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Rainflow fatigue cycles can be easily calculated for a single-degree-of-freedom subjected to a sine or sine sweep base input.  The reason is that each pair of consecutive positive and negative response peaks forms a half-cycle. The relative fatigue damage can then be calculated from the rainflow cycles. Here are Matlab scripts for performing the rainflow […]

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A number of methods have been derived for performing rainflow cycle counting for a response PSD. Note that they tend to be conservative. The Dirlik method is an example of a semi-empirical method for cycle identification. A Matlab script for performing this method is given at: Dirlik_rainflow.zip * * * The following script calculates the […]

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This blog entry is a work-in-progress. Fatigue analysis can be performed in the time domain using rainflow cycle counting.   This is an elegant, brute-force approach.  One advantage of the time domain approach is that it tends to highlight the occurrences of peaks above 3-sigma for the case of random vibration. These higher peaks can also […]

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Endo & Matsuishi (1968) developed the Rainflow Counting method by relating stress reversal cycles to streams of rainwater flowing down a Pagoda.  This method is very useful for fatigue analysis. The rainflow method allows the application of Miner’s rule in order to assess the fatigue life of a structure subject to complex loading. The resulting […]

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Here is a paper. Estimating Fatigue Damage from Stress Power Spectral Density Functions: estimate_fatigue_psd.pdf * * * This following Matlab program calculates the cumulative rainflow fatigue damage for an input stress PSD using the following wideband methods: 1. Wirsching & Light 2. Ortiz & Chen 3. Lutes & Larsen, Single-Moment 4. Benasciutti & Tovo, alpha […]

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Aerospace and military components must be designed and tested to withstand shock and vibration environments. Some of this testing occurs as qualification, whereby a sample component is tested to levels much higher than those which it would otherwise encounter in the field. This is done to verify the design. Now consider a launch vehicle component […]

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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 […]

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Here is a signal analysis package GUI written using Tkinter: vibrationdata_gui_python.zip It is compatible with Python versions 2.7 to 3.3, and hopefully future 3.x versions. vibrationdata.py is the main script. The remaining scripts are supporting functions. These scripts demonstrate the use of multiple windows. * * * The following signal analysis functions are currently available: […]

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There is a need to derive a PSD envelope for nonstationary acceleration time histories, including launch vehicle data, which may be similar to that shown in the above figure. A PSD can be derived using rainflow fatigue cycle counting along with a Miners-type relative fatigue damage index.  The enveloping is then justified using a comparison […]

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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, […]

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I will be teaching two tutorial sessions at: 84th Shock & Vibration Symposium November 3-7, 2013 Atlanta, GA The sessions are: Shock Response Spectra and Time History Synthesis Rainflow Cycle Counting for Random Vibration Fatigue Analysis You are invited to participate. Further information is given at: http://www.savecenter.org/ Thank you, Tom Irvine

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I have put a great deal of effort into this Matlab package.  I offer it freely because NASA has already compensated me in a roundabout way.  But please send me an Email with feedback if you are going to use this software. Thank you, Tom Irvine Email: tom@vibrationdata.com * * * Here is a Matlab […]

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