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Crashing for a cause
By Joseph Ogando, Materials and Fastening Editor -- Design News, February 5, 2001
Troy, MI—Bang! It's a sound you'll hear over and over again in a new crash test facility opened here by GE Plastics and Defiance Testing & Engineering Services Inc.
Capable of moving an actual vehicle or a test sled at speeds up to 16 mph, this barrier-impact test stand fills a gap between the low- and high-speed tests already in use for bumper evaluations. According to Todd Hoff, GE's director of advanced automotive engineering, the tester spans the entire speed range at which bumpers make most of their contribution to crash management. And thanks to the test sled, whose weight can be set from 2,000 to 8,000 lbs, the system enables rapid development of bumper designs without the need to sacrifice an entire car.
Driven by a 100-hp motor, the tester pulls the car or sled into an instrumented concrete barrier. It can perform head-on, offset, or pole crashes needed to meet Federal Motor Vehicle Safety, Insurance Institute of Highway Safety, and European Allianz standards. It can also be used for air bag and sensor evaluations.
Much, though not all, of the tester's time will be taken up by GE Plastics, which will use it prove out new bumper systems that combine steel beams with energy absorbers made from engineering thermoplastics. An alternative to expanded polypropylene (EPP) foam, these energy absorbers are injection molded from impact-modified Xenoy PC/PBT and attach to the front of the steel reinforcing beam with the help of molded-in fastening features. The absorbers consist of corrugated lobes that undergo a controlled, energy-absorbing collapse in a crash. According to John Madej, GE's global director of automotive front and rear end systems, the first of these Xenoy absorbers are slated to appear in the 2004 model year. "We have seven OEM programs under evaluation right now," he reports.
Two design possibilities
True to its name, the energy absorbing bumper does a better job at managing crash energy than bumpers made with EPP absorbers. That effectiveness translates into two distinct design possibilities: As a drop-in replacement for EPP in existing bumpers, the new energy absorber reduces the loads transmitted to the car's frame. Or, as part of a new bumper design, it could reduce the space requirements. "You can optimize for load or displacement," says John Madej, GE's global director of automotive front and rear end systems. And crash tests conducted in the new Defiance facility suggest that the potential reduction for either attribute—load or space—can be 30% higher than EPP.
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