201 5-Optimistic
This scenario involves a vehicle constructed with polymer composites, as is
concept car. Such a vehicle might consist of a continuous glass- or carbon-fiber
structure made by liquid molding techniques, with chopped fiber composite
the GM Ultralite
reinforced plastic
skin and closure
panels made by stamping methods. The GM Ultralite example may be useful to examine the
potential weight savings available in a future graphite composite automobile. The vehicle was
designed from scratch to take advantage of the unique properties of carbon fiber--its high specific
stiffness and strength, which can lead to a 55 percent weight reduction compared with steel on a
component basis. Although the Ultralite’s purpose-built design makes it impossible to compare
directly with an existing steel vehicle, estimates are that its curb weight is from 35 to 40 percent
less than a steel car of the same interior volume.
A more cost-effective composite option would be a continuous glass FRP, although this would
involve a considerable compromise on weight savings. Glass fibers cost less than graphite--about
$1 to $2 per pound; however, glass fibers are much denser than graphite and also have a lower
stiffness (table 3-2), which means more material must be used to achieve an equivalent structural
rigidity.^28 On a component basis, maximum weight savings with respect to steel are probably 25
percent, yielding perhaps a 15 percent reduction in curb weight (roughly half that available in the
maximum aluminum case).
Estimating the costs of a future composite vehicle is difficult, but some guidelines are available.
Assuming that a rapid, low-cost manufacturing method can be developed (it does not yet exist), a
glass FRP vehicle could conceivably cost the same as a steel vehicle.^29 The basic materials cost
more than steel, but comparatively low-cost tooling and part integration help to offset the higher
cost of the resin and fiber.
The graphite FRP vehicle is more problematic from a cost point of view. Graphite FRP parts
for racing cars typically sell today from $100 to $400 per pound. An optimistic estimate of future
carbon fiber production costs, even at high volumes, is $3 to $4 per pound (they are currently
around $15).^30 Even this optimistic result would mean that the vehicle structure would cost
several thousands of dollars more than steel. One estimate is that a graphite composite vehicle
would cost an additional $5,000, assuming fiber costs of $10 per pound.^31
In practice, the cost of an all-aluminum vehicle probably puts a constraint on the cost of a
graphite vehicle, since aluminum offers 75 percent of the incremental weight savings at perhaps 25
percent of the incremental cost. Thus, to be competitive with aluminum, the cost of graphite
structures must be reduced substantially below the most optimistic current estimates, which will
require breakthroughs in both graphite production technology and composite manufacturing
Battery Technology.
(^28) A probable solution would be to use a hybrid composite in which small quantities of high stiffness fibers (e.g., steel or graphite) would be used
in stiffness- 29 criticalareas of the design. This capacity to design the material to fit the fictional requirements is one of the advantages of composites.
National Materials Advisory Board, see footnote 6, p. 34.
(^30) Carbon fiber production is expensive because it involves pulling thin polymer filaments through a high-temperature oven under carefully
controlled atmospheric conditions. 31
Stodolsky et al., See footnote 4.