기능성 플라스틱을 이용한 초경량 범퍼 백빔 설계에 관한 연구

Abstract

Recently, the demand of eco-friendly products with high energy efficiency and low environmental impact has increased to cope with the energy depletion and environmental regulation. Transport vehicle industries begins to make an effort to develop a lightweight component, which satisfies theconsisting of requirements of rigidity, strength and crashworthiness, for the reduction of overall weight and the improvement of the energy consumption rate. Due to these trends, the direction of the development of the automotive bumper is changed from the metal bumper to the plastic bumper. The objective of this thesis is to obtain a proper design of the lightweight bumper backbeam consisting of functional plastics for the automotive. Thermoplastic poly olefin (TPO), poly propylene with 20 % of glassfiber (PP(α)) and glassfiber reinforced mat thermoplastic (GMT) were chosen as alternative materials of the bumper backbeam. In order to obtain mechanical properties and strain-stress relationships with strain rate effects, tensile and high-speed tensile tests were performed. Preliminary impact characteristics, including force-deflection curves, deformation behaviours, energy absorption rates, failures, and fractures, of the alternative materials were investigated through the drop impact tests for the specimen. The results of the drop impact tests showed that the TPO material has a comparable impact property to the GMT material. In order to obtain a proper design of the bumper backbeam, three-dimensional finite element analysis was performed using a commercial code of ABAQUS V6.5 explicit. Collision test conditions of US Federal Motor Vehicle Safety Standard (FMVSS, pendulum collision type) were applied to the FE model. The results of the FE analysis for the FMVSS condition showed that the impact characteristics of the backbeam can be improved as front and rear parts of the backbeam are consisted of TPO and TPO plastic materials, respectively. In addition, it was noted that influence of the ribs in the longitudinal direction on the impact performance is higher than that of the ribs in the width direction. Using these results, alternative designs of the ribs formation (five types) for the backbeam were estimated. The repeated FE analyses for the alternative designs of the ribs formation were carried out. From the results of the FE analysis, the impact characteristics of the backbeam for alternative designs of the ribs formation were compared from the viewpoints of the energy absorption characteristics, strain-stress distributions, intrusion, and deflections. Using this comparison results, a proper rib design of the backbeam was estimated. The collision tests for the FMVSS were carried out to verify the estimated deisgn of the bumper backbeam. The specimen was manufactured from the injection molding of front and rear parts and the vibration welding of the two parts. The results of the collision tests showed that the designed bumper backbeam satisfies the regulation of FMVSS. From this results, it was shown that the proposed design of the bumper backbeam can be applied to the development of the lightweight bumper backbeam. In the future, additional researches, including the FE analyses and the collision tests for the regulation of Insurance Institute for Highway Safety (IIHS, barrier collision type), should be carried out to commercialize the proposed design of the bumper backbeam.