충격 흡수용 경량화 차체구조부재의 안전성능 평가

Abstract

The purpose of this study is to evaluate the safety performance of lightweight vehicular members for the use of impact absorption. The recent trend in vehicular design is aimed at improving both the environment-friendly quality and collision safety requirements for the vehicles. For the former, the trend is toward light-weight of vehicles to improve fuel efficiency and reduce tail gas emission due to the heavier restriction on exhaust levels. For the latter, however, the trend is toward higher safety performance, comfort level, high-efficiency and multi-functional programs which all increase the weight demands. Therefore, the light weight of vehicle must be achieved in a status of securing safety of collision. In this study, the lightweight vehicular members of impact absorption were made of aluminum and composite materials, which are representative light-weight materials. Those members were analyzed by collapse characteristics under axial loading. The axial collapse tests were performed for square, circular and hat-shaped members which are basic shape of vehicle structural members. Because the carbon fiber reinforced plastics (CFRP) are anisotropic materials whose mechanical properties, such as strength and elasticity, change with its stacking condition, special attention were given to the effects of the stacking condition on the collapse characteristics for the vehicular members of impact absorption. Following the above study, conclusions are drawn as below;

1. The collapse modes for the square Al/CFRP compound member are classified into split mode, combination mode, folding mode and fragmentation and splaying mode. Those phenomena were mainly determined by the orientation angle of the CFRP. When the orientation angle of the CFRP was small, the members were separated the each member at the interface after the initial peak load. Those members absorbed energy by progressive deformation of the inner aluminum member and laminar bending of the outer CFRP members. As the orientation angle increases, the fiber withstands the load through the hoop stress. The inner aluminum member collapsed in progressive deformation and fiber of the outer CFRP member was inserted between the folding of inner aluminum member by local buckling.

2. The square Al/CFRP compound members showed better energy absorption as fiber orientation angle of CFRP becomes larger. The most effective energy absorption was shown when it was 0°/90° with 90° orientation angle of outer. And the characteristics of energy absorption are independent on the variation of interface number.

3. The collapse modes for the circular Al/CFRP compound member are classified into split mode, combination mode, fragmentation mode and fragmentation and splaying mode. Those phenomena depend on the orientation angle of the CFRP. When the orientation angle of the CFRP was small, the members were separated the each member at the interface after the initial peak load. Those members absorbed energy by progressive deformation of the inner aluminum member and laminar bending of the outer CFRP members. As the orientation angle increases, the fiber withstands the load through the hoop stress. The inner aluminum member collapsed in progressive deformation and most of the fibers were broken without being inserted between the folding of the aluminum member because the gap in the folding is too small.

4. The circular Al/CFRP compound members showed better energy absorption as fiber orientation angle of CFRP becomes larger like the square Al/CFRP compound members. The most effective energy absorption was shown when it was 0°/90° with 90° orientation angle of outer. And the energy absorbing characteristics are independent on the variation of interface number.

5. The CFRP hat shaped section members were collapsed according to the different orientation angles by compounding of the 4 different modes: transverse shearing, laminar bending, brittle fracture, and local buckling. When the fiber orientation angle was small, the members absorbed energy by laminar bending. As the fiber orientation angle increases, the member was absorbed energy by local buckling and matrix crack due to transverse shearing.

6. As shown the absorbed energy decreases linearly, energy absorption was most effective when the fiber orientation angle of CFRP was 0°/90° and 90°/0° as the fiber orientation angle increases. The absorbed energy increases to the 6 interlaminar number with increasing interlaminar number. However, decreasing trend is observed on moving to the 7 interlaminar number. The energy absorption capability of the members increases as the sectional area ratio (sectional area ratio of flat member to "∩" shaped member) increase due to stress concentration on their edges. The absorbed energy of hat shaped compound members is slightly lower than that of combined effect of the CFRP member and the aluminum members alone. The interaction effect was not shown because inner aluminum member applied load to the outer CFRP members in the form of hoop stress; therefore the CFRP and the aluminum member were split each other.