Pull off testing

Discussion in 'Fiberglass and Composite Boat Building' started by fallguy, May 11, 2018.

  1. gonzo
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    gonzo Senior Member

    I see two major drawbacks to Ampreg. First, the hardeners have different ratios, so it is necessary to have several pumps. Second, the minimum temperature it is formulated for is 18C (64.5F) and the maximum is 25C (77F) which means it is not adequate for repairs in the field. It needs a shop with climate control. Otherwise, there is nothing extraordinary about it.
     
  2. fallguy
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    fallguy Senior Member

    They tell you no vacuum for hours past gel time.
     
  3. rxcomposite
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    rxcomposite Senior Member

    Nowhere did the data sheet tells you that. It says high vacuum at about 50% of worktime and low vacuum if you want to start earlier. Worktime means the resin has not gelled and still workable. When it has gelled or has started to gel (pot life), then it is no longer workable. Ampreg datasheet makes sense.

    And yes, Ondarvr is correct. The numbers will be meaningless to you. Coupon testing is testing to destruction. It tells you at what point it started to yield (or crack or delaminated). The numbers only tell you if you have failed or exceeded the design criteria and the mode of failure is noted. To put it simply, the laminate has been made to perform as intended/exceeded expectations/or failed miserably.
     
  4. gonzo
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    gonzo Senior Member

    Delamination is at ultimate strength not yield.
     
  5. Ad Hoc
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    Ad Hoc Naval Architect

    No that's incorrect.
    Delamination is just a separation or loss of a bond between layers. It typically occurs at around 10-30% of UTS...more and more delamination occurs at around 30-70% of the UTS with increasing laod.
    After which you generally get to resin cracking.
     
  6. rxcomposite
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    rxcomposite Senior Member

    You are mixing up terms gonzo. Those are different failure criterias and delam starts first before ultimate failure.
     

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  7. fallguy
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    fallguy Senior Member

    The challenge of mobile devices! I misread the Ampreg sheets, but they are still important. My epoxy manufacturer makes no vac recommendations.

    So my project. The 100g gel time is 120 minutes. The earliest we applied vac on hull panels was 70 minutes. We had poor results at 50% vac; parts looked better at full vac. More tests to come this week. I will let you all know what I find.

    The bulkheads used either resin; a 60 minute or 120 minute 100g gel time; vac applied usually at 35 minutes on the 60. Probably ?50 minutes on the 120; I used the longer time when laminating two bulkheads at same time as they are small. The bulkheads (biax) are poorer bondline adhesion, but it all needs testing.

    Our temperatures varied from 65-75F in a climate controlled environment.

    rx & ondarvr - the point of testing is to verify whether it has failed miserably; nothing else ... if the plier test is sufficient, then why would Gurit engineers recommend dolly testing?

    I will be setting up some experiments this week.

    Thank you all.
     
  8. rob denney
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    rob denney Senior Member

    Sure it will, as the skin will still be watertight and your laminate is about twice as heavy as it needs to be. If it is a major delam it will be a bit floppy, but will still get you home. A better question is "What will cause a delam?" Water getting in and freezing, constant slamming off big waves at high speed and perhaps excess point loads are the main ones. The first is builder error, the second is so unlikely in a 35' cat as to be non existent and the third would be crew error. None of them are anywhere near "major".

    You read it wrong. Like I told you before, the only resins that may not use full vacuum are the esters, because of their volatile content. It is impossible to squeeze something dry. As long as the vacuum does not reduce while the laminate is under it, you will not remove the resin required to wet the glass. Autoclaves work at 6 times vacuum pressure. The laminate stays wet.

    Thanks. I appreciate the responses.

    The first instruction on the Ampreg sheet is to roll the resin on. This at least gives it a chance to fill the foam bubble voids. Much of the rest of it is incorrect. I suspect it was written when SP first introduced Ampreg to try and match the long cure time resins from ATL in NZ. It is possible the early Ampreg had volatiles in them which would boil off under vacuum, same as with the esters. I haven't used Ampreg for decades, but when I did, it was under full vacuum, as soon as possible.
    Mixing hardeners is nonsense except to minimise the time under vacuum.
    The heat generated by the amounts of epoxy you are/were applying to the job pre vacuum will speed up the cure time noticably. I would not take much notice of the ambient temperature in deciding when to bag. Use the slowest resin you can find, get it on as quickly as possible and bag it at full vacuum.

    Use a chisel as a wedge on a corner of the laminate between the skin and the core. work it in until you can grab a decent chunk of the corner with the pliers (vice grips are better). Stand on the laminate about 12" from the vice grips (or put it in a vice) and pull.
    If you try to tell the supplier the material is below spec, he will want it tested according to the standards in his spec sheet. This will have no reference to glue lines, vac bag or anything else. Just the material.

    Describe the failure, please. Better, post some pictures.

    I wouldn't waste the time and materials.
     
  9. ondarvr
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    ondarvr Senior Member

    The epoxy to core bond will never show a higher number than the point of failure of the core, so there is nothing to gain from knowing more than if the bond line failed, or the core failed. Your goal is to have the core fail, that's all you can do, no amount of improvement in the bond line strength past that point will affect the strength or safety of the structure.

    Yes, more advanced testing can be done to determine the bond line strength, but an epoxy laminate bond line should exceed the core strength easily.

    Post pics of the actual failure, this may answer some questions.
     
  10. gonzo
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    gonzo Senior Member

    Are you referring to the onset of delamination or complete
    That is for laminations with fasteners
     
  11. gonzo
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    gonzo Senior Member

    I consider a foam core laminate as brittle. Are you considering it as a ductile failure?
     
  12. rxcomposite
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    rxcomposite Senior Member

    Look carefully before rushing an answer.
     
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  13. Jim Caldwell
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    Jim Caldwell Senior Member

    Now you know why I say "once you try Infusion you will never go back"
     
  14. fallguy
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    fallguy Senior Member

    Again, thanks to all. Even the semantics is fine.

    Ondarvr - Gurit recommended the dolly testing. I appreciate you responding about the manufacturer and the bondline. That really is important (for me) to realize. (They will not be inclined to care much about the bondline).

    Rob - I will post some pictures. And thanks for answering the most important question. If I hit a log and slice open the bondline; I had visions of the skin peeling off. The boat is a demountable cat and the weakest bondline is on the bulkheads. And, of course, the beams sit atop them. There is a lot of glass there and the sockets are heavily hand laminated into place. It would probably take a lot to have a bondline problem under all that handlaid glass.

    But, of course this assumes the bondline is poor as I suspect based on the biax plier test. Gurit suggested the bond might not be as bad as I think; thus the test.
     

  15. fallguy
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    fallguy Senior Member

    I want to try a sample of that as well; believe me.
     
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