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With the aluminum rod, one solves the tensile strength problem with more cross-sectional area. That isn't hard to do, been done for ages.

The problem is fatigue resistance. Aluminum has none. That means that as the stress cycle number builds up, the actual strength of the aluminum goes down, and it continues all the way to the point where the rod strength equals the stress placed on the rod, then it fails.

There is another issue that has never been definitively answered, though. Does a stress cycle, at less than maximum, count in the total cycle count? I have done numerous literature searches and never found a definitive answer. Maybe someone on the board knows more about it than this, if so speak up.

R.



As a general rule, stress damage is cumulative. Ask the paperclip which you got away with bending once, how it feels after the 5th bend. It's also why we replace rod bolts and why jet engines have time limited parts that get replaced despite no cracks or dimensional changes.