Design and multi-objective optimization of the bumper beams prepared in long glass fiber-reinforced polypropylene

There is an increasing demand for lightweight materials in the automobile industry. In this study, the crashworthiness and crash safety performance of automobile bumper beams made of long glass fiber-reinforced polypropylene (LGFR-PP) composites were evaluated. First, LGFR-PP with the 40% glass fiber was prepared by the hot-melt impregnation method, the mechanical properties and Poisson's ratio of the LGFR-PP specimens were tested, which are essential for the finite element analysis. Then a finite element model of aluminum alloy and LGFR-PP bumpers was established to obtain their peak collision force, maximum intrusion, and energy absorption values under longitudinal and angular low-speed collision conditions. Subsequently, the multi-objective optimization was generated using optimized Latin square sampling and response surface test design, and the section thickness of the bumper beams was optimized. The results showed that Swift and Hockett's hardening model is suitable for the LGFR-PP material. Based on the principle of equal stiffness, the mass of the anti-collision beams made of LGFR-PP is reduced by 17.4%, the specific energy absorption (SEA) is increased by 6%, and the cost is reduced by 69%, and both the peak impact force and the amount of collision intrusion are reduced. The multi-objective optimized Latin hypercube experimental showed that the continuously variable cross-section beam based on the thickness optimization balanced the impact resistance especially SEA and lightweight performance very well.