Science-vibration damping

[zap]

Carbon Composite vs aluminum

Here you go. First study I came across.

http://www.eng.auburn.edu/users/hornikh/upload/KlausHornig_2002_Paper_ICSV09.pdf#search='frequenc y%20vibration%20damping%20of%20carbon%20composite% 20and%20aluminum'

[Brian Smith]

This testing was done with materials pretty differrent from those used to make components of bicycle systems, and both the loads and displacements are not within the ranges those components would typically "see," and the single frequency was specifically chosen in order to avoid a limitation of the apparatus; again, not an application of a real world bicycle condition. The displacements were of 1/2 to 1 tenth of a millimeter. Does this have physiological implications?

Does anyone think/know, par example,* that Easton or FSA creates a better apparatus than this and does more groundwork research to evaluate their carbon cranks/handlebars in comparison to popular pre-existing alternatives? Do you think they keep this research and the advantages it shows "secret" from the public?

Is it all progress, or is partially just "change?"

Is that pasta boiling?

* French for: "for example"

[aLexis]

.

[gasman]

While this is very limited in scope in what they studied I wonder if it does point to carbon really being more dampening than Al. Of course there are so many other variables when making and riding bikes it probably doesn't really matter.
Thanks for the link Zap.

[zap]

Firstly, I posted the link in response to someones claim that there was/is no study that they saw comparing materials and absorption capabilities.

I found this paticular study in 30 seconds and am sure more could be found if someone cared. Granted, this study is quite limited in scope, but it does follow a pretty typical trend.

Although the beam structure of the materials tested are different than what would be used in cycling, one needs to read the conclusion carefully. There is a pretty common method to making carbon composites.

[Brian Smith]

Firstly, I posted the link in response to someones claim that there was/is no study that they saw comparing materials and absorption capabilities.

I found this paticular study in 30 seconds and am sure more could be found if someone cared. Granted, this study is quite limited in scope, but it does follow a pretty typical trend.




10-4 zap. Sorry to jump into your thread.
It's tough when threads are referenced without reference.
I know of no study that shows that the particular vibrations that carbon fiber CAN damp are of any real relevance to riding a bicycle composed in any way of carbon fiber, nor that any of the components of a bicycle have been engineered and tested specifically for that trait. I certainly know of examples wherein the damping qualities have neither tested nor designed for in carbon fiber bicycle products, and it's likely to be more the rule than the exception.
I think there are other reasons people can rally around carbon fiber stuff.
I also think that even if we were presented science that showed the physiological benefit of engineered carbon dampers and offered them for purchase, I would choose metallic items with a better chance of safe failure modes. I think that in light of weight, cost, and safety, the damping possibilites of carbon fiber as a compelling reason to choose bicycle items made of it (instead of items made from metallic alternatives) is a ruse.
Buy/use it anyway - it's hot right now and that's great to have hot stuff.
It MIGHT even be great.
Science hasn't even been applied to answer that question, maybe seat-of-the-pants is compelling enough.
I think marketing trumps science anyway. Who remembers the Velo News test of crank rigidites a while back? The clear winner in E/I$ was an aluminum crank......and the others were being marketed as "stiffer."

[MadRocketSci]

scanned the paper quickly, and basically it deals with additional non-linear behavior (hysterisis, etc) of carbon fiber. But you guys are talking about damping.

Two basic properties of structural materials are K, the spring constant and zeta (symbol z font), the damping coefficient. Materials when forced with function f(t) respond like a spring-mass damper system. Think of the suspension in your car. There are springs and shocks. The springs deflect to absorb energy and the shocks dissipate it (turn it into heat). How much they do each depends on the spring constant K and the damper coefficient zeta. With a higher zeta there is more damping, and resonances are decreased. With no damping at all (zeta = 0) the system will vibrate at its natural frequency forever.

In aerospace structures made out of aluminum we typically assume zeta to be around 0.01 and 0.03. The paper gives carbon fiber a 0.5 value for zeta. Therefore, carbon will damp out resonances, particularly at the natural frequency omega-n. Since zeta isn't 1, carbon doesn't "overdamp".

Carbon is a non-linear material, so it doesn't behave exactly as a spring-mass damper system, particularly at larger deflections. This paper i think attempts to characterize these types of nonlinearities. To me it explains why my bike behaves differently when the road is smoother (muted feel) than when the road is really sh*tty (it gets a little slap-happy).

Just my 2-cent analysis...