I've begun working on an FEA model that has a vibration requirement used for airborne equipment, DO-160F. The requirement indicates prescribed peak-to-peak displacements over the frequency range from 5 to 500 Hz. My question has to do with intepreting the results correctly. All of the other vibration analyses that I've done to date involve random vibration, where the von Mises stresses represent the 1-sigma levels. The highest 1-sigma level is then multiplied by 3 and compared to the fatigue strength of the material. So what about harmonic analysis - what do the resulting von Mises stresses represent? I think the answer is that they represent the highest stresses encountered since there is no randomness to the input - there is no PSD curve. That is, with Harmonic Analysis, there is no 1-sigma nature to the results.

Is this correct? Thanks,

Dave

Hi David: it is supposed to be the maximum magnitude. You can plot stress at some frequency, for example, then, if you probe a point on the structure and graph the response, it should give you magnitude of response graphed against all frequencies, at that point on the structure. In a contour plot, I believe you have to press the option to "Plot bounds across all steps" to see the maximum magnitude across all frequencies, all over the structure.