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regarding carbon vs. e-glass,
Some of what you say is true but a lot depends more on the weave. I've built
a LOT of boats, consulted on their construction and have a 37' all carbon
fiber intermediate modulus, unidirectional layup boat that I designed and
built. I've also worked with America's Cup yachts and was the manager of a
boatyard. Later, when I was designing and marketing composites for Orcon, my
old boss was Andy Marshall. The guy that wrote the book "Composite basics"
and has lectured at Oshkosh since...forever. I also have authored articles
for SAMPE (Society for Advanced Material Processing Engineers) regarding the
limits of ultra light weight boat design. I've been working in composites
since I was 12 when I built my first boat and started surfing and built my
own surfboards.
Carbon is great stuff but as I said earlier, a lot of what you are saying has
more to do with the weave and also the fiber diameter.
1. Carbon wets faster than glass. I doubt it. Try the same weight of
material with the same weave and it should be about the same or glass wetting
slightly faster since for the same weight, glass will be thinner. This is
becasue glass is more dense than carbon by a lot. Carbon has a specific
gravity of about 2.5 and glass about 3.4 as I remember it, (and Kevlar is at
1.41 with Spectra at .96, again working from memory). So the carbon will
have more bulk and will take more resin for it's weight.
2. Carbon lays up easier than glass. Again, a factor more of weave than
material. Unidirectional layups are so dense that they are hard to wet while
the same weight in a plain weave will wet easily and a seven harness satin
weave or crow foot weave faster still. The transparency of glass helps keep
you honest on wet-out though!
3. The bubbles in glass may be that the fibers are smaller for carbon and
also that being opaque, you just don't see them. I assume you are talking
about inter-laminar voids? You can vacuum bag and reduce them or better
still, autoclave. Using numbers from Susan Robille at YLA in Benicia, Ca.
(pre-preggers in aerospace and for many America's Cup Yachts), a bagged
laminate can expect about a 3% void content while an autoclaved part will
have essentially none. The bagged part should have only about 77% of the
strength of the autoclaved part.
4. Carbon is generally stronger than glass but not necissarily by much.
Most carbon that's used for these applications is pretty low tech stuff.
Typically a "Standard modulus" material. This means a modulus of 33 million
and a tensile of about 500-550,000 psi. and you can buy it for around
$9/pound as a raw fiber. The 37' boat I built used Hercules IM-6 which has a
modulus of 45 million and a tensile of 650,000 psi but even that is only
considered intermediate modulus. The cost on that I think is in the
neighborhood of about $35/pound but I haven't priced it in years. I got a
great deal on my stuff buying off-spec and short rolls since I was in the
business but I still used about 450 pounds for the hull and deck of my boat.
The highest modulus material around is about 120 million with a tensile
strength of around 900,000 pounds and costs about $3,000/pound. And it is
REALLY hard to work with! If you hold a strand with your fingers about 6"
apart and bend it , it snaps at about 90 degrees! But that stuff also has
zero coefficient of expansion so it's great for satellite antennas that
require perfect alignment and can't expand or contract as it passes out of
the sun into the Earth's shadow. Also when comparing glass to carbon,
remember that "E" glass (electrical grade) is the most common but "S" glass
(Structural glass) is also available. In reality, for non-military use we
generally are using S-2 glass from Owens-Corning). And "S" glass is actually
as strong as standard modulus carbon. And oddly, "E" glass is not inherantly
much weaker than "S" glass, it's just that they process it in a more crude,
high volume manner which breaks more strands. Nor is it inherantly cheaper.
They are both mainly silica, I think about 70% for the "E" and 65% for the
"S" with varying amounts of cheap additives like alumina, manganese, etc.
thrown in.
5. I haven't ever heard that carbon makes a resin set faster but I could
easily believe it out in the sun or in bright lights since it would heat up
faster. Carbon uses a one part dry-solids, uncross linked epoxy as a surface
coating for the fiber. Glass typically uses cylane.
6. Don't know about sliding in place but it could be.
As for getting carbon inexpensively, one of my best buddies is the material
manager for the "One World" America's Cup challenge and also sells carbon of
all sorts. I purchased some 5 harness satin weave from him that is stronger
than a standard weave due to less fiber crimping, (1/5 as much). I'm not
going to quote what I got it for but it is competitive with the prices you
stated. His number is (925) 254-4911 and his business is "Riley composites".
Plus he has or can get just about any other type of material you need.
Bonding adhesives, toughened epoxies, hi temp, etc.
Last thing is you missed one of the best things about carbon and two of the
worst things about it.
The best thing about carbon is that it has a fatigue life of from 5-10 times
that of aluminum or fiberglass. It is the perfect material for spar caps and
beams.
The two worst parts about carbon are that it is very notch sensitive and
galvanically active. As to notch sensitivity, it's like a china plate.
Dropped, china will shatter. With carbon, with it's low elongation to
failure does not distribute the load over a large area like a more flexible
material would, (like glass or Kevlar).
Also carbon is galvanically more noble than aluminum. If the two are in
contact with each other, the aluminum will be eaten like you wouldn't
believe! A true story I was periferally envolved with. We do business with
a major manufacturer of twin turbine aircraft. They were buying two films
from us for their cabin's acoustic and thermal insulation. One was coated
with a carbon black coating on one side. We also sold them a clear film
without any coating. Someone in their accounting realized that if they used
all black material, they would double their order size and get a discount.
The problem was, the carbon black had originally been on the inside in
contact with the fiberglass trim panels. Now there was direct contact with
the alumiunum fuselage and the carbon black coating. Once water condensed on
the inside, it became a flying battery! They had to do MAJOR structural
repairs on a buch of planes and it cost them something like 50 million
dollars! I saw longerons that were virtually gone! And on my own boat, I
have had stray electrical leaks eat up anodized aluminum sail tracks, hatches
and sheaves.
If you need some unidirectional material, I have some rolls left of standard
modulus and some 4.5 oz uni S2 glass. Most is 12" but I do have some 5" wide
carbon. I'm squirreling away the last of my Kevlar 491 and IM-6 material.
Sorry!
Dan Newland (An ES builder once the papers are signed)
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