Mike is right. As a mechanical engineering Teaching Associate I taught labs on Measurement Techniques. The students measured damping and resonance of simple structures something that always fascinated me, really. The science is well known and the system parameters easily measurable if you have the equipment. By measuring system behavior near resonance you can determine the Q which is related to damping(energy absorption) of a system. Steel absorbs negligable energy until you get to high stress levels. It is a very elastic material weather it is low carbon or chrome moly. The ringing you get is related to wall thickness more then alloy. Steel is nearly a perfect spring unless over stressed, aluminum exhibits hysterisis(absorbs energy) in it stress strain curve even at low stress which is why it will fatique. Tests with unrealisticly high loads play to overbuilt aluminum frames showing they are strong and the overstressed steel weak, but under actual use the loading will not dam age the steel frame but will eventually fatique the aluminum frame. Jerry's paper clip example is for yeilded steel in plastic deformation a very bad condition for a bike frame. The differences in the aluminum and steel behavior is probably the reason(I am not a metallurist but was a ME and stress analyst) that steel does not fatigue unless stressed above its endurance limit which is usually near the yeild stress(say 75% of yeild. There is not an exact point of departure from elastic(does not absorb energy) to plastic( yeilding and absorbing energy) but it is safe to say it is negligable below the endurance limit of the material. Localized stresses due to poor design can cause high localized stresses even when nominal stresses do not seem high(as in the campy crank spider). A good frame builder knows this and avoids these stress concentrations. Steel and titanium have that resilent feel that aluminum and composites do not have because because titanium and ferrous lack of dam ping. The issue of springiness being good or bad is a biomechanics issue that is probably effected by rider adaptation. The frame rebound might help return the leg or maybe you apply work against the rebound that is beyond me but probably depends on each riders pedaling action. I like a stiff BB, give me cheap heavy aelle or thron tubing with heavier walls over 753 anyday. As to where the energy goes in a tuning fork, some is air damped, some is dissipated through the mount especially if it is in your hand. A rigidly mounted steel tuning fork in a vacuum will resonate for quite a while. The other Brian B in Berkeley
http://www.key-to-steel.com/
To: Bikerdaver@aol.com, Philcycles@aol.com, classicrendezvous@bikelist.org From: Michael Kone <bikevint@tiac.net> Subject: Re: [CR]Perpetual Motion discovered, Re: 1962 Raleigh Gran Sport!
My point was that heat loss/energy loss from flex in steel was extemely low - low enough that most engineers consider it trivial in a bike frame. Yes, there is of course some - but don't use that to loose site of the big picture!
Mike Kone in Boulder CO
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