Pull off testing

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

  1. fallguy
    Joined: Dec 2016
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    fallguy Senior Member

    Looking for either a pull off test that I can send to or a pull off test rental or a pull off test recommendation to purchase for my project.

    I think I only need it for a few weeks.

    Buying the equipment is fairly costly; so looking for options.

    I am not near the coasts, so hard to find a surveyor or anyone with the stuff.

    Thanks.
     
  2. PAR
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    PAR Yacht Designer/Builder

    Are you talking about a coating peel tension tester?
     
  3. fallguy
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    fallguy Senior Member

    I want to use it to test the glass to core bond.
     
  4. PAR
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    PAR Yacht Designer/Builder

    Cut a 2" coupon(s) and send it to West System and see if they'll do the deed for you?
     
  5. rxcomposite
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    rxcomposite Senior Member

    If it is going to be a non classed test, just pull the laminate skin at an angle away from the cored laminate sample. You can press down on the sample laminate by hand. To visually check, see if if portions of the core stuck to the laminate, if not, you have poor adhesion or the resin is weaker than the core. Other practical test requires rolling a peeled laminate on a 4" tube to see if the skin adhesion to core is good. The only official way is shear test which is expensive and can tell you if the bondline or the core is the mode of failure.
     
  6. gonzo
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    gonzo Senior Member

    I can do that kind of test. We have INSTRON machines.
     
  7. fallguy
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    fallguy Senior Member

    Is that mobile or would I need to send you samples Gonzo?
     
  8. gonzo
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    gonzo Senior Member

    You would have to send samples. The machines are quite large and heavy.
     
  9. fallguy
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    fallguy Senior Member

    I called and left you my number and you can call me next week during business hours.

    For others and me, are these tests where you glue a dolly to the fiberglass, then cut the glass in a circle with a tool around the dolly, then pull until the glass pulls away from the core?

    And then would you return the samples and the pull values?

    And are you certified or have you ever used the data in any litigation?

    Can you explain typical use of the equipment as well if not dolly testing?

    I can send samples. How big should they be?

    Do you have an estimate of the cost of the service? I think I can buy pull test equipment (not Instron), but the costs are rather high and I would prefer independent review.

    A few other people might be interested. Thank you!
     
  10. gonzo
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    gonzo Senior Member

    The test is pretty much like you describe. However, it the design of the samples takes some consideration.
    The tested samples are usually returned with the results.
    The tests would be done at UW-Milwaukee, which is a Tier-1 rated research center. Many large corporations and the US government hire us for testing and research.
    The machines are normally used for material research, which your test falls within. The samples vary from composites to metals to concrete. They are all routinely calibrated.
    I'll call you and we can discuss size and shapes of samples. We can accommodate samples up to about 18" wide.
    I have worked with insurance companies (for and against) in litigation. It is a matter of keeping good records and back all claims with reliable data.
     
  11. fallguy
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    fallguy Senior Member

    Thank you Gonzo. I look forward to working with you to help me evaluate the product.
     
  12. ondarvr
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    ondarvr Senior Member

    We have an Instron to test bonds and other things, but core bond testing might be of little value.

    I assume you're testing the bond strength of the epoxy laminate to either foam or wood, either core will fail before the epoxy bond will, so all you're testing is the strength of the core. The samples will all have the core still firmly bonded to the laminate, which is all you can ask for.

    I just made a bunch of test coupons for comparing the bond strength of different putties, all the results fell into the same range because the failure was in the laminate. All it proved was that even the lowest cost bonding putty in our test was more than adequet, it did nothing to prove which one was better, but better really makes no difference, all it needs to do is not fail in the intended use.
     
  13. fallguy
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    fallguy Senior Member

    Oh?

    Oh how I wish you were right!

    You might be incorrect. Pretty bad if you are, right?

    If the core has a tensile rating of x and the pull off is 10% or 20% or 60% of x; you have verified a core bond failure or a glass failure. The degree of failure is important because 90% is a lot better than 10%; per Gurit. If the core has 500psi rating and your pull test is 50 psi.. how would you feel about that as a hull value?

    If you pull and get 350psi for a bulkhead; how would you feel about using that?

    I need it checked by a professional who can get me raw data on a variety of samples.

    If the tests result in core failure; that would be good.

    I suspect otherwise and Gurit recommended dolly testing. It has to be done by cutting out around the dolly and pulling to a psi rating.

    I understand your point and I wish you were right.

    But I suspect otherwise; so need to test!!!
     
  14. rxcomposite
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    rxcomposite Senior Member

    There are three components. Core is rated for the shear it can handle at maximum (mid point, near neutral axis). Shear diminishes outwards near the surface of laminate. Between the core and the laminate, there is a shear flow handled by the resin or corebond agent but is lower than the core shear strength. About 50% less than the average shear. In design, this is technically called shear between the web and flange and is included in the ISO calculation/tabulation or a caution in LR that the resin shear must not be exceeded. Shear is parabolic in curve greatest at the middle and diminish towards the flange. Within the limitation of the material properties, the cored laminate is designed.

    So what are you looking for? Failure of the core or failure of the bond line or failure of the skin?
     

  15. rxcomposite
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    rxcomposite Senior Member

    FG- This is the diagram of shear in a cored laminate. The core properties shear and thickness is chosen based on published/recommended values. ISO requires to use 80% of the published values for untested material. LR requires 90%of approved material. The thicker the core, the less shear. The resin used as glue or corebond is such that its shear properties shall not be exceeded in the design. The farther it is from the neutral axis, the less shear. The skin is sized differently as it is either in tension or compression. Shear is not used unless it is going to be riveted (local stress).

    So if the design is sized accordingly, the laminate should not fail within the specified values. If the laminate fails before the specified value is reached, it could be the material, design, or workmanship. Usually it is the design. Values were not chosen correctly. If it fails ABOVE the specified values, then nothing to worry as it has exceeded its DESIGN values.
     

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