PanterroR
Lap Time Luminary
The big talk around the water cooler lately has been about the end of the current horsepower wars. With gas hovering at four bucks a gallon and emissions regulations requiring that cars spew no more CO2 than a bird fart, finding more horsepower in an internal combustion engine will be an exercise in diminishing returns. But the end of the power escalation shouldn't necessarily spell the demise of the performance car. Any speed junkie can tell you there are two factors in the performance equation — power and weight. And with the power side of the formula more or less conquered, the next big battleground will be weight reduction. One material that figures heavily (no pun intended) into the future of performance cars is carbon fiber.
On the timetable of building materials, carbon fiber is a relative newcomer — it was first discovered in the late 1950s when rayon strands were superheated. But rayon is made from cellulose, and the wunder fiber became more viable once mad scientists discovered how to derive it from a polymer base. Carbon fiber derived from cellulose lacks the carbon density that gives polymer-based fibers their superior properties. Today's carbon-fiber filaments can be tailored to the specific demands of their final use, with the base stock from which the carbon is extracted dictating properties ranging from tensile or flexural strength to thermal conductivity.
The superheating process results in strands of nearly pure carbon (up to about 98 percent, with just enough nitrogen to give it its inherent structure) that measure between two and four ten-thousandths of an inch in diameter — or about 1/6 that of a human hair. Like silk, another light and strong filament, carbon fiber becomes truly useful once it is woven into a cloth. Thousands of individual filaments make up the "yarn" that is then woven into the carbon-fiber cloth we all know.
As a construction material, this cloth has to be set into a medium to give it shape and rigidity. Thermoplastic resins like the ones used in fiberglass construction are ideal for this, and on some levels the method for fabricating carbon-fiber reinforced plastic (CFRP) pieces can be similar to the fiberglass process. But to take full advantage of carbon fiber's strength and weight advantages, it must go through a process that compresses the material and squeezes any excess resin out. This takes place in an autoclave, which not only creates a vacuum environment that draws the weave into its mold and squeezes out all but the necessary plastic, but also generates the heat required to set the shape.
The end result is a part that is exceptionally strong and light. Compared with steel, carbon-fiber parts are 75 to 80 percent lighter for the same amount of structural stiffness, and it enjoys a 30 to 40 percent advantage over aluminum. Even the old standard for lightweight composites — fiberglass — can weigh nearly twice as much. It's no wonder carbon fiber is so desirable where weight reduction and strength are critical.
It wasn't long ago that carbon fiber was an exotic material, practical only in expensive applications like fighter jets, Formula 1 cars, and racing yachts. But improvements in technology and increasing demand for high-strength, lightweight materials have brought costs down to the point that car manufacturers are now incorporating it into high-performance vehicles. Porsche was the first manufacturer to build an all-carbon chassis with the Carrera GT, which also featured carbon fiber in its center console, hood, trunk, doors, wheel wells, and seat buckets, and came in some 40 percent lighter than would have been possible with conventional materials. Porsche is not alone in using carbon fiber extensively. For less than a fifth of the Carrera GT's cost, the current Corvette Z06 uses carbon fiber front fenders, wheel housings, and floorboards. The upcoming ZR1 will make even greater use of CFRP, including the hood, roof, front spoiler, and rocker panels.
BMW is also putting the black cloth to work, using it as the roof material for the current M3 and M6 coupes. While the roof panel alone is not exceptionally heavy (the M3's steel piece weighs only 11 pounds more than its carbon counterpart), reducing weight at the highest point of the car lowers the overall center of gravity, improving handling dynamics. BMW also has employed carbon fiber in its bumper structures, which are typically steel and sit at the outermost points of the car.
"Compared with steel, carbon-fiber parts are 75 - 80 percent lighter for the same amount of structural stiffness"
For most of the last decade, the aftermarket has been producing crude, hand-laid carbon-fiber hoods for the tuner car market. While most shave a few pounds off the original unit, it's safe to say they are as much a fashion statement as a functional change, especially when left unpainted. But now Detroit is starting to see another value in the composite material for hoods. Perhaps the most impressive example is Ford's new Shelby GT500KR, which uses carbon not only for its scant mass, but also for its ability to be pressed into complex shapes not possible with metal. More than 100 individual cloth patches make up the inner and outer panels, creating two unique airflow chambers — one for cold intake air, the other for exhausting underhood heat. Unlike the aftermarket, Ford leaves none of the black weave visible, instead painting it like any other body panel.
In the coming years, carbon fiber parts like the GT500KR's hood and the Z06's fenders will likely make their way into more mainstream performance vehicles. But the cost of producing carbon fiber is still high, and the already substantial price tag has been compounded by a shortage of material. Projects like Boeing's new 787 Dreamliner, which will be of roughly 50 percent composite construction, are making a dent in the limited supply of materials and keeping prices up. Nevertheless, most manufacturers recognize the need to reduce weight without sacrificing strength, and few materials are better suited to that task.
There are few materials that can match carbon fiber for its strength, weight, or structural versatility. As the quest for more power gives way to the battle of the bulge, carbon fiber's advantages will certainly ensure its popularity — and if there's a performance car in your future, you can almost be certain it will contain a bit of black magic.
Source: MotiveMagazine.com - Motive Tech:Black Magic Woven - Carbon Fiber
