Doctoral Dissertations

Date of Award

12-2021

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Materials Science and Engineering

Major Professor

Yanfei Gao

Committee Members

Peter K. Liaw, Haixuan Xu, Eric A. Lass, Brett G. Compton

Abstract

The accelerated adoption of magnesium alloys as structural components in the automobile and aerospace industry is driven by their unique properties of low density, high strength-to-weight ratio, and high specific stiffness. In spite of many potential applications due to their superior mechanical properties, magnesium alloys still find many practical restrictions primarily due to our limited knowledge of their failure mechanisms. In-situ and non-destructive diffraction measurements on the microstructural scales are critical in understanding the fatigue crack behavior, which has greater advantages than the macroscopic measurements based on replica technique and the small-scale mechanical testing that cannot easily provide a complete view on the synergy of many scale-dependent deformation and failure mechanisms.

The primary objective aims to identify the roles of the deformation dynamics during fatigue experiments of Mg alloys from in situ diffraction and micromechanical modeling studies, which allows us to bridge the gap between microscopic failure processes and macroscopic fatigue properties. In the present research, the following tasks have been investigated: (1) Deformation mechanisms of Mg alloys under uniaxial loading condition, which was investigated by the state-of-the-art in situ neutron diffraction measurements at the Spallation Neutron Source (SNS), Oak Ridge National Laboratory (ORNL). (2) Plastic anisotropy near the fatigue crack tip, which was studied through the full-field mapping around fatigue cracks by the high-energy synchrotron X-ray diffraction at the Advanced Photon Source (APS), Argonne National Laboratory (ANL), coupled the cohesive interface model and crystal-plasticity model.

The principal outcome of this research will be an improved understanding of deformation dynamics and fatigue mechanisms at inter- and intra-granular scales, and a predictive capability based on the microstructural level understanding with which materials scientists can improve the practical applications of Mg alloys.

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