Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第14575号 / 工博第3043号 / 新制||工||1453(附属図書館) / 26927 / UT51-2009-D287 / 京都大学大学院工学研究科材料工学専攻 / (主査)教授 落合 庄治郎, 教授 粟倉 泰弘, 准教授 奥田 浩司 / 学位規則第4条第1項該当

Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第15647号 / 工博第3305号 / 新制||工||1499(附属図書館) / 28184 / 京都大学大学院工学研究科社会基盤工学専攻 / (主査)教授 岡 二三生, 教授 角 哲也, 准教授 木元 小百合 / 学位規則第4条第1項該当

Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第17137号 / 工博第3627号 / 新制||工||1551(附属図書館) / 29876 / 京都大学大学院工学研究科都市社会工学専攻 / (主査）教授 小池 武, 教授 杉浦 邦征, 准教授 五十嵐 晃 / 学位規則第4条第1項該当

Master of Science / Department of Civil Engineering / Dunja Peric / Integral Abutment Bridges (IABs) are Jointless Bridges whereby the deck is continuous and monolithic with abutment walls. IABs are outperforming their non-integral counterparts in economy and safety. Their principal advantages are derived from the absence of expansion joints and sliding bearings in the deck, making them the most cost-effective system in terms of construction, maintenance, and longevity. The main purpose of constructing IABs is to prevent the corrosion of structure due to water seepage through joints. The simple and rapid construction provides smooth, uninterrupted deck that is aesthetically pleasing and safer for riding. The single structural unit increases the degree of redundancy enabling higher resistance to extreme events. However, the design of IABs not being an exact science poses certain critical issues. The continuity achieved by this construction results in thermally induced deformations. These in turn introduce a significantly complex and nonlinear soil-structure interaction into the response of abutment walls and piles of the IAB. The unknown soil response and its effect on the stresses in the bridge, creates uncertainties in the design. To gain a better understanding of the mechanism of load transfer due to thermal expansion, which is also dependent on the type of the soil adjacent to the abutment walls and piles, a 3D finite element analysis is carried out on a representative IAB using state-of-the-art finite element code ABAQUS/Standard 6.5-1. A literature review focusing on past numerical models of IABs is presented followed by details of the numerical model developed in this study using the interactive environment ABAQUS/CAE 6.5-1 along with the analysis details. A discussion of results for the analysis of the IAB with three different soil conditions and each experiencing three different temperature change scenarios is presented. Conclusions of the study and recommendations for future research wrap up the thesis. The advancement of knowledge enabled by this research will provide a basis for introduction of new guidelines in Kansas Bridge Design Manual.

Doctor of Philosophy / Department of Civil Engineering / Hayder A. Rasheed / The use of laminated composites in aerospace, automotive, and civil engineering applications is ever growing due to their distinguished properties (High stiffness-to-weight ratio, high strength-to-weight ratio, fatigue and corrosion resistance). This growth has resulted in increasing the demand for better understanding the mechanics of laminated composites. Composite columns and wide plates, like any traditional members subjected to axial compression, undergo stability issues prior to failure. Limited amount of research studies has focused on the buckling of laminated anisotropic composite members. Analytical formula for the buckling load of generally anisotropic laminated composite simply supported thin columns and wide plates is derived using the Rayleigh Ritz approximation and bifurcation approach. The effective axial, coupling and flexural stiffness coefficients of the anisotropic layup is determined from the generalized constitutive relationship using dimensional reduction by static condensation of the 6x6 composite stiffness matrix. The resulting explicit formula is expressed in terms of the generally anisotropic material properties as well as the member geometry. The developed formula may be considered an extension to Euler buckling formula using Rayleigh-Ritz approximation and the first of its kind since Euler. This formula reduces down to Euler buckling formula once the effective coupling stiffness term vanishes for isotropic and certain classes of laminated composites. The analytical results are verified against finite element Eigen value solutions for a wide range of anisotropic laminated layups yielding high accuracy. Comparisons with experiments; conducted at Kansas State University for the simply supported case, are also performed showing good correspondence. A brief parametric study is then conducted to examine the effect of ply orientations and material properties including hybrid carbon/glass fiber composites, element thickness, and element type in FE analysis. Relevance of the numerical and analytical results is discussed for all these cases.

The present work has been produced as part of an on-going collaboration between the University of Manchester and Amec, with the primary aim of furthering mechanistic understanding of corrosion processes in zirconium alloys out-of-reactor. Zirconium alloys are used as cladding material for nuclear fuel pellets, and correct understanding of the corrosion process in autoclave is essential to predicting material behaviour in-reactor. This EngD thesis is composed of five proposed papers that investigate observations and hypotheses under the theme of mechanical degradation in oxides formed on zirconium alloys in autoclave. First investigations concern observed stress relaxation in zirconium oxide. Finite element analysis is used to capture mechanical aspects of the corrosion process and apply this to stress behaviour determined previously using synchrotron x-ray diffraction. The results indicate that a mechanism other than creep or hydrogen induced lattice strain must be present to account for the observed stress relaxation. One such potential mechanism is crack formation; statistical analysis of scanning electron microscopy images has been used to identify a link between the development of roughness at the metal-oxide interface, crack formation in the oxide and transition points or acceleration in the corrosion kinetics. Parameters such as the median radius of curvature and profile slope (Rdq) have been applied, as these parameters do not require the definition of a periodic wavelength or amplitude. These and other parameters are related to information in literature to indicate that for samples of Zircaloy-4 and ZIRLOTM, which go through transition, the interface roughness changes in a way that would increase localised stress concentrations. The third material is an experimental low tin alloy, which under the same oxidation conditions, and during the same time period, does not appear to go through transition and does not develop an interface roughness in the same way. A critical assessment of finite element analysis applied to oxidising non-planar interfaces shows the significant limitations in the existing mechanism for representing oxidation expansion and stress formation. Autoclave oxidation experiments of artificially roughened samples of Zircaloy-4 were carried out to further understand the impact of out-of-plane stress generation. The results indicate a divergence based on surface roughness after ~86 days oxidation. SEM examination of images in cross section highlighted accelerated oxidation above surface roughness peaks, and an increased crack area in rougher samples. Finally, finite element analysis of the tetragonal to monoclinic phase transformation showed that biaxial compressive stress relaxation, or the tri-axial tensile stress associated with an advancing crack tip, could reduce the transformation strain energy and destabilise the tetragonal phase. The volumetric expansion and shear strain associated with the phase transformation produces stress in the surrounding oxide sufficient to generate nano-scale cracks perpendicular to the metal-oxide interface. This would allow fast ingress routes for oxygen containing species, and therefore acceleration in the corrosion kinetics.

A 3D nonlinear finite element analysis was developed for simulating the behavior of skewed concrete slabs and to identify the response of the slab with different angles and element sizes. The purpose of this research is helping the engineering and construction industry to utilize the FEM study and results more in different structural applications.Simulations performed in ABAQUS for skewed slabs are also compared to straight and skewed slabs according to the analytical formulation by Timoshenko.The result showed that when the distance increases, the load capacity measured by reaction forces decreases for all different skew angles except angle 0° and 15° which show a stable reaction force along the entire path. .The study reveals that depending on the skew angle and the element size, the stress distribution and vertical displacements in the slab vary significantly from those in a straight slab. It is shown that the displacement decreases with the increase of the skew angle while the stresses increase with the decrease of the skew angle.There are small differences in the vertical displacements and stress distribution between the results obtained by this study and the results obtained by Timoshenko regarding the plates with skews of 0°, 30° and 45°.

In a context where timber is gaining popularity as a building material and glass-fibre reinforced composites (GFRC) are becoming more accessible in a wide variety of formats, it is considered appropriate to reconsider the combination of these two materials. Additionally, given the increasing use of laminated timber elements where stiffness and strength are better controlled, attention is drawn back to the connection between elements. For these reasons, it is considered of interest to study reinforcing possibilities for connections within timber structures. This work consists in a parametric study of a single-dowelled connection between a timber part and a slotted-in steel plate, reinforced wirh GFRC plates glued into the timber slot at both sides of the steel plate. The study was carried out through simulations in ABAAUS Finite Element Analysis software considering the effect of specimen's geometry and the fibre distribution within the GFRC. Results show the increase of stiffness for the different configurations and give an insight of what can be expected from such type of reinforcements.

Aus der Einleitung: "Die Vorteile von Dehnschrauben ergeben sich aus der großen Verformung, die bei der Montage eingestellt und mit Hilfe eines taillierten Schafts ermöglicht wird. Zusätzlich zu dem geringeren Schaftdurchmesser erhöht eine größere Länge die Nachgiebigkeit und damit die Längenänderung. Aufgrund dieser hohen Längenänderung benötigen Dehnschrauben keine Schraubensicherung und sind unempfindlicher gegenüber Setzverlusten."

Miniaturized, self-sufficient bioelectronics powered by unconventional micropower may lead to a new generation of implantable, wireless, minimally invasive medical devices, such as pacemakers, defibrillators, drug-delivering pumps, sensor transmitters, and neurostimulators. Studies have shown that micro-enzymatic biofuel cells (EBFCs) are among the most intuitive candidates for in vivo micropower. In the fisrt part of this thesis, the prototype design of an EBFC chip, having 3D intedigitated microelectrode arrays was proposed to obtain an optimum design of 3D microelectrode arrays for carbon microelectromechanical systems (C-MEMS) based EBFCs. A detailed modeling solving partial differential equations (PDEs) by finite element techniques has been developed on the effect of 1) dimensions of microelectrodes, 2) spatial arrangement of 3D microelectrode arrays, 3) geometry of microelectrode on the EBFC performance based on COMSOL Multiphysics. In the second part of this thesis, in order to investigate the performance of an EBFC, behavior of an EBFC chip performance inside an artery has been studied. COMSOL Multiphysics software has also been applied to analyze mass transport for different orientations of an EBFC chip inside a blood artery. Two orientations: horizontal position (HP) and vertical position (VP) have been analyzed. The third part of this thesis has been focused on experimental work towards high performance EBFC. This work has integrated graphene/enzyme onto three-dimensional (3D) micropillar arrays in order to obtain efficient enzyme immobilization, enhanced enzyme loading and facilitate direct electron transfer. The developed 3D graphene/enzyme network based EBFC generated a maximum power density of 136.3 μWcm-2 at 0.59 V, which is almost 7 times of the maximum power density of the bare 3D carbon micropillar arrays based EBFC. To further improve the EBFC performance, reduced graphene oxide (rGO)/carbon nanotubes (CNTs) has been integrated onto 3D mciropillar arrays to further increase EBFC performance in the fourth part of this thesisThe developed rGO/CNTs based EBFC generated twice the maximum power density of rGO based EBFC. Through a comparison of experimental and theoretical results, the cell performance efficiency is noted to be 67%.