平織CFRP複合材의 modeⅡ層間破壞 및 AE特性에 關한 硏究

Abstract

Recently, composite materials are used in many fields because their properties are high strength, high stiffness, and they have light weight, good corrosion resistance and good thermal conductivity.However, composite materials have relatively a lot of problems, especially delamination, compared with common materials such as a steel and aluminum, etc. Therefore, having the interlaminar fracture toughness for a laminate composite is important. In this study, the end notched flexure (ENF) specimens are employed in order to evaluate modeⅡ interlaminar fracture toughness for CFRP laminate composites. ENF specimens using fabric carbon prepregs are fabricated in a hot-press that is controlled with the gauge pressure and temperature. Three kinds of pressure levels are adopted for fabricating laminate to examinate the effect of the pressure variation on the interlaminar fracture toughness. And three kinds of a/L ratio was applied to these specimens. Also, we discuss the relation of crack growth and the interlaminar fracture toughness in terms of AE characteristics using ENF test. The experiment material used a commercial material of CF 3327 EPC in plain woven carbon prepreg(Hankuk Carbon Co.). The measure tester used universal dynamic tester (50kN) of Hyunyang Co. AE evaluation was acquired by PC system with AE DSP 32/16 board. AE data was analyzed by AE analysis software in MISTRAS-2001. The crack length was measured by traveling microscope. For plain woven CFRP composite, three-point bending test with the ENF specimen was conducted to evaluate the modeⅡ interlaminar fracture toughness and AE characteristic estimation with AE energy, and the conclusions are as following. 1) The load tends to linearly decrease. And the crack grew rapidly at the sudden decreasing load point. It was independent of pressure variation. Also the rapid crack extension length was decreased along with the molding pressure. The maximum load was decreased by the molding pressure from 0.98MPa to 5.88MPa. And crack initiation was delayed, but resistant force of crack extension was increased. 2) The modeⅡ interlaminar fracture toughness, GⅡc was obtained similarly for molding pressures of 0.98MPa, 3.43MPa and 5.88MPa, respectively. Therefore, interlaminar fracture toughness was regardless of the pressure variation. In contrast to, the resistance of energy release rate, G for the crack length was increased with a parabolic curve. This is maybe because of the specific fiber-bridge phenomenon of woven fabric, which was not able to be seen in homogenous material. 3) The AE count needed at least that of 1.74×10², 3.35×10², 3.32×10² to crack extension for the molding pressures of 0.98MPa, 3.43MPa and 5.88MPa.Also AE amplitude can be used as the meaningful characteristics for modeⅡ fracture toughness of plain woven CFRP.