fiberglass cloth thickness and strength

Discussion in 'Fiberglass and Composite Boat Building' started by wet-foot, Apr 17, 2007.

  1. wet-foot
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    wet-foot Senior Member

    is there away to predetermine the amount of layers of glass cloth needed to achive a certain thickness? Also strength added per layer? Also what is the glass to resin ratio with regular lay-up compared to vacuum bagging?
     
  2. Roly
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    Roly Senior Member

    David Gerrs "Elements of boat strength" does most of that bar the specific tensile/compressive value for laminates.But he does give a recommended laminate schedule for your size boat via a scantling number.And the build thickness of various fabrics.

    Depends how diligent you are with each layer, I guess, & whether you use peelply.
    I just did an epoxy layup of 810gm triaxial (4 layers) non-vacuumed and achieved 55/45% resin/glass ratio.Dunno how good that is? Perhaps somebody who knows can chime in..............
    I do find that if I want a void free "peelplyed" stipple you sometimes have to add a little xtra resin on top and squeegee out. Just a tad.
     
  3. frosh
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    frosh Senior Member

    Common wisdom says that about a 10% improvement is obtained in glass/resin ratio when going from a careful hand layup, to a vacuum bagged peel ply, bleeder cloth method. Maybe 55% resin 45% cloth to 50/50.
     
  4. marshmat
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    marshmat Senior Member

    Vectorply http://vectorply.com/lamdesign/vectorlam_sw.htm publishes a free laminate design software that works as a plugin to Excel. It's a bit tricky to learn but can calculate most of what you're looking for, for an arbitrary laminate.
     
  5. SamSam
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    SamSam Senior Member

  6. wet-foot
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    wet-foot Senior Member

    great chart

    sam sam the chart really helped, thanks.
     

    Attached Files:

  7. Bijit Sarkar
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    Bijit Sarkar Naval Architect

    The chart is very helpful Samsam

    The class ( ABS & IRS) rules say the glass content ratio should be .5 for woven rovings and .34 for chopped strand mat or sprayed.

    There is a complex formula for calculating thickness of a layer depending on which of these is being used but it generally works out .6 to .72 mm, and that tallies well with Samsam's table.
     
  8. gonzo
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    gonzo Senior Member

    The ratios and final thickness also depends on the type of fabric. For example, roving and mat will give a larger thickness than a unidirectional or stitched fabric.
     
  9. SukiSolo
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    SukiSolo Senior Member

    Might be good to make a small test laminate with the desired 'cloths' to see what you actually get. As /\ the total thickness will vary depending on type, roving, uni etc etc. As for resin ratio, that can also vary but can be controlled within reason by weighing. You can get a well thought out hand laminate to a very reasonable standard with a little care and preparation. I've been down close to 40% resin with carbon woven cloths.

    Worth using pretty slow setting epoxies if using them as the resin (over vinyl or poly), as this can give more time to marginally adjust, wet out, roller down, ensure no trapped air etc etc.
     
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  10. Bijit Sarkar
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    Bijit Sarkar Naval Architect

    Computation of skin thickness of laminates for GRP

    This is a small excel file I made for skin thickness estimate. Please note this is without the gelcoat thickness.
    Hope this is of use. If not , sorry :confused:
    If you want any help mail sarkar.bijit@gmail.com
     

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  11. gonzo
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    gonzo Senior Member

    Thanks. I like simple to use tables.
     
  12. TANSL
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    TANSL Senior Member

    Thanks for the formula, very useful. Is it the weight of dry fiber?
     
  13. PAR
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    PAR Yacht Designer/Builder

    Most every fabric supplier has the thicknesses of their products listed. Fiber Glass Industries has an applet, that shows their product weights dry and with various resin/fiber ratios. So, if you want to know what thickness and weight 4 layers of 1208 might be . . .
     
  14. TANSL
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    TANSL Senior Member

    This is the nominal thickness, which is not the same as the measured thickness of a fiber. The nominal values are used to convert the breaking load and deformation in strength and elastic modulus. (paragraph copied from ISO 12215-5)
     

  15. gonzo
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    gonzo Senior Member

    :DYou propose to check fibers individually?
     
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