京都大学 / 0048 / 新制・課程博士 / 博士(人間・環境学) / 甲第19071号 / 人博第724号 / 新制||人||174(附属図書館) / 26||人博||724(吉田南総合図書館) / 32022 / 京都大学大学院人間・環境学研究科相関環境学専攻 / (主査)教授 内本 喜晴, 教授 田部 勢津久, 准教授 藤原 直樹 / 学位規則第4条第1項該当 / Doctor of Human and Environmental Studies / Kyoto University / DGAM

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The globally increasing energy demand that results from the rapid development of modern society has created intensive attention towards the importance of energy efficiency. The areas of energy storage and energy conversion have become one of the most important topics in scientific community at present. As new generation energy storage elements, supercapacitors have exhibited promising practical prospects in the information, transportation, electronics and other sectors due to their charge and discharge performance at high rate, high power density as well as long cycle life. Energy density, including gravimetric energy density, areal energy density and volumetric energy density, is one of the most critical indicator evaluating the performance of supercapacitors. The electrochemical performance of supercapacitors depends mainly on the electrochemical activities and kinetic properties of electrode materials. Carbonaceous materials are deemed to be highly promising, and therefore are extensively investigated energy storage materials for supercapacitors because of their environmental friendliness, low-cost production and outstanding chemical inertness during charging-discharging processes. The specific surface area has been long thought to be the main factor influencing the capacitance of carbonaceous materials. However, the pore structure is of similar importance. High specific surface areas are always arising from a high content of micropores. However, pore radii in the sub-nanometer range impede the ionic charge transfer ability significantly and thus cause a damping of capacitance. In this thesis, hierarchical porous carbons and their composite materials were fabricated by using polyacrylonitrile as carbon precursor for a tailored step-by-step pore forming method, including phase inversion, CaCO3 activation and KOH activation. The materials were thoroughly characterized by XRD, SEM, TEM, BET, XPS and Raman spectroscopy to ascertain the chemical and structural features. The electrochemical properties were studied by cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS) in detail to analyze the pore effect, which strongly influence their electrochemical properties. Porous carbons with high specific surface areas up to 2315 m2 g-1 and high pore volume of 1.9 cm3·g-1 were prepared. A step-wise pore forming method was employed to ensure a high specific surface area and high content of macro/mesopore at the same time. The relationship between pore structure, electrochemical capacitance and rate capability was investigated by changing the content of micropores. For a same specific surface area, a higher micropore content led to a lower capacitance and poorer rate capability. Based on these results, the capacitance was optimized to be 286.8 F g-1. The areal energy density of the supercapacitors can be improved by increasing the mass loading in a certain area directly. However, insufficient electrochemical reaction may be caused by a lack of unhindered electrical and ionic charge transfer routes, resulting in inefficient material utilization. This problem is addressed by designing hierarchical pore structures with embedded conductive additives. Thus, hierarchical porous carbons were modified by embedding carbon nanotubes (CNTs), followed by coverage with thin layers of birnessite. Owing to the hierarchical pore design and the very high pore volume, the birnessite coverage did not cause pore blocking. At the same time, an intimate contact between carbon and birnessite was established. A high area energy density of 627.8 μWh·cm-2 was obtained based on an optimized mass loading of 13.9 mg cm-2. The volumetric energy density of supercapacitors was determined by the density and porosity of active materials. Similarly, the dense active materials not always generate high specific capacitance because of an increased dead mass. However, too porous active materials do not provide sufficient volumetric capacitance due to a waste of space. Thus, density and porosity must be balanced by hierarchical pore structure design so that all pores are interconnected and can be accessed by ions. At the same time, the content of these pores should be as low as possible to save space. Based on the results, highly hierarchical porous carbons were synthesized and embedded into conductive carbon foam to combine electronic conductivity with ionic transfer. In that way, a volumetric energy density as high as 19.44 µWh cm-3 at a volumetric power density of 500 mW cm-3 was generated.

The desire for energy and resource savings brings magnesium alloys as lightweight materials with high specific strength more and more into the focus. Most structural components are subjected to cyclic loading. In the course of computer aided product development, a numerical prediction of the fatigue life under these conditions must be provided. For this reason, the mechanical properties of the considered material must be examined in detail. Wrought magnesium semifinished products, e.g. magnesium sheet metals, typically reveal strong basal textures and thus, the mechanical behavior considerably differs from that of the well-established magnesium die castings. Magnesium sheet metals reveal a distinct difference in the tensile and compressive yield stress, leading to non-symmetric sigmoidal hysteresis loops within the elasto-plastic load range. These unusual hysteresis shapes are caused by cyclic twinning and detwinning. Furthermore, wrought magnesium alloys reveal pseudoelastic behavior, leading to nonlinear unloading curves. Another interesting effect is the formation of local twin bands during compressive loading. Nevertheless, only little information can be found on the numerical fatigue analysis of wrought magnesium alloys up to now. The aim of this thesis is the investigation of the mechanical properties of wrought magnesium alloys and the development of an appropriate fatigue model. For this purpose, twin roll cast AM50 as well as AZ31B sheet metals and extruded ME21 sheet metals were used. Mechanical tests were carried out to present a comprehensive overview of the quasi-static and cyclic material behavior. The microstructure was captured on sheet metals before and after loading to evaluate the correlation between the microstructure, the texture, and the mechanical properties. Stress- and strain-controlled loading ratios and strain-controlled experiments with variable amplitudes were performed. Tests were carried out along and transverse to the manufacturing direction to consider the influence of the anisotropy. Special focus was given to sigmoidal hysteresis loops and their influence on the fatigue life. A detailed numerical description of hysteresis loops is necessary for numerical fatigue analyses. For this, a one-dimensional phenomenological model was developed for elasto-plastic strain-controlled constant and variable amplitude loading. This model consists of a three-component equation, which considers elastic, plastic, and pseudoelastic strain components. Considering different magnesium alloys, good correlation is reached between numerically and experimentally determined hysteresis loops by means of different constant and variable amplitude load-time functions. For a numerical fatigue life analysis, an energy based fatigue parameter has been developed. It is denoted by “combined strain energy density per cycle” and consists of a summation of the plastic strain energy density per cycle and the 25 % weighted tensile elastic strain energy density per cycle. The weighting represents the material specific mean stress sensitivity. Applying the energy based fatigue parameter on modeled hysteresis loops, the fatigue life is predicted adequately for constant and variable amplitude loading including mean strain and mean stress effects. The combined strain energy density per cycle achieves significantly better results in comparison to conventional fatigue models such as the Smith-Watson-Topper model. The developed phenomenological model in combination with the combined strain energy density per cycle is able to carry out numerical fatigue life analyses on magnesium sheet metals.

Ce travail présente la mise en oeuvre d’un protocole de synthèse de gradients deconcentration dans les oxydes lamellaires riches en Li et en Mn. Le but a été dedévelopper la formation d’oxydes lamellaires riches en Li et Mn au coeur des agrégatssphériques du matériau actif et, en se rapprochant de la surface, d’enrichir lacomposition de l’oxyde lamellaire en Co et en Ni, afin de combiner une forte densitéd’énergie (apportée par le coeur du gradient) et une excellente stabilité thermique etstructurale (apportée par la surface du gradient). La synthèse a été réalisée en deuxétapes, une co-précipitation pour former un carbonate de métaux de transition suivied’une calcination à haute température pour obtenir le matériau actif lithié. L’influencede différents paramètres (pH, débit d’injection, taille du réacteur, composition, …) surla nature du carbonate à gradient de concentration ainsi formé a été étudiée. De lamême façon, le contrôle du ratio Li/M (ici M = Ni, Co, Mn), de la température et de ladurée de calcination s’est révélé important pour parvenir à maintenir le gradient deconcentration dans le matériau lithié. Le ratio Li/M est également déterminant pourcontrôler la nature des matériaux obtenus (lamellaire - spinelle ou lamellaire –lamellaire). Des caractérisations extrêmement pointues, et complexes à mettre enoeuvre, ont été menées afin d’obtenir des informations pertinentes sur la distributiondes phases au sein des agrégats (composition et structure), de la surface au coeur dugradient : différentes techniques de microscopie (EPMA, MEB-EDX et FIB-STEM) ontainsi été largement utilisées. Les matériaux les plus intéressants ont été étudiés enbatteries Lithium-ion avec une électrode de graphite à la négative, les performancesélectrochimiques et la stabilité thermique à l’état chargé de la batterie sont largementdiscutées par rapport à l’état de l’art et notamment au matériau de coeur riche en Li eten Mn. / This work describes in details the implementation of the synthesis protocol for theformation of Li- and Mn-rich layered oxides with concentration-gradients. The purposewas to develop the synthesis of Li- and Mn-rich layered oxides in the bulk of sphericalaggregates of active material and, moving to the surface, to enrich the layered oxides’composition with Co and Ni, in order to combine a high energy density (provided bythe bulk) and an excellent thermal and structural stability (provided by the surface).The synthesis was performed in two steps, a coprecipitation to form a transition metalcarbonate followed by a calcination at high temperature to obtain the lithiated activematerial. The influence of several parameters (pH, feeding rate, size of the reactor,composition …) on the nature of the carbonates formed with concentration-gradientswas studied. Similarly, the control of the Li/M ratio (with M = Ni, Co, Mn) and of thetemperature and duration of calcination was revealed to be important to maintain theconcentration-gradient in the lithiated materials. The Li/M ratio is also the keyparameter to control the nature of the materials obtained (layered - spinel or layered -layered). Advanced characterizations, complex to be implemented, were performed inorder to obtain in-depth information on the distribution of phases within the aggregates(composition and structure), from the bulk to the surface: complementary microscopytechniques (EPMA, SEM-EDS and FIB-STEM) were widely used. The most interestingmaterials were studied in Lithium-ion batteries with graphite at the negative electrode,their electrochemical performance and the thermal stability in the charged state of thebattery were compared to the state of art, and particularly to the bulk Li and Mn-richlayered oxide.

Synthetic vascular grafts are useful to bypass diseased arteries. The long-term failure of synthetic grafts is primarily due to intimal hyperplasia at the anastomotic sites. The accelerated intimal hyperplasia may stem from a compliance mismatch between the host artery and the graft since commercially available synthetic conduits are much stiffer than an artery. The objective of this thesis is to design a method for fabricating a vascular graft that mechanically matches the patients native artery over the expected physiologic range of pressures. The creation of an optimized mechanical graft will hopefully lead to an improvement in patency rates. The mechanical equivalency between the graft and the host artery is defined locally by several criteria including the diameter upon inflation, the elasticity at mean pressure, and axial force. A single parameter mathematical for a thin-walled tube is used to describe of the final mechanical behavior of a synthetic graft. For the general problem, the objective would be to fabricate a mechanics-matching vascular graft for each host artery. Typically, fabrication parameters are set initially and the properties of the fabricated graft are measured. However, by modeling the entire fabrication process and final mechanical properties, it is possible to invert the situation and let the typical output mechanical values be used to define the fabrication parameters. The resultant fabricated graft will then be mechanically matching. As a proof-of-concept, several prototype synthetic grafts were manufactured and characterized by a single Invariant to match a canine artery. The resultant graft equaled the diameter upon inflation, the elasticity at mean pressure, and axial force of the native canine artery within 6%. An alternative to making an individual graft for each artery is also presented. A surgeon may choose the best graft from a set of pre-manufactured grafts, using a computer program algorithm for best fit using two parameters in a neighborhood. The design optimization problem was solved for both canine carotid and human coronary arteries. In conclusion, the overall process of design, fabrication and selection of a mechanics matching synthetic vascular graft is shown to be reliable and robust.

Part 1: Theoretic background information - Review of Hooke’s law for linear elastic materials - The strain energy density of linear elastic materials - Hyperelastic material - Material laws for hyperelastic materials - About selecting the material model and performing tests - Implementation of hyperelastic material laws in Mechanica - Defining hyperelastic material parameters in Mechanica - Test set-ups and specimen shapes of the supported material tests - The uniaxial compression test - Stress and strain definitions in the Mechanica LDA analysis Part 2: Application examples - A test specimen subjected to uniaxial loading - A volumetric compression test - A planar test - Influence of the material law Appendix - PTC Simulation Services Introduction - Dictionary Technical English-German / Teil 1: Theoretische Hintergrundinformation - Das Hookesche Gesetz für linear-elastische Werkstoffe - Die Dehnungsenergiedichte für linear-elastische Materialien - Hyperelastisches Material - Materialgesetze für Hyperelastizität - Auswählen des Materialgesetzes und Testdurchführung - Implementierung der hyperelastischen Materialgesetze in Mechanica - Definieren der hyperelastischen Materialparameter in Mechanica - Testaufbauten und Prüfkörper der unterstützten Materialtests - Der einachsige Druckversuch - Spannungs- und Dehnungsdefinition in der Mechanica-Analyse mit großen Verformungen Teil 2: Anwendungsbeispiele - Ein einachsig beanspruchter Prüfkörper - Ein volumetrischer Drucktest - Ein planarer Test - Einfluss des Materialgesetzes Anhang: - Kurzvorstellung der PTC Simulationsdienstleistungen - Wörterbuch technisches Englisch-Deutsch

Part 1: Theoretic background information - Review of Hooke’s law for linear elastic materials - The strain energy density of linear elastic materials - Hyperelastic material - Material laws for hyperelastic materials - About selecting the material model and performing tests - Implementation of hyperelastic material laws in Mechanica - Defining hyperelastic material parameters in Mechanica - Test set-ups and specimen shapes of the supported material tests - The uniaxial compression test - Stress and strain definitions in the Mechanica LDA analysis Part 2: Application examples - A test specimen subjected to uniaxial loading - A volumetric compression test - A planar test - Influence of the material law Appendix - PTC Simulation Services Introduction - Dictionary Technical English-German / Teil 1: Theoretische Hintergrundinformation - Das Hookesche Gesetz für linear-elastische Werkstoffe - Die Dehnungsenergiedichte für linear-elastische Materialien - Hyperelastisches Material - Materialgesetze für Hyperelastizität - Auswählen des Materialgesetzes und Testdurchführung - Implementierung der hyperelastischen Materialgesetze in Mechanica - Definieren der hyperelastischen Materialparameter in Mechanica - Testaufbauten und Prüfkörper der unterstützten Materialtests - Der einachsige Druckversuch - Spannungs- und Dehnungsdefinition in der Mechanica-Analyse mit großen Verformungen Teil 2: Anwendungsbeispiele - Ein einachsig beanspruchter Prüfkörper - Ein volumetrischer Drucktest - Ein planarer Test - Einfluss des Materialgesetzes Anhang: - Kurzvorstellung der PTC Simulationsdienstleistungen - Wörterbuch technisches Englisch-Deutsch

This diploma thesis deals with the different possible calculations of crack path. Specifically, it focuses on criteria based on maximum tangential stress, minimal strain energy density, crack tip displacement, and local symmetry. These criteria are used for calculations in ANSYS software to estimate possible crack paths on four simple structures. The thesis also contains the codes created in ANSYS. Using these, the crack trajectory of a given structure can be calculated by any of the four criteria described.

Part 1: Theoretic background information - Review of Hooke’s law for linear elastic materials - The strain energy density of linear elastic materials - Hyperelastic material - Material laws for hyperelastic materials - About selecting the material model and performing tests - Implementation of hyperelastic material laws in Mechanica - Defining hyperelastic material parameters in Mechanica - Test set-ups and specimen shapes of the supported material tests - The uniaxial compression test - Stress and strain definitions in the Mechanica LDA analysis Part 2: Application examples - A test specimen subjected to uniaxial loading - A volumetric compression test - A planar test - Influence of the material law Appendix - PTC Simulation Services Introduction - Dictionary Technical English-German / Teil 1: Theoretische Hintergrundinformation - Das Hookesche Gesetz für linear-elastische Werkstoffe - Die Dehnungsenergiedichte für linear-elastische Materialien - Hyperelastisches Material - Materialgesetze für Hyperelastizität - Auswählen des Materialgesetzes und Testdurchführung - Implementierung der hyperelastischen Materialgesetze in Mechanica - Definieren der hyperelastischen Materialparameter in Mechanica - Testaufbauten und Prüfkörper der unterstützten Materialtests - Der einachsige Druckversuch - Spannungs- und Dehnungsdefinition in der Mechanica-Analyse mit großen Verformungen Teil 2: Anwendungsbeispiele - Ein einachsig beanspruchter Prüfkörper - Ein volumetrischer Drucktest - Ein planarer Test - Einfluss des Materialgesetzes Anhang: - Kurzvorstellung der PTC Simulationsdienstleistungen - Wörterbuch technisches Englisch-Deutsch