Reliability and durability of fiber grating sensors in structural monitoring applications

There is strong interest to develop fiber-optical sensing systems for long term surveillance and structural monitoring. Although many detection schemes have been proposed, industrial acceptance of optical fibers as validated replacement of other sensors is limited. Low cost manufacturability, reliability, and long term stability are very important for usability in concrete and composite material structures. Lifetime for major structures in civil engineering of 50-100 years are very demanding on the sensors and require accurate aging models and test data to demonstrate their reliability and durability. Acceleration factors of several orders of magnitude can be achieved under reasonable testing conditions depending on temperature, mechanical stress, humidity, chemical environment and activation energy of the damaging process. We report on accelerated aging tests and failure mechanisms of optical fibers and Bragg gratings at elevated temperature, humidity and mechanical stress. Aging behaviour is discussed and results from field measurements of large civil structures are presented.