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Thread: Carbon FIber vs. Kevlar vs. Fiberglass ??

  1. #1
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    Default Carbon FIber vs. Kevlar vs. Fiberglass ??

    Does or has - anyone ever done a comparison spreadsheet or similar to compare cloth/fabric weights between the various types of composite materials?

    I ask, because I was asked in an email - if there is any cross-reference charts that show fabric weight and thickness comparisons? As an example, I have found nothing less than 3 oz. carbon, yet in fiberglass there are weights down to 1/2 oz. Most carbon being easily found and sold "seems" to be in the 5 oz. range - and Kevlar seems to follow with size/weights more closely tied to carbon cloth than to fiberglass cloth. I was unable to provide an answer, so thought I would ask here.

    Since Carbon and Kevlar are so light in weight - does the weight difference make up for the higher weight per ounce - and does the width of the cloth play any role when weights are advertised? It would seem not as weight is usually oz./sq. yard - or grams/sq. cm.

    Basic question was would a hull of 5 oz. carbon be lighter in eventual weight than a hull of (perhaps) 2 layers of 1 or 2 oz. cloth? My initial response would be no - even if resin weight were disregarded - but the two layers would seem to have less pin-hole possibilities than only one layer of the heavier weight carbon.

    Anyone care to offer their opinions?

  2. #2

    Default Re: Carbon FIber vs. Kevlar vs. Fiberglass ??

    Hi Dick, I think you are missing the point, it is not gust the weight of the cloth but the weight to stiffness of the cloth, 5oz carbon is about the same as 2 layers of 4oz glass, for about a 35 percent weight saving.
    john

  3. #3
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    Default Re: Carbon FIber vs. Kevlar vs. Fiberglass ??

    Ya -

    in retrospect, I guess a pound of feathers vs.a pound of steel is still the same weight. I did remind him of stiffness for carbon, and abrasion and "toughness" of Kevlar, but got too far down the road to give thought to the basic point you made, John.

    Ohhhh boy !

  4. #4
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    Default Re: Carbon FIber vs. Kevlar vs. Fiberglass ??

    FYI, you can get a .2oz/yd2 carbon "veil" from fibreglast.com. I'm not sure what you would use it for, but it is out there. They also have 3.5 oz/yd2 carbon, but it's kinda pricey!

    http://www.fibreglast.com/showproduc...%20Tow-15.html

    It would be interesting to know what a finished laminate weight would be for each. Would one hold more resin than another, resulting in a higher total weight? And the same numbers after vacuum bagging the same sample.
    Last edited by hew565; 04-02-2009 at 10:34 PM.

  5. #5
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    Default Re: Carbon FIber vs. Kevlar vs. Fiberglass ??

    Laminate weights

    Laying up fibreglass/kevlar/carbon/etc by hand (not vacuuming) at the best you might get around 50% cloth, 50% resin ratio. Inside a small female hull mould it would be a struggle to get near that ratio. Vacuuming alone and vacuuming using pre-preg could/should get lower ratios than that.

    One trouble in the case of small hulls requiring minimal cloth weights (read 1, or 2 layers of cloth) is when reducing the resin content too much (below 40%?) means LOTS of voids between the cloth structure (pinholes !!!) that need dealing with. (more weight)
    Vacuuming also makes the laminate thinner than hand layup, and for the same weight cloth, it is therefore more flexible, seemingly softer. (more cloth needed, but is then it is super tough in collisions)

    As a general rule, cloth weights about 200g/m2 (6 oz/yard2) are the cheapest, with prices increasing either direction from there (and significantly so if lowering the weight with "exotics")

    Jon
    Last edited by jon.holmes; 04-03-2009 at 03:35 AM. Reason: a spelling error

  6. #6
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    Default Re: Carbon FIber vs. Kevlar vs. Fiberglass ??

    Lightweight carbon tissue,

    While I remember - loading outside my local fibreglass store was a small truck. I happened to see the invoice while waiting to be served - MANY thousands of dollars of carbon tissue!

    OK, I knew it was being used in the model aircraft, model boats etc, but about 20 rolls???




    Turns out it was for electrical insulation purposes on "fiberglass" shelters used in Antarctica

  7. #7
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    Default Re: Carbon FIber vs. Kevlar vs. Fiberglass ??

    Dick
    I used for my models all types of carbon cloth from 90g/mē very espensive up to 160g/mē
    Generally the proportion between carbon and epoxy is 50/50 as has been said in previous posts.
    I used kevlar cloth of 75g/mē - one particular attention, I never use this material as an external cloth- this material is very dens of micrometric fibers and do not accept sanding like glass or carbon. I got bad experience in the past. Is a good material capabable to absorb chocks and therefore very usefull if mixed with carbon that has lesser resistance against chocks. Carbon - Kevlar- Carbon is a good combination, Kevlar (inside) - Carbon - Carbon is also good, Carbon inside - Carbon - Kevlar outside is a disaster !!!
    Because of the fiber density Kevlar requires more resin in a ratio of 40/60.
    I used mixed cloth carbon/kevlar - similar remarks as for kevlar. It is a nice looking fiber but need to be covered with glass for final looking.
    Finally I use more and more often glass of any weight, simply because is cheaper.
    The spread fashion of using Carbon is not, in my opinion, justified for our models, the strenght of stailess steel is not needed. The mecchanical analysis could show in terms of efforts, that glass is largely adeguate for the hull structures.

    My calculations are very simple, according to my experience, the "skin" values are in fonction of the hull lenght : The skin is given in g/dmē The skin is composed by cloth and resin.

    4.5 g/dmē to 5.5 g/dmē for hull lenghts of 50cm to 80cm
    5.5 g/dmē to 6.5 g/dmē for hull lenghts of 80cm to 110cm (Class IOM)
    6.5 g/dmē to 7.5 g/dmē for hull lenghts of 110cm to 130cm ( class M)

    These values are referred to cloths and resin on a ratio of 50/50, therefore the tissus have half of the weights g/dmē illustrated.

    As an example : 4 layers of glass of 80g/mē are equivalent to :
    0.8g/dmē x 4 = 3.2g/dmē . Adding an equivalent weight of resin the final weight will be 6.4g/dmē. Obviously is not easy to achieve without experience in lamination. Using vaccuum some gains in weight could be obtained.
    Actually a Hull of 39dmē will have a weight of 39dmē x 6.4g/dmē = 249.60g

    4 layers of 80g/mē glass are much better then 2 of 160g/mē; further better strenght and waterproof is obtained.

    In general the lower range I use it if carbon is employed and the higher range is reserved to glass cloths and epoxy.

    In this moment I'm experimenting a new material : the cotton fabric wich weight around 112g/mē.
    With cotton there is a large amount of various color, and all sort of ornamental drawing.
    Obviously I cannot consider this fabric as strong as glass, but his presenting the advantage for choosing a large amount of decorations, never achievables with paints or aerographs. A final cloth of glass protect the fabric.

    Hope this could be of any help, this is the way I'm doing.
    Claudio

  8. #8

    Default Re: Carbon FIber vs. Kevlar vs. Fiberglass ??

    S- glass and carbon are close in strength/weight, so the real advantage to carbon is its stiffness/weight. Great for fins ,rudders ,masts or selectivly reinforcing( for stiffness) spots in the hull and deck.
    Carbon tissue has poor strenght/weight and poor stiffness/ weight compared to glass cloth( not even worth using)
    Last edited by robert; 04-19-2009 at 07:42 PM.

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