Strength of carbon composite—sound logic?


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njl
njl
njl
posted 9 Years Ago HOT
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Hi all,

I'm new to this forum and new to carbon fiber composites in general.

My current project is a mast for a sailboat dinghy.

As my first question on this forum, I'd like to ask if my logic is sound regarding the strength of a carbon fiber component.

I have a hollow wooden mast 12 feet (3.6 meters) high and would like to replace it with a carbon fiber mast of the same diameter.
The wooden mast is 3 inches (75 mm) in diameter with a wall thickness of 0.75 inches (20 mm).

(The carbon cloth I plan to use will be bi-axial twill sleeve, along with West System epoxy.)

When I compare the material properties of the wood to the carbon fiber, I find:
in compression, carbon fiber composite is between 12—16 times stronger
and in tension, carbon fiber composite is between 9—12 times stronger.

As I understand it, I can build the dinghy mast with the same height and diameter.
If I divide the wall thickness of the wooden mast by 9, I get 0.08 inches (2 mm) for the corresponding carbon fiber mast.

So a carbon fiber mast with a wall thickness of 0.08 inches (2 mm) would be similar in tension and much stronger in compression than the corresponding wooden mast.

Is my logic sound?

Thanks for your help!
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Chris Scott
Chris Scott
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You have to take in consideration as to what exactly the strength values of the carbon fiber means.

A bi-axial twill sleeve will have a fiber orientation of ~45*, sleeves will change the angle orientation slightly depending on how much you stretch or compress it to fit.  

Your estimation is an aggressive estimation, I would say that you've assumed all the fibers to be unidirectional along the length of the mast and is subject only to pure bending, tension, or compression loads (no torsional).

Comparing two materials with different anisotropic properties is not as straight forward as that.  If you were switching from steel to aluminum then that would be an appropriate approach.
GO

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