Graduation Semester and Year

2010

Language

English

Document Type

Thesis

Degree Name

Master of Science in Aerospace Engineering

Department

Mechanical and Aerospace Engineering

First Advisor

Haiying Huang

Abstract

Corrosion plays a detrimental effect on the structural integrity of many engineering structures. It can compromise the safe operation of these structures by forming corrosion pits that deteriorates the structural surfaces and causes stress concentrations. Therefore, it is critical that corrosions are detected before structural integrity is compromised and repair becomes economically prohibitive. However, corrosions usually occur at intricate places that are hard to inspect visually. Manual inspection of the structures for corrosions requires dismantling the structures, which incurs high maintenance costs and could potentially cause damage to the components. One approach to reduce this cost is to detect and monitor corrosions using corrosion sensors that are capable of give an early indication of corrosion without requiring disassembly. Among various types of sensors, optical fiber sensors are particularly attractive because they are small, lightweight, easily multiplexed and most importantly, inexpensive to manufacture.This thesis is focused on the development of an optical fiber corrosion sensor based on the principle of light reflection. The fabrication, analysis, and evaluation of the sensors are presented. The sensor consists of two parts, a sacrificial metallic film welded to a steel tube using laser beam welding (tube/film subassembly) and an optical fiber sensor probe that measures the reflectivity of the sacrificial film. The side of the sacrificial film under inspection is finely polished and isolated from the environment while the other side of the sacrificial metallic film is exposed to the corrosive environment. Corrosion pits are first formed on the surface of the sacrificial film exposing to the environment and progress into the material as the exposure time increases. Once the corrosion pits penetrate through the thickness of the sacrificial film, the surface reflectivity of the polished side of the film decreases, resulting in a reduction in the amount of light collected by the sensor probe. Therefore, this corrosion-induced reflectivity decrease can be detected by monitoring the intensity of the sensor output, which serves as an indicator of the corrosion development. Since the corrosion sensor detects the presence of corrosion pits only when the corrosion is severe enough to penetrate through the thickness of the sacrificial film, the sensitivity of the corrosion sensor is therefore determined by the thickness of the sacrificial film. A flexible manufacturing technique was developed to assemble the sensor probe and the tube/film subassembly in a compact water-proof package. A multiplexing scheme that enables monitoring multiple sensors using a single set of instruments was also developed. The packaged corrosion sensors were evaluated by submerging them in saline solutions of different concentrations. The relationship between the optical power of the collected light and the corrosion development were characterized. Experimental results, analysis, and suggestions for future improvements are presented.

Disciplines

Aerospace Engineering | Engineering | Mechanical Engineering

Comments

Degree granted by The University of Texas at Arlington

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