Nondestructive inspection and characterization of complex engineering materials via ultrasound techniques.
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Stair, Sarah L., 1990-
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Nondestructive evaluation methods have grown increasingly popular and necessary in a variety of industries. For example, the aerospace industry uses such techniques to inspect aircraft components for damage prior to making a repair. The focus of the present dissertation is the development of ultrasonic techniques for inspecting highly attenuative materials. The first study presented in this work involved a pulse-echo ultrasound technique for inspecting damage at the bondline between a carbon fiber reinforced laminated composite and aluminum. The sample was inspected from both the aluminum side as well as from the composite side, and the areas of delamination were successfully identified. The novelty of this inspection technique was the bondline inspection between dissimilar materials since previous studies focused on the bondline inspection between similar materials. The second study presented in this dissertation involved using a normal incidence through transmission ultrasound technique for monitoring the phase and temperature of a material. Using the proposed technique, two different waxes, EcoSoya wax and Rigidax machinist wax, were inspected as they were melted and allowed to re-solidify. From the results of the study, the phase of the material can be identified from the ultrasound data, and a correlation between the ultrasound data and temperature data was identified. The final study of this dissertation involved the design and implementation of an oblique-incidence through transmission c-scan ultrasound technique. As laminated composites are incorporated into new aircraft, there is an increased desire for nondestructive methods for not just damage inspections but also for characterizing the material properties of the part post-manufacturing or after extended use in the field. Aluminum and carbon fiber reinforced laminated composites were inspected with this technique, and the wave scatter was observed using a c-scan technique. The wave scatter varied considerably from the isotropic aluminum plate to the laminated composite plate, and the wave scatter is shown to be a function of the number of lamina within the part. Future work involves comparing the measured results from this dissertation with results generated via a mathematical model, based on the model developed by Newberry , to determine the elastic constants of the laminated composite.