Plasma surface interactions play an important role in the operation of a fusion reactor. One phenomenon is that of radiation blistering, where gas-filled blisters are formed on the surface region of the irradiated solids. The mechanisms for bubble-formation have been extensively studied at higher energies ( > 10keV), although comparatively little work has been done on the effects of low-energy (5keV) ion irradiation.

Thermal emission is the phenomenon of heat dissipation in crystalline materials undergoing deformation. Analysis of the thermal emission from materials subject to strain in the form of mechanical tests is possible by measuring the specimen temperature locally with high resolution temperature sensors. The mechanism of heat dissipation depends intrinsically on a material's mechanical properties and stress history. It is shown that analysis of the thermal emission response to deformation can quantify these properties and provide evidence of microstructural damage. A number of different materials have been studied, including steels, aluminium and nickel alloys, and a carbon/epoxy composite. Simple stress regimes were imposed on the specimens, e.g. creep, fatigue and impact damage, and their thermal emission characteristics were analysed during a following tensile test. It was found that the thermoelastic response of the materials was in some cases sensitive to the level of pre-stressing or damage. In addition information was often contained in the thermal emission responses which was not present or unclear in the stress and strain data. It is concluded that deformation mechanisms cannot be fully understood unless the complete thermomechanical process is examined, involving the measurement of temperature as well as the usual stress and strain. It is envisaged that thermal emission could be developed into a tool for non-destructive damage assessment operating as a complement for established techniques.

No description available.

京都大学 / 0048 / 新制・課程博士 / 博士(エネルギー科学) / 甲第22088号 / エネ博第396号 / 新制||エネ||76(附属図書館) / 京都大学大学院エネルギー科学研究科エネルギー変換科学専攻 / (主査)教授 星出 敏彦, 教授 今谷 勝次, 教授 川那辺 洋 / 学位規則第4条第1項該当 / Doctor of Energy Science / Kyoto University / DGAM

Forming is the fastest way of changing the shape of a piece of metal. It is the most economical process to use for high-volume mass production when the shape of a part is such that it can be made by one of the forming operations

Global challenges associated with extreme climate events and increasing energy demand require significant advances in our understanding and predictive capability of coupled multi- physical processes across spatial and temporal scales. While classical approaches based on the mixture theory may shed light on the macroscopic poromechanics simulations, accurate forward predictions of the complex behavior of phase-changing geomaterials cannot be made without understanding the underlying coupling mechanisms among constituents at the microstructural scale. To precisely predict the multi-physical behaviors originated by smaller scales, fundamental understandings of the micromechanical interactions among phase constituents are crucial. Hence, this dissertation discusses mathematical and computational frameworks designed to capture coupled thermo-hydro-mechanical-fracture processes in phase-changing porous media that incorporate necessary microscopic details. To achieve this goal, this dissertation aims to introduce a practical way to investigate how phase transition and evolving microstructural attributes at small scales affect the applicability of meso- or macroscopic finite element simulations, by leveraging the phase field method to represent the regularized interfaces of phase constituents. Firstly, a multi-phase-field microporomechanics model is presented to model the growth and thaw of ice lenses. In specific, we extend the field theory for ice lens that is not restricted to one-dimensional space. The key idea is to represent the state of the pore fluid and the evolution of freezing-induced fracture via two distinct phase field variables coupled with balance laws, which leads to an immersed approach where both the homogeneous freezing and ice lensing are distinctively captured. Secondly, a thermo-hydro-mechanical theory for geological media with thermally non-equilibrated constituents is presented, where we develop an operator-split framework that updates the temperature of each constituent in an asynchronous manner. Here, the existence of an effective medium is hypothesized, in which the constituents exhibit different temperatures while heat exchange among the phases is captured via Newton’s law of cooling. Thirdly, an immersed phase field model is introduced to predict fluid flow in fracturing vuggy porous media, where crack growth may connect previously isolated voids and form flow conduits. In this approach, we present a framework where the phase field is not only used as a damage parameter for the solid skeleton but also as an indicator of the pore space, which enables us to analyze how crack growth in vuggy porous matrix affects the flow mechanism differently compared to the homogenized effective medium while bypassing the needs of partitioning the domain and tracking the moving interface. Finally, we present a new phase field fracture theory for higher-order continuum that can capture physically justified size effects for both the path-independent elastic responses and the path-dependent fracture. Specifically, we adopt quasi-quadratic degradation function and linear local dissipation function such that the physical size dependence are insensitive to the fictitious length scale for the regularized interface, which addresses the numerical needs to employ sufficiently large phase field length scale parameter without comprising the correct physical size effect.

Thesis (Nucl.E)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1980. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Includes bibliographical references. / by Benito de Celis. / Nucl.E

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1982. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Bibliography: leaves 144-147. / by Benito De Celis. / Ph.D.

No description available.

<p> Small scale tests were utilized in order to obtain characteristic fracture mechanics parameters such as the crack opening displacement (C.O.D.) and the J-integral. Two main types of steels were used (H.S.L.A. and AISI 4340) in obtaining data over a wide range of yield strengths and ductilities. Tests were done to see the effect of both notch geometry and sample geometry·in one of the H.S.L.A. steels, and it is verified that the minimum value of C.O.D., at crack initiation in plane strain, is independent of the geometry and plastic zone size. Further the development of a simple single specimen J-integral test method is done during this work. In terms of the data obtained both the minimum C.O.D.i values and the Jlc values increase with increasing ductility of the materials tested. In the attempt to relate the magnitude of the fracture toughness with microstructural parameters and the limiting processes occuring at the crack tip prior to fracture, the concept of the process zone is discussed. For this study a simple plain carbon steel spheroidized with different carbon contents was examined in addition to the H.S.L.A. and 4340 steels. From the data obtained the minimum C.O.D.i at crack initiation was found to be approximately equal to the product of the materials plain strain ductility and a characteristic distance scaling with the spacing between large non metallic inclusions or the spacing between the bands of the sulphides. </p> / Thesis / Master of Engineering (MEngr)