Titanium is a widely used metal in industrial and commercial applications. It retains anisotropic mechanical properties at room temperature due to its HCP crystal structure. The effects of crystal orientation have been studied theoretically and through modeling though there is a lack of empirical data available on the topic. The work presented here uses laser-machined voids along with EBSD analysis to study the ductility of grains in different orientations to better understand the microscale fracture process in α-titanium. Experimental results show that hard grains with their c-axis parallel to the tensile direction behave in a less ductile manner than grains with their c-axis oriented away from the tensile direction. This is due to the basal slip systems activating in the former case and prismatic slip systems in the latter. Models utilized include the McClintock model for void growth, Brown-Embury model for void coalescence and FEM crystal plasticity simulations

京都大学 / 0048 / 新制・論文博士 / 博士(農学) / 乙第13247号 / 論農博第2872号 / 新制||農||1070(附属図書館) / 学位論文||H31||N5171(農学部図書室) / (主査)教授 松村 康生, 教授 丸山 伸之, 教授 谷 史人 / 学位規則第4条第2項該当 / Doctor of Agricultural Science / Kyoto University / DFAM

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Different rock formations may appear within the same mass, or even within the same formation there may exist layers of different materials, creating interfaces between layers (an interface may be defined, in more general terms, as a frictional contact that separates two similar or dissimilar materials). Currently, there is no well-established experimental work that investigates the influence of frictional interfaces, interface orientation and flaw geometries on crack behavior (i.e. initiation, propagation and coalescence) in brittle specimens under compressive loading. A series of experiments on homogeneous gypsum specimens, used as a rock-model material, containing two pre-existing open flaws and a frictional interface has been performed under uniaxial compression. The experiments investigate how cracks interact with interfaces and how different variables (i.e. flaw geometry, interface inclination angle and interface roughness) affect crack behavior in homogeneous materials separated by an interface. The specimens are 203.2mm high, 101.6mm wide, and 25.4mm thick. The two flaws, with 0.1mm aperture and 12.7mm length (2a), are created through the thickness of the specimen. The spacing (S) between flaws, continuity (C), and inclination angle, measured from the horizontal, (β) define the geometry of the flaws. Three flaw geometries are tested: S=0, C= -2a= -12.7mm, β= 30° (i.e. a left-stepping geometry); S= 2a= 12.7 mm, C=a=6.35 mm, β= 30° (i.e. an overlapping geometry) and S= 3a= 19.05mm, C=0, β= 30° (i.e. a right-stepping geometry). Smooth and rough unbonded interfaces are created by casting the specimen in two parts. The first half of the specimen is cast against a PVC block with an inclined face (i.e. 90°, 80° or 70°) with respect to the vertical axis of the specimen. The second half is then cast against the first one. Sandpaper may be attached to the PVC block to provide different roughness to the interface; a debonding agent applied to the interface ensures a cohesionless contact. In the experiments, digital image correlation (DIC) is used to monitor crack propagation on the specimen surface. The experiments indicate that the interface itself is an important contributor to new cracks and its presence in the specimens reduce crack initiation stress. Furthermore, the increase in roughness and inclination of the interface (i.e. from horizontal to 70° from the vertical) causes crack initiation stress to decrease. It was also observed that the angle between the incident crack plane and the interface affects whether an incident crack will penetrate an interface or be arrested: Tensile cracks that meet the interface at 30° to 60° angle get arrested, while those at or above 70° cross the interface with an offset of 0 – 1.2 mm. While shear cracks that meet the interface at 20° to 63° angles get arrested at the interface, while those at or above 70° cross the interface with an offset in the range of 0 – 1.76 mm. Another relevant finding is the fact that changes in interface roughness or inclination angle did not affect the angles at which cracks initiate or reinitiate at the interface.<div>A numerical study was conducted using the Extended Finite Element Method (XFEM) capability in ABAQUS, to further investigate the fracture behavior observed in the experiments and, more specifically, the influence of the different types of interfaces. An extensive investigation of the stress fields around the tips of the flaws and of the new cracks, as well as along the interface in the specimens, was conducted to determine the relationship between stresses and crack initiation and propagation (i.e. type and direction of cracks). The stress-based approach yields predictions of tensile and shear cracks location and initiation direction that are in good agreement with experimental results. The numerical investigation indicated that rougher horizontal interfaces induced slightly higher tensile stresses around the interior and exterior flaw tips than smoother interfaces, which may explain why tensile cracks at these locations initiated earlier in specimens with a rough interface. Moreover, inclined interfaces induced higher tensile stresses around the interior and exterior flaw tips than horizontal interfaces, which may justify that, in the experiments, inclined interfaces promoted crack initiation earlier than horizontal interfaces.</div>

<p>Cilj ove doktorske disertacije je da d&acirc; doprinos u proučavanju nedovoljno poznatih fenomena koalescentne filtracije, kako bi se smanjio obim potrebnih poluindustrijskih istraživanja prilikom projektovnja filtera za neku konkretnu primenu. Svi materijali kori&scaron;ćeni u ovoj doktorskoj disertaciji su otpadni materijali, čija primena kao filtarskog punjenja predstavlja poseban doprinos održivom razvoju. Jedan od ciljeva ove doktorske disertacije je proučavanje istovremenog uticaja promene permeabilnosti sloja i debljine vlakana na osobine sloja, pad pritiska i efikasnost separacije dispergovanog ulja iz kontinualne vodene faze. Uticaj geometrije sloja proučavan je na slojevima homogene i heterogene geometrije po dubini. Realizovano je detaljno ispitivanje izgleda, morfologije vlakana, kao i strukture sloja, izgleda i rasporeda njegovih pora, primenom skening elektronske mikroskopije i optičke mikroskopije. U radu je dat pregled istraživanja primene vlakana različite prirode (slobodnih i međusobno povezanih, krutih i elastičnih, različite debljine te time i različite vijugavosti) i njihovih slojeva. Takođe, dat je doprinos proučavanju istovremenog uticaja promena ulazne koncentracije dispergovane faze i permeabilnosti sloja. U veći deo ostvarenih istraživanja ukjučeno je i proučavanje uticaja prirode uljne faze, pri čemu je neophodno istaći da su sva kori&scaron;ćena ulja mineralnog porekla. Cilj optimizacije rada koalescera bio je da se pronađu uslovi u kojima se postiže maksimalna vrednost kritične brzine uz minimalni pad pritiska.</p> / <p>The aim of this doctoral dissertation is to contribute to the study of insufficiently known phenomena of coalescent filtration, in order to reduce the number of pilot plant experiments required for designing filters for some specific applications. All the used materials are waste materials the use of which as a filter media contributes to sustainable development. One of the goals of this doctoral dissertation is to study the simultaneous effect of changes in bed permeability and fiber thickness on bed properties, pressure drop and the efficiency of the dispersed oil separation from a continuous aqueous phase. The effect of bed geometry was studied by applying the beds of homogeneous and heterogeneous geometry in depth. A detailed examination of the appearance and morphology of the fibers, as well as the structure of the bed and the appearance and arrangement of its pores, was performed by scanning electron microscopy and optical microscopy. The doctoral dissertation gives an overview of the testing of fibers of different nature (free and interconnected, rigid and elastic, of different thickness and thus of different meandering) and their beds. The simultaneous effect of the changes in the input dispersed phase concentration and the bed permeability was also investigated. Much of the conducted research includes the study of the impact of the nature of the oil phase, and it is necessary to point out that all used oils are mineral oils. The goal of optimizing the operation of a coalescer was to find the conditions providing the maximum critical velocity value with a minimum pressure drop.</p>

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This project deals with the mixed micellar and interfacial properties of mixtures of three surfactants [sodium dodecyl sulphate (SDS), cetyltrimethylammonium bromide (CTAB), and tetraethylene glycol monododecyl ether (C12E4)] with ABA symmetrical triblock copolymer (Pluronic F127), which has many industrial applications. Evidence of F127 micellisation and interaction with surfactants in the aqueous phase is inferred through interfacial tension measurements. The solution containing diluted monomeric F127 showed complex formation with surfactants before the latter self-aggregate as pure micelles. The simultaneous presence of ionic surfactants and micellar F127 in solutions displayed a decrease of interfacial activity and led to the conclusion of F127 micelles disruption. C12E4 was found to interact differently with micellar F127 in forming mixed micelles, and no loss of interfacial activity was recorded. This “association-dissociation” behaviour of F127 and surfactants was leveraged to understand the stability of mineral oil in water emulsions formulated with them in the presence of sodium phosphate (Na3PO4). The mechanisms of emulsions breakdown were found to rely on aggregation behaviour and complex structure of F127 and surfactants mixtures in solution. Laser diffraction showed that unlike SDS and CTAB, mixed-emulsifier systems containing C12E4 are stable to both flocculation, Ostwald ripening and coalescence. Due to electrostatic repulsion between its head group and F127 hydrophilic block, and also because of the combined effect of Ostwald ripening and coalescence, CTAB emulsifier containing systems displayed quicker instability than SDS. SDS containing systems showed a progressive shifting of droplets size distributions to bimodality as SDS concentration was increased and heat exposure pursued, revealing the activity of two distinct population of droplets in the emulsions. More insight on the mechanisms underlying the stability of the three mixed emulsifier systems was gained in performing optical microscopy and rheology measurements; the results were found to be consistent with particle size distribution. / Dissertation (MSc (Applied Science: Chemical Technology))--University of Pretoria, 2020. / Chemical Engineering / MSc (Applied Science: Chemical Technology) / Unrestricted

There exist several different numerical models for predicting bubble coalescence and breakup using computational fluid dynamics (CFD). Various combinations of these models will be employed to model a bioreactor process in a stirred reactor tank. A mass transfer coefficient, Kla, has been calculated and compared to those found experimentally by Thermo-Fisher Scientific, to validate the accuracy of currently available mathematical models for population balance equations. These include various combinations of bubble breakup and coalescence models coupled with the calculation of mass transfer coefficients.

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