Fiber Direction and Placement

Discussion in 'Fiberglass and Composite Boat Building' started by fallguy, Sep 15, 2017.

  1. fallguy
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    fallguy Senior Member

    So, I am using stitched triaxial 0/+/-45 fabric. I think rxcomposite is the local expert on this subject, but perhaps someone else might know.

    Should the 0 be away from or against the corecell or doesn't it matter? Perhaps it matters for the exterior parts more than interiors. When I place the 45 against the corecell; the failure early before a long cure time seems to be on the 90 degree delta (or between the 45s).

    I am using a surfacing veil (now) as well. The veil seemed to like to combine more with the 0 strands which likened to cause more ability even still for shear between the 45s. But if I placed the 45 next to the veil, it might like to shear even more as the 0 strands would be further inside the laminate.

    Is there a general rule I missed?

    Lots of ways to look at things, but the 0 strands on the outside of the matrix probably make the most sense, unless there is something counterintuitive.

    To complicate this a bit more. If you were going to double the fabric, would you end up modifying the approach? I might double my hull laminates on the exterior at a cost of 50# per hull.

    tia
     
  2. TeddyDiver
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    TeddyDiver Gollywobbler

    Perhaps someone more educated on the subject will chime in.. I would look at the panel size and orientation ie have to the longer direction fibers on the the surface.

    BR Teddy
     
  3. rxcomposite
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    rxcomposite Senior Member

    Fallguy- The short answer is, orient the 0 degree fiber on the outermost surface away from the core and oriented along the long side of the panel. That means your panel must be equal to or greater than 2:1 aspect ratio.

    The lengthy explanation is there are three formulas used in the equation. The core is in shear and the skin or outermost fiber receives the highest stress. The longer the panel, the higher is the bending moment. The nearer the skin is to the neutral axis, the higher the stress. Thus, a thicker core reduces stress on the skin. The shear stress on the core is also reduced.

    If a stitched triaxial is used, it is assumed that the fibers are layers of uni's arranged in layers of different orientation. For a uni, the maximum strength is in the 0 degree orientation and loses its strength as it deviates from 0 with the least strength at 45 degree and further diminishes at 90 degree. At 45 or 90, the remaining strength is around 10% of maximum.

    The panel is calculated/tested on the short side and the long side. On the short side, The bending moment is small, on the long side it is greater. A long span will create a high bending moment and the maximum stress is on the outermost fiber, thus the highest strength of the fiber orientation at 0 degree is used, followed by 45 degree as it comes closer to the core. The stress diminishes as it moves away from the outer surface. Keep your 0 at the outermost surface at the longer side of the panel.

    Care must be taken as the second layer at 45 degree has only 10% remaining strength. It might pass the short side test but not the long side test.
     
  4. fallguy
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    fallguy Senior Member

    Thanks. I kind of thought the 0 was best on the outside. What I hate is my parts look much better with the zero on the inside! And you didn't say so, but I am assuming the 0 on the outside would be on each side of the same panel, so the 45s always lie against the foam. If you don't flip the template; you would end up with one fabric the wrong way. My boat waterline panels are about 3' x 33' long and the next panel up is about the same with a hard chine in between. Again, thanks.
     
  5. rxcomposite
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    rxcomposite Senior Member

    0 on the outside means it can be the innermost or outermost layer referencing from the core mid line/neutral axis.
     
  6. rxcomposite
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    rxcomposite Senior Member

    By panel, it means the inner dimension of panel bounded by the frames/stiffeners. It cannot be 3' x 33'. Somehow it must be subdivided by frames and corresponding longitudinals. In most cases, the supported rectangular panel is horizontal but if the design is transversely framed (wide beam boats) where the transverses are close together, the panels become vertical.
     
  7. fallguy
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    fallguy Senior Member

    Catamaran hull, approximately 4' wide with 7 bulkheads, vee for'd to flat bottom hull aft, two main panels with hard chines, deck above. Lower starboard side panel is on the vac table as I write. The breather film doubled on the end is a little test, just to see if the panel looks any different. And yes, our breather fabric moved on us when we bagged it and we missed it, so no breather fabric over the bottom part of the keel. I noticed we got a couple bubbles on the edges from that.

    The zero strands on this panel are down against the table (hull exterior) and up against the peelply (hull interior), the foam got the 45s on both sides.

    File Sep 18, 8 51 24 PM.jpeg
     
    Last edited: Sep 18, 2017
  8. fallguy
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    fallguy Senior Member

    So, another question, same sort of topic. When you hand laminate something like 22 ounce triax and the spec calls for 3 layers, would you lay the layers differently? I was thinking it might be best if one of the zeros went on the 90. The interesting thing is the spec calls for 3, but I will end up doing 5, so I could do the outside and inside layers on the zeros, and turn the other 3 any direction that would provide the best results. The area to hand laminate is 12' long by 10" wide each side of the keel and it is the bow. What would you recommend? I have no spec other than 3 layers, but I am going to do the 3 layers and peelply the top and add another layer after the other 3 cure, and then the bottom will be getting done another time post flip. Anyhow, if you were laying 5 layers of triax in the bow keel vee section, how would you do it?
     
  9. rxcomposite
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    rxcomposite Senior Member

    Fallguy. You may be overthinking it. Post your waterline length, beam waterline, spacing of frames/transverses, spacing of longitudinals/chine, depth at waterline, design max speed of the cat, operating condition (inshore/offshore), the type of core you used and the thickness.

    I will check if your lam sched is correct for the pressure it is designed to operate.
     
  10. fallguy
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    fallguy Senior Member

    I am not concerned with the total scantlings since I have a reputable naval architect design. I am only trying to understand the best way to orient the glass in the forward section that is solid fiberglass and no core. We are using 5 layers of 22 oz triax. Outside layer is 0 on the outside +/- to the core. Inside layer same. The other 3 are artist's pallette. I'd just like it to be strong. I will add a beaching keel with aramid, too, but that is just fyi.
     
  11. sailhand
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    sailhand Senior Member

    How big is this cat, mines 44ft 14 years old plenty of miles and one layer of 800 gram triax. This must be a massive boat, 5 layers of triax, how thick is the core.
     
  12. TANSL
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    TANSL Senior Member

    I think 5 layers of triax is an exaggeration. The weight is greatly increased with fibers, the closest to the neutral axis, which do not need as much resistance. But the NA that designed them is sure to have an explanation.
     
    Last edited: Sep 20, 2017
  13. AndrewK
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    AndrewK Senior Member

    Sailhand, there is no core where fallguy wants to put 5 layers of triax, its solid laminate.
    Fallguy, you are over thinking this. But the ideal is to have only 45 deg between plies, this is why expensive triax is +45/0/-45.
    I would alternate the orientation and do it all in one hit.
    Also in relation to a question in one of your other posts, some suggestions for your bagging.
    You need more pleats.
    Dont place the vacuum lines on to the job, one line on to the breather off the job is enough. But the breather must be bigger than the job.
    The green material around the perimeter of the job, is this your air chanel? if so some breather fabric touching this and one vacuum line is enough.
    Cheers
    Andrew
     
  14. fallguy
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    fallguy Senior Member

    Thank you Andrew. I think my troubles are all related to using 0/+/- and testing the 90 degree too early. I scrapped my first two large waterline panels because I did not like the part shearing off on the 90 degree delta. Of course, about ten days later, it doesn't shear anymore, so tested early and prior to a post cure as well. I honestly wish Noah's had carried the other option because I would have spent the xtra for the 45 delta stuff. What is so odd is my parts look perfect with the 0 degree to the foam, but I did follow rx's advice on this last panel and the 0s are the further away.

    My table is 34' long. I read somewhere you need one line per some xx number of square feet, so I have four vac lines for my table.

    Okay on the overthink. Thanks, as well. I started to overthink after seeing the parts shear on the 90 degree delta in some testing. Who wants to build a custom boat with expensive materials and have a fish fin hit the boat and have it shear apart?

    And the breather was bigger than the job, but we lost track of it until after turned on vac (slides ez on the film), and since we were so close to the window on the resin, I didn't change it.

    I think we will try pleating the edges with one large pleat today and see if we can help the bag down into the part edges, but at 34' long, it'll be unlikely to make it all the way without help.

    Green material is frog tape, just as a border for waxing. There is no wax under the gum tape.

    I am doing the 5 layers because that is the forward section of the boat and if you are going to hit something underwater head on, that is the spot.

    This is a B vessel, not A.

    Many thanks.
     

  15. rxcomposite
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    rxcomposite Senior Member

    For the bow section, 5 layers of 22 oz/yard2 (750 gr/m2) is about 4.6 mm thick total at 50% glass content for the single skin laminate. It will pass the ISO standard Offshore category but not the LR standard. Just a little bit of failure at the inner and outermost skin. There is very little stress at midplane, close to neutral axis. The single skin keel plate 300 mm wide needs to be at least 10 mm thick from the keel, carried forward to the stem up to 50 mm above waterline.
     
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