Hi! I'm trying to find a good way to predict fatigue caused by a random vibration (given PSD). I know at least 2 ways of doing it but i'm questioning them both. One of them is using the rain flow count algorithm at a simulated acceleration/time signal to generate a certain amount of cycles at a certain loadfactor. A Wöhler(S/N)-curve and Miners rule is used to calculate the fatigue. This one does not take the fact that a great part (even though most of them of very small amplitudes) of the cycles having a mean value inequal to 0. In classic fatigue analysis one usually talks about an R-factor (smax/smin) giving other properties to the wöhler-curve. A very large amount of different R-values is found in a random vibration. Is it possible to say that since the mean value of all "R-values" are -1 one can treat all cycles as they where acting around 0? Is it possible to find any sources on this? Next question concerns the fatigue caused at different vibration modes. Let us take a cantilever beam with given natural frequenc-y/ies and damping. The first frequency(fn1) concerns the mode close to the fastening and the second one(fn2) a point a bit from the middle. Is it possible to not take the second natural frequency into account by saying that the stresses acting on the second mode(due to the excitation in fn2) is so much smaller than in the first mode? Sources/references at this? I'm sorry if the text is badly written and hard to understand! Thank you!