Re: Composite vehicles (was: Please allow me to introduce myself...)

["David Brandt" <davidbr13@hotmail.com>]

Chris Tromley wrote:  "An all-composite vehicle is a tantalizing 
possibility.  It can be very
light, very strong and offer good crash protection (all at the same time!).
Cost can be a big issue.  Either it takes lots of hand work, increasing
manufacturing variability and labor costs, or it requires big capital
outlays for tooling, so it's not viable financially except for high volumes.
Correct me if I'm wrong, but I don't think there's much in between."

Actually, composite tooling is quite different from tooling required to make 
standard metal car components.  Tooling can be made from other composites, 
plastics, etc.  Where I work we can easily make composite tooling for 
autoclave bonding composite parts using nothing but a little graphite cloth 
and a steel tube framework to hold it up off the ground (with wheels, of 
course).

Then Chris wrote:  "I would still be all for it, but for one concern.  In 
the real world people
have minor crashes.  When that happens to a unibody, tube frame or ladder
frame vehicle, any good body repairman can see the extent of the damage and
fix it with equipment readily at hand.  Show that same repairman a wrecked
composite vehicle, and he's a stranger in a strange land.

He has no clue how to find and recognize delaminations, what foam materials
were used where, how they were bonded, why some fibers are unidirectional
and others are woven, what resins to use, etc. etc. etc.  An alternative (if
the design is not too "cutting edge") is to take it to a boat builder, but I
doubt your insurance company would go for that.  To make a composite vehicle
fully practical, you have to design it to be so simple that it's difficult
to repair incorrectly, or make the entire body/chassis disposable (which
gets us into environmental issues)."

Yes!  Precisely what I deal with every day!  Although we are equipped to 
repair composites, the parts are not designed to be repaired to begin with!  
If nothing else, design the structure to be repairable!

One idea I had was to make the frame and/or body out of several detachable 
sections (not too many, 4 or 5) which would bolt together.  Bolted joint 
design in composites is difficult, but not impossible.  With this design, if 
a portion was damaged, you could just replace that section, and spare 
sections could easily be manufactured and kept on hand.  This would get you 
back on the road quickly, and the damaged portion could then be sent to a 
shop that specialized in repairing composites, limiting the number of spares 
that were required.

That said, it is relatively easy to repair a composite item, but as you say, 
you have to know what it was made from to begin with, and you have to know 
how to work with these materials.  To a lot of people, they are still just 
smoke and mirrors.  (Some of the EAA people have a saying..."Friends don't 
let friends fly plastic airplanes.")

Of course what I have been exposed to is thermoset composites, where you lay 
up prepreg or cloth and resin, cure it, and it is never fluid again.  With 
thermoplastic composites, the resin melts at higher temperatures, and the 
cloth is actually molded using heated dies.  So tooling costs go back up, 
but field repairs could be easier, and could be done using heat lamps and a 
vacuum pump.  (These can be done for thermosets, too, but the adhesives and 
prepregs in general are nasty to work with and have a shelf life, and are 
picky as to their storage conditions.)  A thermoplastic repair could 
concievably be performed by using a heat lamp to melt repair patches (fiber 
and resin) into the damaged area and to melt a surfacing patch (mostly 
resin) onto the outer surface to maintain a smooth paintable surface.

In any case, definitely take the need for future repairs into account.

David Brandt, '86 Escort EV



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