Measurement of Cure Shrinkage Strain of Resin by Optical Fiber Strain Sensors

Abstract

Strain monitoring of resin during cure process is an effective method to manufacture high-quality FRP products because it is known that residual stress generated during molding decreases strength of final products. Although both cure and thermal shrinkage occur during cure process, it is difficult to measure cure shrinkage of FRP products due to dramatic changes in mechanical properties of resin by cure reaction. Among cure monitoring methods, it is proven that fiber optic embedded strain sensors can measure cure shrinkage of resin. However, quantitative evaluation of cure shrinkage strain measured by optical fiber strain sensors has not been conducted. In the present paper, we monitored curing shrinkage of epoxy resin by an embedded EFPI sensor. Mechanical and thermochemical properties of the resin during cure process were experimentally obtained by several methods. Volume shrinkage of resin during cure process was also measured by a dilatometer. In this paper, a viscoelastic model during cure process was driven and the model was used for FEM analysis of cure shrinkage strain generated in the embedded EFPI sensor. From the results, it appeared that the calculated cure shrinkage strain of the EFPI sensors agreed well with the measured strain especially when the degree of cure was high. Therefore, it was concluded that an embedded EFPI sensor can measure cure shrinkage strain quantitatively.