Smart cure cycles for the adhesive joint of composite structures at cryogenic temperatures

Adhesive joints are employed for composite structures used at the cryogenic temperatures such as LNG (liquefied natural gas) insulating tanks and satellite structures. The strength of the adhesive joints at the cryogenic temperatures is influenced by the property variation of adhesive and the thermal residual stress generated due to the large temperature difference (ΔT) from the adhesive bonding process to the operating temperature. Therefore, in this work, the strength and thermal residual stress of the epoxy adhesive at cryogenic temperatures were measured with respect to cure cycle. Also, the cure cycles composed of gradual heating, rapid cooling and reheating steps were applied to the adhesive joints to reduce the thermal residual stress in the adhesive joints with short curing time. Finally, a smart cure method was developed to improve the adhesive joint strength and to reduce the cure time for the composite sandwich structures at cryogenic temperatures.