Development and Validation of the Finite Element Model for the Human Lower Limb of Pedestrians

An impact test procedure with a legform addressing lower limb injuries in car-pedestrian accidents has been proposed by EEVC/WG17. Although a high frequency of lower limb fractures is observed in recent accident data, this test procedure assesses knee injuries with a focus on trauma to the ligamentous structures.

The goal of this study is to establish a methodology to understand injury mechanisms of both ligamentous damages and bone fractures in car-pedestrian accidents. A finite element (FE) model of the human lower limb was developed using PAM-CRASH™. The commercially available H-Dummy™ lower limb model developed by Nihon ESI for a seated position was modified to represent the standing posture of pedestrians. Mechanical properties for both bony structures and knee ligaments were determined from our extensive literature survey, and were carefully implemented in the model considering their strain rate dependency in order to simulate the dynamic response of the lower limb accurately. The element elimination option in PAM-CRASH™ was used to simulate both bone fractures and ligamentous ruptures. Bone models were validated against test results obtained from literature in both static and dynamic conditions. The dynamic response of the knee joint was validated against the response corridors from a series of experiments with Post-Mortem Human Subject (PMHS) presented in the literature. In addition, the lower limb model was validated against published experiments with isolated lower limbs subjected less motorized countries. The lower limb is one of the most frequently injured body region in severe injuries to pedestrians mainly due to direct impact from a vehicle front. According to the Pedestrian Crash Data Study (PCDS) database by NHTSA, lower limb injuries are the second most frequent region accounting for 26% of all AIS3+ injuries in pedestrians. Lower limb injuries are also very costly and often lead to long-term disability or impairment.

The validated FE lower limb model was integrated with an upper body model with rigid segments to obtain a full-body pedestrian model. Computer simulations using both the pedestrian model and a FE model for the car front were conducted to reconstruct a published car-pedestrian impact test with PMHS. Leg fracture observed in the experiment was reproduced from the FE car- pedestrian model. The developed FE model can be used as an effective tool to investigate injury mechanisms of the lower limb in car-pedestrian accidents.