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No description available.

Laser induced shock experiments were performed to study the dynamics of various solid state material processes, including shock-induced melt, fast rate fracture, and elastic to plastic response. Fast rate fracture and dynamic yielding are greatly influenced by microstructural features such as grain boundaries, impurity particles and alloying atoms. Fast fracture experiments using lasers are aimed at studying how material microstructure affects the tensile fracture characteristics at strain rates above 106 s-1. We used the Z-Beamlet Laser at Sandia National Laboratories to drive shocks via ablation and we measured the maximum tensile stress of aluminum targets with various microstructures. Using a velocity interferometer and sample recovery, we are able to measure the maximum tensile stress and determine the source of fracture initiation in these targets. We have explored the role that grain size, impurity particles and alloying in aluminum play in dynamic yielding and spall fracture at tensile strain rates of ~3x106 s-1. Preliminary results and analysis indicated that material grain size plays a vital role in the fracture morphology and spall strength results. In a study with single crystal aluminum specimens, velocity measurements and fracture analysis revealed that a smaller amplitude tensile stress was initiated by impurity particles; however, these particles served no purpose in dynamic yielding. An aluminum-magnesium alloy with various grain sizes presented the lowest spall strength, but the greatest dynamic yield strength. Fracture mode in this alloy was initiated by both grain boundaries and impurity particles. With respect to dynamic yielding, alloying elements such as magnesium serve to decrease the onset of plastic response. The fracture stress and yield stress showed no evidence of grain size dependence. Hydrodynamic simulations with material strength models are used to compare with our experiments. In order to study the strain rate dependence of spall in aluminum we used a shorter pulsed laser and thinner targets. From these experiments we do not observe an increase in spall strength for aluminum up to strain rates of ~2x107 s-1. / text

Hydraulic fracturing is an important method used to enhance the recovery of oil and gas from reservoirs, especially for low permeability formations. The distribution of pressure in fractures and fracture geometry are needed to design conventional and unconventional hydraulic fracturing operations, fracturing during water-flooding of petroleum reservoirs, shale gas, and injection/extraction operation in a geothermal reservoir. Designing a hydraulic fracturing job requires an understanding of fracture growth as a function of treatment parameters. There are various models used to approximately define the development of fracture geometry, which can be broadly classified into 2D and 3D categories. 2D models include, the Perkins-Kern-Nordgren (PKN) fracture model, and the Khristianovic-Geertsma-de. Klerk (KGD) fracture model, and the radial model. 3D models include fully 3D models and pseudo-three-dimensional (P-3D) models. The P-3D model is used in the oil industry due to its simplification of height growth at the wellbore and along the fracture length in multi-layered formations. In this research, the Perkins-Kern-Nordgren (PKN) fracture model is adopted to simulate hydraulic fracture propagation and recession, and the pressure changing history. Two different approaches to fluid leak-off are considered, which are the classical Carter's leak-off theory with a constant leak-off coefficient, and Pressure-dependent leak-off theory. Existence of poroelastic effect in the reservoir is also considered. By examining the impact of leak-off models and poroelastic effects on fracture geometry, the influence of fracturing fluid and rock properties, and the leak-off rate on the fracture geometry and fracturing pressure are described. A short and wide fracture will be created when we use the high viscosity fracturing fluid or the formation has low shear modulus. While, the fracture length, width, fracturing pressure, and the fracture closure time increase as the fluid leak-off coefficient is decreased. In addition, an algorithm is developed for the post-fracture pressure-transient analysis to calculate formation permeability. The impulse fracture pressure transient model is applied to calculate the formation permeability both for the radial flow and linear fracture flow assumption. Results show a good agreement between this study and published work.

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Hard ceramic films of micrometric thickness deposited on a soft metallic substrate have ushered in a new era in the fabrication of structural, tribological, microelectronic and optical components. The mechanical performance of these components is however critically dependent on the strength and toughness of these films as well as on those of the film-substrate interface. Recent studies have shown that cylindrical and radial cracks can propagate through the film during nanoindentation tests with spherically tipped and pointed indenters, resulting in steps in the load versus displacement curve. In this thesis, the mechanics of fracture of thin hard films bonded to soft substrates, during nanoindentation is studied by carrying out finite element analyses. The role of plastic yielding in the substrate on the above issue is examined. Another important objective of this work is to propose a method by which finite element simulations can be employed to interpret nanoindentation test results and yield information related to the fracture behaviour of hard films. To this end, axisymmetric finite element analyses of spherical nanoindentation of a TiN film of thickness t = 1 //m, on a steel substrate are carried out. Numerical algorithms for large deformation, contact simulation and computation of energy release rate are employed in the analyses. The film is assumed to be linear elastic, whereas, an elastic-plastic constitutive model is used for the substrate. A nanoindentation analysis of the uncracked film is first carried out. The development of plastic yielding in the substrate and its influence on the load P versus penetration h characteristics is examined. The stress fields around the indenter for different depths of indentation are studied. The results show that the radial stress attains a tensile peak at the film surface, just outside the indented zone. However, it becomes compressive with increasing distance below the surface. Interestingly, a tensile radial stress prevails at the film-substrate interface at large indentation depth. The shear stress increases to a peak value at a distance of 0.052 to OAt below the film surface depending upon the radial location and then reduces. Next, circumferential cracks extending downwards from the film surface are introduced at different radial distances R from the axis of symmetry. Finite element analyses are carried out till the indented zone extends almost up to the crack surface. The energy release rate J is computed as a function of indentation depth for different crack lengths c (in the range from O.lt to 0.9t). The results show that shallow cracks are essentially under Mode II loading with closure of crack faces caused by compressive radial stresses. However, a mixed-mode state prevails if the crack length is large (c > 0.62), with crack faces opening out due to tensile radial stress near the film-substrate interface. The variation of J with c/t for cracks located at different radial distances R is examined. It is found that for small R, there is a decreasing branch in the J versus c variation between c = 0.2i to 0.75£ which indicates that crack extension in this range will be stable. On the other hand, for large R, J increases monotonically with c/t which implies that unstable fracture of the full film thickness will occur following crack initiation. A composite nomogram is generated in the P — h plane where constant J lines are plotted along with load-displacement curves for different crack lengths. If now a nanoindentation (experimental) load-displacement behaviour is superimposed on this nomogram, the initial crack length (of a pre-existing flaw), the final crack length and fracture energy of the film can be inferred. In the last part of the thesis, the effect of the substrate yield strength on the indentation mechanics is studied. It is found that upon decreasing the yield strength, the load at a given indentation depth decreases while the residual depth at unloading increases. Also, the energy release rate for a given radial location and crack length reduces considerably at large depths of indentation.

Der Zugang zu wirtschaftsstrategischen Bodenschätzen ist für moderne Industriegesellschaften von essenzieller Bedeutung. Für Deutschland besteht für die Versorgung mit nichtenergetischen Rohstoffen wie Stahlveredlern und Seltenen-Erden eine weitgehende Importabhängigkeit. Vorhandene heimische Lagerstätten weisen eine komplexe geologische Struktur mit geringen Abbaumächtigkeiten in großen Teufen auf. Um diese Lagerstätten nutzen zu können, soll ein untertagetaugliches Positionierungs- und Navigationssystem, UPNS4D+, für die Erkundung der Lagerstätte entwickelt und als Demonstrationssystem gebaut werden. Das Institut für Markscheidewesen und Geodäsie der TU Bergakademie ist Teil des Entwicklerkonsortiums. Es ist zuständig für die markscheiderische und bergmännische Nutzbarkeit der mit dem Erkundungssystem gewonnen Daten. Entsprechend dem aktuellen Arbeitsfortschritt werden im vorliegenden Beitrag die Lösungen für die Kluftflächen- und die Haufwerksanalyse vorgestellt. Die teilautomatisierte Haufwerksanalyse dient der Detektion großer Partikel und deren Lagebestimmung in einem relativen Koordinatensystem. / Access to strategic mineral resources is essential for modern industrial societies. Germany is largely dependent on imports of non-energy raw materials such as steel refiners and rare earth elements. Existing indigenous deposits have a complex geological structure with low extraction thickness in large depths. In order to use these deposits, an underground positioning and navigation system, namely UPNS4D+, as a demonstration system has to be developed for deposit exploration. As part of the developer consortium, the Institute for Mining Surveying and Geodesy of the TU Bergakademie Freiberg is responsible for the utilization of the acquired data in the field of mining. According to the current work status, in this paper the solutions for rock fracture analysis and grain size analysis are presented. The partly automated grain size analysis is used for the detection of large particles and their position in a relative coordinate system.

A importância das indústrias de cana-de-açúcar no cenário nacional cresce exponencialmente, desde sua origem. Porém nas últimas três décadas este tipo de indústria deixou de ser tipicamente familiar e passou a produzir em grande escala açúcar, etanol, produtos químicos derivados, levedura e planta de CO2 (para indústria de bebida e ou alimentos), além da venda do excedente da energia que é gerada na própria indústria. Um dos principais equipamentos em uma usina de açúcar e álcool é a caldeira, nome popular dado ao vaso de pressão que gera vapor a partir do aquecimento da água em um ambiente de alta pressão. Este calor é usado como fonte para produção de energia. Os aços ligados ao Cr e Mo têm sido cada vez mais aplicada neste tipo de equipamento. O presente trabalho tem por objetivo entender a influência dos parâmetros de tratamento térmico pós-soldagem nas propriedades mecânicas e na microestrutura de um tubo sem costura de aço ASTM A 335 Gr P91, através da determinação dos valores de: resistência à tração, limite de escoamento, percentual de alongamento, dureza, tenacidade à fratura e CTOD do material base, metal de solda e zona termicamente afetada (ZTA) da região soldada de tubos unidos por solda. Para a realização desta pesquisa serão aplicados os conceitos da teoria da mecânica da fratura elasto-plástica (Crack Tip Open Displacement, CTOD) e os conceitos de comportamento mecânico dos materiais, para o estudo da influência dos parâmetros de tratamento térmico pós-soldagem. / The importance of sugar cane industries on the national scene grows exponentially since its origin. But in the last three decades these became from cottage industries to large-scale production of Ethanol, Chemicals derivatives, yeast and plant CO2 (for food or drink industry). One of the main equipment in a sugar and alcohol plant is the boiler, popular name given to the pressure vessel that generates steam from the heating of water in a high pressure environment. This is used as heat source for energy production. One of the alloy that has been increasingly applied in projects of this equipment are martensitic steels (Cr Mo alloys). The present study aims to understand the influence of post weld heat treatment parameter´s on mechanical properties and microstructure of a seamless tube, steel ASTM 335 Gr P91, the determination of values of tensile strength, yield strength, percentage of elongation, hardness, fracture toughness and CTOD of the base material, weld metal and heat affected zone (HAZ) of the welded region of tubes welded together. In this research the concepts of the theory of mechanics of elastic-plastic fracture (Crack Tip Open Displacement, CTOD) and the concepts of mechanical behavior of materials will be applied.

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No description available.