(A-19) Evaluation of force displacement corridors from legform bumper tests and headform hood tests on small U.S. passenger cars.

Introduction:: Introduction: Pedestrian fatalities by motor vehicle crashes have been on the rise in the U.S since 2010, and 6516 pedestrians were killed by motor vehicles in 2020 [1]. Euro NCAP/GTR has a detailed procedure on performing tests to validate vehicles for pedestrian safety and has developed generic FE vehicle models representative of different vehicle classes for the same purpose [2,3]. NHTSA performed a study in 2019 to evaluate pedestrian safety on U.S. vehicles using Euro NCAP pedestrian procedures [4]. This study calculated force vs displacement corridors from lower legform to bumper tests and headform to hood tests on two “small passenger cars”, a 2016 Toyota Prius and 2016 Honda Fit, from NHTSA’s study. NHTSA’s classifications for passenger cars are based on wheelbase and are used in vehicle-to-vehicle impacts [5]. The corridors may assist in generic vehicle modeling to quantify front end stiffness and assess the risk of leg and head injuries in a pedestrian to vehicle impact from the U.S. fleet. The hypothesis was that the force vs displacement corridors of the bumpers and hoods will be similar because the vehicles are both classified as “small passenger cars”.


Materials and Methods:: Materials and Methods: Raw acceleration data was obtained from NHTSA’s lower legform to bumper and headform to hood tests for the 2016 Toyota Prius and 2016 Honda Fit. A total of seven impacts located at the center, off-center, and corner of the bumpers, as well as sixteen impacts across the hoods were analyzed between the two vehicles. For the legform tests, t₀ of the test was defined as the time when the lower legform acceleration exceeded 2g. Acceleration was multiplied by the lower legform mass of 13.2 kg [6] to obtain the force of the impact. The acceleration was double integrated using MATLAB to calculate the displacement of the impact. Force vs displacement curves were plotted for all legform impacts of both vehicles and were truncated at their peak force. Force vs displacement curves for the headform tests were obtained in a similar manner.


Results, Conclusions, and Discussions:: Results: Lower legform to bumper: For the Honda Fit, the average peak impact forces at the center, off-center, and corner were 63.7 kN, 62.1 kN, and 58.2 kN, respectively. The corresponding average displacements were 46.3 mm, 75.1 mm, and 84.7mm, respectively. For the Toyota Prius, the average peak impact forces at the center, off-center, and corner were 17.1 kN, 16.3 kN, and 42.7 kN, respectively. The corresponding average displacements were 69.1 mm, 124.6 mm, and 50.4 mm, respectively. The calculated mean impact force and displacement for the test with the Honda Fit was 61.3 kN, and 68.7 mm, and 25.4 kN, and 81.4 mm for Toyota Pirus. Headform to hood: The calculated mean impact force and displacement across the hood for the Honda Fit was 3.1 kN and 40.2 mm, and 2.8 kN and 102.2 mm, for the Toyota Prius.

Discussions: The mean peak impact force on the bumper for the Honda Fit was approximately 60% greater than the Toyota Prius, while the corresponding mean displacement was approximately 15% less than the Toyota Prius. The mean peak impact forces for the hoods were similar, but the corresponding displacement for the Honda Fit was 60mm less. This indicates the Honda Fit’s bumper and hood is stiffer than that of the Toyota Prius and would cause more severe leg and head injuries. The difference in bumper peak impact force between the two vehicles is likely due to different bumper geometries resulting in different impact locations of the lower legform. When testing vehicles for pedestrian safety, it may not be useful to group them based on wheelbase. Considering bumper geometry and using measurements such as ground to bottom bumper height and wrap around distance (WAD) from ground to top of the bumper may be more useful.

Conclusions: The Honda Fit exhibited a greater peak impact force on the bumper and hood than the Toyota Prius. This suggests vehicle front end geometry should be considered when comparing pedestrian impacts. This observation was based on two small passenger vehicles. Additional analysis of more vehicles of the small passenger category is needed.


Acknowledgements (Optional): :

References (Optional): : References:[1] NHTSA (2020). 2020 Data: Pedestrians. [2] Euro NCAP (2018). [3] Klug. et al (2017). [4] Suntay et al., (2019). [5] NHTSA (2022). NHTSA Field Crash Investigation. [6] GTR 09 (2009).