(A-35) Investigation of rear seat occupant injury risk during frontal crashes using finite element analysis

Introduction::
Front seats in cars have traditionally been the focus of government crash test regulations and safety innovations because of their vicinity to instrument panel. However, with modern vehicles and restraint systems, the front seats have become much safer than the rear seats for certain occupants and specific crash types. This poses a problem, as rear-seated occupants are still at risk of injury or death, and the rise of autonomous driving systems (ADS) could increase rear-seat occupancy and injury risks. The objective of this study is to investigate the safety performance of current vehicle rear seats using human body models. The study involved evaluating rear-seat models of six vehicles, using validated Finite Element (FE) models of Hybrid III male 50th percentile Anthropomorphic Test Devices (ATDs), and Global Human Body model Consortium (GHBMC) male 50th percentile occupant (M50-O) positioned in each seat model, applying frontal New Car Assessment Program (NCAP) crash pulses to each vehicle, and assessing injury likelihood. The results showed reasonable comparison with the test data. Lower injury values were observed in GHBMC compared to ATD. The seats with advanced restraints and/or a steep seat pan angle had the lowest injury risk, and there is significant room for improvement in the design of rear seats.




Materials and Methods:: The rear-seat models of six vehicles, developed based on their geometry reconstructed from three-dimensional (3D) digitizer scans, were utilized in frontal crash simulations using scaled sled pulses. Seat foam material parameters were extracted from individual seat testing [1]. Validated Finite Element (FE) models of GHBMC M50-O and Hybrid III male 50th percentile Anthropomorphic Test Devices (ATDs) were positioned and settled in all the seat models. Each car underwent frontal New Car Assessment Program (NCAP) crash pulses. Figure 1a) and 1b) shows rear seated GHBMC M50-O simulations during a frontal crash at 0 ms and 100 ms, respectively. A summary of the AIS3+ risk curves for the head, neck, and chest was used to determine the potential of injury. Based on the test results, the restraint system type and occupant pre-crash posture were slightly modified. The accuracy of the numerical approach to investigate the safety of rear seats was evaluated under varying scaled NCAP pulses against sled test data. Overall, the seat models with advanced restraints (e.g., pretensioners, load limiters) and/or a steep seat pan angle had the lowest injury risk. The time histories of the ATD and GHBMC response signals and belt loads were compared to the corresponding sled data using CORrelation and Analysis (CORA) software. Also, the GHBMC M50-O showed some differences from the ATD simulations, as observed in figure 1c), and head accelerations were lower than the values seen in ATD.


Results, Conclusions, and Discussions::
In this study, we numerically investigated and evaluated rear seats in terms of occupant safety during a frontal crash. By using only, the exterior surface of the rear seat and compression test data of the seat cushion, we were able to use simplified seat models in our simulations. The results of the simulations with varying impact pulses showed reasonable agreement with test data that validate the numerical assessment of rear-seat safety proposed in this study. The total injury risk ranged from ~40% to near certainty, indicating significant room for improvement in the design of rear seats. The results of our study showed that the developed numerical methodology was able to predict the ranking of different seats, as confirmed by sled test data. Furthermore, our study found that advanced restraint systems and steep seat pan angles have the potential to reduce the risks of occupant injuries. Our study has important implications for the design of rear seats, particularly as the rise of autonomous driving systems is expected to increase rear-seat occupancy. We believe that the results presented in this study could be used to optimize the rear seat in future studies and improve the protection of rear-seat occupants. Finally, we would like to note that our study used the GHBMC M50-O human body model and Hybrid-III M50 ATD, to simulate frontal crashes. The GHBMC M50-O was able to show sensitivity to the loading conditions; however, some differences from the ATD simulations were seen. While this model has been validated in previous studies, it has limitations and may not fully capture the variability of human response in crashes. Therefore, further studies using other human body models or incorporating additional crash scenarios would be valuable for developing a comprehensive understanding of rear-seat safety.




Acknowledgements (Optional): :

References (Optional): : [1] Meng, Y., Yates, K., and Untaroiu, C., "Numerical Investigation of the Performance of Current Vehicle Rear Seats Using Finite Element Analysis," SAE Int. J. Trans. Safety 10(2):377-401, 2022, https://doi.org/10.4271/09-10-02-0014.