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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 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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Here is a Matlab GUI multi-function signal analysis package: vibrationdata.zip The main script is: vibrationdata.m The remaining scripts are supporting functions. This is a work-in-progress. Some features are not yet installed but will be in a future revision. Please check back for updates. * * * Currently installed features include: autocorrelation & cross-correlation Bessel, Butterworth & […]

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Here is a paper for… Extending Steinberg’s Fatigue Analysis of Electronics Equipment Methodology to a Full Relative Displacement vs. Cycles Curve electronic_rd_n.pdf extending_Steinberg.pptx This paper also shows in a very roundabout way that “fatigue damage equivalence” between sine and random vibration occurs when the sine amplitude (zero-to-peak) is approximately equal to the random vibration 2-sigma […]

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Matlab MEX

Matlab is a great programming language and environment because of its ease of use, great visualization, and rapid prototyping abilities. Matlab has a feature called MEX, Matlab Executables.   See:  Matlab MEX Introduction MEX files allow Matlab scripts to call user-supplied functions written in C/C++ and Fortran. * * * The first step is to install […]

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Launch vehicle avionics components must be designed and tested to withstand random vibration environments.  These environments are often derived from flight accelerometer data of previous vehicles.    This data tends to be nonstationary as shown in the figure above. The typical method for post-processing is to divide the data into short-duration segments.  The segments may overlap.  […]

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