Comparison of rear seat occupant injuries in AM50 and AF05 in frontal crashes

Abstract

For rear seat occupants involved in motor vehicle fatal crashes, the number of fatalities of the unbelted rear seat occupants is approximately 3.8 times higher than that of the belted rear seat occupants. In part because of this finding, the National Police Agency decided that wearing a seatbelt would be mandatory for rear seat occupants in Japan from June 2008. In addition, the Japan New Car Assessment Program (J-NCAP), beginning from 2009, considered an evaluation of rear seat occupant safety. For the evaluation test, the J-NCAP has to select from either male (Hybrid III AM50) or female (Hybrid III AF05) dummies. The purpose of the present study is to evaluate different kinematic and response characteristics of Hybrid III AM50 and AF05 dummies seated in rear seats in frontal crashes. For this study, a full-frontal rigid barrier impact test and a frontal offset deformable barrier impact test were conducted following the Japanese-type approval test procedure using a small passenger car with engine displacement of 1496 cc. For occupant restraints, three-point seatbelts were worn by both Hybrid III AM50 and Hybrid III AF05 dummies in rear seats to evaluate their different kinematics. In the full-frontal rigid barrier impact test, the measured injury criteria from AF05 dummy of HIC15, neck extension moment, Nij, and 3-ms clip chest acceleration did exceed the Injury Assessment Reference Values (IARVs) for the AM50 dummy. However, in the full-frontal rigid barrier impact test, the measured injury criteria from AM50 dummy for the 3-ms clip chest acceleration did exceed IARV. Using the measured injury criteria, the injury risks of the AF05 dummy were determined to be greater than those of the AM50 dummy in the full-frontal rigid barrier impact test. Especially, the AIS3+ neck injury risks determined from the tension force, neck extension moment and Nij of the AF05 dummy were larger by 27% to 31% when compared with the risks of the AM50 dummy. The chest deflection of the AF05 dummy (45 mm) was similar to that of the AM50 dummy (43 mm); however, the AIS3+ chest injury risk from the chest deflection of the AF05 dummy (63%) was almost twice than that of the AM50 dummy (33%). From the full-frontal rigid barrier impact test results, an ‘unconstrained ilium by the lap belt’ phenomenon (that is, the lap belt slipped up and over the ilium) was seen in the AF05 dummy, as observed from the drastic drop in chest acceleration. The test results also indicated that this phenomenon also affected head acceleration and neck load. No such phenomenon was observed in the AM50 dummy test results. In the frontal offset deformable barrier impact test, the injury criteria measured from the AM50 dummy seated on the barrier-impacted side were of higher values than those measured from the AF05 dummy seated on the nonimpacted side in the rear seat. In this offset test configuration, the left-side sill acceleration (49 G) on the impacted side was higher than the right-side sill acceleration (27 G) on the nonimpacted side. This indicates that the factor of vehicle acceleration on injury criteria is similar to the factor of dummy body size on injury criteria. The results also indicated that injury criteria from the AF05 and AM50 dummies did not exceed IARVs and that the injury risks of both dummies are very similar. The measured injury criteria and injury risks in the full-frontal rigid barrier impact test results are higher than those in the frontal offset deformable barrier impact test results.

Keywords:

• rear seat occupant
• frontal crash
• J-NCAP
• full-frontal rigid barrier impact test
• frontal offset deformable barrier impact test

Acknowledgement

The authors are indebted to Hisao Ito, Hideki Watanabe, Masami Kubota, JARI, Touta Kanehiro, Takashi Kawabe, NAC Image Technology Inc., Makoto Yaguchi, Kyowa Electronic Instruments Co. Ltd., Yutaka Takahashi, Osamu Masada, JATA, Etsuo Tokuda, Mitsuteru Murai, Akira Kashiwaya and automobile type-approval test department of NTSEL for their valuable assistance in the frontal impact tests; Prof. Koji Mizuno of Nagoya University for his valuable comments on the analysis of injury risk; Takahiro Ikari, NASVA, for providing J-NCAP test data with valuable suggestions; Shinichiro Ito and Kazuyuki Narusawa, NTSEL, for their valuable suggestions on conducting the current project.