Strain Behaviors of FRP Measured by In-Situ Fiber Optic Sensors during Molding(International Workshop on Smart Materials and Structural Systems, W03 Jointly organized by Material & Processing Division, Material & Mechanics Division, Dynamics & Control Division and Space Engineering Division.)

Abstract

Recently complex-shaped and integral molded fiber reinforced plastics (FRP) have been developed due to low cost and high strength. In the molding of the FRP parts, it is important to know residual strain produced during the molding. In the present paper, strain behavior of carbon fiber reinforced plastic (CFRP) textile composites during a resin transfer molding (RTM) process was measured by using FBG (Fiber Bragg grating) fiber optic sensors From the results of the strain monitoring, it was found that the embedded FBG sensors could measure small variation of strain in the specimens during the molding. However it was shown the sensor output jumped during cooling. To consider the reason of the jump, the transition of the reflected spectra from the sensor Was investigated. In addition, tensile and thermal loading tests were conducted after the molding. From the experimental results, it can be concluded that the jump of the sensor output shows jump of strain behavior of the specimens during the cooling. We consider that the jump of strai!l behavior was resulted form frictional constraint between the specimen and the mold. Since FBG sensors do not need calibration, certain residual strain can be obtained to conduct the measurement after unmolding.