Originally Posted by
sstorkel
Wikipedia says: "One important structural limitation of aluminium alloys is their fatigue strength.
Unlike steels, aluminium alloys have no well-defined fatigue limit, meaning that fatigue failure eventually occurs, under even very small cyclic loadings. This implies that engineers must assess these loads and design for a fixed life rather than an infinite life."
Didn't Mr. Beanz break an aluminum crank in the same fashion? I think a couple of guys over in the Road Forum has posted similar pictures.
Well, this is the first time I've done it, and that crank has only been on the bike a few months as I had one that evidently wasn't torqued down enough work it's way loose and strip itself in the process. That said, if I remember correctly, the crank that failed came out of a spares (used) bin at my LBS, so who knows how much fatigue it had already suffered under before it had the bad luck to meet me!
I don't check out the road bike forums, I don't enjoy bikes with drop bars, am the opposite of weight conscious about my bicycle or its equipment and generally don't like road bikes. It's quite possible folks over there posted similar failures, I would have missed it. I didn't catch Mr. Beanz similar crank failure either, but if it happened before I joined about four years ago I would have missed it, because I didn't spend any time lurking before joining and discovered the Clyde sub forum right after.
It's funny, as because of what you've quoted above from wikipedia, I've steered clear of aluminum bikes for me for touring and riding around the city, because of the miles and hours I put my bikes through, but somehow I never even considered that the very same limitation would apply to cranks. Makes the utmost sense once realized, but like all assumptions was invisible up to that point!
Now the quest for some not terribly expensive off-road crankset that hopefully will stand up to the kind of abuse I dish out for some time! Welcoming suggestions!