FOAM SURROGATES FOR USE AS KNEE BOLSTERS AND KNEE BOLSTER AIRBAGS IN FRONTAL SLED TESTS: EVALUATION OF COMPRESSIVE PROPERTIES AND RESPONSES DUE TO OCCUPANT LOADING

摘要

Although knee bolster airbags (KBABs) have been implemented in the vehicle fleet, data concerning the effect of KBABs on injury prevention are limited due to the challenges associated with performing full scale tests on KBABs and knee bolsters (KBs) in the laboratory. Therefore, the purpose of this research was assess the efficacy of rigid polyurethane foams as KB and KBAB surrogates by first characterizing the compressive properties of several rigid polyurethane foams and then validating the occupant response to the selected foam surrogates in full-scale frontal sled tests. Indentation tests were performed on seven foams with different compressive strength ratings (CSRs) at three loading rates. The foam stiffnesses obtained from these tests were compared to production bolster stiffnesses reported in the literature. An ANOVA was performed to evaluate whether CSR and loading rate influenced the compressive properties. The initial stiffness, secondary stiffness, and yield force were significantly associated with CSR. Regression lines relating initial stiffness and yield force with CSR were determined. Based on the indentation tests, the 19 psi foam had the lowest initial stiffness, and the 65 psi foam had an initial stiffness closest to the average KB stiffness reported in the literature. Consequently, the 19 psi and 65 psi foams were chosen to simulate the KBAB and KB, respectively, in the full-scale frontal sled tests. A Hybrid III anthropomorphic test device (ATD) was used as a human surrogate in each sled test. The ATD chest acceleration, pelvis acceleration, femur forces, and tibia forces for each restraint condition were then compared to analogous full-scale crash tests conducted for the New Car Assessment Program (NCAP) in order to validate the use of the foams as surrogates. The sled tests produced comparable results to the NCAP tests for all parameters. Therefore, the foams were concluded to be reasonable surrogates for KBs and KBABs. Overall, this study provides a method for accurately simulating frontal motor vehicle collision lower extremity loading in the laboratory and assessing injury risk due to different restraint conditions.