Detonations in gases usually propagate with lateral strain rates, in either weakly confined or varying-cross-section or curved or even small-sized geometries. Lateral strain rates have been generally known to significantly impact the detonation dynamics, i.e., decreasing the propagation speeds lower than the theoretical Chapman-Jouguet (CJ) velocities, increasing the propagation limit pressures as well as cell sizes. Since the detonation-based engines require the reliable control of the accurate ignition and stable propagation of a detonation wave, it is desirable to have the predictive capability of the response of detonation dynamics to lateral strain rates, for achieving the practical purposes of detonation applications. Therefore, the present thesis aims to provide such predictability, by quantifying the effect of lateral strain rates on detonation dynamics from both the experimental and numerical modelling perspectives. Experimentally, this study extended the exponential horn technique of Radulescu and Borzou (2018) to a range of characteristic mixtures with varied detonation instability levels, i.e., from the weakly unstable system of 2H₂/O₂/7Ar to the highly unstable one of CH₄/2O₂. Steady detonation waves were obtained at the macro-scale, with the very regular H₂/O₂/Ar detonation cellular structures characterized by reactive transverse waves while the unstable hydrocarbon-oxygen detonation reaction zone structures in the presence of significant unreacted gas pockets. The meaningful D-K curves characterizing the relationships between the detonation mean propagation speeds and lateral strain rates were directly obtained from experiments. Comprehensive comparisons were then made between experiments and predictions from the generalized ZND model with lateral strain rates. Excellent agreement was found for the stable H₂/O₂/Ar detonations due to the much longer thermally insensitive reaction zone lengths compared to the characteristic induction zone lengths, while substantial departures exist for the highly unstable CH₄/2O₂ detonations. The degree of departure was found to correlate well with the detonation instability. As compared to the laminar ZND wave, the more unstable hydrocarbon-oxygen detonations manifested themselves in the significantly enhanced global rates of energy release with the notably suppressed thermal character of ignition. Implications of such a globally enhanced burning mechanism highlight the important role of diffusive processes involved in turbulent burning of the unreacted gas pockets. Finally, empirical global reaction rate laws were developed for effectively capturing the dynamics of unstable detonations. Numerically, this work proposed a novel model for evaluating the effect of boundary layer losses on cellular structures of 2D detonations in narrow channels. The boundary-layer-induced lateral strain rate was evaluated using the negative boundary layer displacement of Mirels' theory. With the theoretical Mirels' constant KM reduced by a factor of 2, the experimentally obtained 2H₂/O₂/7Ar detonations can be very well reproduced by simulations using the resulting quasi-2D formulation. It was further found out that detonation cellular cycle dynamics can be modified by the presence of boundary layer losses, yielding larger velocity fluctuations and more rapid decay rates of the lead shock. The exponential sensitivity of detonation cell sizes to velocity deficits, controlled by the global activation energy, highlights the importance of providing the detonation speed when reporting experimentally measured cell sizes.

Increased interest in and use of additive manufacturing has made it an important component of advanced manufacturing in the last decade. Material Extrusion Additive Manufacturing (MatEx) has seen a shift from a rapid prototyping method harnessed only in parts of industry due to machine costs, to something widely available and employed at the consumer level, for hobbyists and craftspeople, and industrial level, because falling machine costs have simplified investment decisions. At the same time MatEx systems have been scaled up in size from desktop scale Fused Filament Fabrication (FFF) systems to room scale Big Area Additive Manufacturing (BAAM). Today MatEx is still used for rapid prototyping, but it has also found application in molds for fiber layup processes up to the scale of wind turbine blades. Despite this expansion in interest and use, MatEx continues to be held back by poor part performance, relative to more traditional methods such as injection molding, and lack of reliability and user expertise. In this dissertation, a previously unreported phenomenon, irreversible thermal strain (ITε), is described and explored. Understanding ITε improves our understanding of MatEx and allows for tighter dimensional control of parts over time (each of which speaks to extant challenges in MatEx adoption). It was found that ITε occurs in multiple materials: ABS, an amorphous polymer, and PLA, a semi-crystalline one, suggesting a number of polymers may exhibit it. Control over ITε was achieved by tying its magnitude back to part layer thickness and its directionality to the direction of roads within parts. This was explained in a detail by a micromechanical model for MatEx described in this document. The model also allows for better description of stress-strain response in MatEx parts broadly. Expanding MatEx into new areas, one-way shape memory in a commodity thermoplastic, ABS, was shown. Thermal history of polymers heavily influences their performance and MatEx thermal histories are difficult to measure experimentally. To this end, a finite element model of heat transfer in the part during a MatEx build was developed and validated against experimental data for a simple geometry. The application of the model to more complex geometries was also shown. Print speed was predicted to have little impact on bonds within parts, consistent with work in the literature. Thermal diffusivity was also predicted to have a small impact, though larger than print speed. Comparisons of FFF and BAAM demonstrated that, while the processes are similar, the size scale difference changes how they respond to process parameter and material property changes, such as print speed or thermal diffusivity, with FFF having a larger response to thermal diffusivity and a smaller response to print speed. From this experimental and simulation work, understanding of MatEx has been improved. New applications have been shown and rational design of both MatEx processes and materials for MatEx has been enabled.

<div>Multifunctional characteristics of Bismuth-based oxides offer great opportunities to design a variety of devices exploiting either a single functionality or the synergistic multifunctionalities. In the past decades, strain engineering of thin films arose as a solution for fabrication of novel structures with highly desired properties. In this thesis, strain engineering has been applied to Bismuth-based oxides to explore the strain effect on thin film structures and functionalities.</div><div>BiFeO₃ (BFO) servers as the first study platform, because of its strain-induced phase transition and the corresponding diverse polarization properties. The strain effect of SrRuO₃ (SRO)-buffered substrates on ferroelectric and optical properties of BFO thin films has been investigated. A wide range of strain states have been achieved in BFO films. The ferroelectricity and bandgap have been effectively tuned even with partial strain relaxation. However, pure BFO suffers from high leakage current and large coercive field. To overcome these limitations, Sm-doped BFO (BSFO) systems emerged and has been used in controlling the microstructure and properties of BFO. Our detailed structure analysis proves the Sm doping amount in BSFO thin films can be tuned effectively via deposition temperature. Consequently, the Sm dopant influences phase formation of BSFO and the macroscopic ferroelectric properties. </div><div>Another member in Bismuth-based oxide family, Bi₂WO₆ (BWO), has been selected as the base material for the design of the two-phase nanocomposites, because of its unique layered structure and ferroelectric property. To introduce ferromagnetic component into BWO, two methods have been explored. The first method incorporates Mn cations into the BWO matrix (BWMO), and the second method couples CoFe2O4 (CFO) as secondary phase with BWO to form a vertically aligned nanocomposite (VAN) system. Both systems exhibit robust ferromagnetic and ferroelectric response at room temperature and demonstrate their promise as room temperature multiferroics for future spintronics and memory applications. </div><div>The studies in this dissertation demonstrate the great structure flexibility and tunable functionalities of BFO and BWO systems. It shows the potential structure modification and property control of other Bi-based oxides. In the last chapter, new experimental plans and directions are proposed. The connections between the strain engineering and the tunable material properties are being built for various applications. </div><div><br></div>

京都大学 / 新制・課程博士 / 博士(工学) / 甲第23502号 / 工博第4914号 / 新制||工||1768(附属図書館) / 京都大学大学院工学研究科機械理工学専攻 / (主査)教授 平方 寛之, 教授 北條 正樹, 教授 嶋田 隆広, 教授 井上 康博 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

In the United States, symptoms caused by pathogenic strains of Escherichia coli are on the rise. A major source of these pathogenic strains is the E. coli in the digestive tract of cattle. The purpose of this project was to determine if E. coli are transferred between individuals of the same species and if interspecies transmission is possible. Proximity of cattle was also studied as a contributing factor to the transfer of E. coli. To accomplish this goal, E. coli isolates from cattle and cohabitating ground squirrels were compared through a new method of bacterial strain typing called pyroprinting. Bulls from the Cal Poly Bull Test were sampled every summer from May to September when around 200 bulls from ranches across California are housed together to be tested and eventually auctioned off. The impact of cattle origin (ranch, city) and habitation (pen) on E.coli isolate strain type were evaluated via pyroprinting . The cattle were studied to see if transfer was related to proximity of cohabitation. Since the complete population of intestinal E. coli could not be sampled, transfer could not be directly seen. The probability of sharing E. coli in each time point was used to infer transfer. There was an increase in the probability of sharing E. coli from the May sample date to the September date, indicating that some form of transfer was occurring. There was an even greater increase in the probability of sharing E. coli when the bulls were housed in close proximity. Lastly, ground squirrels cohabitating in the area were found to house some of the same strains as the cattle. This makes transfer between squirrels and cattle a possibility. Overall, this paper shows that the intestinal E. coli composition of bulls may be readily altered by the introduction of new bulls into a population.

The thesis presents a manufacturing technology proposition for a terminal pin made of copper according to ČSN 42 3001.1 located in combution engine distributor in a series of 320 000 pcs. Based on a literature study, 3 versions of operation sequence were proposed, 2 of them with concern for lowest number of operations possible and the third, chosen one, was designed so the strain and therefore mechanical properties were equal in whole volume of final part. Forming force and work were calculated, utilizing the Johnson-Cook material model. Overall calculated forming force was 64,5 kN and total work for one part 189 J. Subsequently technical drawings of die and punch for the second operation of forward extrusion of shaft were processed along with workspace assembly drawing for the Šmeral TPM 5 machine, which was chosen for the fabrication. Economic evaluation set the costs for one part manufactured 0,09 Eur and equilibrium point, after which the production generates profit, located at 170 000 pcs produced.

The thesis solves the design of tools for pressing round eyelet 10 mm diameter from steel sheet of DX51 0,5 mm thick. The ring is produced on the press LENA 25 C. Based on a literary study of shearing, expanding and neck drawing, a tool was developed that combines the hole punching of the sail and expanding of the ring end. The study of the circle edge appearance on SSM 3-E stereo microscope and the measurement of wall thickness using the ATOS Core 80 was performed. A simulation of the strain on the press was performed. The proposed tool was experimentally verified as working.

The main goal of this diploma thesis was the stress-strain analysis of iliac artery with atheroma.This problem was solved using finite element method (FEM).For the calculation purposes three two-dimensional models were created. The geometry was gained from transversal sections through the iliac artery with ateroma. This geometry is educed from used literature review. The main calculation process was run by ANSYS 11.0 program system.

The thesis deals with the design of a suitable technology for serial production of a pin. The component material is structural steel 11,320 5R. Due to the series production and material savings, the molding technology was chosen to be cold. For production, the CM 4-5 ECO HATEBUR process press was designed with a nominal force of 1 700 kN. Progressive tool and drawing documentation of tools for the final operation were also designed. The tool load was verified by manual calculation, and the finite element method was calculated to heat the formed blank due to molding.

Increased interest in and use of additive manufacturing has made it an important component of advanced manufacturing in the last decade. Material Extrusion Additive Manufacturing (MatEx) has seen a shift from a rapid prototyping method harnessed only in parts of industry due to machine costs, to something widely available and employed at the consumer level, for hobbyists and craftspeople, and industrial level, because falling machine costs have simplified investment decisions. At the same time MatEx systems have been scaled up in size from desktop scale Fused Filament Fabrication (FFF) systems to room scale Big Area Additive Manufacturing (BAAM). Today MatEx is still used for rapid prototyping, but it has also found application in molds for fiber layup processes up to the scale of wind turbine blades. Despite this expansion in interest and use, MatEx continues to be held back by poor part performance, relative to more traditional methods such as injection molding, and lack of reliability and user expertise. In this dissertation, a previously unreported phenomenon, irreversible thermal strain (ITε), is described and explored. Understanding ITε improves our understanding of MatEx and allows for tighter dimensional control of parts over time (each of which speaks to extant challenges in MatEx adoption). It was found that ITε occurs in multiple materials: ABS, an amorphous polymer, and PLA, a semi-crystalline one, suggesting a number of polymers may exhibit it. Control over ITε was achieved by tying its magnitude back to part layer thickness and its directionality to the direction of roads within parts. This was explained in a detail by a micromechanical model for MatEx described in this document. The model also allows for better description of stress-strain response in MatEx parts broadly. Expanding MatEx into new areas, one-way shape memory in a commodity thermoplastic, ABS, was shown. Thermal history of polymers heavily influences their performance and MatEx thermal histories are difficult to measure experimentally. To this end, a finite element model of heat transfer in the part during a MatEx build was developed and validated against experimental data for a simple geometry. The application of the model to more complex geometries was also shown. Print speed was predicted to have little impact on bonds within parts, consistent with work in the literature. Thermal diffusivity was also predicted to have a small impact, though larger than print speed. Comparisons of FFF and BAAM demonstrated that, while the processes are similar, the size scale difference changes how they respond to process parameter and material property changes, such as print speed or thermal diffusivity, with FFF having a larger response to thermal diffusivity and a smaller response to print speed. From this experimental and simulation work, understanding of MatEx has been improved. New applications have been shown and rational design of both MatEx processes and materials for MatEx has been enabled.