<p>This doctoral thesis presents a modeling method fordemonstrating the behavior of inclusions and their surroundingmatrix during plastic deformation of steels.</p><p>Inclusions are inescapable components of all steels. Moreknowledge about their behavior in processes such as rolling andforging is necessary for carrying out the forming processes ina more proper way so that the properties of the final productare improved. This work is focussed on deformation ofinclusions together with void formation at the inclusion-matrixinterface. The topic of the work is analyzed by differentFE-codes.</p><p>The relative plasticity index is considered as an importantmeasure for describing the deformability of inclusions. Theindex could be analyzed quantitatively, enabling a deeperunderstanding of the deformation mechanisms. The workingtemperature is found to be an important process parameter. Thisis very clear when the deformation of silicate inclusions in alow-carbon steel is studied during hot rolling. Here a narrowtransition temperature region exists, meaning that theinclusion behaves as non-plastic at lower temperatures and asplastic at higher. The results are in agreement withexperiments published by other authors.</p><p>Regarding void formation, the simulations have been carriedout by utilizing an interfacial debonding criterion. Thedifference in yield stress between the matrix and the inclusionis one common reason for void initiation and propagation.During large compressive deformation the evolution of voidsgoes through a sequence of shapes, from convex with two cuspsto concave with three cusps together with self-welding lines.It is concluded that the formation of voids is alwaysassociated with a large relative sliding between the inclusionand the matrix.</p><p>In order to study the local behavior of the material closeto inclusions during hot rolling a mesomechanical approach isused. Uncoupled macro- and micro- models have been developed.By means of the macro-model, the stress-strain historythroughout each sub-volume of the steel is evaluated. Thestress components or velocity fields are recorded with respectto time as history data. No consideration is taken to theexistence of inclusions. The micro-model, which includes bothinclusion and steel matrix, utilizes the stress components orthe velocity fields from the macro-model as boundaryconditions.</p><p><b>Keywords</b>: Inclusion; Steel; Plastic deformation; Void;Rolling; Forging; Finite Element; Mesomechanical approach.</p>

Large-scale structures we see in the universe, such as galaxies, galaxy clusters and structures beyond the scale of clusters, result from gravitational instability of almost isotropic and homogeneous density distribution in the early universe. The degree of the initial anisotropy of the universe and the subsequent growth of gravitational instability, coupled with the expansion rate of the universe, determine the scale and abundance of the structures formed in the universe at later times. A galaxy survey directly observes a distribution of structures in the sky using galaxies as a tracer of the underlying density distribution, and yields constraints on cosmological models when compared to a physical theory of structure formation based on a given cosmological model. Among many cosmological and astronomical phenomena to be understood from a galaxy survey, the nature of the observed accelerated expansion of the universe is the most profound problem in the modern physics. Motivated by various planned and on-going galaxy surveys, including our own Hobby-Ebery Telescope Dark Energy eXperiment (HETDEX), we show the way to fully exploit the data from a galaxy survey. We improve a model of structure formation to include the effect of baryonic pressure and the free-streaming of massive neutrinos at a mildly non-linear regime. Future galaxy surveys are to reach the level of accuracy, where the effect of massive neutrinos on the observed power spectrum is no longer negligible. Proper understanding of these effects gives a way to measure the absolute masses of neutrinos: one of the most fundamental particles, which, by itself, will be a major development in the field of particle physics. Yet, most of the space (~80%) observed by galaxy surveys is occupied by voids. An ellipticity probability distribution function of voids offers yet another way of probing cosmology. Especially, a distribution of ellipticities in the redshift space provides a unique way to measure a growth rate of the structure in the universe apart from other cosmological parameters when combined with the galaxy power spectrum. / text

The focus in this thesis is to improve knowledge of the BWR related uncertainties void, channel bow, and control rods. The presence of void determines the moderation of neutrons in BWRs. A high void fraction is less efficient in moderating neutrons than a low one. As a consequence, the ratio of thermal to fast neutrons is dependent on the surrounding void fraction. In this thesis, calculations with 2D/3D codes corroborate this dependence, the void correlation, to be linear and very robust to changes in different reactor parameters. The void fraction could be predicted from the ratio of simultaneously measured reaction rates from thermal and fast neutron detectors over the whole core with an uncertainty of ±1.5%. The only parameter found disturbing the void correlation significantly is channel bow. However, since channel bow is the only phenomenon found biasing the void correlation, it is found that the void prediction methodology can be used to indicate channel bow with a sensitivity of 4% per mm bow. Consequently, large channel bows could easily be detected. Increased knowledge of void fractions and channel bow could increase both safety and economy of nuclear power production. This thesis also investigates how 2D/3D codes used in production perform in calculating detailed impact of control rods on pin powers and their ability to perform control rod depletion calculations in the reflector region. It is found that the axial resolution used in 3D nodal codes has very large impact on pin power gradients, i.e., using a standard nodal size of ~15 cm can cause underestimations of 50% in pin power gradients, which could lead to fuel damages. In addition, two methods for determining the neutron flux in the control rod when it is withdrawn from the core are presented. Both methods can be used in a 3D nodal code to reproduce the neutron flux in the reflector region with an uncertainty of ±3%. / Felaktigt tryckt som Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 715

The influence of casting voids on spheroid cast iron cracking threshold is investigated. The experimental results and their analytical and numerical analysis basing on linear fracture mechanics is presented. / Nagrinėjamas liejimo tuštumų poveikis stipriojo ketaus pleišėjimo slenksčiui. Pateikiami eksperimentiniai rezultatai ir jų analitinė bei skaitinė analizė, remiantis tiesine irimo mechanika. / Исследуется влияние литейных пустот на порог трещиностойкости чугуна с шаровидным графитом. Представлены результаты экспериментального исследования и их аналитический и численный анализ, опираясь на линейную механику разрушения.

Nagrinėjama liejimo tuštumų įtaka konstrukcinių elementų iš stipriojo ketaus stiprumui esant daugiacikliam apkrovimui. Eksperimetiškai nustatytas pleišėjimo slenksčio mažėjimas prie labai mažo plyšio plitimo greičio tiriamas analitiniais ir skaitiniais metodais, remiantis tiesine irimo mechanika. Pristatoma bandinių paviršiaus fraktografinė analizė. Siūloma patobulinta stiprumo skaičiavimo metodika. / The influence of casting voids on spheroid cast iron structure elements high-cycle fatigue strength is investigated. The experimentally established cracking threshold decrease at very small crack growth rate is investigated using analytical and numerical methods basing on linear fracture mechanics. The specimen surface fractographic analysis is presented. The improved strength calculation method is proposed. / Исследуется влияние литейных пустот на прочность элементов конструкций из чугуна с шаровидным графитом. Экспериментально установленное снижение порога трещиностойкости при очень малой скорости распространения трещины исследуется аналитическими и численными методами, опираясь на линейную механику разрушения. Представлен фрактографический анализ поверхности образцов. Предлагается усовершенствованная методика расчёта прочности.

Dual-phase (DP) sheet steels are a class of advanced high strength steels which boast a desirable combination of properties for the forming of automotive components, including: high strength, continuous yielding behaviour, and a high initial work hardening rate. The higher strength of DP steels relative to predecessors used to form automotive components allows for a reduction in part gauge, translating to the potential for reduced automobile weight, emissions, and fuel consumption. However, a form of premature failure during component forming known as `shear fracture' has become a prominent challenge to manufacturers' adoption of DP steels. Martensite particles in DP steel microstructures act as nucleation sites for the development of void damage during deformation, resulting in a deleterious effect upon formability and thought to contribute to the observed shear fractures. This dissertation contributes to the overall goal of offering guidance for the improvement of DP steel microstructures for more desirable fracture behaviour. Specifically, the role of non-ferritic phase/constituent (NFP) volume percent and spatial distribution in the accumulation of void damage in DP steels was investigated. Void damage accumulation in ten DP steel microstructural variants tested to failure under near plane-strain deformation was qualified and quantified in three dimensions using an X-ray micro-computed tomography technique. These results were correlated to the microstructural parameters of the variants, which clearly indicated the detrimental effects of NFP banding in DP steels. It was observed that DP microstructures with increased severity of NFP banding (generally aligned in the sheet rolling direction) incurred a reduced strain to failure. Often, microstructural variants with NFP bands aligned transverse to the major loading direction incurred a reduced strain to failure, accumulated a greater number of voids, and exhibited a larger void volume percent than a specimen with oppositely oriented NFP bands. Void damage spatial distribution was generally reflective of the spatial distribution of the most coarse NFP bands through the sheet thickness. In microstructural variants with NFP bands aligned transverse to the major loading direction, accumulated void damage was often observed to be highly elongated in the direction of NFP banding. / Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2011-09-30 11:49:18.645

A series of experiments and finite-element simulations were performed in order to assess existing void coalescence criteria and propose a new model for the coalescence of cylindrical holes in a pure metal matrix during uniaxial stretching. The finite-element simulations were performed so that various plastic limit-load models could be evaluated at each strain increment during deformation, rendering predictions concerning the farfield strains required for coalescence. The experiments were performed in order to identify the actual far-field strain at the moment of incipient coalescence for the specimen geometries considered. The cylindrical-void models of Thomason (1990) and McClintock (1966) outperformed all of the other considered models in their original states. A modified form of the Ragab (2004) plastic limit-load model is proposed in the present work and is shown to have good agreement with the experimental results. The present model accounts for ligament work-hardening and ligament orientation.

Gas lift is a means of enhancing oil recovery from hydrocarbon reservoirs. Gas injected at the production riser base reduces the gravity component of the pressure drop and thereby, increases the supply of oil from the reservoir. Also, gas injection at the base of a riser helps to mitigate slugging and thus, improving the performance of the topside facility. In order to improve the efficiency of the gas lifting technique, a good understanding of the characteristics of gas-liquid multiphase flow in vertical pipes is very important. In this study, experiments of gas/liquid (air/water) two-phase flows, liquid/liquid of oil/water two-phase flows and gas/liquid/liquid (air/oil/water) three-phase flows were conducted in a 10.5 m high 52 mm ID vertical riser. These experiments were performed at liquid and gas superficial velocities ranging from 0.25 to 2 m/s and ~0.1 to ~6.30 m/s, respectively. Dielectric oil and tap water were used as test fluids. Instruments such as Coriolis mass flow meter, single beam gamma densitometer and wire-mesh sensor (WMS) were employed for investigating the flow characteristics. For the experiments of gas/liquid (air/water) two-phase flow, flow patterns of Bubbly, slug, churn flow regimes and transition regions were identified under the experimental conditions. Also, for flow pattern identification and void fraction measurements, the capacitance WMS results are consistent with those obtained simultaneously by the gamma densitometer. Generally, the total pressure gradient along the vertical riser has shown a significant decrease as the injected gas superficial velocity increased. In addition, the rate of decrease in total pressure gradient at the lower injected gas superficial velocities was found to be higher than that for higher gas superficial velocities. The frictional pressure gradient was also found to increase as the injected gas superficial velocity increased. For oil-water experiments, mixture density and total pressure gradient across the riser were found to increase with increasing water cut (ranging between 0 - 100%) and/or mixture superficial velocity. Phase slip between the oil and water was calculated and found to be significant at lower throughputs of 0.25 and 0.5 m/s. The phase inversion point always takes place at a point of input water cut of 42% when the experiments started from pure oil to water, and at an input water cut of 45% when the experiment’s route started from water to pure oil. The phase inversion point was accompanied by a peak increase of pressure gradient, particularly at higher oil-water mixture superficial velocities of 1, 1.5 and 2 m/s. The effects of air injection rates on the fluid flow characteristics were studied by emphasizing the total pressure gradient behaviour and identifying the flow pattern by analysing the output signals from gamma and WMS in air/oil/water experiments. Generally, riser base gas injection does not affect the water cut at the phase inversion point. However, a slight shift forward for the identified phase inversion point was found at highest flow rates of injected gas where the flow patterns were indicated as churn to annular flow. In terms of pressure gradient, the gas lifting efficiency (lowering pressure gradient) shows greater improvement after the phase inversion point (higher water cuts) than before and also at the inversion point. Also, it was found that the measured mean void fraction reaches its lowest value at the phase inversion point. These void fraction results were found to be consistent with previously published results.

Multiphase flows occurring in pipelines with a serpentine configuration is an important phenomenon, which can be encountered in heat exchangers used in a variety of industrial processes. More specifically, in many industrial units such as a large cracking furnace in a refinery, the tubes are arranged in a serpentine manner and are relatively short. As flow negotiates round the 180o bend at the ends of the tubes, the generated centrifugal force could cause flow maldistribution creating local dry spots, where no steady liquid film is formed on the adjacent straight sections of the pipe. As a result, events including coking, cracking and overheating of heat transfer surfaces may occur and lead to frequent shutdown of the facilities. Consequently, this could increase operating costs and reduce production revenue. Thus, it is desirable to know the effect that the bends exert on the flow in the straight part of the pipe. Apart from this, knowledge of the bend effects on the flows in the pipeline could also be important for the design of other pipelines for gas/liquid transport, e.g. offshore gas and oil pipelines. Quite a large number of studies have been found in the literature. The majority of them were for two-phase flow with small diameter pipes (i.d. ≤ 50 mm). However, studies with large diameter pipes (i.d. ≥ 100 mm), have increasingly been considered in recent years as problems related to large diameter vertical pipes are being encountered more and more often in industrial situations. This thesis studies the effect of 180o bends on the characteristics and development of gas-liquid two-phase flows in large diameter downward and upward pipes. The study particularly focuses on the influence of serpentine configuration on flow structure, cross-sectional void distribution and circumferential liquid film profiles and their development along the downward and upward sections. It was found that both the top and bottom bends have considerable impacts on flow behaviour, although to varying degrees. These impacts were highly dependent on the air and water flow rates. For sufficient flow rates, the bends were observed to create flow maldistribution in the adjacent straight section, due to the effects of centrifugal force. The air moved towards the inner zone of the bend and the water towards the outer zone, while a lesser quantity of water was identified on the other surfaces of the pipe. Investigation of the film thickness development in the downward and upward sections showed that, the liquid film behaviour close to the bends was significantly different from those located further away. This can be attributed to the centrifugal force of the bends. Examination of the power spectral density (PSD) along the downward and upward sections showed that, the shape of PSD located in the adjacent section to the bends, was substantially different from those located further away. Furthermore, several flow regime maps were generated which showed that, in addition to bubbly, intermittent and annular flows, unstable flows existed along the upward section, particularly for low gas and water flow rates. In this study it was found that, the lower bend was periodically blocked by the liquid and then blown through by the accumulated air. The data obtained from this study were compared with different theoretical correlations found in the existing literature. Some discrepancy between the results of the current study and those of previous published materials was noted. Updated correlations were presented which provided well results when they applied for the data obtained from the current study and previous studies.

In this study, a two phase investigation of the hydraulic conductivity parameters of silty soils was performed. In the first phase, double-ring infiltrometer tests were used to measure infiltration rates in-situ at two sites in the Piedmont physiographic province of Georgia. The efficacy of predicting saturated hydraulic conductivity for Piedmont soils via published soil surveys from the National Resource Conservation Service and pedotransfer functions was then investigated. Work focused on the development of a consistent test methodology for soils (sandy, to silts and clays) in the Piedmont, and the final test method utilized being the constant head test, using a double-ring infiltrometer with Mariotte tubes to maintain the head. In the second phase of the investigation, laboratory based measurements of the saturated hydraulic conductivity of binary mixtures of fine sand and nonplastic silt were performed to investigate the effects of particle mixtures on hydraulic conductivity. The materials used were ASTM 100/200 sand and Sil-Co-Sil 40 non-plastic silt, chosen based on the ratio of the mean particle diameters. Significant effort was invested in the development and comparison of methodologies to produce uniform specimens of the binary mixtures for hydraulic conductivity testing, with the final being modified dry tubing. Two fixed densities were used to investigate the effects of particle packing on the hydraulic conductivity of binary mixtures, with critical fines contents chosen to ensure the finer particles primarily filled the pore volume of the coarse particles. Incremental fines contents, by mass, up to this theoretical fines content were tested. The measured saturated hydraulic conductivity was evaluated in terms of fines content, global and intergranular void ratio, and confining stress. Models for predicting extreme void ratios and saturated hydraulic conductivity of binary mixtures were also investigated.