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 Post subject: exploding divinicell core.
PostPosted: Mon Jan 30, 2006 1:31 pm 
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Location: tarifa-spain
Hi im trying a new costruction on some of my protos, http://www.kctarifa.com
and the other day something really strange happened, a pro rider broke one of the new boards, but it didnt broke in twoand it didnt delaminate. the board just broke inside the core foam (15mm -80kg divinicell)(it kind of blow up, in the center)
How can i avoid this (im gonna have a talk with some engineers i know)
If someone there has knoledge about forces and tensile and compresion efforts.
Maybe i just have to use two 7.5mm divinicell layers laminated in between with a thin fiber layer?
being told this increases core strenght a lot.
Tnx for your help.
Carlos Saez.


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 Post subject:
PostPosted: Mon Jan 30, 2006 7:33 pm 
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shear forces.....from the skins.

thinner foam with a glass layer


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 Post subject:
PostPosted: Tue Jan 31, 2006 3:24 am 
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Location: St pete Florida
I know a guy that broke a wakeboard like that... I'm going to guess it just happens.

FYI, wakeboards are a ton stronger then kiteboards.


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 Post subject:
PostPosted: Wed Feb 01, 2006 9:09 pm 
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Joined: Sat Dec 27, 2003 11:59 pm
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Location: Leeuwarden, Netherlands.
I always use 2 layers of corecell foam and glue it together with a layer of glass.
Some people think it doesn't help to strengthen the core, but it does. With a strong (not too light) layer of glass between the core, you are creating a double sandwich construction, which is very strong.
Some people think it gives more weight on the board, but because of the extra glass in the middle, you can eliminate some of the glass on top of the board. I've also been thinking of putting a layer of thin woodcore between 2 layers of foam, but haven't tried that yet.

But also boards with a middle glass layer can break, I discovered. But this was a very (too) light board. Board only was 1510 grs. It broke underneeth the footpad after landing a downloop. For the replacement board I used an extra layer of glass on top and an extra on the bottom. After 5 months of abuse, it's still alive (1900 grs board only)

By the way, nice website. Is your shop in the main road in Tarifa? Maybe I'll come visit it in June!


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 Post subject:
PostPosted: Thu Feb 02, 2006 1:00 am 
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most laminar core seperations come from the core literally being torn apart, it happens when the bond to the outer skin is stronger than the molecular bond between the core particles.

heavier foams, stiffer foams are the worst culprits.


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 Post subject: going on
PostPosted: Thu Feb 02, 2006 5:52 pm 
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Location: tarifa-spain
i just asked an engineer (ship, boats), and told me the only way of ovoid this to happen is
1- a higher density foam core or 2- doing a double layer divinicell core, but he told me the fiber layer in between the core is not necesary, the construction should work just using an epoxi loaded of microspheres resin. (He said that fiber used in in the middle is doing nothing because it gets neutraliced by the forces between the down side of first divinicell layer and top side of the layer beneath)
Is this correct?
Thanks for your mails, im happy to discuss this problem and learning from everybody´s knoeledge kindly given to improbe.
Thanks again, any ideas are welcome.
ps- Im not interested in saving weight as riders are telling me they want them heavier, cause it helps them with unhooked stile rotations landings, as happens with wakeboarders


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 Post subject: Re: exploding divinicell core.
PostPosted: Thu Feb 02, 2006 7:12 pm 
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Location: Saddleworth, UK
surferazul wrote:
the board just broke inside the core foam ez.


Sounds like voids in the foam. I have had batches with bad quality control in the density, that only show up if you hold up against a strong light.

The skin could buckle under compression causing the foam under tension to part.


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 Post subject:
PostPosted: Fri Feb 03, 2006 1:03 am 
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Location: rhode island
lots of opinions.
has anyone actually seen the inside of this board yet?
any pics?

core failure is a good guess
but the shear stress isn't all that high
like SQ said the problem seems to show up with the more brittle, high density foams.

you could try to brute force the problem with denser foam and more glass

or use a linear PVC foam like Airex, as opposed to the cross-linked divinycell.

linear PVC has better allowable strain so is less likely to be the limiting factor in high flex fatigue type applications (us).
but i'm guessing too.
-bill


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 Post subject: Fotos of the core.
PostPosted: Fri Feb 03, 2006 1:42 pm 
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Location: tarifa-spain
Here, i made some pics today.
I hope they help ALL GUESSING WHAT HAPPENED HERE!
how to avoid it?
TNX, CARLOS.

This doent happen usually, this board was taken to the limit, it has a stong construction on reinforcements and layers, outside, that obiously hadnt been the issue.[/img]


Attachments:
Broken board core.JPG
Broken board core.JPG [ 48.95 KIB | Viewed 2789 times ]
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 Post subject:
PostPosted: Fri Feb 03, 2006 3:47 pm 
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Location: Wasaga Beach Ontario Canada
Switch to a better type of core foam as zfennell mentioned, and your problems will be over -- simple as that!

Try 5 or 6 lb density Corecell if you can get it.

I've made hundreds of kiteboards with it -- ZERO failures to date!

Before I switched to Corecell, just about every Divinicell (wakeboard) I made broke whether there was a glass sandwich in the center core or not , so I don't think that will help you very much.

Good luck!

Lee
http://www.roguewaveboards.com


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