Fiber optic joint sensor

The invention is a failure detecting system including fiber optic cables of different lengths disposed in the vicinity of a secured region between two or more adherends, and an electro-optical analysis circuit for analyzing signals detected by the fiber optic cables. The fiber optic cables extend transversely across the connected adherends, with each cable extending a different length so that the width of the structure is divided into discrete regions. In this way, the measurable strain can be integrated over the entire length of the fiber where the fiber remains bonded to the material. The cables are coupled to laser means, detector means and network analyzer means, and signals from the cables are processed in the network analyzer means using a Fast Fourier Transform to reduce complex frequency information to time domain representation of reflection pulses. Thereafter, they are compared with reference signals to indicate the presence and degree of disbond. Upon determination that a predetermined threshold parameter has been attained or exceeded, the system can be designed to activate an alarm as well as any corrective equipment or process. The system can be embodied as a static failure detecting system, or as a real-time system capable of generating and maintaining an updatable library of reference signals.