Detail fatigue analysis exceedance spectra determined from random multidirectional force components

Prediction of fatigue life of structural details currently relies on semiempirical methods based on test data from specimens undergoing cyclic loading in one direction. In actual service many structural details undergo cyclic loading from random externally applied forces in many directions. Components of internal loads in a structural detail resulting from random externally applied loading are also random and are generally statistically correlated. Procedures are provided for determining the loading exceedence spectrum in a single critical direction for a specific structural detail undergoing random loading from many directions. These procedures include both time domain and power spectral density applications and both direct and covariance treatments.