Nomex honeycomb core vs Divinycell

Discussion in 'Fiberglass and Composite Boat Building' started by Fgayford, Nov 30, 2011.

  1. Fgayford
    Joined: Nov 2011
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    Fgayford Junior Member

    To All
    If one were to make, lets say, a 1/4 thick panel. Carbon fiber inner and outer layers. Is there really any big strength and weight advantage using nomex honeycomb core over using infused Divinycell. (both epoxy)
    It seems to me that if there is only a bit more shear strength and lightness in honeycomb, the complexity of using it is not worth it.(I am thinking aircraft parts here.)
    Infusion is a one step process. The honeycomb is three and the cost is way up there. Thanks
    Fred
     
  2. rxcomposite
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    rxcomposite Senior Member

    You cannot infuse honeycomb. The resin will fill up all the empty cell of honeycomb.

    Honeycomb is best in aircraft parts and prepreg fabric. It has an equivalent strength in Divinycell but the shear strength is way too low for boat application. Besides, they don't use honeycomb for the hulls for obvious reason. Cabin sidings maybe usable.
     
  3. Fgayford
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    Fgayford Junior Member

    I meant that the Divinycell was infused and the nomex honey comb was done by bonding skins so the cells are not filled. I was told that honecomb core has a much greater shear strength than Divinycell. weight and cost are what I was after. in comparison to strength.
    Thanks
     
  4. rxcomposite
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    rxcomposite Senior Member

    Not exactly. In my data, Standard Nomex has 32 kg/m2, 0.36 Mpa shear strength and OX has 29 kg/m2, 0.32 Mpa shear strength comparable to Divinycell H30 which has 38 kg/m2 and 0.35 Mpa shear strength.

    But using shear specific (more strength per weight) the honeycomb is slightly better than H30. Except that I have not seen honeycomb with higher shear strength.

    It lacks the shear strength so use is limited to cabinetry and wall division in boats. It cannot take up the dynamic loads imposed on the hull.

    In aerospace application, weight is important so it is combined with high modulus skin and it works.
     
  5. rxcomposite
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    rxcomposite Senior Member

  6. groper
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    groper Senior Member

    the 144kg/m3 aramid honeycomb has a shear strength of 3.5Mpa down to the 29kg/m3 with a shear strength of 0.5Mpa...

    Only prepreg is compatible with honeycomb, and its very expensive... nuff said...
     
  7. latman
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    latman Junior Member

    I have made a few kayaks with 3mm OX Nomex and wet epoxy resin over 10 years ago and it worked fine , the main issue was to keeping resin webs bonding the core to the skins in a 5.2 metre craft with only 7 or 8 kg to play with. (overall it was a pain and i pursued 2-3mm PVC Foam or 1.5mm Spheretex cores after that)
     
  8. rxcomposite
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    rxcomposite Senior Member

    You can pre wet the fiber on a table with plastic sheet backing then flip it over and smooth over the hull with the nomex bonded. Remove the plastic sheet afterwards when the resin is partially cured. you do section at a time.
     
  9. Joakim
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    Joakim Senior Member

    I have been studying your "core shear formula" excel: http://www.boatdesign.net/forums/at...692-choosing-deck-core-core-shear-formula.xls

    I noticed that you have very low shear strength values for balsa. They seem to be only ~60% of these: http://www.gurit.com/files/documents/balsaflexwev1pdf.pdf Why is that?
     

  10. rxcomposite
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    rxcomposite Senior Member

    I googled whatever I can find in the net to complete the database which ranged from cardboard to styrofoam and anything I can find. Feel free to upgrade it for your use.
     
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