Lower Leg Injury in Relation to Vehicle Front End

Abstract

Objective: To set up a prescreening tool for vehicle front-end design, allowing numerically forecasting of the results of EC directive tests, with reference to pedestrian lower leg impact.

Methods: A numerical legform model has been developed and certified according to EC directive. The frontal end of the vehicle has been simulated through a lumped-parameters model, having considered the predesign stage when the target overall behavior is being established. The stiffness behaviors of the bumper and of the spoiler have been estimated by means of more detailed numerical models.

A parametric analysis has been performed to outline the effects of bumper and spoiler stiffness, bumper vertical height, and the longitudinal distance between the spoiler and the bumper.

An analytical model has been introduced to predict tibial acceleration, knee shear displacement, and knee lateral bending, given the bumper and spoiler characteristics as input.

Results:The parametric analysis has demonstrated that bumper stiffness, bumper profile height, and spoiler stiffness do have an impact on knee lateral bending, knee shear displacement, and peak tibial acceleration. Increasing bumper stiffness can result in higher knee bending, knee shear displacement, and peak tibial acceleration. Increasing bumper profile height produces lower knee bending and shear displacement. Increasing spoiler stiffness can determine higher knee shear displacement and peak tibial acceleration but lower knee bending. Spoiler stiffness and position have a strong correlation: higher bumper stiffness needs to be coupled to a moved forward spoiler position.

The mechanical responses of the spoiler and of the bumper can be assumed to be linear: the softening behavior of the expanded polypropylene foam balances the hardening behavior of the fascia (due to contact area increase).

The predictive model is well correlated to experimental findings (R ² > 0.74)

Conclusions: This simplified computer model can be used as a prescreening design tool to demonstrate general vehicle front-end design trade-offs and provide approximate results without physical testing.

Keywords:

• pedestrian
• vehicle front end
• lower leg
• spoiler
• bumper

Acknowledgments

The authors thank Massimiliano Faone, Massimiliano Salaorno, and Fabio Vasta for taking part in the experiments and for performing numerical simulations.