4. Effect of Degree of Cure on Damage Development in FRP

We have developed a fiber-optic sensing system for measurement of degree of cure (DOC) of FRP laminates. By applying this system to monitoring of cure process of FRP laminates, molding time cam be optimized. However, it is considered that some part of the composite has incomplete DOC due to non-uniformity of molding temperature when the optimized molding process is conducted. Therefore, the effect of DOC on quality of FRP must be clear to manufacture high quality FRP using the optimized molding process. In the present paper, GFRP cross-ply laminates were manufactured with arbitrary DOC. Tensile tests to investigate the effect of DOC on the damage development behavior of the cross-ply laminates were conducted. DOC of the specimen was monitored by the fiber-optic sensing system developed by our laboratory. Matrix cracks were observed during the tensile tests. From the experimental results, it was found that the lower DOC specimen showed the lower crack initiation stress and the slower development rate of transverse crack in 90° layer. In addition, it appeared that many splitting cracks were generated in 0° layers when the DOC was less than 100 % due to the low toughness of resin. From these results, it was found that DOC governs damage development behavior of FRP laminates strongly.