The mechanism of the through-thickness gas leakage of carbon fiber-reinforced plastics (CFRP) laminates is investigated in view of propellant leaks for composite tanks of reusable launch vehicles. In this study analysis of leakage caused by the existence of matrix cracks acting as the chain of leakage paths is developed under the simple assumption that conductance for leakage is a function of crack-opening displacements. The analytical results in consideration of mechanical and thermal loads are compared with experimental results, which are measured as helium gas leaks through carbon fiber-reinforced plastics laminates containing matrix cracks at room temperature. Good agreement between the analytical and experimental data is confirmed. Numerical analysis based on the proposed method can be used to evaluate the influence of mechanical loads on propellant leak through CFRP cross-ply laminates. The analytical calculations show that the increase of propellant leakage can be caused by the enlargement of crack-opening displacements caused by mechanical and thermal loads, increase of crack density, and decrease of temperature.
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