Fabric layouts

[Bloefeld]

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)

I'm not sure about that. If the ski is under torsional load the majority of it has to be along the 90 degree. Remember my good friend that the 0/90 are not independent from one another, they are anistropic, they are composite and they do not look the same way at the forces put on them as if they were independent. I absolutely do not agree that the torsional load is only in shear. I know that from floating 80.000 lb rigs over muskeg. I'm going to run this idea past one of my aerospace composite guys and see if I am on the right track or you are simply correct and I should just get on board with the triax.

By my way of thinking however the two major issues of skis revolve around torque and flex. I may be right that isolating the two to as great a degree as possible gives better performance. Or I may be wrong and the status quo is right.

I do not know of any ski made with my structure. So the only way I will really find out is by building some and reporting to you the results. Or get someone to do about $25 grand worth of FEA for pretty much free.

Cheers,

Bloefeld

[twizzstyle]

So the only way I will really find out is by building some and reporting to you the results.

That's exactly the spirit and passion of everyone on the forum! Build and see! (and don't worry I'm not trying to spark up an argument, but I still disgree 100% about the 90 deg fibers doing anything Curious what your aerospace buddy has to say!)

[twizzstyle]

I absolutely do not agree that the torsional load is only in shear.

*runs home from work to check his composites and structures textbooks*

This is going to drive me crazy now!

[Bloefeld]

I absolutely do not agree that the torsional load is only in shear.

*runs home from work to check his composites and structures textbooks*

This is going to drive me crazy now!

Good, its been driving me so nuts that I have decided to learn from expert home brewers how to build skis so I can test my probably dumb theory.

I can tell you that I have searched my books for any real hint and got nowhere.

I'm going to torture my real composite friends (remember I am just an inventor of these things, not an engineer)

Great debate, fun to work through.

Cheers,

Bloefeld

[skidesmond]

I just want to interrupt for a moment and say Dynamic VR17 was THE ski in it's day. It was my last favorite pair of straight skis until the shape ski hit the scene. I loved them! Finally tossed them out about 10yrs ago. I was getting them cleaned up for a race just for kicks, adjusted the bindings for new boots. When I stepped in the binding the rear binding exploded and the spring shot across the basement. They RIP in a landfill now.

Carry on.....

[Bloefeld]

I just want to interrupt for a moment and say Dynamic VR17 was THE ski in it's day. It was my last favorite pair of straight skis until the shape ski hit the scene. I loved them! Finally tossed them out about 10yrs ago. I was getting them cleaned up for a race just for kicks, adjusted the bindings for new boots. When I stepped in the binding the rear binding exploded and the spring shot across the basement. They RIP in a landfill now.

Carry on.....

Weren't they great. I had breakfast with Jean Claude Killy 25 years ago. VR 17's were one of his top 5 favourite skis in those days.

I was sponsored by Spalding and so they have always been my touchstone ski.

What a great sport. I'm going to go make some turns right now.

Cheers,

Bloefeld

[MontuckyMadman]

So the only way I will really find out is by building some and reporting to you the results.

Or taking some you know work well apart.

That's exactly the spirit and passion of everyone on the forum! Build and see! (and don't worry I'm not trying to spark up an argument, but I still disgree 100% about the 90 deg fibers doing anything Curious what your aerospace buddy has to say!)

Why would they use them in skis then?
i have personally ripped apart skis with this 90 layer in there and all of the G3 skis use a layer of 90 right now.
i agree doesnt make sense but its in the industry to some degree.

[nate]

I think these braided Fiberglass sleeves are really cool. You could wrap with a tube of 0 and then a tube of 45/45. Maybe skip sidewalls and leave the fiberglass exposed. Or if you had a good cassette that could hold sidewalls on you could add them during layup.

[OAC]

Dynamic and Spalding....please..

[Richuk]

Based on feedback and having built the same ski repeatedly last year. Increasing the CF tape (woven 0/90) by 200 mm changes the feedback from "I'd like to take them into the soft stuff" to "These are crazy on ice, great for long radius turns"

I'll be really interested to hear the results of this debate, once Bloefeld has gone through the detail.

[Bloefeld]

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)

Hi Twizzle

I was way off on this one. Thanks for pointing me in the right direction. Here is what my guy at Vector Ply had to say. I took out the part where he smacked me upside the head :-)

"The main reason most ski manufacturers use the +/-45 degree plies is to increase torsional rigidity (stiffness) of the ski. Since torsional forces act at 45 degrees to the longitudinal, this is the most effective way to orient the fibers.

However, for some lower coat skis, some builders do use 0/90 laminates. While the 90 degree ply isn’t ideally oriented to take on the torsional forces, it does provide more torsional stiffness than the 0 degree plies. Typically, the 0/90 fabrics are less expensive than the 0/+45/-45, hence why they are used in lower cost skis.

I hoped this helps! Please let me know if you have any other questions."

Regards,

Trevor Gundberg
Director of Composites Engineering
Vectorply Corp.

Giving the relationship between the torsional loads on my road mats and the mass of glass used, I can now see why those loads on 0/90 are mostly irrelevant.

You pointed out a serious error on my part and have saved me a lot of experimental fiddling about. For this you have my thanks and gratitude.

Cheers,

Bloefeld

[twizzstyle]

Phew, glad I wasn't just spouting BS, then I really would have looked like a nob! Thanks for digging into it and getting a real answer!

[Bloefeld]

Phew, glad I wasn't just spouting BS, then I really would have looked like a nob! Thanks for digging into it and getting a real answer!

Twiz,

No knobs around here. Just a bunch of folks trying to help each other and stimulate conversation. Ya made me think hard and that was a good thing.

Someone needs to write a ski specific FEA product!

Cheers,

Bloefeld. (The Knob!)

[WhitePine]

Someone needs to write a ski specific FEA product!

I wonder if this could be done in SolidWorks Simulation. I've never looked at doing composites. I would imagine it would have trouble with any sort of adhesive, or matrix type material. I'm thinking the layers would likely have to be replaced with a pseudo material which represents the composite matrix as a whole. Which wouldn't get you anywhere because the values for the tensile modulus and such would probably have to be derived through testing. And would defeat the purpose since you'd want to simulate a design prior to actually spending the time and money on building the proto. At any rate, I'll look into it.

[rsotak]

Solidwork simulation premium has a composite module where you can apply the fiber direction in multiple layers. I believe you have to calculate the composite modulus for the X and Y directions and make that a custom material.