Question:Carbon fibre tubes

[josch]

Hello,
I want to design a composit fibre tube and would like to know how to consider the laminate construction in terms of fibre direction, etc.....
The fibres of choice are: E-Glass, Aramid and Carbon, in any variation.

I would be gratefull for any help

josch

J.Schlieben@web.de

[Phil Locker]

Tell us more about the tube (what it will be used for, what the loadings will be.... eg is there a torsional load, or is it all longitudinal?)

You can hand roll a composite tube over a core if you're patient and layup only a few plies at a time. To make life easy, consider using a light weight core that you just leave in. After carefully rolling your fabric on, with the fiber orientation(s) in the desired direction (wetting it out as you go) wrap it very tightly on the diagonal with long narrow strips of peelply. Some people will use heat shrink tape instead, and heat it after wrapping. You can't vacuum bag a tube very easily as the fabric will squish and wrinkle. Once the first layers have cured to at least a green state, unwrap the peelply or shrink-tape, sand off any significant wrinkles, and then repeat the whole process until you finally get the wall thickness that you're after.

Hope this helps
Phil

www.philsfoils.com

[josch]

It is a tube or better a catamaran Cross beam it is loaded by a vertikal Moment of 240kN a horizontal moment of 160kN and also a vertikal force of 80kN and a horizontal force of 50kN.

Moreover there is a choice of Cross sections. Circular section (diam max 500mm) and a box section (max beam section 500mm as well)

The problems I have are more from the theoretical side than from the practical one.

What I am after is who do professionals go thrugh these kinds of problems, what would they do???


The Cross beam is an exercise at my course, I attend the course in the final year, where all the basic composit structures are dealed in detail in the first two years, what means there is a basic piece of knowledge missing and there are nearly no books available as far as I know.

Thank you for your answer

[eckmuhl]

You have to use as much UD as you can along the tube axis, then you will need few biaxial for torsion stress and other impact which can happen on catamaran.
For material everything is a matter of cost and the weight of the beam you're looking at. All the materials can reach the strength you need . By the way you can forget Kevlar cause it's too expansive for the mechanical proporties it has ; the only reason to use Kevlar is when carbon is forbiden by rules. "Use sandwich panel is a great idea"
For the shape both can work ; circular section will be heavier but really easier too built. Box section will be lighter but don't forget you will need to have radius on each corner and add extra layup between each side if you've got small radius.
By the way I believe ur teacher just want 2show u that the best solution is a mix between both of them ; so just find the best solution for every case and write on your discussion that the best solution is only function of what you wanna do with the cat , & how much money you've got!!!!!.
If you wanna see what is the best solution when you've got plenty of money look at what is done on maxi catamaran as Orange2 or PlayStation , and on racing trimaran as B&Q and all the ORMA trimaran (it's a racing 60ft trimaran organisation) check on internet.
Good luck

[josch]

thank you very much your reply is a big help
Do you have any idea of the E-modulus (E1 and E2)of typical fibres, like HS carbon, E-Glass, and perhaps Kevlar as well????
thanks again for your reply

josch

[AVMan]

Typical longitudinal moduli (E1)
HS Carbon: 34 Msi (235 GPa)
E-Glass: (10 Msi (72 GPa)
Aramid or Kevlar: 19 Msi (130 GPa)

As for transverse moduli (E2) of just the fibers, you probably won't find any data. Please keep in mind that these are fiber properties, not composite properties. Composite properties depend on your resin & fiber sizing & how well they translate the fiber properties...

[AVMan]

Also these are only tensile moduli values...

[josch]

Hhmh, Ok thank you than,
I found a nice formula, with wich E2 can be calculated, all the mentioned variables and compenents are taken into account, and the relations make sense, books can be so helpful
Thanks to all of you

josch

[Phil Locker]

a reference of mechanical specs by fabric type & architecture can be found at
http://www.vectorply.com
----> Products
-----> Reinforcements by Fiber Type

I thought your question concerned the engineering of the cross member. This is when I'd pick up the phone and call a structural engineer, but engineering beam theory (lots of examples on the web) will get you in the ballpark for your vertical forces. Try http://www.efunda.com/formulae/formula_index.cfm

Cheers,
Phil

www.philsfoils.com

[josch]

Hey you are all great,
I have spent hours to find properties in the net and hours to find the right way to go for doing the job...... and here they are.
In the boatdesign forum.
I guess my job now is to sort all that information and then I have my proper cross-beam. You just have made a student very happy


Cheers

josch