Leak Prevention of Nitrogen Gas for Plain Woven CF/Epoxy Composites by Filling Nanofiller under Cryothermal Fatigue

Abstract

Carbon fiber reinforced plastics (CFRP) are widely used as structural components and are regarded as the major candidates for reducing the structural weight. Especially, application of CFRP to the cryogenic liquid fuel tanks is one of the most yearnings for achieving the drastic weight reduction. To apply CFRP for the fuel tank instead of the aluminium alloy, behaviors of CFRP such as fuel leakage or gas permeation under the cryogenic temperature should be cleared. The purpose of this study is to improve the nitrogen gas permeation properties of Plain-Woven CFRP. To improve the permeation properties of CFRP (V-CFRP), the nanoclay filler, which is montmorillonite is compounded (M-CFRP). The leakage pathway of nitrogen gas through the laminates is also revealed in order to identify the major factor of leakage. The leak rate of CFRP after cryothermal fatigue tests was increased as cyclic number increases. This is because that the interfacial debonding and micro cracks were initiated in CFRP due to cryothermal cycling. The increase of leak rate due to crack initiation was significantly higher than that due to the nitrogen diffusion through the matrix. The micro crack density and crack length of M-CFRP were improved compared to V-CFRP. This is because that the fracture toughness of epoxy resin improved by filling the montmorillonite. Therefore, the leak rate of M-CFRP was decreased, and the permeation properties can be improved by filling montmorillonite. The velocity of diffusion of M-CFRP until reaching steady leakage was lower than that of V-CFRP. It should be said that the montmorillonite, which is the inorganic material plays the role of the obstacle for nitrogen molecule.