WOW !
LeRoy Cordes
AMA 16974
Chicago, IL
In God We Trust
On Sat, 8 Nov 2008 08:25:37 -0800 (PST) Kurt Krempetz
<krempetz_at_yahoo.com> writes:
> Hi Gary,
> I wrote up something awhile back and have it on
> www.amaglider.vze.com under carbon fiber facts. I hope this might
> help you some.
> Carbon tow is basically carbon fiber thread or rope. It is
> made up for many little short filaments which are about 7 microns in
> diameter. The 12K means it has per cross section about 12,000
> filaments. The fiber area cross section of 12K tow is .000070
> in^2. Carbon Tow also comes in 1K, 2K, 3K, 6K.
> Now I never had great success working with carbon fiber tow
> which I try to split apart like you describe. I know some other
> modelers do this and when I talked with them they told me they are
> just very careful about separating some fibers out.
> What I do is a little different and I have some logic behind
> it. First try to get the 1K carbon fiber, it is hard to find but I
> have seen it from time to time being sold. Next I saturate the
> carbon fiber tow with glue then I place it between two flat plates
> and apply as much pressure as I can using C-clamps. The logic
> behind this is that carbon fiber is a composite and its properties
> are a function of its components. Typically we are interested in
> the stiffness of carbon fiber laminate per its weight. We don't want
> to have any non-glued filaments or voids so we need to make sure the
> thread is saturated with glue.
> Now the carbon fiber is pretty stiff. A number which describes
> this stiffness is called modulus. The "typical" carbon fiber has a
> modulus of 30,000,000 psi. It about the same as steel. Now the
> other component that going to determine the stiffness of
> the composite laminate is the glue. All glues have a poor modulus
> compared to carbon fiber, typically about 620,000 psi. So the
> composite stiffness really depends on the ratio of carbon fiber to
> glue. So for example something that has a lot of glue in it, say 25%
> glue 75% fiber will have a composite modulus of 5,460,000 psi. Now
> if I can get some of that glue out say 60% fiber and 40% glue then
> the modulus of the composite is 17,200,000 psi. So getting the fiber
> saturated with glue but also getting the glue out is very important.
> My experiment indicated that on average if you applied no pressure
> you get around 75% glue. If I put as much pressure as I can then I
> get the glue down
> to about 40%.
> So this is why I squeeze the thread or threads(layed side by
> side with tension to keep the threads straight) between two plates.
> Squeezing also helps to flatten the fiber out and make a very thin
> part. The glue spills out the sides and ends. Once it cures then I
> cut the width I want. Then I glue this part onto the wood spar.
> That is what works for me, I hope this helps you.
>
> Cheers,
>
> Kurt
>
>
> --- On Fri, 11/7/08, Warthodson_at_aol.com <Warthodson_at_aol.com> wrote:
>
> From: Warthodson_at_aol.com <Warthodson_at_aol.com>
> Subject: [Indoor_Construction] carbon tow
> To: Indoor_Construction_at_yahoogroups.com,
> freeflightml_at_yahoogroups.com
> Date: Friday, November 7, 2008, 2:41 PM
>
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> I have some carbon tow that is described as "12K" which I purchased
> from "CST". It is a 25' long ribbon that is Approx. 1/4" wide &
> Approx. 0.004" thick.
> I cut a piece about 10" long & tried to separate out a few "strands"
> which I wanted to glue onto a spar to stiffen it. I could not get a
> 10" long strip, unless I had quite a few (I don't know how to be
> more specific) "strands" More "strands" than I wanted. I have never
> worked with carbon tow before. Is this normal? Am I using the
> correct stuff?
> Gary Hodson
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LeRoy Cordes
AMA 16974
Chicago, IL
In God We Trust
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Received on Sun Nov 09 2008 - 09:15:15 CET