Does ski flex / stiffness breakdown with age?

[anthill]

Searched the forums but couldn't find anything on this jongy question.

Head's advertising "Liquid Metal" laminate in their new Monster skis as stopping ski flex breakdown over years of use. Is this really a problem?

If so, what construction materials or structure make more durable skis?

[Skidog]

Searched the forums but couldn't find anything on this jongy question.

Head's advertising "Liquid Metal" laminate in their new Monster skis as stopping ski flex breakdown over years of use. Is this really a problem?

If so, what construction materials or structure make more durable skis?

Yes they do breakdown...some tech probably had a better explanation of it than I can provide so ill leave it to them..

Usually wood is best...now as to particular type of wood I dont know.. I do know that "foam" core skis tend to break down considerably faster becoming soft...

Personally I never noticed. I just put em on my feet and point em down the fall line...if something gets in my way...I turn.

m

[leroy jenkins]

Foam=will soften up

Foam+metal=might

Wood=probably not

Wood+metal=almost no softening over time.

Different woods hole their flex better as well, I've been sending emails back and forth with the guys at igneous trying to figure out the details of some skis i will probably be getting from them, and they told me that maple holds its flex better than ash.

[AsheanMT]

So I wonder how aspen wood cores hold up?

[the Mad]

East coast tree's make better skis bitch. Think Maple.

[dps]

somewhat spamish factoids ... but hopefully of interest and educational one way or another:

in a nutshell, fiberglass has twice the modulus of wood. So, in a fiberglass ski (which also applies to metal skis, because they all have glass), the life and liveliness of the ski is very much influenced by the core material. The physical properties of the core and and fiberglass are so close to one another that each has a significant impact on the performance of the ski.

Fiberglass breaks down- it loses its reactivity.... (the skis loses its energy and pop quite rapidly).

In a foam core/fiberglass ski, it happens fast, like noticeably within a few days if you are ripping. By adding higher modulus/ heavier woods- maple being one of them- the core starts to bolster the fiberglass and extends the flex life of the ski. Core material makes a big difference in a fiberglass ski. however, even with heavier woods and thick glass, the wood and glass in the ski are breaking down (and the energy coming into and out of the turn diminishes.

The only technology in existence that doesn't break down over time is a carbon ski(yes, we have a biased interest in it and are the only ones building them in a sandwich construction where the laminates can excel, but flex life is is one of the big reasons why we have invested so much time, money, and effort in developing the technology and why we think the value is added in the price of a well built carbon ski.

Carbon has 10x the modulus of wood/foam while being lighter than fiberglass... so it totally dominates the core material- it renders the core material pretty much irrelevant in terms of its flex life- it's just space filler. Carbon, with its practically infinite flex life, is the dominant player. Carbon elongates only .5% before it begins transmitting your energy into the snow. By comparison, fiberglass elongates almost 10% and that number quickly grows as you hammer on your skis, which means the performance keeps getting sapped out of them. Carbon will stick in the neighborhood of .5% ad infinitum, which means the ski has a lot more snap out of the box (big difference in all snow conditions), and continues to hold that snap while the conventionally built ski is breaking down.

Carbon skis retain their flex life for all practical purposes, infinitely. So, five years down the road, assuming the edges/base are still in good shape, the carbon sandwich ski is going to ski with the exact same power as your first day on them, whereas any glass/wood blend has long been replaced by another few sets of fiberglass/wood blend skis.

now if you aren't truly bending and loading the ski up in the turn... all of this is somewhat irrelevant and moot as the instrinsic power and energy transmission of any ski won't be noticed anyway.

[anthill]

Thanks dp, very interesting and informative. So it sounds like Head's marketing is BS :rolleyes:, if it's the fiberglass and/or wood that deteriorates with time. Not surprising I guess. So is this process just skiing-time dependent, or does shelf life factor in?

Offtopic, but since carbon has such a higher modulus how do you deal with the shearing forces between the carbon fiber laminates and the base material? Failure in that location would be a delamination, I guess, but can it happen more subtly, like glassfiber/wood's drop in tensile elasticity?

[Idris]

I'm going to stick my head out on this one and say that iun some ways dp you are correct but in your details you are wrong.

True a cheaply made foam core ski will degrade quickly.

Yes Carbon elongates less than glass. But if you elongated a fiberglass ski 4.7% it would snap, let alone the 10% you quoted - carbon is stiffer but if it snaps sooner.

Yes Carbon skis can last longer than glass ones. But well made glass/wood ski will degrade less in five years than you will notice skiing it. There are plenty of fiberglass products around that prove this, think light aeroplanes and boats.

In short carbon skis can be made lighter, stiffer, stronger and last than fiberglass ones. But there is not an order of magnitude difference between them. A well made ski will outlast, out ski and out perform a poorly made one regardless of what it's made out of.

I've seen 10 year old Explosives with 100's days on them with plenty of pop left in them. And warn out carbon noodles in their first season.

[pechelman]

first of all, I just love these blanket generalizations that "foam" will always breakdown fast.
There are literally thousands of different types of stuctural foams out there, some of which will last indefinitely under normal skiing.
Theres a reason why tons of aerospace companies use foam instead of wood in their composite sandwhiches.
Briefly, its because they exhibit exceptional long term properties ie fatigue, are very hygroscopically stable ie do not expand much with changes in moisture content because they are closed cell, and are also thermally stable when subjected to changes in temperature. Additionally, Ive seen foams which take impacts much better than Ive seen wood fair.
Anyone with half a brain can see why foam would be an excellent choice for use in skis.

Now that thats over, I too have some disagreements with some of the things and comments to make on whats typed above.


> In a nutshell, fiberglass has twice the modulus of wood. So, in a fiberglass ski (which also applies to metal skis, because they all have glass), the life
> and liveliness of the ski is very much influenced by the core material. The physical properties of the core and and fiberglass are so close to one another
> that each has a significant impact on the performance of the ski.

In a nutshell, "liveliness" is a qualitative measurement of natural frequency which has to do with the ratio of stiffness to weight.
Wood skis are more "lively" because the core itself imparts a stiffness as opposed to a sheet of foam, which is generally not "springy".
Only in that sense does the core contribute at all to this sensation. Infact, the face sheets of the composite sandwhich, whether carbon, metal, or glass
contribute much more significantly to this qualitative liveliness and quantitative natural frequency. The reason being has to do with moment of inertia
factors, and that the contribute in stiffness is equivalent to the CUBE of the distance from the nuetral axis of the ski (which roughly runs down through the center of the core). Plainly put, its like an I-Beam. The larger the center web and the further the flanges are away from the center, the stiffer the beam.

> Fiberglass breaks down- it loses its reactivity.... (the skis loses its energy and pop quite rapidly).

Its true that it may lose its initial stiffness quick, but once it settles, its generally not going anywhere.
The same is true for most any composite thats constructure properly.
If this degradation taken into account, a ski can be made the "degrades" or "break-in" to its happy designed spot.
Unfortunately this is a bit tricky and really just required lots of physical r\d.


> The only technology in existence that doesn't break down over time is a carbon ski(yes, we have a biased interest in it and are the only ones building them
> in a sandwich construction where the laminates can excel, but flex life is is one of the big reasons why we have invested so much time, money, and effort
> in developing the technology and why we think the value is added in the price of a well built carbon ski.

I understand your biased interest, but give me a break. Carbon isnt some miracle fountain of youth material that lasts forever.
Infacts its much less tolerant to damage and is extremely brittle, moreso than glass. Next time youre around your manufacturing, pickup a dry tow of carbon,
bend it, pinch it with your fingers, and watch how easy the fibers "snap". Then do this with glass or kevlar and see that it doesnt. Everyone needs to be aware of that the next time they accidentially chip their carbon topsheet to file it smooth and put a dab of epoxy. Having said all of that, I definitely
agree with your decision to use Carbon, and thats definitely where the industry is headed.

> Carbon has 10x the modulus of wood/foam while being lighter than fiberglass... so it totally dominates the core material- it renders the core material
> pretty much irrelevant in terms of its flex life- it's just space filler.

This goes along with what I was saying earlier, and in addition to the "space filler" comment, id like to add that its the "center web of the I-beam" in that it places the carbon reinforcement away from the center\nuetral axis of the ski to more easily tailor its stiffness.

> Carbon, with its practically infinite flex life, is the dominant player. Carbon elongates only .5% before it begins transmitting your energy into the snow.
> By comparison, fiberglass elongates almost 10% and that number quickly grows as you hammer on your skis, which means the performance keeps getting sapped > out of them. Carbon will stick in the neighborhood of .5% ad infinitum, which means the ski has a lot more snap out of the box (big difference in all snow
> conditions), and continues to hold that snap while the conventionally built ski is breaking down.

I think you're confusing some numbers. Your .5 and 10% numbers are strain to failures aka elongation at break. (at least i think this is what youre confusing
because most e% are around 1.5ish% for cF). Im also not quite sure how you quantify this, as any materials once elongated transmits your energy, in this case
your energy causes a beam displacement which then results in a force.

Anyway, its true carbon will take less displacement than glass to generate higher loads. This could be good or bad depending on who you ask.
Im not going to go into that right now cause itll take up a lot more space. I can go into it on request if someone wants.

I didnt mean this to shoot you down or anything, but just to provide a bit more "balanced" perspective to some of the miraculous claims you made about carbon. But like I said, carbon is long overdue to begin taking over the ski industry. I wont really say its the "future" mainly cause its such old
technology, but its definitely needed for companies to stay competitive.

Out of curiousity, what grade CF are you all using at DP? IM7, AS4, T-XXX's, etc? If thats too proprietary, pitch or pan?

Lastly, I think its incredibly awesome of you and the other smaller ski builders to frequent this site and chime in.
Another great reason to support the guys like you!

[mtcham]

My 2 cents,

Having been a custom recurve bowyer (archery) for 10 years has anyone looked into or talked to the industry leaders in this field. The core materials and top sheets must withstand tremendous abuse and most older well made bows don't lose their pop even after 50 years.

At the time I stopped building bows(1994) maple laminate cores were by far the liveliest core material. Many bowyers were using red elm, locust, koa, rosewoods, etc., but the fastest bows always had the maple cores. Soft woods were very rarely ever used.

When we decided to end the business we were just starting to contemplate the use of a carbon layer in conjunction with fiberglass to pick up a little more speed but never got to it.

Perhaps the archery manufacturers have already done some of the experimentation you seek.