적층구성이 다른 CFRP 사이드 부재의 충돌안전특성

Abstract

This study quantitatively analyzed the impact collapse characteristics and collapse modes with respect to changes in section shapes and stacking angle changes by fabricating CFRP members with different section shapes, namely, square, single-hat, and double-hat shapes. The goal was to obtain design data that can be applied in the development of optimum lightweight structural members for automobiles. The conclusions of this study are as follows.

1. The CFRP structural members with the stacking angles of [-15°/+15°]4 collapsed in the splaying mode, in which energy absorption occur sowing to longitudinal cracks, laminar bending, and external expansion. The member with the stacking angle of [90°/0°]4 collapsed owing to transverse cracks in the fragmentation and splaying mode. Further, the member with the stacking angle of [-45°/+45°]4 collapsed in the splaying/fragmentation mode, which is the combination of the collapse modes of the members with the stacking angles of [-15°/+15°]4 and [90°/0°]4. When the stacking angle was close to 0°, the collapse occurred in the splaying mode. However, when the stacking angle was close to 90°, it occurred in the fragmentation mode. 2. The maximum collapse load, average collapse load, average stress, absorbed energy, and the absorbed energy per unit mass of the CFRP member with the square-shaped section had the highest values when the stacking angle was [90°/0°]4. These values decreased in the order of the stacking angles of [90°/0°]4, [-15°/+15°]4, and[-45°/+45°]4. Inparticular, the absorbed energy per unit mass was approximately 30% higher for the stacking angle of [90°/0°]4 than that for [-15°/+15°]4. This was because, during the impact collapse, the lamination at 90°counter acted the collapse. It is considered that the absorbed energy and the absorbed energy per unit mass were comparatively higher owing to the slightly greater debris dispersion. 3. The impact characteristics of the CFRP member with the single-hat-shaped section were of the highest quality when the stacking angle was [-15°/+15°]4. They degraded in the order and less excellent in the order of the stacking angles of [90°/0°]4, [-15°/+15°]4, and[-45°/+45°]4. Particularly, the absorbed energy per unit mass of the CFRP member with the single-hat-shaped section and stacking angle of [-15°/+15°]4 was approximately 53% and 76.7% higher than that of the members with the stacking angles of [-45°/+45°]4 and [90°/0°]4, respectively. 4. The impact characteristics of the CFRP member with the double-hat-shaped section and stacking angle of [-15°/+15°]4 were also of the highest quality. Specifically, the maximum collapse load, collapse stress, and the absorbed energy per unit mass of the member with the stacking angle of [-15°/+15°]4 were approximately 67.7%, 80%, and 70% higher than the respective characteristics of the members with the stacking angles of [-45°/+45°]4 and [90°/0°]4. The values of the impact characteristics of the CFRP members with double-hat-shaped sections and stacking angle of [-45°/+45°]4 and [90°/0°]4 were similar. This demonstrated that the CFRP member with the double-hat-shaped section was influenced to a lesser degree by the stacking angles of 45°,0°,and 90°compared to the CFRP member with the single-hat-shaped section. Therefore, the CFRP member with the double-hat-shaped section was confirmed to have the most stable and highest quality impact characteristics. 5. In the case of a squared cross-sectional CFRP members, interlaminar/ intralaminar cracks of plate members were expanded outward with the gradual progress and four locations of member edges were observed to be ripped off. When the fiber breakage was generated, ripped-off parts were shown in the CFRP members; so it was confirm that such phenomenon brought lots of impact energy to be absorbed. In the case of a single cap-shaped members, crush of ‘ㄷ’-shaped member was generated and proceeded along the fiber direction and the fiber breakage was shown at the edges which caused of almost impact absorbed energy. It was thought the rapidly stress concentration at the edges with the suddenly changing cross-section brought fiber breakage and expansion phenomenon of plate bonding area to be generated in both‘ㄷ’-shaped members and plate cross-sectional members. 6. In the case of a single-hat CFRP members, cleave phenomenon to outward expansion between plate member and the flange locations of bonding area in ‘ㄷ’-shaped member was obseved; but such cleave phenomenon was no shown in double-hat CFRP members. It was thought that such cleave phenomenon at the flange locations was generated due to asymmetry curing between ‘ㄷ’-shaped member and plate members. However, such cleave phenomenon at the flange locations was not observed due to symmetry curing for double-hat member. Therefore, a single-hat member could not resist enough loading because cleave phenomenon occurred between ‘ㄷ’-shaped member and plate members; but impact resistance was considered to be higher because cleave phenomenon occurred between ‘ㄷ’-shaped member and plate members was not generated with increasing number of edges and thickness effect of flange portion.