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Cost-effective polymer composite structures that exhibit "crush control" in crash tests are being developed to compete with mass-produced steel car bodies.
PRACTICAL PLASTIC CAR bodies came a step closer to reality when an automotive front-end section built from glassfiber-reinforced polymer composites passed a key 35-mile-per-hour barrier crash test. The tests were conducted earlier this year by the Automotive Composites Consortium (ACC), a precompetitive research partnership established by the Big Three American automakers-Chrysler, Ford, and General Motors-and their suppliers to integrate advanced composite materials into car structures. ACC engineers installed the experimental composite assembly in a steel Ford Escort, fitted it with sensors, and sent the test vehicle crashing into a wall as highspeed cameras recorded the impact in detail.
"This was the first demonstration that a composite front-end structure, designed for mass-production manufacturing, could display outstanding energy-management performance," said Alan Taub, ACC board director and manager of the Materials Science Department at the Ford Research Laboratory in Dearborn, Mich. In the past, Taub said, handlaid-up composite front-end units had displayed this capability, but they were only technical feasibility demonstrations.
The crash tests, the culmination of the ACC's focal project 1, showed that composites can manage the energy of vehicle crashes as safely as steel, according to John Fillion, an ACC board director and manager of organic materials engineering at Chrysler Corp. in Auburn Hills, Mich. "There is no safety trade-off when you replace steel with a correctly designed composite part."
When a car crashes, Fillion explained, the goal is for the structure to fail in a relatively gradual, predictable way that absorbs much of the impact energy, keeping it away from the occupants. The trick in crash-energy management is to create what's called a controlled crush.
"Car designers know how to produce a controlled crush with steel because they've been using it for so long," Fillion said. But polymer composites are different. "Where a steel component plastically deforms rather slowly on impact, absorbing crash energy as it folds up, composite parts have to be specially designed to fracture in a manner that uses up the impact energy."
When an appropriately designed composite part-typically a stiff, hollow tube-is hit on the end, it tends to tear down its length in several places around the tube's perimeter...