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Estimating Wetted Fiberglass Cloth Weight?

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jmmome

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I'm using 6 ounce fiberglass cloth. I understand that it weighs 6 ounces per square yard. When the laminating epoxy is added. what would be a good weight estimate to use per square yard for the fiberglass and epoxy combination? Thanks!

Mike Momenee
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REK

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I'm using 6 ounce fiberglass cloth. I understand that it weighs 6 ounces per square yard. When the laminating epoxy is added. what would be a good weight estimate to use per square yard for the fiberglass and epoxy combination? Thanks!

Mike Momenee
TRA #12430 L3
Fiberglass is a bit more annoying to wet out than carbon fiber. Glass usually requires a 50:50 ratio.

Whatever the fabric weighs measure that same amount of epoxy plus ten percent extra for loss in brushes, rollers, etc.

Here is a fabric calculator I use all the time. It is very useful when getting the exact epoxy amount needed.

https://www.ginifab.com/feeds/ozyd2_gm2/

Hope this helps


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rharshberger

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Fiberglass is a bit more annoying to wet out than carbon fiber. Glass usually requires a 50:50 ratio.

Whatever the fabric weighs measure that same amount of epoxy plus ten percent extra for loss in brushes, rollers, etc.

Here is a fabric calculator I use all the time. It is very useful when getting the exact epoxy amount needed.

https://www.ginifab.com/feeds/ozyd2_gm2/

Hope this helps


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+1, weight of FG +10% method
 

ECayemberg

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1:1 ratio to wet out the fabric. Most people use more resin than necessary...not necessarily a bad thing, just doesn't add any strength to the structure once the fabric is fully wetted.

Have never found fiberglass more difficult to laminate than carbon fiber. All fabric is not created equal, your mileage may vary.:)
 

jmmome

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Thanks fellas! Just trying to get a gestimate as to the final weight of my Delta Clipper pyramid-shaped rocket. It's at 28.6 pounds without the fiberglass skin. Rocket is 52" tall and 18" at the bottom, so that will give me a good estimate of what the final weight will be. Was trying to keep it around 30 pounds total so that I can use a 75mm K1000 or K1275 motor. Won't go especially high, but should be fun to watch.

Mike Momenee
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REK

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1:1 ratio to wet out the fabric. Most people use more resin than necessary...not necessarily a bad thing, just doesn't add any strength to the structure once the fabric is fully wetted.

Have never found fiberglass more difficult to laminate than carbon fiber. All fabric is not created equal, your mileage may vary.:)
Its not essentially difficult, but rather you cant get the same results with carbon.

I have done recent tubes made out of carbon with a 70% fiber to 30% resin content. I cant do that with fiberglass.

Like you said your mileage may vary ;).


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bobkrech

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To add to Alex's post.

The density of E-glass is 2.54 g/cc, and the density of laminating resins range varies from 1.15 g/cc to 1.35 g.cc depending on the specific epoxy formulation. For a standard woven fiberglass cloth using a 1.25 g/cc epoxy, the ideal epoxy to glass w/w ration is ~1:1. (Actually 98:100 with a range of 90:100 to 106:100.)

The density of Carbon Fibers vary with grade. Commercial grade T-300 fibers have a density of 1.76 g/cc. Higher strength spec fibers have a higher density which I have not looked up.

T300 Fibers (568Ksi, 34Msi)
AS4 Fibers (640Ksi, 34Msi)
T700 Fibers (711Ksi, 34Msi)
IM7 Fibers (820Ksi, 40Msi)

Since the higher strength grade fibers have higher density, the lower weight % of epoxy is require to make a optimum composition composite however the tightness of the weave will influence the % epoxy in any composite.
 

REK

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To add to Alex's post.

The density of E-glass is 2.54 g/cc, and the density of laminating resins range varies from 1.15 g/cc to 1.35 g.cc depending on the specific epoxy formulation. For a standard woven fiberglass cloth using a 1.25 g/cc epoxy, the ideal epoxy to glass w/w ration is ~1:1. (Actually 98:100 with a range of 90:100 to 106:100.)

The density of Carbon Fibers vary with grade. Commercial grade T-300 fibers have a density of 1.76 g/cc. Higher strength spec fibers have a higher density which I have not looked up.

T300 Fibers (568Ksi, 34Msi)
AS4 Fibers (640Ksi, 34Msi)
T700 Fibers (711Ksi, 34Msi)
IM7 Fibers (820Ksi, 40Msi)

Since the higher strength grade fibers have higher density, the lower weight % of epoxy is require to make a optimum composition composite however the tightness of the weave will influence the % epoxy in any composite.
Interesting, I have been told that carbon also required a 50:50, but to me that did not seem true. This of course changes all of that. Thanks for the info Bob.


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jmmome

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Thanks again, fellas. The amount of knowledge about the various areas of our hobby (passion?) is astounding.

Mike Momenee
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bobkrech

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A simple way to estimate the theoretical weight of a composite is to look at ratio of the volume of the fiber and the surrounding matrix. It is never achieved in practice with woven fabric but can be approached with uni-directional composites.

If the diameter of the fiber is D, the cross-section of the fiber is pi x (D/2)^2 = 0.785 x D^2. The total theoretical cross-section of the surrounding resin and the fiber is D^2, so the theoretical cross-sectional resin is (1-0.785) x D^2 = 0.215 x D^2. So the ideal theoretical volume of composite is 21.5% resin and 78.5% fiber.

The theoretical ideal weight of the composite is 21.5% of the resin density plus 78.5% of the fiber density, Common lightweight aliphatic resins have a density of 1.15 g/cc (high temperature phenolic resins can have densities up to 1.35 g/cc) and e-glass fiber has a density of 2.54 g/cc (or oz./cu.inch), the ideal theoretical composite density is 0.215 x 1.15 + 0.785 x 2.54 = 0.247 + 1.99 = 2.24 g/cc, and the theoretical resin to fiber weight ratio is 0.247/1.99 = 0.124! This is never the case in a woven fabric composite since the weave of the fabric is open and porous and not packed as tightly as possible.

An e-glass fabric from https://www.solarcomposites.com/composites/compositefiberglass.html#Fiber has a thickness of 0.008" and a weight of 8.8 oz./sq.yard = . This is 0.0068 oz./sq.inch. The equivalent thickness of glass 0.0068/2.54 = 0.00267". The volume of resin is (0.008-0.00267)=0.00533". The composite weight is 0.0068 oz/sq.inch + 0.00533 x 1.15 = 0.0068 + 0.00613 = 0.0129 oz./sq.inch. The resin/fiber weight ration is 0.00613/0.0068 = 0.9 for a resin with a density of 1.15 and 1.05 for a resin density of 1.35. This is close enough to a 1:1 weight ratio so a 10% weight excess resin should be ok for real fabrics.

I'll leave it for you to do the same calculation for CF cloths.
 
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