An approach in dynamic monitoring using long-gage fiber optic sensors

Fiber Bragg grating (FGB) sensors offer a significant advantage for structural health monitoring due to their ability to simultaneously monitor both static and dynamic strain while being durable, lightweight, capable of multiplexing, and immune to electromagnetic interference. Drawing upon the benefits of FBG sensors, this research explores ways to use a series of long-gage fiber optic sensors for damage detection. Typically, structural identification relies upon determining the frequency and modal shapes of the system. However, relying purely on these parameters has proven challenging for damage detection as they are not sensitive enough. Long gage FBG sensors offer a promising alternative as the same sensors can be used for both frequency and modal analysis and overcome some of the disadvantages associated with traditional dynamic measurement methods through the strain and curvature analysis. Small scale experimental testing was performed using an aluminum beam instrumented with a series of FBG optical fiber sensors. Dynamic strain measurements were obtained as the beam was subjected to various support and loading conditions and damage was simulated by creating imperfect support constraints for the aluminum beam. From the dynamic strain measurements, the curvature as well as the natural frequencies of the structure can be determined. Additionally, a normalized parameter based on the strain and curvature from the dynamic strain measurements has been developed as a potential means of damage detection. Theoretical predictions and experimental data were compared and conclusions carried out. The preliminary results demonstrated potential of FBG longgage sensors to facilitate dynamic monitoring at both the local and global scale, thus allowing assessment of the structures health.