Don's point is that with steel, the the cyclic stress is low enough, there will be no failure no matter how many cycles the article is subject to. This is not so with aluminium.
To design this way for steel I vaguely remember you use a "Goodman Diagram".
Joe Bender-Zanoni Great Notch, NJ "More confidence in 75 year old BSA cranks than 25 year old Campagnolo"
> Donald Gillies wrote:
> >
> > Richard has a good point about aluminum crank failure. Aluminum has
> > no lower fatigue limit. When you have applied XYZ stress cycles of
> > force PDQ, and F(XYZ, PDQ) > max, the crank WILL fail. Steel has a
> > lower fatigue limit - if you can keep your stress cycles below this
> > limit, a 531 steel frameset will last forever.
> >
> > In other words, in 100 years we may still be riding our cambio corsa
> > bikes, but by that time all the nuovo record bikes will be TOAST.
> >
> > - Don Gillies
> > San Diego CA
>
>
> Well not exactly, as there is plenty of documentation of steel cranks
> failing at the pedal eye just as aluminum cranks do.
>
> Crank failure is very low on my list of things that can or will harm me.
>
> I've always maintained my equipment as if it was a light airplane and
> inspected for cracks whether it was something made from steel, aluminum
> or carbon.
>
> Chuck "life will kill ya" Schmidt
> South Pasadena, Southern California
>
> .