composite design

I have contemplated something similar.

I think you would be best to wind the tubes using a carbon / glass tow
material and epoxy around a mandrell. Tow would be a lot cheaper then
wrapping the tubes in cloth and would allow the properties of the tube to be
optimised by changing the winding angle.

Pro's and Con's ....

It is going to cost more than alumnium.
Might save a little weight.
Joints will be hard to make at intersections of tubes.
The composite tubes will lake the ductility of the alumnium tubes and hence
crashworthiness will be compromised.


wrote in message
ups.com...

Robert Dorsey wrote:
I took a composite stress analysis mechanical engineering class at a
major university (the only class offered). We didn't use any
textbook,
but used a series of pdf files. Anything in particular you looking
for?


On 21 Jan 2005 11:51:18 -0800, wrote:

Any recommendations for textbooks addressing designing, especially
stress
analysis, with composite materials?

Mr/Ms Mitchell has posted quite a list of books.

My particular interest is in stress analysis so as to be able
to compare strength to weight ratios for various choices of
materials. In particular I'd like to see if there is any
advantage to substituting composite members for wood or metal
members in stick and rag designs. For instance, one could
use swim noodles wrapped in a hard shell of epoxy filled
carbon fiber, glass or kevlar tapes and cloth to make tubular
members.

--

FF

.......... :-)) wrote:
I have contemplated something similar.

I think you would be best to wind the tubes using a carbon / glass
tow
material and epoxy around a mandrell. Tow would be a lot cheaper
then
wrapping the tubes in cloth and would allow the properties of the
tube to be
optimised by changing the winding angle.

Pro's and Con's ....

It is going to cost more than alumnium.
Might save a little weight.
Joints will be hard to make at intersections of tubes.
The composite tubes will lake the ductility of the alumnium tubes and
hence
crashworthiness will be compromised.


Wrapping in cloth or tape would be a lot easier and faster if doing
the layup by hand. It would also be trivial to orient it so that
half the fibers of the cloth or all the fibers of unit-directional
tape run the length of the tube to maximise bending strength.

Before doing anything of the sort I want to be able to calculate
that strength, hence the original question.

Joints could be made with tows/cloth/tapes to fabricate saddle-like
fittings perhaps in-situ.

Crash-worthiness remains an important issue.

--

FF

My two cents: for a reasonably simple structure such as the "carbon
around swim tube" proposed, I think the best approach may be to simply
build one or two of them and test it/them to destruction. Compare this
against a likewise destructive test of the wood part you're proposing
to replace. Allow a generous margin for error -- especially if others
are going to be building it from your plans, because there can be a
great variance in composite strength depending on the builder's skill
and environmental conditions.

Greg