This paper introduces the concept of a fail-safe sensor to monitor the structural health of a composite repair. The low-cost
fiber Bragg grating (FBG) sensor system consists of a light source, two specially designed fiber Bragg gratings and
a photodiode detector. This system is applied to a typical bonded composite scarf joint often employed in aerospace
structures. A finite element model is developed to assess the change in strain distribution as the result of a structural
debond. The proposed monitoring system will be validated through an experimental investigation.