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The Future is Plastics Foretold What Corvette Already Knew

John Gilbert Apr 19, 2018
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On the track, off the track, or looking forward into the future the Corvette has always been ahead of the curve. “The future is plastics as foretold in “The Graduate” a 1967 movie where Dustin Hoffman’s character Benjamin Braddock is given career advice coincided with the last year the traditional means of manufacturing a Corvette body in fiberglass ended.

A member of Chevrolet Truck Communications at the time Monte Doran wrote, “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.

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Legendary designer Harley Earl first considered fiberglass, the lightweight, rustproof composite material, for use on a GM vehicle. 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.

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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.”

Plastic springs eternal another futuristic Corvette premonition in 1984 the new C4 Corvette introduced a lightweight, composite plastic transverse front leaf spring. It was matched with a composite plastic rear spring.

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Photography by GM Archives

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