Material Properties of Carbon Fiber

[afgbikes]

Do you guys know how can I justify that carbon fiber has isotropic / orthotropic material properties?

if it is isotropic, how can i justify
some papers suggest they are orthotropic?
is it because when it undergoes curing process, in the oven
it becomes elastic brittle (which induce to orthotropic rather than isotropic in its original mode (graphite/carbon)

many thanks
hope you could give me some lights

 

[Demon3]

Fibers only reinforce in the direction that the long part of the fiber is aligned in anyway so it really doesn't matter if they the fiber properties are isotropic. All you need is the properties in the fiber long direction which you can find online. One compensates for the fact the the reinforcement is only in one direction by aligning in the fibers, or layers of fibers in different directions to create reinforcement in those other directions too.

There are reasons why a carbon fiber would have anisotropic properties. For example, many are made from PAN fibers (polyacrylonitrile) which contain highly aligned polymer chains from the spinning process. These would then carbonize to give aligned graphitic sheets.

Chris DeArmitt - PhD FRSC

Materials Consulting & Training

http://www.phantomplastics.com

 

[IRstuff]

One would think the fact that a material that is described as "fiber" would almost have to make it anisotropic.

TTFN
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[Demon3]

Right, that makes it anisotropic in shape but not necessarily in properties.

Chris DeArmitt - PhD FRSC

Materials Consulting & Training

http://www.phantomplastics.com

 

[IRstuff]

That's true, but the shape ultimately drives the properties, otherwise, there would be no need to to lay down differing directions of fibers, unlike starting with a sheet-oriented material to begin with.

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[Demon3]

Correct. That's exactly what I said in my first post here

Chris DeArmitt - PhD FRSC

Materials Consulting & Training

http://www.phantomplastics.com

 

[afgbikes]

I have a bit of understanding now, especially when you said the geometry have influence on material properties
so it seems vendor of carbon fibre as general couldn't give generic material properties for all direction then

 

[IRstuff]

Sure, if you were to sell rope, would it make sense to measure or specify its transverse tensile strength?

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