Application of optical fiber sensors technology to structural health monitoring

Recently, based on the smart structure concept, optical fiber sensors have been increasingly applied to monitor the various engineering and civil structural components. These fiber optic smart structures allow engineers to add nervous systems to their designs, giving structures capabilities that would be very difficult to achieve by other means, including continuous assessment of damage processes. Several studies associated with crack monitoring using optical fiber sensors have been reported. In this study we combined the fracture mechanics concept with the optical fiber technology using TEFPI (Transmission-type Extrinsic Fabry-Perot Interferometric) optical fiber sensors. The fracture mechanics concept means that crack growth causes the redistribution of the displacement field around the crack. This idea has been utilized as the basis of compliance technique that is a useful indirect method for fatigue crack length measurement in the laboratory. The objective of this study is to evaluate the potentiality of application of TEFPI optical fiber sensors to the monitoring of crack growth behavior of composite patch repaired structures. The sensing system of TEFPI and the data reduction principle for the detection of compliance changes are presented. Finally, experimental results from the tests of center-cracked-tension aluminum specimens repaired with bonded composite patch is presented and discussed.