Maximum permissible glass content

Discussion in 'Class Societies' started by Deep6lue, Sep 10, 2019.

  1. Eric ruttan
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    Eric ruttan Senior Member

    lol. 79% is the area of a square minus the area of a circle of the same diameter. It's pretty basic.

    Its like a high school SAT question for the rest of it.

    I said it is a theoretical max.

    The problems with prepreg are obvious. Thick, cold, over epoxied fibers are stacked and layered. That obviously leaves trapped air that distorts fibers as it adds voids.

    Now if you build a thick steel autoclave and heat the thing to several hundred degrees and put 100 tons on it, you can crush those voids and squeeze out all that extra resin. And that will force the fibers back in place.

    However, if you dry stack and vac, the fibers are locked in place. Let in a proper low viscosity epoxy and it just fills the voids.

    Way better than prepreg without an autoclave.

    No, I'm not gonna go find a paper. Its simple physics.
     
  2. rxcomposite
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    rxcomposite Senior Member

    Opinions are welcome in this forum but should not be presented as facts.
     
  3. fallguy
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    fallguy Senior Member

    Oh, I well understand the area of a circle vs a box of the same diameter, but there is no fabric woven in the fashion you suggest.

    So, it is wrong to post theoretical, invalid maximums.

    Boat building is hard enough without errant information. If anyone tried to build to that number the laminate would fail. Keep in mind no bond between parallel fibers would also be a problem.
     
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  4. Eric ruttan
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    Eric ruttan Senior Member

    No.
    Given you are;
    comparing a lower ratio to a higher ratio.
    Have fully wetted the fibers.
    Thr epoxy and fibers are selected for the needs.

    Higher ratios, assuming above are always better. And they are cheaper than wasting resin.
    if you could have each fiber coated in a one molecule layer of epoxy, that would be perfect.
    As a mind experiment it may be possible to imagine pressures so high the one molecule layer is pressed out, but that is not really possible. At the molecular scale those forces are quite strong compared to macro pressure force.
    given the above, why would they?

    I would like to address @gonzo 's point above.

    While it is true that additional toughness can be observed with richer epoxy laminates, it is almost always better to have the laminate (fiber and epoxy) engineered for toughness, and get a higher ratio. A tough epoxy layer one molecule thick is the toughest.
     
  5. Eric ruttan
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    Eric ruttan Senior Member

    Is not uni pretty much that?
     
  6. fallguy
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    fallguy Senior Member

    3B6FF0DD-4405-48CE-B064-4B2CFB0C4F54.png Here is a cross section of uni carbon of sorts. The problem with your theory is a molecule of epoxy won't bond neighboring fibers because they are not touching each other or even close really.
     
  7. Eric ruttan
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    Eric ruttan Senior Member

    Ah, anecdotal evidence to refute theory.

    I bow before your wisdom.
     
  8. fallguy
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    fallguy Senior Member

    Your theory is not reality. The anecdote is not one, but all fabrics. The anecdote is presented to explain reality.

    RX-why not give Mr. Ruttan the data? Then he can reflect on one paragraph of being right in an entire world of glass fabrics that do not live up to pie divide 4?

    Or this could work.

    I pardon you knave.

    Actually, thanks Eric.

    RX sent me a whitepaper and I realized my tested vac sample weights are perfect or just a tad rich for .405 fiber volume content which is typical for biax and triax. I have been nervous about starvation for awhile now. It is actually quite scary to run near ideal maximums and you do end up with some microvoids. Another shot of reality against the theoretical world.is laminating defects at maximums...

    To complicate your theoretical maximums; adding a core also requires more resin.... pretty common now as well. All my work is with core, so my tad rich is probably related to filling core surface....

    Sorry if this wandered. Too sleepy...
     
    Last edited: Sep 18, 2019
  9. gonzo
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    gonzo Senior Member

    Eric:
    You contradict yourself by stating that
    In fact, a higher resin content can be used to engineer a tougher laminate. Engineered laminated are not equivalent to low resin content. Further, toughness is a measurable engineering characteristic of a material. Unless you have test results available, it is only the type of anecdotal claim you so much deride.
     
  10. Eric ruttan
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    Eric ruttan Senior Member

    hi gonzo.

    Can you show me anywhere where the composite engineering suggests one should raise the epoxy fiber ratio get better toughness?
    I have only seen the suggestion to use a tougher epoxy. So that would be informative.
     
  11. Eric ruttan
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    Eric ruttan Senior Member

    Are you suggesting all laminiates look like this?
    Are you suggesting this is an ideal laminate?
    Are you suggesting you are getting good ratios?
    The windmill guys get over 70%. How does you .405 compare to that?
     
  12. fallguy
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    fallguy Senior Member

    No laminate is pi/4 tight.

    No. But it is also not imperfect, but typical.

    Yes, but not bragging, just glad I am not dry.

    .405 is cross sectional fiber content...not the ratio of glass in a laminate by weight...pretty sure you are a bit apples and oranges there, but 70 percent by weight is far, far from a .78 fiber content...stitched unis are more like .432 per the whitepaper RX sent me and .432 fiber volume equates to 65.5% by weight for a assumed 2.5 delta on glass density v resin.

    We can work backwards to get to your 70% citation, but we will never get anywhere near pi divide four for fabric content. I am assuming, knowing zilch about fabic or methods used in windmills, that they are pushing fiber content and using a custom fabric that will still wetout or using pressure. Edit - or just a woven uni ?under vac it appears after some math...

    Another thing you forgot is a tightly packed laminate will not flow resin... Anyone with building experience understands this issue. More fibers is harder to wetout. Builders experience this phenomena quickly, although wetout is not only affected by fiber volume..

    Working backwards to a custom uni for windmills to meet 70 percent by weight with vac would give a fiber volume of .482, which is still nowhere near pi divide 4.

    40-50% fiber volume versus 78.5% fiber volume is not anecdotal Eric, but fact...
     
    Last edited: Sep 18, 2019
  13. fallguy
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    fallguy Senior Member

    Also, according to RXs sheet, the ultimate cross sectional fiber content is from prepeg or autoclave unis and they are getting 58.4% fiber volume which is really great, but still 20 percent less than your ideals.

    And I am only mentioning it for the discussion. I have zero knowledge about the methods.
     
    Last edited: Sep 18, 2019
  14. rxcomposite
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    rxcomposite Senior Member

    Here for reference. The work of Schofield. Schofield004a.jpg
     
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  15. fallguy
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    fallguy Senior Member

    Thank you for publishing that RX. It is an exceptionally well done piece and despite arguing with Eric over the lead paragraph; it is really helpful for gaining an understanding.
     
    Last edited: Sep 18, 2019
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