mixing kevlar with glass matt and rovings in a lamination.

Discussion in 'Materials' started by viking north, Dec 29, 2012.

  1. viking north
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    viking north VINLAND

    If I were to build up a lamination of say, Example, Epoxy resin, 2 matt, 1 roving, 2 matt ,1 kevlar 2 matt. Would the kevlar layer cause any problems within the lamination or is this a common proceedure to mix and match where additional strength is required. I have never worked with kevlar but the idea here is to gain additional transverse strength in bonding to a FRP hull.
  2. Landlubber
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    Landlubber Senior Member

    ...when you say strength, please explain in what way do you require "strength", do you mean impact resistance, high compression or what exactly are you trying to achieve above standard glass lamination.

    But, yes, the Kevlar is just another laminate between as you say.
  3. tunnels

    tunnels Previous Member

    Why do you want to mix dissimular materials ?? would you add aluminum and steel together ??
    Kevlar has lots streach and could pull out of the resin where as the glass dosent have that much streach !!
    Strength ?? you have to discribe in more detail the strength you are refering to or lookin for :confused:????
  4. michael pierzga
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    michael pierzga Senior Member

    All my experiences with Kevlar have been, Bad, Bad Bad, and even worse. Hard to cut, hard to impregnate, hard to repair, wicks water....

    You really need a special purpose like anti pirate ... bullet proof wheelhouse, before using it

    If someone gave me a whole brand new roll of exotic kevlar , Id say thanks !!!!!!!!!!!!!, sell it on Ebay, then use the cash to purchase some exotic Sglass.
  5. tunnels

    tunnels Previous Member

    Exactly my throughts as well Its like mixing carbon and Kevlar . one streachs and the other dosent so whats the point ?? .
    Kevlar used to be the in thing in the late 1980/90 but then it died out very quickly . :)
  6. powerabout
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    powerabout Senior Member

    If you want something to hold together under impact kevlar is the way to go
    Carbon goes to dust
  7. midnitmike
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    midnitmike Senior Member

    While alternating materials in a laminate is indeed common practice your hypothetical lay-up schedule isn't. Unless there were some extraordinary circumstance involved that might require me to alter my normal lay-up it would go something like this resin, matt, roving, matt, roving, matt.

    When bonding to a original FRP hull laminate I like to grind the surface to remove any contaminates then apply what I've always termed a hot coat, this freshens up the surface layer to allow for a better bond. Then apply my laminates in the manner described above alternating matt and whatever other woven material I'm using (roving, cloth, biaxe, triaxe, etc). The last layer is normally matt which leaves me with a better surface for any additional lay-ups or gelcoat if that's my final layer.

    As Tunnels metioned back in the day Kevlar was the big thing and we built quite a few of those monstrosities when I worked for Crusader in the early and mid 80's. Nothing but a pain in the @ss in terms of cutting, lay-up, grinding, fitting out, you name it using Kevlar made it more difficult. Hulls subjected to extreme impacts delaminated at the Kevlar layer everytime. Other then as a promotional gimmick at the time I could see little value in incorporating the material into the hulls.

  8. viking north
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    viking north VINLAND

    Thankyou -- my question has been more than answered with education to boot. I suspected as much but thought it best to ask the experts who have worked with the product. It was an idea I was playing around with in relation to my build. I can see now it would be better to stick with a glass based product designed for strength in a given direction. --Thanks again Geo.
  9. upchurchmr
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    upchurchmr Senior Member

    The extreme impact issue just shows you that Kevlar is very good, and the rest of the layup is not.
    If you want extreme impact protection go all Kevlar.
    You can't just throw in a different material and expect magic to happen.

    First throw out the mat since it is the the worst strength of the choices. if you are using Epoxy.
  10. PAR
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    PAR Yacht Designer/Builder

    Yep, finally someone caught it, toss the mat in an epoxy laminate, as it does nothing but suck up excess resin and makes the finished laminate more brittle.

    If you want to use a little bit of Kevlar or one of the other high modulus fabrics, for improved impact and penetration resistance, place them on the inside of the hull shell, not in the middle of the laminate or near the outside of the hull shell layup. A better schedule would be a finish cloth as the inside layer, with Kevlar next, then your regular laminate layup sequence. This places the "tough stuff" as far away from the point of impact, where it will have best mechanical advantage. Lastly, make sure these fabrics are covered with something, as you don't want to have to finish them, which is the point of the light weight cloth first, before the Kevlar goes in.

    Again, screw the mat, particularly in a epoxy/Kevlar composite. It's like using a Pinto engine in a Corvette body.
  11. Steve W
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    Steve W Senior Member

    You got that right Michael, for some reason S glass is the most under appreciated material in the composites world, everyone gets all goo goo over carbon and ignores s glass, not sexy enough i guess. I just bought some 9oz uni for some new rudders i am building.

  12. rberrey
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    rberrey Senior Member

    So with a foam core build the kevlar should go inside for puncture resistance? My plan was to have a below the water line lay up next to the core with two layers heavy biax wet on wet on top to keep it from floating. Rick
  13. tunnels

    tunnels Previous Member

    Inside as on top of the core ??? if so why ?? what are you thoughts ?? Floating what floating the Kevlar or the core ?? :confused::confused:
  14. rberrey
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    rberrey Senior Member

    I was told kevlar is prone to float with hand lay ups. I want some punture resistence , I removed all mat from my scantlings and replaced it with biax ,so a bit thinner glass lay up. I replaced my 6% finish with 5.7% S glass and I want a layer of kevlar for puncture restance below the water line, inside or out. When I brought this up on the forum before I thought most votes were for out side. PAR says inside , and when PAR speaks. Rick

  15. tunnels

    tunnels Previous Member

    Are you building inside a mould ??
    Glass will float as well if you have lots of resin !!
    yes kevlar is lighter and more bulky for its weight so dont lay it by its self put another glass over the top at the same time !!
    what resin are you using ?? :?:
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