Vibration fatigue

An excited structure responds according to its natural-dynamics modes, which results in a dynamic stress load in the material points.

As the profiles of excitation and response are preferably analyzed in the frequency domain it is practical to use fatigue life evaluation methods, that can operate on the data in frequency-domain, s power spectral density (PSD).

When the time history is not known, because the load is random (e.g. a car on a rough road or a wind driven turbine), those cycles can not be counted.

It then becomes viable, with the use of vibration-fatigue methods, to calculate fatigue life in many points on the structure and successfully predict where the failure will most probably occur.

However, certain statistical properties can be extracted from a signal sample, representing a realization of a random process, provided the latter is ergodic.

[3] By exciting different modes, the spread of vibration energy over a frequency range directly affects the durability of the structure.

Various vibration-fatigue methods estimate damage intensity based on moments of the PSD, which characterize the statistical properties of the random process.

[8] There are some approaches with adaptation of narrow-band approximation; Wirsching and Light proposed the empirical correction factor in 1980[9] and Benasciutti presented α0.75 in 2004.

[13] The computational effectiveness of vibration-fatigue methods in contrast to the classical approach, enables their use in combination with FEM software packages, to evaluate fatigue after the loading is known and the dynamic analysis has been performed.