Multiplexed optical fiber sensors for air frame repair patch monitoring

This paper describes the use of two multiplexed in-line fiber etalon (ILFE) sensors for air frame repair patch monitoring. The ILFE sensors are multiplexed using a combination of coherence division and frequency division multiplexing. Cantilever beam tests are used to verify the ILFE strain sensor performance and to measure multiplexing cross talk. The multiplexed ILFE sensors are then used to monitor the load transfer in a boron/epoxy patch utilized to repair cracks that occur in aging aircraft. The experiments show a clear relationship between a normalized measure of the strain inside the repair patch and crack extension in an aluminum single-edge notch specimen.

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