Development of flexible pedestrian legform impactor FE model and comparative study with leg behavior of human FE model THUMS

Miyazaki, Hiroshi; Kitagawa, Yuichi; Yasuki, Tsuyoshi; Kuwahara, Masaaki; Matsuoka, Fumio

The current legform impactor in pedestrian safety tests uses a steel shaft connected to metal plates to represent the femur and tibia. It evaluates leg fracture risk based on tibia acceleration, and knee ligament rupture risk based on knee bending angle and shear displacement. However, the impactor does not generate the tibia deflection that occurs when a vehicle impacts a pedestrian. The new flexible pedestrian legform impactor (Flex-PLI) currently under development is designed to simulate the impact behavior of the human leg, reproducing tibia deflection with flexible shafts and representing the knee ligaments using wires. As a result, it can be used to help assess injury based on deformation by estimating the risk of tibia fracture from the bending moment of the tibia shaft and the risk of knee ligament rupture from the elongation of the wires.

In this study, a finite element (FE) model of the Flex-PLI was developed to examine the impact test protocol for pedestrian leg injury assessment, comparing the impactor behavior and response with that of a whole human FE model. The Flex-PLI FE model was created by reverse engineering that reproduced the shape and mechanical properties of each part. The impact velocity of the impactor was set to 40 km/h based on accident data. An impact height of 75 mm above the ground has been proposed for the Flex-PLI in contrast to the current protocol, which specifies an impact height of 0 mm. The study compared results at the base impact height of 75 mm with those obtained at different heights. It also investigated the effect of adding mass to simulate the upper body of a pedestrian. Vehicle-to-pedestrian impact simulations were conducted with the Total Human Model for Safety (THUMS) to estimate the behavior and response of a human leg for comparison with the results from the impactor model. The bending moment of the tibia and the elongation of the knee ligament wires in an impact varied depending on the impact height and additional mass. Impactor behavior was closest to THUMS at a height of 0 mm, but a closer response to THUMS for bending moment and ligament elongation was obtained at 75 mm. It was also found that adding a mass of 6 kg to the upper end of the impactor in SUV impacts created a closer response to THUMS.

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