Consider a single-degree-of-freedom system subjected to base excitation where the input is an arbitrary time history.
The response of the system can be calculated via a digital recursive filtering relationship, which is the numerical engine embedded in the SRS calculation. This is done for each natural frequency and amplification factor Q of interest.
Next, a rainflow cycle count can be performed for each time history response permutation.
Then a relative damage index can be calculated for each fatigue exponent b case of interest using a Miners-type summation.
The damage index can then be plotted as a function of natural frequency, with separate curves for each Q and b pairs. This is a Fatigue Damage Spectrum (FDS).
The fatigue damage spectrum is useful for comparing the relative damage potential between two different base inputs, particularly for the case of a nonstationary input.
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An FDS program in C/C++ is:
Note that C/C++ is the optimum language to use for speed because the rainflow calculation requires deleting intermediate rows from the amplitude array.
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An alternative would be to use a Matlab MEX script that calls a C/C++ program. A script set is posted at: Matlab MEX
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The following presentation gives further information on Fatigue Damage Spectra: SAVE_conference_2013_Irvine_fatigue
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See also:
Dirlik Rainflow Counting Method from Response PSD
Fatigue Damage Spectra, Frequency Domain
Sine Vibration Rainflow & Fatigue Damage
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– Tom Irvine
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Hi Tom,
Thanks for the article, this is a topic I have done research on, as well, I’d like to see your presentation/material, but the link is failing.
Thanks,
Doug
On Mon, Sep 30, 2013 at 2:15 PM, Vibrationdata
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