Fatigue Damage Spectrum of a Random Vibration

The fatigue damage spectrum (FDS) of a random vibration is obtained by plotting the variations of damage to a single-degree-of-freedom linear system versus its natural frequency for a given damping ratio. In this chapter, FDS is derived from a power spectral density. The chapter then discusses the calculation of the FDS with Dirlik's probability density. The up-crossing risk fatigue damage spectrum (UFS) gives the largest value of the damage for a given risk of exceedance which can be chosen as very low. To this effect, it could be used to size a structure instead of the FDS when this spectrum is used. It can also enable us to compare the severity of a random vibration with that of a series of shocks or with a nonstationary phenomenon. Finally, the chapter describes the sinusoidal vibration superimposed on a broadband random vibration, and the swept sine superimposed on a broadband random vibration.