Actually Aluminum is a rather ductile metal, that is it is
quite easy to form by bending, or pounding. It also will stress harden
rather easier than some other metals. After stress
hardening, it is rather prone to metal fatigue or more properly stress
cracking. My Grandfather, an old school German toolmaker, called it
crystallization. It used to be called that because when it does break the
fracture line follows the grain structure of the metal and you can see crystals,
which actually were there all of the time.
Truman is right about the need for inspection. The
aircraft industry found out about this in the '50's with the mysterious crashes
of the British Comet jetliner. Since then all aircraft undergo scheduled
detailed inspection to find cracks before rather than after the
crash.
I suspect that the wide variation in service life of
stirrups probably has something to do with equitation. I weigh about 220
lbs and used the same pair of Al. stirrups for over 10 years with no
problem. It may be that I put less weight into them than other
folk. I do know that I have never had problems with the bottoms of my feet
hurting during a ride. I also had a really bad knee injury in the
'70's. Today I would have had surgery, then I just did my exercises and
learned how to ride putting little strain on the knee, and thus less weight on
my feet.
Ed & Wendy Hauser 2994 Mittower
Road Victor, MT 59875
