Basically, there is no deformation so miniscule that it lasts forever. It just affects how many cycles/how long it takes. Steel however, if you deform it only v

Basically, there is no deformation so miniscule that it lasts forever. It just affects how many cycles/how long it takes. Steel however, if you deform it only very little, lasts practically forever. You just need to design it to not deform too much at normal operation. Incidentally, this fatigue vs. approaching the strength limit issue is why airplanes have limited flights. The fuselage/hull is made to last long enough, but not necessarily do well longer than that.