Direction of stitched glass fiber laminate?

Discussion in 'Fiberglass and Composite Boat Building' started by Roy Berntsen, Apr 10, 2016.

  1. rxcomposite
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    rxcomposite Senior Member

    I have to use a more sophisticated program to analyze the quad layup. I have tabulated the results (attached).

    Triax or Quads are meant to be symmetrical or mirror image of each other when used as a single skin or cored. Taken singly and symmetrically, this is what shows.

    1. The 0/90/+45/-45 shows two distinct shear failure of the resin between 0/90 and +45-45 group. The layers are 90 degree apart. I can only deduce that it is the shear distortion. Thought the table shows higher stress failure of the 0/90/+45/-45 quad, it is tension failure not shear. Shear comes from distortion.

    2. When the quads where made symmetrical, the shear distortion disappeared. Only fiber/resin-tension/compression failure.

    Fiber stacking is very important. Second is groupings. Theoretically, the 0/90 and +45-45 are "balanced" fabric and should not induce shear distortion but when combined it becomes critical that all are symmetrical as the second set showed. It did not care whether it is the 0/90/+45-45 or the 0/+45/90/-45 angle layup.
     

    Attached Files:

  2. rxcomposite
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    rxcomposite Senior Member

    That is a good balanced laminate and should work well with core. The skin coat does not count or if in the outermost (wet) side, it compensates for the losses in compression. Fibers have lower value in compression than tension.

    Lab test are supposed to set the standards. In homebuilts, if the builder cannot afford test coupons, the ultimate value is reduced to 90%. ISO allows only 80% of their published calculated values if no test coupons are presented.
     
  3. Steve W
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    Steve W Senior Member

    The laminate schedule is not necessarily dictated by the structural requirements but sometimes the construction method plays an equal part, the cat I mentioned was hand laid in a female mold so the skin coat was there to minimize print through, bed the core etc if the same boat were to be infused for example with the expectation of painting it there would be no reason for any of the mat in the mix but you could upsize the structural glass without a weight penalty.
    But getting back to the ops original question before he was driven away, Using the above mentioned laminate schedule as an example, why do some designers specify 0/90 while others specify a +/- 45 laminate? If one were to simply substitute +/- 45 for the 0/90 in the above example would it be a more or less efficient laminate?
     
  4. rxcomposite
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    rxcomposite Senior Member

    That is what the OP must have meant to ask. What direction is the angle of the ply? In relation to what?

    There are two types of structural arrangement, the transversely framed and the longitudinaly framed. In practice, panels are always rectangular and there is a reason for that.

    Now, if the boat is longitudinally framed (long narrow boats), there are more longitudinals along the length length of the boat. The long side of the panel is arranged longitudinally. The panel with longitudinal are analyzed along the long side for bending, so the 0 of the fibers are aligned along the longitudinals.

    If the boat is transversely framed, (short fat boats), there are more transverses on the boat and the long side of the panel is arranged transversely. The panel with transverse stiffeners is still analyzed along the long side but now it is rotated 90 deg from the length of the boat.

    Now to your question. Why 0/90 degree? Because you cannot make a mistake no matter how you align it because the weft and the fill strength is nearly the same. Same goes for the +-45. It is the same. Biax are used to strengthen the laminate against twisting as FRP itself is very flexible. It loses strength on the X direction but gains some stabiltiy when the frames move. As a rule you cannot take away the 0/90 and substitute a +-45. Biax are added, not substituted. Composite is trying hard to behave like metal boats.

    The only critical time is when the boat is rather long (12+ meters) is one should be careful on just substituting biax for the 0/90 as it will lose longitudinal strength. It is common that additional 0 degree fabric is added along the midship section of the boat for longitudinal strength. Or there are more 0/90 fabric than biax.

    And to throw a monkey wrench to the whole, panels are analyzed on the SHORT side for bending strength and analyzed again on the LONG side when the longitudinals/transverses are attached. Be very careful on the ply angle stacking sequence.
     
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  5. Vilo
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    Vilo Junior Member


    Best answer. To the point. When I think of bridge construction I see the same thing.
     
  6. upchurchmr
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    upchurchmr Senior Member

    This may be a nice short answer, and it is typically correct.
    BUT, the better answer gives more information.
    And Vilo is most right when he says " the laminate should be properly engineered".

    Thumb rules can get your thumb chopped off.
     
  7. KD8NPB
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    KD8NPB Junior Member

    Thou shall point the fibers in the direction of the stress.

    I prefer a lot of 0 degree, less 90 degree, lesser so +\- 45 mixed with some CSM or CFM for random orientation.

    I typically use CFM blended quads for infusion, or 0/90 3610 and/or 2408, with one layer of +/- 45 mixed in. Usually 1708, or 1700.

    ///

    Ps if one of y’all posts the laminate schedules, I can run numbers for theoretical analysis and post screenshots of values.
     

  8. upchurchmr
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    upchurchmr Senior Member

    Lot of mumbo jumbo going on here.
    First you have to understand what the stress is.
    Lots different in different parts.

    Personally I'd prefer the layup in Harry Potters wand. Obviously stronger.

    Use CSM when you just want it to weight more!
     
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