VDS Damping Properties

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Alex13
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VDS Damping Properties

Post by Alex13 »

It's been a couple months since I visited the forum - was flat out with uni until recently.

This was part of my thesis with uni - I thought it could be of interest to some.

Background
My thesis was on torsional stiffness and vibration control in snowboards. I built two snowboards - a reference snowboard with basic layup (base, edges, vds along edges, wood core, two layers of 22oz triax, wood veneer topsheet, inserts) and a damped snowboard (identical, but with 0.2mm VDS in the direction of the second torsional mode).

The reason behind trying to control vibrations in snowboards or skis is to increase edge hold at high speed, and decrease injury through Human Response to Vibration (HRV). The The frequency response of snow has been measured to be between 20-80Hz, which has been confirmed to match K2's research by a K2 engineer (yes, I can supply a reference here if necessary). Vibrations have been shown to have negative effects on humans below 100Hz, therefore this project focussed on the range of 0-125Hz. Vibrations above this range would have negligable effect on edge hold or injury to the rider.

To determine the torsional modes and frequency response, I used a laser vibrometer with an electromagnetic shaker, and used a rectangular scanning grid on the surface of the board, as seen below:

Image

Torsional and Bending modes are the natural frequencies of the snowboards that cause it to deflect. The modal shapes of a snowboard can be seen below:
Image

These are rectangular as this was the shape of the scanning grid.

The layup of the VDS can be seen here for the damped board:

Image



Results

The results can be seen below in the frequency response graph of each board.

Image

The graph above shows the response of the reference snowboard and the damped snowboard. Here we would expect to see the peaks occurring at the same frequencies, with the damped snowboard showing lower peaks than the reference board, especially at the second torsional mode (the peak around 71Hz).

We see that the peaks for the damped board are slightly earlier, which indicates the board is slightly softer, which is probably due to minor differences in the wood core.

Importantly though, the peaks in the damped board are the same height or slightly higher, particularly in the second torsional mode. This indicates that the VDS used has zero damping effects below 125Hz.

What we can conclude from this is that VDS is used, as many on the forum have suggested, as a gasket between the edges and the first fibreglass layer, and not for vibration damping at all.

Note: I used 0.2mm VDS here. Thicker VDS may have an impact on vibrations in the lower frequencies, however from my research I do not believe that any effective vibration damping would happen with a thickness of less than about 1.2mm, which is pretty thick to be putting in a board layup without cutting some serious grooves in your core to allow it.
Damon
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Re: VDS Damping Properties

Post by Damon »

Alex13 wrote: Importantly though, the peaks in the damped board are the same height or slightly higher, particularly in the second torsional mode. This indicates that the VDS used has zero damping effects below 125Hz.

What we can conclude from this is that VDS is used, as many on the forum have suggested, as a gasket between the edges and the first fibreglass layer, and not for vibration damping at all.
Awesome. I love it when engineering data reinforces the laymans' consensus. Any details on torsional stiffness?

Good work!
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endre
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Post by endre »

That's very nice work!
This confirms that the VDS-name is a sales hoax, and a widely used argument for dampening while it mostly prevents water from entering the construction (and thereby delaminate from rust)

thank you!
skidesmond
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Post by skidesmond »

Excellent work! I love it when some one with the resources can conduct such tests. In one set of skis I added additional VDS to the top of the skis between the tip and toe for a dampening effect. From a human stand point it made no difference. And I always wondering how much a thin strip of material like that could provide dampening properties especially after being pressed, now I know.
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Post by Jekul »

Great to see some engineers are still doing engineering work! Thanks for posting the results.
twizzstyle
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Post by twizzstyle »

Top notch Alex. Awesome data, thanks for presenting it.
Richuk
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Post by Richuk »

Great work Alex - hope you got the grades you deserve! Is the full report still on your website?
doughboyshredder
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Post by doughboyshredder »

what about a full layer of vds?

what about sandwiching carbon fiber between the vds?
OnDeck
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Post by OnDeck »

Agreed, this is good work.

If anyone wants to sell their stockpile of VDS after reading this, holla at me!
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MontuckyMadman
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Post by MontuckyMadman »

Nice work as always. We don't need a laser to tell us that however.
Check this out from splat:
http://www.tetongravity.com/forums/show ... p?t=206684
The rubber damping material you hear about in indie skis is seldom true rubber damping material. The stuff we and prolly every other indie uses (except one outfit that I know of that uses the true damping rubber) is a polymer that is a rubber foil, but it's primary function is to maximize the adhesion of the glass and resin to the metal edges. It is not going to make a ski so damp that it is noticeable. There is a thicker polymer that is used above the base and between the tangs of the edges to offset that edge tang height that is specifically designed to perform as a true damping material. It's expensive and not used much because it typically needs to be profiled to drop into place. It adds a significant additional material/labor cost. If your fiberglass ski is too damp, it's more likely because it has a lot of fiberglass or hardwood in it and it has nothing to do with the anti vibration rubber foil most companies tout. You can't build a ski without that stuff or the edges will separate from the glass and resin. If you put a drop of resin on a piece of steel or aluminum and drop it on a concrete floor, the non porous metal will not bond to the resin and it will fall off the metal on impact. The rubber foil allows a good bond to occur on the metal edges.
Alex13
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Post by Alex13 »

Sorry all, I've been absent a while again and haven't got back to you.
doughboyshredder wrote:what about a full layer of vds?

what about sandwiching carbon fiber between the vds?
A full layer of VDS would make a difference only because it increases the weight of the board, which by default increases the damping properties if it doesn't increase the stiffness. The end result would still be more detrimental to the ride due to the added weight than any benefit from damping properties. I'd expect that this would even add stiffness and reduce damping further, as there would be an additional resin layer.
MontuckyMadman wrote:Nice work as always. We don't need a laser to tell us that however.
Check this out from splat:
http://www.tetongravity.com/forums/show ... p?t=206684
It's hardly news to most of the forum users on here, I just thought people may like to see some real world data that substantiates the theory. I'd like to know what the "thicker polymer" is though, from the research I've done I highly doubt it would have any positive effect either. In damping high frequencies, perhaps, but these have no detrimental effect to board handling.
Alex13
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Re: VDS Damping Properties

Post by Alex13 »

Damon wrote: Awesome. I love it when engineering data reinforces the laymans' consensus. Any details on torsional stiffness?

Good work!
Torsional stiffness was interesting. I laid the core up much the same as with the damped board, but with uni directional carbon fibre rather than VDS, and above the core rather than below. I found an increase of 5% or so in torsional stiffness, however this came with a corresponding increase in bending stiffness of around 8%. I think I could make some VERY light snowboards with a little fine tuning, the "stiff" board I made was a little too stiff, but as the purpose of the project was to increase the stiffness not design a perfect snowboard, it was successful.

Note - I made 4 boards total, one was a test board (as it turned out, read about it in my journal), one reference board, one damped board and one stiffened board. I said above that I made 2 snowboards rather than 4 as that was all that was relevant to this post.
Richuk wrote:Great work Alex - hope you got the grades you deserve! Is the full report still on your website?
I updated it to include the full details of my project, which is basically a web version of my thesis. I'm not sure whether it's still available, depends whether my uni has taken it down. If anyone is interested in reading it (the full thesis or the abbreviated "technical paper") I'm happy to post it up. Note - there's a fair bit of "engineering speak" in it.

As for the grade - a HD @ 94% isn't too bad ;)
Last edited by Alex13 on Tue Jan 04, 2011 3:37 am, edited 1 time in total.
Alex13
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Post by Alex13 »

OnDeck wrote:Agreed, this is good work.

If anyone wants to sell their stockpile of VDS after reading this, holla at me!
I'm taking this as a joke as intended, but for those who don't - this isn't meant to be a "don't use VDS" post. It's still highly beneficial as a gasket-type medium, there's a reason everyone uses it!
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endre
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Post by endre »

Alex13 wrote:
OnDeck wrote:Agreed, this is good work.

If anyone wants to sell their stockpile of VDS after reading this, holla at me!
I'm taking this as a joke as intended, but for those who don't - this isn't meant to be a "don't use VDS" post. It's still highly beneficial as a gasket-type medium, there's a reason everyone uses it!
There is no question about the benefits of rubber strips in the layup (I use it every time) but it won't dampen vibrations
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