The aging of both civilian and military aircraft is a critical concern and the National Research Council has concluded that there is a need for better non-destructive evaluation techniques to monitor the condition of aircraft. Aging processes degrade both structural and electrical aircraft systems. Aircraft structural degradation is often characterized by the development and growth of cracks that can ultimately lead to failure. Similarly, electrical wire damage due to chemical, thermal, mechanical, and electrical mechanisms can impair the function of aircraft equipment and potentially cause catastrophic systems failure.

We will report on the application of a large area optical fiber distributed sensing technique for structural and wire system monitoring. The system utilizes optical frequency domain reflectometry to demodulate the reflected signals from thousands of weakly reflecting gratings photo-etched along a single optical fiber. Fiber-optic sensors offer unique advantages over conventional gages including small size and weight, ease of installation, and immunity to electromagnetic interference. Data from a distributed array of sensors are used to record the damage state of the material being interrogated, such as monitoring crack growth on aircraft panels or detecting insulation damage in simulated wiring. The sensor data enables the clear visualization of crack growth over time using strain contour maps for structural elements and composite patches. The distributed sensor array is also capable of detecting transient loads and permanent changes in state along the length of wire insulation. The data from these sensing systems will provide inputs for aircraft prognostic health monitoring of structural and wiring elements. Better health monitoring capabilities can reduce the chance of failure and support condition-based maintenance to significantly lower operating costs.