Re: [Paddlewise] carbon-kevlar weave

I am suspicious about the structural efficience of a mixed weave.  If the 
fabric is on the surface of a deformed laminate, all of the fibers will have 
the same strain.  The stiffest fibers will carry most of the load.  (stress = 
strain x stiffness).

Thus, the stiffer carbon fibers in the weave will have the highest stress and 
carry most of the load.  The kevlar won't get involved in carrying the load 
until the carbon fibers break.

>From this assessment, it appears that, to make best use of the carbon fiber, 
the outer surface should be all carbon fiber.  Using the more elastic kevlar 
in the weave could prevent catastrophic failure of the structure, but the 
stiff carbon fibers will fail at smaller deflections --before the kevlar is 
called upon to take its share of the load.

On the other hand, if the kevlar were laminated between skins of carbon 
fiber, the majority of the composite stiffness would come from the stiff 
outer skins.  This would be sort of a thin sandwich structure, one with a 
core of kevlar instead of foam or honeycomb paper.

bob phillips
SE MI
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