Staged curing of composite materials

In this paper the composites processing technique of stage curing is developed. Stage curing is especially suited for the fabrication of thick composites in which thermal spiking and non-uniform consolidation are problematic. It is also useful for assessing the effects of lengthy lay-up times on mechanical integrity for large, complex composite structures. The effects of stage curing on the mode I interlaminar fracture toughness and interlaminar shear strength were investigated by double cantilever beam and interlaminar shear strength testing. From the results of these tests, no degradation was found for the staged cure cycles investigated. Additionally, the feasibility of reducing void content by stage curing was demonstrated. The interruption of the cure cycle with an intermediate cooldown under pressure before gelation results in shrinkage and collapse of voids. Subsequent gelation of the resin can give materials with reduced void content compared with conventional curing.