><< I'm not a materials scientist or mechanical engineer, but advise folks to
> be a bit skeptical about reports of "fatigue" failures of Al w/o
> pre-existing cracks. I do think, though, that failures of Al tubes, etc.
> are more likely to be sudden; >>
>Aluminum always cracks first, then breaks, usually without warning, unless
>you are smart enough to keep your bike clean and see incipient cracks
>developing. It always seems sudden. Steel "talks to you" first and is usually
>a more progressive failure.
agreed. recently caught a hairline developing at the ol' spider/crankarm junction on a pair of old campy cranks on my work bike - went from 2mm to 7mm (and 1/3 of the way through crankarm, diagonally) in the space of the 2 months it took for my new crankarms to get to me - at 300 miles/week, thats a fair bit of riding. had i not looked at the crack religiously, or not noticed it in the first place, it would have been a "catastrophic" failure at some point.
but now i have a reference point for campy cranks... if i find a crack in a pair, figure 2500 miles left! har har. dont try that at home. danger danger.
every alu part ive ever broken has shown dirt in the oldest portion of the crack when looked at after failure.
ive never pressed a solid steel part to failure, but the tubes ive cracked (stems) have all been kind enough to ask me to inspect them before theyve torn (stem "tick tick tick creak tick". joel "hmm better check that out...")
-joel
--
joel metz : magpie@messengers.org : http://www.blackbirdsf.org/
i know what innocence looks like - and it wasn't there,
after she got that bicycle...