Short-Term Creep Effect on Strain Transfer from Fiber-Reinforced Polymer Strips to Fiber Bragg Grating-Optical Fiber Sensors

In this study, the short-term creep effect (STCE) on strain transfer from fiber-reinforced polymer (FRP) strips to fiber Bragg grating-optical fiber (FBG-OF) sensors was investigated. Thirty OF sensors attached to FRP strips were investigated through three primary test parameters: bond length (40, 60, 80, 100, 120, and 150 mm); adhesive type (epoxy resin, CN adhesive, and epoxy resin combined with CN adhesive); and bonding method (embedded and external bonding methods). The strain transfer ability of the OF sensors was evaluated based on the strain ratio of the OF sensor to the FRP strip under different sustained stresses of 20, 40, 50, and 60% of the FRP ultimate tensile strength (f_u). From the test results, it was found that the debonding phenomenon occurred at the interface between the FBG-OF sensor and the adhesive and was clearly observed after applying a load for three days. It was also found that the CN adhesive showed better strain transfer compared to the other adhesive types. Regarding the OF sensors bonded by epoxy resin, in order to maintain strain transfer ability under a high level of sustained stress (0.6f_u), minimum bond lengths of 100 and 120 mm were required for the embedded and external bonding methods, respectively.