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Strenght and flexibility

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FrederikS
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Re: Strenght and flexibility

Postby FrederikS » Sun Feb 17, 2013 7:44 pm

BWD wrote:Skin only takes all the load when it's way stiffer than the core.
I'm talking about building something besides a standard composite I-beam...
The wood core can control some aspects of flex (how much, damping etc...), while unidirectional fibers near the neutral axis add some stiffness and reflex but are away from impact, point loads and supported against buckling, the primary failure mode for kiteboards.
I don't envision this idea mainly for light foam or balsa but maybe it could be good with spruce, larch, fir, cedar poplar etc. It could apply with various fibers. Carbon for example, likes to be unkinked and well supported, and most efficiently used used in flat unidirectional sheets and tows...
I would try this with cedar or paulownia with a light bias e glass on the outside, and E S or CF unis at the core.
Just an idea...


Ah ok so you are going to use a structural wood rather than sandwich types. Could be good then :)

BWD
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Re: Strenght and flexibility

Postby BWD » Sun Feb 17, 2013 7:56 pm

It's just a thought, and I am no engineer, maybe we'll see some day.
The drawback is the cores have to be very planar or you end up adding too much extra weight in gluing the layers together.
Having done some 2 layer boards though, it definitely makes getting the rocker right easier!
Lot of work hand planing the layers to be flat though, need to get a thickness planer or sanding drum machine. Conventional type of construction works pretty well too....

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Bille
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Re: Strenght and flexibility

Postby Bille » Tue Feb 26, 2013 7:29 pm

BWD wrote:Skin only takes all the load when it's way stiffer than the core.
I'm talking about building something besides a standard composite I-beam...
The wood core can control some aspects of flex (how much, damping etc...), while unidirectional fibers near the neutral axis add some stiffness and reflex but are away from impact, point loads and supported against buckling, the primary failure mode for kiteboards.
...
Just an idea...


An array of 50K carbon uni , (which is quite easy to wet-out , on both sides of
your wood core will absorb stress to the point where the skin itself could be
kinda light because the main stress in going through the entire length of the
board. Now This is where i could recommend a +/- 45deg fiberglass to control
torsion on the twisting axes. Other wise the use of carbon Tow is a better choice
of materials.

The moment that carbon is woven, you can loose up to 30% in compression strength.
Same goes for fiberglass ; a light , ((12oz "Stitched" fiberglass )) is nearly as strong as
a 16oz woven fiberglass of the same make-up.But remember that your also spreading
12oz of epoxy -Vs - 16oz of epoxy + the extra glass, for the same strength.

If your gonna
use glass, then at least use the, (bi or tri) -stitched-uni.
Here is an example with NO mat between the glass uni-fibers, mat absorbs Tuns
of epoxy, and it's hard to control the weight because of it.

http://www.raka.com/Stitched_woven_biax ... axial.html

Bille

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Re: Strenght and flexibility

Postby plummet » Tue Feb 26, 2013 8:31 pm

Bille wrote:
BWD wrote:Skin only takes all the load when it's way stiffer than the core.
I'm talking about building something besides a standard composite I-beam...
The wood core can control some aspects of flex (how much, damping etc...), while unidirectional fibers near the neutral axis add some stiffness and reflex but are away from impact, point loads and supported against buckling, the primary failure mode for kiteboards.
...
Just an idea...


An array of 50K carbon uni , (which is quite easy to wet-out , on both sides of
your wood core will absorb stress to the point where the skin itself could be
kinda light because the main stress in going through the entire length of the
board. Now This is where i could recommend a +/- 45deg fiberglass to control
torsion on the twisting axes. Other wise the use of carbon Tow is a better choice
of materials.

The moment that carbon is woven, you can loose up to 30% in compression strength.
Same goes for fiberglass ; a light , ((12oz "Stitched" fiberglass )) is nearly as strong as
a 16oz woven fiberglass of the same make-up.But remember that your also spreading
12oz of epoxy -Vs - 16oz of epoxy + the extra glass, for the same strength.

If your gonna
use glass, then at least use the, (bi or tri) -stitched-uni.
Here is an example with NO mat between the glass uni-fibers, mat absorbs Tuns
of epoxy, and it's hard to control the weight because of it.

http://www.raka.com/Stitched_woven_biax ... axial.html

Bille


Bille's advice is good.

uni - directional for longetudinal stiffness, double bias on the 45's for torsional stiffness.
Triaxle is a uni layer and double bias layers on the 45's in one cloth. Awesome for kiteboard construction! very hard to find in carbon tho.

With that combo you can make the stiffest lightest and most efficient layup. plain weave as Bille states is not as efficient.

Also there is Zero point having fibres running at 90 Deg to the board length. its doing nothing! its simply a waste of material.

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Bille
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Re: Strenght and flexibility

Postby Bille » Wed Feb 27, 2013 5:47 pm

plummet wrote:


... Awesome for kiteboard construction! very hard to find in carbon tho.

...


Don't know what shipping would be to your side of the world there --plummet--
but the same place that sells the stitched fiberglass, also carries the carbon
in a few different weights.

http://www.raka.com/stitched_carbon.html

If you use stitched carbon , be careful on the weight you choose, remember
that Carbon in stitched form is a BUNCH, ((GOBS)) stronger than the 20+ oz of glass
woven stuff you are use to working with !!

I would recommend that if Stitched carbon is use for the skins, then start
with a light one ; a layer of plane-weave can be applied Later if necessary.
For this reason i would peal-ply the entire board so you can go with paint
or a finish layer of carbon or glass later.

ALSO-- stitched carbon doesn't make for a very pretty cosmetic surface , so
paint is usually added unless you can afford a 1 or 2K carbon woven for
the finish out-side layer ; the one i use for my RC helicopter bodies, is 50" wide
and $75 a running yd, with a weight of 3.7oz,(yd)sq. At that price, the paint sounds
appealing if Ya don't need More stiffness ?
BLACK isn't a very good choice of colors with a foam-core anyway ...

Bille

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Re: Strenght and flexibility

Postby plummet » Wed Feb 27, 2013 8:48 pm

I've got a handle on using carbon Bille. But thanks for caring.

Here's my last carbon build

http://vimeo.com/53148418

Carbon/bamboo landboard with intergrated carbon trucks. by all accounts a significantly harder build than a kiteboard.

PS i like the carbon uni finish!

Next up for me is a bamboo/glass skim board.
Then i'll be onto carbon/bamboo mutant build!.

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Bille
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Re: Strenght and flexibility

Postby Bille » Thu Feb 28, 2013 9:57 pm

plummet wrote:I've got a handle on using carbon Bille. But thanks for caring.


...


That must-a came across the wrong way ; i thought i was more speaking
to the guys who never used carbon-stitched before ---------------Sorry !

plummet
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Re: Strenght and flexibility

Postby plummet » Fri Mar 01, 2013 12:18 am

hehehe...no worries bro.

Benit
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Re: Strenght and flexibility

Postby Benit » Thu Mar 07, 2013 3:28 pm

Well, that is great sir that your sons are into surfing. :) I myself was just like you, drinking more water then staying on the surfboard. I am really anthusiastic about how to make a board so, was checking if i could get anything to start out, and i think i got it. Flexibility and strength. i will just check out more on it into boards, and hope you get the answer to your question :) Good Luck
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Re: Strenght and flexibility

Postby mattthieu » Mon Apr 29, 2013 2:06 am

so, guys, if i read you corectly, the strenght comes from the skins ( using foam core ) !!

what about : 2 layers of foam glued together ( cause i coul'n get more then thick one ) and, during the glue togeter process, il' ad glass fiber tape ( 9 oz 3 inch tapes ) in x patern from one tip to the other ( and in other paterns i could think of ). this dome ON a rocker table ( and concave to ) so, the core itself stands alone AND in my mind there would be added stiffnes !

would i be adding stiffnes VS putting the same quantity of glass on the top or bottom ? or lose some ?

just thinking, 3 plies are stiffer then 2 ? for the same weith ???

or am i all wrong ?

maybe using , in the future, center Carbon uni fibers ????


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