Development of X-ray Phase Contrast and Microtomography Methods for the 3D Study of Fatigue Cracks

In this work, two innovations were demonstrated for in-situ 3D study of fatigue cracks and their closure as a function of applied load. The first related to improvements in how absorption microtomography is used to study fatigue cracks. The second is a new approach to 3D crack mapping relying on X-ray phase imaging and stereometric approaches. Absorption microtomography was used to determine crack surface positions. Crack opening was measured from absorption microtomography data both before and after crack extension and patterns of opening at several loads were analyzed for both cases. X-ray phase contrast imaging, an alternative approach to absorption microtomography, whose sensitivity to cracks is not strongly affected by the shape of the specimen, was also investigated. Increased sensitivity of phase imaging to cracks, compared to that of the absorption X-ray methods, allowed detecting crack positions up to the crack tip with no load applied to the sample. Stereometry reconstruction based on the phase microradiographs was carried out, and the results were compared with those of absorption microtomography on the same specimen. This study demonstrated that it is possible to reconstruct accurate 3D positions of features inside optically opaque sample by recording several X-ray phase microradiographs.Ph.D.Committee Chair: Stock, Stuart; Committee Member: Johnson, Steven; Committee Member: Sanders, Thomas; Committee Member: Snyder, Robert; Committee Member: Wilkinson, Angu