에너지의 변화에 따른 경량화용 CFRP구조부재의 충돌 안전 특성

Abstract

In the present study, the impact properties of a CFRP structural member under an impact load were intentively investigated for passenger safety protection under assuming the commercial use of carbon fibers reinforced plastic (CFRP) structural members in lightweight cars; in addition, the superiority of the impact properties depending on its layer configuration was experimentally investigated. Especially, the impact properties and collapse modes depending on the cross-sectional shape of the CFRP material, the outermost layer angle, and interlaminar number were studied to obtain the optimum data for lightweight vehicular body design with improved fuel efficiency and passenger safety performance. The obtained results from this research are the following:

1. With an impact energy of 611.52 J, the smallest collapse length of CFRP material with a circular cross-section was 54.7 mm when the outermost layer angle was at 0° however, at 90°, the smallest collapse length was 34 mm, which is approximately 60% shorter. Hence, in order to secure the internal space for guaranteed passenger safety after a collision, the outermost layer angle of the CFRP material with a circular cross-section is 90°, and the impact property seems to be the most outstanding when the interlaminar number is 6.

2. For an impact energy of 372.4 J, for CFRPs with a rectangular cross-section, the smallest collapse length of 64.0 mm occurred with an outermost layer angle of 0° however, the length decreases to 59.5 mm at an angle of 90°, which is about 8% shorter. Therefore, in order to secure the internal space for guaranteed passenger safety after a collision, the outermost layer angle of CFRP material with a rectangular cross-section is 90°, and the impact property seems to be the most outstanding when the interlaminar number is 2.

3. When the outermost layer angle was 0°, the CFRP member with a circular cross-section collapsed due to the gradual propagation of interlaminar and intralaminar cracks, followed by the outwardly expanding Spline phenomenon in the member. Moreover, the laminar flexure caused by the propagation of interlaminar and intralaminar cracks, the movement accompanied with the collapsed surface, and the packaged-laminar friction at the load surface mainly absorbed the energy, and it was collapsed in a brittle fracture mode of combined transverse shear and fiber flexural modes along the fiber direction. However, in the case of the outermost layer angle of 90°, longitudinal fibers at 0° tried to expand outward in the member at impact collapse, but the members, along with the fibers at 90°, broke and collapsed in a ductile fracture mode.

4. For the CFRP members with a rectangular cross-section, when the outermost layer angle is at 0°, the laminar flexure due to the propagation of interlaminar and intralaminar cracks in the plate member, the packaged-laminar and matrix rupture due to the transverse shear mode in the corner member, the flexure of packaged-laminar, and the rupture of fibers absorbed most of the energy. Moreover, the plate members expanded outward with progressive propagation of interlaminar and intralaminar cracks when the outermost layer angle is at 90°but the corner member collapsed into a combined form of the packaged laminar fiber and matrix rupture and the laminar flexure due to transverse shear mode.