Ernest Christley wrote:
wrote:

Perhaps more to the point, I just suggested a rib as
an example. Being able to bend graphlite rod like
one steam bends wood opens up a lot of design
possibilites.


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.

I first tried heating the rod in boiling water and bending it.
No dice. I then tried heating it with a heat gun, still
wouldn't bend. But that time I heated the middle of the
rod, not the end. I'll go back and try heating the end.

Then I may take up your suggestion, but bending the
rod to a tight curve while it is at room temperature is
NOT trivial.

Phenolic resins are thermosetting. While they do have
a glass transition temperature, that GTT increases when
the material is heated, making it a moving target. My
impression is that most phenolic resins will char befor
they soften.

There are thermoplastic resins that have a reproducible
GTT. Dunno if anybody makes pultruded rod using them
though. I am also less than confident in the vendor's
published descriptions of the products. Even if they
were accurate when written the vendor may change
their source to a similar product without updating the
description.


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 and a preceding author both raised this point and it is well
taken. Maybe if the rod is bent 'monotonically', I.e. bent
onto the form without wiggling it the fibers will slip in only
one direction and retain their approximately equal tension.

--

FF