Analysis of gas leakage through C/C composites Original Research Article

Gas leakage through carbon-fiber-reinforced carbon matrix composites (C/Cs) was examined with respect to the application of C/Cs in heat exchangers in an engine system for a future space plane. Because C/Cs have many cracks and pores, gas readily leaks through them. To predict and prevent this gas flow through the C/Cs, leakage rates were measured as a function of pressure, and gas flow paths were identified by microscopic observations of C/Cs. Several analytical models were then used to clarify the principal mechanisms yielding gas-flow resistance. Laminar flow models in tubes and slits were found to give excellent leak-rate predictions compared with experimental results for unidirectionally and three-dimensionally reinforced C/Cs, respectively. A model based on adiabatic expansion and compression, which is used for gas leaks through labyrinth seals, resulted in reasonable agreement with the leak rates through a cross-ply laminated C/C.