A Materials and Structure Perspective on the Feasibility of Automotive Frontal Protection Systems Meeting the Proposed Pedestrian Safety Test Criteria

Abstract

This article describes an investigation into the material and structural requirements of an automotive frontal protection system (FPS), i.e. ‘bull bar’, for an off-road sports utility vehicle, to meet the proposed pedestrian safety test criteria. An analytical impact model has been developed to investigate the feasibility of an FPS meeting the 2006 requirements of upper legform to leading edge and possible child headform to FPS tests. The results show that a 520 mm high and 760 mm wide FPS should be designed to have an effective cantilever flexural rigidity (EI_eff) in the range 800-1200 Nm² or less, depending on the local contact stiffness. These levels of flexural rigidity are only likely to be achievable with a deformable hollow or foam-filled plastic-type construction. Metallic and structural composite structures are too stiff or, if thin-walled, are likely to fail prematurely. The operation of the FPS relies both on cantilever bending and local crush of the structure at the impact point to absorb the required energy. Limiting EI_eff values for higher or shorter FPSs are obtained by scaling the above figures in the ratio of the height cubed. Whereas for the child headform test, the FPS can absorb the energy within the currently proposed 80 mm FPS to vehicle gap, and still pass the test requirements, this is not the case for the upper legform test. In the latter, some of the energy will need to be absorbed by the vehicle leading edge on the FPS contact. The article concludes that the analytical model is a useful tool for preliminary design to meet pedestrian safety legislation requirements.