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

 I was told that carbon fiber causes severe corosion to aluminum;
 I would certainly check if this is true.

 JP

There is a few different things here.

1: Fiberglass/foam core composite construction.
2: Degradation of carbon fiber with age.
3: Bonded aluminum construction without welding.

We know not to paint foam core components a dark color because heat from
sunlight will cause a failure at the foam. Plain GRP is very durable.

I was asking about possible failure of carbon fiber with age. Possibly
brought
on by severe environment of open wheel racing. The failure I read about
could
have been caused by a repair made years prior.

The bonded aluminum construction and getting proper adhesion. Do they use
like
the West etch or some equivalent or does the heat of the oven cure it to
adhere?

Thanks

Dale Davies

Hello all, found a coating system in my travels, might interest you regarding Al.
The plastic resin can be used with glass, or carbon fibre.
They use a primer before overlay of fibre, falconavia use it on their
spitfire scaled replica's .  www.hipec.falconavia.com.
I was told by a trustworthy source that GRP's were not succeptable to
cycling issues
as with metals, however over-loading beyond its elastic range will
cause permanent
internal structural weakening, and structural failure like metals.
Therefore if you over
load anything beyond its design limit it will break, usually sooner
then later. Build it
light and weak, prepare to replace it, if you can't afford it to
break (aviation) build it to suit.
Does anyone remember the America's Cup challenger Australia One. It
broke amid-ship like
an egg and sank in 30 seconds, the seas were very rough and neither
team wanted to race
fearing damage asking for a postponement, all hands were rescued by
the kiwi's,
at the time I was an Aussie in Kiwiland so I wont forget it. BTW
Kiwi's took the cup home.
Those guys use Cabon fibre sails, light, bloody dear, and dont like
being scrunched-up so
 last about a dozen uses only..
cheers
Graeme

That ten ton lead keel will do it every time :)

Racing sailing boats are some of the highest stress devices known to man.
I crewed on a racing boat once. Once was enough :)  We beat to 40 Kt weather for over 1000 miles coming up Baja and the poor Cal 40 boat was coming apart. We would launch off the back side of the waves and slam into the trough. I expected the external bolted on lead keel to fall off and capsize us at any minute.

I suspect there is a another failure mode for composites used
in aircraft. If a crack or void happens between layers water could get
in and freeze expand  and cause the de-laminated area to increase every time
it gets wet and freezes at altitude. This is the process that causes boulders to turn into gravel over time.


Paul Lamar