Monitoring of fatigue crack growth of cracked thick aluminum plate repaired with a bonded composite patch using transmission-type extrinsic Fabry-Perot interferometric optical fiber sensors

Abstract

Recently, optical fiber sensors have been increasingly applied to monitor 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 used recently developed transmission-type extrinsic Fabry-Perot interferometric (TEFPI) optical fiber sensors for the monitoring of fatigue crack growth behavior of cracked thick aluminum plate repaired with a bonded composite patch. The TEFPI optical fiber sensor has both the advantages of reflection-type EFP1 optical fiber sensors and a simpler and more effective function to distinguish strain direction than do reflection-type EFP1 optical fiber sensors. The objective of this study is to evaluate the potentiality of the application of TEFPI optical fiber sensors to the monitoring of the fatigue crack growth behavior of composite patch repaired structures. The sensing principle and the sensor construction of the TEFPI optical fiber sensor are presented. The experimental results from fatigue tests of center cracked tension aluminum specimens repaired with a bonded composite patch are presented and discussed. TEFPI optical fiber sensors are embedded and surface bonded to the composite patch at several locations. The experimental results show that it is possible to monitor the fatigue crack growth behavior of composite patch repaired structures using TEFPI optical fiber sensors.