Made available in DSpace on 2014-10-09T12:24:29Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:04:16Z (GMT). No. of bitstreams: 1 01067.pdf: 2998898 bytes, checksum: e9f770339c4991339b8954534223a004 (MD5) / Dissertacao (Mestrado) / IEA/D / Escola Politecnica, Universidade de Sao Paulo - POLI/USP

Les systèmes de corrosion du mobilier archéologique ferreux sous-marin et terrestre présentent des phases réactives et chlorurées. Leurs transformations au contact de l'air impliquent des dégradations majeures de l'objet en sortie de fouilles. Afin d'extraire le chlore en conservant l'intégrité des objets, des processus de stabilisation sont utilisés. Le traitement subcritique (NaOH, 180°C, 35 bars) accélère la déchloruration. Pour comprendre les transformations physico-chimiques induites un corpus d'objets archéologiques est étudié avant et après traitement par des techniques d'analyses complémentaires. La description multi-échelles de faciès de corrosion hétérogènes et complexes montre que la phase formée en milieu subcritique, dépend du degré d'oxydation de la phase d'origine. L'étude de systèmes modèles (oxyhydroxydes de fer synthétiques et archéologiques) montre que les tailles et formes de particules, les surfaces spécifiques, la composition chimique influencent leurs réactivités. Par ailleurs l'application d'une rampe de chauffe progressive conduit à un mélange goethite/hématite en-dessous de 150°C et d'hématite au-delà. L'étude de l'akaganéite, au taux de chlore variable, à différentes étapes de sa transformation, montre que le chlore adsorbé et une partie du chlore de structure est tout d'abord retiré. Ce phénomène, ajouté à une déshydroxylation sous l'effet de la température conduit dans un second temps, à la dissolution de la phase. Ces résultats permettent d'identifier la nature des transformations de phases et de proposer des mécanismes en vue d'améliorer les protocoles de stabilisation subcritique selon le type d'objet archéologique. / Iron archaeological artefacts from submarine and terrestrial origins have developed reactive and chlorinated corrosion systems. After excavation, their transformations in contact with air involve severe damages to the artefacts. In order to extract the chlorine and to maintain the artefacts’ integrity, stabilization processes are used. The subcritical treatment (NaOH, 180°C, 35 bars) accelerates the dechlorination process. Several artefacts are studied before and after treatment with subcritical techniques. The multi-scale description of heterogeneous and complex corrosion system shows that the phase precipitation in subcritical conditions depends on the precursor chemistry. The study of model systems (synthetic and archaeological iron oxyhydroxides) shows that particle sizes and shapes, specific surface area, chemical composition change their reactivity. The application of a heating ramp leads to the precipitation of goethite/hematite below 150°C and hematite above. The study of akaganeite at various stages of its treatment shows that the adsorbed chlorides and part of the structure ones are first removed. Then, a dehydroxylation under the effect of temperature leads to the phase dissolution. These results allowed to identify the nature of phase transformations and to propose mechanisms in order to improve stabilization protocols of archaeological artefacts by subcritical treatment.

Pas de résumé / This thesis consists in two separate parts: one on subcritical fracture experiments, and another one on earthquake statistics. The dynamics of these processes was mainly studied through their scale invariant dynamics, reflected in power law distri- butions of event sizes and times between events. The analyses focuses particularly on the variation of their exponent values and the origins of these variations. Subcritical fracture was studied by two experimental set-ups: creep experiments on paper, and constant-strain fracture of fibre bundles. Paper fracture has been studied in our group for more than 10 years now by visually observing the propaga- tion of the crack. We added acoustic emission monitoring to the experimental set-up in order to compare it to visualisation. The comparison between low frequency image analysis and the high frequency acoustic monitoring allowed to identify the impor- tance of the frequency of analysis for temporally correlated systems, and acoustic emission monitoring revealed the existence of aftershocks in the dynamics of paper fracture. The fibre bundle experiments concentrate on the temporal distribution of the frac- ture events, which follows an Omori law. We studied the influence of the temperature and stress on its exponent, and compared it with results from fibre bundle model analytical predictions and simulations. Our work on earthquakes was initially motivated by the results obtained on pa- per fracture experiments. Hence it starts by a study of aftershock sequences, their Gutenberg-Richter exponent, and the influence of the frequency of analysis on this exponent. By lowering the frequency of the time-magnitude signal we showed that at low frequencies the exponent of the Gutenberg-Richter law depends on the expo- nent of the Omori law. The last chapter of this thesis is concentrated on the early aftershocks. We in- spected the evolution of the properties of an aftershock sequence with time, and observed differences between aftershock occurring shortly after a mainshock, and late aftershocks. These results can be related to the recent proposition of existence of magnitude correlations in earthquakes

To make energy production sustainable and reduce carbon dioxide emissions it is necessary to stop using fossil fuels as our primary energy source. The Accelerator Driven Subcritical Reactor (ADSR) could provide safe nuclear power. It uses thorium as fuel, which is more abundant than uranium, and produces less long lived waste. An ADSR uses neutron spallation, caused by a high power proton beam impacting a metal target, to drive and control the reaction. The beam needs to have an energy of around 1 Ge V and a current of 10 mA with a very high reliability, the combination of which is beyond the capabilities of existing particle accelerators. Cyclotrons and synchrotrons both have trouble producing such a beam, while a suitable linac would be several hundred metres long, and expensive. A more compact accelerator design would allow multiple accelerators to be combined to improve reliability. This thesis examines the use of a Fixed-Field Alternating-Gradient (FFAG) accelerator as the proton driver. FFAGs are compact, and can simultaneously achieve higher energies than a cyclotron at higher repetition rates than a synchrotron. However, it is still a challenge to reach the high currents required. A 35 to 400 MeV non-scaling FFAG was designed to demonstrate issues encountered at high currents. Two methods were investigated in order to increase the number of particle bunches that could be simultaneously accelerated. One uses multiple solutions to the harmonic conditions for acceleration, and the second injects bunches after the acceleration has started. Neither was found to give significant practical improvement in current. Space charge is a destructive force at high currents. Software was developed to simulate the effect of space charge in an FFAG using several models. Space charge tune shifts were measured for a range of energies and currents, and peak currents of above 1 A were found to be unstable. In order to provide 10 mA of average current, acceleration would need to occur in around 100 turns, which will require a very rapid RF sweep.

京都大学 / 0048 / 新制・論文博士 / 博士(農学) / 乙第13066号 / 論農博第2841号 / 新制||農||1046(附属図書館) / 学位論文||H28||N5020(農学部図書室) / (主査)教授 安達 修二, 教授 谷 史人, 教授 保川 清 / 学位規則第4条第2項該当 / Doctor of Agricultural Science / Kyoto University / DFAM

No description available.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第21552号 / 理博第4459号 / 新制||理||1640(附属図書館) / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)准教授 藤 定義, 教授 佐々 真一, 教授 早川 尚男 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

No description available.

A lifetime prediction scheme is proposed based on the assumption that the lifetime (time to failure) of rocks under load is governed by the growth of microstructual defects (microcracks). The numerical approach is based on linear elastic fracture mechanics. The numerical calculation scheme is implemented as a cellular automat, where each cell contains a microcrack with length and orientation following certain distributions. The propagation of the microcrack is controlled by the Charles equation, based on subcritical crack growth. The zone inside the numerical model fails if the microcrack has reached the zone dimension or the stress intensity factor of the crack reached the fracture toughness. Macroscopic fractures are formed by these coalesced propagating microcracks, and finally lead to failure of the model. In the numerical approaches, elasto-plastic stress redistributions take place during the forming of the macroscopic fractures. Distinct microcrack propagation types have been programmed and applied to the proposed numerical models. These numerical models are studied under different loading conditions. Numerical results with excellent agreement with the analytical solutions are obtained with respective to predicted lifetime, important parameters for the microcracks, fracture pattern and damage evolution. Potential applications of the proposed numerical model schemes are investigated in some preliminary studies and simulation results are discussed. Finally, conclusions are drawn and possible improvements to the numerical approaches and extensions of the research work are given. / 本文认为微结构缺陷（微裂纹）的扩展决定了受力岩石的寿命（破坏时间）。基于此假设，提出了岩石寿命预测方法。利用线弹性断裂力学理论，通过FLAC进行了数值模拟。数值模型中每个单元定义一条初始裂纹，其长度与方向服从特定分布。基于亚临界裂纹扩展理论，由Charles方程决定微裂纹的扩展（速度）。如微裂纹发展至单元边界，或应力强度系数到达断裂韧度，则单元破坏。宏观裂纹由微裂纹所联合形成，并最终贯穿模型导致破坏。在形成宏观裂纹的过程中，发生弹塑性应力重分布。在数值模型中，编制了不同类型的微裂纹扩展方式，并在不同的受力条件下加以分析。数值模型的岩石寿命，裂纹形状，破坏方式以及一些重要的参数的数值模拟结果与解析解有较好的一致性。对本文所提出的数值模型的初步实际应用进行了分析，并讨论了计算结果。最后讨论了本文所提出的岩石寿命预测方法的可能改良与发展，并对进一步的研究工作给出建议。

Assessing long-term rock stability is an important aspect in the analysis of slopes, dam and bridge foundations, and other infrastructure. Rock behavior over tens to thousands of years must be anticipated when predicting the performance of, for example, an underground containment facility for nuclear waste. At such long time scales, the time dependence of rock failure, typically ignored in short time scale analyses, has a significant effect and must be included in the analysis. Since time-dependent rock behavior is thought to be caused by the subcritical growth of microcracks, a time-dependent analysis should incorporate a method of simulating subcritical crack growth. In this thesis, a rock bridge damage model was developed using the finite element program Abaqus to simulate subcritical crack growth for all three modes of crack tip displacement in three-dimensional rock masses. Since subcritical crack growth is not among the damage initiation and evolution criteria available in Abaqus, its effect was included in the model through the USDFLD user subroutine. Material properties for the damage model were obtained through laboratory fracture toughness testing of Escabrosa limestone from Kartchner Caverns. Tests included the grooved disk test for mode I, the punch-through shear with confining pressure test for mode II, and the circumferentially-notched cylindrical specimen test for mode III. The subcritical crack growth parameters n and A were calculated for all three modes using the constant stress-rate method. Fracture test results were compared with a previous study by Tae Young Ko at the University of Arizona, which tested Coconino sandstone and determined that the subcritical crack growth parameters were consistent among modes. This thesis expands upon Ko's work by adding the characterization of a second rock material in all three modes; results indicate that for Escabrosa limestone the subcritical crack growth parameters are not consistent among modes. Additionally, the Escabrosa limestone composing the caverns ranges from a more homogeneous, even-grained texture to a more heterogeneous texture consisting of coarse-grained veins and solution cavities set in a fine-grained matrix. To determine if the veined regions are more susceptible to fracturing and act as the nuclei of rock bridge failure, the fracture toughness tests were conducted separately for each texture. Results indicate that the more heterogeneous limestone has a higher fracture strength, fracture toughness, and subcritical crack growth index n than the more homogeneous limestone. This is in agreement with previous studies that determined that a more complex and heterogeneous microstructure produces a larger microcrack process zone and a more tortuous crack path, leading to higher fracture energies and larger values of n. Application of the rock bridge damage model to a simplified Kartchner cave room with a single roof block provided visualization of decreasing rock bridge size and produced time-to-failure estimates of 1,251 to 65,850 years. Multiple models were run to study the effect of (i) using material properties from each of the two textures identified in the Escabrosa limestone and (ii) varying the in-situ stress ratio, K. Both the value of K and the choice of Escabrosa texture had a large effect on the estimated time-to-failure, indicating that for future modeling of Kartchner accurate estimation of the in-situ stress ratio is as important as field identification of homogeneous vs. heterogeneous textures.