Some questions about ISO 12215-5: 2019

Discussion in 'Class Societies' started by TANSL, May 7, 2021.

  1. rxcomposite
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    rxcomposite Senior Member

    There must be something wrong in the equation, a typo error or something or the ISO has deviated so much from the basic principle. The basic equation for a bending moment is p l^2/12 with l being the length which can be either the short side "b" or the long side "lu". 12 being the divisor for a fixed end beam.

    The basic equation can be further modified by the addition of correcting factors for curvature of panels and aspect ratio correction, thus:

    (1/12) * curvature correction * AR factor * pl^2. The (1/12) * 1000 is the 83.33 factor the old ISO uses for the bending moment. This is replaced by the alpha/beta equation for a 2 way bending rule method of analysis. Bending moment rule ISO.jpg

    So the question is what is the new ISO about?
     
    Last edited: Oct 24, 2021
  2. rxcomposite
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    rxcomposite Senior Member

    The only thing that will change a lot is the (1/12) bending moment factor because it depends on the fixity of the edges. For a fully fixed edges, it is 1/12, for a partially fixed edge, it can be 1/10. 1/8 means it is not fixed to anything. What can go lower than 1/8? See post #61.
     
  3. TANSL
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    TANSL Senior Member

    @Ad Hoc, what I do, and I do it with total honesty, is to offer a calculation tool that follows, almost to the letter, the procedures indicated by the ISO. And I say that almost to the l,etter because I try to correct the errors that the ISO has, and it has some. I am not a scientist, I am not trying to explain the theory behind the ISO procedures, all I tell the buyer of my software is that instead of doing the calculations by hand, he should use my software. When the ISO says that two variables be multiplied, my software does it for the user, avoiding the work of doing it by hand, giving the user a certain assurance that the multiplications are well done, and saving him a lot of time in uncreative operations, so that he can spend his time coming up with solutions. I am not trying to charge a fee to explain the theory of continuous beams or thin plates under bending. I only charge to facilitate some calculations. If someone does not know where a formula comes from, I will try to help, but will not charge for it. If anyone has a question about how the ISO does it (not why it does it), I try to help, free of charge.
    Have you used any CAD / CAM software that teaches its users the theory behind it?
    I'm wrong sometimes, like everyone else, but I don't lie, I don't cheat on anyone, and I always, always try to be honest and considerate with my clients. You have no need to try to tarnish my image.
     
  4. Ad Hoc
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    Ad Hoc Naval Architect

    So you place disclaimers that the results of your software may not be correct, because you are not sure why certain coefficients are used nor how they are applied?
     
  5. TANSL
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    TANSL Senior Member

  6. rxcomposite
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    rxcomposite Senior Member

    Thanks. That is the uncorrected one?
     
  7. TANSL
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    TANSL Senior Member

    I think so but, I cannot assure you of anything. All I can say is that using the formula as it is, you get results that don't seem logical. I do not know anything else and therefore I cannot offer clarifications to something that I do not know where it comes from. I have analyzed it according to other formulas relating to thin plate theory and I don't see much similarity :(
     
  8. rxcomposite
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    rxcomposite Senior Member

  9. TANSL
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    TANSL Senior Member

    That (Paragraph 6.- FORMAL IMPROVEMENTS) is what I have used to correct some things in my software. But as you can see, Mr. Soupez says what needs to be corrected but he does not explain further.
     
  10. rxcomposite
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    rxcomposite Senior Member

    It must be official then and that is what ISO 2019 is using.

    I can only compare the methods. LR uses the 1/12 and the k constants to modify p s^2 formula.

    Other CS uses it too, in various forms like BV, ABS, ISO. Robin Loscombe has published an excellent study on the forms of bending moment equations in an article on Professional Boatbuilder's magazine April/May 2017 issue. Even the Timoshenko and ISO 2 way bending rule was covered. He has been involved in the development of ISO 12215 so he is an authority too and should give light to the method.

    The Excel version is no longer available but managed to get one early.
     
    Last edited: Oct 26, 2021
  11. rxcomposite
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    rxcomposite Senior Member

    Uh oh! Souppez has a
    "9. DISCLAIMER The views expressed in this paper are those of the author only and do not necessarily reflect those of the ISO/TC188/WG18. All information presented are for guidance only and do not replace compliance with the relevant regulatory framework and applicable requirements."

    Let's see if ISO corrects its new publication.
     
  12. Ad Hoc
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    Ad Hoc Naval Architect

    That's what disclaimers are for... as previously noted :p
     

  13. rxcomposite
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    rxcomposite Senior Member

    If you want to be a designer of composite Formula boats, Aerospace, or at the very least, satisfy the New Generation ISO 12215 – 2019 edition Developed Method as put forth by Souppez, here is the Classic Lamination Theory. Be forewarned though as it involves quadratic equations and matrix algebra. The learning curve is steep and may require some effort to understand the spreadsheet. Fortunately, there are useful tutorial in YouTube.

    https://aerospaceengineeringblog.com/wp-content/uploads/2016/01/General-Laminate-Analysis.xls

    Introduction East Carolina University



    What it boils down to is that you need a good data on material mechanical properties. At least 4 basic in tension + 4 basic in compression plus two more, the positive and negative shear strain.

    To obtain good mechanical property data you need coupon testing. I remember ISO requires 5 samples of each test. Actually, 7 samples. You throw away the highest and lowest values and get the mean of the remaining 5. Expensive.

    The Tsai-Hill and Tsai-Wu mentioned in the press release is not part of the spreadsheet but can be programmed as well in Excel. It is a method of finding the safety factor given a set of data, ie, the mechanical properties and the load you wish to apply. This applies only to single ply laminate.

    If you want to investigate single ply or crossply or woven rovings, use the Engineering Constants that I have posted here in the forum sometime ago. For exotics like Kevlar/Carbon, Triaxial, Quadriaxials, use the matrix algebra and the ABD matrix provided in the CLT spreadsheet.

    Tsai Wu



    Tsai Hill- University of Cambridge
     
    Last edited: Nov 13, 2021
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