파괴역학적 접근법을 통한 CFRP-PVC폼 코어 샌드위치 복합재의 특성에 관한 연구

Abstract

The light weight composite materials have been replacing in high performance structures. The object of this study is to examine the effects of the initial crack location on the delamination in a PVC foam cored sandwich composite that is used for the strength improvement of structures. To analysis the effects of the initial crack location on the delamination, the thickness of fiber laminates were changed with three types. The modeⅠ and MMB(modeⅠ+Ⅱ) specimen was used for evaluating the fracture toughness and crack behaviors. The material used in the experiment is a commercial twill carbon prepreg in CFRP material and Airex in PVC foam core. Sandwich laminate composites are composed by PVC foam core layer between CFRP face sheets. The face sheets were fabricated as 3 types of 3, 5 and 8 plies. The initial cracks were located in a PVC form core and the interface of upper CFRP sheet. From the results of the DCB tests, the crack initiation was affected with the location of the initial crack inserted in the PVC foam core. The initiation of the crack firstly affected by the initial crack insertion location, and the initial crack insertion at the center of the PVC foam showed a rapid progress. Among them, the lamination of CFRP with 8 plies made the most rapid progress. And the critical energy release rate was 0.09 kJ/m2, which is the lowest value when the initial crack was inserted into the interface between a PVC foam core and CFRP laminated with 3 plies at face sheet. Meanwhile, the highest value of 1.70 kJ/m2 was obtained when the initial crack was located at the center line of PCV foam in case of the 8 plies face sheets. On the MMB tests, the crack initiation was affected with the location of the initial crack inserted in the PVC foam core. Among them, the initial crack at center of the PVC foam core was the most rapid progression. And the critical energy release rate was 1.24 kJ/m2, which is the lowest value when the initial crack was inserted into the center of a PVC foam core and CFRP laminated with 3 plies. Meanwhile, the highest value of 11.60 kJ/m2 was obtained when the initial crack was located at the interface between a PVC foam core and CFRP in case of the 8 plies. On the MMB tests applied fulcrum location change, the crack initiation was affected with the location of fulcrum location. Among them, the critical energy release rate was 1.93 kJ/m2, which is the lowest value when the fulcrum location was 90 mm and CFRP laminated with 3 plies. Meanwhile, the highest value of 27.25 kJ/m2 was obtained when the fulcrum location was 90 mm in case of the 8 plies.