Characterization of Fatigue Damage in Adhesively Bonded Lap Joints Through Dynamic, Full-Spectral Interrogation of Fiber Bragg Grating Sensors

In this work we demonstrate that dynamic, full-spectral scanning of FBG sensors embedded in the adhesive bond can identify changes in bond quality through the measurement of non-linear dynamics of the joint. The lap joint specimens were then subjected to fatigue loading, with regular interrogation of the FBG sensors at selected load cycle intervals. The FBG data was collected during vibration loading of the lap joint to represent an in-flight environment. Changes in the lap joint dynamic response, including the transition to non-linear responses, were measured from both the fullspectral and peak wavelength FBG data. These changes were correlated to initial manufacturing defects and the progression of fatigue-induced damage independently measured with pulse phase imaging and visual inspections of the failure surfaces. Finite element simulation of the lap joint dynamic response verified that the FBG response was due to the fatigue-induced damage.