Study of cryogenic mechanical strength and fracture behavior of adhesives for CFRP tanks of reusable launch vehicles

Bonding strengths of three types of adhesives were evaluated at different temperatures. The effects of temperature and adhesive thickness on the strength were clarified from the results. It concluded that EA9394 cured at room temperature is the overall best performing adhesive for CFRP applications at cryogenic temperatures. The initial failure mode of double-lap specimens was also discussed from the results by strain/stress analysis. And also the cryogenic fracture performance of bonded structure between CFRP using AF163-2K is examined. The tensile Mode-I and shear Mode-II fracture strengths of CFRP/AF163-2K bond joints are evaluated at room temperature and cryogenic temperature. The results indicate that both cryogenic Mode-I and Mode-II fracture strengths of CFRP/AF163-2K bond joints dropped considerably. The mismatch of coefficients of linear expansion between CFRP and AF163-2K is considered to be the primary reason. On the other hand, feasibility investigations of CFRP composite as applied to unlined CFRP cryogenic tank was conducted. Reflecting the results of the previous two phase tests on small prototype filament-wound tank conducted at room temperature and cryogenic temperature, the improved third phase of FW tank test was conducted and the result show the feasibility of CFRP tank and identified the problem to be resolved.