Assembly2 assembly meshing of boolion unioned parts min size .1 in or .05" in never seems to finish windows shows not re

About the development of the FEM module/workbench.

Moderator: bernd

thschrader
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Location: Germany

Re: Assembly2 assembly meshing of boolion unioned parts min size .1 in or .05" in never seems to finish windows shows no

Postby thschrader » Mon Aug 20, 2018 2:18 pm

Hi josheeg,
I did a "quick and dirty" cfd-run, to get a feeling what forces are
put on the tubes
profile: span=2500 mm, length 1100 mm, thickness 140 mm
windspeed: 10 m/s = 36 km/h
drag-x=2,15 N (which gives cd=0,1)
total lift 145 N (both wings produce 29 kg lifting force)
For each wing-tube you should use a load of 145/2 /2,5=29 N/m
perpendicular to the wind direction.
wing_cfd.JPG
wing_cfd.JPG (72.43 KiB) Viewed 611 times
velocity.JPG
velocity.JPG (23.7 KiB) Viewed 611 times
thschrader
Posts: 1702
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Location: Germany

Re: Assembly2 assembly meshing of boolion unioned parts min size .1 in or .05" in never seems to finish windows shows no

Postby thschrader » Mon Aug 20, 2018 3:06 pm

When looking at the pressure-distribution, there should be an additional
Moment. The left tube gets more load then the right one.
But how to get the momentum in paraview?
momentum_tubes.JPG
momentum_tubes.JPG (28.33 KiB) Viewed 608 times
josheeg
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Re: Assembly2 assembly meshing of boolion unioned parts min size .1 in or .05" in never seems to finish windows shows no

Postby josheeg » Wed Aug 22, 2018 5:25 pm

Wow impressive analysis.
I got the 98 in tube with carbon fiber material under 100 newtons abs deflection. Does when it turns red show it will break?
Or when will it show signs and wear?
98flexunder100N.png
98flexunder100N.png (190.8 KiB) Viewed 588 times
If red means it will break the next shorter tube may need to be used because when a kite is setup in crosswind and tethered it gets more forces on it I don't think the wikipedia equation is right but here is my one page.
one page CWKP.png
one page CWKP.png (76.76 KiB) Viewed 588 times
70-90km/h at 7m/s wind.
schupin
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Re: Assembly2 assembly meshing of boolion unioned parts min size .1 in or .05" in never seems to finish windows shows no

Postby schupin » Wed Aug 22, 2018 5:57 pm

Freecad won't show you if it break.
From a material point of view, you're modeling a very simple material behaviour : linear elasticity.

It means that the stress rises lineary when the strain increases. The slope of this beahoviour law is the Young modulus you entered.
In your FEM calculation, you never gave a "max strain" or "max stress" value. So FC won't know it for you.

In your case, you have to know when the linear behaviour ends.
If you look this picture :
Image
(taken from here : https://en.wikipedia.org/wiki/Stress%E2 ... rain_curve)

Your model is valid if you stay in the first linear part of the curve (in blue). If you excess (for your material) this area, you're simulation will be meaningless.
So, in your documentation, perhaps you have a linear elasticity limit ?
If you find a stress or strain limit, you'll have to look on your results to see if you've passed this limit or not.
josheeg
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Re: Assembly2 assembly meshing of boolion unioned parts min size .1 in or .05" in never seems to finish windows shows no

Postby josheeg » Thu Aug 23, 2018 6:26 am

600 ksi is that a unit it is in tensle strength. They have data sheets at dragon plate.
Will it compare with my analysis?
Screenshot_2018-08-23-02-22-54.png
Screenshot_2018-08-23-02-22-54.png (345.75 KiB) Viewed 558 times
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bernd
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Re: Assembly2 assembly meshing of boolion unioned parts min size .1 in or .05" in never seems to finish windows shows no

Postby bernd » Thu Aug 23, 2018 6:54 am

@schupin
very well explained :)
josheeg
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Re: Assembly2 assembly meshing of boolion unioned parts min size .1 in or .05" in never seems to finish windows shows no

Postby josheeg » Thu Aug 23, 2018 2:05 pm

I see in the wikipedia article

"This stress is called the tensile stress because every part of the object is subjected to tension. The SI unit of stress is the newton per square meter, which is called the pascal.
1 pascal = 1 Pa = 1 N/m2"

So I should be looking for pascal or N/m^2?
josheeg
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Re: Assembly2 assembly meshing of boolion unioned parts min size .1 in or .05" in never seems to finish windows shows no

Postby josheeg » Thu Aug 23, 2018 3:52 pm

600 ksi to ~4k Mpa
shown in this online calculator.
Then I looked at some of the different analysis results mesh radio button options for stress and the max seems well below 4k Mpa so it should not break under loading?
600ksitompadragonplatecf.png
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vonmasstressmpa.png
vonmasstressmpa.png (191.22 KiB) Viewed 516 times
maxprincipalstress.png
maxprincipalstress.png (190.57 KiB) Viewed 516 times
maxsheer67mpa.png
maxsheer67mpa.png (227.49 KiB) Viewed 516 times
schupin
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Re: Assembly2 assembly meshing of boolion unioned parts min size .1 in or .05" in never seems to finish windows shows no

Postby schupin » Thu Aug 23, 2018 7:17 pm

Yes, it seems to be right.

As a first approach, you can look a the von mises stress and put the max value to 4GPa (or 4 000MPa).
If you see anything red, it means the the stress exceed your max value and it might break.

You might have to think about a "safety factor". Just for an idea, you can say that your limit is 0.8*4100MPa = 3250 MPa.
I started to read some interesting thing here that explains quite clearly these notions : http://feaforall.com/calculate-safety-factor/
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bernd
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Re: Assembly2 assembly meshing of boolion unioned parts min size .1 in or .05" in never seems to finish windows shows no

Postby bernd » Thu Aug 23, 2018 9:20 pm

- create a Vtk pipeline
- create a scalar filter
- set scalar clip options to van Mises stress
- set in result clip option to Surface with edges and van Mises stress
- set to your maximaum allowabalse stress

in the screen you see all nodes above 350 N/mm2 from the FEM 3D example and transparent all stresses.


Screenshot_20180823_231946.png
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