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A dummy with sense.

A new crash-test dummy is being developed to replace Hybrid III, the stalwart professional accident victim who has withstood abuse by auto safety engineers for over two decades. Compared to his predecessor, Thor (for Test Device for Human Occupant Restraint) is much more the sensitive type, with over 120 sensors to measure the accelerations, displacements, and impact forces experienced in car crashes.

"Thor has more extensive instrumentation in almost every body area, which provides localization of impact loading,"said Mark Haffner, manager of advanced crash-test device development at the National Highway Traffic Safety Administration (NHTSA) in Washington, D.C.

Much like Hybrid III, Thor stands at about 5 feet 9 inches, weighs about 168 pounds, and is built mainly of steel, aluminum, and carbon composites with an aramid fabric covering. Thor, however, has greater biofidelity - that is, Thor's body parts closely mimic the behavior and shape of real body parts.

In 1994, NHTSA awarded a $2.5 million contract to Gesac Inc. of Boonsboro, Md., to design and build a next-generation frontal crash-test dummy. The engineering challenge was to design a dummy that is sensitive enough to effectively evaluate not only today's seat belts and air bags, but also future safety-restraint systems.

Hybrid III, which was developed by General Motors Corp. in the late 1960s and early 1970s, reflects the design philosophy and technology of its time. "Instrumentation, car designs, safety systems, and the prevalent injury types have changed since then," said Nagarajan Rangarajan, Gesac president. "And if you want to evaluate the performance of some future safety system, you need a dummy that's more responsive than Hybrid III."

Gesac won a $570,000 contract from the U.S. Air Force in 1989 to adapt a mainframe software package, used to evaluate the workings of aircraft ejection seats, to personal computers. Gesac ended up with an "occupant-simulation" software product. During Thor's development process, Rangarajan added, "we used the occupant-simulation model all the time. It saved us a lot of time and money, because we didn't cut metal" until the model determined that the dummy design would operate as planned.

Thor's chest features human-like thorax anthropometry and rib contours, as well as new rib-bonding materials and techniques. Gesac created a precision two-bar linkage that provides the three-dimensional displacement of a point in the front of the chest with respect to the back.

Thor's 3-D thorax-deflection measurement system can distinguish between the compression signatures of seat belts and air bags. Another improvement is a restorable abdomen design. Thor's abdomen is a foam-filled sack that should withstand thirty trials, and contains a 3-D penetration measurement system based on a double-gimbaled string potentiometer originally developed at the University of Michigan's Transportation Research Institute in Ann Arbor.

The new dummy's pelvis, besides holding more instrumentation, has more humanlike pelvic segmentation. "When people don't use belts," Rangarajan noted, "they can slide under the dashboard and their knees can contact the vehicle. We need to know what loads are being transferred to the pelvis, so we installed load cells."

The lower leg area was also reworked. "Thor has a new compliant femur that has an improved impact response, as well as a new foot/ankle design," Haffner said.

Gesac revised Thor's shoulder design so that it mimics a real shoulder joint. The new structure, which includes a realistic representation of a human clavicle, maintains load path fidelity for shoulder belt loads.

Thor's face has a restorable load-sensing design, with reusable compliant foam and a load cell array. The dummy also has a multi-directional neck design, and a flexible joint in the spine that allows it to hug an airbag as a human being would.

To find broad acceptance, crash-test dummies must meet the requirements of the automakers. Several prototype assemblies have been circulating to international laboratories for evaluation trials after being tested at NHTSA's Vehicle Research and Test center in East Liberty, Ohio. Additional tests will continue this year under the sponsorship of the Big Three automakers.

Thor eventually will be a New Age family man when he is joined by a larger male dummy and a smaller female dummy.
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Title Annotation:crash-test dummy
Author:Ashley, Steven
Publication:Mechanical Engineering-CIME
Article Type:Column
Date:Jul 1, 1998
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