A comparative study on empty and foam-filled hybrid material double-hat beams under lateral impact

In previous research, an innovative hybrid material double-hat thin-walled beam has been proposed for vehicle bumper system, which has demonstrated great potentials for improved pedestrian safety and reduced weight. In this work, we have used aluminum foam to fill the hybrid double-hat beam to further its application in vehicle bodies with increased bending resistance and energy absorption efficiency. Bending behaviors of both empty and foam-filled hybrid beams were numerically investigated using the validated LS-DYNA models. Three representative loading positions including the mid-span, 50 mm and 100 mm offsets from the mid-span were simulated to reveal the effect of load position uncertainty. It was found that the foam filler could increase the specific energy absorption (SEA) by more than 30% and double the bending moment (Mb) of the empty hybrid beam by changing its deformation pattern. Moreover, the foam-filled beam shows more robust crashworthiness performance against load position variation. Using radial basis function (RBF) metamodels, the multi-objective design optimization (MDO) problems were formulated for both empty and filled hybrid beams to maximize SEA and Mb and minimize the initial peak force (Fip). The multi-objective particle swarm optimization (MOPSO) was used to seek the Pareto fronts of the MDO problems. The MDO results show that the foam-filled beam has much broader performance space in terms of Fip, SEA and Mb and has great potentials for high-energy crash applications. It was also found that the Pareto front varies for different loading positions for either empty or filled hybrid beam. Including multiple loading positions could achieve a more robust design against load uncertainty. Appropriate weighting factors should be chosen for different loading positions to yield realistic and more robust designs of the proposed hybrid beams.