Date of Award

Winter 2025

Project Type

Thesis

Program or Major

Mechanical Engineering

Degree Name

Master of Science

First Advisor

Marko Knezevic

Second Advisor

Daniel J Savage

Third Advisor

Brian M Patterson

Abstract

This work presents three experimental investigations analyzing the microstructural evolution, void nucleation and growth, and failure in titanium and magnesium. The first study compares the void nucleation and growth of Grade 2 and Grade 4 commercially pure titanium during monotonic tensile testing and cyclic-bending-under-tension. Voids were characterized by X-ray computed tomography (XCT). It was shown that CBT (cyclic bending under tension) did not suppress the growth in void volume but allowed for further plastic deformation despite it. The second study investigates the relationship between microstructural evolution and void accumulation in high-purity titanium during interrupted tensile testing. The initial microstructure of the specimens was measured using diffraction contrast tomography, and then intermittent tensile tests were performed without causing the specimens to fail. After each unloading, voids were characterized and tracked with XCT. Through electron backscatter diffraction (EBSD) measurements of the deformed specimens, it was determined that the microstructure was so heavily fragmented before the first observable voids formed, that predicting void nucleation sites based on the initial microstructure was infeasible. The third study examined the microstructure and crystallography of fracture planes in pure magnesium single crystals, oligocrystals and coarse-grained polycrystals after failure. The surface energy necessary to create fracture planes of all orientations was also calculated. These results were combined to analyze the relationship between habitual fracture planes and the surface energy necessary to form them. It was shown that fracture planes generally occur in orientations requiring lower amounts of energy.

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