A New Approach to Multibody Model Development: Pedestrian Lower Extremity

Objective: The goal of this study was to develop a mathematical model of the 50th percentile male lower extremity capable of predicting injury risk and simulating the kinetic and kinematic response of the pedestrian lower extremity under vehicle impact loading. Methods: The hip-to-foot multibody model was developed for the MADYMO software platform using exterior and interior geometry and inertial properties from a detailed finite element model (FEM) of the human lower extremity and stiffness and failure tolerance data from the literature. The leg and thigh models' structural and contact parameters were simultaneously optimized to validate model response in simulations replicating previous dynamic bending experiments. The aggregate model's full-scale kinematic response was verified by comparing 3-D local (knee bending angles) and global (linear accelerations and velocities) frame leg and thigh kinematics from vehicle impact simulations with data generated from seven vehicle-pedestrian (PMHS) impact experiments. Results: By optimizing contact and structural response variables, the applied moment vs. deflection response of the leg and thigh showed excellent correlation with the experimental corridor averages in component-level bending simulations. The full-scale kinematic response of the 50th percentile male model showed good correlation with the PMHS response data in both the rate of valgus knee bending ( 3 degress/ms) and in the timing and magnitude of the peak thigh and leg accelerations (250 g and 400 g). Additionally, as a result of vehicle interaction, both the model and the experiments showed that the thigh and leg are initially accelerated upward (100 g) and downward (100 g), respectively, and then downward (60 g) and upward (100 g), respectively. The model also predicted a valgus knee injury and a tibia fracture similar to those seen in the PMHS. Conclusions: The use of a facet surface model of the lower extremity skin and simultaneous optimization of the model's structural response and contact parameters resulted in a model capable of accurately predicting the detailed kinematic response of the lower extremity under vehicle impact loading at 40 km/h. The model can be scaled to represent varying pedestrian anthropometries and can assess the risks associated with sustaining the most common pedestrian injuries. As a vehicle design tool, the model can be used to optimize front-end designs, or it can be used in combination with a detailed FEM to reduce the vast design space prior to FE simulations. Additionally, the model can be used as a tool to study pedestrian impact kinematics, real-world case reconstructions, or particular vehicle countermeasures.