bd73
Python version: 2.7.13
Qt version: 4.8.7
Coin version: 4.0.0a
OCC version: 7.1.0
Locale: English/UnitedStates (en_US)
Attachments
pipe.fcstd
(43.91 KiB) Downloaded 26 times
disk.fcstd
(30.04 KiB) Downloaded 24 times
HoWil
Posts: 840
Joined: Sun Jun 14, 2015 7:31 pm
Location: Austria

Re: FreeCAD FEM moment of inertia & axial torsion

Postby HoWil » Mon Aug 21, 2017 5:49 am

Dear blubee,

I am not sure if applying rotational load does work at the moment... Please see also https://forum.freecadweb.org/viewtopic.php?f=18&t=23778 there you find also some further information in the listed links.

But you can simply create a test case.
Regarding the size of the model you should consider simply deleting the mesh information by right clicking on the mesh object. One can than still remesh your model with the all stored settings.

BR,
Howil
blubee
Posts: 31
Joined: Sun Jun 18, 2017 5:04 pm

Re: FreeCAD FEM moment of inertia & axial torsion

Postby blubee » Mon Aug 21, 2017 12:54 pm

HoWil wrote:
Mon Aug 21, 2017 5:49 am
Dear blubee,

I am not sure if applying rotational load does work at the moment... Please see also https://forum.freecadweb.org/viewtopic.php?f=18&t=23778 there you find also some further information in the listed links.

But you can simply create a test case.
Regarding the size of the model you should consider simply deleting the mesh information by right clicking on the mesh object. One can than still remesh your model with the all stored settings.

BR,
Howil
Thanks, with that I attempted to do a little test. Would anyone be willing to take a look at this results file?
https://filetea.me/n3wU1YLHUMpSPOYoV6TSFLh1Q
pipe_0.jpeg
pipe_0.jpeg (103.49 KiB) Viewed 951 times
I am trying to figure out how to get the data that I need.

There are constraints on both ends of this pipe, then there's force applied [500] is that MPa? Then after a little while I get the result which looks like this:
pipe_1.jpeg
pipe_1.jpeg (155.89 KiB) Viewed 951 times
when I animate the displacement it gets really strange results:
pipe_2.jpeg
pipe_2.jpeg (172.45 KiB) Viewed 951 times
I just want to know what's the MPa that would cause any part of this model to fail.
When applying force, it only asks for a number; is that Newtons, N.M, N.M^2, MPa, ft-lbs, etc?
UR_
Posts: 994
Joined: Tue Jan 03, 2017 8:42 pm

Re: FreeCAD FEM moment of inertia & axial torsion

Postby UR_ » Mon Aug 21, 2017 3:22 pm

blubee wrote:
Mon Aug 21, 2017 12:54 pm
it gets really strange results
The funny part of this analysis is, you caused millions of floating point operations, done by ccx, just to obtain this:
Shear stress rod under torque.png
Shear stress rod under torque.png (2.66 KiB) Viewed 937 times
:shock:
UR_
Posts: 994
Joined: Tue Jan 03, 2017 8:42 pm

Re: FreeCAD FEM moment of inertia & axial torsion

Postby UR_ » Mon Aug 21, 2017 3:55 pm

blubee wrote:
Mon Aug 21, 2017 12:54 pm
When applying force, it only asks for a number; is that Newtons, N.M, N.M^2, MPa, ft-lbs, etc?
Are you talking about this input box?
FEM Constraint Force.png
FEM Constraint Force.png (11.6 KiB) Viewed 928 times
As you can see, there is asked for an "area load". Load's unit is Newton. This load will be distributed equally to selected face.

BTW this issue is on the run:
Bugtracker.png
Bugtracker.png (13.69 KiB) Viewed 928 times
blubee
Posts: 31
Joined: Sun Jun 18, 2017 5:04 pm

Re: FreeCAD FEM moment of inertia & axial torsion

Postby blubee » Mon Aug 21, 2017 4:17 pm

UR_ wrote:
Mon Aug 21, 2017 3:22 pm
blubee wrote:
Mon Aug 21, 2017 12:54 pm
it gets really strange results
The funny part of this analysis is, you caused millions of floating point operations, done by ccx, just to obtain this:
Shear stress rod under torque.png :shock:
Well that doesn't look good on me, but i am learning. I'm a programmer first, fell into physics sorta out of necessity.
UR_ wrote:
Mon Aug 21, 2017 3:55 pm
blubee wrote:
Mon Aug 21, 2017 12:54 pm
When applying force, it only asks for a number; is that Newtons, N.M, N.M^2, MPa, ft-lbs, etc?
Are you talking about this input box?
FEM Constraint Force.png

As you can see, there is asked for an "area load". Load's unit is Newton. This load will be distributed equally to selected face.

BTW this issue is on the run:
Bugtracker.png
Thank you for the clarification.
thschrader
Posts: 1422
Joined: Sat May 20, 2017 12:06 pm
Location: Germany

Re: FreeCAD FEM moment of inertia & axial torsion

Postby thschrader » Mon Aug 21, 2017 6:44 pm

EDIT 21.08.2017 (UR_, I am getting older... :oops: )
Hello blubee,
according to the above formula from UR_ for calculating shear-stress under torsional loading, you can
apply a torsion-loading of 0,231 kNm at the 20 mm transmission (when using steel S235 with a maximum
allowable shear stress of 136 MPa). The distance between the holes in the disk and the axis of the transmission is 30 mm,
so you must apply a load of 7100 N at both holes to get the Torsion of 0,231 kNm at both ends of the transmission.
If you run the calculation with your modell, you will get good results (plot: shear-stress). Attached is the modell
with the cleared mesh (doubleclick on mesh, mesh it hyperfine as you did before and have a pizza during ccx-run... :) )
regards thomas
pipe_neu.fcstd
(85.79 KiB) Downloaded 28 times
welle1.JPG
welle1.JPG (66.2 KiB) Viewed 902 times
Last edited by thschrader on Mon Aug 21, 2017 7:23 pm, edited 1 time in total.
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bernd
Posts: 8442
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Location: Zürich, Switzerland

Re: FreeCAD FEM moment of inertia & axial torsion

Postby bernd » Mon Aug 21, 2017 6:51 pm

UR_
Posts: 994
Joined: Tue Jan 03, 2017 8:42 pm

Re: FreeCAD FEM moment of inertia & axial torsion

Postby UR_ » Mon Aug 21, 2017 7:02 pm

thschrader wrote:
Mon Aug 21, 2017 6:44 pm
dann kannst du beim Rechenlauf in Ruhe eine Pizza essen...
That's right.
But can you please translate this to english. ;)