Building in Triaxial vs Unidirectional - Which is better?

Discussion in 'Fiberglass and Composite Boat Building' started by CatBuilder, Nov 9, 2010.

  1. CatBuilder

    CatBuilder Previous Member

    The plans for my Kurt Hughes in foam are coming tomorrow and I have a lot of quotes in on the materials list.

    The designers says that a 34oz triaxial (specified in the plans) is basically the same as 4(qty) 9oz unidirectional laminations.

    So which do I order to work in?:confused:

    The triaxial seems harder to find, but seems like it will go faster and wet out with a lower resin content. The uni seems easier to find, but seems like it might get resin-rich for a novice doing a hand layup. The uni also seems like it will require 4 times the work (in hours) that the triaxial would.

    Any ideas which way to go with this?
     
  2. AndrewK
    Joined: Mar 2007
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    AndrewK Senior Member

    In your case your laminate is 2 x 34oz triaxial, so to do that in 8 layers of UD is just too much work.
    Putting the practicality aside the UD would make a better laminate and is cheaper, here it is $5/kg for the UD and $7/kg for the tri.

    I also recommend that you get samples of all your cloths before you order as some are easier to drape and wet out than others.
     
  3. War Whoop
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    War Whoop Senior Member

    I used to build exclusively out of Uni , the stuff wets out instantly and lays dead flat, there is no bundling of the filament like in the knitted and the worst offender self destructive woven roven ,There are numerous advantages to using it ,one is the strongest laminate possible can be had from whatever process you are using.
     
  4. tunnels

    tunnels Previous Member

    Theres more than one triax so careful which one they spec 'd
    0/45/45 and another 90/45/45 !!!
    was the orientation of the glass listed ??:(

    Look ,read and understand what war whoop has said Its not much extra cutting uni''s and Makes for a hell of a job thats for sure !!:D:p:)
     
  5. rxcomposite
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    rxcomposite Senior Member

    The Uni's are great as it has a lot of strength in the longitudinal direction. But it loses strength quickly as the load goes out of plane. At 45 degree, only the strength of the resin is keeping it together.

    Since most of the load in a panel is at nearly 45 degree, Biax (with a light CSM backing) seemed to fit the bill.

    WR's although bulky, loses only 25% of its strength in a 45 degree out of plane load.

    In cases where there is longitudinal load, a biax and uni is great combination.

    Or the Triax. The triax I am seeing now are 3D fabrics, +60,-60,90.
     
  6. War Whoop
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    War Whoop Senior Member

    the oneoffs it gave me great freedom and I was able to create whatever was needed and squeezed the last gram out of it ,example on the transom outside facing ,we had it in 6 - 0-90's but turning the corner to hullshell I used only the 0 to get it to lay down flat as the 90 was just going along for the ride.
     
  7. CatBuilder

    CatBuilder Previous Member

    Ok, good input everyone... thanks.

    Not sure which way I'll go. Probably triax for large, time consuming things and uni if I have something that seems to call for it.

    The designer said it was pretty much my choice, but I think he assumed I'd use triax.
     
  8. fg1inc

    fg1inc Guest

    G'day Catbuilder,
    reading your last post i was reminded of a job many years ago where we had to build a large hardtop for a 65 sportfish. We were told to use 2 layers of bi-ax on top and one underneath, and a SAN core. The SAN cores were new then and seemed rather flimsy. "Off-axis" laminating saved the day. One bi-ax put down fore and aft, and the second one off axis by about 20 degrees to the first resulted in a 20% better stiffness. We laid up a bunch of test coupons and destroyed them and the results were eye-opening. 2 tri-ax equals 3 bi-ax, but with the off-axis advantage. So if you have any problems with the tri-ax, it might be worth considering. If i recall correctly, the only down side was a bit of waste, but the upside was easier processing. Now, we pretty much do everything off-axis.
     
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  9. rxcomposite
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    rxcomposite Senior Member

    In your application it works great. You wrote in one of your post you are building in VE and foam core. Great combination. Thin skin, high impact stregth.
     
  10. rxcomposite
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    rxcomposite Senior Member

    Sorry I was wearing my designer's hat and did not answer correctly.

    As a general rule, you can substitute several layers in lieu of what the designer has specified as long as the weight of each layer is equivalent to the layers in triax. Say your triax is 9 oz./ft2, then 3 oz +45, 3oz -45, 3 oz 0degree. Safe to say that you can use 6 oz biax + 3 oz Uni. Or to put it another way, you can layup 6 oz 0/90 WR in a diagonal orientation then apply uni on top. As tunnels has also said, watch out for original triax orientation if one of the ply is 0 or 90.

    If you go for all Uni's have at least one layer of CSM 220 or 300 just to be safe. Thin is not always good as it leads to flexing. Too much flexing will lead to cracks. When the designer has specified triax, he has computed the sum of all the stress the laminate will be subjected to, including the laminated thickness.
     
  11. War Whoop
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    War Whoop Senior Member

    Sir Exactly Good Eye.
     
  12. AndrewK
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    AndrewK Senior Member

    Catbuilder, dont be fooled into thinking that its not much extra work to make a laminate with 8 layers of UD in place of 2 triaxial. Cutting it all up is one thing but just visualise the stacking and wetting out sequence for your self, remember you are on your own.

    Other than the two weft and warp triaxials mentioned above by tunnels you can get triaxials that are +45/0/-45 or +45/90/-45, these are better.

    You mentioned the hull laminates were 3 x 20oz tri / core / 2 x 34oz tri, how are these orientated? because if you are finding it difficult to find the right triaxial cloth a combination of biaxial 0/90 and double bias +45/-45 may be a suitable alternative that may also be cheaper. This is assuming that you are laying the triaxial at 90 degrees to each other.

    Locally the UD and biaxial are approx $5/kg, DB is $6.0 - 6.5 and the tri is $6.5 - 7.5/kg
     
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  13. Landlubber
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    Landlubber Senior Member

    ....most of the above is correct, but remember also that the more layers you put in the more resin you use, it is both expensive and heavy to use more than is required for the job. The real advantages of tri and bi ax cloths is the speed of appliacation and minimal use of resins ( I am assuming you are hand laying of course).
     
  14. gonzo
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    gonzo Senior Member

    Triaxial is sometimes hard to form when there are sharp curves. It is easier to handle though.
     

  15. CatBuilder

    CatBuilder Previous Member

    Cool. Thanks again for all the input. I'm leaning toward the triaxial for the hulls. Seems like a times saver and if come out a little less resin-rich in a hand layup, PERFECT! :)

    The structural bulkheads are specified as (literally) 8 or 10 different layers of uni. I wonder if I can use triax here? I guess that's probably a question for the designer.
     
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