Re: Aluminum - The Middle Child of Frame Materials?

Cyclo wrote:

> That it still has a finite number of cycles to fatigue

As does every bicycle frame, regardless of material. The idea of a
fatigue limit is certainly of academic interest, and may be of some
practical application where a known, exactly repeatable load is
applied, such as in a clock mechanism. But a bicycle frame is subject
to a wide variety of loads - different pedal forces, hitting potholes,
swaying out-of-the-saddle motions, etc. For any realistic frame design
and material, some of these forces will exceed the fatigue limit and
therefore the frame will eventually fail. Depending on the frame's
design and tubing thickness, that "eventually" can easily be longer
with a material that has no fatigue limit than in a material that does
have one (or vice versa, the key is the proper design rather than the
material)..

In addition, even for materials with a fatigue limit, it only applies
in the absence of a corrosive environment:
http://www.corrosion-doctors.org/Forms/fatigue.htm
So those of us who ride our bicycles somewhere other than in carefully
dehumidified and unpolluted air can't count on the existence of a
fatigue limit regardless of frame material.

> when it fails, it
> tends to fail catastrophically.

> Anecdotal evidence cannot change metallurgy.

Depends on what you mean by "metallurgy." If you mean the natural laws
that govern how metals behave, then anecdotal evidence can't change
them, but it can help reveal to us what those laws are. OTOH, if by
metallurgy you mean our understanding of those natural laws then
anecdotal evidence can and has played a major role in improving our
knowledge and in designing appropriate experiments to further refine
our understanding.

Unfortunately two of my steel frame 'anecdotes' didn't interpret their
own metallurgy in the way you do as they both suffered sudden
unexpected fatigue failures - one of which resulted in a nasty crash.

Fortunately my current aluminum frame, with over three times the miles
of either of those steel frames, also has a different take on
metallurgy since it hasn't had any problems.

.

Relevant Pages

  • Ebooks - Database
    ... 775 Damage in Composite Materials* ... 787 Composite Materials: Testing and Design (6th ... 798 Probabilistic Fracture Mechanics and Fatigue ... 813 Long–Term Behavior of Composites* ...
    (sci.med.cardiology)
  • Ebooks - Database
    ... 775 Damage in Composite Materials* ... 787 Composite Materials: Testing and Design (6th ... 798 Probabilistic Fracture Mechanics and Fatigue ... 813 Long–Term Behavior of Composites* ...
    (sci.med.nutrition)
  • Re: SWAGs on shop cost
    ... I know the actual price will vary with location, materials, and options, ... $12K for the slab & footings. ... I am building a timber frame metal clad shop. ...
    (rec.crafts.metalworking)
  • Re: "brittle" vs. non-ductile
    ... materials and not typical of metallic materials ... commonly used in bicycles ... Catastrophic failure. ... the frame remains in continuous use since then. ...
    (rec.bicycles.tech)
  • Re: CFRP drawbacks
    ... frames(early OCLV, Kestrel) but to imply that the only frame material ... worth designing into a bicycle is carbon fiber is..well, ... *All* materials have strengths and weaknesses. ... denegrated, called old fashioned and heavyby any bike shop ...
    (rec.bicycles.tech)
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