Lay up sequence - carbon next to wood

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Gilo
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Lay up sequence - carbon next to wood

Post by Gilo » Fri Oct 26, 2018 12:23 am

Hello everyone

I seem to remember that someone told me that in a lay up, it is best to have the FG next to the core rather than the CF - something to do with differential expansion and contraction rates between the wood and CF?

Am I right in thinking this, and does putting the CF next to the core make any difference to potential delam rates or risks?

I bow before your superior knowledge

giles

mammuth
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Post by mammuth » Fri Oct 26, 2018 2:23 am

Some say carbon cuts into soft woods, dont know im just using ash.

I had no problems with carbon directly on the core, but im not using gf on my carbon boards.

Thermally during curing gf and carbon act the opposite way. So if you mix ... ???
Tom

SleepingAwake
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Post by SleepingAwake » Fri Nov 09, 2018 7:10 am

I have seen plenty of problems with carbon directly on wood. If you need to do this then use a thin glass or polyester fleece inbetween to give a tougher interface. The problem is the huge difference in stiffness that creates big shear stresses at the interface. For the same reason the diagonal layers should go against the core and the UD layer away from it.

cheers, Reto

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SHIF
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Post by SHIF » Fri Nov 09, 2018 10:25 am

My usual composite schedule places unidirectional carbon fiber right against the core top and bottom and I've never had an issue. Some of my skis have over a hundred days on them. But I'm using bamboo for core material and bamboo is not wood.

It's all voodoo anyway.

Gilo
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Post by Gilo » Mon Nov 12, 2018 2:30 am

Thanks for the replies - hmm, seems there's no real consensus. I shall try both and see what happens.

Gilo

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MontuckyMadman
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Post by MontuckyMadman » Mon Nov 12, 2018 2:39 pm

There will be a difference in laminate stiffness whether the carbon is facing away on both sides of the core or towards the core. If its dicernable is one thing but measurable for sure.
sammer wrote: I'm still a tang on top guy.

SleepingAwake
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Post by SleepingAwake » Wed Nov 14, 2018 11:29 pm

Was curious of how much it would change a quickly ran the numbers. for a pure carbon layup:

the tip is about 11% stiffer when diagonal layers are facing the core
the center is about 3% stiffer when diagonal layers are facing the core

The difference is bigger with flax on the diagonals as due to the low density a layer with the same weight is thicker.

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vinman
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Post by vinman » Fri Nov 16, 2018 9:17 am

I always remember “warp out�. In case some don’t get this reference the warp fibers are the 0 deg and the weft fibers are the diagonal fibers.

Placing the warp farther away from the core increases its effectiveness.

The numbers quoted above about making things stiffer depending which way the fiber is facing seems spot on to what I’ve learned and what I’ve been told by folks in the big time snowboard biz.
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