I read a lot of posts on the forum regarding vibration dampening skis and figured I'd share some wealth. It's a really cool idea that Head (and probably others) tried to accomplish with thei "Intellifibre" design.
Piezoelectrics, or PZTs, are materials that react to electric currents and re-align their molecules. Quartz is the most common, being used in most watches where one second is defined as something like 10,000 vibrations when some sort of voltage is sent through it.
But the first man made PZT was Lead Zirconium Titinate... which some people have already mentioned on this website. This is a ceramic, and can be made relatively light (compared to other ceramics), but is still somewhat heavy. Another option is a polymer, Polyvinylidene Fluoride, PVDF, which would replace the epoxy for that layer in a bulk form, or if pulled into fibres and woven into a cloth (think Batman Begins) it could be laminated in an epoxy matrix within the ski.
So, if these were in skis, a quartz crystal (which can also generate electricity) could be embedded in the ski, and when the ski starts to vibrate, it would generate a large voltage and realign the molecules in the ski to stiffen it. Since there is a force generated, it would stiffen the ski and hopefully reduce vibrations.
I'm not sure where to get more information on these, but it'd be a cool idea, and you could probably find more info by googling it. I'm not making skis yet, but I will as soon as my surfboard for the Great Lakes is done. haha.
I need to go get my snow fix for the day and watch some ski videos or something.
PM me if you are interested in looking more into Piezoelectrics and I'll see if I can help.
Ski Dampening - Piezoelectric materials
Moderators: Head Monkey, kelvin, bigKam, skidesmond, chrismp
The matrix material in a composite connects the fibres which deliver most of the stiffness. Therefore the bond between the matrix and the fibre is more important for the quality of the composite than the stiffness of the matrix. The stiffness of the matrix is quite low compared to the stiffness of the fibre and won't affect the stiffness of the composite much. This is very important to keep in mind when considering piezoelectric construction, if you use it as a matrix material it won't make much of a difference. (actually it probably won't make a difference, it will make a cool marketing story though 
)
)Here are some useful information on ski vibration.
http://www.ansys.com/magazine/issues/1- ... s-edge.pdf
http://www.ansys.com/magazine/issues/1- ... s-edge.pdf
damping
The goal of using the piezoelectric as a matrix material would not be to increase its modulus of elasticity (stiffness), but to increase its dampening effect. Inducing a force in the matrix material would hopefully dampen the vibrations, while not stiffening the ski (because this could mess with the arc of the turn). A dampener is affected only by velocity (or that's what its supposed to do in the ski) and it would attempt to reduce the amplitude of vibrations.
haha, wow. I just read my post, and I did say that it'd change stiffness. I'm an idiot, sorry about that. I think I was tired when I wrote that. So ya, not change stiffness, change dampening properties.
matrixes usually have modulus of elasticities around 4 GPa, while reinforcements can be around 200 GPa. So even if you could double the stiffness of the matrix, it wouldn't change the overall stiffness by much.
my bad. sorry.
I'm going to look into this more, and maybe read what I write before I post stuff, so I don't look so stupid.
haha, wow. I just read my post, and I did say that it'd change stiffness. I'm an idiot, sorry about that. I think I was tired when I wrote that. So ya, not change stiffness, change dampening properties.
matrixes usually have modulus of elasticities around 4 GPa, while reinforcements can be around 200 GPa. So even if you could double the stiffness of the matrix, it wouldn't change the overall stiffness by much.
my bad. sorry.
I'm going to look into this more, and maybe read what I write before I post stuff, so I don't look so stupid.
Re: damping
I was just trying to save you the money! But your last post shows you have some knowledge about composites and doesn't look stupidAxelerate wrote:haha, wow. I just read my post, and I did say that it'd change stiffness. I'm an idiot, sorry about that. I think I was tired when I wrote that. So ya, not change stiffness, change dampening properties.
Goodluck with your further research on piezoelectric dampening.
at my day job, i work with piezos and other similar materials. but not for skis, unfortunately --- for an entirely different application: high-speed, high-resolution positioning.
i haven't thought much about using piezos for skis. but i know about K2's and Head's efforts. there are certainly challenges with using piezos in skis to control/alter a ski's dynamic characteristics. off the top of my head: durability -- piezos are fragile; manufacturing; cost; and of course, power. for example power: to cover a ski with a sheet of piezo material (not even over the entire length) would mean you have to find a way to power it. piezos are capacitive devices, and as the frequency increases, the power required to drive them also goes up, that is, you will need a heap of current to actuate the device -- recall that the impedance of a capacitor is 1/(jw*C), where 'w' is frequency, 'j' is our friend the imaginary number, and C is capacitance. interestingly, capacitance goes up with the surface area of the piezoelectric actuator. so, at high frequency and with a large surface area, the impedance becomes low. to provide a particular level of power, the current must increases because the impedance drops, and this means a large power supply (like a big, big battery).
PVDF is a neat material -- a polymer version of the cermanic piezo, but one needs lots and lots of voltage to drive them --- like in the kilovolt range. building a kilovolt power supply sounds fun, but not trival.
one could consider some of the newer ionomers which operate on lower voltages, but they are not cheap to make or buy and in some case you'll need to hydrate them...
i like the idea of using passive methods to power the 'smart' material, like a PVDF to generate the voltage from stress which gets fed to the piezo to control damping. again, it's going to require some work to figure out whether there's enough power generated by one device to control the other.... there are lots and lots of work in the scientific journals on this stuff... i need to dig and dig...
davide: that's a really good article. thanks for pointing it out. i think they have a point with the viscoelastic material. i'm going to play around with this more. but what is not clear in the article is what mode of vib. they were referring to and how they measured the vibration (i just glanced over the article so i might have missed the details). anyway, i'm assuming that the <15 Hz resonance is the first mode of vibration -- cantilevered. in one of my skis, the Hero, i measured the first mode at 11 Hz, which seems consistent with their result. the 2nd is around 50Hz, and it goes up from there. my belief is that the second affects the edge-holding ability of the ski. the first mode affects other things, etc. but of course the challenge is that the boundary conditions play a huge roll in how a ski will vibrate. i'm not sure what is a good boundary condition to consider. when i measured the Hero's response, i fixed the ski at cord center similar to the article. whether this is true when a ski is on snow is beyond me.
i haven't thought much about using piezos for skis. but i know about K2's and Head's efforts. there are certainly challenges with using piezos in skis to control/alter a ski's dynamic characteristics. off the top of my head: durability -- piezos are fragile; manufacturing; cost; and of course, power. for example power: to cover a ski with a sheet of piezo material (not even over the entire length) would mean you have to find a way to power it. piezos are capacitive devices, and as the frequency increases, the power required to drive them also goes up, that is, you will need a heap of current to actuate the device -- recall that the impedance of a capacitor is 1/(jw*C), where 'w' is frequency, 'j' is our friend the imaginary number, and C is capacitance. interestingly, capacitance goes up with the surface area of the piezoelectric actuator. so, at high frequency and with a large surface area, the impedance becomes low. to provide a particular level of power, the current must increases because the impedance drops, and this means a large power supply (like a big, big battery).
PVDF is a neat material -- a polymer version of the cermanic piezo, but one needs lots and lots of voltage to drive them --- like in the kilovolt range. building a kilovolt power supply sounds fun, but not trival.
one could consider some of the newer ionomers which operate on lower voltages, but they are not cheap to make or buy and in some case you'll need to hydrate them...
i like the idea of using passive methods to power the 'smart' material, like a PVDF to generate the voltage from stress which gets fed to the piezo to control damping. again, it's going to require some work to figure out whether there's enough power generated by one device to control the other.... there are lots and lots of work in the scientific journals on this stuff... i need to dig and dig...
davide: that's a really good article. thanks for pointing it out. i think they have a point with the viscoelastic material. i'm going to play around with this more. but what is not clear in the article is what mode of vib. they were referring to and how they measured the vibration (i just glanced over the article so i might have missed the details). anyway, i'm assuming that the <15 Hz resonance is the first mode of vibration -- cantilevered. in one of my skis, the Hero, i measured the first mode at 11 Hz, which seems consistent with their result. the 2nd is around 50Hz, and it goes up from there. my belief is that the second affects the edge-holding ability of the ski. the first mode affects other things, etc. but of course the challenge is that the boundary conditions play a huge roll in how a ski will vibrate. i'm not sure what is a good boundary condition to consider. when i measured the Hero's response, i fixed the ski at cord center similar to the article. whether this is true when a ski is on snow is beyond me.
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RudolphTheSkiingReindeer
- Posts: 9
- Joined: Thu Mar 29, 2007 8:41 pm
What if you used a material like d3o?
It's a gel like substance that can be mixed into foam. The molecules lock together when it's impacted.
I wonder if there are any other materials like this. Or maybe the recipe could be fine tuned to respond to certain vibrations.
Imagen a strip of VDS-like rubber set into the core, that would stiffen the ski only when needed, while still not becoming too rigid. No need for a power supply either.
It's sort of off topic, but the results might be similar.
Just my .02.
-Camen
It's a gel like substance that can be mixed into foam. The molecules lock together when it's impacted.
I wonder if there are any other materials like this. Or maybe the recipe could be fine tuned to respond to certain vibrations.
Imagen a strip of VDS-like rubber set into the core, that would stiffen the ski only when needed, while still not becoming too rigid. No need for a power supply either.
It's sort of off topic, but the results might be similar.
Just my .02.
-Camen
BigKam: I talked to the guy who did the measurements about one year ago, and I stepped in the article few weeks ago, just by chance.
If I remember well, the first mode has one nodal point, aroud mid-ski, while second mode has two nodal points, about 15/20 cm from tip and tails, and so on.
They say that the first mode is the bad one, affecting edge grip. Second mode is not that bad, but they found that placing the dapening devices around the second mode nodes only (the devices are about 15 cm long), the first mode is trongly damped, while higher frequency modes are not affected. High frequency vibrations are good to have a reactive ski.
It seems that placeing thick dampening rubber all over the ski lenght damps also the high frequency modes.
If I remember well, the first mode has one nodal point, aroud mid-ski, while second mode has two nodal points, about 15/20 cm from tip and tails, and so on.
They say that the first mode is the bad one, affecting edge grip. Second mode is not that bad, but they found that placing the dapening devices around the second mode nodes only (the devices are about 15 cm long), the first mode is trongly damped, while higher frequency modes are not affected. High frequency vibrations are good to have a reactive ski.
It seems that placeing thick dampening rubber all over the ski lenght damps also the high frequency modes.
if the ski was fixed at the center (boundary condition), then the first mode would be a cantilever motion: essentially two cantilevers if you also consider waist-to-tail. the second mode would have a node near the tip. as you said, higher modes will have nodes between the point where the ski was fixed (center/waist) and the tip. but also, there can be other funky modes, like swaying side-to-side stuff. i agree that the first mode may affect edge hold, but here what i was thinking. when a ski goes into a turn, the waist is loaded effectively acting like the B.C. the tip/tail of course flaps in its first mode, but there's the second mode where the waist and tip/tail are in contact. then a large second mode means that the ski could possibly loose edge hold -- that is, edge contact between the tip and the waist. likewise, the same might be true between the waist and to the tail. i'm not sure if i'm making any sense....davide wrote:... If I remember well, the first mode has one nodal point, aroud mid-ski, while second mode has two nodal points, about 15/20 cm from tip and tails, and so on.
They say that the first mode is the bad one, affecting edge grip. Second mode is not that bad, but they found that placing the dapening devices around the second mode nodes only (the devices are about 15 cm long), the first mode is trongly damped, while higher frequency modes are not affected. High frequency vibrations are good to have a reactive ski.
It seems that placeing thick dampening rubber all over the ski lenght damps also the high frequency modes.
anyway, damping is effective in areas of large strain (hence strain rate). i'm not sure, but i think the target areas to concentrate damping material is right at the boundary condition for the cantilever mode (1st mode). but doing this may not be enough. i've considered targeting the center between the B.C. and the node of the second mode. i've been experimenting with this and it seems to work, but i don't have any data yet to back it up. but then again, it could be other factors...
i'd like to run some experiments.... now back to the lab...
You are right, but probably the amplitude of the first mode is much larger than the amplitude of the second mode, so loosing edge hold between and tip/tail and waist is negligeble.bigKam wrote: ... then a large second mode means that the ski could possibly loose edge hold -- that is, edge contact between the tip and the waist. likewise, the same might be true between the waist and to the tail. i'm not sure if i'm making any sense....
Regarding the best place where putting the damping device, on World Cup downhill skis they are located around the second mode nodes. By the way, the damping devices are a piece of alumium alloy attached with double side tape: the shearing friction in the tape dissipate vibrations. It is clear that on commercial skis a ProLink or a V.A.S. are much more fancy, even if they are less effective.
That is definitly the best way to set up things.bigKam wrote:i'd like to run some experiments.... now back to the lab...
Ah, I read that materials with good damping properties at room temperature can loose them at low temperature, so you should do your tests outside and in winter...
Piezio
K2 built a ski with some piezio quartz in it about 16 years ago. It lit an LED so you could show your pals that you had cool skis. It did nothing to alter the damping of the ski.
The piezio is more useful to alter the shape of the fibre, energy in changes its shape or vice versa.
I suspect that the best possible use of piezio fibre would be to power your IPod while you are skiing.
Bloefeld
The piezio is more useful to alter the shape of the fibre, energy in changes its shape or vice versa.
I suspect that the best possible use of piezio fibre would be to power your IPod while you are skiing.
Bloefeld