Effect of medium and tall hood leading edge vehicle front-end characteristics on pedestrian torso injuries

OBJECTIVE: Field data analysis has shown that SUVs and pickup trucks cause more torso injuries than sedans, and the rapid increasing proportion of SUVs among the U.S. vehicle fleet will likely increase the importance of pedestrian torso protection. The objective of this study is to use finite element (FE) vehicle and human body models to investigate effects of vehicle front-end geometry and stiffness characteristics on pedestrian injuries, specifically focusing on SUVs and pickup trucks and pedestrian torso injuries. METHODS: Front-end geometries of 74 U.S. vehicles, including 41 with hood leading edge (HLE) > 1000 mm and 33 with 750 mm < HLE < 1000 mm, were collected and analyzed using principal component analysis (PCA). The resulting parametric vehicle front-end geometry model was then linked to an FE generic vehicle (GV) model, so that the GV model can be morphed into a wide range of vehicle front-end geometries representing the fleet. Impact simulations using GHBMC F05, M50, and M95 pedestrian models and three detailed vehicle FE models were conducted with the pedestrian perpendicular to the vehicle front-end located at the center of the vehicle. These simulation results were used to calibrate the stiffness values and contact definitions of the hood and hood leading edge components of the morphed GV models. After GV model calibration, several parametric studies were conducted, resulting in a total of 306 vehicle-to-pedestrian crash simulations using 34 morphed GV models with varied front-end geometric and stiffness characteristics and three pedestrian models under three impact velocities (30, 40, and 50 kph). Pedestrian torso injuries were measured by lateral torso deflections at 17 locations across the chest and abdomen regions. Multiple regression was used to test the significance of the variables. RESULTS: PCA results showed that the top three principal components (PCs) captured over 90% of the variation in vehicle front-end geometries, primarily reflecting HLE height/length, HLE roundness, and overall front-end shape. Simulation results suggested that HLE height and impact velocity were the two dominant factors influencing pedestrian torso injury predictions. Torso injury metrics were the highest when the HLE height was equal to or slightly lower than (<150 mm) the pedestrian's mid-sternum height. In addition, increased HLE roundness and a more compliant HLE were associated with reduced pedestrian torso injuries. CONCLUSIONS: This study generated a comprehensive set of vehicle-to-pedestrian impact simulation data, enabling a systematic evaluation of how vehicle front-end geometric and stiffness characteristics influence pedestrian torso injuries.