What is the Splitter Made From?
When the Car of Tomorrow was first introduced, there were a lot of concerns about whether it would stand up to short-track and road-course racing, but the last few CoT races have borne out the assertions of NASCAR researchers that the splitter is more than durable enough.
The wing on the Car of Tomorrow is made of carbon fiber composite, a material that has been used in motorsports for some time; however, the splitter is made of a new material that is cheaper and – as has been proven a couple of times now – plenty strong.
The graphite form of carbon is made up of sheets of carbon atoms arranged in a hexagonal pattern as shown below. Graphite isn’t very strong because the bonds within the planes are strong, but the bonds between planes are weak. Graphite shears easily, which means that it is easy to separate the planes. The ability to separate the planes makes graphite a good lubricant. A layer of graphite that is only one atom thick is called graphene. There is a lot of interest in graphene because electrons behave very differently in graphene than in other forms of carbon. Graphite is not an ideal material for structures because it is weak; however, if you fold and interlock the sheets, the resulting fibers have exceptional strength.
Graphite is relatively cheap, but carbon fiber is not because the process necessary to make carbon fibers is complex and requires a lot of time. The process starts with a carbon-containing polymer (chain of molecules) like polyacrylonitrile (PAN). The polymers are heated under an increasing series of temperatures that cause most of the non-carbon atoms to evaporate and help the remaining carbon atoms form a carbon fiber. Even though the fibers are mostly carbon at this point, they don't have either exceptional strength or elasticity without further processing. The fibers are heated at temperatures ranging from 1500 °C – 3000 °C, usually in the presence of a carbon-containing gas.
A composite is a material made of two different components. The composite has properties different from either of the constituent materials–and hopefully better than either. Carbon fibers are strong and they can be woven into cloth, but they need some help before they can be used in a splitter.
Carbon fiber composite is made by embedding carbon fibers in another material. For motorsports, the second material is most often a resin or epoxy. (Glass fibers and resin make the composite material fiberglass, which is similar to carbon fiber composite, but heavier and usually not as strong.) Carbon fiber composites are formed by layering carbon fiber fabric or threads in a mold and saturating them with epoxy. The epoxy dries and holds the fibers together, forming a strong piece. Sometimes other fibers, like Kevlar, may be used along with the carbon fiber. Carbon fibers can be used to reinforce metal or even graphite, which is the material used for the space shuttle's nose cone.
Carbon fiber composites are very strong, but also lightweight. Carbon fiber composites are used in applications such as aircraft, bikes, the monocoques of Formula One cars, boats, golf clubs, and tennis racquets. The combination of light weight and strength makes it an ideal material for aircraft: The Boeing 787 “Dreamliner” will be about half carbon fiber composite.
Making carbon fiber composites is inherently expensive because the process takes a long time and has to be carefully controlled. In the last few years, there has been an additional problem: There is so much demand – mostly from the aerospace and military industries – that there is a shortage of carbon fiber, which has driven up the price even further. The cost of carbon fiber and resin runs four to six times the cost of aluminum.
The shortage has spurred scientists to develop alternative materials. One you may have heard about is the carbon nanotube, which is a graphene sheet rolled up into one or more tubes. Nanotubes have diameters about a millionth of a meter in diameter and they tend to be pretty short; however, researchers have developed ways to 'spin' carbon nanotubes into fibers. Despite these advances, nanotubes are available in fairly small quantities and they are pretty expensive at this point, which restricts their use to smaller items like tennis racquets and golf clubs.
Although the rear wing is made of carbon fiber composite, the splitter is made of a new material called Tegris created by Milliken & Company. The material originally was called MFT, which stands for Mouldable Fabric Technology, but the company re-branded it this year. The word Tegris comes from a Greek word meaning "you are protected" and reflects the material's applications in shielding and armor. Tegris is made using polypropylene-based tapes that feature a very strong center core sandwiched by a lower-melt polypropylene co-polymer, as shown in the diagram below.
The polypropylene structure is co-extruded as a film, which is then slit into tapes and drawn (pulled on) to impart stiffness. The tape yarn is woven into a fabric and the splitter made by pressure thermoforming, which is a fancy way of saying that the materials are pressed together and heated to form a single piece. The outside layers melt together, playing the same role that the epoxy or resin plays in a carbon-fiber composite, while the strong core serves as reinforcement. The thicker the part, the more layers of fabric have to be stacked. For the NASCAR splitter, 100 layers of fabric are stacked and pressed together at very high pressure, then cut using water jets. If you look at a splitter, you’ll notice it has a woven appearance due to the fabric from which it is made.
Tegris is not as light or as stiff as carbon fiber composite; however, it has about 70% of the strength of carbon fiber composite and–most importantly to NASCAR–it is only about 10% of the cost of carbon fiber. Tegris also is fully recyclable, unlike carbon fiber composites. One of the most important characteristics of Tegris is that it doesn’t splinter when it breaks, which prevents having sharp pieces of splitter lying on the track after a wreck. Tegris
The splitter’s performance has impressed some pretty demanding drivers. Jeff Burton said, "I think the splitter is not as big of an issue as we believed it would be. The splitter has proven to be an extremely durable piece of material." The main complaint at Richmond seemed to be that the splitter picked up clumps of grass when it runs through the infield.
The solution, of course, is to keep the car on the track and not in the grass. Although NASCAR designed it to be durable, the new car wasn't designed for off-roading.
Thanks to Dr. Heather Hayes at Milliken & Company for her assistance with this entry.