Permeability of carbon fibre PEEK composites for cryogenic storage tanks of future space launchers

This work presents an experimental investigation into the permeability of carbon fibre (CF) polyetheretherketone (PEEK) for cryogenic storage tanks for space applications. The effects of cryogenic cycling, manufacturing method, PEEK matrix type, fibre type, cryogenic temperatures, pressure, and thickness on the permeability of CF-PEEK laminates are investigated. Laminates are manufactured using autoclave, press and in-situ laser assisted automated tape placement (ATP) consolidation. Optical microscopy is used to characterise the microstructure of test samples. The results show that, for undamaged autoclaved CF-PEEK samples, the permeability remains essentially constant for the ranges of pressures and thicknesses tested. Samples manufactured using the ATP process and samples which were damaged by cryogenic cycling, had a higher leak rate than autoclaved and pressed samples. For cryogenically cycled samples, the leak rate was shown to be dependent on the damage state of the microstructure.