Date of Award
Master of Science
Leonard J. Bond
As the combustion temperature of modern turbine engines climbs higher and higher for greater fuel efficiency, new materials are needed to survive the increased temperature. As a result, there is much research interest in the areas of ceramic coatings, such as environmental barrier coatings (EBC) along with its abradable top coat and ceramic matrix composites (CMC’s), as these advanced materials can withstand the higher operating temperature of new generation turbines and offer significant weight savings as well. As such, it is essential to be able to evaluate the integrity of these materials as manufactured and in service. It is also increasingly important to do so nondestructively.
Recently, Terahertz time-domain imaging has emerged as one of most promising modalities for inspecting and evaluating dielectric materials such as ceramic coatings and composites. This thesis aims to improve the understanding of the interaction of terahertz radiation with abradable/EBC coating systems and oxide/oxide CMC’s, as both are expected to be vital components of future gas turbine engines. The first half of this work performs an experimental validation of how the THz signal variation is affected by the porous abradable top coat. An ad-hoc model was developed to correlate the signal amplitude variations in an experimental C-Scan image with the density of voids over slices of the abradable coating. In the second half of the work, an automated data processing procedure was developed for detecting embedded test flaws in a group of oxide/oxide ceramic matrix composites and then evaluating their signal-to-noise ratios. In addition, signal processing was done to remove most of the predictable signal variation resulting from the terahertz reflections in the multilayered material.
Nagel, John, "Nondestructive evaluation of layered ceramic materials using terahertz imaging" (2019). Graduate Theses and Dissertations. 17522.