Experimental Research Of Detecting Debonding In FRP Reinforced Elements By Using Fiber-optic Interference

With the wide application of fiber reinforced polymer (FRP) in the repair ofcivil infrastructures, the de-bonding between the internal reinforced interface layers,which often leads to severe brittle failure of structures, have drawn people’sattention increasingly. Hence, finding out a fast, convenient, and effectivenondestructive testing method of detecting the de-bonding in structures, and thusrestore it in the early stage is of great significance to the serviceability of structures.In this paper, a non-destructive testing method, i.e. the optical fiber-based strainmeasurement method, is introduced. It has been verified by the comparison oftheoretical analysis and experimental results that both the size and location ofstructural de-bonding can be determined by measuring the strain of FRP. Theprinciple of this method is that by loading on the surface of FRP board point bypoint, the total strain could be measured using the optical fiber attached on thesurface of the FRP board. Then the integral curve, which describes the relationshipbetween the de-bonding point and optical fiber, could be obtained. Cause theintegral variables are different when loading in the non-de-bonding area andde-bonding area, which induces bumps on the integral strain curve, both the sizeand location of structural de-bonding could be detected by determining the locationof bumps.The main task of this paper is to verify the validity of the proposed method inde-bonding detection through experimental studies, and evaluate the effect of all thepotential influencing factors on the experimental results, thus provide a preliminaryreference for its further application in practical projects.Through the experimental studies, it is concluded that for the simple andcontinuous supported FRP components, the proposed method is effective indetermining the size and location of structural de-bonding; for the continuoussupported FRP components, the bumps could be detected by the fiber interferometerwhen both the optical fiber and loading line surpass the de-bonding area, and theseverity degree of bumps decreases with the reduction of the length of de-bondingarea. However, the severity degree has little to do with the width of de-bonding area;For the simple supported FRP components, it is also essential for de-bonding detection that the optical fiber and loading line should surpass the be-bonding area,and the severity degree of integral strain bumps shows a downward trend with thereduction of both the length and width of de-bonding area. The experimentalresearch shows that the proposed method is more effective for continuous supportedFRP components other than simple supported ones, and it is even more sensitive ifthe loading line and the optical fiber pasting line are close to the de-bonding center.