초기 균열길이 및 섬유방향이 CFRP/GFRP 하이브리드 적층재의 층간 파괴에 미치는 영향

Abstract

Renewable energy resources, of which wind energy is prominent, are part of the solution to the global energy problem. Considering the wind power system and the rotor blades which are composed of much technology, the wind power blade would be the most dangerous part because it revolves at high speed and weighs about dozens of tons, if the accident happens. Therefore, the light weight composite materials have been replacing as substitutional materials. The object of this study is to examine the delamination and damage for CFRP/GFRP hybrid laminate composite that is used for strength improvement of a wind power blade. The influence of the initial crack length and fiber orientation for the interlaminar delamination was estimated for the safety of blade. Plain woven CFRP instead of GFRP material was inserted into the layer of the box spar for the improvement of strength and blade life. Fracture toughness and damage examination of interlaminar delamination were evaluated by using DCB(Double Cantilever Beam) specimen. The materials used in the experiments are a commercial material known as CF 3327 EPC (Hankuk Carbon Co.) in plain woven carbon prepreg and UD glass fiber prepreg (Hyundai Fiber Co.). The 5kN universal testing machine and a traveling microscope connected to a PC were used for the experiments. From the results, crack growth rate have not so different according to the initial crack length. ModeⅠ interlamainar fracture toughness of fiber direction 0° is higher than those of 45° . Interlaminar fracture have an effect on fiber orientation and K decreased with lower value according to the increasing initial crack length. Also energy release rate fracture toughness was evaluated because CFRP/GFRP hybrid composite with a different thickness in each layer is under the mixed mode condition. The interlaminar fracture was almost governed by mode I fracture even though the mixed mode condition. After crack advanced along the interface of CFRP and GFRP layers, growing crack stops and restart at the GFRP layer. After that, crack grew toward the interface again. GFRP fiber strands were pulled-out and show the bridging effect which connecting the CFRP and GFRP layers. And other fiber of GFRP were shown as truncated form. The crack initiates from 5mm and 3mm displacement for a= 0.42 and 0.375, respectively regardless of CFRP fiber orientation. The crack growth rate for the load displacement at the 45° case is lower than 0° case. According to the initial crack length, the crack growth rate was not much different. The total energy release rate G is 0.67kJ/m and the mode I contribution G is 0.664kJ/m for the fiber orientation 0° and a=0.42. Therefor, the interlaminar fracture is governed by the mode I. In other cases, similar results are obtained. The mode mixity angle is obtained as = 6.61°.