"The flex cycle life is extremely long if the metal is all kept in its elastic zone, and essentially no fatigue should be expected."
I wish I had my materials engineering books at work, but they are at home.
The bottom line is that steel will eventually fatigue even if it is kept within its elastic zone. However, its behavior in this respect is well known and it is easy to design around the fatigue characteristics of steel. The equations are readily available for anyone doing such work. I spent way too many hours doing problem sets on fatigue when I was in school. Once I got out, we tended to just use a relatively large safety factor and call it good, but I've never worked on projects where weight was super-ultra-mega-primo important.
Of course, steel has much better fatigue characteristics than aluminum, but I don't really need to tell you folks that, do I?
Yours,
Forbes Bagatelle-Black Santa Clarita, CA
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