Which Carbon Fiber to choose?

Discussion in 'Materials' started by Erwan, Dec 21, 2019.

  1. Erwan
    Joined: Oct 2005
    Posts: 377
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    Location: France

    Erwan Senior Member

    Hi
    In order to make a beach cat spar with carbon, I don't know which of these 2 carbon fibers will best fit the spar?
    In this project Reliability in a capsize is more important than saving a few 100 grs.

    So here are the 2 carbon fiber candidates:
    1-FIBER A Tensile Strength: 4137 MPa Tensile Modulus: 242 GPa Elongation @ brake: 1.5%
    2-FIBER B Tensile Strength: 4900 MPa Tensile Modulus: 230 GPa Elongation @ brake: 2.1%

    Any advice or comments are welcome

    Best regards & Merry Xmas

    EK
     
  2. ziper1221
    Joined: May 2018
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    Location: florida

    ziper1221 Junior Member

    I'd assume you'd want the second one. Higher ultimate strength, and a little less stiffness doesn't matter because you want the spar to bend to alter sail shape anyway.
     
  3. Erwan
    Joined: Oct 2005
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    Location: France

    Erwan Senior Member

    Thank you Ziper, for taking time to answer,
    In fact it is the bottom part of the tube/spar inside a little wing-sail around 14 m^2

    It is a circular section around 90 mm diameter & 5700mm long.
    The point is to minimize bending under load, otherwise, it is impossible to control the AoA.
    Torsion load must be addressed too, as it is the twist control of the wing.

    The top part of the wing spar will be the top part of a North Platinium serie 100% carbon.
    a very cost effective solution, and stiff enought as I tested it with a serie of bottles of water more or less full in order to mimick the top part of an elliptical aerodynamic spanload distribution.

    In fact I dont want it to bend; Instead I prefer it remains straitght under load and more forgiving in a shock, that is why, intuitively I would have chosen the second one too.

    But I am embarrassed not to have a rational explanation to support this choice.

    Best Regards
    EK
     
  4. ziper1221
    Joined: May 2018
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    Location: florida

    ziper1221 Junior Member

    Will it be stayed or free standing? I know the typical construction is to have a round spar, upon which the wing can twist, but I've been thinking about building one where the skins takes up the loading, for better sectional properties. Perhaps I could get the structure to twist like an I beam, but more likely I think the leading element will have to be mostly rigid and the twist would only come from the aft element.
     
  5. fallguy
    Joined: Dec 2016
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    Location: usa

    fallguy Senior Member

    How do you determine the number of layers of carbon?

    just curious...
     

  6. Erwan
    Joined: Oct 2005
    Posts: 377
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    Location: France

    Erwan Senior Member

    It will be stayed with a bearing-ball system at 5700 mm height.
    Above I will plug a windsurf mast like the top part of a 5200mm NORTH platinium serie.
    Total span will be 5700mm + 2300mm+ a little tip extension = 8550mm

    You are right, a cost effective solution is to build a normal wing with non twistable longeron for the first element and manage the twist with the second element (flap).

    In my plan there is only one element with a morphing section, as a result the only common points with existing wingsails is 1-the 2 vertical spars inside,
    2-the loads which depend mostly on righting moment.

    Very good question FallGuy.
    I sized the bending with EXCEL, then I add one 90° inside + 1 one outside.
    Then from a total weight target, derived from real world datas, I allocate the difference in weight for the 45° .
    A bit redneck-tech for sure!
    Of course I should run matrix calculation with Classic Laminate Theory, but I am tired
     
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