From: cjs1722@zeus.tamu.edu (STEPANIAN, CHRISTOPHER JOHN)
Newsgroups: sci.materials
Subject: carbon fiber bows
Keywords: composites, bows, etc...
Date: 8 Apr 92 19:21:00 GMT
Organization: Texas A&M University, Academic Computing Services
News-Software: VAX/VMS VNEWS 1.41

>From: akarpowicz@mta.ca (Adam Karpowicz)
>Subject: Carbon fibre composites

>I have some questions about carbon composites, and specifically:

>What is the difference in composition and mechanical properties
>between carbon and graphite fibre?
>Why carbon fibre materials are generally considered better than
>fiberglass?
>What is carbon foam (used in construction of bow limbs)
>Where to get carbon composites in small quantities?

>I am thinking of making a bow using carbon fibre comp. alone or with 
>fiberglass. I got quite a bit of help from netters on alt.archery, i.e.
>that carbon fibre makes bows faster and carbon foam (?) helps to stabi-
>lize and waterproof the bows, also allowing more bending within elastic
>limits (less stacking). Before I get intio this, I thought I'd rather
>ask here too.

>Thanks for help

>Adam

The way we knew it at Hercules was that carbon fibers only had to go 
through one 'low temp' furnace while the graphite fibers had to go
through both the 'high and low temp' furnaces. The majority of the 
fibers we made were made with a pre-cursor called PAN. The pan was 
modified by the heat to yield a predominantly carbon-based (containing
the element carbon) fiber. The higher the temp the less impurities in
the fiber. The 'carbon fiber' that Hercules turned out came in numerous
tweaked forms. The most common form was called AS4. One of the more
popular 'graphite fibers' that they made was UHM. The carbon fibers,
generally, had higher strength than the graphite fibers while the 
graphite fibers had a higher Young's modulus(stiffer). Your best shot might
be to give them, or any other material supplier a call for a more
detailed description. You could also check the library for most any
intro to composites text; if they are worth their salt, they should
have this information also. I know a composites text by Argarwal (sp?)
has this...

Carbon fiber, in general, has a higher stiffness than glass fibers
which would allow you to use less fibers for the same stiff bow. The
only problem is that the strength is not necessarily as good as the
fiberglass. 

To make the bow even stiffer while keeping the same weight, the 
graphite/epoxy(?) is placed on both sides of a strip of foam. This
allows for stiffness without all the without all the weight. This is 
my guess as to what you mean by 'carbon foam'.

If I was to design a bow, I would determine what a user wants from
the device (a certain shape, an energy distribution, etc...). Then
I'd sit down with a flat plate analysis program (a fairly close
analogy to the bow) and get the curvatures or stresses that you want
for your ideal bow. Materials, thicknesses, and ply orientations can
be chosen at this point... Kinda vague?  I know, but I really don't 
know what makes a bow good?!

Feel free to drop be a line...

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Chris Stepanian			| "Its my wife, and its my life"
Dept of Ocean Engineering	|
Texas A&M University		|     Lou Reed/Velvet Undergound
CJS1722@ZEUS.TAMU.EDU		|
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Newsgroups: sci.materials,rec.autos,rec.autos.tech