Cure and health monitoring of RTM molded FRP by using optical fiber strain sensors

摘要

In this paper, in situ cure and health monitoring techniques by using optical fiber sensors were applied to textile fiber reinforced plastics (FRP) manufactured by a resin transfer molding (RTM) method. Reinforcements were glass cloths and matrix was epoxy resin. Two kinds of popular optical fiber strain sensors, Fiber Bragg grating (FBG) sensors and extrinsic Fabry-Perot interferometric (EFPI) sensors, were used for strain measurement. These sensors were embedded perpendicularly or parallel to direction of resin flow. Experimental results of FBG sensors, which were embedded perpendicularly, showed poor reproducibility until they were constrained by cured resin. In addition, it was found that FBG and EFPI sensors had good reliability at the cooling stage. As for parallel embedding configuration, FBG sensors showed good reproducibility during molding process. Strain behaviors of EFPI sensors of 1mm gauge length were different from that of EFPI sensors of 4mm gauge length. These results indicate that embedding configuration and gauge length of optical fiber sensors affect accuracy of strain measurement when the sensors are embedded in textile FRP. After cure monitoring, cyclic loading tests were conducted with measuring internal strain by embedded optical fiber sensors. Experimental results of the loading tests showed that strain from FBG sensors has a good agreement with that from attached strain gauges. From the results obtained in this study, it is concluded that embedded optical fiber sensors are powerful to monitor internal strain of RTM molded FRP in the curing process and in service.