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TWENTY-six of motor racing’s fastest cars will start the British Grand
Prix on Sunday. Scrapes and bumps are inevitable, and a serious crash or
two is likely. The Formula 1 drivers stand a better chance of surviving
the race, and even of winning it, because their vehicles are made of advanced
composites. These are carefully matched layers of different materials that
combine their properties to produce a streamlined shield that is both robust
and light. According to Brian O’Rourke, a senior engineer with Williams
Grand Prix Engineering, one of the sport’s British teams, ‘everyone in motor
racing uses composite materials’. Builders of racing cars abandoned aluminium
in favour of composites early this decade, he says. Yet the full benefits
of composites have still not reached the average motorist; steel remains
the major component of mass-produced vehicles. But researchers are now finding
ways of making composites more suitable for the production line.

Williams uses plastics reinforced with carbon fibres to make its cars
. Such composites offer a combination of properties that cannot be found
in any single material. The carbon fibres make the composite strong and
stiff; the plastic matrix keeps its weight down. Stiffness is important
because the car’s structure must resist large forces during a race, as much
as eight times the force of gravity, without distorting: O’Rourke says the
forces are comparable with those on a modern fighter aircraft. If the structure
distorts too much, the car becomes difficult to handle and the driver loses
control. Keeping the weight down means the car can go faster and does not
use as much fuel.

Composites must also be able to withstand great impacts to meet the
stringent regulations for Formula 1 cars laid down by the sport’s governing
body, Federation Internationale du Sports Automobile (FISA). To meet the
‘frontal impact test’, which FISA introduced for the start of the 1985 season,
the front end of a car must survive impact with a mass of 780 kilograms
moving at 10 metres per second, or about 22 miles per hour. Survival means
containing the damage to the section in front of the driver’s feet, which
is only 820 millimetres long.

Before the introduction of composites, Williams made its cars from a
large number of small metal parts joined together with bolts or rivets.
These joints were a potential source of failure during a race, and they
also lowered the car’s aerodynamic performance. In addition, they took a
long time to put together. Using plastics reinforced with carbon fibres,
Williams can reduce the number of components by making many small elements
as a single piece, or as one integrated part. The car’s surface is consequently
smoother and more aerodynamic, and the vehicles are built more quickly.
O’Rourke estimates that the quickest the team could build an aluminium car
was 300 worker-hours, compared with 250 worker-hours for a composite one.

All the major manufacturers of mass-produced vehicles use composites
to make some parts for their cars. According to the American Society of
Metals (ASM), car makers used 314 million kilograms of reinforced plastics
last year; ASM says this is an increase of 6 per cent on 1987’s figures
and it predicts a 2-per-cent rise this year. As early as the 1950s Chevrolet,
a division of the American manufacturer General Motors, made its Corvette
with a reinforced plastic skin; in September or October this year Chevrolet
will introduce its Lumina all-purpose vehicle (APV) with body panels and
bumpers made of composites. The Lumina APV, designed as a commercial minivan
that can also be used as a family car, will contain about 150 kilograms
of plastics reinforced with glass fibre. Manufacturers tend to restrict
composite materials to body panels; they still make the main structural
components from steel. To exploit composites further the industry must find
ways to make large numbers of structural components at least as cheaply
as they can make them from steel or other materials.

Mike Owen, who leads a research group at the University of Nottingham
that collaborates with the manufacturer Ford, does not believe that raw
composite materials will ever compete with steel on cost alone. He says
the only way a composite car will be as cheap as a steel one is if engineers
can reduce the number of components by integrating separate parts into one
piece. Owen estimates that launching a new model costs a manufacturer up
to $1 billion, of which 70 per cent is spent on new machinery to press the
steel. Fewer parts require fewer pressing machines.

Until recently an association of 22 manufacturers based in Britain,
including Ford Europe, Austin Rover and Volvo Trucks (UK), were sponsoring
work on composites at the National Engineering Laboratory in East Kilbride,
the research centre that the British government plans to privatise. The
team came up with a plastic suspension system, reinforced with glass fibre,
that combines the functions of springs, suspension arms and torsion members,
which are separate components in most vehicles. The programme has ended
but Alan Wootton, who led the work and has since left NEL, says the team
successfully tested the system on an Austin Maestro, a family saloon car.
He adds that the team designed the component so that manufacturers could
mass-produce it, which means being able to turn out 1.5 million of them
per year.

Manufactuers make most composite parts for their cars with compression
moulding techniques; Citroen, for example, uses the method to make the roofs
of its AX and BX models, and General Motors the body panels of its Corvette
Coupe and Lumina APV. In compression moulding, the composite takes one of
two different forms: a plastic sheet reinforced with continuous fibres,
known as sheet moulding compound (SMC); or a lump of plastic mixed with
short fibres, about 6 millimetres long, known as bulk moulding compound
(BMC). (In Britain, BMC is known as dough moulding compound (DMC) because
the short fibres and plastic are mixed together like bread dough.) Workers
place a weighed amount of SMC or BMC in an open press mould, which they
close and heat, squeezing the material between the mould’s two shaped surfaces
to harden, or cure. The process is fast and manufacturers can make complicated
shapes to tolerances as tight as 0.25 millimetres.

Suppliers of materials to the American car industry, such as GenCorp,
have recognised the importance of compression moulding. They have established
the SMC Automotive Center in Detroit, home of the industry in the US, to
look into the increased use of this method. One of the main problems the
centre will have to consider is the need to improve the quality of the surface
finish. At the moment manufacturers must polish the surface of the composite
after moulding to achieve the finish we expect on new cars. This is called
a ‘Class A’ finish by the manufacturers. The centre will also need to investigate
the difficulties in maintaining consistent mechanical properties of composites,
such as strength and stiffness, as manufacturers reduce the time allowed
for curing to meet the requirements of a production line.

Suppliers of plastics are trying to tackle these problems by developing
new plastics or additives for plastics. The aim is to produce SMC sheets
that are stiff enough for workers or machines to handle easily but not so
stiff that the sheets are difficult to mould. Additives that thicken the
SMC ensure that the reinforcing fibres are distributed more evenly, right
up to the edges of the moulds, and that the SMC cures faster. Union Carbide,
based in Danbury, Connecticut, has made a thickener that it says helps to
produce a ‘Class A’ finish without the need for polishing. It describes
the additive as a ‘urethane-based, dual-isocyanate, alkaline earth oxide/hydroxide’.
Koppers, a supplier based in Pittsburgh, Pennsylvania, has also developed
a thickener by mixing a polyol or hydroxyl with an isocyanate ester. It
says its additive helps to control the viscosity of SMC composites.

Some manufacturers, such as Ford, believe they must develop new ways
of building cars to make the most of composite materials in mass-produced
vehicles. Owen’s group at Nottingham is investigating resin transfer moulding
(RTM). The researchers place a fibre mat in a mould, close the mould and
inject the plastic, which they cure with heat or by adding a catalyst. RTM
allows the researchers to lay the reinforcing fibres in different directions
and monitor the effect on the properties, particularly the strength, of
the final component. As far as mass-produced cars are concerned, the process
is at an early stage of development but Chevrolet, for instance, already
uses it to make the bumpers for the Lumina APV. In addition, automated machines
may soon be able to make pre-shaped mats with precisely oriented fibres.
Ali El-Shiekh, a textile engineer at North Carolina State University, has
developed a computer-controlled machine that he claims can weave complicated
three-dimensional shapes (‘Computers weave materials for the space age’,
New ÐÓ°ÉÔ­´´, 15 April 1989). NASA aims to use this device to reinforce
composite parts in the spacecraft it is developing for a proposed mission
to Mars.

Curing is fast with RTM, typically taking only five to ten minutes,
but not fast enough to mass-produce cars; Owen and his team must find ways
of completing curing in under one minute for that. They must ensure the
plastic penetrates the fibres evenly without disturbing their orientation
during the shorter injection time. To do this they are developing surface
treatments for the fibres and chemical binders that will help the plastic
to stick to the reinforcement more quickly. The researchers are also trying
to design a system that ensures the plastic has enough time after being
injected to spread evenly throughout the mould, to cure and to set consistently.

As scientists learn to overcome these problems, car makers will use
more composites and motorists may begin to enjoy the advantages composites
offer Grand Prix drivers. Not least among these is safety, as Nelson Piquet,
of Williams, and Ferrari’s Gerhard Berger can testify. Both drivers owe
their lives to the improved safety of Formula 1 cars, which is a result,
at least in part, of the new materials that engineers use to build them.

Berger crashed at the San Marino Grand Prix on the Imola circuit in
April. He left the track at close to 240 kilometres per hour, or 150 miles
per hour, and hit a concrete retaining wall head on. In practice for the
1987 San Marino Grand Prix, Piquet crashed at the same corner, the Tamburello
left-hander. He spun off the track at more than 300 kilometres per hour,
or 190 miles per hour, and hit the surrounding fence. Fire engulfed Berger’s
car but track officials dragged him to safety; Piquet literally walked away.
How many motorists would expect to do the same if they crashed their cars
in a similar way? Composites offer the motorist far more than just the dream
of a lightweight, corrosion-free car.

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HOW TO BUILD YOUR OWN GRAND PRIX RACER

THE MAIN body of a Formula 1 car, one of the fastest in motor racing,
is a central tube that contains the driver’s cell, the fuel tank, and the
front suspension. Attached to the back of the tube is the engine, connected
to the gearbox and supported by the rear suspension. Fixed to the front
of the tube is the cone-shaped nosebox and, below, an underbody that must
withstand frequent impacts with stones thrown up from the track and with
the track itself – the underbody is only 25 millimetres from the ground.
The front and rear wings are aerodynamic features that keep the car from
taking off when it reaches high speeds. These must be stiff so that they
do not distort when subjected to the large forces they experience in racing
conditions.

Williams Grand Prix Engineering, one of Britain’s motor racing teams,
builds these parts of the chassis from plastics reinforced with carbon fibres.
Workers at Williams use a technique known as ‘hand lay-up’ to make them;
the method is labour intensive but it gives Williams absolute control over
the properties and quality of the product. The team makes around eight drivers’
cells and up to 80 underbodies a year.

The builders lay a resin sheet that already contains the carbon fibre
reinforcement, known as a ‘prepreg’, in a mould. The suppliers of the prepregs,
companies such as ICI or Ciba-Geigy, have treated the resin, usually by
heating it, so that it has partially hardened. This makes the material easy
to handle but flexible enough to be fitted to the shape of the mould.

Williams then places the mould in a large pressure-tight oven, or autoclave,
which treats the prepreg to a temperature of 125 Degree C and a pressure
of a few atmospheres. The pressure holds the prepreg firmly in place while
the heat makes the resin set hard, or cure.

Manufacturers of prepregs can arrange the reinforcing fibres in particular
orientations so that the strength of the final composite is higher in one
direction than in the others. By laying the prepreg sheets on top of one
another, with fibres in different directions, members of the Williams team
can design the piece to have the highest strength and the greatest stiffness
where they want them.

Nick Butler edits Advanced Composites Bulletin.