[MikeK]

Originally Posted by dean from bozeman

MikeK,
Agreed. Now, does a constant operating temperature for an extended period of time add proportionally more than shorter periods to the natural fatigue life of parts that are under stress?

Cyclic metal/alloy fatigue is a function of stochastic process and inherently independent of period of frequency(time) between stress applications. If thermal state is nulled (constant) there will be no statistical variance in failure probability between parts that are constantly vs. sporatically stressed. Failure probability will be the same.

If, however, thermal cycles are applied, a different and additional external subset of stresses will be applied to the grain boundaries within the metal/alloy. It is for that reason some critical parts, like jet turbine blades are often cast with a single nucleation point, resulting in a large part that is a single 'grain' or crystal. Normally in metalwork finer grain structure is better. But not always!

So, to answer your Q, "no". Clear as mud?