Fiber Optic Sensors for Static Fracture Studies and Dynamic Wave Propagation Problems

An experimental study is conducted to investigate the applicability of fiber-optic sensors for static fracture and dynamic wave propagation problems. The type of sensor considered for fracture studies is the Mach-Zehnder interferometer. Mode I stress intensity factors, which completely define the stress field near a crack tip, are obtained using surface attached and embedded fiber-optic sensors in single edge notched specimens. The experimental results compare well with the theoretical predictions. In dynamic applications it is important to know both the magnitude as well as the sign of the strain field. The results from the Mach-Zehnder interferometer are difficult to interpret if the strain changes sign during the observation period. To overcome this problem a novel combined interference and polarization technique is developed. The performance of the Mach-Zehnder interferometer is extremely good at very low frequencies, but at higher frequencies it failed to give meaningful results. Thus a polarimetric sensor is used for high frequency wave propagation studies. A distributed fiber-optic sensor based on polarimetric technique is developed to study acoustic wave propagation in materials. The feasibility of using this sensor to detect flaws and characterize materials is performed.