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Automated Air Force Lug Analysis

  1. Jun 13, 2016 #1
    Air Force Lug Analysis (section 9 here and summarized here) seems to be the best generalized method for comprehensive lug analysis. However, it relies on charts developed by the USAF in the late sixties. Every source I've found on the method uses those same images.

    I'm trying to make an automated solver using MathCad (though excel, matlab, mathematica, etc could easily do it). But that relies on my code being able to read the charts or solve the underlying empirical equations.

    Does anyone know what the source equations are for these charts or whether there is software that can solve them? The only thing I've thought of is plugging each curve into excel and then running through a best fit curve of each different equation type until I find something that fits well. This just doesn't seems precise enough to me.

    Thanks in advance.

    PS: any tips on how to improve the post are also appreciated

    Edit: Attached is a first pass at 1/40 of the excel method. The original chart is underlain

    Attached Files:

    Last edited: Jun 13, 2016
  2. jcsd
  3. Jun 13, 2016 #2


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    Peterson's Stress Concentration Factors has a section detailing lug analysis. Although it doesn't seem as thorough as the AF reference, it may give you a reference paper to follow-up on regarding any charts provided. I have found that some reference charts/curves in this book (and so possibly in the Air Force reference) are empirically derived, it may be there is no equation to solve unless you fit a polynomial curve to it...
  4. Jun 14, 2016 #3
    Yeah I figured that was the issue I was just hoping someone had the original empirical data but realistically I just wanted to know if anyone had curve fitting software recommendations. I used http://arohatgi.info/WebPlotDigitizer/ but if I had matlab installed I'd probably use that
  5. Jun 14, 2016 #4


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    Curve fitting to empirically derived charted data of unknown quality is not a good thing to do .

    You could use FEA to generate all new data which could be validated properly .

    Personally though with FEA available I would just use it direct .

    For frequent use and/or use by non FEA specialists it would not be too difficult to set up a parametric general model and have a simple spread sheet plus graphics front end for data entry and results display .

    Some FEA software allows extensions to be embedded for specific applications . This would allow you to control the entire model generation , analysis and results display from a simple pull out data entry box on the standard FEA viewing screen .
    Last edited: Jun 14, 2016
  6. Nov 10, 2016 #5
    The site that you linked to that summarized the Air Force Lug Analysis method includes a lug analysis calculator. The calculator is based on the Air Force methodology and uses all of the charts that you mentioned. This calculator is simple to use, and it generates a formatted report as part of the output which includes the equations used and the charts specific to your analysis. You can find the calculator here:
  7. Dec 16, 2016 #6
    I have been using the software available here:


    The software assumes you are familiar with the foundation of lug analysis but is very efficient. The documentation indicates it uses the USAF method.

    Best of Luck!
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