Carbon Fiber

July 12,1999

Q: What is this carbon fiber I’ve been hearing about so often in Formula One racing? How is this material made and can it be used for regular road cars?
A: Regarding your question on chassis material for F1 cars:

The actual material used in modern F1 cars is not carbo-steel but carbon fiber. Of course you know that steel is an alloy of iron and carbon (0.05%-1.7% C). Carbon steel simply has a carbon content at the higher end of the scale to make the steel stronger. Almost all passenger cars use steel as the material for the chassis or monocoque.

On the other hand, carbon fiber starts out as rayon or acrylic fiber, wound to frames and heated to 2600 degrees C. This carburises the contents, producing pure carbon or graphite. These are then woven into sheets of the material. The sheets are glued together with adhesives and cured at high pressure to produce the various parts of the chassis.

Carbon fiber is a polymer which is a form of graphite. Graphite is a form of pure carbon. In graphite, the carbon atoms are arranged in big sheets of hexagonal aromatic rings.

The sheets, which look a lot like chicken wire are actually long and thin. Bunches of these sheets, or ribbons are packed close together to form fibers. Because of this special structure, carbon fiber is strong and durable. However, it is not used by itself.
In normal conditions, carbon fiber is used as a reinforcing material to other materials, mostly thermosetting materials such as epoxy resins. Carbon fibers are often used in airplane parts as well as space shuttle missions. In our case, carbon fiber’s better weight to strength ratio compared to aluminum or steel makes it perfect for Formula One.

Carbon fiber is not directly made. Rather, it is made from another polymer called polyacrylonitrile, which is then superheated to form carbon fiber. By itself polyacrylonitrile has no commercial value. It’s value is only realized when this polymer is combined with other co-polymers in the knitting of socks and sweaters or in the creation of super-strong polymers like carbon fiber. Polyacrylonitrile is heated and when this reaction happens, the cyano repeat units form cycles.

After this, the resulting polymer is re-heated again, this time at an even higher temperature. At this point, the carbon atoms kick off their hydrogens and the rings become aromatic. This polymer is a series of fused pyridine rings. After the removal of hydrogen atoms, the resulting polymer is re-heated again at a slow-rate of around 400 to 600 degree Celsius. This will cause the adjacent chains to join together in a certain fashion.

The reaction expels hydrogen gas and a ribbon-like ring polymer is formed. This time, it is heated once again from 600 degrees to a hot 1300 degrees Celsius. This is cause the ribbons to join themselves together to even wider ribbons. When this happens, we expel nitrogen gas.
As you can see on the polymer we get, it has nitrogen atoms along its edges, and these new wide ribbons can then merge to form even wider ribbons. As this happens, more and more nitrogen is expelled. When we’re through, the ribbons are really wide, and most of the nitrogen is gone, leaving us with ribbons that are almost pure carbon in the graphite form. That’s why we call these things carbon fibers.

The main advantage to using carbon fiber is its immense strength to weight ratio. It actually has about half the strength of steel but only one-fifth of the weight. Stiffness is about five times that of steel per unit weight. Thus a car can be lighter and yet have endure enormous crushing and torsional loads. This makes it safer in car crashes, enabling many drivers to walk away from 200 km/h collisions. The stiff chassis also allows designers to optimize suspension settings as they know that the chassis will not flex or bend much when the suspension hits bumps or curbs.
You might be interested to know that aside from the chassis, many of the components in an F1 car are made from carbon fiber. The suspension arms holding the wheels are also carbon fiber, are as the airbox channeling air to the engine. (The airbox opening is right above the driver’s head.) Seats and steering wheels are also carbon fiber. Brakes are also made from carbon material, enabling them to endure intense heat during the race; they can slow the car from 300 km/h to about 40 km/h in just a few meters. Finally, some road cars have actually been constructed from carbon fiber. The McLaren F1 and Ferrari F50 are two very-high-performance road cars that benefit from the high strength and low weight of this material. However, note their price tags of about $500,000 for the F50 and $1,000,000 for the F1. A sheet of carbon fiber costs up to $550 per square meter. This is the main reason why we won’t be seeing carbon-fiber Corollas or Civics on the street soon.

By Redline and Tamago | Photos From CAR Magazine

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