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more carbon fiber testing results
http://w-ww.luthiersforum.com/forum/viewtopic.php?f=10101&t=18947		 Page 1 of 1
Author:  Burton LeGeyt [ Fri Sep 26, 2008 10:08 pm ]
Post subject:  more carbon fiber testing results
Hey everyone. After the carbon thread the other day I did some tests and thought i would share the results.

I was trying to mimic the stiffness results with a 1/8x3/8 bar using less CF in a different configuration than a bar. It worked! The deflection was done over a 17" span with a 1.5 kg weight (some lignum vitae). All of the rods were 1/4x3/8x18 and all CF to mahogany glue joints are with CA.

bar #1: 1/8x3/8x18 CF bar with 1/16 mahogany on each side
weight: 28grams
deflection: .039

bar #2: .19x.285 mahogany with .045x.19 CF on top and bottom and .03x.375 CF on sides
weight: 23grams
deflection: .033
This amount of CF is 85% of a 1/8x3/8 CF bar

bar #3: .25x.285 mahogany with .045x.25 CF on top and bottom
weight: 22grams
deflection: .035
this amount of CF is 50% of a 1/8x3/8 CF bar

bar #4: .25x.375 solid CF bar
weight: 39grams
deflection: .02
this amount is 2 times a 1/8x3/8 CF bar

I also tried a bar which was .045x.25 CF on top and bottom and another .045x.25 CF in a curve in the middle. I mean that it touched the bottom on the ends and bent so the top of the curve was at the top of the bar in the middle. I was trying to use the compression aspects of CF to see if trying to flex it down on that curve helped the stiffness and I was surprised that it did not(weight 24grams, deflection .033 with middle bar like a frown and .036 with middle bar like a smile).

What I am taking from this is that the CF on the top and bottom is where it is important. Using half of the CF but using it only on the top and bottom (bar #3) makes a lighter and stiffer bar than the normal 1/8x3/8 bar in the same footprint (bar#1). Specifically, 20% lighter but 10% stiffer. This has all been said here before but I thought people would be interested in the hard data.
Author:  Burton LeGeyt [ Sat Sep 27, 2008 8:39 am ]
Post subject:  Re: more carbon fiber testing results
Agreed Todd, as I said this is nothing new.

ToddStock wrote:
Nothing new here...we use simple rectangular or square pieces of material because it is simpler to manufacture, transport, install, or maintain or simply cheaper then optimal beams.


Except for slightly quicker to install I don't find any of these reasons to be true.
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