In a message dated 04/08/05 20:41:56 GMT Daylight Time, diarmaede@yahoo.com
writes:
> 1 - Is it possible to design a "lightweight" steel
> bicycle frame which will not show any signs of fatigue
> over the stress cycles likely to be seen in several
> hundred years of use?
Yes, such a frame could be designed, but would have to be slightly
"overdesigned" in a few areas to compensate for manufacturing processes that would cause
an unknowable (within limits) amount of weakening. Weight and strength could
be taken out of other areas. It will not be done because it would be both
expensive and pointless. Modern (and classic) butted steel tubes probably take
us as far as we want to go in this direction, except for further metallurgical
improvements - i.e. they are (and were) pretty good.
> 2 - Is it possible to design a "lightweight" steel
> bicycle frame which keeps the stresses within the
> endurance limits of the material, which would take
> fatigue concerns completely off the table? (Thanks,
> Joe!)
Ditto
> 3 - Is there a reasonable explanation as to why
> fatigue or other results of repeated cycling would
> cause a frame to "soften" before failing?
A frame will "soften" if there is any cracking prior to complete fracture. The cracks could be numerous and small and could be masked by paint or not visible without very close examination. Corrosion, internal or external, will also reduce the stiffness of the tubes, ultimately to zero.
Hugh Thornton
Cheshire, England