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This study is concerned with a thermo-elasto-plastic continuum in which the thermodynamic coupling between material deformations, heat generation and flow are included. The elasto-plastic behavior is represented by a linear "rate-type" theory and restricted to infinitesimal deformations. The heat flow equations are posed in incremental form for the linear theory of heat conduction. The theory is such that the conservation laws of thermodynamics are satisfied. A displacement formulation is used and the field equations are shown to be linear operator equations. The operators are tested for symmetry and positive-definiteness in order to test their suitability for solution by a variational method. It is shown that the special case of thermo-elasticity may be solved by minimisation of a functional and that convergence of approximate solutions may be predicted. In the general case of thermo-elasto-plasticity, the operator is shown to be unsymmetric. Therefore an iterative functional is introduced in order to obtain a solution by a variational method. Approximate solutions to some illustrative problems are found using a finite-element-formulation, and it is shown that the results are consistent with expected physical behavior. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

The system Zn-0.2 wt. % Al has been investigated to determine under what conditions of strain rate, grain size and temperature the phenomenon of superplasticity may be observed. The analysis and experimental conditions were based on established procedures which have been applied to known superplastic alloys. However the continually decreasing strain rate and grain growth during testing complicate the normal analysis. Based on this study the requirements for superplastic behavior are a fine-grained microstructure, grain boundaries which are relatively free of obstructions and a homolohous temperature of at least 0.42. A model incorporating grain boundary shear and non-continuous grain growth has been proposed to account for the observed superplastic behavior where grain boundary migration is the rate controlling process. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

An investigation of creep deformation in pure zirconia, using a creep-in-bending method with programmed temperature increase, showed the occurrence of superplasticity at temperatures near the monoclinic to tetragonal phase transformation. An interesting phenomenon was observed in a temporary halt to the creep process which occurred with continuing temperature increase beyond the phase transformation. Temperature dependence tests at a maximum fibre stress of 3140 psi gave overall activation energies for the creep process in pure zirconia in the monoclinic and tetragonal phases of 44 and 103 kcal/mole respectively. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

Hydrogen Embrittlement (HE) is a very common failure mechanism induced crack propagation in materials that are utilized in oil and gas industry structural components and equipment. Considering the prediction of HE behavior, which is suggested in this study, is one technique of monitoring HE of equipment in service. Therefore, multi-scale constitutive models that account for the failure in polycrystalline Body Centered Cubic (BCC) materials due to hydrogen embrittlement are developed. The polycrystalline material is modeled as two-phase materials consisting of a grain interior (GI) phase and a grain boundary (GB) phase. In the first part of this work, the hydrogen concentration in the GI (Cgi) and the GB (Cgb) as well as the hydrogen distribution in each phase, were calculated and modeled by using kinetic regime-A and C, respectively. In the second part of this work, this dissertation captures the adverse effects of hydrogen concentration, in each phase, in micro/meso and macro-scale models on the mechanical behavior of steel; e.g. tensile strength and critical porosity. The models predict the damage mechanisms and the reduction in the ultimate strength profile of a notched, round bar under tension for different hydrogen concentrations as observed in the experimental data available in the literature for steels. Moreover, the study outcomes are supported by the experimental data of the Fractography and HE indices investigation. In addition to the aforementioned continuum model, this work employs the Molecular Dynamics (MD) simulations to provide information regarding bond formulation and breaking. The MD analyses are conducted for both single grain and polycrystalline BCC iron with different amounts of hydrogen and different size of nano-voids. The simulations show that the hydrogen atoms could form the transmission in materials configuration from BCC to FCC (Face Centered Cubic) and HCP (Hexagonal Close Packed). They also suggest the preferred sites of hydrogen for each case. The connections between the results for different scales (nano, micro/meso and macro-scale) were suggested in this dissertation and show good agreements between them. We finally conclude that hydrogen-induced steel fracture and the change of fracture mode are caused by the suppression of dislocation emission at crack tip and changing in the material structure due to accumulation of hydrogen, which is driven by the stress fields. This causes the brittle fracture to occur as inter-granular in the GB and trans-granular in the GI.

Epithelial-mesenchymal plasticity (EMP) describes the interconversion of cells between epithelial and mesenchymal phenotypes. During the epithelial-mesenchymal transition (EMT), epithelial cells lose defining characteristics, such as stable cell-cell junctions, and gain the ability to migrate and invade through extracellular matrices. This plasticity contributes to tumour progression, promoting therapy resistance and immune cell evasion. Despite its importance, defining molecular features of this plasticity have largely remained elusive due to the limited scale of most studies. Here, I present my studies applying comparative single-cell genomics to map transcriptional changes associated with the EMT in diverse experimental conditions and EMP in tumours, I identify regulatory features associated with these dynamics, and explore opportunities to pharmacologically restrict them. This work provides critical steps towards building quantitative models of EMP, which will inform effective strategies to restrict these dynamics in cancer and improve patient prognosis.

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