FEA Carbon Prepreg Boat Hull

Discussion in 'Boat Design' started by an2reir, Jan 26, 2017.

  1. an2reir
    Joined: Sep 2001
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    Location: Chichester West Sussex UK

    an2reir fifty boat designs

    Hi there


    I am doing a testing by FEA of a carbon boat hull we made here in West Sussex

    [​IMG]


    The values I am using for mechanical properties of generic carbon epoxy prepreg laminate are as follows:

    Elastic Modulus 90000 MPa
    Poisson Ratio 0.27
    Tensile Yield Strength 915 MPa
    Ultimate Tensile Strength 862 MPa
    Ultimate Compressive Strength 848 MPa


    Your feedback will be greatly appreciated in regards accurate values of mechnaical properties of carbon epoxy prepreg laminate



    Thank you
     
    Last edited: Jan 29, 2017
  2. Ad Hoc
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    Ad Hoc Naval Architect

    No piccie?

    If you are doing a "real" FEA of your boat, then you need to make coupons of your layup and get them tested to establish the correct as-built values, rather than rely on any sales or theoretical values.
     
  3. gonzo
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    gonzo Senior Member

    Also, any laminate will have different values depending on the direction of the fibers. Are these values the lower ones?
     
  4. PAR
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    PAR Yacht Designer/Builder

    Yep, get out the drill and take some samples for testing. Your figures look like the usual published figures, which might be close to what you have, then again, might not. You'll never know without tests (bring your wallet). The first word in the acronym you've used, suggests this is required.
     
  5. SukiSolo
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    SukiSolo Senior Member

    Bit unusual to do the testing AFTER the hull has been built...

    unless to confirm the values of an FEA study with reality. More normal to test custom samples of the proposed laminate to enable a reasonable FEA model to be examined. Perfectly OK to test samples from the real build to confirm values. This seems to be reverse engineering the build structurally....
     
  6. TANSL
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    TANSL Senior Member

    I agree SukiSolo, doing tests with the finished hull can lead to unpleasant results. However, the ISO standard for example, considers this method as one of the possible evaluation levels of the mechanical properties of the laminate. In any case, obtaining samples with a drill for homologated mechanical tests does not seem the most appropriate.
     
  7. Alik
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    Alik Senior Member

    For testing of mechanical properties, samples cut from hulls can't be used. Read appropriate ISO standard on testing or any classification societies rules, usually there are 5 samples in each direction, for each area, and for some types of tests specimens are 1m long. So after such testing the hull can be scrapped.

    Advice: take CLT method from classification society (say, DNV-GL) or ISO12215-5, define properties of laminate, and run FEA based on these properties. If it is global strength study for catamaran, it is smart to limit the model to bridgedeck/raft structure only.
     
  8. amazon5
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    amazon5 New Member

    Ultimate strength?




    Tensile Yield Strength 915 MPa
    Ultimate Tensile Strength 862 MPa ???
     
  9. an2reir
    Joined: Sep 2001
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    Location: Chichester West Sussex UK

    an2reir fifty boat designs

    FEA Carbon Boat Hull and Structural Parts

    Hi there thank you for your feedback.

    I am fully aware that an accurate FEA of a composite carbon boat structure would of course require a specialised software
    that is capable of analysing composites.
    It is of course understood that testing by Finite Elements Analysis does work for isotropic materials and is no to be considered as reliable for non isotropic materials like the composites.

    It is well known and understood that the proper way to go about structural design is by making sample laminates and by having the samples of laminates tested- and of course that is before the design process.

    In full awareness of the above , I do however consider that the testing of the carbon structure by FEA by asimilating the carbon structure to an isotropic generic "ideal" material does deliver results that are relevant and useful to the design spiral


    I am doing two different thigs , and both of them may seem un orthodox but actually they do prove to be efficient

    1. One is I am working to establish a procedure of FEA based on 3D scan of already built carbon structure. In full knowledge of the limitations of this procedure that is to be applied to non isotropic materials, my FEA is in this case of a structure that is complex

    2.Two is I am testing by FEA structures that I design prior to their building. Yes, I will ask my carbon supplier for confirmations on my laminates mechanical properties


    I do however find very useful any feedback you may have on mechanical prioperties of carbon laminate

    And I thank those who took time to drop a few words
     

  10. SukiSolo
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    SukiSolo Senior Member

    One thing worth doing is to make laminate 'samples' ie same as build when doing the build. These can serve as accurate pieces for testing ie same carbon, same epoxy, same cure etc. These will act as a real verifier of the build. Sometimes metal samples ie aluminium extrusion/plate is kept back for the same reason.
     
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