On 2008-04-02, jim beam wrote:
Ben C wrote:
On 2008-04-01, Jay Beattie wrote:
On Mar 31, 5:10?pm, John Thompson wrote:
On 2008-03-31, Tom Sherman wrote:

John Thompson wrote:
How do you "wear out" a frame? Damage, yes -- either through neglect or
abuse, or what have you. But "wear out?"
Corrosion (metal frames),
I'd file that under "neglect."

fatigue (metal and composite)
Not an issue with a properly designed steel frame, but certainly a
potential issue with aluminum. I'm not aware of composites having
fatigue failures, but I may just be ignorant on that point.

and degradation of epoxy and adhesives (composite).
Disposable frames, then. I'll stick with steel, thank you.
Steel as a material has an infinite fatigue life with the loads
applied by whimpy cyclists, but as actually used in bicycle frames, it
does not -- at least based on my experience.

I think what Jim was saying was only some kinds of steel have an
infinite fatigue life (or "no endurance limit").

that's muddled.

Correct. I always get that muddled.

an endurance limit is where infinite fatigue life is demonstrated.


I think it's mild steel
that does.

correct.


So maybe a $60 Roadmaster Fury has an infinite fatigue life
below some load. If so someone should tell their marketing department.

The steel used for decent bikes is different alloys, with
cleverly-designed impurities in it (and maybe more carbon?) which make
it stronger but mean it does fatigue eventually just like aluminium,
whatever the load.

correct.



You might think "no endurance limit" meant "endures forever", but it
doesn't, it means "no stress below which you don't get any fatigue".

endurance limit, is the maximum cyclical load at which you can still
achieve infinite fatigue life.

Yes, so if you have no endurance limit, then you can't have infinite
fatigue life.