Carbon Fibre strength?

["Graydon D. Stuckey" <graydon@apollo.gmi.edu>]

On Fri, 10 May 1996 STEADIRIC@aol.com wrote:

> >     Carbon fibre's attributes don't lie in torsional rigidity.
> >     
> >     Except in the case of pehaps a complete monocoque where there are many 
> >     different surfaces. I don't think that a sigle tube would have the 
> >     strength that is need to be bennificial in that application.
> 
> Bzzzzttttt.....  Your loading a strut tower brace in Tension and 
> Compresion.  Exactly what carbon is for.....

Actually, any fibre, not just carbon, has much more strength on tension
than in compression.  Its the old adage that you can't push on a rope. 
However, if you form the fibres into a shape like a tube, then it will
have some compression strength (not as much as its bending or torsional
strength.) You can even calculate how much compression it will take before
it buckles.  You have to be carefull with crabon though, because it is
sometimes difficult to prevent delamination.  This is more of a problem
when you mix carbon with kevlar, but is still prevalent in carbon-only
composites.  The problem is that the epoxy that holds it all together is
not nearly as strong as the carbon, so if you have to rely on the epoxy to
hold the carbon fibres together (which is true of any application except
tension) then the assembly will not likely be as strong as the carbon
fibre individually.  Personally, I think that a good steel or aluminum has
the concentrated strength required of a strut brace, but for a street car,
a carbon brace can be made to work. 

	A quick note on torsion - if the fibres are wound at a 45 degree 
angle, then a carbon tube can have tremendous torsional rigidity.  The 45 
degree angle is the direction of the greatest strain in a tube in 
torsion.  This also happens to be tension, so the carbon fibre works very 
well.  A filament wound tube, with 45 degree orientation to the winding 
is the ultimate!

Later,								
Graydon D. Stuckey								
graydon@apollo.gmi.edu								
Flint, Michigan   USA
'86 Audi 5000 CS Turbo Quattro, GDS Racing Stage II