In-Situ Synchrotron Studies of Microstructural Effects on Brittle Fracture

Author: Gorske, Sara Frances

Year: 2026

Degree: Dissertation (Ph.D.)

Advisor: Faber, Katherine T.

Committee Members: Bhattacharya, Kaushik; Fultz, Brent T.; Voorheese, Peter; Faber, Katherine T.

Option: Materials Science

Abstract

Brittle fracture, despite having been mathematically described more than a century ago, has remained a difficult topic of experimental and computational study. While the end states of brittle materials which have failed via fracture have been characterized using post-mortem fractography, sequential focused-ion beam studies, and tomography, the intermediate stages of brittle crack growth are difficult to study due to the unstable and fast nature of crack propagation. As a result, only partial characterization of a full crack front in a brittle material has been achieved, via two-dimensional studies or in simple systems that lack the complexity of most materials used in real-world applications. Presented in this thesis is a novel method of studying brittle cracks and their interaction with material microstructures using a combination of high-energy synchrotron X-ray radiation, precise loading, and a geometry capable of achieving stable crack growth, the double-cleavage drilled compression geometry. Cracks in two materials, a glass-ceramic with an alkali-aluminosilicate matrix and cubic crystals, and polycrystalline aluminum oxynitride, are characterized using this method. Full three-dimensional reconstructions of cracks at multiple loading steps are obtained via X-ray micro-computed tomography; the sizes, orientations, and strains of grains in the surrounding microstructures are characterized using both near-field and far-field high-energy diffraction microscopy; and the relationship between the crack paths and the microstructures is explored, elucidating behavior such as crack deflection in the presence of residual stress, intergranular versus transgranular crack motion through grains, and crack arrest after extension. Individual grain orientations and mechanical states are not found to be predictive as to whether a grain will crack in a certain manner, but average and cumulative properties for ensembles of grains around and ahead of the crack front have a significant effect on the length to which it extends and the fracture toughness.