京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第19893号 / 工博第4209号 / 新制||工||1651(附属図書館) / 32970 / 京都大学大学院工学研究科材料工学専攻 / (主査)教授 辻 伸泰, 教授 白井 泰治, 教授 松原 英一郎 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

Formable Advanced High-Strength Steels (AHSS) have a unique combination of strength and ductility, making them ideal in the effort to lightweight vehicles. The AHSS in this study, Quenched and Partitioned 1180, rely on the Transformation Induced Plasticity (TRIP) effect, in which retained austenite (RA) grains transform to martensite during plastic deformation, providing extra ductility via the transformation event. Understanding the factors involved in RA transformation, such as local strain and grain attributes, is therefore key to optimizing the microstructure of these steels. This research seeks to increase understanding of those attributes and the correlations between microstructure and RA transformation in TRIP steels. To measure local strain, the viability of using forescatter detector (FSD) images as the basis for DIC study is investigated. Standard FSD techniques, along with an integrated EBSD / FSD approach (Pattern Region of Interest Analysis System), are both analyzed. Simultaneous strain and microstructure maps are obtained for tensile deformation up to around 6% strain. The method does not give sub-grain resolution, and surface feature evolution prevents DIC analysis across large strain steps; however, the data is easy to obtain and provides a natural set of complementary information for the EBSD analysis. In-situ tensile tests combined with EBSD allow RA grain and neighboring attributes to be characterized and corresponding transformation data to be obtained. However, pseudo-symmetry of the ferrite (BCC) and martensite (BCT) phases prevents EBSD from accurately identifying all phases. Measuring the relative distortion of the crystal lattice, tetragonality, is one approach to identifying the phases. Unfortunately, small errors in the pattern center can cause significant errors in tetragonality measurement. Therefore, this research utilizes a new approach for accurate pattern center determination using a strain minimization routine and applies it to tetragonality maps for phase identification. Tetragonality maps based on dynamically simulated patterns result in the most accurate maps and can also be used to predict approximate local carbon content. Machine learning is then used on the collected data to isolate key attributes of RA grains and provide a decision tree model to predict transformation based on those attributes. Among the most relevant attributes found, RA grain area, RA grain shape aspect ratio, a “hardness” factor, and major axis orientation are included. Possible correlations between these factors and transformation improve understanding of relevant attributes and show the advantage that machine learning can have in unravelling complex material behavior.

This work aims at giving a systematic review of the numerical approaches and obtained results published in recent years. Focus is set on both the recent trends and achievements as well as challenges and open questions. Thesis critically reviews work done in previous thesis related to food packaging material and design, at Blekinge Institute of Technology with the collaboration of Tetra Pak liquid food packaging company. Here, 27 numbers of master’s thesis are critical review all the while using 4 PHD works for referencing.  Focus of these thesis works relates to the mechanics and its sub-branch fracture mechanics. Due to this all the theory related to mechanics and fracture mechanics, which is compulsory to know for understanding is defined initially. Main material which are under consideration throughout the work are PP, LDPE, PET-LDPE, and aluminum foil. As three materials are used in the liquid food packaging which are PE, paper board and aluminum. Uses of this material and there required physical properties are measured. Testing methods which are used to check whether the material meets the required parameters are tensile testing, tear testing, peel testing and shear test.  Also, some methods are used along with these tests to perform the test more precisely, to evaluate and compare result i.e., Nakajima test, Digital image correlation. DIC testing technique is used to compare the results obtained from simulation. It is also understood that DIC method provided the user with increased quality of obtained results.  Most of the topics of discussions have been reviewed for corresponding thesis, displaying the used ideas, theory, applied experimentation and realized conclusions. Using these above it was able to derive a conclusion based on the developed research questions and hypothesis. Defined problems in previous work are studied also solution as a future work is suggested to overcome these problems. Mainly the slippage issue while holding PE in clamps. Furthermore, various development is discussed which is done to introduce new material which is more possible being used in the future.

This dissertation contains the results from an experimental study, numerical, and analytical study conducted on quasi-isotropic carbon fiber laminates containing a center hole (notch) subjected to constant amplitude tension-tension fatigue loading in order to investigate the effect of fatigue damage development on the residual properties. Quasi-static tests were initially performed on notched composites using digital image correlation (DIC) to determine the strain profiles at selected transverse sections of the outer ply of the laminates and the static strength of the laminates. Subsequently, tension-tension fatigue tests were carried out at 70%, 75% and 80% of the nominal static failure load. A finite element model was developed using Abaqus and Digimat in which Digimat was used to implement the damage evolution model via a user-defined material subroutine. Damage initiation has been assessed using Hashin's failure criteria and the Matzenmiller model was adopted for damage evolution. A second finite element model was developed using Abaqus and Autodesk Simulation Composite Analysis (ASCA) in which ASCA was used to implement the user-material subroutine. The subroutine includes a failure initiation criterion based upon multi-continuum theory (MCT) and an energy-based damage evolution law. Numerical and experimental strain results were presented and compared for different section lines on the outer surface of the laminate at different loading stages. Additionally, the experimentally measured notched composite strength was compared with the predictions from the finite element solutions. These results are used as baseline for subsequent comparison with strain profiles obtained using DIC for specimens fatigued at different stress levels and fatigue lifetime fractions. The results showed a significant effect of fatigue damage development on strain redistribution even at early stages of fatigue. The results also showed the capability of DIC technique to identify damage initiation and its location. Furthermore, X-ray computed tomography (CT) was used to examine the sequence of damage development throughout the fatigue lifetime and to connect the observed damage mechanisms with the occurred change of strain profiles. Experimental vibrational modal analysis tests were also conducted to assess the effect of fatigue damage on the residual frequency responses (RFRs). Vibrational measurements were initially performed on pristine notched composites. The results are used as baseline for subsequent comparison with strain profiles obtained with DIC. Finite element models based on the classical plate theory (Kirchhoff) and the shear deformable theory (Mindlin) within the framework of equivalent single-layer and layer-wise concepts as well as the three-dimensional theory of elasticity are developed to predict the natural frequencies of non-fatigued specimen. These models are implemented using the finite element software, Abaqus, to determine the natural frequencies and the corresponding mode shapes. In addition, an analytical model based on Kirchhoff plate theory is developed. Using this approach, an equivalent bending-torsion beam model for cantilever laminated plates is extracted taking into account the reduction in local stiffness and mass induced by the center hole. Numerical and analytical natural frequency values are then compared with those obtained through experimental vibrational tests, and the accuracy of each finite element (FE) and analytical model type is assessed. It is shown that the natural frequencies obtained using the analytical and FE models are within 8% of the experimentally determined values. / Ph. D.

The pavement system is subjected to complex stress states under vehicular loading. A combination of axial and shear stress has been identified as a potential cause of top down cracking (or more precisely near surface cracking) in asphalt surface. Therefore, in terms of modeling the material response a pertinent question is whether the typical one-dimensional viscoelastic properties of the material are affected by a multi-axial stress state. Such changes are referred to as interaction non-linearity. The objective of this study was to evaluate whether or not asphalt composites are susceptible to such interaction effects. The study was conducted using fine aggregate matrix (FAM), which comprises graded sand and asphalt binder. To provide multi-modal loading, the rectangular prismatic FAM specimens were used with the Arcan apparatus. This apparatus ensures low bending stress and offers adjustments in the setup to provide different proportions of axial and shear stress. Finite element modeling was done to evaluate the stress state for different orientations of the sample in the Arcan apparatus. For measurement of strain, the study used digital image correlation (DIC), which is an optical, non-contact measurement technology. The strain thus measured was used to compute shear compliance. Fitting parameters of the shear compliances were estimated for power-law and Prony series for different loading orientations. When compared, the measured shear compliances do not show perceivable variation with respect to different proportion of axial stress applied in conjunction. However, further testing with different temperatures and other magnitudes of shear stress is necessary. This study is the first step to allow modeling of stress and crack propagation behavior near the pavement surface where complex stress state is present. / text

Les paramètres de loi de comportement s'identifient habituellement à partir d'éprouvettes standardisées présentant des champs de déformations homogènes. L'essor actuel des méthodes inverses incite à l'utilisation d'essais plus hétérogènes. L'objectif de cette thèse est de développer une procédure d'identification inverse en utilisant une méthode de recalage de modèles éléments finis basée sur des expériences à hétérogénéités croissantes des champs de déformation. À cette fin, des essais plans avec différentes géométries d'éprouvettes, en titane commercialement pur, ont été effectués et un essai original hors plan fortement hétérogène a été mis au point. Dans ce dernier cas, un essai unique réalisé à l'aide d'une machine de traction uni-axiale permet d'obtenir des sollicitations d'expansion, mais aussi de traction et de cisaillement selon deux directions orthogonales. Des mesures de champs cinématiques planes et non planes (stéréo-corrélation d'images) sont utilisées afin d'évaluer les déformations jusqu'à striction. À partir de ces mesures en grandes déformations, on propose de mener une comparaison entre les informations issues de l'expérience et un modèle dupliquant les conditions expérimentales (conditions aux limites issues de la corrélation d'images). Cette comparaison conduit, via un processus d'optimisation, à l'actualisation itérative du jeu de paramètres de la loi de comportement utilisée dans le modèle éléments finis. Le nombre de paramètres ainsi identifiés varie selon le modèle de comportement : élastique anisotrope puis élasto-plastique anisotrope. Différentes validations ont mis en évidence l'intérêt de considérer des champs de déformation fortement hétérogènes. Dans ce cadre, des prédictions numériques d'opérations d'emboutissage, réalisées à l'aide des différents jeux de paramètres identifiés sont comparées à l'expérience. On montre que la prise en compte d'un modèle élastique anisotrope plutôt qu'isotrope fournit un état de contrainte plus réaliste en début de plasticité, améliorant considérablement l'identification du modèle plastique. Enfin, une approche couplée entre mesures de champs cinématiques et thermiques (thermographie infrarouge) a été développée. Les paramètres d'un modèle mécanique sont identifiés puis utilisés pour l'évaluation d'un modèle thermique calculant les sources de chaleur. Par cette méthode, plusieurs modèles d'évolution de la fraction d'énergie dissipée sous forme de chaleur ont été identifiés (coefficient de Taylor et Quinney).

The current thesis focuses on the deformation behaviour and strain distribution in the microstructure of ductile iron during tensile loading. Utilizing Digital Image Correlation (DIC) and in-situ tensile test under optical microscope, a method was developed to measure high resolution strain in microstructural constitutes. In this method, a pit etching procedure was applied to generate a random speckle pattern for DIC measurement. The method was validated by benchmarking the measured properties with the material’s standard properties. Using DIC, strain maps in the microstructure of the ductile iron were measured, which showed a high level of heterogeneity even during elastic deformation. The early micro-cracks were initiated around graphite particles, where the highest amount of local strain was detected. Local strain at the onset of the micro-cracks were measured. It was observed that the micro-cracks were initiated above a threshold strain level, but with a large variation in the overall strain. A continuum Finite Element (FE) model containing a physical length scale was developed to predict strain on the microstructure of ductile iron. The materials parameters for this model were calculated by optimization, utilizing Ramberg-Osgood equation. For benchmarking, the predicted strain maps were compared to the strain maps measured by DIC, both qualitatively and quantitatively. The DIC and simulation strain maps conformed to a large extent resulting in the validation of the model in micro-scale level. Furthermore, the results obtained from the in-situ tensile test were compared to a FE-model which compromised cohesive elements to enable cracking. The stress-strain curve prediction of the FE simulation showed a good agreement with the stress-strain curve that was measured from the experiment. The cohesive model was able to accurately capture the main trends of microscale deformation such as localized elastic and plastic deformation and micro-crack initiation and propagation.

Understanding the drivers of climate change requires knowledge about the global carbon (C) cycle. Although inland waters play an important role in the C cycle by emitting and burying C, streams and lakes are in general overlooked in bottom-up approached C budgets. In this thesis I estimated emissions of carbon dioxide (CO2) and methane (CH4) from all lakes and streams in a 15 km2 subarctic catchment in northern Sweden, and put it in relation to the total catchment C exchange. I show that high-latitude aquatic systems in general and streams in particular are hotspots for C emission to the atmosphere. Annually, the aquatic systems surveyed in this study emitted about 10.8 ± 4.9 g C m-2 yr-1 (ca. 98 % as CO2) which is more than double the amount of the C laterally exported from the catchment. Although the streams only covered about 4% of the total aquatic area they emitted ca. 95% of the total aquatic C emission. For lake emissions, the ice break-ups were the most important annual events, counting for ca. 45% of the emissions. Overall, streams dominated the aquatic CO2 emission in the catchment while lakes dominated CH4 emission, 96 % and 62 % of the totals, respectively. When summing terrestrial and aquatic C fluxes together it showed that the aquatic emissions alone account for approximately two thirds of the total annual catchment C loss. The consequence of not including inland waters in bottom-up derived C budgets is therefore a risk of overestimating the sink capacity of the subarctic landscape. However, aquatic systems can also act as C sinks, by accumulating C in sediment and thereby storing C over geological time frames. Sediment C burial rates were estimated in six lakes from a chronology based on 210Pb dating of multiple sediment cores. The burial rate ranged between 5 - 25 g C m-2 yr-1, which is of the same magnitude as lake C emissions. I show that the emission:burial ratio is about ten times higher in boreal compared to in subarctic-arctic lakes. These results indicate that the balance between lakes C emission and burial is both directly and indirectly dependent on climate. This process will likely result in a future increase of C emissions from high-latitude lakes, while the C burial capacity of these same lakes sediments weaken.

Dans les dernières années, le renforcement des bâtiments en maçonnerie a connu une usure massive des bandes CFRP. Ces matériaux composites, attachés sur les éléments à renforcer, sont exposés à une fracture prématurée pour délaminage (...). Une façon pour accroître la résistance maximale du système renforcé par CFRP est d'améliorer la cohésion entre support et composite en utilisant des ancrages mécaniques. Ces derniers sont réalisés en utilisant les mêmes typologies de fibres de renforcement et en les insérant dans le support comme des «clous». Les recherches scientifiques sur l'usure de cette façon d'ancrage sur support en maçonnerie ont été très limitées et, dans ce contexte, il n'y a pas d'études expérimentales sur le projet et le placement des ancrages. L'objectif principal du présent travail de thèse est de quantifier l'efficacité des ancrages en fibre de carbone appliqués sur brique (...) par les bandes CFRP. Cette recherche est la première phase d'une étude plus vaste sur les systèmes de maçonnerie-CFRP renforcés par « carbon fiber anchor ». Dans l'étude, l'analyse des déplacements et des déformations de la surface renforcée a été faite en utilisant la Corrélation des Images (DIC), une avantageuse méthode optique jamais utilisée pour l'étude des systèmes «support-CFRP band- ancrages».Le présent travail de thèse démontre que les ancrages en CFRP augmentent le résistance maximale et la ductilité des renforcements par bande de composites. Donc, cette typologie d'ancrage augmente la sécurité des personnes pendant les tremblements de terre et ne permettent pas la fracture fragile de la structure renforcée. La corrélation des images a été un bon outil pour l'étude des déformations, des avantages et des inconvénients de cette méthode et ont été évalué pendant la recherche / In these recent years, the strengthening of masonry building has known a massive use of CFRP sheets. Those composite materials glued on the elements to reinforce are exposed to prematurely debonding crisis due to a tension load which is much smaller than the tensile strength of the CFRP. A way to upgrade failure load of CFRP-to-support bonded joint is to reinforce the cohesion between the fibers and the support by the use of mechanicals anchors built with the same fibers of the composite and fastened in the support like “nails”. Research on the use of anchors for masonry supports has been limited and, in this framework, there are no experimental analyses related to the design and the placement of fiber anchors. The aim of this thesis is to provide experimental data to quantify the efficiency of the carbon fiber anchors applied on a reinforced fire brick. This is a ground work to study CFRP to masonry bonded joint fastened by fiber “nails”. Specifically, the analysis of the displacement and the strain fields of the reinforced surface have been realized by means of Digital Image Correlation (DIC), an optical appealing method never used to study a FRP to support bonded joint fastened by FRP anchor. The research demonstrates that the use of the CFRP anchor increases the resistance and the ductility of the reinforcements. The latter are important to augment the mechanical features of the structural members and, especially, to increase the safety of people during earthquakes by avoiding the brittle collapse of the strengthened elements. The digital image correlation has been a good tool for the strain field analysis; strengths and weaknesses of this method have been evaluated

Esta tese contempla o desenvolvimento de uma prensa para conformação biaxial superplástica com sistema de controle in situ e real time de pressão e de temperatura, como também um módulo de monitoramento de deformação através da técnica de correlação digital de imagem. A referida prensa é capaz de atingir durante a conformação ótimas condições superplásticas através da instrumentação e do controle dedicado dos parâmetros que caracterizam o processo de conformação fluidoestática biaxial, pressão, temperatura e taxa de deformação. São seis os principais temas abordados e desenvolvidos nessa tese: (a) técnicas, métodos e requisitos da superplasticidade da liga de titânio Ti6Al4V; (b) concepção e construção da prensa que atenda aos requisitos do projeto; (c) instrumentação do ferramental; (d) implementação do sistema de controle; (e) definição e aplicação de metodologia de ensaio superplástico para conformação fluidoestática biaxial e (f) fabricação da peça modelo. A aplicação e desenvolvimento do sistema de controle em expansão fluidoestática biaxial envolve desde a escolha das condições de conformação, determinação do ciclo de pressão, implementação de controles dedicados que atendam aos requisitos de conformação até os métodos de determinação dos coeficientes de interesse (m, n e K). Com tal instrumentação é possível determinar os coeficientes a partir de ensaios biaxiais, ao invés de simplesmente utilizar os coeficientes de ensaios de tração uniaxiais. Realizou-se um ensaio superplástico fluidoestático biaxial de chapas de liga de Ti6AL4V controlado em torno de sua condição ótima. Em suma sobre o controle, o sistema de controle térmico minimiza o intervalo de tempo de estabilização da temperatura, sem sobressinal, reduzindo o tempo de exposição do material superplástico a altas temperaturas; o sistema de controle de pressão aplica um ciclo de pressurização que é responsável por realizar a conformação de forma que resulte em uma taxa de deformação específica que represente a condição de maior índice de sensibilidade a taxa de deformação, assim se caracteriza como ponto ótimo do processo. Os principais resultados são o Ferramental instrumentado e controlado para realização de conformação superplástica em atmosfera controlada e os sistemas de controle de temperatura, pressão e deformação, validados e testados de forma integrada em ensaios de conformação superplástica / This thesis contemplates the full development of a superplastic biaxial forming Press which contains an in situ and real time pressure and temperature control systems, as well as a deformation monitoring module that applies digital image correlation technique. The Press can achieve optimum superplastic forming conditions supported by dedicated instrumentation and control of the parameters that characterize the superplastic forming process; these parameters are pressure, temperature and strain rate. Six main topics are discussed: (a) techniques, methods and Ti6Al4V alloy superplastic requirements; (b) design and construction of the press that meets the project requirements; (c) Press instrumentation; (d) control system implementation; (e) definition and implementation of a new superplastic test methodology for bulge test and (f) a part model manufacturing. The application and development of the control system in biaxial forming process involves the selection of forming conditions, pressure cycle determination, implementation of dedicated controls that meet the forming requirements, besides methods for calculating important coefficients (m, n K). With the referred instrumentation, it is possible to determine these coefficients from biaxial tests, rather than simply using the uniaxial tensile tests coefficients. A Ti6Al4V alloy fluid static superplastic biaxial test was conducted, controlled around its optimum condition. Summarizing the control system, the thermal control system minimizes the stabilization temperature time, avoiding temperature overshooting, reducing the material time exposure at superplastic temperatures. The pressure control system applies a pressurization cycle, responsible for conducting the forming process, to achieve a specific strain rate. This represents the condition of maximum strain rate sensitivity, thus characterized as optimal process point. The main results are the instrumented and controlled superplastic biaxial forming Press efficient to conduct superplastic forming in a controlled atmosphere, and temperature, pressure and deformation control systems validated and tested in an integrated Superplastic forming tests.