Analysis of the influence of passenger vehicles front-end design on pedestrian lower extremity injuries by means of the LLMS model

Objective: The work aims at investigating the influence of some front-end design parameters of a passenger vehicle on the behavior and damage occurring in the human lower limbs while impacted in an accident. Methods: The analysis is carried out by means of finite element analysis using a generic car model for the vehicle and the Lower Limbs Model for Safety (LLMS) for the purpose of pedestrian safety. Considering the pedestrian standardized impact procedure (as in the 2003/12/EC Directive) a parametric analysis, through a DOE plan, was done. Various material properties, bumper thickness, position of the higher and lower bumper beams and the position of pedestrian, were made variable in order to identify how they influence the injury occurrence. The injury prediction was evaluated from the knee lateral flexion, the ligaments elongation, and the state of stress in the bone structure. Results: The results highlighted that the offset between the higher and lower bumper beams is the most influencing parameter affecting the knee ligament response. The influence is smaller or absent considering the other responses and the other considered parameters. The stiffness characteristics of the bumper are, instead, more notable on the tibia. Even if an optimal value of the variables could not be identified trends were detected, with the potential of indicating strategies for improvement. Conclusions: The behavior of a vehicle front-end in the impact against a pedestrian can be improved optimizing its design. The work indicates potential strategies for improvement. In this work, each parameter was changed independently one at a time: in future works the interaction between the design parameters could be also investigated. Moreover, a similar parametric analysis can be carried out using a standard mechanical legform model in order to understand potential diversities or correlations between standard tools and human models.