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Status Report, Vol. 36, No. 9 | October 6, 2001 Subscribe

Institute to begin dynamic testing with new sled

The Institute's new sled, which will be installed at the Vehicle Research Center, is similar to this one designed by DSD of Linz, Austria. In addition to testing seats and head restraints, the Institute's sled will be used to evaluate other vehicle parts and components such as child restraints.

A new crash test sled being installed at the Institute's Vehicle Research Center will facilitate dynamic testing of seats and head restraints without crashing cars. The International Insurance Whiplash Prevention Group, of which the Institute is a member, is at work developing such a test.

Benefits of dynamic testing

Since 1995 results of the Institute's high-speed frontal offset crash tests have helped consumers assess the overall crashworthiness of passenger vehicles. Even more important, these tests have prompted improvements across the vehicle fleet (see Status Report special issue: crashworthiness improvements, March 20, 2001).

A sled test program focusing on head restraints holds equal promise. Good geometry is the necessary first step in assessing static head restraints, but seat characteristics such as stiffness also can influence whiplash injury risk. Such characteristics can only be evaluated dynamically. And when it comes to active head restraints, geometric measurements aren't relevant. These designs can only be assessed in dynamic tests. For these reasons, "sled testing is the next logical step in the Institute's program of evaluating head restraints," says Institute chief operating officer Adrian Lund. Sled tests also will be used to conduct crash simulations to evaluate other safety components like child restraints and belt/airbag systems.

Versatility of sled testing

Crash test sleds run on fixed rails. Vehicle bodies, called bucks, can be mounted on top of the sleds in different orientations, as can individual vehicle components like seats.

Sleds simulate crash forces, re-creating the accelerations (side or rear impacts) or decelerations (frontal crashes) that occur inside occupant compartments during full-vehicle crashes. The changing acceleration or deceleration over the time duration of a crash is referred to as a crash pulse. The key aspect of crash sleds is their ability to be programmed to produce specific crash pulses and thereby simulate corresponding full-vehicle crashes.

Multiple test capability

Because sled tests don't involve damage to vehicles, they're much less time-consuming and expensive to conduct than full-scale crash tests. Repeated testing becomes more feasible. This is especially important when repeated tests over a range of crash severities are needed to evaluate performance. For instance, no single test speed or crash severity is optimum for evaluating whiplash injury risk. Ideally, good performance of a seat/head restraint should occur in a range of impacts from low to moderate speeds. Conducting a wide range of tests would be prohibitively expensive if each test involved crashing a new vehicle, but conducting multiple tests on a sled involves minimal costs per test.

Similarly, child restraints don't have to be evaluated in full-vehicle tests. Simulation with appropriate crash decelerations is sufficient. Although multiple tests normally wouldn't be required to assess child restraint performance, the issues of restraint durability and replacement after relatively minor collisions can be thoroughly investigated in repeated sled tests.

Installation of the new sled test device at the Institute's Vehicle Research Center requires a major expansion of the facility. The design-and-build phase will be complete by April 2002.

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