There is an occasional need to compare the effects of two different power spectral density (PSD) base input functions for a particular component. This would be the case if the component has already been tested to one PSD but now must be subjected to a new PSD specification.
A comparison can readily be performed using a Vibration Response Spectrum (VRS) if the PSDs have the same duration. This requires estimates of the bounds for both the amplification factor Q and the natural frequency.
The task is more complex if the PSDs have different durations. A Fatigue Damage Spectrum (FDS) comparison can be performed as an extension of the VRS method. This also requires estimates of the fatigue exponent.
The method is demonstrated using an actual case history: psd_fatigue_comparison.pdf
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Here is the source code for a C++ vibration response program which has a fatigue damage spectrum option: vrs.cpp
The calculation can also be performed using:
Matlab script: Vibrationdata Signal Analysis Package
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– Tom Irvine