| MadSci Network: Engineering |
The primary advantages of carbon and graphite fibers are their low density (typically 1.85 to 2.15 grams per cubic centimeter), high strength (3000 to >5500 megapascal) and high stiffness (200 to 325 gigapascal)
For an F1 car, the real measure of how good a material is would be the specific properties - the property divided by the density. For purposes of comparison, let's look at Thornel T-650/35 carbon fiber and Type 304 stainless steel. The strength of the T-650/35 fiber is 4.28 GPa, and its density is 1.77 g/cm3. That gives this carbon fiber a specific strength of 2.42 GPa/(g/cm3) The strength of 304 stainless steel is 0.515 GPa, and its density is 8.00 g/cm3. That gives it a specific strength of 0.064 GPa/(g/cm3), a value nearly 38 times smaller than the T-650/35 carbon fiber.
This strength and low density is what makes the use of carbon fibers in composites so attractive in a race car and in aerospace applications.
There are several caveats to using carbon fibers. First, the fibers alone cannot be made into a part. They are made into a part by embedding them into a polymer (polymer matrix composite or PMC), metal (metal matrix composite or MMC) or ceramic (ceramic matrix composite or CMC). For CMCs, carbon can be used to hold the carbon fibers together to make what is referred to as a carbon-carbon or C/C composite. The composites are very strong in the direction of the fiber but very weak in the direction across the fibers. Complex architectures with many layers of carbon fibers or woven carbon cloths are used to impart good strength in all directions or at least the directions that will bear loads in the part. There are also some losses in strength due to poor bonding between the carbon fibers and the matrix (polymer, metal or ceramic).
The other issue with carbon fiber reinforced composites is price. A composite can cost 1 to 1,000 times a comparable piece made from metal depending on the number made and the complexity of the part. Common, mass produced composite items such as tennis racquets have dropped in price to the point that they are the same or even less than older style metal or wooden frame racquets. At the other extreme more applicable to F1 racing, low volume custom parts with the carbon fibers being laid up by hand result in a very high price per part relative to say a stamped metal part used on a passenger car.
Even with these issues for Materials Scientists and Manufacturing Engineers to overcome, carbon fiber reinforced composites almost always outperform metals. In racing where money is not as much a concern as it would be for a typical passenger car, the decreased weight which can make the difference between a first place finish and a last place finish justifies the higher prices.
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