Cryogenic characteristics of composite materials and application to the cryogenic propellant tank

Abstract

In the development of launch vehicles, the weight reduction of cryogenic propellant tanks is a great concern because it occupies most of their weight. Carbon fiber reinforced composites are promising materials for this purpose. The systematic procedure, however, is inevitable from the development of composite material for cryogenic use to its application to actual structure, which is the main goal of this research. For the purpose of developing carbon fiber reinforced composites suitable for cryogenic use, the mechanical properties of 6 types of matrix resin systems, which had been developed through formulating 2 component epoxy resins with different additives, were measured both at RT (room temperature) and -150 ℃ after thermo-mechanical cycles from RT to -150 ℃. As a result, it was found that the longitudinal tensile stiffness was little influenced as the resin composition changed and additives were added to their resin composition. The longitudinal tensile strength, however, was greatly influenced by the resin composition. Furthermore, the tensile strength of the composite to which newly developed resin had been applied increased considerably even after it was exposed to cryogenic condition for 108 hours, which was 30% higher than that of a baseline material. In addition, the cryogenic bonding characteristics of adhesives, which are necessary to bond the composite and metal liner in a Type 3 cryotank, were investigated. For this purpose, three film types of adhesives were selected, and the joint strength was measured at RT and -150 ℃ through double-lap joint tests. From the experimental results, it was shown that the excellence of bulk adhesive strength did not always guarantee that of the joint strength, and bonding characteristics largely depended on service temperature and adherends. Various design factors of a Type 3 cryotank were evaluated using ring specimens, which can simulate geometrical shape and continuity of reinforcing fibers of the actua...