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FIber layup suggestion

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aeberl
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FIber layup suggestion

Postby aeberl » Fri Jul 31, 2009 6:06 pm

I am half way thru my first balsa-carbon project. The core (1340 x 390 x 12mm) is shaped and ready for lamination. Usually I would have used 3 x 6oz plain weave e-glass on top and bottom to achieve the desired flex pattern. Now I want to reduce layup weight and achieve similar board stiffness. I have 8oz plain waeve carbon, will it be enough if used one layer per side? How much e-glass should I add (if any) to get similar flex?

BWD
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Re: FIber layup suggestion

Postby BWD » Fri Jul 31, 2009 8:19 pm

I don't know if you will get similar flex.

Probably the core would have to be thinner and/or softer to approximate the flex from the the E glass board, since the skins will be so much stiffer.

Heard a rule of thumb for boat hulls, if done really well, half the weight of cloth gives similar strength to E glass. Not sure how it translates to boards.

I would think about thinning the core compared to the core to use for Eglass, at least at the tips, and using a light glass layer (2-4 oz) over the carbon.
But that is just an experimental idea....

aeberl
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Re: FIber layup suggestion

Postby aeberl » Fri Jul 31, 2009 10:25 pm

Thanks a lot, the local market has helped me since there is no 2oz colth to be found, so I will just give it a try with the 8oz cabon + 4oz e-glass. The core is allready thinned to about 3mm on the tips, 11mm between pads.

andre_9111
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Re: FIber layup suggestion

Postby andre_9111 » Tue Sep 15, 2009 9:44 pm

Tell me how this lay up(8 oz carbon +4 oz e glass) has worked for you.

I am planning to do exactly the same . I would like to know if the stiffnes /flex is correct.
Thank you.

aeberl
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Re: FIber layup suggestion

Postby aeberl » Wed Sep 16, 2009 2:01 am

It turned out to be stiffer than expected. Usually I use a total of 18oz of glass per side on a 11mm balsa core, which results in just the right flex.
The 8oz carbon + 4oz glass resuts in about half the flex of the all 18oz all glass (good for a stiff freestyl board, but oo stiff for an all round freeride board). I would suggest to reduce core thickness to 8 or 9mm or use lighter carbon fabric.

K1W1
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Re: FIber layup suggestion

Postby K1W1 » Wed Sep 16, 2009 6:57 am

Don't no how true this is ,but I was told that carbon is about 4 times stiffer than glass?

zfennell
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Re: FIber layup suggestion

Postby zfennell » Wed Sep 16, 2009 2:59 pm

aeberl wrote:It turned out to be stiffer than expected. Usually I use a total of 18oz of glass per side on a 11mm balsa core, which results in just the right flex.
The 8oz carbon + 4oz glass resuts in about half the flex of the all 18oz all glass (good for a stiff freestyl board, but oo stiff for an all round freeride board). I would suggest to reduce core thickness to 8 or 9mm or use lighter carbon fabric.


sounds like a good test

matweb is still a good place for material properties:
generic carbon
density : 1.8
modulus: 33.5 million psi
max strength : 600, 000 psi

generic e-glass
density : 2.5
modulus: 10.5 million psi
max strength : 250, 000 psi

so comparing 8 oz carbon to 18 oz glass
equivalent weight of carbon has approx 30% more volume than glass and 3 times the stiffness
so 8oz carbon x 1.3 x 3 = 31 + 4 oz glass = 35 oz glass
remarkably close to twice the overall stiffness of 18 oz glass

stiffness and strength are not the same thing.
if you look up S glass, you will find it has similar modulus (stiffness) to e-glass
but strength comparable to carbon
perhaps a better way to keep the flex you are looking for.

carbon is lighter, but you'll need much better acounting to get significant benefits.
the resin and core make up so much of the totals that the carbon numbers get diluted.

science in action,
-bill

andre_9111
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Re: FIber layup suggestion

Postby andre_9111 » Wed Sep 16, 2009 10:25 pm

Thank you AEBERL for the kwick answer. I think that I will use 1 layer of carbon /kevlar 6 oz and 1 layer of 4 oz eglass top and bottom over a 9,65 mm Cherrywood core(in the middle). It wil be a light wind board 146x49 with 3 stage rocker +/- 20 mm.

My first board was made of 20mm(in the middle) corecell wrap with 2 layers of 6 oz carbon an 1 layer of 4oz eglass on top and 1 layer of 6 oz carbon an 1 layer of 6 oz kevlar and 1 layer of 4oz eglass on bottom. Combine with a 5 mm concave it end up with a too stiff board with barely no flex.
136mm X 40mm 32 mm tail , continuous curve and 35 mm rocker.
It rides fine but gives a rought ride.

Thank you zfennel for the matweb info . I did not knew that fabulous website.

Andre
Attachments
composite sandwich stiffness.jpg
sandwich thickness and stiffness understanding
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