Entry level FEA for composite keel grid ???

Discussion in 'Software' started by fcfc, Nov 17, 2010.

  1. fcfc
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    fcfc Senior Member

    What are entry level FEA systems that can do a composite keel grid analysis per ISO 12215-9 ? At what approximate price ?

    I have used time ago some scholar free FEA code, but were limited to isotropic materials and von mises failure criteria. Acceptable for steel (except buckling was an issue, if i remember well) but a bit limited for composite. Also, geometric data entry sligthly painful ...

    Thanks.
     
  2. Ad Hoc
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    Ad Hoc Naval Architect

    Technically any FEA software can do this.

    The problem you have with modelling composite is, the material properties are not isotropic. Often not even orthotropic. The behaviour of the material, whilst you may get “typical material properties” from manufacturers for each laminate and then the resin etc, how does it REALY behave?

    The FEA wont give you that. It will only give you a “theoretical” value, but is often incorrect owing to localised stiffness issues, but that also depends upon the software and how the properties are inputted for computation.

    Bottom line is, you still need to have “known” values. And the known values are of a layup that is the same or very similar to the one you are proposing.

    You will get composite techies tell you can FEA the layup…but they use endless values and fudge factors which you are not party to, for endless different reasons. Coupled with that, they will do their own in-house testing to validate the results, ergo, their fudge factors.

    So, the only way, is to make coupons for real mechanical testing. Test the coupons in each direction to obtain E for each plane. Then you can use these values as inputs into your FEA.

    Unless of course you are able to find an authority that is willing to accept a series of pretty pictures which has no basis for verification of the results and doesn’t care if the numbers are real or not.

    I always obtain coupons test first before I model composites in FEA. It is the only way to get real data for realistic results.

    And nevr ever read the results "between layers" and/or "through thickness"...how do you know these are real??....you don't. You can never strain gauge between the layers to verify it, not without huge sums of money and time, which of course you don't have. All you ahve are results of E for each direction/plane.

    PS...the one factor i forgot, the most importnat one....quality control. Two yards will never obtain the same properties of the same layup. Thus which value is correct?
     
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  3. fcfc
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    fcfc Senior Member

    I am surprised of the limited answers.

    How do small design office plan to comply with CE (in europe) or ISAF (everywhere) (both will require 12215-9 ) for sailboats within a few years ?

    Not only single skin GRP, but also plywood epoxy, strip planking, or foam cored.
     
  4. Ad Hoc
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    Ad Hoc Naval Architect

    It of course depends upon the Authority approving the structure. However, small design offices, if they are unable to calculate, or rather prove to the satisfaction of the Authority, that the deisgned structure is adequate (by their own methods), then they shall do what has always been done....they will subcontract this part of the work to others that can do it for them.
     
  5. fcfc
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    fcfc Senior Member

    Again...
    What structural software for small sailboats ???

    For what is the bunch of composite leisure craft absolute maximum length 80 ft (24m) but more average on 30 - 60 ft (9 -18m) ?

    Excel will have hard time to deal with keels outside the simplified case.
     
  6. Ad Hoc
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    Ad Hoc Naval Architect

  7. sorenfdk
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    sorenfdk Yacht Designer

    From time to time, some of us still use an ancient tool called "pen and paper" (and a pocket calculator!) ;)
     

  8. fcfc
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    fcfc Senior Member

    And the slide ruler .....:p

    But pen and paper (or even spreadsheets) are completely inadequate for keel structures, except the simplified case described in 12215-9 annexes.
     
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