Innovative Structural Health Monitoring Using Smart Sensors

Civil, mechanical, and aerospace engineering structures, which serve as the foundation for modern society, undergo continuous strength deterioration due to loading and environmental impacts, and may suffer from the associated potential of damage accumulation. Structural health monitoring (SHM) is a process in which damage identification strategies are implemented for determining the presence, location, and severity of damages, and the remaining life of the structure after the occurrence of damage. There are numerous smart sensors available targeted at various SHM applications, and among which the fiber optic sensors and piezoelectric sensors are two of the most widely adopted smart sensors. Fiber optic sensors are passive, which have the advantages of small size, remote sensing, corrosion resistance, immunity to electromagnetic interference, and excellent multiplicity. Piezoelectric sensors work on the direct and inverse effect of piezoelectricity, which can be used as both sensors and actuators. This dissertation explores five innovative designs and applications of these two types of smart sensors in the field of SHM, especially in civil engineering, with two of them are based on fiber optic sensors and the other three are based on piezoelectric sensors. In the first study, a novel rebar corrosion detection technique for reinforced concrete structure was proposed based on active thermal probe. The active thermal probe was designed and fabricated according to the combined fiber Bragg grating and carbon fiber. The magnitude of the temperature response of the thermal probe correlates to the corrosion severity. In the second study, a novel type of ferromagnetic distance-based metal loss sensor was proposed based on the principle of fiber optic macro-bend loss. The practicality of the proposed distance sensor for metal loss measurement was validated through scanning the fabricated corrosion samples. The third study presented the feasibility of using smart aggregates, which are a type of embedded piezoelectric sensors, as embedded acoustic emission sensors for the health monitoring of concrete structures. The performance of the embedded smart aggregates were compared with the traditional surface mounted acoustic emission sensors in their ability to detect and evaluate the damage to the concrete structure. The fourth study experimentally investigated the feasibility of debonding characterization in fiber-reinforced polymer rebar reinforced concrete using acoustic emission technique. The results demonstrated a clear correlation between the damage evolution of carbon-fiber-reinforced polymer rebar pullout and the acoustic emission parameters. The final study employed an electromechanical impedance-based structural health monitoring technique by applying piezoelectric sensors to detect the debonding damage of a carbon fiber reinforced polymer rebar reinforced concrete. Statistical damage metrics, root mean square deviation and mean absolute percentage deviation, were used to quantify the changes in impedance signatures measured by the piezoelectric sensors due to various debonding conditions.