SAE International Study on Engine Hood with Negative Poisson's Ratio Architected Composites Based on Pedestrian Protection 2017-01-0368

The conventional hood with single material and stiffener structural form conceals some limitations on pedestrian protection and lightweight, not satisfying the requirements of structural strength, pedestrian protection and lightweight contradictory with each other at the same time. In this paper, a novel type hood is proposed to develop sandwich structure using architected cellular material with negative Poisson's ratio (NPR) configuration based on the decoupling thought of structural strength and energy absorption. Core-layer aluminum alloy material with NPR is used to meet the requirement of impact energy absorption, inner and outer skin using carbon fiber is selected to achieve high structural stiffness needed. This paper starts from the relations between geometric parameters of core-layer architected cellular material and mechanical properties, on this basis, the optimal geometric parameters can be expected using the multiobjective optimization method. Eventually, the optimal novel hood can be obtained using three layer thicknesses as optimization variables, minimum HIC value and minimum mass as objectives. It should be noted that global stiffness of the novel hood is not less than that of conventional hood, and entire thickness of the novel hood is not larger than conventional hood and impact intrusion of novel hood is less than safe distance between hood and engine. Based on limitations above, optimal layer thicknesses of architected cellular structure can be achieved. Then, the novel hood is compared with the conventional hood. The results show that the average HIC value of corresponding collision points in the novel hood decreases by 45%. In addition, bending stiffness of the novel hood achieved increases by 33%, and torsional stiffness increases by 67%. While the weight is reduced, 18.95% exactly. Thus, the novel hood proposed in this paper demonstrates outstanding performance in terms of pedestrian protection, structural stiffness enhancement and weight reduction.