Fabric layouts

For discussions related to the type of materials to build skis/snowboards and where to get them.

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Bloefeld
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Joined: Mon Mar 28, 2011 7:29 pm

Fabric layouts

Post by Bloefeld »

Yet more stupid questions, sorry in advance.

I have read a lot about the lay-ups that people here are using. I am wondering why the fabrics used are chosen and what styles are used.

For example, do you prefer to use woven over say knit fabrics. Triaxial fabric in 0/60/60 or 0/45/45.

What is your thinking behind these selections.

For example; in the products I have developed I use mostly knit fabrics over woven roving or twill types. My reason is that because knits have no crimp, you get a 25% increase in end properties without costing a dime more per unit of weight.

Care to chime in?

Thanks,

Bloefeld

twizzstyle
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Location: Kenmore, Wa USA

Post by twizzstyle »

You'll find 0/45/45 triax is the most commonly used fabric around here. Structures theory would say that in a constant cross-section homogeneous beam, shear stresses are at 45 degrees in twisting. The 0 deg fibers give you the longitudinal stiffness, the 45 deg layers give you torsional stiffness. That's the idea anyways.

Have you seen how K2 does their composites? It's pretty impressive, giant braiding machine wraps fiberglass and carbon fiber completely around the core.

Image

sammer
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Post by sammer »

The majority of us are using either 19 or 22oz stitched triax.
I'm using this http://www.vectorply.com/pdf/etlx1900.pdf.
It's not woven.
Most of us understand weaving leaves voids where warp and weft meet.
Good quality stitched triax 0,-45,+45 gives about the best beam and torsional reinforcement in one layer.
Most of us understand that we could probably get better results with individual layers of fabric.
In my case the extra time is not worth the hassle.
Plus repeatability is a big issue. Being able to use the same glass every time takes it out of the equation when proto-typing.

I'm sure I'm not the only one who will pipe in here.

sam
You don't even have a legit signature, nothing to reveal who you are and what you do...

Best of luck to you. (uneva)

Bloefeld
Posts: 77
Joined: Mon Mar 28, 2011 7:29 pm

Great response

Post by Bloefeld »

sammer wrote:The majority of us are using either 19 or 22oz stitched triax.
I'm using this http://www.vectorply.com/pdf/etlx1900.pdf.
It's not woven.
Most of us understand weaving leaves voids where warp and weft meet.
Good quality stitched triax 0,-45,+45 gives about the best beam and torsional reinforcement in one layer.
Most of us understand that we could probably get better results with individual layers of fabric.
In my case the extra time is not worth the hassle.
Plus repeatability is a big issue. Being able to use the same glass every time takes it out of the equation when proto-typing.

I'm sure I'm not the only one who will pipe in here.

sam
Sam,

Thanks for the reply. After seeing the braiding it brings to mind the possibility of using braided tube to make the ski. I wonder how you would apply the edges?

http://www.braider.com/

Are a great supplier.

Interestingly we assumed the same as you did when we were designing a road mat product I invented. We paid an engineering firm a wheel-barrow load of cash to prove this right in 4 point beam tests. What we found was odd, the 45/45 bias was weaker than the 0/90.

I think that using fabrics like Vector Ply knits is every bit as good as laying up separate plies. We aren't building F-35's here.

I may be wrong entirely, but I think the big issue in ski performance is the relationship between the torsional resistance (for grip) and flex (for turning dynamics). So I was going to try off balance 0/90 knit. The idea is that the 90 will give torsional stiffness and the 0 will give pretty easy flex.

Because everyone in and out of the industry uses the formula you use, I am probably just freakin' nuts. I am just extending this idea from a design that has zero relationship to skis.

What do you think of this idea?

Cheers,

Bloefeld.

sammer
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Post by sammer »

0 degree fibers will give you beam strength but I think 90 is a waste of time.
skis are so narrow and cores so thick that they don't really bend in that direction.
They do however twist that's where the 45 or 60's come into play.
Remember that the widest parts of your ski are the tip and tail.
They have to twist to a certain degree to allow you to slarve a turn.
with just 0/90 you would have no real control over twist.
At least that's my belief.

sam
You don't even have a legit signature, nothing to reveal who you are and what you do...

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sammer
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Post by sammer »

Using a braided sleeve around your core has been done a lot in the past.
google "Torsion box"
You would have to make a cap ski though or you'd be cutting out all your benefits with your flash.

sam
You don't even have a legit signature, nothing to reveal who you are and what you do...

Best of luck to you. (uneva)

Bloefeld
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Torsion Box

Post by Bloefeld »

Hi Sam,

Dynamic VR17's were wet-wrapped torsion box. I think you just solved my question about edges.

You are probably way to young to have skied on VR17's but they had so much grip on ice it was incredible, the problem was that they were normally so stiff that you had to be a monster to carve them.

Cheers,

Tony

twizzstyle
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Re: Great response

Post by twizzstyle »

Bloefeld wrote:The idea is that the 90 will give torsional stiffness and the 0 will give pretty easy flex.
As an expert, I'm pretty surprised to hear you say that. 90 deg fibers will give you virtually zero torsional stiffness. At that point any torsional stiffness is coming from the epoxy alone. 90 deg fibers will give you lateral stiffness, which might be useful in something as wide as a snowboard, but on a ski I personally think it's just added weight. Unless I'm missing something, this is what my intuition, and memory from school tells me (I am an aeronautical engineer, but only did a few courses in composites, as my expertise is in the aerodynamics and stability/control area)

The edges have nothing to do with how you do your composites :) Still a bit more to learn on general ski construction ;)

twizzstyle
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Post by twizzstyle »

Unless by edges you meant sidewalls? Cause yes, sidewalls would be tricky.

sammer
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Re: Torsion Box

Post by sammer »

Bloefeld wrote:Hi Sam,

Dynamic VR17's were wet-wrapped torsion box. I think you just solved my question about edges.

You are probably way to young to have skied on VR17's but they had so much grip on ice it was incredible, the problem was that they were normally so stiff that you had to be a monster to carve them.

Cheers,

Tony
Thanks for the compliment young feller 8)
My first time on skis was at Mt Norquay 1968.

sam
You don't even have a legit signature, nothing to reveal who you are and what you do...

Best of luck to you. (uneva)

Bloefeld
Posts: 77
Joined: Mon Mar 28, 2011 7:29 pm

Re: Great response

Post by Bloefeld »

twizzstyle wrote:
Bloefeld wrote:The idea is that the 90 will give torsional stiffness and the 0 will give pretty easy flex.
As an expert, I'm pretty surprised to hear you say that. 90 deg fibers will give you virtually zero torsional stiffness. At that point any torsional stiffness is coming from the epoxy alone. 90 deg fibers will give you lateral stiffness, which might be useful in something as wide as a snowboard, but on a ski I personally think it's just added weight. Unless I'm missing something, this is what my intuition, and memory from school tells me (I am an aeronautical engineer, but only did a few courses in composites, as my expertise is in the aerodynamics and stability/control area)

The edges have nothing to do with how you do your composites :) Still a bit more to learn on general ski construction ;)
Hi Twizzle,

Sorry but you are not correct on the 90 fibres. They provide all of the torsional stiffness on my road panels. We use nothing but 0/90 knit (96 oz.) We use these panels to float big rig trucks loaded with D-11 Cat's over swamps. They see some torsion and loads higher than those found on essentially any road. We have not yet had a failure.

This of course does not mean I am not wrong in this case. I can certainly see your point and in thinking more about it more consideration has to be given to the relationship between the 0/90. Keep in mind that these materials are anisotropic, vectors of force will travel along the fibre matrix and those vectors are subject to a great deal more control over their properties than more isotropic materials commonly used in aeronautical engineers are more typically familiar with (weird and cool aluminium and other alloys).

You are right about one thing for certain, I have a lot more to learn about making skis, and it is help from giant brains like yours that I hope to learn from.

I guess the idea here is to build some skis and see how they work.

On the edge question I was wondering how one would attach them using braided sleeves instead of lay-up.

Thanks again,

Cheers,

Bloefeld

Bloefeld
Posts: 77
Joined: Mon Mar 28, 2011 7:29 pm

Re: Torsion Box

Post by Bloefeld »

sammer wrote:
Bloefeld wrote:Hi Sam,

Dynamic VR17's were wet-wrapped torsion box. I think you just solved my question about edges.

You are probably way to young to have skied on VR17's but they had so much grip on ice it was incredible, the problem was that they were normally so stiff that you had to be a monster to carve them.

Cheers,

Tony
Thanks for the compliment young feller 8)
My first time on skis was at Mt Norquay 1968.

sam
Sam,

Cool, that was my home hill in my last year of racing in 1974. I am now a Calgarian although originally from Edmonton.

I envy you getting to live in Fernie. How's the snow these days. I can see us making some turns in the future. You can tell me how crappy my first skis are in person.

Cheers,

Bloefeld

sammer
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Post by sammer »

Snow on the hill kinda sucks right now,
but I'm a snob.
I'll go up make 1 run and say this sucks and go home.
Sunday at Fernie wilderness was pretty good!
You don't even have a legit signature, nothing to reveal who you are and what you do...

Best of luck to you. (uneva)

twizzstyle
Posts: 2203
Joined: Tue Mar 07, 2006 8:25 pm
Location: Kenmore, Wa USA

Post by twizzstyle »

I would love if you could explain how 90 deg fibers can add any torsional stiffness, because I just don't buy it. There is zero load path for the shear stresses to follow. As you just said, the load is carried along the fibers, and all torsional stress is in shear, no?

?

This is settled by a pretty simple test... layup a simple core with only longitudinal fibers (0 deg), then another with the same longitudinal fibers, but the addition of lateral fibers (90 deg). Twist and see which takes more force. Everything I've always known about composites would tell me it'll be nearly the same (ignoring the additional epoxy, which carries some load of course)

Bloefeld
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Joined: Mon Mar 28, 2011 7:29 pm

Who's the old guy

Post by Bloefeld »

Sam,

I am now in my 50th season. When I first started skiing at Norquay it was still subject to geologic upthrusts.

Weird mountain, it started out steep, then it got sort of flat, then it got steep again. My geologist friend tells me that this is not true, but I know it is.

Sorry to hear that the snow isn't great, but you should be a total snob, why ski the take it or leave it stuff us goofs have to.

Cheers,

Bloefeld

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