A New Development in Pedestrian Safety: the FLEX PLI GTR LS-DYNA Model

The lower limb is one of the most frequently injured body regions in crashes involving pedestrians. A biofidelic FLEXible-Pedestrian Legform Impactor Global Technical Regulations (FLEX-PLI GTR) device has been developed under directions of the Flex-PLI Technical Evaluation Group (FLEX-PLI TEG). First Technology Safety Systems (FTSS) is developing a LS-DYNA model in addition to the hardware counterpart. The FLEX-PLI GTR is the latest development and successor of the earlier GT version. The FLEX-PLI GTR device has three regions: femur, knee and tibia. Outer rubber and neoprene foam layers represent the skin and flesh. The femur and tibia regions are segmental to achieve flexible bending behavior representing human like responses during pedestrian crashes. The central bone cores of the tibia and femur have bending moment measuring capabilities at several locations. The knee region has ligament elongations measuring capabilities to be used as injury criteria in regulations. This paper documents the development and dynamic validations of the FTSS FLEX-PLI GTR LS- DYNA model. The model geometry and inertia properties are obtained from available drawings and hardware. The model connectivity and structural integrity are inspected by experiments and verified against hardware. The model material properties are implemented from material test data. The model is then validated against dynamic calibration test for FLEX-PLI assembly without outer skin, and a full legform test against a flat rigid impactor (called inverse test). The femur and tibia bone bending moments and knee ligament elongations from the model output are compared to test data to evaluate model performance and injury predictability. The FTSS FLEX-PLI GTR LS-DYNA model revealed very promising performance in all validation cases and can be potentially used in future pedestrian safety regulations. The model has a 0.85 micro second time step and was found to be very cost effective (in terms of CPU times) and reliable for pedestrian safety simulations.