lets take a component like a fan blade as an example. Is it right to conclude that it will fail even when the stress is within permissible limits but its operating frequency is close (close enough than the resonance separation margin) to first mode natural frequency?
Kindly let me know your views. Thanks
It depends on what it is made of, and how large the vibratory stresses happen to be. If the stresses are low and the material is steel, it is possible that a fatigue failure due to crack propagation will not occur, so long as the stress is below that steel's fatigue limit. It is more likely to occur with higher stresses and aluminum instead of steel, because aluminum and its alloys do not possess a fatigue limit.
More information on metal fatigue can be had from an introductory materials science text like Shakelford or Van Vlack.
