Thesis (M.S.)--University of Wisconsin--Madison, 1982. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 76-79).

Thesis (M.S.)--University of Wisconsin--Madison, 1988. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 43-46).

Thesis (Ph.D.) - University of Queensland, 2005. / Includes bibliography.

Risers in offshore operations are subjected to corrosion during their service life cycle. The use of relatively inexpensive, high strength to weight ratio fibre reinforced polymer composite (FRPC) as a load bearing pipe repair sleeve is an emerging technology that is becoming common for offshore applications. Risers experience complex loading profiles and experimental investigations often incur substantial time, complicated instrumentation and setup costs. The main aim of this research is to develop a design tool for the repair of offshore riser that suffers from external corrosion damage on its surface using FRPC material. The simplest configuration of a fixed platform riser in the form of a vertical single-wall pipe is being considered. Characterization of the stress-strain behaviour of the FRPC laminate in the composite repair system subjected to various load profiles of a common riser is performed. The means of composite repair takes into account the ease of automated installation. The final repair method considers the use of unidirectional pre-impregnated (prepreg) FRPC that is assumed to be helically wounded around the riser. Finite element models of the composite repair system were developed via ABAQUS. Global analysis of the entire length of the riser was omitted as external corrosions usually occurs in a localised manner on the surface of the riser. Instead, local analyses were conducted where boundary conditions were applied to mimic an infinitely long cylindrical structure such as the riser. The local analyses FEA models were made to capture the stress-strain behaviour of the FRPC laminate subjected to different load profiles including static loadings such as internal pressure, tensile load and bending load. The design loads were calculated based on a limit analysis known as Double-Elastic Curve method developed by Alexander (2008). Proper element selection and mesh convergence were carried out to determine the FE model that can minimize the time and CPU memory needed for the simulation without compromising the accuracy of the results. The second part of this research integrated experimental tests to validate the FE model developed using the ABAQUS general purpose code. Due to constraints on cost and supply of materials and equipment, small-scale tests were conducted. Similitude relations were used to determine the scale properties between the model and the prototype. The final results showed that the FE model can represent the real-life tests of corroded riser repaired with off-axis FRPC laminate with great accuracy of more than 85%. Hence can be a useful tool for design and parametric study of the composite repair system. Using the validated FE model, an extensive parametric study of the composite repair system with respect to varying corrosion defects was conducted. The thickness and length of the repair laminate were compared to the ASME PCC-2 standard. Optimum thickness and length of the composite laminate were determined based on the maximum allowable strains computed using the Double-Elastic Curve method. In addition, varying fibre angle orientation of the unidirectional prepreg was considered as it is one of the main factors in helical winding. Based on the results from the parametric study, a simple relation was developed to predict the required thickness of the composite repair system subjected to combined loading. This relation combined with the developed FE model can be used to provide a quick design and performance validation of a composite repair system for offshore riser, which is the main novelty aspect of this research.

The 7175-T7351 aluminium alloy was studied to determine its suitability for the step-aside gearbox housing on the Rolls Royce Trent 1000 engine. The industrial motivation of this work was to reduce the weight of the gearbox housing using this lightweight material to ultimately improve the specific fuel consumption of the aircraft. This involved obtaining the mechanical properties of the aluminium alloy via a series of uniaxial mechanical tests with parameters based on the operating conditions of the gearbox housing during a typical flight cycle. Furthermore, a constitutive viscoplasticity model, with the inclusion of material ageing parameters, was developed to predict the material’s cyclic response under strain-controlled isothermal fatigue conditions at the gearbox housing’s operating temperatures. With this capability, a prediction for when the strength of the gearbox housing falls below the required design strength for safe use could be made. The room temperature hardness tests demonstrated the effect of time spent at elevated temperatures on the material’s hardness. It was found that the higher the soak temperature, the greater the initial rate of decrease in room temperature hardness and the lower the asymptotic value of hardness that was reached. For example, up to 24 hours of soaking at 200◦ C, the hardness decreased by 33%, and up to 1000 hours the hardness had decreased by 55%. For the same durations at 180◦ C, the hardness decrease was 17% and 47% respectively. Soaking at 120◦ C had an insignificant effect on the hardness of the material, indicating that the microstructure was thermally stable. Hardness testing could be used as a method to assess the strength of the gearbox housing for service monitoring during certifcation. Similar to the hardness tests, the elevated temperature tensile test results also revealed degradation in the mechanical strength of the alloy after prior soaking at elevated temperatures. The tests at 200◦ C on the as-received material decreased the yield stress by 31% and after soaking at test temperature for 20 hours prior to testing, the yield strength dropped by 52%. After a 2 hour temperature, the yield stress decreased from 220MPa to 165MPa which is alarming since the gearbox housing spends about 18 minutes at 200◦ C and 190MPa during climb. This suggests that in less than 6 flight cycles, the material’s strength will fall below the maximum operating stress of the gearbox housing and will be unsafe for continued use. Samples were soaked for up to 400 hours at 200◦ C and prepared for microstructural analysis. EBSD images showed that the grains were no significantly affected by the temperature exposure and showed no signs of coarsening. TEM and EDX analysis revealed that the majority of the particles within the grains were zinc-magnesium rich particles and were assumed to be MgZn 2 precipitates based on the TEM particle identification. The precipitate size and inter-particle spacing were found to increase with soak time. The change in monotonic yield strength was therefore attributed to the coarsening of these precipitates. The material characterisation suggested that, although the 7175-T7351 aluminium alloy initially appeared to have desirable mechanical properties, it is unsuitable for this or similar applications due to the rapid decrease in strength and thermally unstable microstructure. Furthermore, if an aluminium alloy is considered for this application, then it may be vital to account for material ageing behaviour. The unified, uniaxial viscoplasticity Chaboche model was implemented to predict the material response strain-controlled isothermal fatigue tests at 160◦ C and 200 ◦ C. A material ageing term was added to the model to account for the material ageing that decreased the yield strength with time. With this addition, two assumptions were made: 1) material ageing only affects isotropic hardening and 2) isotropic hardening can be de-coupled into material ageing (as a function of time at elevated temperature) and mechanical softening (a function of accumulated plastic strain). The tests at 160◦ C and 200◦ C showed that numerical and experimental results were in good agreement, providing accurate isothermal cyclic stress behaviour of the 7175-T7351 aluminium alloy. Furthermore, it was shown that the mechanical softening and material ageing components could be de-coupled. However, when the model was used to predict stress-controlled isothermal fatigue data and a cyclic stress relaxation tests, a number of deficiencies arose. The predicted ratcheting and ageing rate was greater than expected. The material ageing term may require an additional function to change the ageing rate depending on whether the material is elastically or plastically loaded. Norton’s creep power law could not predict term long stress relaxation behaviour but it was sufficient enough to describe to short- term viscous effects under the strain-controlled fatigue conditions. Despite these deficiencies, the model provided an initial point for a unified, viscoplasticity model for the 7175-T7351 alloy. Due to the rapid ageing of the material, the model could be used to predict if or when a material’s strength is unsuitable for safe operating use.

<p> Metal production in the United States contributes significantly to the national and global economies due to resource demands. As mineral reserves are becoming scarce, demand has driven mining companies to operate at increasing depths underground. Along with this, production has continued to increase year after year, as lower grade ores are excavated economically. However, the increased mining depths and increased production have resulted in enlarged heat loads in the underground mine environment. Increased heat loads can result in temperatures, which are too high for mine workers to safely work. This may cause heat related illness, injuries or even death. Mine operators must pursue heat reduction strategies in order to maintain safe temperatures to protect mine workers. </p><p> There are a number of heat mitigation methods and strategies which mine operators can implement. The most common means is through the use of ventilation to provide cool air volumes to reduce the heat load and dilute the contaminants generated in the production workings below their threshold limit values (TLV). This can be done by increasing the fresh air volumes through surface accesses such as shafts, raises, adits, ramps, or other mine entrances. When ventilation alone cannot provide acceptable climatic conditions in the production workings and throughout the mine, artificial cooling methods need to be used. These methods can be very effective, however, they require large capital investments, continuous maintenance, and additional operating costs. This includes central cooling, spot cooling, and micro-climate cooling systems. Though reducing the heat load is effective, another strategy is to reduce the source of the heat generation. One such source is the heat generated by diesel engine equipment fleet. This can be decreased by switching to a battery/electric engine equipment fleet. All of these strategies can be compared based off their heat reduction, temperatures, and operating costs. This study does exactly this by using an underground metal mine&rsquo;s ventilation system to compare various scenarios, and identify the most effective cooling method or system that can be used in deep and hot US mines.</p><p>

<p> Gold deposits in rocks of the Silver Peak metamorphic core complex in west-central Nevada are contained in highly deformed, sheeted milky quartz veins that cut Neoproterozoic metasedimentary rocks and Cretaceous peraluminous granite and migmatite. Gold production at Mineral Ridge since discovery in 1864 has been approximately 1 million oz. Gold-bearing veins are concentrated in a major low-angle ductile shear system active during the Late Cretaceous. However, a broadly coincident brittle detachment cuts the ductile shear, separating metasedimentary and foliated granitic rocks from overlying non-metamorphosed Cambrian carbonates and Cenozoic volcanics. The Mineral Ridge biotite-muscovite granite pluton bounds the ductile shear along its roof, defining a wedge of prospective metamorphic rocks generally &lt;50-m-thick. Zones of intense shearing generally correspond to highest vein density and therefore, gold grades, and such zones are overprinted with strong but narrowly defined quartz-sericite-pyrite-carbonate alteration. Vein boudins are subparallel to the strong planar to anastomosing shear fabric best developed over 1-10 meter thicknesses at contacts between muscovite schist and/or marble, and foliated granite. Goldbearing veins contain Au:Ag of &ge;4, zoned base metals, low As, Sb, and Hg, but high Bi, the latter correlating with gold.</p><p> Vein-bearing granites at Mineral Ridge yield U/Pb zircon ages of 91.7+/-0.3 Ma and 89.9+/-0.5 Ma and likely derive from crustal melts during peak metamorphism. Hydrothermal monazite in goldbearing quartz veins yielded a U/Pb age of 76.0+/-1.8 Ma, indicating veins are unrelated to granites and formed during retrograde greenschist conditions. Previous cooling ages on mica in granites of &sim;42 and 53 Ma further define the cooling path to &sim;300&deg;C. Mineral Ridge is interpreted as an orogenic gold system associated with a brittle-ductile shear that formed at depths as much as 11-20 km during the waning stages of Late Cretaceous Sevier contraction. Major exhumation occurred in the late Miocene in association with detachment and transtension in the Walker Lane deformation belt.</p><p>

Thesis (DTech (Chemical Engineering))--Cape Peninsula University of Technology, 2017. / Explosives are used to achieve certain functions in diverse environments, including mining, civil construction, military operations, and demolition. Irrespective of the application, the basic principle of augmentation of energy applies. Energy in the form of heat and shock is released by an initiator. This energy is taken up by an intermediary charge, which in turn propagates to the main explosive charge. Ultimately the energy released from the main explosive charge performs the functions. Initiating systems make use of this exact principle within their own boundaries of confinement. The rate at which this energy transfer takes place as well as the magnitude of augmentation is to a great extent influenced by parameters such as the type of confinement, chemical composition and density of the explosives, as well as other environmental conditions. Traditionally lead azide has been used as the primary explosive component in an initiating system. Pressure from international environmental agencies has discouraged the use of heavy metals in commercial products. Nano-porous silicon has been used together with an oxidiser to form an explosive mixture. The literature has shown that nano-porous silicon-based explosive formulations are sensitive enough to pick up from the energy released by the pyrotechnic composition. The reaction of such nano-porous silicon explosive compositions changes from a deflagration to a detonation. However, their ability to initiate the base charge of an initiating system has not yet been demonstrated. A nano-porous silicon/nitriminotetrazole-based explosive system was developed and characterised. A relative reactivity concept was developed and successfully used to further characterise the new nano-porous silicon explosive. The lead azide primary explosive replacement has been shown to be sensitive enough to pick up from the heat output generated by the delay composition and strong enough to reliably initiate the base charge explosive. The performance of the base charge explosive is primarily a function of its density and the confinement it is used in. An explosive system was developed whereby the base explosive was coated with a polymer to give it compressible characteristics. A ballistic ball indentation evaluation method was developed and effectively applied to characterise explosive performance behaviour under various conditions, including density and confinement. Explosive pellets, pressed separately and at a higher density, have been shown to increase performance compared with explosives consolidated inside an aluminium casing.

Laser sintering (LS), an additive manufacturing (AM) technology, allows for the production of 3-dimensional parts by fusing together successive layers of polymer powder without the need for tooling. Its potential and applicability, however, is still constrained due to the limited repertoire of materials available and the lack of detail in understanding both the important process-material interactions and consequently the requirements for the development of new materials. Past research has mainly focused on polyamide 12 (PA12) as the standard material, hence most of the empirically grown or theoretical, often idealized, process models are based on this polymer. As a result, it was shown that there are strong interactions between the material and the process leading to an undesired deviation of part properties. Thermoplastic elastomers (TPEs) for LS have gained more and more popularity for the production of, for example flexible parts in the recent past but they are a group of polymers that is neither well studied nor understood regarding their use in LS. Therefore, this PhD investigation has focused on TPEs in order to reveal their process specifics throughout the processing chain in LS. As the properties of parts manufactured by LS are, amongst others, influenced by the packing and flow efficiencies of the powders, the bulk (static) and flow (dynamic) characteristics of the observed TPEs were examined on the powder scale as well as their effects on the process and parts. The resulting part properties were evaluated in terms of their tensile properties, surface roughness and density. In contrast to previous studies which have rarely taken into account the characteristics of the un-sintered particles, this work provided a novel approach quantifying and describing the interconnection between the powder characteristics as well as its performance and the part properties, thus providing valuable input on future material design. As mentioned before, for typical semi-crystalline thermoplastics such as PA12, different idealized process models describing the Pre-Process specifics exist, but they might not necessarily be applicable for thermoplastic elastomers with significantly different thermal characteristics. Consequently, the important interactions during processing of TPEs have been studied by high speed and high resolution thermography helping to indicate the most important material properties in combination with calorimetric analysis. The resulting understanding of crystallization and melting behaviour helped to derive a design of experiments revealing the possible range for the process management in terms of temperature control as well as energy input and the resulting part properties. Moreover, it is known that polymers used in LS change their intrinsic properties due to processing conditions that are close to the crystalline melting temperature. As a result, within this PhD investigation the ageing behaviour of TPEs was studied. Both the powder and the sintered parts were examined for chemical and physical ageing effects. The results showed that the materials observed could be used without refreshing throughout the applied ageing cycles, however, changes in the processing behaviour as well as in the parts’ mechanical properties were evident. These changes were due to the differing ageing states of the LS-powder showing an increase in the particle size affecting the bulk materials packing density. In the literature, modifications in the rheological properties due to thermal loads during LS are already known on basis of PA12. It was shown that they tend to experience an increase in molecular weight with increasing processing cycles. In this work it was found that TPEs exhibit the exact opposite trend in a slight decrease of molecular weight likely to reduce the mechanical strength of tensile specimens. By using novel process adapted methods in order to reveal vital interactions of TPE powders for LS, this thesis makes a significant contribution to an AM database. In addition, the comprehensive observation and applications of these methods over the whole processing chain helped expanding the understanding of important requirements for the development of new polymers for LS and builds a substantial basis for future work and quality assurance.

<p> Normalization of deviance has been thoroughly studied and proven to have a dramatic impact on the medical industry, particularly in the field of anesthesiology, and for the National Aeronautics and Space Administration (NASA). Few such studies have been conducted in the mining industry. This research was designed to show whether normalization of deviance is occurring within the subculture of mining engineers.</p><p> This research project was based on a cross-sectional surveillance of a group of mining engineers and consultants belonging to the Society for Mining, Metallurgy and Exploration (SME).</p><p> There were three hypotheses for this research: 1) there is a correlation between ethics, compensation, risk tolerance, and normalization of deviance; 2) there are either positive or negative associations between each of the independent variables&mdash;ethics, compensation, and risk tolerance&mdash;to the dependent variable&mdash;normalization of deviance; 3) the data would make it possible to predict normalization of deviance among mining engineers. All three hypotheses were proven true in this study.</p><p> This research is important because it shows that normalization of deviance exists among mining engineers.</p><p>