The objectives of this study were to compare the response differences of the Flex PLI and TRL legforms under various test conditions and to assess their repeatability. A test fixture with four control factors was designed and fabricated to simulate a generalized front structure of a light truck. Using this fixture, thirty-six impact tests with the Flex PLI and the TRL legforms were performed at an impact speed of 32 km/h.

The responses from the two legform impactors, specifically, moments in the Flex PLI and acceleration in the TRL, MCL elongation in the Flex PLI and bending angle in the TRL, and ACL elongation in the Flex PLI and shear displacement in the TRL were compared. The Taguchi method was applied to compare the responses from these three pairs of measurements. The shape and magnitude of the response time histories were used to evaluate the repeatability of the Flex PLI and TRL legforms.

Some results from this limited study indicate that the two legforms did not consistently respond to the same test conditions in the same way and could potentially drive countermeasures in opposite directions. For example, increasing the protrusion of the lower bumper stiffener relative to the bumper generally resulted in lower moments in the upper tibia with the Flex PLI, but higher accelerations with the TRL legform. However, the MCL from the Flex PLI and bending angle of the TRL legform trended consistently with changes of all four fixture factors, although with differing sensitivity.

A repeatability analysis indicated that most measurement parameters of each legform were repeatable or marginally repeatable across the spectrum of the test conditions. However, the MCL elongation of the Flex PLI and the bending angle of the TRL were non-repeatable in some test conditions.