Influence of cure parameters in polymer matrix composites using embedded optical fibers

The influence of cure processing parameters was investigated using strain distributions from embedded optical fibers. The determination of optimized cure parameters is often needed to achieve material properties which meet aerospace industry design requirements. Optical fibers were embedded near the midplane of thin (5 mm; [0/90/90/0] 3s ) composite laminates to monitor the internal strain during cure for two different cure cycles (manufacturer-recommended and an alternative two-step cure). Each laminate was fabricated using a vacuum-assisted resin transfer molding process. The internal strain with respect to the spatial position and time were monitored. During cure, greater variations in the strain near the vicinity of the laminate edges were observed. However, a two-step cure cycle revealed that the variation of strain near the laminate edges is reduced. The results demonstrate the capability of high-spatial resolution optical fibers to measure the in-situ cure and residual strain during the processing of composite structures.