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Cross-section Shape Design of an Aluminum Crash Box for Crashworthiness Enhancement (충돌성능 향상을 위한 알루미늄 크래쉬 박스의 단면 형상 설계)
Crash box is situated in the front and rear end of the body structures to absorb energy at low speed impacts. Aluminum alloys have become attractive in the design of auto-body because their low weight reduces the fuel consumption and emission and aluminum has the ability to be recycled. This paper deals with the crashworthiness and behavior of aluminum crash box for an auto-body. Various cross-sections and rib shapes are evaluated for crashworthiness enhancement through FEM analyses. Alloy A7003 temper T7 is considered as the material of aluminum crash box. Typical true stress-true strain curves of the material were found by static and dynamic tensile testing to apply the crash analysis. Three cross sections of rectangle, hexagon and octagon were considered for the crashworthiness evaluation and effect of shapes of rib in the cross section was investigated. In case of the pure axial crushing, the analysis result shows that the octagon cross section shape has higher crashworthiness than other cross section shapes. The diaphragm which connects the face with the face in the cross section shows higher specific energy absorption and lower peak load than the diaphragm which connects the edge with the edge. Differently from unit analysis of the pure axial crushing, simplified auto-body model for the front of the full car was proposed. This simplified auto-body model consists of bumper beam, crash box, front side member and subframe. Mass points and moment of inertia were controlled to represent the behavior of full car. Simplified auto-body model considers mutual relation in front parts of full car and is effective compared to full car analysis. The analysis result shows that the rectangle cross section has higher crashworthiness than other cross section shapes. In case of hexagon and octagon cross section, as the width of crash box reduces, collapse modes of torsion and buckling are observed. The diaphragm which connects the edge with the edge shows higher specific energy absorption and lower peak load than the diaphragm which connects the face with the face. This paper presents new design method of a crash box through the comparison of simplified auto-body model analysis with unit analysis of pure axial crushing.