Diffusion-controlled gas permeability through CFRP laminates was experimentally investigated as a fundamental research of the feasibility of composite propellant tanks. Using helium gas and a helium leak detector, through-the-thickness gas permeability in CFRP laminated tubes with or without matrix cracks was measured at room temperature. Effect of loadings on the in situ gas permeability was also clarified. It is shown that although gas permeability through CFRP laminates increase on account of the existence of matrix cracks and tensile loadings, these effects turned out not to be crucial in comparison with the leakage through multi laminar matrix cracks, which is three or four orders higher than the diffusion-controlled permeation. These results suggest that the existence of no less than one intact layer is important for feasibility of composite propellant tank. Finally, a diffusion model including the combined effects of damages and loads is applied to the experimental results and successful characterization of gas permeability is presented.
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