A central paradigm for classifying the phases of correlated electron systems is their symmetry. Having the ability to controllably tune symmetry-related properties of the system is therefore a powerful probe. In this thesis experiments on quasi-two-dimensional metals Sr₃Ru₂O₇ and Sr₂RuO₄ are reported, where uni-axial strain was used as a means of lifting the native tetragonal symmetry. Uni-axial strain was applied to the samples using a piezo-electric based device which can apply both positive and negative strains to the sample, to study the symmetry of the response about zero strain. Sr₃Ru₂O₇ exhibits a magnetic-field-tuned quantum critical point, in the vicinity of which a novel phase is stabilized. The transport properties of the phase were previously shown to be highly susceptible to in-plane magnetic fields. We show that resistivity inside the phase responds strongly to strain applied along one of the in-plane crystal axes, with the responses parallel and perpendicular to that of the applied strain mirroring each other about zero strain. Our results suggest that the underlying symmetry of the phase is C₄ rather than C₂ symmetric. Sr₂RuO₄ is an unconventional superconductor which was predicted to have an order parameter of the form pₓ ± ip[sub]y. This should result in a splitting of the transitions of the two components as a function of strain, with a cusp in T[sub]c versus strain at zero strain, where T[sub]c is the upper of the two transitions. We find that the response of T[sub]c to strain along [100] is large and symmetric about zero strain, whilst the response to [110] strain is weak and mostly anti-symmetric. No cusp is observed for either strain direction. We argue that although our results are in contradiction with the simplest pₓ ± ip[sub]y models, they may still be consistent with certain scenarios where the cusp would have been too small to be observed.

Thesis (MTech (Mechanical Engineering))--Cape Peninsula University of Technology, 2009 / Sophisticated measurement methods are currently used extensively to determine the residual stresses in materials. The capabilities of the Hole-Drilling Method, Debro-30 Ultrasonic System and Digital Shearography to determine residual stresses have been explored. The accuracy of these techniques in measuring residual stresses in mild steel specimens is thoroughly examined and discussed. The results obtained from the experiments are consistent with the expected outcomes. Related literature review, experimental procedures, results and their discussion have been outlined. It is hoped that the information provided in this thesis will be of importance to end users, especially engineers and technologists who use these non-destructive methods to evaluate residual stresses in components and materials.

Thesis (MTech (Chemical Engineering))--Cape Peninsula University of Technology, 2008. / Certain non-Newtonian fluids exhibit a yield stress which can be measured with a variety of instruments varying from very sophisticated rotary and tube viscometers to hand-held slump cones and cylinders of various sizes. Accurate yield stress measurement is significant for process design and disposal operations for thickenend tailings. The slump value was first related to the yield stress by Murata (1984). Later, that work was corrected by Christensen (1991) for an error in the mathematical analysis. Slump, based on a circular cylindrical geometry was first investigated by Chandler (1986). These concepts led to the study by Pashias et al., (1996) that formed the basis for the current research. The Flow Process Research Centre (FPRC) at the Cape Peninsula University of Technology developed a slump meter designed to lift the cone or cylinder vertically at controlled lifting speeds. In addition the simple hand-held cylinder which is an adaptation of slump cones which were originally developed by the concrete industry to determine the flowability of fresh concrete was also used. The vane technique was used as a control. Cones and cylinders made of stainless steel and PVC were fitted to the slump meter. The yield stresses of four non-Newtonian fluids at different concentrations were tested in four different configurations at different lift speeds to ascertain whether the measuring position, lift speed, slip, geometry, wall surface material, and stability has an effect on the value of yield stress measured. The effect of different predictive models was also ascertained.The cylinder, lump and cone models relating slump to yield stress was used in the dimensional analysis of the results. The objective of this work was to determine if the slump tests (cone, cylinder and the hand-held cylinder) would generate yield stress values comparable to those found using the vane technique. It was establised that there was no significant effect of lift speed, stability, geometry and wall surface material on the value of yield stress. The effect of measuring position on the value of yield stress calculated gave a difference of 25%. Using dimensional analysis, the lump model (Hallbom, 2005) more accurately predicts the material yield stress when using the hand-held cylinder as well as all the cone results (due to its specific geometry), and cylinder configurations, thus affirming the work of Clayton et al., 2003. It is concluded that, although the materials and concentrations tested induced errors within 40%, the hand-held cylinder shows promise as a reliable, quick and simple way of measuring the yield stress.

M.Ing. / In the design and analysis of components and structures, detailed information on the material behaviour and its properties is required. When a material is loaded dynamically, such as in metal punching, the material properties may not be the same as when loaded statically. This is known as the strain rate sensitivity of a material, which implies that properties such as the yield strength, tensile strength and ductility may vary with the rate at which the material is loaded. South Africa is one of the large stainless steel producing countries. Seventy percent of the known chromium ore reserves are found in the Bushveld Igneous Complex in the Northern Province and Mpumalanga. To compete on the global stainless steel market it is essential that the South African producers have all the relevant product information directly available. Considerable research has been performed on mild steel at different strain rates and temperatures[1]. Work has also been done on some austenitic stainless steels. Very little, or no work has been done in this regard on ferritic and martensitic stainless steels and on the proprietary alloy 3CR12[2]. The aim of this thesis is to investigate the strain rate sensitivity of Types 304, 430 and 316 stainless steel, 3CR12 corrosion resistant steel and mild steel at different temperatures. To achieve this, tensile tests are performed. at strain rates between 10's -1 to approximately 100s -1 and at temperatures ranging from -40°C to 140°C. Shear tests are also performed at various strain rates, to investigate the effect that material behaviour has on a typical metal working process. The results obtained show that all the materials tested are strain rate sensitive. The strain rate sensitivity varies as a function of the material tested and the testing temperature. Constitutive models which take into account the strain rate sensitivity at room temperature for all the materials are also presented. These models describe the behaviour of the material fairly accurately. Three dimensional plots are also presented which depict how the yield strength, tensile strength and elongation vary as a function of both strain rate and temperature. These plots clearly show material trends for the strain rates and temperatures tested.

No description available.

This thesis presents a method which facilitates rapid determination of the cable tension in suspension bridges. A set of tables and curves is included for use in the application of the method. The method is valid for suspension bridges with stiffening girders or trusses either hinged at the supports or continuous. A modified superposition method is discussed and the use of influence lines for cable tension in non-linear suspension bridges is demonstrated. A derivation of the suspension bridge equations is included and various refinements in the theory are discussed. A computer program to analyse suspension bridges was written as an aid in the research and for the purpose of testing the manual method proposed. A description of the program is included along with Its Fortran listing. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

Specimens of quarter-hard electrolytic copper, twenty feet in length and one-quarter inch in diameter, were statically pre-stressed and subjected to impact loading. Dynamic strain vs time traces, for both loading and unloading waves, were obtained using resistance-type strain gages mounted at various positions along the specimens. Permanent strain increments resulting from each impact were determined. Prestress levels ranged from values well below the yield point of the material to values exceeding the yield point. Impact velocities and impact durations were also varied. The experimental strain wave shape and propagation velocity in bars prestressed well below the yield point were found to compare favorably with the theoretical elastic wave shape and velocity. The unloading waves propagated in bars prestressed above the yield point were found to be similar in shape to the elastic waves observed and to propagate at the elastic velocity without diminution of amplitude. For loading waves propagated in material prestressed above the yield point the incipient portion of plastic strain waves was found to propagate at the elastic velocity. The lower strain increments of the plastic strain waves were found to propagate at higher velocities and the highest strain increments were found to propagate at lower velocities than would be predicted from a strain-rate-independent theory. For the loading waves, a method was developed to approximate the dynamic loading curves (stress-strain relation followed during impact loading). Prom the dynamic loading curves, the peak stress levels of the plastic strain pulses were found to be significantly higher than the stresses at equivalent strains on the static stress-strain curve. The results tended, at least qualitatively, to support a strain-rate-dependent wave propagation theory rather than a strain-rate-independent one. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

A method is developed for construction of deflection curves of beam-columns stressed into plastic range by thrusts and equal end moments producing single curvature bending. Actual deflection curves are plotted for 8x8 WF 31 lb/ft section acted upon by moments and thrusts of different magnitudes. These are used for construction of the end moment vs. end slope diagrams and the interaction curves which present in graphical form the ultimate strength of beam-columns of different lengths under various combinations of thrusts and moments. The latter are compared with similar graphs contained in current specifications. The study is based on moment vs. curvature relations developed at Lehigh University. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

The fracture problem due to the singular stresses arising from the sudden change of geometric properties around cracks and notches was studied both analytically and experimentally. The failure models of the cracked and the notched specimens were derived by using linear elastic fracture mechanics methodology, which led to the determination of the critical stress intensity factors. Experiments were conducted to determine fracture toughness for different modes as well as the effect of variations in the crack-front width, specimen size and moisture content. Subsequently, failure surfaces for cracks and notches were developed based on the experiments undertaken, describing in each case the interaction between mode I and mode II fracture toughness. To verify the reliability of these experiments, the results obtained were compared with the published literature. As an application, design curves for a 90 degrees-cracked beam and a 90 degrees-notched beam are presented. These curves allow the prediction of the failure loads due to the rapid crack propagation under different loading conditions. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

Plenty of bridges in U.S. are suffering from prestress force loss and foundation settlements. The loss of prestress force in bridge load-carrying members such as girders may lead to the malfunction and even failure of the prestressed bridges that comprises more than 55% of all new and replaced bridges built in US between the year 2000 and 2012. Settlement of foundations supporting the bridge piers and abutments impairs the superstructure integrity and serviceability of the bridge, or even collapses the bridge if the settlement is over a certain limit. In present study, the dynamic interaction between vehicles and the bridges subjected to prestress force loss and foundation settlement has been investigated. Based on modal superposition technique and principal of virtual works, new bridge-vehicle interaction models have been created to take the effects of prestress and foundation settlement on dynamic bridge and vehicle responses into account. With the developed models, numerical simulations have been performed to show that the prestress force makes the distribution of impact factors along the bridge unbalanced and the existence of foundation settlement may couple with road surface roughness of the bridge deck to possess an aggregated overall effect amplifying the bridge responses. In general, the vehicle responses are vulnerable to the prestress force loss and foundation settlement, which harms the riding comfort of passengers. The existed direct and indirect methods used for prestress loss identification are all based on the measurement collected from sensors deployed on the outside or inside of the bridge, which is not only costly but also inconvenient. The current study proposes to detect the prestress force loss of the bridge through the analysis of vehicle responses. Through simulations, it is found that light, low-frequency vehicles moving at low speeds have a better performance in detecting the bridge prestress loss than the heavy, high-frequency vehicles with high speeds. The advantage of the proposed method is that it only needs a few sensors installed on the vehicle, and works without interrupting the ongoing traffic, which is efficient and cost-effective.