Design and optimization of the composite automobile frontal bumper system under high speed impact loading

This study consists of three stages. In the first stage, the thickness of the thin-walled steel energy absorber tube was optimized. Then the study aimed to evaluate the effect of plastic forming history carried out for thickness optimization on crashworthiness performance of the optimized energy absorber subjected to high speed impact to achieve the desired tube form. Thus, the impact performance of the energy absorber tube was obtained by evaluating the coupled effect of the thickness distribution and the plastic forming processing of the tube. In the second step, the layer thickness and orientation of the bumper beam made of carbon fiber composite material was optimized under the impact loads with reference to the bumper beam made of steel. The third and final phase of the study covers the studies on arranging the connection between the composite bumper beam and the thin-walled steel energy absorber tube. Adhesive bonding was preferred for joining method. Three adhesives with different mechanical properties were evaluated in this joint area and the most suitable one was selected in terms of impact performance. Afterwards, the geometric properties of the selected adhesive were optimized by considering the impact behavior of the frontal bumper system. The results showed that impact performance of the energy absorber was highly affected from the thickness distribution and plastic forming processing. Furthermore, it was observed that neglecting the coupled effect of the thickness distribution and the plastic forming processing yields misleading conclusions. Additionally, it was determined that the carbon fiber composite bumper beam exhibited at least as good impact performance as the steel bumper beam, while its weight was significantly reduced. The studies with adhesives have shown that adhesive thickness and bumper beam radius directly affect the impact performance of the hybrid front bumper system. Thus, it has also been shown that the adhesive bonding can safely be used in the junction areas of the automobile hybrid frontal bumper system.