If I run a stress analysis with a random vibration input spectrum, the output stresses will be in Grms (1-sigma), and therefore for a fatigue analysis I can also determine the 2-sigma and 3-sigma stresses. However, the thing I'm uncertain about is how to determine the number of cycles at each stress level. It seems unrealistic to base the number of cycles on the peak input frequency. Alternatively, I can calculate the resonant frequencies, but since this is effectively a flat random profile, all resonances will be excited simultaneously.
Any suggestions gratefully received.
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