Date of Award

2017

Document Type

Open Access Thesis

Department

Mechanical Engineering

Sub-Department

College of Engineering and Computing

First Advisor

Addis Kidane

Abstract

An investigation into the localized microstructural response of pure magnesium under both quasi-static and dynamic loading is presented in the form of several experimental works. The meso-scale events were examined using Digital Image Correlation techniques, which provide a methodology for mapping the in-situ full-field material strain behavior.

Firstly, an analysis of the grain boundary activity specifically under dynamic conditions at high magnification is discussed. An area of interest in the region of multiple grain boundaries and triple junctions is selected for characterizing the evolution of the strain and local rotation. This is followed by a study experimentally verifying the causes of the material failure in the quasi-static case, while simultaneously accounting for the effects of grain arrangement on the global response and quantifying the contributions of both inter and intragranular deformation. Finally, we discuss the variations in the localized strain patterns of rolled magnesium under tension with respect to the multi-scale grain sizes in the material, and the local deformation characteristics which are possibly affected.

In summary, the influence of various granular properties was correlated with the fullfield material response and the structurally weak regions of the material were identified. In all scenarios tested, it was verified that the grain boundaries were mechanically weak and fracture initiation took place primarily in these regions. Additionally, the intergranular deformation quantified in the dynamic regime was seen to occur preferentially at triple junction points.. Lastly, it was observed that large relative differences in grain size within a single specimen may dictate the locations of mechanically susceptible failure points in the microstructure, as well as the formation of possible deformation mechanisms.

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