I have read that a plastic topsheet actually affects the dampness of the laminate. Obviously this makes sense but I just didn't think about it.
I also saw in a deconstruction of a legend pro(I think) a layer of plastic in the laminate.
Someone surmised it may be ABS, could be uhmw also.
The only plastic I have used is in my base. UHMW sidewalls also adds dampness as well I understand.
The question is if I add plastic for dampening where in the layup would it be most effective?
Above the core below the core, compression or tension?
Does it matter, should I just suck it up and get a plastic topsheet and sidewalls?
I just don't like the plastic bonding nightmares I see.
I like wood. But I like dampness. I like to keep it easy and simple.
Also have yet to explore the usage of AL in the core laminate. This will add dampness but may be harder than the use of plastics.
Thought on plasti dampening?
Thanks I could never do it without you folks.
Plastic for dampening
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knightsofnii
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i think the parts of the board/ski that suffer the most from being underdamped are the tips.
We stepped up the amount of plastic in our tips. Using Crown surplus stuff, factory treated, no issues other than errors by our own work.
And its been sitting on the shelf for almost 2 yrs now and still bonds, not sure why or how that relates to what people have said about flame treating only working for a little while. I've pulled out base material that's from 1995, yes circa 1995, and it bonded like i had just received it. Not here to argue the statement of having to re-flame or whatever, just sayin.
Yea I'm sure the plastic sidewalls add dampening too. I thought about that when i was having a conversation with someone about why we switched to bamboo sidewalls and I was saying the main reason is the bond strength but that the plastic offers nothing more than a barrier where the wood actually provides flex properties, when i suddenly realized that the plastic could be providing dampening.
Your resin is a good source of dampening properties. Lots of people choose resins with "rubber modifiers" added to them or something like that. Roy (RIP) at QCM explained to me to NOT go with something that contained rubber added into it, but I think he was thinking that I was mixing some kind of rubber into the resin seperately. He told me to go with EMV0043 and ECA408 to get the dampening properties I wanted, that the ECA 408 had "flex modifiers" in it but it was something other than rubber. I honestly question that as this stuff flows like water.
Factory I worked for got stuff from Huntsman and it had some kind of rubber stuff added to it, super thick, but yea the boards were definitely dampened right, you could see it in video comparisons to burton boards, the burton board would chatter and vibrate around turns and this one wouldnt move at all. I've not been able to get someone from huntsman in contact with me to get that or a similar product.
We stepped up the amount of plastic in our tips. Using Crown surplus stuff, factory treated, no issues other than errors by our own work.
And its been sitting on the shelf for almost 2 yrs now and still bonds, not sure why or how that relates to what people have said about flame treating only working for a little while. I've pulled out base material that's from 1995, yes circa 1995, and it bonded like i had just received it. Not here to argue the statement of having to re-flame or whatever, just sayin.
Yea I'm sure the plastic sidewalls add dampening too. I thought about that when i was having a conversation with someone about why we switched to bamboo sidewalls and I was saying the main reason is the bond strength but that the plastic offers nothing more than a barrier where the wood actually provides flex properties, when i suddenly realized that the plastic could be providing dampening.
Your resin is a good source of dampening properties. Lots of people choose resins with "rubber modifiers" added to them or something like that. Roy (RIP) at QCM explained to me to NOT go with something that contained rubber added into it, but I think he was thinking that I was mixing some kind of rubber into the resin seperately. He told me to go with EMV0043 and ECA408 to get the dampening properties I wanted, that the ECA 408 had "flex modifiers" in it but it was something other than rubber. I honestly question that as this stuff flows like water.
Factory I worked for got stuff from Huntsman and it had some kind of rubber stuff added to it, super thick, but yea the boards were definitely dampened right, you could see it in video comparisons to burton boards, the burton board would chatter and vibrate around turns and this one wouldnt move at all. I've not been able to get someone from huntsman in contact with me to get that or a similar product.
Doug
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MontuckyMadman
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Plastic sidewalls most definitely provide dampening, look at Ride's vid on slimewall tech.
The most effective place for dampening materials is in torsion, not bending. Have a look at viscoelastic dampers on race skis.
My final year project / thesis for my mech eng degree is on snowboard torsional vibration dampening and torsional stiffness, so soon enough I will be able to provide a ton of info on it.
The most effective place for dampening materials is in torsion, not bending. Have a look at viscoelastic dampers on race skis.
My final year project / thesis for my mech eng degree is on snowboard torsional vibration dampening and torsional stiffness, so soon enough I will be able to provide a ton of info on it.
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knightsofnii
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Plastic sidewalls will provide some damping.
In general, if you want to optimise the damping effect of a layer in a sandwich you want to put them as far away as possible from the centre of the core. But; a layer of black rubber on top of you fibreglass probably won't give you a nice finish.
Putting a layer between sheets of fibreglass might give rise to some large stresses (known as free edge stresses) as well as some other unwanted effects (e.g. what is known as bend-twist coupling; causes composites to warp) that could negatively affect the ski.
So from a damping point of view either the top or bottom of your core should be optimal. However, I'd put the stuff on the bottom. A typical sandwich made with composite skins is much more prone to failure on the compressive surface than the tensile surface. Some of the failure modes (eg. face sheet wrinkling or microbuckling) on the compressive surface would be negatively affected by a soft layer underneath the skin.
Not entirely certain about a torsion specific damper based on 'viscoelastic' dampers in race skis. All dampers are by definition visco-elastic, in fact pretty much everything in a ski is viscoelastic to some extent. Anyway, the stuff they put on the 'race' skis you buy in stores are gimmicks. Race stock skis that you get from the factory are old school and effective; wood core, fibreglass and three plates of spring steel...and they're awesome.
I'd guess that if you were going to use a damping material then you be using a sheet of some sort of suitable material (this is where I'd start). Should be simple to do and the layer will act as a damper in all directions/degrees of freedom.
In general, if you want to optimise the damping effect of a layer in a sandwich you want to put them as far away as possible from the centre of the core. But; a layer of black rubber on top of you fibreglass probably won't give you a nice finish.
Putting a layer between sheets of fibreglass might give rise to some large stresses (known as free edge stresses) as well as some other unwanted effects (e.g. what is known as bend-twist coupling; causes composites to warp) that could negatively affect the ski.
So from a damping point of view either the top or bottom of your core should be optimal. However, I'd put the stuff on the bottom. A typical sandwich made with composite skins is much more prone to failure on the compressive surface than the tensile surface. Some of the failure modes (eg. face sheet wrinkling or microbuckling) on the compressive surface would be negatively affected by a soft layer underneath the skin.
Not entirely certain about a torsion specific damper based on 'viscoelastic' dampers in race skis. All dampers are by definition visco-elastic, in fact pretty much everything in a ski is viscoelastic to some extent. Anyway, the stuff they put on the 'race' skis you buy in stores are gimmicks. Race stock skis that you get from the factory are old school and effective; wood core, fibreglass and three plates of spring steel...and they're awesome.
I'd guess that if you were going to use a damping material then you be using a sheet of some sort of suitable material (this is where I'd start). Should be simple to do and the layer will act as a damper in all directions/degrees of freedom.
knightsofnii got the right idea:
"Your resin is a good source of dampening properties. Lots of people choose resins with "rubber modifiers" added to them or something like that. Roy (RIP) at QCM explained to me to NOT go with something that contained rubber added into it, but I think he was thinking that I was mixing some kind of rubber into the resin seperately. He told me to go with EMV0043 and ECA408 to get the dampening properties I wanted, that the ECA 408 had "flex modifiers" in it but it was something other than rubber. I honestly question that as this stuff flows like water. "
Rubber modifiers are not bits of rubber added to resin. Rather, rubber toughened resins contain additional components that react and phase separate (fancy engineering term for 'bits of it appear when the stuff hardens') on curing to from micron size particles of rubber within the resin. This should increase the loss modulus (damping) of the resin. However, the stuff I've encountered requires a pretty well controlled cure temperature profile and I'm not sure the average DIY ski press could achieve this. The rubber particles slightly decrease the stiffness of the resin too.
As an alternative you might want to try a nano-toughened resin. Fancy name but easy to do! Nano-toughened resins have nano-scale particles of ceramic added to them o increase their stiffness, strength and toughness. And just because something has the word 'nano' in it doesn't mean it needs to be expensive either. Titanium dioxide powder is available in a very controlled size product (around 600 nanometres). This is because its the stuff used to make things white.... really, really white. Its whats added to paints/plastics etc to get a brilliant white finish. To make a 'ghetto' nano-toughened resin just add some of this powder (5-10%) to the resin. I've also used talcum powder to toughen epoxy. The process used to make nano-toughened resins for high end applications (e.g. aerospace) is a bit more advanced, but not by much! Although the purpose of the nano-particles is principally improved toughness (strength and stiffness is a nice bonus too) the presence of a different phase of material within the composite should improve damping.
"Your resin is a good source of dampening properties. Lots of people choose resins with "rubber modifiers" added to them or something like that. Roy (RIP) at QCM explained to me to NOT go with something that contained rubber added into it, but I think he was thinking that I was mixing some kind of rubber into the resin seperately. He told me to go with EMV0043 and ECA408 to get the dampening properties I wanted, that the ECA 408 had "flex modifiers" in it but it was something other than rubber. I honestly question that as this stuff flows like water. "
Rubber modifiers are not bits of rubber added to resin. Rather, rubber toughened resins contain additional components that react and phase separate (fancy engineering term for 'bits of it appear when the stuff hardens') on curing to from micron size particles of rubber within the resin. This should increase the loss modulus (damping) of the resin. However, the stuff I've encountered requires a pretty well controlled cure temperature profile and I'm not sure the average DIY ski press could achieve this. The rubber particles slightly decrease the stiffness of the resin too.
As an alternative you might want to try a nano-toughened resin. Fancy name but easy to do! Nano-toughened resins have nano-scale particles of ceramic added to them o increase their stiffness, strength and toughness. And just because something has the word 'nano' in it doesn't mean it needs to be expensive either. Titanium dioxide powder is available in a very controlled size product (around 600 nanometres). This is because its the stuff used to make things white.... really, really white. Its whats added to paints/plastics etc to get a brilliant white finish. To make a 'ghetto' nano-toughened resin just add some of this powder (5-10%) to the resin. I've also used talcum powder to toughen epoxy. The process used to make nano-toughened resins for high end applications (e.g. aerospace) is a bit more advanced, but not by much! Although the purpose of the nano-particles is principally improved toughness (strength and stiffness is a nice bonus too) the presence of a different phase of material within the composite should improve damping.
Problem is, rubber is heavy and often difficult to bond to epoxy. A full sheet of the stuff would likely add significant weight to the ski/board and do more harm than good. It's not a terrible idea though, I may look at throwing this one in as another comparison if I can find a suitable material.
I should have said tuned viscoelastic dampers - ones designed to dampen specific vibration frequencies. I've read some data (I'll look for it and see if I can post it) that suggests some vibrational frequencies (>100Hz from memory) are actually beneficial for edge hold in a ski/board. You're right that pretty much all the material in a ski/board is viscoelastic, but I'm talking about specific polymers here that are developed to optimise the damping provided by converting the energy to heat.
What kind of temperature profile is required to cure resin with rubber modifiers? How accurate does it need to hold?
I should have said tuned viscoelastic dampers - ones designed to dampen specific vibration frequencies. I've read some data (I'll look for it and see if I can post it) that suggests some vibrational frequencies (>100Hz from memory) are actually beneficial for edge hold in a ski/board. You're right that pretty much all the material in a ski/board is viscoelastic, but I'm talking about specific polymers here that are developed to optimise the damping provided by converting the energy to heat.
What kind of temperature profile is required to cure resin with rubber modifiers? How accurate does it need to hold?
Rubber is about the same density as epoxy so shouldn't affect the density of the material whether it phase separates to form an new phase or whether rubber chains and epoxy from a co-polymer.
If the rubber is added as a separate layer then it doesn't need to be very thick to have an effect so a thin layer shouldn't add much mass.
Tuned visco-elastic dampers sounds more interesting though. How are you going to tune the dampers? Passively by materials selection and geometry, mechanically (using MR fluid damper?) or actively (e.g. piezoelectrically)? I know a piezoelectric approach would be easy (assuming you can get an accurate frequency response for the ski) to do but dded it! Go with the passive approach! I've never come across a UG project similar to this at my Uni. Piezoelectric damping has been done to death. It seems like loads of students get given the exact same project every year; 'determine the frequency response of composite w under boundary conditions x, program and implement a system that actively damps the vibration in y degree of freedom/s and compare experimental with predicted results from Analytical or FE model theory z. Same thing every year. I feel sorry for the guys who get stuck with it, must be annoying knowing that your just repeating someone else's work. Would definitely be more interesting if you were doing a ski but sounds like quite a lot of work for an undergraduate project, how much time have you got? I guess you'd need to drop any modelling unless you are ridiculously awesome at it.
As you initially said torsional damping I'm guessing you focusing on the resonant frequencies corresponding to this degree of freedom. How are you going to determine/separate out the frequency response for all the different degrees of freedom? I'm guessing you're going to use accelermoters and analyse using a Fast Fourier Transform technique. Are you coding the FFT yourself or are there off the shelf packages which can do this for something like a ski? I don't know much about dynamics and I've got very little experimental experience with dynamic analysis techniques. I'm interested in learning more so would be interested to hear what your planning
As for cure temperature profile accuracy...not really sure. Last time I used toughened resins was for autoclave cured prepregs so I just followed the cure cycle Airbus gave me and never worried about the control as our Autoclave is very well controlled, even for a commercial autoclave. I know Airbus had problems with the material using their autoclaves and if its because their autoclave wasn't accurate enough then its going to be pretty much impossible to do this without a precision lab oven with multi-loop PID control. On the other hand I know guys who have produced epoxies toughened with phase separated rubber particles in my lab using single loop PID controlled ovens. These ovens are research ovens but not particularly great. I guess it just depends on the system you use.
If the rubber is added as a separate layer then it doesn't need to be very thick to have an effect so a thin layer shouldn't add much mass.
Tuned visco-elastic dampers sounds more interesting though. How are you going to tune the dampers? Passively by materials selection and geometry, mechanically (using MR fluid damper?) or actively (e.g. piezoelectrically)? I know a piezoelectric approach would be easy (assuming you can get an accurate frequency response for the ski) to do but dded it! Go with the passive approach! I've never come across a UG project similar to this at my Uni. Piezoelectric damping has been done to death. It seems like loads of students get given the exact same project every year; 'determine the frequency response of composite w under boundary conditions x, program and implement a system that actively damps the vibration in y degree of freedom/s and compare experimental with predicted results from Analytical or FE model theory z. Same thing every year. I feel sorry for the guys who get stuck with it, must be annoying knowing that your just repeating someone else's work. Would definitely be more interesting if you were doing a ski but sounds like quite a lot of work for an undergraduate project, how much time have you got? I guess you'd need to drop any modelling unless you are ridiculously awesome at it.
As you initially said torsional damping I'm guessing you focusing on the resonant frequencies corresponding to this degree of freedom. How are you going to determine/separate out the frequency response for all the different degrees of freedom? I'm guessing you're going to use accelermoters and analyse using a Fast Fourier Transform technique. Are you coding the FFT yourself or are there off the shelf packages which can do this for something like a ski? I don't know much about dynamics and I've got very little experimental experience with dynamic analysis techniques. I'm interested in learning more so would be interested to hear what your planning
As for cure temperature profile accuracy...not really sure. Last time I used toughened resins was for autoclave cured prepregs so I just followed the cure cycle Airbus gave me and never worried about the control as our Autoclave is very well controlled, even for a commercial autoclave. I know Airbus had problems with the material using their autoclaves and if its because their autoclave wasn't accurate enough then its going to be pretty much impossible to do this without a precision lab oven with multi-loop PID control. On the other hand I know guys who have produced epoxies toughened with phase separated rubber particles in my lab using single loop PID controlled ovens. These ovens are research ovens but not particularly great. I guess it just depends on the system you use.
The plan is passively by materials selection and geometry. Piezo's were thrown out there as an idea, but like you said, it's been done to death. Head and K2 have patented it in snowboards to various degrees, and my uni encourages us to do our final year projects on "new research" - so things that as far as we can ascertain, have not been done before.
I'm basically building a "reference board" without any stiffness or damping improvements (basic base, fibreglass, edge, sidewall, topsheet layup), then going to use a laser vibrometer in free-free mode to determine the torsional modes and frequencies of the snowboard. Then I'll build a few more boards using the same materials and dimensions but with dampening material to dampen those frequencies in the direction of the torsional modes. The intent was to look at doing an external damper (on top of the board) as well as something internal in the layup.
The project idea was one I developed with my project supervisor. I wanted to do something on snowboards so I'd be motivated to actually work on it. A student last year did the basic work in determining the vibrational modes and frequencies in a few off the shelf snowboards, my project is just taking his research one step further. I can send you the paper if you're interested.
Time - I've got until November, but really I need testing done during the Australian snow season, so I'll need a lot of the lab research done by July/August. FEA modelling is planned, but will take place just to confirm the lab data obtained is accurate, and may be cut out if I run out of time.
As for epoxies, my press when built will use a single PID controller for top and bottom heat blankets. The thermocouple will be based on the bottom blanket. There will be a second PID monitoring the top blanket temp for comparison, but both blankets are controlled by the first PID. A basic setup but should be good enough for my purposes, though possibly not sophisticated enough for some of the resins you mentioned.
I'm basically building a "reference board" without any stiffness or damping improvements (basic base, fibreglass, edge, sidewall, topsheet layup), then going to use a laser vibrometer in free-free mode to determine the torsional modes and frequencies of the snowboard. Then I'll build a few more boards using the same materials and dimensions but with dampening material to dampen those frequencies in the direction of the torsional modes. The intent was to look at doing an external damper (on top of the board) as well as something internal in the layup.
The project idea was one I developed with my project supervisor. I wanted to do something on snowboards so I'd be motivated to actually work on it. A student last year did the basic work in determining the vibrational modes and frequencies in a few off the shelf snowboards, my project is just taking his research one step further. I can send you the paper if you're interested.
Time - I've got until November, but really I need testing done during the Australian snow season, so I'll need a lot of the lab research done by July/August. FEA modelling is planned, but will take place just to confirm the lab data obtained is accurate, and may be cut out if I run out of time.
As for epoxies, my press when built will use a single PID controller for top and bottom heat blankets. The thermocouple will be based on the bottom blanket. There will be a second PID monitoring the top blanket temp for comparison, but both blankets are controlled by the first PID. A basic setup but should be good enough for my purposes, though possibly not sophisticated enough for some of the resins you mentioned.