Skis w/ metal vs. skis w/o metal

[cantunamunch]

Interesting story. In the paper they talk about something similar being used to dampen vibrations in aircraft panels, so this type of gadget has been used for other applications with success.

Can't do torsion modes with just buttons. Notice the black strip across the shovel of the K2 in the second series of pics? I suspect they have one of these on there:

Vibration Control - Damping Systems - DTI

DTI's custom-designed passive damping systems reduce resonant vibrations that cause unwanted noise and harmful vibration.

www.damping.com

I have rented skis with the UVO buttons and could hear noise from them in some cases. Hard for me to tell what they are doing exactly without a direct A/B comparison (ie with and without the buttons).

Don't forget that, by the time *noises* created by ski/snow contact get to the UVO button, there are 15 dozen other modes in which they propagate to your ear - including ones that mostly propagate in air, that the UVO can do absolutely nothing about.

Do also notice that every ski has a sort-of-UVO built into it - the portion of the ski between contact point and ski tip can easily act as a flexing mass damper. You can change the frequency response by changing the mass and the flex zone layup. Kinda sheds a new light on super-light tips and holes in them, eh?

The paper also mentions that the boot/binding interface may have most of the dampening in the ski setup, so it may be hard for people to actually feel the dampening differences between skis.

Completely agreed - and I have made this point in other threads. I argued there that what people are actually feeling is *not* damping but suspension stiffness/deflection rate. Especially suspension stiffness that has a strong frequency dependence, so that higher frequencies do not propagate equally.

I think my hard stance on this point might have pissed off some people, because they love using the word 'damping' to indicate sensations on the spectrum between limp response, like a Caddy with saggy springs and underinflated tires , and really stiff suspension response, like a Jeep with off-road springs driven across potholes.

 

[pete]

I've tended towards metal for stiffness, due to my mass. I was going to joke that I want rubber skis when I ran across Pirelli sourcing rubber for Blossom skis. Makes sense as their experts in the material.

Limited Edition - Blossom Skis

www.blossomski.com

 

[DanoT]

I've tended towards metal for stiffness, due to my mass. I was going to joke that I want rubber skis when I ran across Pirelli sourcing rubber for Blossom skis. Makes sense as their experts in the material.

Limited Edition - Blossom Skis

www.blossomski.com

Metal makes a ski torsionally stiff not longitudinally stiff but a heavy skier needs greater torsional rigidity.

Fiberglass resin layup and sidewall material and construction determine the longitudinal stiffness of a ski.

 

[Uncle-A]

Metal makes a ski torsionally stiff not longitudinally stiff but a heavy skier needs greater torsional rigidity.

Fiberglass resin layup and sidewall material and construction determine the longitudinal stiffness of a ski.

Metal layers top and bottom in a sandwich construction have to add some longitudinal stiffness. They have used that construction for decades, and some of the skis made without fiberglass at all.

 

[DanoT]

Metal layers top and bottom in a sandwich construction have to add some longitudinal stiffness. They have used that construction for decades, and some of the skis made without fiberglass at all.

Metal adds weight but it would be the "meat" in that metal sandwich that creates the stiffness; and the sidewall.

 

[Uncle-A]

Metal adds weight but it would be the "meat" in that metal sandwich that creates the stiffness; and the sidewall.

Maybe if the metal is as soft as a wet noodle but it has to add stiffness especially when adhesive is added and pressed into the sandwich.

 

[DanoT]

Maybe if the metal is as soft as a wet noodle but it has to add stiffness especially when adhesive is added and pressed into the sandwich.

So are you saying that adhesive stiffens up the metal?

If you had a piece of aluminum 6'x3" and as thin as metal in a ski, how many rolls could you roll it up and how tight? Compare that to how difficult it would be to twist that piece of metal and how many twists would you get? That metal is stiffer torsionally than it is longitudinally and that is what it does to a ski (and add weight and dampness).

 

[Noodler]

Maybe if the metal is as soft as a wet noodle but it has to add stiffness especially when adhesive is added and pressed into the sandwich.

Nope. At the typical thickness used, the Titanal sheet is quite limp. There are a number of ski manufacturing videos that show just how "noodly" it is when they're placing the sheet into the sandwich. @DanoT has this right.

 

[Uncle-A]

Nope. At the typical thickness used, the Titanal sheet is quite limp. There are a number of ski manufacturing videos that show just how "noodly" it is when they're placing the sheet into the sandwich. @DanoT has this right.

I guess you will have to hook me up with some of those videos. Not all metal skis are Titanal are they what about other metals?

 

[cantunamunch]

*wears evil grin*. I'll just put this right here. Check out the shiny bits.

 

[LiquidFeet]

@cantunamunch, may I assume those dark linear bits in the centers of some of these are metal whose purpose is to stiffen the longitudinal flex?

 

[cantunamunch]

@cantunamunch, may I assume those dark linear bits in the centers of some of these are metal whose purpose is to stiffen the longitudinal flex?

Some of the dark linear bits are carbon fiber. Others are vibration control material. The shiny linear bits adjacent or sandwiched by the black bits are metal. The pure white bits are epoxy or fiberglass/epoxy.

The really interesting thing about central core ribs like ^that^ happens when the ski goes on edge. The bending response to the skier is exactly the same - but the snow becomes considerably disadvantaged in bending the ski, because paralllel axis theorem. So the longitudinal stiffness top to bottom is NOT the same as the longitudinal stiffness as seen by the snow when the ski is on edge.

 

[Seldomski]

Nope. At the typical thickness used, the Titanal sheet is quite limp. There are a number of ski manufacturing videos that show just how "noodly" it is when they're placing the sheet into the sandwich. @DanoT has this right.

Honeycomb composite panels are extremely stiff. They are extremely stiff even though all the basic ingredients are very pliable (core, skins, adhesive). The skins (top/bottom) sheets are very thin metal. The structure when bonded together functions like an I-beam. When the composite structure is bent, the metal mainly resists in tension/compression. As a structure, the material has very high strength to weight properties and is greater than the sum of the parts.

I find it hard to believe that a metal clad ski core (wood usually) would be as stiff as a core without cladding. The metal cladding does add stiffness. It also adds weight.

What I don't understand is what is the difference between cladding the core with titanal vs fiberglass (or carbon fiber)? This is something I don't understand, since fiberglass and aluminum appear to be pretty close in terms of density and modulus (tensile). So there is something else going on here?

 

[cantunamunch]

I find it hard to believe that a metal clad ski core (wood usually) would be as stiff as a core without cladding. The metal cladding does add stiffness. It also adds weight.

The stiffness of a wood core goes as the cube of the core height. The apparent stiffness of the extra cladding layer only varies as the square of the core height. The thicker the core is, the less relevant the stiffness of the cladding layer becomes to the longitudinal flex of the ski.

Put another way, if the Nomex honeycomb is thick enough, we can face it with Kraft paper instead of 0.3mm Alu and not see significant changes.

What I don't understand is what is the difference between cladding the core with titanal vs fiberglass (or carbon fiber)? This is something I don't understand, since fiberglass and aluminum appear to be pretty close in terms of density and modulus (tensile). So there is something else going on here?

Leaving aside other planes (cross wise, twist), just look at the percentage elongation at rupture. CF is 1.4%, E-glass is 4.8%, Al alloys are 10%+

That means you can clad a CF part in E-glass and gain strength, you can clad an E-glass part in Al alloy and gain strength - but NOT the other way.

Or watch an F1 engineer say the same thing - just add a column for Alu:



Takeaway: use metal where you need the exact same stiffness AND high elongation before rupture.

 

[Seldomski]

Proportional limits for metals are generally below 1% (except for really weird stuff, like shape memory alloys). Strain above that results in permanent deformation and changes to the metal crystalline structure.

 

[Noodler]

Honeycomb composite panels are extremely stiff. They are extremely stiff even though all the basic ingredients are very pliable (core, skins, adhesive). The skins (top/bottom) sheets are very thin metal. The structure when bonded together functions like an I-beam. When the composite structure is bent, the metal mainly resists in tension/compression. As a structure, the material has very high strength to weight properties and is greater than the sum of the parts.

I find it hard to believe that a metal clad ski core (wood usually) would be as stiff as a core without cladding. The metal cladding does add stiffness. It also adds weight.

What I don't understand is what is the difference between cladding the core with titanal vs fiberglass (or carbon fiber)? This is something I don't understand, since fiberglass and aluminum appear to be pretty close in terms of density and modulus (tensile). So there is something else going on here?

Already well covered previously, but we're not talking about more "interesting" structures like a Hexcel honeycomb or the Liberty VMT. The primary source of ski stiffness is the vertically laminated wood core profile and the glass/resin composites used.

 

[Uncle-A]

Already well covered previously, but we're not talking about more "interesting" structures like a Hexcel honeycomb or the Liberty VMT. The primary source of ski stiffness is the vertically laminated wood core profile and the glass/resin composites used.

So in a metal sandwich construction when the ski flexes the bottom layer of metal does not resist flex and the top layer does not resist compression?

 

[Noodler]

So in a metal sandwich construction when the ski flexes the bottom layer of metal does not resist flex and the top layer does not resist compression?

I think it absolutely does. However, what we're stating here is that the presence of metal layers alone does not imply that a ski must be stiff. It's all based on the design of the core construction. I don't know if you recall the old Elan 999, but that was a ski with a wood core sandwich/double layer metal construction and it was an absolute noodle. So soft you could hand flex bend the ski into a "U". Compare that to the Hart Pulse, a ski with no metal, and was seriously stiff. That's the point a few of us are trying to make. Most skiers see the word "metal" in a ski description and assume it will be stiff, but it's a poor assumption.

 

[Uncle-A]

I think it absolutely does. However, what we're stating here is that the presence of metal layers alone does not imply that a ski must be stiff. It's all based on the design of the core construction. I don't know if you recall the old Elan 999, but that was a ski with a wood core sandwich/double layer metal construction and it was an absolute noodle. So soft you could hand flex bend the ski into a "U". Compare that to the Hart Pulse, a ski with no metal, and was seriously stiff. That's the point a few of us are trying to make. Most skiers see the word "metal" in a ski description and assume it will be stiff, but it's a poor assumption.

Thank you, I never said it was the only thing, it is a contributing factor. I think that a metal sandwich construction makes some of the better GS skis and fiberglass makes the better SL skis and a GS ski is soft lateral flex than a SL ski. But that is only my opinion.

 

[Noodler]

I think it absolutely does. However, what we're stating here is that the presence of metal layers alone does not imply that a ski must be stiff. It's all based on the design of the core construction. I don't know if you recall the old Elan 999, but that was a ski with a wood core sandwich/double layer metal construction and it was an absolute noodle. So soft you could hand flex bend the ski into a "U". Compare that to the Hart Pulse, a ski with no metal, and was seriously stiff. That's the point a few of us are trying to make. Most skiers see the word "metal" in a ski description and assume it will be stiff, but it's a poor assumption.

Couldn't have said it better myself:

Metal versus Carbon in your skis

Blizzard skis measured nearly identical from Ti version to Ca version. When skis contain metal laminates (Ti), do you expect them to be stiffer? Many companies have a model that contains metal and a counterpart that doesn't. What's the difference? The metal commonly used is NOT titanium, as most...

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