경량화용 Al/CFRP 혼성부재의 충격압궤특성

Abstract

The number of car parts as the configuration is made up of various materials. This material need of consumers and the environment continue to change and has been developed. According to these demands, too much is changing automotive materials. As well as high-strength materials, light-weight metal and plastic, environmentally-friendly materials and nano-materials have been developed. To the Light-weight materials the aluminum, magnesium alloy, non-ferrous metal, Glass Fiber Reinforced Plastics (GFRP) and Carbon Fiber Reinforced Plastics (CFRP) is used. The research for these applications is advanced and the use will extend is predicted. In this study, the compound members were manufactured using aluminum and Carbon Fiber Reinforced Plastics (CFRP) which are representative light-weight materials. The disadvantages of aluminum and CFRP members were considered to be mutually complimentary while the advantages of each member were combined to exhibit collapse characteristics of effective structural members. Impact axial collapse tests were carried out for the compound members, which comprised an aluminum member externally reinforced by stacking CFRP. In particular, among the design variables of the anisotropic CFRP, axial collapse characteristics have been examined according to the changes of orientation angle. The CFRP is an anisotropic material whose mechanical properties, such as strength and elasticity change with its fiber orientation angle. The collapse mode and energy absorption capability of compound member was analyzed with change of the fiber orientation of CFRP and interface number. Following the above study, conclusions are drawn as below;

1. The collapse modes of the square compound member are categorized into split mode, combination mode, folding mode and fragmentation and splaying mode. The collapse modes of the circular compound impact absorbing member are categorized into split mode, combination mode, fragmentation mode and fragmentation and splaying mode.

2. When orientation angle was stacked similarly to axial direction, the member was separated the each member at the interface after the initial peak load. This member absorbed energy by progressive deformation of the inner aluminum member and laminar bending of the outer CFRP member. 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.

3. The square and circular compound member 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 energy absorption characteristics are independent of the variation of interface number.

4. It was found out that absorbed energy do not affect significantly on the changes of interface number. The reason is that the biggest factor of absorbed energy of CFRP member is the fiber breaking and propagation of crack and crack can largely be classified into inter-laminar crack, intra-laminar crack and central crack. Therefore, in case of CFRP member, it was found out that it is effective for the absorbed energy as the number of frequency of generating cracks between layers according to the increase of interface number increases. However, in case of the compound member, it is estimate that influence of energy absorption capability by interface number is not appearing, because energy is absorbed mainly by the fiber breaking and stabled plastic deformation of aluminum than the propagation of crack.

5. The absorbed energy of circular member was appeared approximately 47% higher than square member. Since stress is concentrated on their edges when strength member receives axial load and therefore, it is believed that circular member that has infinite number of corners absorbs more energy than square member that has four corners.