lamination shear strength

Discussion in 'Fiberglass and Composite Boat Building' started by powerabout, Aug 12, 2008.

  1. powerabout
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    powerabout Senior Member

    Does anyone know where I can find the shear strength of a solid lamination re pulling bolts through it in shear.
    I would prefer not to include data for kevlar and carbon so woven biax etc
     
  2. TollyWally
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    TollyWally Senior Member

    I see from your various posts it looks like you are puzzling over how big a load through bolts can handle before ripping through a hull skin. Perhaps rigging loads etc.

    Just thinking out loud, perhaps you could laminate a chunk of metal within your laminate schedule. A strap captured within then drilled along with the usual precautions might take a pretty big load.
     
  3. powerabout
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    powerabout Senior Member

    TW
    I will repair my boat with the same stuff as it was when new as they dont have a problem. ( it rotted)
    My interest is how did the designers come up with the ubiquitious chain plate that any structual engineer would tell you is very poor design.
    The boat structual designers must have also known how much strength they expected in the plywood which not being a homogonous material would vary tremendously.
    Or are they relying on the lamination?
    The more I ask and the more there is silence is no surprise in the yacht industry (guesswork)
     
  4. PAR
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    PAR Yacht Designer/Builder

    Your question seems simple enough, but there isn't a quick and easy answer for you. Calculating panel, laminate, scantling or hard point loading can get quite involved. What boat do you have (make, model, year)? This would go a long way toward helping address you concerns, as it's likely one of us will have scantling and other design information in a data base, possibly with other related information, such as common flaws, design alterations and corrections, model run changes to address issues, etc.

    The questions you pose about sheer and pullout strength are covered in several engineering texts and is included in many software packages.

    Engineers, NA's and designers make mistakes, just like everyone else, though lives can possibly be at stake, so careful checking and rechecking is usually preformed. When issues arise (they always do) then updates and alterations are incorporated into the spec's of a particular project. Plywood is a homogonous material as is cured resin. Plywood is also stronger then steel, pound for pound.

    So, if you provided the boat type, it's likely we could tell you if it was an issue, what was done about it and how well these "fixes" addressed the problem.
     
  5. powerabout
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    powerabout Senior Member

    Par
    it a J24
     
  6. TeddyDiver
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    TeddyDiver Gollywobbler

  7. Manie B
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    Manie B Senior Member

    Please post pics of the "rotted" area

    i am very surprised at this thread - seeing that it is a J24 of all boats from a big builder
     
  8. powerabout
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    powerabout Senior Member

    Its made in the 80's and with slack production plenty of them from this era have rotted bulkheads and decks
    Large fleet has nothing to do with quality build that is just marketing and almost every large fleet is the same.
     
  9. PAR
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    PAR Yacht Designer/Builder

    Considering the large family and focus available for these boats, I'm surprised you haven't found a "group" that have addressed these issues before. I'm familiar with the issues and location you're having problems with, but most just reinforce the laminate, either with more plywood or other material, then increase the laminate schedule in the general area.

    Delaminating bulkheads, rotten decks, pulled chain plates are typical, especially on a boat that likely had the first half of it's life strained hard on the race course. This is a pretty normal affair in a 20+ year old racer.
     
  10. mongo75
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    mongo75 Senior Member

    In an attempt to keep it simple, why not just laminate the bigest piece of 1/4" aluminum you can fit under the bolt? Yeah that might be more than necessary, but it'll take any questions of structural integrity out of the loop.
     
  11. powerabout
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    powerabout Senior Member

    mongo75
    yes that would work if the sheet of aluminium was also bolted to the bulkhead in enough places to exceed the chain plate holding force.
     
  12. PAR
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    PAR Yacht Designer/Builder

    I don't understand the problem. Grind a healthy taper, use plywood (better bond then aluminum with epoxy) to span the void, well bedded in thickened epoxy (silica and milled fibers), then use multiple layers of biax to tie the repair into the surround area. The high modulus fabric and the epoxy will over come the short falls of the polyester resin and mat originally used. The area will be stronger and less prone to rot or moisture ingress.
     
  13. powerabout
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    powerabout Senior Member

    what I wanted to know was where do I find the data on a various solid laminations and their shear strength with various bolt sizes.
    I have this data for plywood but not laminates.
    Are all the boat builders just guessing when they design chain plates?
     
  14. fcfc
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    fcfc Senior Member

    You can find some data there : ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19880005638_1988005638.pdf

    You can probably find standard values strength in compression, tension and shear for marine composite in ABS ORY.

    You are probably right that before this publication, boat builders were just guessing. Most serious one were simply trying various bolting patterns and layup, and selected the one that did not fail. Without understanding why some failed, and others not.

    The next step, now you have a way to transmit your force from metal chainplate to the entry point of a composite structure, is now to compute the strength of your composite structure up to the canceling force (probably ballast counteracting). This is also wild wild guess.

    I fear only recently and only very big names rely on composite Finite Element Analysis to rationaly compute things.
     

  15. mongo75
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    mongo75 Senior Member

    I looked through that document, and now the smoke alarms are going off, from the smoke coming out of my ears. uuuuhhhhh........ LOL
     
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