Thesis (M.S.)--West Virginia University, 2004. / Title from document title page. Document formatted into pages; contains xii, 168 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 165-168).

Thesis (Ph. D.)--Lehigh University, 2003. / Includes vita. Includes bibliographical references (leaves 210-215).

Thesis (M.S.)--University of North Texas, May, 2009. / Title from title page display. Includes bibliographical references.

Thesis--Ph. D., University of Hong Kong, 1977.

Defect assessment against fracture initiated failure is carried out using fracture characterising parameters determined under quasi-static rates of loading. In practice, however, there are many instances where much higher loading rates prevail such as collision, blast and earthquake damage; and in transport. For these situations the rate sensitivity of the material to fracture should be considered. Fracture toughness tests (COD) have been conducted on C-Mn steel weld metal over a range of temperature and loading rates. The effect of increased loading rates is to reduce the crack-opening displacement whilst changing the fracture behaviour, such change being accompanied by an increase in the ductile-brittle transition temperature. Thermally activated flow is found to be the predominant mechanism governing plastic flow at intermediate strain-rates. It is then possible to evaluate the effect of strain-rate and temperature on the yield strength as a function of rate parameter kT 1n (A/ε), based on the Arrhenius equation. An attempt is presented to model the influence of temperature and loading rate on the fracture initiation toughness, COD. It may be fairly said that numerical results quite well describe the behaviour of the experimentally determined variation of COD with temperature and loading rate over the range 0.1 < K < 10⁶MPam^{1/2 s}^-1 and O < T < 500^oK. Thus, it has been demonstrated that the constitutive surface δI (T, K_I) can be produced numerically using the constitutive relation σy (ε,ε, T). Consideration of the defect sizes for engineering critical assessment showed that a significant reduction in maximum allowable defect size, bar a_max can result as a consequence of increased loading rate.

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Transformation Induced Plasticity (TRIP) steels have both high strength and high ductility. Retained austenite in the microstructure, upon straining, transforms to martensite and this absorbs energy and improves the work hardening of the steel, giving improved elongation. The transformation can be either stress-assisted or strain-induced and the initiation and the mechanism depend on the composition of, the size and shape of, and the phases surrounding, the austenite grains. It is important to understand the relationship between these variables and the properties of the TRIP steel. The aim of this work was to determine how the microstructure of the TRIP steel affects the transformation. Four experimental microstructures were developed, containing austenite grains with different sizes, shapes, and surrounding phases. The Fine microstructure had thin elongated austenite laths between fine bainitic ferrite laths, the Coarse microstructure had elongated austenite grains between coarser bainitic ferrite laths, the Equiaxed microstructure had equiaxed austenite grains in a matrix of equiaxed ferrite and the Acicular microstructure had elongated austenite grains surrounded by recovered ferrite laths. Tensile tests were performed and detailed characterization, using neutron diffraction, was done of samples with the four microstructures. The variation in the amount of austenite during deformation was measured. The tensile tests revealed that the microstructures had different mechanical properties and different transformation behaviours. Fine had the lowest elongation and the highest strength. Acicular and Equiaxed had good elongation but lower strength. Coarse had intermediate strength and Equiaxed had sustained work hardening. The transformation in Fine and Coarse was minimal. Coarse had some slow, steady transformation, but Fine may have had none. The transformation in Equiaxed was larger. It started quickly and then slowed at higher strains. The austenite in Acicular transformed steadily. The predominant mechanism of transformation was stress-assisted transformation, with strain-induced transformation occurring only in Equiaxed. The results of this work showed that the influence of the surrounding phases on the stability of the austenite is significant. The differences in the transformation behaviour of the four microstructures seemed to be due more to the surrounding phases than the grain size or the composition, although both these factors also played a role. / Thesis (Ph.D, Mechanical and Materials Engineering) -- Queen's University, 2007-12-14 13:35:07.248

Extensive computer predictions have been carried out by the author to study flow, addition dispersion and particle motion during central gas injection into cylindrical vessels. In conjunction with numerical computations, experiments were conducted in a 0.30 scale water model of a 150 ton steel processing ladle, using a Froude number scaling criterion. Two typical gas injection configurations (i.e., conventional central injection and C.A.S. alloy addition procedure) were investigated. / Flow visualization studies were carried out using a suspended network of silken threads, mean velocity vectors and overall flow patterns were determined by video recording techniques, while mean velocity vectors and associated turbulence level were also measured with laser doppler velocimetry. These measurements show very reasonable agreement with equivalent numerical predictions. / To simulate the subsurface motion of additions, spherical wooden balls of various densities were dropped from typical heights, and their subsurface trajectories, immersion times, etc., recorded by means of a video recorder. Frame by frame analysis of the video tapes showed trends which are in good accord with computed trajectories. / Mixing times of simulated molten additions were measured by the conductivity measurement technique. These were compared with prediction from an equivalent tracer dispersion model and excellent agreement achieved. / For industrial application, flow, particle motion, and mixing times in a 150 ton steel processing ladle have been predicted and their technological significance discussed.

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