08-17-2012, 08:17 AM #1
Fiberglass to Carbon Fiber: Corvette’s Lightweight Legacy
Fiberglass to Carbon Fiber: Corvette’s Lightweight Legacy
For 60 years, Corvette’s performance driven by advanced materials
DETROIT – It’s a scientific fact: Low weight plus high horsepower equal exhilarating performance. That combination has defined the Corvette for six decades, as increasing power output matches the use of advanced materials to minimize curb weight.
The 2013 Corvette Z06 exemplifies that philosophy. With a curb weight of only 3,199 pounds (1,451 kg) and 505-horsepower (377 kW), it is not only one of the lightest sports cars available in America, it has one of the best power-to-weight ratios of 6.33:1. That’s better than the Aston Martin DBS (7.5:1 – 510 horsepower/3,836 pounds), Porsche 911 Turbo S (6.7:1 – 530 horsepower/3,561 pounds) and Nissan GT-R (7.1:1 – 545 horsepower/3,887 pounds).
“Horsepower isn’t the only measure of performance,” said Harlan Charles, Corvette’s marketing manager. “Balance and low weight are just as important and that’s where the Corvette excels. It has a heritage of employing cutting-edge technologies and materials to help optimize performance.”
Corvette’s use of advance materials began in 1953, when the first Corvettes were produced with all-fiberglass bodies. Every Corvette since has featured a composite-material body.
Fiberglass, the lightweight, rust-proof composite material, was first considered for use on a GM vehicle by legendary designer Harley Earl. Besides being an exotic choice for the early Fifties and having an undeniable weight advantage, fiberglass offered an economical way to create the low-volume Corvette without the expense of large sheet metal stamping dies.
Starting with the third generation in 1968, the body parts were manufactured with a press mold process, whereby the fiberglass material and resin were shaped in a die-like tool that produced smoother parts more quickly. It was a significant advancement in forming technology and laid the groundwork for a change in the body panels’ material in 1973. That year, the composition changed from conventional fiberglass to sheet-molded composite, or SMC, which was composed of fiberglass, resin and a catalyst formed under high heat and pressure. The ratio of resin to fiberglass was reduced with SMC, while the fiberglass itself was a bit coarser. The new material helped produce panels that were smoother right out of the mold, resulting in higher-quality paint finishes.
All Corvettes since 1973 have used SMC body panels, but the material composition has changed dramatically, featuring less traditional fiberglass and more lightweight plastic. The early SMC material created parts that were stronger and more rigid, but more brittle. As SMC technology and production experience evolved, Corvette engineers were able to alter the material composition and the body parts’ specifications to trim the Corvette’s curb weight. Mostly, that happened through making thinner body panels, because SMC was denser and stronger than conventional fiberglass.
It’s rare that a next-generation model of any vehicle is lighter than its predecessor, but that was the case with the fifth-generation (C5) Corvette in 1997. In fact, the 1997 Corvette was larger overall – longer and wider – than the 1996 model, but it weighed nearly 100 pounds less. A greater emphasis on advanced materials was the reason.
The contributors that helped drive down the C5’s curb weight included the use of SMC body panels with more plastic than ever before. The material, basically the same used in the current sixth-generation (C6) Corvette, was composed of about 40 percent resin – polyester, vinyl ester, styrene or a blend of all three – 33 percent calcium-carbonate filler, 20 percent chopped fiberglass, The remaining 7 percent is resin and hardeners that improve the out-of-mold surface finish.
The C5’s panels were exceptionally light, but so was the Corvette’s all-new chassis, which used beefy rails and hydroformed sections to provide strength with less complexity and weight. The floor sections used a sandwich of materials including featherweight balsa wood – a renewable material – to minimize mass. That continues with the C6 cars.
Even the C5’s Gen III small-block V-8 contributed to weight savings and overall greater balance. Compared to the Gen II small-block it replaced, it delivered a lightweight aluminum cylinder block, aluminum heads and a composite intake manifold that weighed less than 10 pounds. The Gen II engine used a heavier iron cylinder block and aluminum intake manifold. A lighter engine improved the front-to-rear weight balance.
The C5 also introduced titanium and carbon fiber to the Corvette. The 2001-04 high-performance Z06 model used a 26-pound titanium exhaust system that was 70 percent lighter than the conventional muffler/tailpipe assembly of other models. A lightweight carbon fiber hood was used on a special-edition 2004 Z06 model and it was nearly 11 pounds lighter than the already lightweight standard SMC hood.
The introduction of the C6 Z06 in 2006 brought an aluminum-based chassis structure and a greater percentage of carbon fiber body panels, representing the most significant advanced materials initiative in Corvette history. Despite looking like the steel chassis of the base Corvette, the C6 Z06’s aluminum frame weighs nearly one-third less. Magnesium is used for the roof structure, engine cradle and some of the other suspension attachment points for greater mass reduction. On the outside, the Z06 uses carbon fiber panels for the front fenders, front wheel houses and rear fenders.
The Corvette ZR1 uses the same aluminum chassis structure as the Z06 and incorporates even more carbon fiber body parts, including the roof panel, rocker panels and more. The new 2013 427 Convertible model also uses lightweight carbon fiber in the hood, fenders and floor panels.
Another advanced material found on today’s Corvette is the carbon ceramic brake rotors that are standard on the ZR1 and available on the Z06. These space-age composite components deliver a significant weight savings over conventional iron brake rotors, while offering exceptional wear resistance.
“Corvette has never been focused on an exclusive material – be it aluminum, carbon fiber, or fiberglass,” said Corvette Executive Chief Engineer Tadge Juechter. “Instead, we are constantly looking for the best materials structure, powertrain, and chassis to improve the performance of Corvette.”
Founded in 1911 in Detroit, Chevrolet is now one of the world's largest car brands, doing business in more than 140 countries and selling more than 4 million cars and trucks a year. Chevrolet provides customers with fuel-efficient vehicles that feature spirited performance, expressive design and high quality. More information on Chevrolet models can be found at www.chevrolet.com.
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