Bending graphlite rod

"Ernest Christley" wrote in message
...

I think you're missing the forest for the trees. A wood steamer is your
answer. Make a form out of sheet metal, then bend the graphlite around
it. Tg is around 180F for most epoxies, so an hour at 212F should turn it
to it's plastic state throughout. The internal bending stresses will pull
themselves out. Take it out of the oven, and it should hold whatever
shape it had been forced into.

Now, what I understand of graphlite is that it gets it's strength from
having all the fibers aligned and equally tensioned. Doing the above, you
will probably get something only marginally better than a hand layup. But
you won't know until you try.

You are making some assumptions that are incorrect.
First, movement of the fibers inside a resin system heated to Tg
degrades the mechanical properties of the mass after it cools. This is
because Tg is a temperature point that is usually used to define destruction
of the member due to it's inability to maintain designed mechanical
properties.
In your description, epoxy is a thermoplastic that can be heated/formed and
cooled
repeatedly without loss of properties. In reality it is a thermoset and is
not remoldable.
The loss of mech properties happens as a microshear failure inside the
matrix as
the resin and fiber move relative to each other "crumbling" the crystaline
structure of the resin.
Be very careful when suggesting that heating a laminate to Tg, bending it,
allowing it to cool
is an answer to "reshaping" the part without serious degradation of the
properties of the resin.
OBTW, Graphlite is a BIS F Epoxy with a Tg of 100C.

J.Kahn wrote:
Bob Kuykendall wrote:
Earlier, wrote:


I'm thinking like making a stick rib.


Maybe try making the rib out of straight pieces, and let the rib truss
lock in the curve for the upper and lower cap strips. I bet that'd
work.

Also, Graphlite comes in a variety of round, square, and rectangular
cross-sections. I think the standard round sections go down to 0.020";
it might not show on the Web but Jim Marske can get it for you.

Thanks, Bob K.

Go to this page on graphlite
http://www.aist-nara.ac.jp/~rieken/projects/composites.html The
stuff is rolled into coils for shipment. Scroll down and check out the
flat version bent by hand into a half circle.


Yes, mine came rolled into a circle. When you cut the tape
it straightens back out. I want it to hold a curve by itself. If
I have to add other materials to hold it into the curve I want
that kinda defeats some of the advatange to using it in the
first place.

If you are using a material to reinforce something, pre-stressing
the reinforcement may or may not be a good idea, depending
on whether it is pre-stressed in the same orientation as the
applied stress, or contrary to it.

For wing spars, it may be helpful to droop the rod down as it
runs along the spar flange from root to tip. The leading edge
of a stick rib would be another matter.

Yes, there are other ways to make ribs.

--

FF