Fiber reinforced polymer (FRP) composites have been extensively used in aerospace, marine and defense industries due to the many advantages they offer including light-weight, corrosion resistance and excellent thermo-mechanical properties. Increasing fuel-efficiency demands and reducing green-house emissions has also propelled the use of FRP composites in the automotive industry. However, despite excellent mechanical properties of FRPs, their anisotropy, brittle nature and the vulnerability to flaws during fabrication and service has propelled the need of nondestructive evaluation (NDE) and structural health monitoring (SHM) techniques. This dissertationpresents three major contributions to the fields of NDE and SHM of structural composites:• optical transmission scanning (OTS) for rapid, non-contact and quantitative NDE of glass and aramid FRPs;• optical frequency-domain reflectometry (OFDR) for distributed monitoring of strains in FRPs using single-mode (SM) optical fibers and Rayleigh back-scattering;• hybrid acousto-optic health monitoring of FRPs using guided waves (GW) and Fabry-Perot interferometric sensors based on chirped fiber Bragg-gratings (CFBG-FPI).Chapter I presents an OTS system for quantitative NDE of GFRP samples. The technique provides high-resolution, rapid, and non-contact optical transmittance scans. Experimental implementation of the technique and advanced data analysis protocol developed for impact damage evaluation are presented. Obtained experimental results show that other defects and certain microstructural variations in GFRP composites can be easily identified by OTS, because the technique is sensitive to localized changes of optical properties such as radiation absorption and scattering. The applications of OTS are extended to GFRP plates with improperly mixed resin, inclusions, and delaminations. Finally, the capabilities of the technique to evaluate the distribution of adhesive and detect fatigue damage in adhesively bonded GFRP joints are demonstrated.Chapter II describes the development of advanced signal processing algorithms for strain sensing in optical fibers using Rayleigh back-scattering and the OFDR technique. Distributed displacement and strain sensing along the fiber length is implemented using the OFDR-1000 system from General Photonics Corporation (Chino, CA). Performance of the system is validated by measuring strains introduced in the optical fiber by the piezoelectric fiber stretcher. Chapter III lays out the approach for diagnostic imaging of plate-like structures using hybrid acousto-optic technique. Guided waves are excited with surface-bonded piezoelectric wafers and are sensed with pairs of chirped fiber Bragg-gratings that form Fabry-Perot interferometers inside the surface-bonded optical fiber. Initial experimental results obtained on aluminum plates demonstrate that CFBG-FPIs are sensitive to both symmetric and antisymmetric fundamental GW modes. Structural damage is successfully located using Delay-and-Sum (DAS) imaging.
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