Great post! I've had similar musings. I think the early buzzphrase on Ti in
the '70s was essentially "as strong as steel at half the weight" which was
in some senses sorta kinda almost true and led to some conceptually questionable practices- speccing Ti instead of steel for parts without significantly changing the dimensions. The yield strength or UTS of the sorts of Ti alloys commonly used back then in military aerospace aplication s like alpha-beta phase 6Al-4V was indeed better than the most prosaic mild
steels. Part of the problems of early Ti applications I think may in part
have been that those applications generally used CP Ti, a "lesser" engineering material in most senses. Another consideration in the problems seen by substituting Ti for steel wa s the massive difference in the relative moduli of elasticity between steel
and Ti. Many parts on a bicycle are more stiffness limited than strength limited, and a steel part replaced by a dimensionally similar one of Ti wil l be far "flexier" than its steel equivalent. All engineering metals save *real* exotics like AlBeMet or some metal matrix composites have remarkably
similar *specific* moduli, so there is frequently little to be gained by substituting one for another if stiffness is the primary design case, ignoring buckling failures in thin wall sections. This alone explains why a
stiffness case design optimized for steel will frequently see very little
reduction in mass when optimized in another "more exotic" material. Marketing considerations may be more significant than engineering ones in
many of these cases where "low tech" steel is replaced by "high tech" metal s I'll leave out consideration of CFRP composites because that material was
FAR rarer than Ti in CR list timeline lightweights. Anisometries and differing failure modes make direct comparisons there difficult anyway. Kurt Sperry Bellingham WA
John Thompson wrote:
>
>
> As for titanium use predating the SR group, consider that the SR-71, whic
h
> was conceived in the era of the Chevy Bel Aire was made primarily from
> titanium. 40+ years later it's also still the fastest jet ever in service
> (that we know of). Cold War tax dollars allowed Lockheed to learn all sor
ts
> of stuff about Ti fabrication, some of which may still be secret. (Check
out
> "Skunk Works" by Ben Rich for more).
>
> Drifting a bit closer to topic, I think Campy still suffers from this
> "retain the basic design, apply the cool new material" approach. In fact,
> they are worse than ever, replacing aluminum with carbon all over the pla
ce
> with little revision in design. I guess it's good for marketing, but I
> refuse to accept that this does not lead to either weaker parts, or parts
> that are stronger (heavier) than necessary. Looking back at the second ge
n
> BB, you can see where Campy's inability or unwillingness to really change
> the basic BB design lead to a part that did not best exploit the properti
es
> of a new material. By the time they made it solid, the weight benefit was
> significantly reduced, and it was still said to be a more flexible part.
A
> more common example would be "early" aluminum frames, like Alans, that
> retained lugs and the basic dimensions of a steel bike. Compare this to a
> Klein, and the far better bikes that this would lead to, in which the wal
l
> thickness, diameter and profiles
> of the tubes were much better suited to exploit aluminum's
> characteristics. Look also at Shimano's current crank and BB, which total
ly
> revises the entire design, but still uses the steel spindle and alloy arm
.
> They are pursuing the best designs with the established materials while
> Campy is reusing old designs on new materials, which seems pretty stupid
to
> me. Of the old square taper BB, for example, the faithful will say "tried
> and proven design, backward compatible, etc...." To which I respond
> "outdated, not opitmal for the material, thinking inside the box." Yikes,
I
> spoke "office."