Hi Paul,

I was on the thinking seat, and remembered something I read about the
deterioration or break down of carbon fiber race car tubs. I do not know if
this was a result of the material failing due to age or from the abusive
environment of a race car. The stiff suspension and repetitive shock loading
from bumps on the track may be the cause. Or is it a result of exposure to
UV
light and or dark paints?

How would this relate to carbon fiber aircraft construction? I know that
composite construction is sensitive to color from heat build up from dark
paints. Turbulence and hard landings will put a stress into the structure.
All
materials will fail eventually due to applied stresses. That was the cause
of
the Air Hawaii failure. Part of the solution is the design of attachment
points to dissipate applied stresses to reduce them safely.

I also saw recently on How Stuff is Made about the construction of Kenworth
trucks and also the new Lotus car. The both bond parts of the cab (truck)
and
chassis (Lotus) together.  The Lotus uses extruded aluminum to make the
chassis. The epoxy is applied and the parts are held together, until they
can
be cured for a couple of hours in an oven. Does the curing enable the proper
adhesion or is there a chemical etch like you recommend also used? This
could
make for very clean aluminum skins. You would not have the stress points
that
you have with rivets and stresses would be dissipated over a large area.

Dale Davies

I have no knowledge of that. There are some fiberglass boats still
around after 60 years. It does not appear to fatigue and crack like metal.
When we were racing fiberglass tubs back in the 1960's they never seemed to
develop any problems.

Paul Lamar

Dale,

Unprotected epoxies are subject to degradation in U.V. (sunlight).
Polyester and vinylester resins have much more resistance to U.V.  The
mechanism for fatigue in composites is microcracking, but good resins are
very resistant to it.  Composite helicopter blades can have unlimited life.

Oven cured resins (adhesives) tend to have higher strength and service
temperatures, 250 degree F. resins are adequate for our uses, using 350
degree cure systems when you don't have to just exacerbates CTE (Coefficient
Thermal Expansion) mismatch problems.  There are some very good paste,
ambient cure adhesives out there now; Nemesis NXT was put together with one
from Loctite/Hysol.  Most metal bonding uses a primer/adhesion promoter and
it works well but you must always be aware of built in stresses due to CTE
mismatch when hot bonding aluminum to carbon.  Also, carbon should not be
directly bonded to aluminum--it needs a glass ply in the bond area to
insulate the two materials or it will become a very nice battery.

If you want to see an all bonded aluminum airplane, go look at a Grumman
American Aircraft such as a Grumman Cheetah or Tiger.  It works very well.

Steve Brazil