Performance Assessment and Optimal Design of Hybrid Material Bumper for Pedestrian Lower Extremity Protection

Abstract Lower extremity injuries have exhibited a great proportion in pedestrian-vehicle accidents. This study aims to assess the performance of an innovative aluminum-steel hybrid material bumper for pedestrian lower extremity protection. Finite element (FE) models of the hybrid bumper and its two single-material counterparts were built, validated, and integrated into an automotive front-end structure. The Transport Research Laboratory (TRL) legform model was used to obtain values of the lower extremity injury indicators including the knee-bending angle α, the knee-shearing displacement Disp, and the tibia acceleration Acc, upon impacting on the three types of bumpers. Numerical results showed that the aluminum and the hybrid bumpers result in much less pedestrian lower extremity injuries than the steel bumper due to the lower stiffness and strength of the constitutive material. Besides, the hybrid bumper is superior to its homogeneous counterparts as to the requirements for both pedestrian protection at low-speed and load transfer at high-speed crashes. Moreover, multi-objective optimization designs (MOD) of the three bumpers were performed to minimize the pedestrian's lower extremity injuries, by means of the non-dominated sorting genetic algorithm (NSGA-II) and the radial basis function (RBF) meta-models. The optimal results confirmed the greatest potential of the hybrid bumper for pedestrian lower extremity protection. By virtue of the entropy weight method to determine the weighting factor of each injury indicator, Technique for Order Preference by Similarity to an Ideal Solution (TOPSIS) was used to sort the obtained Pareto designs and to select the comprehensive optimal bumpers. The TOPSIS optimum of the hybrid bumper is much closer to the ‘utopian point’, showing again its advantages over the homogeneous counterparts for pedestrian lower extremity protection in pedestrian-vehicle accidents.