Pressurization of CF/epoxy model tank at LN2 temperature and identification of leak path formation in tank wall

A review of six years research project for accumulation of basic knowledge about cryogenic composite tank of future RLV conducted in NAL/NASDA will be given first. An emphasis is placed on the final part of pressurization of the model tank made of CF/Epoxy at liquid nitrogen temperature. Some typical results of preliminary steps in the research route will be also given. In the final cryogenic pressurization, an advantage of the difference in the matrix crack initiation strain levels at room temperature and at LN ₂ temperature played a key role to conduct the present test possible under safety requirements. The matrix crack free strain (stress) levels were obtained for the same composites as used for the tanks in the research programs conducted in NAL/University of Tokyo in parallel to this program. In the present cryogenic pressurization, leak path formation was detected at real time by nonlinear gas pressure - strain behavior and by sudden rise in gas pressure in the vacuum chamber. Later, the exact locations of the leak path were identified by a sniffer scan using a helium leak detector and by snoop tests using leak check solvent. Finally, the strain level of the leak path formation was compared with the matrix crack formation and evolution strain levels obtained by coupon tests. It is clarified that the leak path formation strain level coincides well with the strain level of matrix crack propagation in coupon detected by AE sensors, almost identical to the matrix crack initiation strain of tubular specimens. This conclusion seems to be appropriate if we notice that the present composite model tanks have no edges.