The continuous curing process for thermoset polymer composites. Part 2: Experimental results for a graphite/epoxy laminate

A new composite manufacturing method called continuous curing has been developed to alleviate problems in the processing of thick composites such as long manufacturing cycle times and material degradation due to thermal spiking. A 10 cm-thick graphite/epoxy (AS4/3501-6) laminate was fabricated using the continuous curing method. The thermal distributions were measured during the process and the final cure distribution was obtained by DSC testing. The mechanical performance of the laminate was analyzed by destructive testing of 16-ply mechanical test specimens removed from the bulk laminate. These specimens were distributed at five locations across the thickness of the laminate. Results for longitudinal compressive strength, transverse tensile strength, and interlaminar shear strength show some degradation. An attempt to quantify the factors contributing to the lower measured strengths is presented. Optical microscopy and image analysis was performed to obtain void and fiber volume distributions across the laminate thickness. Longitudinal layer waviness was measured by optical microscopy. The degradation in strength can be attributed to the high degree of layer waviness, nonuniform consolidation, and excessive voids. These manufacturing defects are attributed to less than optimal processing parameters chosen for the demonstration experiment.