Divinycell vs Core Cell

Discussion in 'Materials' started by CatBuilder, Dec 23, 2010.

  1. AndrewK
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    AndrewK Senior Member

    Do you have brands and product codes for these high elongation VE resins?
    I want a resin that has an elongation greater than 5% at ambient cure, this is the main reason why I am using epoxy.

    thanks
    Andrew
     
  2. CatBuilder

    CatBuilder Previous Member

    :D:D When it's your life's savings... you know how it goes.
     
  3. War Whoop
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    War Whoop Senior Member

    LOL or your life.
     
  4. CatBuilder

    CatBuilder Previous Member

    Exactly!
     
  5. rxcomposite
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    rxcomposite Senior Member

    Andrew,

    Sorry I don't have listings. I throw away my material data sheet after 3 to 4 years because material specs changes every so often.

    Mine is a design guide after after which I search for the materials available. I have used VE Derakane 411 by Dow Chemicals though.

    Try asking War Whoop as he has used VE on his fast boats. Also when switching to higher elongation resin, check first the ultimate strength of the resin you intend to use. It is tensile strength that is important. My table shows that Derakane 411-45 has a higher tensile strength than Gouegon GLR 125. 11-12 ksi v.S. 7 ksi for epoxy.
     
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  6. rxcomposite
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    rxcomposite Senior Member

    Why are you looking for a resin with high elongation? Just curious.

    The E glass fiber has an ultimate elongation of 4.8%. The fiber and resin acts in unison. When the fiber stretch, the resin should stretch at more or less the same rate.

    If you use brittle resin, the resin cracks first before the fiver breaks giving you a very low overall laminate tensile strength. Inversely, if you use high elongation resin, the fiber will break first before the resin. Unfortunately, most ambient cured resin is only 10-12% of the fiber ultimate strength. So a fiber with 100,000 psi will have a laminate (resin + fiber) property of only 10,000 psi.

    Have you considered post curing process? some epoxy doubles its strength and ultimate elongation when post cured and surpasses postcured VE.
     
  7. Ad Hoc
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    Ad Hoc Naval Architect

    I’m no composite expert, however, having gone through the same exercise myself and now having a 16m composite catamaran currently being built and approved to DNV rules, some basics are worth noting with composites. If you’re aware of these my apologies, but I don’t deal with composites day in day out, thus had to re-educate myself again.

    An “ideal” resin has a curve with a high UTS, high stiffness and high elongation to break. So initially it is stiff (elastic region), but, will not suffer from brittle failure. The plastic region of the stress/strain curve is much greater than the elastic region.

    Epoxy has a ‘typical’ elongation to break of around 8%*. But more importantly the plastic region is much greater than that of polyester (~3%*) or vinylester (~4.5%*) which is near non existent. Thus epoxy with a large plastic region tells us it is tougher and more resilient, and therefore it is ‘easier’ to match elongation of the resin to the fibre. (*figures are nominal)

    So having 4.8% may sound ok, but the plastic region, or elongation in the plastic region, is very small and thus may not be ideal for high performance.
     
  8. fcfc
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    fcfc Senior Member

    One thing that surprise me, is in ISO 12215-5 2008, scantlings.

    They give tabulated data for different fibers (mat, roving, UD, double bias etc ...). They give tabulated data for core (Generic cross linked PVC, and within that group Rigid PVC I, rigid PVC II).

    But for resin, they are dry. Only polyester. Not even a word on vinylester or Epoxy.
     
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  9. War Whoop
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    War Whoop Senior Member

    Most of the Vinylesters we used have elongation in the 6% range and work just fine, I build highly stressed cored structures and have done well with them,sometimes we can be oversold on resins.
     
  10. rxcomposite
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    rxcomposite Senior Member

    Thanks Ad Hoc. That was very informative. Now I have a deeper understanding of how high elongation resin behave.

    I probably did not express myself well. The “brittle” resin is the polyester group with a short toe or plastic region. The “tough” resin are the VE and Epoxy whose elongation is nearer to that of fiber (4.8%). To expound further, failure does not occur in the microcracking range as the mutual influence of the matrix and fiber extends the failure. I am attaching the graph of Azo Composite fig. 2 and fig. 3 for the others to see.

    I am also attaching the graph by Composite Fabrication on the curve of pure resin and a laminate. While not exactly what we are discussing, a little imagination will do to see how the longer elongation resin fits the laminate curve.
     

    Attached Files:

  11. CatBuilder

    CatBuilder Previous Member

    Does anyone know the proper temperature to heat form Core Cell at?
     
  12. AndrewK
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    AndrewK Senior Member

    The reason for wanting >5% elongation comes from a composite design book I read.
    It stated that the basic requirement for a good laminate is that the matrix elongation should be greater than that of the reinforcement, so in case of e-glass >4.8%.

    It further argued that local strains can be in excess of 8 times the bulk strain.
    Say you have a laminate designed for 0.5% bulk strain then you can have local strain >4.0%. So if you want a good quality tough laminate without high temperature post cure epoxy resin is the only choice for me so far as the locally available VE elongation is 3.5%.

    I do post cure at low temperatures up to 65'C but I prefer a resin where this is optional not mandatory.
     
  13. War Whoop
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    War Whoop Senior Member

    A-500 foam 65 C would be a good starting point, maximum would be @120 C there is a learning curve here and people get away with heat guns in some cases.
     
  14. AndrewK
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    AndrewK Senior Member

    Which grade corecell?
    For corecell A my supplier said not to exceed 75'C, also only recommends up to 65'C post cure.

    You can get the data sheets online.
     

  15. War Whoop
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    War Whoop Senior Member

    Thermoforming ,Depends on who you talk to.
     
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