Degree Type

Thesis

Date of Award

2020

Degree Name

Doctor of Philosophy

Department

Aerospace Engineering

Major

Engineering Mechanics

First Advisor

Valery I Levitas

Abstract

Large plastic deformation of materials result in the ultrafine-grained materials with highly improved properties, like a combination of high ductility and high strength. The high-pressure-torsion (HPT) is the most effective severe plastic deformation technique that is widely used for producing nanograined materials and promotion of the phase transformations in various materials. Diamond anvil cell (DAC) and rotational diamond anvil cell (RDAC) are powerful tools to generate high pressure and large shear and in-situ studying material behavior including the phase transformations under extreme conditions. Constitutive models and finite element method (FEM) algorithms are developed, and FEM simulations are performed to study: (a) behavior of a copper sample in a HPT setup, and (b) plastic straining and strain-induced phase transformation in zirconium in different HPT setups and also in DAC and RDAC. Various experimental data are interpreted and the effect of different setups on the phase transformation is investigated. Majority of measurements and discussions about processes in DAC are related to pressure only. However, study of physical, chemical, geological, and mechanical phenomena, and synthesis of new phases in a sample, as well as the increasing range of achievable pressures, depend on knowledge of all components of the stress and plastic strain tensors. A coupled experimental-theoretical-computational approach is proposed to determine and verify all stress and plastic strain tensorial fields, elastoplastic properties, and contact friction rules for a tungsten sample at different pressures up to 382 GPa.

DOI

https://doi.org/10.31274/etd-20200624-104

Copyright Owner

Mehdi Kamrani

Language

en

File Format

application/pdf

File Size

140 pages

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