## fem analisys on carbon tube specs?

About the development of the FEM module/workbench.

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josheeg
Posts: 82
Joined: Tue Nov 12, 2013 3:10 pm

### fem analisys on carbon tube specs?

fem analisys on carbon tube specs?
I am looking at the specs page of dragon plate and want to design something with it but do not know how to get their specs into freecad for puting forces on them?

I have gotten fem to work just now I need to make a material.

dpspecs.png (449.41 KiB) Viewed 732 times
schupin
Posts: 416
Joined: Sun Jan 21, 2018 1:43 pm

### Re: fem analisys on carbon tube specs?

If I understand well you're question, you just have to find the :
• density (kg/m3) (you can have it from your picture with the weight, the inner and outer diameters)
I'm not familiar with british units, but you might find a density in kg/m3 with the formula :
D = 2.76799e4 * W / (12*PI*((OD/2)² - (ID/2)²)
With W the weight in lbs/ft ; OD and ID in inches
• Young Modulus (GPa) (it's a Elasticity modulus on the datasheet, just convert the msi to GPa)
34msi = 234 GPa
• Poisson number (-) it's always the most difficult data to find.
Let's say 0.2 is a good guess for carbon/resin composites
When you've got all that, you can take any of the material proposed in the FEM material menu and change it's properties.
You can then save it with the "save custom material" button.
josheeg
Posts: 82
Joined: Tue Nov 12, 2013 3:10 pm

### Re: fem analisys on carbon tube specs?

This is what I got with the calculation

calccfconv.png (237.45 KiB) Viewed 684 times
josheeg
Posts: 82
Joined: Tue Nov 12, 2013 3:10 pm

### Re: fem analisys on carbon tube specs?

So far what I have in freecad for .5 in carbon fiber tubes
486 kg/mm^3

Young Modulus (GPa) (it's a Elasticity modulus on the datasheet, just convert the msi to GPa)

msi -> psi is what I think freecad would want?
GPA is a unit but freecad fem module says psi?
34000000 psi
josheeg
Posts: 82
Joined: Tue Nov 12, 2013 3:10 pm

### Re: fem analisys on carbon tube specs?

kg/m^2 /2000 to get mm
0.486 kg/mm^3

msi to psi 34 msi 34000000psi

0.2 position ratio
freecadfem.png (184.51 KiB) Viewed 680 times
schupin
Posts: 416
Joined: Sun Jan 21, 2018 1:43 pm

### Re: fem analisys on carbon tube specs?

Oh, you don't have the same units than I have in freecad !
I did forgot that we don't have all the same settings...
josheeg wrote:
Sat Jul 28, 2018 3:48 pm
msi to psi 34 msi 34000000psi

0.2 position ratio
That part seems ok, but I've got a doubt for your density.
Usually carbon/resin composites are heavier (density of water is 1000 kg/m3, I think you should find around 1500 kg/m3 = 1.5E-6 kg/mm3)

I'll do some math to see want I get !

EDIT : I did some "maths"
ID = 0.4" = 0.01016 m
OD = 0.53" = 0.013462 m
W = 0.05 lbs/ft = 0,0744082 kg/m

Then, the surface of the tube section is S = pi*((OD/2)^2 - (ID/2)^2) = 6.126093.1E-5 m2
And D = W/S = 1214.6 kg/m3 = 1.2146E-6 kg/mm3
josheeg
Posts: 82
Joined: Tue Nov 12, 2013 3:10 pm

### Re: fem analisys on carbon tube specs?

When I put in 0.0000012146 under kg/mm3 the numbers blank out to 0.00
Is it too large of a number?
THe material I make doen't seem to want to hold the values and I can't go back to check after I select ok for the material except make a new one.???

I tried that material to analyse a tube and I get a gmesh error

0.0: We are going to start ...
0.1: Start Gmsh ...
3.7: Error : Self intersecting surface mesh, computing intersections (this could take a while) Error : Could not open file 'intersect.pos' Warning : Volume 1 consists of no elements Warning : OCC Project Point on Surface FAIL Warning : OCC Project Point on Surface FAIL Warning : OCC Project Point on Surface FAIL Warning : OCC Project Point on Surface FAIL Warning : OCC Project Point on Surface FAIL Warning : OCC Project Point on Surface FAIL Warning : OCC Project Point on Surface FAIL Warning : OCC Project Point on Surface FAIL Warning : OCC Project Point on Surface FAIL Warning : OCC Project Point on Surface FAIL Warning : OCC Project Point on Surface FAIL Warning : OCC Project Point on Surface FAIL Warning : OCC Project Point on Surface FAIL Warning : OCC Project Point on Surface FAIL Warning : OCC Project Point on Surface FAIL Warning : OCC Project Point on Surface FAIL Warning : OCC Project Point on Surface FAIL Warning : OCC Project Point on Surface FAIL Warning : OCC Project Point on Surface FAIL Warning : OCC Project Point on Surface FAIL Warning : OCC Project Point on Surface FAIL Warning : OCC Project Point on Surface FAIL Warning : OCC Project Point on Surface FAIL Warning : OCC Project Point on Surface FAIL Warning : OCC Project Point on Surface FAIL Warning : OCC Project Point on Surface FAIL Warning : OCC Project Point on Surface FAIL Warning : OCC Project Point on Surface FAIL Warning : Surface mesh: worst distortion = -6.45584 (avg = 0.500218, 44 elements with jac.
3.7: Gmsh done!
schupin
Posts: 416
Joined: Sun Jan 21, 2018 1:43 pm

### Re: fem analisys on carbon tube specs?

I think you could directly enter 1214.6 kg/m3 as a density value ?
Freecad seems to understand the units you write.
josheeg
Posts: 82
Joined: Tue Nov 12, 2013 3:10 pm

### Re: fem analisys on carbon tube specs?

Wouldn't that be incorrect because it had e-6 at the end so move the decimal point 6 places to the left.?
schupin
Posts: 416
Joined: Sun Jan 21, 2018 1:43 pm

### Re: fem analisys on carbon tube specs?

If you fill it just like this :
FEM_WB_Prop.png (24.11 KiB) Viewed 650 times
It will be correct.
NB : on my version I put 34000000 psi as a young modulus and it has been automatically converted into GPa.