This thesis investigated the microstructure and mechanical property of RRR( high purity) and RG (low purity) niobium (Nb) sheet material. RRR Nb is used in the fabrication RF cavities. Our method involves processing bulk niobium by equal channel angular extrusion (ECAE) and then cross rolling to obtain sheets. This work is a study of the effect different thermomechanical processing variables have on the microstructure niobium sheets. Recrystallization behaviors strongly depended on the purity levels. Tensile tests on sheets clearly indicated the anisotropy in the sheet material. The ductility of the sheet was found to be the largest at an angle of 45o to the rolling direction. There was no apparent relationship observed in the yielding behavior in the different samples. The formability of the sheet measured by the anisotropy ratio suggested a strong dependence of anisotropy on texture. Texture results obtained show that different routes of ECAE can lead to variety of textures in final sheet material. Correlations between the microstructure and the ECAE routes suggest that effective control of microstructure is possible by the thermomechanical steps followed in this study.

There have been numerous efforts in processing metallic alloys into fine-grained materials, so as to exhibit high strain rate superplasticity (HSRSP) and/or low temperature superplasticity (LTSP). The current study is to apply the most simple and feasible one-step extrusion method on the commercial AZ31 magnesium billet to result in low temperature and high strain rate superplasticity (LT&HSRSP). The one-step extrusion was undertaken using a high extrusion ratio at 250-350oC, and the grain size after one-step extrusion became ~1-4 mm. The processed AZ31 plate exhibited high room temperature tensile elongation up to 50%, as well as superior LTSP and/or HSRSP up to 1000%. Meanwhile, the AZ31 alloy was also conducted by equal-channel angular pressing (ECAP). It is demonstrated that an elongation of 461% may be attained at a temperature of 150oC, equivalent to 0.46 Tm where Tm is the absolute melting temperature. This result clearly demonstrates the potential for achieving low temperature superplasticity. A detailed investigation, using x-ray diffraction (XRD), electron back scattering diffraction (EBSD), and transmission electron microscopy / selected area diffraction (TEM/SAD), revealed different textures in the as-extruded and as-ECAP bars. These dominant textures were characteristic of <10 0>//ED in the extruded bars and < 76>//ED in the ECAP condition, where ED is the extrusion direction. The results show that the basal planes tend to lie parallel to the extrusion axis in the extruded bars but there is a rearrangement during ECAP and the basal planes become reasonably aligned with the theoretical shearing plane. As to the extruded plates, the {0002} planes tended to lie on the plane that contains the extrusion axis. At different tensile temperatures, different deformation mechanisms would be dominant. Over the lower loading temperatures within 150-200oC, the true strain rate sensitivity, mt, after extracting the threshold stress is determined to be 0.28, suggesting that power-law dislocation creep but the Qt value is not related to any creep mechanism. It should be partly due to thermal activated dislocation slip mechanism. However, more data need to be tested systematically this part in the future study in order to define the correct deformation mechanism. As to the loading temperatures over 250-300oC, the mt value and the true activation energy for the extruded specimens are calculated to be ~0.4-0.5 and ~90-100 kJ/mol, implying that the major deformation mechanism is grain boundary sliding plus minor solute drag creep, with the rate controlling diffusion step being the magnesium grain boundary diffusion.

FOUR 6061 AL SYSTEMS WERE PREPARED, INCLUDING THE CAST 6061 ALLOY BY TMT OR ECAP, THE PM 6061 ALLOY, AND THE MODIFIED PM 6061 ALLOY ADDED WITH 1 VOL% NANO-SIO2. THE MODIFIED 6061/1%NANO-SIO2 ALLOY POSSESSED A GRAIN SIZE~0.5 UM AND MAINTAINED FINE GRAIN SIZE UPON LOADING AT HIGH TEMPERATURE, RESULTING IN HSRS OVER 300% AT 550-590 OC AND 1-5X10-1 S-1. THE GRAIN BOUNDARY MISORIENTATION DISTRIBUTION IN THE MODIFIED 6061/1%NANO-SIO2 ALLOY WAS ALSO MOST RANDOM COMPARED WITH OTHER THREE UNMODIFIED 6061 ALLOYS. THE CURRENT RESULTS SUGGEST THAT THE ADDITION OF A SMALL AMOUNT OF CHEAPER SIO2 OR AL2O3 NANO-PARTICLES INTO COMMERCIAL AL ALLOYS CAN EFFECTIVELY SUPPRESS GRAIN GROWTH AT HIGH TEMPERATURES AND ENHANCE HSRS, SIMILAR TO THE EFFECTS BY ADDING 15-25VOL% MICRO-SIZED SIC OR SI3N4 REINFORCING PARTICULATES OR WHISKERS.

This artist??s area of research is the appropriate use of matte paintings within the context of completely computer generated films. The emphasis of research is the adaptation of analog techniques and paradigms into a digital production workspace. The purpose of this artist??s research is the development of an original method of parenting perspective projections to three-dimensional (3D) cameras, specifically tailored to result in 3D matte paintings. Research includes the demonstration of techniques combining two-dimensional (2D) paintings, 3D props and sets, as well as camera projections onto primitive geometry to achieve a convincing final composite.

published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

The time course of texture segregation was studied for three different measures of segregation (detection, localization and identification of an embedded texture region) under three different raster width conditions (26$ sp prime$, 43$ sp prime$ and 61$ sp prime$ of arc) by using a backward masking paradigm. The masking data were described with an exponential model the parameters of which represent rate of performance improvement and asymptotic performance level. The results indicate that: (1) information supporting localization accrues more rapidly than information supporting identification, (2) increasing element spacing had a more detrimental effect on identification than on localization, (3) under most spacing conditions, performance on detection fell between that for localization and identification. In conclusion, these three widely used texture segregation tasks cannot be considered equivalent measures of a single process. However, comparisons among their respective time courses may enable us to better characterize the mechanisms underlying the segregation process.

The tables describing the geometry of the yield surface are derived. They concern only fcc metals which undergo isotropic hardening, and which glide on the 24 {111} slip systems. The tables list all five dimensional vertices, and edges of the fourth, third and second order limiting the yield surface as well as the slip systems with which they are associated. A direct method for calculating the yield vectors for any orientation, in five dimensional stress space is established, which enables the user to obtain the yield surface without need of knowing the six deviator stress components. / The relaxed constraint theory, which, by contrast to the classical theory, prescribes only part of the strain increment tensor, is applied to the case of the fixed end torsion test. By taking account of the deformed shape of the grains, three strain components are prescribed; axisymmetry of the sample, which is assumed for every grain, leads to the prescription of another strain component. A further equilibrium condition on the stress associated with the absence of surface tractions leads to an additional constraint. The Yield Subsurface Analysis, which consists of cutting the five dimensional yield surface by the planes of the prescribed stresses, and selecting the p dimensional vertices (p being the number of prescribed strains) that provide maximum work, is carried out. The results are compared with the ones of the classical theory where all the strain components are known. / The simulations are carried out to shear strains of 10, and the orientation changes are calculated incrementally assuming the shear plane and shear direction to be fixed in space. / The texture results are similar up to shear strains of about 3, but differ significantly at larger strains. The relaxed constraint theory predicts the strengthening of the {100} texture component and the development of an equally strong {hk1} fiber component at the expense of the {111} fiber component, whereas the classical theory predicts a very strong {111} fiber component. At large strains, the experimental results agree better with the relaxed constraint predictions. / The average Taylor factors do not exhibit the same trends, since the Bishop and Hill theory predicts a continuous decrease and the RC theory a slight decrease followed by a continuous increase. . . . (Author's abstract exceeds stipulated maximum length. Discontinued here with permission of author.) UMI

Zr-2.5Nb is used as pressure-tube material in CANDU (CANada Deuterium Uranium) reactors. Under reactor operating conditions, pressure tubes undergo anisotropic dimensional changes, and thermal creep contributes to this deformation. In a previous study, the limited textures available to Zr-2.5Nb significantly restricted the understanding of the relationship between texture and creep anisotropy. Moreover, there has been no research performed to investigate textures and stress states simultaneously for this material, which would provide a valuable resource for developing creep anisotropy models and optimizing textures to improve creep resistance. Cold-worked Zr-2.5Nb fuel sheathing (FS) and micro pressure tubes (MPT) with various textures and microstructures were used as experimental materials. The tubes were machined as thin-wall standard (ratio of axial to transverse stress 0.5) and end-loaded (ratio of axial to transverse stress = 0.25~0.75) capsules and were internally pressurized and sealed. Stress and temperature dependence tests were performed on standard capsules under transverse stresses of 100~325MPa at 300~400°C to establish a regime in which dislocation glide is the likely strain producing mechanism. An average stress exponent vaule of 6.4 was obtained, indicating that dislcation creep is the likely dominant mechanism. Texture and stress state dependence tests were performed on standard and end-loaded capsules under a nominal transverse stress of 300MPa at 350°C. It was evident that creep anisotropy strongly correlates with textures under different stress states. A self-consistent polycrystalline model SELFPOLY7 based only upon crystallographic texture was employed to simulate the creep anisotropy of the tubes. However, the model cannot fit all the experimental data well by using a uniform critical resolved shear stress (CRSS) ratio of the operating slip systems. A modification was made, by taking into account the pre-existing dislocation distributions generated during cold work, and an improvement was achieved. This work provides a valuable resource for understanding the effect of texture, stress states and microstructure on anisotropic creep of cold-worked Zr-2.5Nb tubes. The current research also provides a strategic direction to improve creep anisotropy predictions. The large sets of experimental data supply a database to evaluate and develop improved models. / Thesis (Ph.D, Mechanical and Materials Engineering) -- Queen's University, 2009-08-14 11:16:08.67

This study focuses on investigating the effect of post-harvest handling conditions and storage time on the dehulling efficiency and cooking quality of two varieties of red lentils, as well as optimizing the dehulling conditions. The effects of storage time, storage moisture content and storage temperature, as well as the effect of different storage pre-treatments aiming to simulate post-harvest handling, were studied. Dehulling efficiency was mostly affected by the pre-milling moisture content, regardless of the storage conditions. Pre-treatments involving moisture content changes lowered the dehulling efficiency of both varieties of red lentils, whereas freezing and thawing cycles had less of a negative effect on the dehulling characteristics. Textural parameters were mostly affected by storage time; samples became harder after storage. The final recommendation arising from this study is to monitor the moisture content of lentils during storage as it has a detrimental effect on both the dehulling and cooking quality.

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