Evaluation of lower limb injury mitigation from inflatable carpet in sled tests with intrusion using the Thor Lx

Real-world crash investigations have suggested that lower limb injury risk is increased with the occurrence of toepan intrusion in a frontal collision. In order to more closely evaluate the effects of different modes of toepan intrusion, a rotational and translational intrusion device was built for the test sled at the University of Virginia. Sled tests were performed at a velocity of 56 km/h with a belted Hybrid III occupant and a simulated knee bolster and steering wheel air bag. Lower limb injury risk measures were obtained with Hybrid III and Thor Lx dummy lower extremities.

Dummy response variables of interest included tibia axial and shear loads, tibia bending moments, ankle rotations and foot and tibia accelerations. The tests were conducted with no intrusion and with a translational intrusion with a peak deceleration of approximately 175 g's with 14 cm of translation. A lower limb injury mitigation device, the Inflatable Carpet (InCa), was used in comparison tests to evaluate its efficacy in reducing loads imparted to the lower limb for varying initial foot positions. Results from the tests indicate that intrusion causes an increase in tibia axial load mainly due to acceleration, and ankle dorsiflexion mainly due to translation, both potentially increasing injury risk. The InCa resulted in large load reductions in the clearance position, and also reduced dorsiflexion angles. The design of the air bag used in this study was optimized for use in settings with toepan rotation in addition to translation. Occupant response was sensitive to a number of factors, such as knee bolster design and Inflatable Carpet geometry, which have to be taken into account in the tuning of the InCa design. Additional tests were conducted in a static setting, with various out-of- position lower limb configurations. These tests did not identify any potential harmful effects of accidental InCa deployment.