Flexural strength enhancement study of aluminum and carbon fiber composite at liquid nitrogen temperature

The adhesive bonding strength enhancement of aluminum substrate and carbon fiber composites at cryogenic temperature has attracted far-ranging attention with their application expanding to rocket booster. Aiming at the potential bonding interface defect of epoxy joint, we adopted the anodizing and sanding treatments to modify surface performance of Al substrate and carbon fiber panel respectively. The resin pre-coating (RPC) technique was used to eliminate the originally existing defect caused by macromolecular epoxy at the root of porous Al substrate. The carbon nanotubes were applied as additives to be impregnated into channels on Al substrate surface via RPC technique and construct the quasi-Z directional fiber bridging, which can further improve the adhesive bonding strength of epoxy joint. The three-point bending (3-P-B) results show the flexural strength of aluminum substrate and carbon fiber composites after treated have been enhanced by 14.6% at room temperature, and even higher 27.6% at liquid nitrogen temperature based on that of the one only cleaned by acetone. Failure mode exhibits the weaker adhesive failure on bonding interface have been transformed into main structure fracture failure of CFRP after combined surface treatments at both room temperature and liquid nitrogen temperature. Overall, the effective treatment methods can offer an alternative reference in industrial application of cryogenic liquid fuel tank.