Divinycell Testing

Discussion in 'Fiberglass and Composite Boat Building' started by Jolly Mon, Feb 16, 2020.

  1. Jolly Mon
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    Jolly Mon Junior Member

    I’ve made and tested some samples to get a feel for the materials. I made one sample that was 1’x 2’. It’s core was 2 layers of 1/4” divinycell h60 glued together with cabosil thickened epoxy. I squeegeed the “bog“ into all the “grain” of the foam and then painted on a little extra to ensure a good bond. After I put the two epoxied surfaces together I put it on a flat surface and added some weight to hold them in place while the epoxy cured. Both outsides were laminated with 2 layers of 1208. Neat epoxy was painted onto the divinycell before applying with 1208. Each layer of 1208 was wetted out individually and rolled out. Peel ply was added last. Some days later we took it to the parking lot and did our usual stomp test on it and it came apart. The divinycell sheared. Maybe our stomp test is too rigorous of a test for the size sample. I just don’t know. I’d love to know what you all think. I’ll attach a picture of the failed sample.
    Rob
     

    Attached Files:

  2. fallguy
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    fallguy Senior Member

    The divinycell is supposed to shear on a fabric pull, that is the goal and the weakest thing in the system. I am a little confused about what you are attempting to test. Stomping on something is a dynamic loading where the weakest compressive strength item would fail by getting crushed, if all items were of varying strengths and one was crushable per se. I don't know how to measure a stomp test, but let's say you are stomping 500 pounds of pressure onto a 4x4" area. That would be 500 pounds on 16 inches or roughly 30psi. That impact could be on a point or a corner of the heel and could be applied to a single square inch or less or roughly 500 psi. It is just too random to be very useful. Most hull laminates are not designed to be stomped on. Go stomp on just a piece of divinycell and nothing else and see what it does. I can guarantee it will crush. That is all you are testing.
     
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  3. Mr Efficiency
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    Mr Efficiency Senior Member

    The stomp was a weird, undignified dance craze banned in some buildings because it was feared it might cause structural damage. I'd say the picture does not look like any Divinycell I have used. What is the density ?
     
  4. Jolly Mon
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    Jolly Mon Junior Member

    It’s divinycell h60, 4lbs/ft3
     
  5. Jolly Mon
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    Jolly Mon Junior Member

    thank you for your thoughts and you’re exactly right about the gelcoat being heavy. I won’t be using gel coat . I’m considering coosa for the transom or HD urethane foam. I’m not sure what the difference is between them other than some fiberglass reinforcement. In old posts on this site, they’ve talked about urethane foam getting old and turning to powder. I wonder if Coosa is some different formulation?
     
  6. fallguy
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    fallguy Senior Member

    Coosa is 26#/cuft or more.
    HD urethane I doubt is that dense.

    All depends on horsepower plan...

    I am going to use a 12# density insert and a clamp board both on mine, but only gonna have a 2.5 stowed. If we are in a harbor; gonna make my wife row while I stand on the bow with a whip.
     
  7. Jolly Mon
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    Jolly Mon Junior Member

    I’m planning to go with a 9.9 Hp Mercury weighing in at 84 lbs. I’ll probably be attaching some knees to the transom and tunnel sides.
     
  8. Jolly Mon
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    Jolly Mon Junior Member

    Fallguy its all good but I think you’ve gotten the two threads mixed up. The one fellow is building an OC tender while I’m building a catamaran. I didn’t mention using 1/4” divinycell in my plans :)
     
  9. fallguy
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    fallguy Senior Member

    Yes I did in my morning haze. Let me go back and clean up my mess!
     
  10. KD8NPB
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    KD8NPB Junior Member

  11. Jolly Mon
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    Jolly Mon Junior Member

    KD,
    Thank you for your opinion. I’m curious why core to core is a no-no and why it would result in very low shear. In reading over the guidelines that you sent it says that bonding Airex cores to themselves generally dose not pose any problems.

    Rob
     
  12. Jolly Mon
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    Jolly Mon Junior Member

    97921371-EE80-438B.jpg
    At first I didn’t think there was anyway that sample was dry on the resin, but I believe you’re right. I found a publication from Diab’s technical center. I’ll try to attach the part about the bedding compounds.
    However for hand layups they’re talking about a layer of mat, 3/4 oz to 3 oz (230-900g) ft2 with 73-80% resin be used between the divinycell and the structural cloth to ensure a good bond.
    Wow! That’s some weight!
     
  13. fallguy
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    fallguy Senior Member

    in our early vac bag work; we varied core wetouts and found that it absolutely requires wetting and we use the prescribed rates.. the trouble for me is it wetouts best with a 1/8" paint roller and the roller drinks quite a bit of resin

    we are using Gurit core and wetout the core at 0.64#/yd^2 or 0.35kg/m^2 - those are Gurit rates

    The idea of using mat is sort of counterintuitive, but it probably resists peeling better. Still, who would want to...

    after wetting the core; I usually attempt to squeegee the 4-6 oz of resin it drinks...the losses are rather absurd if using epoxy at 80 cents and ounce and a 2.50 cent roller; you are throwing away 5-7 dollars each time.

    Yesterday I laminated 4 yards of 17-18 oz glass and my total resins were 78. A loss of 7 ounces in the roller would be 10%! I generally use the roller at the end for any dry areas. But plenty of rollers hit the can fully wet. Obviously, wet bagging has other losses not going into the part, but if I end up at 40% resin or say 28 ounces of resin in 4 yards of glass; I am throwing away 50 ounces of resin! If you hand laminate that with 3/4 oz mat; you would end up needing 100 ounces for the wetout and it all goes to the part for a staggering difference of 72 extra ounces of resins and 27 ounces more glass or nearly 8 pound heavier panels....

    corrections desired; I want to believe my numbers are wrong
     
  14. Jolly Mon
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    Jolly Mon Junior Member

    I got an email back from diab on bonding sheets of divinycell, but wasn’t able to share due to copy, share...blah, blah, blah.

    Regardless, the answer is YES you can bond layers of divinycell together. It does not degrade the strength of the foam and will make it a stronger bond than 100% foam.
     

  15. Mr Efficiency
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    Mr Efficiency Senior Member

    I wasn't clear on why he thought laminated cores were a problem either. Just extra work and weight though.
     
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