Thesis (M. S.)--Civil and Environmental Engineering, Georgia Institute of Technology, 2010. / Committee Chair: Laurence J. Jacobs; Committee Member: Jianmin Qu; Committee Member: Jin-Yeon Kim. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Thesis (Ph.D)--Mechanical Engineering, Georgia Institute of Technology, 2010. / Committee Chair: Ume, Charles; Committee Member: Chen, Ye-Hwa; Committee Member: Michaels, Jennifer; Committee Member: Sadegh, Nader; Committee Member: Vachtsevanos, George. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Thesis (Ph. D.)--University of Canterbury, 2006. / Typescript (photocopy). "November 2006." Includes bibliographical references (p. [153]-161). Also available via the World Wide Web.

No description available.

The European Corn Borer (ECB), Ostrinia nubilalis, is an agricultural pest which bores small holes in the rind of maize stalks and then proceeds to consume the pith. Because most of the damage to the stalk is internal, it is difficult to quantify the damage to an individual stalk without time-consuming, manual examination. This work explored the hypothesis that internal damage could be detected and quantified using non-destructive, electromagnetic measurements. Laboratory experiments and numerical simulation studies predicted changes in capacitance of stalks due to hollow core ECB damage. A guarded probe device to measure electrical impedance from 500 Hz to 100 kHz was designed and constructed for data collection. A field test with the measurement device was conducted and frequency-swept impedance measurements were taken on field-grown plants with and without ECB damage. Field measurements demonstrated that statistically significant capacitance changes associated with ECB damage could be detected in agreement with numerical simulations of stalk damage. Numerical, laboratory, and field test results all supported the hypothesis that electromagnetic impedance measurements, in particular, capacitance, provide a promising new avenue for ECB damage evaluation. While further research will be needed to further refine this concept, this measurement approach is non-destructive, thus allowing measurements to be performed without sacrificing the infested plants.

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Modern engineering structures often incorporate new materials and complex designs for which existing techniques for nondestructive evaluation prove inadequate, especially for dynamic and in-service measurements. At the same time, optical fiber sensors have been identified as an ideal candidate for embedded and attached measurements of material parameters such as strain, temperature, or state of damage. In particular, sensors based on optical fiber modal interference phenomena have been shown to be capable of highly sensitive detection of static and dynamic strain. This work reviews known applications of modal domain sensing to measurement science to date, and discusses the principles behind the method. A general expression for the intensity distribution emerging from a multimode fiber is formulated, covering both few mode and highly multimode fibers, and new expressions for their sensitivity to both radial and axial strain are derived. Optimized multimode fibers are seen to show an intrinsic phase sensitivity which rivals or even surpasses that of the single mode interferometer, especially in the case of applied radial strain. The use of modal domain sensors for real-time ultrasonic wave transduction is described as a particular application to NDE, with experimental results being presented with regard to acoustic emission monitoring as well as the detection and analysis of shock waves due to impact. Finally, optimization schemes and alternatives for such sensors are addressed, and recommendations for future work are raised. / Ph. D.

New materials and manufacturing processes, and the quest for economy and user safety, have necessitated the development of nondestructive testing methods to quantify the life and reliability of a product during manufacture and service. Described herein, is a testbed to be used in the research and development of these testing methods. A brief motivation for using ultrasonics applied to nondestructive evaluation is followed by a chapter on the feasibility of using a unique testing method and animated data presentation on advanced composite materials. This testing method, conceived by the author, utilizes oblique injection of ultrasound into the specimen. Several cycles of the ultrasonic waveform radiated from the specimen downstream of the injection area is digitized and recorded. The data has three independent dimensions; cartesion location and time. The time variable is the key to the presentation of the data as an animated two dimensional image. It was this work that illustrated the need for a flexible scanning imaging research testbed, not only for the discussed method, of which it is an integral part, but for advanced development of other techniques. Software development and integration of off -the-shelf parts into a unified computer controlled testing facility is the contribution by the author in the second phase of this research. Chapters on the description of the system, an example showing the capabilities of the system analogous to traditional ultasonic C-scanning, accomplishments, and a look to the future conclude this thesis. The appendices include listings of the programs developed for the system, a manufacturer address list. A videotape of the animation data presentation is included as a second volume of this thesis. / Master of Science

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