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Old Apr 14, 2007, 01:41 AM
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Carbon fiber vs kevlar (aramid) vs glass?

Hi, can someone enlighten me to the differnces and relative advantages of carbon fiber vs. kevlar (aramid) vs. fiber glass?

Is carbon fiber stiffer than kevlar but more brittle?

Anyone know of any good articles that explain these differences in simple terms?
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Old Apr 14, 2007, 01:46 AM
Throw Caution to the Wind
Lavawing's Avatar
Grand Junction, Colorado
Joined Feb 2004
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Not as complicated as it seems at first:

Carbon fiber is black.

Kevlar is yellow.

Fiberglass is white.


All clear now?

--Greg
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Old Apr 14, 2007, 02:05 AM
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Bellevue WA,
Joined Dec 2003
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Do a search and you will find what you seek.
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Old Apr 14, 2007, 02:10 AM
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A Sasquatch took my plane! Tujunga. Ca.
Joined May 2004
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Quote:
Originally Posted by Lavawing
Not as complicated as it seems at first:

Carbon fiber is black.

Kevlar is yellow.

Fiberglass is white.


All clear now?

--Greg
Professor Greg is seen here testing his latest composite LampSchtick.

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Old Apr 14, 2007, 02:17 AM
Throw Caution to the Wind
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Grand Junction, Colorado
Joined Feb 2004
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Quote:
Originally Posted by D.S.
Professor Greg is seen here testing his latest composite LampSchtick.
That was a composite construction of wood/tape/lampshade. Flew as good as it looked.

--Greg
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Old Apr 14, 2007, 07:42 AM
No fuse too fat
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USA, CA, Redondo Beach
Joined Apr 2002
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Carbon has stronger fibers than glass and is good for applications where the fibers are in tension like on a wing spar or in a stressed-skin wing construction.

Kevlar is more flexible than CF and is often used to create live hinges. It doesn't tear easily so if you use it in your fuse, you will have a nice carrying bag for all of your radio gear after you auger in.
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Old Apr 14, 2007, 11:13 AM
Circle Jockey
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A Sasquatch took my plane! Tujunga. Ca.
Joined May 2004
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Quote:
Originally Posted by Lavawing
That was a composite construction of wood/tape/lampshade. Flew as good as it looked.

--Greg
I thought the shades were kevlar

Dean
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Old Apr 14, 2007, 12:07 PM
Where's the wind?
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United States, CO, Denver
Joined Jun 2004
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I sell black glass. It doesn't fit your mold Greg.

Andrew
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Old Apr 14, 2007, 12:40 PM
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San Francisco
Joined Mar 2003
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Think of kevlar like leather, carbon fiber like wood, and fiberglass like, uh, glass fiber.

Imagine sanding leather that's what it's like to sand kevlar. But it has great toughness and *relative* flexibility.

Carbon fiber is more rigid and sands well slopeiron has a perfect description of it's applications above.

Fiberglass is still my favorite. Not as flexible as kevlar but more so than carbon. S-glass is almost as strong as carbon in the same application (just as Target!). Epoxy likes glass more than it does kevlar and glass is much, much easier to cut. Fiberglass sands well.

They all have their place, obviously, but use glass until you get comfortable with the processes (curing times, wetting out, etc.). That will save you some $$ and probably some heartache.
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Old Apr 14, 2007, 09:42 PM
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My understanding is that Carbon has great compression/tension strength, kevlar has great surface strength (I am not sure what the correct term is but it is strong in a sheet against deflective forces which is why it makes good bullet proof vests and wing skins) and fiberglass is just a nice all around cheaper option.
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Old Apr 15, 2007, 01:54 AM
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Carbon is extremely strong in tension and compression and (most importantly) is by far the stiffest of the fibers. However, it is brittle, so the fiber's aren't as tough as kevlar or glass. This is very important, because composites have such a strong ultimate strength that they are usually designed more for stiffness than strength.

Bottom line: Carbon will give the stiffest, most flutter resistant wings, but isn't as tough as kevlar or S-glass.
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Old Apr 15, 2007, 02:42 AM
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USA, HI, Makawao
Joined Oct 2002
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does it matter what the "wet out" medium is? Certain epoxies or polyester resins that really bring out the accoutremonts of the media?
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Old Apr 15, 2007, 03:27 AM
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Joined Jul 2005
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polyesters don't stick to exotic fibres so they are a bad choice. Vinylester will stick to kevlar, but if you are using these materials then IMO epoxy is best. As a general rule, carbon is good for wings. S-Glass comes in after carbon, though needs a heavier layup. Kevlar and S-Glass is good for fuzes as it is strong.

Note strength is different to stiffness. I.e. Carbon is stiff, but will fail after minimal strain (stretch) Kevlar ain't so stiff, but will take lots of strain, and will still be happy even after the matrix (epoxy resin) has failed.

Another thing to consider is the compatability of glues etc for the remainder of the build out and other aspects, i.e 5 min epoxy sticks better to an epoxy substrate then polyester, polyester eats polystyrene foam etc.

Sam,
who hasn't broken a kevlar fuz yet
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Old Oct 30, 2013, 01:34 AM
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zombie alert.
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Old Oct 30, 2013, 02:32 AM
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I heard the only way to kill them is with a Jart.
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