Laminate stack calculation

Discussion in 'Class Societies' started by willfox, Mar 20, 2012.

  1. willfox
    Joined: Oct 2008
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    willfox Junior Member

    I was wondering. If you had a stack of differing plies, e.g. Glass uni directional, CSM, double bias, quadrax etc.and were going to test them in tension once laminated. They all had slightly different fibre weights which effected their ultimate tensile properties and E value. With the values of their E values and ultimate tensile loads you can find the strain. You can then see the limiting strain which will be one of the plies. You can then set the strain for the remaining laminates to this limiting strain. Using the E value, you can then calculate the maximum stress for each ply before the first ply fails. If you know the thickness and the length of each ply, the tensile area is known. Then can you use your calculated limited stress and area to work out how much force each ply absorbs. This is then sum-mated and therefore gives your achievable force before the first ply breaks? Does this sound plausible?
     
  2. tunnels

    tunnels Previous Member


    Jesus i been working all these years and never knew laminating could be so difficult !! All of what you have written makes no sense at all .why would any one want to know such useless impractical information as that !! Is tv boring where you live ??, are you having trouble sleeping at night??? ! Maybe you need a change of diet or even a new hot randy women in you life . wow i cant belie:eek::confused::?::idea:ve that !!
     
  3. willfox
    Joined: Oct 2008
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    willfox Junior Member

    Yes, I'm a divorced insomniac living in a shed with wifi.
     
  4. tunnels

    tunnels Previous Member

    Hi got ya !!
    Me im and old bugger twice divorced and six kids !!Im shacked up with a horny energetic randy chinese women and loving every minute of it !!
    Glassing is simple !! keep it simple and you stay out of trouble !! once you lose the plot and get into complicated mumbo jumbo go light the bar Be and crack open a cold one and watch the stars . Glassing is simple so keep it simple !!
    what works works well if ya get it wrong it will break , how simple can that be !!
    :)
     
  5. rxcomposite
    Joined: Jan 2005
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    rxcomposite Senior Member

    It is called the "maximum strain theory". You arrange the stacking sequence in a table and calculate the thickness, the elastic modulus, the force, and finally the strain. The laminate with the max strain exceeding the allowable fails. Please note that in the attached illustration (Composite Aircraft, M. Hollmann), the modulus is dependent on the orientation of the ply. Ply strength/stiffness varies depending on ply orientation.

    If you are going to test for transversial load, the arrangement is the same except longer and more complex. You will have to find the neutral axis and the direction of load, the maximum bending moment, ect. The strength of the the ply will not be symmetrical as one side (from the neutral axis) will be in compression, the opposite in tension. It will be in quadratic equation, arranged in an excel table. This is the "progressive failure analysis theory" or "first ply failure theory" depending on what you are looking at.

    Or you can use the "rule of mixture" where it assumes that the total stiffness/strength of a laminate is equal to the sum of the products of the stiffness/strength of each ply times its thickness divided by the total thickness of the laminate.
     

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  6. thudpucker
    Joined: Jul 2007
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    thudpucker Senior Member

    Holy Cow! RX is as Serious as an Engineer!

    I was thinking of the beginnings of engineering doing calc's of Beams as I read the question.
    With a bunch of Books full of tables and a Slide Rule, that Calc would be a week long nightmare.
    It's be interesting to find out what he was going to use as an Anchor for the 'other' end of the Composite Beam he's proposing.

    When a Beam like that fails, the "CRAAK" would shock your hair to stand up!
     
  7. tunnels

    tunnels Previous Member

    Baffel them with science thats the story matey !!

    You asked the question and opened pandoras box and out pours the answers !! wont make head not tail of any of it but its there . the old story if you cant convince em confuse em applies here . computers cant even make a simple cup of coffee so how the hell can you get a simple straight answer out of them .Theres a million laminate scheduals to make almost any sized boat and they will all work !! Just some are better than others put them all in a hat and draw one out !! Its will work !! Why shouldnt it work ?? its only there to keep the water out !! :confused::?:
     
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  8. rxcomposite
    Joined: Jan 2005
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    rxcomposite Senior Member

    I do that for a living but when the numbers bugs me. I resort to this. Hehe
     

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  9. tunnels

    tunnels Previous Member

    Good one !!:D
     
  10. ABoatGuy
    Joined: Aug 2004
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    ABoatGuy Member

    And you have to let the guys in the shop glue it up . . . you will take too much time and do too good a job.
     
  11. tunnels

    tunnels Previous Member

    Making a good job and understanding the workings of the laminate stack becomes second nature and is a mind set !! Thats all !!
    Its like breathing ! do you have to think about breathing ??
    Like listening to a machine doing a particular job when something happens you know instinctively because the sound changes .
    Glassing is the same !! immediatly you look at a particular boat you know instinctivly what the schedual of the laminate for the hull could be .
    Decks are the same and hardly ever change just the size of the mould !
    I have spent the last few months doing the same with hull lay ups for the boats we make the formular for the laminates is the same for each hull just the number of layers changes . :?: :D
     
  12. meren
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    meren Junior Member

    Laminate stack analysis... There are some standards like ISO 12215-5 (annex C, H) to give assumptions in case there are no material tests made or if made what ever... Just put the data in for both or all of three "directions" ... as You will. And You'll get the answer which of the plies fails first. Remember that After all the hard work, the calculation is just the fairly rough estimate of the optimum stack of plies for the application You design.
     
  13. tunnels

    tunnels Previous Member

    Have i got a small spanner to drop in the works ??

    With all the tests and figures that pop up we are asuming that all glass is the same strength !!,every fibre from every molten pot of hot and sticky is the same and every bundle of fibres has the same number of strands and everything is equal and the same !!.
    Dont think so !!!! there must be a % to be added or subtracted from the testing !!.
    Ok so making panels for testing is done by weight but whats stronger a big bundle of big fibres or lots a small bundles of smaller fibres ?? so the weight is the same .
    So does that put the spanner anywhere near the working parts ??

    So glass fibres made in china are exactly the same in every way possible as fibres made in USA or India or Ireland or even Australia ?? Dont think so some how !!
    What about kevlar ? its man made and every batch is exactly the same as the hundreds of batchs before , And Basalt fibres are the same no matter what part of the world the raw product comes from ??
    Am i being a little picky or what ?? :confused:
     
  14. TANSL
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    TANSL Senior Member

    Please, see attached Table, according ISO 12215-5
     

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  15. rxcomposite
    Joined: Jan 2005
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    rxcomposite Senior Member

    You are quite right Tunnels. The basic calculation for the strength of the fiber takes into account the diameter of the fiber and the length of the fiber before it is bundled.

    Luckily for us, the manufacturer/weaver furnishes the data of the finished product so we only have to worry with the resin volume fraction and the strength of the resin we wish to use.
     
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