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Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2023; Aachen 1 Online-Ressource (2023). = Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2023, In the industrial applications, thermally-driven manufacturing approaches such as welding and additive manufacturing are widely used to assemble and create metallic parts. The Gas tungsten arc welding (GTAW) is fusion welding process used to join two or more metallic components together. On the other hand, additive manufacturing (AM) is a revolutionary manufacturing technique used to construct objects of sophisticated geometries by successively melting layers of metallic powder. In both GTAW and AM, the material being treated undergoes complex multiphysical phenomena driven by the rapid heating-cooling cycles. Therefore, understanding and investigating these fusion processes are essential to gain insight into the coupled multiphysical phenomena occurring during melting, remelting, and solidification processes. One of the main aims in the underlying work is to establish an approach to understanding the distribution mechanism of stresses and deformations. It has been reported that modeling the thermomechanical responses in welding and AM is very time consuming and computationally demanding. Therefore, simplifications are required to improve the performance and allow the modeling of larger domains with a sufficient accuracy. In this thesis, a thermomechanical modeling approach is developed to understand the fundamental physics of thermally-driven processes with the aim of predicting the temperature field and the final state of residual stresses in GTAW and AM. To this end, a macroscopic material modeling approach is developed based on a continuum mechanical framework in which the welded or AM part is represented as a homogenized continuous medium. Following the thermodynamically consistent formulation, the approach leads to volume-coupled nonlinear partial differential equations (PDEs). The formulations employ the phase-field method (PFM) in a novel way to describe the state of the material and to track its phase change from solid (hard) and unconsolidated powder to liquid (soft) and finally to a solidified state. Furthermore, PFM enables the definition of the material properties as functions of the material state, i.e., hard, soft, or powder state. The material states (phases) are separated by a diffuse interface that allows smooth transition of these states across the interface. In particular, the phase-field and phase-field history variables are utilized to propose expressions for phasefield-dependent material properties. In this treatment, a realistic description of the material parameters is achieved based on the material state, which leads to a reduction in the modeling complexity. The formulation of the phase-field thermo-elastoplastic model leads to the coupled governing PDEs, which are complemented by constitutive relations and evolution equations. Regarding the elastoplastic response in metals, two different plasticity models are described and implemented, i.e., the return mapping method and the incremental method, following the J2 theory with the isotropic strain hardening law. Furthermore, numerical investigations are performed to compare the performance of the implemented models using the open-access finite element package FEniCS Project. To validate our modeling approaches, representative examples of two and three-dimensional GTAW and selective laser melting are implemented and solved using the finite element method. In these initial-boundary-value problems, the temperature fields and residual stresses are compared with reference solutions from the literature., Published by Aachen

Linear friction welding (LFW) is a solid-state joining technique that involves the rapid reciprocating motion of two workpieces under large compressive pressure, in order to generate friction heat and plastically deformed material at the contacting surfaces of workpieces. It is an advanced joining technology used for manufacturing and repairing complex assemblies like blade integrated disks (blisks) of aeroengines. LFW can avoid fusion welding defects such as hot cracking, pores, pin holes, solute segregation and solidification structures because it does not involve the remelting of weld material. In practical terms, it can be very difficult to use experimental methods to characterise some phenomena and processes such as the evolution of stress, strain, strain rate and microstructure of welds during the LFW. These challenges have motivated high demand for computational modelling of LFW, which can be used to not only predict these phenomena and processes but also explain or interpret the relationship between heat transfer, deformation of weld, and material microstructural evolution during the LFW. This research enabled the integrated computational modelling of the LFW process for the manufacture of Inconel 718 (IN718) alloy welds by sequentially (one-way) coupling a thermomechanical sub-model with two different microstructural sub-models. The thermomechanical sub-model of the integrated computational modelling involved two-dimensional and three-dimensional (2D and 3D) computations developed for two deformable IN718 workpieces. The thermomechanical sub-model employed Hooke’s law for material elasticity and the strain-compensated Arrhenius constitutive model for material plasticity. One microstructural sub-model formulated the process of dissolution of the δ phase of IN718 by using the time-temperature equivalence method. The other microstructural sub-model formulated the dynamic recrystallization of the primary γ grains during the LFW by using the Johnson-Mehl-Avrami-Kolmogorov (JMAK) model. The integrated computational modelling was implemented within the general-purpose finite element software package Abaqus in conjunction with related custom-written subroutines. On the scale of the overall weld, the integrated computational modelling predicted the macroscopic processes of flash formation, axial shortening, and the evolution of displacement, temperature, stress, strain and strain rate of IN718 during the LFW. The integrated computational modelling also predicted the volume fraction of the δ phase, the volume fraction of recrystallized γ grains, and the average size of γ grains of the weld. The integrated computational modelling was verified by comparing its modelling results of weld temperature, axial shortening, formation of flash, volume fraction of the δ phase and average size of γ grains of the weld to related experimental results of other researchers. The integrated modelling was subsequently used for optimising the LFW process parameters and determining the process windows of the LFW of IN718. By systematically analysing the influence of 10 to 20 different sets of LFW process parameters (using different combinations of friction pressure, oscillation frequency and oscillation amplitude), the friction pressure was identified as the most influential process parameter determining the weld temperature, axial shortening, dissolution of the δ phase and the DRX of γ grains during the LFW of IN718. It is the first time that such integrated computational modelling has been developed for LFW of an alloy. With regard to the contribution to the body of knowledge, the integrated computational modelling provided insight into the relationship and interaction between heat transfer, deformation of weld, and material microstructural evolution during the LFW of IN718. With regard to the contribution to the industry, this project’s integrated computational modelling developed an effective and efficient tool that can be directly used by the manufacturing industry to design and/or optimise its process parameters for LFW of IN718.

Tese de Doutoramento em Engenharia de Segurança aos Incêndios apresentada ao Departamento de Engenharia Civil da Faculdade de Ciências e Tecnologia da Universidade de Coimbra. The manufacturing process of several materials adopted in industry, in civil construction and in our daily life has processes performed at high temperatures, such as melting and heat treatments. Thus, these production processes require products that resist to high temperatures, maintaining their physical and chemical properties in service. Refractory ceramics, due to their properties, have been used for this purpose, having crucial importance in high temperature processes. Refractory linings (composed of refractory ceramics) are used in industrial vessels to produce steel, iron, cement, non-ferrous metals, glass, metallic alloys, in melting process, in petrochemical industry, in incinerators, in mineral processing, in power plants and many other applications. The service temperature of these vessels is around 1650ºC for the steel ladles and 1450 ºC for the cement kilns, however, some processes may reach 2000ºC. In spite of the economic importance of the refractory ceramics, there are few researches on the thermomechanical behaviour of such structures at large scales. Due to the elevated prices of the products and the high costs of large scale tests, the biggest part of the experimental campaigns are focused on small specimens. Nevertheless, the experimental campaigns in large scale specimens are required to calibrate and validate the numerical models developed to simulate the industrial linings. The focus of this study is to fully characterize the thermomechanical behaviour of dry stacked refractory masonry under diversified situations. Therefore, a large experimental campaign was performed covering the behaviour of the brick, the behaviour of the joints and the behaviour of the masonry panels. The refractory bricks are injected into the moulds, pressed and then fired during their production processes. Consequently, the ceramics present an anisotropic behaviour. Therefore, the material was characterized using specimens extracted from different types of bricks and from different directions in the same bricks. It was observed that the bricks present a higher compressive strength in the direction of the pressing. The compressive strength of the material was characterized both at room and elevated temperature (600 ºC, 800ºC and 1000 ºC). The dry joints formed between the stacked bricks play an important role on the thermomechanical behaviour of the masonry panel. The presence of joints reduces the stiffness of the masonry, therefore, the compressive stresses developed in the linings during the heating of the vessels are reduced. The bricks’ shape imperfections were found to have the largest influence on the dry joints behaviour, therefore, a statistical analysis of the distribution of the bricks’ shape imperfections was carried out. Several studies were carried out on the normal behaviour of the joints: classical joint closure test; bed joint closing action in a masonry wallet measured with a DIC; effects of brick’s height imperfections on its loadbearing capacity; effects of brick’s height imperfections on the wall’s behaviour at ambient and high temperatures and a comparison between the bed and head joints behaviour. To characterize the joint’s tangential behaviour at high temperatures a novel device was developed and successfully used. Aiming to assess the behaviour of the masonry panels a large experimental campaign was developed. The main purpose was to fully characterize the masonry walls at different temperatures and different loading conditions. Several aspects that may influence the behaviour of these walls have been tested, namely the loadbearing capacity, the behaviour under cyclic loading and the restrained thermal elongation. Masonry panels were tested under uniaxial and biaxial loading conditions at ambient and elevated temperatures. The experimental results allowed to identify the effects of the stress concentrations caused by brick’s height imperfections in the mechanical behaviour of the bricks and in the loadbearing capacity of the specimens, the evolution of the wall’s stiffness with the load application, the developed crack patterns and the mechanical behaviour of the specimens at ambient and high temperatures. The effects of the viscoplastic strains developed due to creep and relaxation were also investigated. Finally, numerical models were also developed to simulate the behaviour of the walls under different testing conditions and a good agreement with the experimental results was obtained. The concrete damaged plasticity model, using a micro-modelling approach, proved to be suitable for representing the behaviour of these walls at ambient and intermediate temperatures. For temperatures above 1000 ºC, creep effects starts to raise and the Norton-Bailey creep law was successfully used to represented the material behaviour O processo de fabricação de diversos materiais adotados na indústria, na construção civil e no nosso dia a dia possui processos realizados em altas temperaturas, como fusão e tratamentos térmicos. Portanto, esses processos produtivos exigem produtos que resistam a temperaturas ainda mais altas, mantendo suas propriedades físicas e químicas em serviço. Cerâmicas refratárias, devido às suas propriedades, têm sido utilizadas para esse fim, tendo importância crucial nestes processos produtivos. Revestimentos refratários são usados em vasos industriais para produzir aço, ferro, cimento, metais não ferrosos, vidros, ligas metálicas, em processos de fusão, na indústria petroquímica, em incineradores, no processamento de minerais, em usinas de energia e diversas outras aplicações. A temperatura de serviço desses vasos é em torno de 1650 ° C para as panelas de aço e 1450 ° C para os fornos de cimento, porém, alguns processos podem chegar a 2.000 ° C. Apesar da importância económica das cerâmicas refratárias, existem poucas pesquisas sobre o comportamento termomecânico dessas estruturas em larga escala. Devido aos preços elevados dos produtos e aos altos custos dos testes em larga escala, a maior parte das campanhas experimentais é desenvolvida com pequenos provetes. No entanto, as campanhas experimentais em provetes de maior escala são necessárias para calibrar e validar os modelos numéricos desenvolvidos para simular os revestimentos industriais. O foco deste estudo é caracterizar completamente o comportamento termomecânico de alvenaria refratária de junta seca em situações diversificadas. Portanto, uma grande campanha experimental foi realizada com o objetivo de estudar o comportamento do bloco, o comportamento das juntas e o comportamento dos painéis de alvenaria. Os blocos refratários são injetados nos moldes, prensados e queimados durante seu processo de produção. Consequentemente, as cerâmicas apresentam comportamento anisotrópico. Portanto, o material foi caracterizado a partir de amostras extraídas de diferentes tipos de blocos e de diferentes direções nos mesmos blocos. Observou-se que os blocos apresentam maior resistência à compressão na direção da prensagem. A resistência à compressão do material foi caracterizada em temperatura ambiente e elevada (600 ºC, 800 ºC e 1000 ºC). As juntas secas formadas entre os blocos empilhados desempenham um papel importante no comportamento termomecânico do painel de alvenaria. A presença de juntas reduz a rigidez da alvenaria, portanto, as tensões de compressão desenvolvidas nos revestimentos refratários durante o aquecimento dos vasos são reduzidas. Constatou-se que as imperfeições de forma dos blocos têm a maior influência no comportamento das juntas secas, portanto, foi realizada uma análise estatística da distribuição das imperfeições na forma dos blocos. Vários estudos foram realizados sobre o comportamento normal das juntas: teste clássico de fechamento de juntas; influência do fechamento da junta em um painel de alvenaria medida com DIC; efeitos de imperfeições de altura do bloco na sua capacidade de carga; efeitos das imperfeições de altura do bloco no comportamento da parede em temperatura ambiente e em altas temperaturas e uma comparação entre o comportamento das juntas da cama e da cabeceira. Para caracterizar o comportamento tangencial da junta em altas temperaturas, um novo dispositivo foi desenvolvido e usado com sucesso. Com o objetivo de avaliar o comportamento dos painéis de alvenaria foi desenvolvida uma grande campanha experimental. O objetivo principal era caracterizar completamente as paredes de alvenaria em diferentes temperaturas e diferentes condições de carregamento. Vários aspetos que podem influenciar o comportamento dessas paredes foram testados, nomeadamente a capacidade de carga, o comportamento sob carregamento cíclico e o alongamento térmico restringido. Os painéis de alvenaria foram testados sob condições de carregamento uniaxial e biaxial em temperaturas ambiente e elevadas. Os resultados experimentais permitiram identificar os efeitos das concentrações de tensões causadas por imperfeições em altura do bloco no comportamento mecânico dos blocos e na capacidade de suporte dos provetes, a evolução da rigidez da parede com a aplicação de carga, os padrões de fissuras desenvolvidos e o comportamento mecânico das amostras em temperatura ambiente e em altas temperaturas. Os efeitos das deformações visco plásticas desenvolvidas devido à fluência e relaxamento também foram investigados. Finalmente, também foram desenvolvidos modelos numéricos para simular o comportamento das paredes sob diferentes condições de teste e uma boa concordância com os resultados experimentais foi obtida. O modelo de CDP, utilizando uma abordagem de micro-modelação, mostrou-se adequado para representar o comportamento dessas paredes em temperaturas ambiente e intermediárias. Para temperaturas acima de 1000 ºC, os efeitos de fluência começam a aumentar e a lei de fluência de Norton-Bailey foi usada com sucesso para representar o comportamento do material.

The manufacturing process of several materials adopted in industry, in civil construction and in our daily life has processes performed at high temperatures, such as melting and heat treatments. Thus, these production processes require products that resist to high temperatures, maintaining their physical and chemical properties in service. Refractory ceramics, due to their properties, have been used for this purpose, having crucial importance in high temperature processes. Refractory linings (composed of refractory ceramics) are used in industrial vessels to produce steel, iron, cement, non-ferrous metals, glass, metallic alloys, in melting process, in petrochemical industry, in incinerators, in mineral processing, in power plants and many other applications. The service temperature of these vessels is around 1650ºC for the steel ladles and 1450 ºC for the cement kilns, however, some processes may reach 2000ºC. In spite of the economic importance of the refractory ceramics, there are few researches on the thermomechanical behaviour of such structures at large scales. Due to the elevated prices of the products and the high costs of large scale tests, the biggest part of the experimental campaigns are focused on small specimens. Nevertheless, the experimental campaigns in large scale specimens are required to calibrate and validate the numerical models developed to simulate the industrial linings. The focus of this study is to fully characterize the thermomechanical behaviour of dry stacked refractory masonry under diversified situations. Therefore, a large experimental campaign was performed covering the behaviour of the brick, the behaviour of the joints and the behaviour of the masonry panels. The refractory bricks are injected into the moulds, pressed and then fired during their production processes. Consequently, the ceramics present an anisotropic behaviour. Therefore, the material was characterized using specimens extracted from different types of bricks and from different directions in the same bricks. It was observed that the bricks present a higher compressive strength in the direction of the pressing. The compressive strength of the material was characterized both at room and elevated temperature (600 ºC, 800ºC and 1000 ºC). The dry joints formed between the stacked bricks play an important role on the thermomechanical behaviour of the masonry panel. The presence of joints reduces the stiffness of the masonry, therefore, the compressive stresses developed in the linings during the heating of the vessels are reduced. The bricks’ shape imperfections were found to have the largest influence on the dry joints behaviour, therefore, a statistical analysis of the distribution of the bricks’ shape imperfections was carried out. Several studies were carried out on the normal behaviour of the joints: classical joint closure test; bed joint closing action in a masonry wallet measured with a DIC; effects of brick’s height imperfections on its loadbearing capacity; effects of brick’s height imperfections on the wall’s behaviour at ambient and high temperatures and a comparison between the bed and head joints behaviour. To characterize the joint’s tangential behaviour at high temperatures a novel device was developed and successfully used. Aiming to assess the behaviour of the masonry panels a large experimental campaign was developed. The main purpose was to fully characterize the masonry walls at different temperatures and different loading conditions. Several aspects that may influence the behaviour of these walls have been tested, namely the loadbearing capacity, the behaviour under cyclic loading and the restrained thermal elongation. Masonry panels were tested under uniaxial and biaxial loading conditions at ambient and elevated temperatures. The experimental results allowed to identify the effects of the stress concentrations caused by brick’s height imperfections in the mechanical behaviour of the bricks and in the loadbearing capacity of the specimens, the evolution of the wall’s stiffness with the load application, the developed crack patterns and the mechanical behaviour of the specimens at ambient and high temperatures. The effects of the viscoplastic strains developed due to creep and relaxation were also investigated. Finally, numerical models were also developed to simulate the behaviour of the walls under different testing conditions and a good agreement with the experimental results was obtained. The concrete damaged plasticity model, using a micro-modelling approach, proved to be suitable for representing the behaviour of these walls at ambient and intermediate temperatures. For temperatures above 1000 ºC, creep effects starts to raise and the Norton-Bailey creep law was successfully used to represented the material behaviour.

Vessels used in industrial high temperature processes of steel and cement production are protected by refractory linings built with dry-stacked masonry, which plays a crucial role on the overall behaviour of the vessels. This paper presents the results of an experimental and numerical research on dry-joint refractory masonry subjected to uniaxial compression. Its main purpose is to fully characterize the masonry walls at different temperatures and different loading conditions. Several aspects that may influence the behaviour of these walls have been tested, namely the loadbearing capacity, the behaviour under cyclic loading and the restrained thermal elongation. The experimental results allowed to identify the effects of the stress concentrations caused by brick’s height imperfections in the mechanical behaviour of the bricks and in the loadbearing capacity of the specimens, the evolution of the wall’s Young’s modulus with the load application, the developed crack patterns and the mechanical behaviour of the samples at ambient and high temperatures. Numerical models were also developed to simulate the behaviour of the walls under different testing conditions and a good agreement with the experimental results was obtained. The concrete damaged plasticity model, using a micro-modelling approach, proved to be suitable for representing the behaviour of these walls at ambient and high temperatures., This work was supported by the funding scheme of the European Commission, Marie Skodowska-Curie Actions Innovative Training Networks in the frame of the project ATHOR - Advanced THermomechanical multiscale mOdelling of Refractory linings 764987 Grant.

Tribological Surface Transformations (TST), known as White Etching Layer (WEL) in the wheel-rail contact, correspond to progressive and irreversible transformations on the rail surface that can lead to cracking and then failure of the rails. These areas of nanocrystalline structures are made up of several phases which show severe plastic deformation and temperature rises (which can exceed the austenitization temperature). A scenario of progressive formation of WELs has been proposed by introducing stages of microstructure evolution in the case of pearlitic steels used in railways. These stages are defined by indicators obtained by a multi-scale observations method (optical analyses and EBSD). A thermomechanical model taking into account a coupling between hydrostatic pressure, shear stress and temperature is presented. 2-D finite element simulations representative of the wheel-rail contact conditions have successfully qualitatively reproduced WEL spots. This model is also able to capture the effects of the rail dynamics on the formation kinetics of WEL, which could explain the sparsely scattered formation of WEL by island.Representative tests of wheel-rail contact conditions were carried out to validate the role of shear stress in WEL formation. On the one hand, cyclic tests of pure shear under controlled temperature ("hat-shaped" specimen) were carried out using the GLEEBLE thermomechanical simulator (Mateis-LaMCoS, INSA Lyon). On the other hand, “roller on circular rail” experiments (Triboring test rig, LaMCoS, INSA Lyon) were performed to determine the pressure-shear coupling.; Un scénario de formation progressive des WEL a été proposé par l’introduction de stades d’évolution de la microstructure dans le cas d’aciers perlitiques utilisés dans le ferroviaire. Ces stades se définissent par des indicateurs obtenus par une méthode d’observations multi-échelles (analyses optiques et EBSD). Un modèle thermomécanique prenant en compte un couplage entre pression hydrostatique, cisaillement et température est présenté. Des simulations 2-D par éléments finis représentatives des conditions du contact roue-rail ont permis de reproduire qualitativement des zones de WEL. Ce modèle est de même capable de rendre compte des effets de la dynamique ferroviaire sur la cinétique de formation de WEL qui pourrait plus particulièrement expliquer la formation éparse de WEL par ilot.Des essais représentatifs des conditions du contact-roue rail ont été effectués pour valider le rôle du cisaillement dans la formation de WEL. D’une part, des essais cycliques de cisaillement pur sous température contrôlée (éprouvette « chapeau ») ont été réalisés en utilisant le simulateur thermomécanique GLEEBLE (Mateis-LaMCoS, INSA Lyon). D’autre part, des essais de type galet sur rail circulaire (banc Triboring, LaMCoS, INSA Lyon) ont été menés pour déterminer le couplage pression-cisaillement.

Rolling contact fatigue (RCF) is an important form of damage in wheels and rails that typically has surface and subsurface cracks. Squats are one of the major RCF defects that occur in the running band of rails and can create high dynamic forces and cause rail fracture if they are not detected and treated in time. In the current research, three advanced methods are developed in order to obtain a better understanding of the formation mechanism of RCF defects and, especially, squats in rails: 1) A new thermomechanical tool for numerically modelling the wheel–rail contact, 2) A new experimental setup for physically simulating the wheel–rail interaction and 3) A new computed tomography (CT) procedure for characterizing the wheel–rail defects. The first part presents a coupled thermomechanical modelling procedure for the wheel–rail contact problem and computes the flash–temperature and stress–strain responses when thermal effects are included. The contact temperature and thermal stresses could be driving factors for squats initiation. A three–dimensional (3D) elasto–plastic finite element model is built considering the wheel–track interaction. When the wheel is running on the rail, frictional energy is generated in the contact interface. The model is able to convert this energy into heat by using a coupled thermomechanical approach. The numerical models calculate the flash–temperature and thermomechanical stresses in the wheel and rail. In the second part, a new downscale test setup is designed and built for investigating the interaction between wheel and rail, especially under impact–like loading conditions, which are supposed to be often associated with rail squats. The test rig is intended to remedy the lack of dynamic similarity between the actual railway and the existing laboratory testing capability, by considering the factors that contribute to high–frequency dynamics of the wheel–track system. This part of the thesis further presents the results of some experiments carried out using the newly–built setup to verify the ideas behind its development. The third part presents the development of a computed tomographic (CT) scanning technique to reconstruct the 3D geometry of the RCF cracks in the railhead. Squat defects are associated with complex crack networks at the subsurface. Sample rails having squats of different severities are taken from the Dutch railway network. Various specimens of different sizes are prepared and investigated with the CT scanner. A detailed procedure of the CT experiment and post–processing is described. The proposed 3D visualization method, together with the necessary geometric definitions, is then used for enabling effective measurement and characterization of the squat cracks. Based on this research, the main new insights into the formation of rail squats are as follows: i) the WEL formation via martensitic phase transformation turns out to be possible; this is confirmed through the thermomechanical wheel–rail contact modelling; ii) the impact–like loading conditions and high–frequency dynamic characteristics of the wheel–track system appear to be essential for the squat formation; this is confirmed through the vehicle–track testing using the new test rig; and iii) the occurrence of different crack orientations followed by the primary and secondary V–shaped cracks turns out to be important in the squat formation; this is confirmed through the CT scanning and metallographic observations.

The Paleozoic Saharan platform including the peri-Hoggar Basins (i.e. Murzuq, Illizi, Mouydir, Ahnet, Reggane and Tim Mersoï basins) are defined as intracraonic basins. Their histories have been dominated by slow long-wavelength vertical motions leading to overall low subsidence rate (i.e ca. 10 m/Ma to 50 m/Ma) and accumulation of an extensive cover of platformal sediments (i.e. shallow deposits environments), rhythmed by pulsatile periods of increasing and decreasing rate probably triggered by regional geodynamic events. The vertical motions of the platform produced several arches also called domes, swells, highs, ridges (e.g. the Tihemboka, Amguid El Biod, Arak-Foum Belrem and Azzel Matti Arches) and basins (syncline-shaped) with different wavelengths going from several hundred to more than a thousand kilometres. The persistence of a rather uniform pattern of vertical motions seems to control the architecture of the basins indicating a large-scale control (i.e. lithospheric). This latter controls spatially and temporally the deposition and the erosion dynamics. Several major erosion events significantly truncated the pre-existing sediments over wide areas, producing regional unconformities, especially restricted and amalgamated on arches, which separate the platformal cover into divisions. Through an original multidisciplinary integrated approach going from a geological basin analysis, coupling the substrate and the basin architecture to a numerical thermo-mechanical modelling of the lithosphere, this study has led to decipher the forcing factors of the intracratonic basins of the Saharan platform.The Arches-Basins architecture is highlighted through the identification of tectono-sedimentary structures (growth strata, truncatures…). This architecture is featured by thickness variation and facies portioning, organized by sub-vertical planar normal faults (sometimes blind faults) forming horst-graben systems associated with forced folding in the cover. Connected and nucleated to major mega-shear zones, horst-graben systems are inverted (positive inversion) or reactivated (forced folds) during successive geodynamic events (e.g. Cambro-Ordovician extension, Ordo-Silurian glacial rebound, Siluro-Devonian “Caledonian” extension/compression, late Devonian extension/compression and “Hercynian” compression).Formed under a Precambrian lithosphere of accretionary type, inherited during several paleo-orogenies (e.g. Eburnean, Pan-African), a substrates zonation of the Arches-Basins framework is described, where the Archean to Paleoproterozoic terranes are forming the structural highs and the Meso-Neoproterozoic terranes the structural lows.Based on these geological observations and the hypothesis of conserved differential densities (implying an isostatic potential) between the inherited different accreted terranes in the lithosphere (i.e. archean and proterozoic terranes), a 2D thermo-mechanical numerical model is proposed. The first and second order forcing factors, respectively recorded in the subsidence rate pattern by the low long-lived and by their cyclic deviations, are well constrained reconciling the singular Arches-Basins tectono-stratigraphic architecture. The different simulations have shown the importance of thermal anomaly, tectonics (weak strain rate) and external sediment supply on the dynamic of these intracratonic basins. Where, sediment flux controls the speed and the duration of basin infill until achievement of the isostatic equilibrium. The thermal anomaly and the tectonics compel the tectono-stratigraphic complexification such as the arches framework (intra-arches, boundary secondary arches…) and the stratigraphy architecture (wedges, diachronic unconformities) (…)., La plate-forme Saharienne paléozoïque, comprenant les bassins péri-Hoggar (Murzuq, Illizi, Mouydir, Ahnet, Reggane et Tim Mersoï) sont définies comme des bassins intracratoniques. Ils ont été dominés par des mouvements verticaux lents et à grande longueur d'onde, conduisant à une subsidence globale à faible vitesse (i.e. ca. 10 m/Ma à 50 m/Ma) et à l'accumulation d'une couverture sédimentaire étendue de type plate-forme (environnements de dépôts peu profonds), rythmée par des périodes pulsatiles d’augmentation et de diminution du taux de subsidence probablement déclenchées par des événements géodynamiques régionaux. Les mouvements verticaux de la plate-forme ont créé plusieurs arches également appelés dômes, paléo-topographies (e.g. les arches de la Tihemboka, d’Amguid El Biod, d’Arak-Foum Belrem et de l’Azzel Matti) et des bassins (en forme de synclinal) de différentes longueurs d'onde allant de plusieurs centaines à plus de milliers kilomètres. La persistance d’un ensemble assez uniforme de mouvements verticaux semble contrôler l’architecture des bassins, ce qui semble indiquer un contrôle à grande échelle (i.e. lithosphérique). Ce dernier contrôle spatialement et temporellement la dynamique sédimentaire de dépôt et d'érosion. Plusieurs périodes d'érosion majeures ont considérablement tronqué les sédiments préexistants sur de vastes zones, produisant des discordances régionales, restreintes et amalgamées sur les arches, qui séparent la couverture sédimentaire de la plateforme. À travers une approche intégrée multidisciplinaire originale allant d’une analyse géologique de bassin, associant le substrat et l’architecture de bassin à une modélisation thermomécanique numérique de la lithosphère, cette étude a permis de décrypter les facteurs de forçage des bassins intracratoniques de la plate-forme saharienne (bassins péri-Hoggar).L'architecture en Arches-Bassins est mise en évidence par l'identification de structures tectono-sédimentaires (onlap divergents, troncatures…). Cette architecture se caractérise par des variations d'épaisseur et des partitionnements de faciès, organisés par des failles normales planes sub-verticales formant des systèmes d'horst-graben souvent associés à des plis forcés dans la couverture. Connectés et nucléés aux grandes zones de méga-cisaillement, les systèmes d'horst-graben sont inversés (inversion positive) ou réactivés (plis forcés) au cours d'événements géodynamiques successifs (par exemple : extension cambro-ordovicienne, rebond glaciaire ordo-silurien, extension/ compression Siluro-Dévonien «Calédonienne», extension/compression du dévonien tardif et compression «hercynienne»).Formée sous une lithosphère précambrienne de type accrétionnaire héritées de plusieurs paléo-orogénèses (e.g. Eburnéenne, Panafricaine), une zonation des substrats sous l’architecture en Arches-Basins est observée : Les terranes Archéen à Paléoprotérozoïque se situent sous les hauts structuraux et les terranes méso-néo-protérozoïques sous les dépressions.Sur la base de ces observations géologiques et de l’hypothèse de densités différentielles conservées (impliquant un potentiel isostatique) entre les différents terranes accrétées héritées (i.e. les terranes archéennes et protérozoïques) dans la lithosphère, un modèle numérique thermo-mécanique 2D est proposé. Les facteurs de forçage du premier et du second ordre, respectivement caractérisés par de faible taux de subsidence et par leurs déviations cycliques pendant de longues durées (250 Ma), sont bien contraint par le modèle réconciliant aussi l’architecture tectono-stratigraphique singulière en Arches-Basins. Les différentes simulations ont montré l’importance des anomalies thermiques, de la tectonique (faible taux de déformation) et de l’apport externes en sédiments sur la dynamique de ces bassins intracratoniques. Le flux sédimentaire contrôle la vitesse et la durée de remplissage du bassin jusqu'à l'équilibre isostatique (…).

The Paleozoic Saharan platform including the peri-Hoggar Basins (i.e. Murzuq, Illizi, Mouydir, Ahnet, Reggane and Tim Mersoï basins) are defined as intracraonic basins. Their histories have been dominated by slow long-wavelength vertical motions leading to overall low subsidence rate (i.e ca. 10 m/Ma to 50 m/Ma) and accumulation of an extensive cover of platformal sediments (i.e. shallow deposits environments), rhythmed by pulsatile periods of increasing and decreasing rate probably triggered by regional geodynamic events. The vertical motions of the platform produced several arches also called domes, swells, highs, ridges (e.g. the Tihemboka, Amguid El Biod, Arak-Foum Belrem and Azzel Matti Arches) and basins (syncline-shaped) with different wavelengths going from several hundred to more than a thousand kilometres. The persistence of a rather uniform pattern of vertical motions seems to control the architecture of the basins indicating a large-scale control (i.e. lithospheric). This latter controls spatially and temporally the deposition and the erosion dynamics. Several major erosion events significantly truncated the pre-existing sediments over wide areas, producing regional unconformities, especially restricted and amalgamated on arches, which separate the platformal cover into divisions. Through an original multidisciplinary integrated approach going from a geological basin analysis, coupling the substrate and the basin architecture to a numerical thermo-mechanical modelling of the lithosphere, this study has led to decipher the forcing factors of the intracratonic basins of the Saharan platform.The Arches-Basins architecture is highlighted through the identification of tectono-sedimentary structures (growth strata, truncatures…). This architecture is featured by thickness variation and facies portioning, organized by sub-vertical planar normal faults (sometimes blind faults) forming horst-graben systems associated with forced folding in the cover. Connected and nucleated to major mega-shear zones, horst-graben systems are inverted (positive inversion) or reactivated (forced folds) during successive geodynamic events (e.g. Cambro-Ordovician extension, Ordo-Silurian glacial rebound, Siluro-Devonian “Caledonian” extension/compression, late Devonian extension/compression and “Hercynian” compression).Formed under a Precambrian lithosphere of accretionary type, inherited during several paleo-orogenies (e.g. Eburnean, Pan-African), a substrates zonation of the Arches-Basins framework is described, where the Archean to Paleoproterozoic terranes are forming the structural highs and the Meso-Neoproterozoic terranes the structural lows.Based on these geological observations and the hypothesis of conserved differential densities (implying an isostatic potential) between the inherited different accreted terranes in the lithosphere (i.e. archean and proterozoic terranes), a 2D thermo-mechanical numerical model is proposed. The first and second order forcing factors, respectively recorded in the subsidence rate pattern by the low long-lived and by their cyclic deviations, are well constrained reconciling the singular Arches-Basins tectono-stratigraphic architecture. The different simulations have shown the importance of thermal anomaly, tectonics (weak strain rate) and external sediment supply on the dynamic of these intracratonic basins. Where, sediment flux controls the speed and the duration of basin infill until achievement of the isostatic equilibrium. The thermal anomaly and the tectonics compel the tectono-stratigraphic complexification such as the arches framework (intra-arches, boundary secondary arches…) and the stratigraphy architecture (wedges, diachronic unconformities) (…)., La plate-forme Saharienne paléozoïque, comprenant les bassins péri-Hoggar (Murzuq, Illizi, Mouydir, Ahnet, Reggane et Tim Mersoï) sont définies comme des bassins intracratoniques. Ils ont été dominés par des mouvements verticaux lents et à grande longueur d'onde, conduisant à une subsidence globale à faible vitesse (i.e. ca. 10 m/Ma à 50 m/Ma) et à l'accumulation d'une couverture sédimentaire étendue de type plate-forme (environnements de dépôts peu profonds), rythmée par des périodes pulsatiles d’augmentation et de diminution du taux de subsidence probablement déclenchées par des événements géodynamiques régionaux. Les mouvements verticaux de la plate-forme ont créé plusieurs arches également appelés dômes, paléo-topographies (e.g. les arches de la Tihemboka, d’Amguid El Biod, d’Arak-Foum Belrem et de l’Azzel Matti) et des bassins (en forme de synclinal) de différentes longueurs d'onde allant de plusieurs centaines à plus de milliers kilomètres. La persistance d’un ensemble assez uniforme de mouvements verticaux semble contrôler l’architecture des bassins, ce qui semble indiquer un contrôle à grande échelle (i.e. lithosphérique). Ce dernier contrôle spatialement et temporellement la dynamique sédimentaire de dépôt et d'érosion. Plusieurs périodes d'érosion majeures ont considérablement tronqué les sédiments préexistants sur de vastes zones, produisant des discordances régionales, restreintes et amalgamées sur les arches, qui séparent la couverture sédimentaire de la plateforme. À travers une approche intégrée multidisciplinaire originale allant d’une analyse géologique de bassin, associant le substrat et l’architecture de bassin à une modélisation thermomécanique numérique de la lithosphère, cette étude a permis de décrypter les facteurs de forçage des bassins intracratoniques de la plate-forme saharienne (bassins péri-Hoggar).L'architecture en Arches-Bassins est mise en évidence par l'identification de structures tectono-sédimentaires (onlap divergents, troncatures…). Cette architecture se caractérise par des variations d'épaisseur et des partitionnements de faciès, organisés par des failles normales planes sub-verticales formant des systèmes d'horst-graben souvent associés à des plis forcés dans la couverture. Connectés et nucléés aux grandes zones de méga-cisaillement, les systèmes d'horst-graben sont inversés (inversion positive) ou réactivés (plis forcés) au cours d'événements géodynamiques successifs (par exemple : extension cambro-ordovicienne, rebond glaciaire ordo-silurien, extension/ compression Siluro-Dévonien «Calédonienne», extension/compression du dévonien tardif et compression «hercynienne»).Formée sous une lithosphère précambrienne de type accrétionnaire héritées de plusieurs paléo-orogénèses (e.g. Eburnéenne, Panafricaine), une zonation des substrats sous l’architecture en Arches-Basins est observée : Les terranes Archéen à Paléoprotérozoïque se situent sous les hauts structuraux et les terranes méso-néo-protérozoïques sous les dépressions.Sur la base de ces observations géologiques et de l’hypothèse de densités différentielles conservées (impliquant un potentiel isostatique) entre les différents terranes accrétées héritées (i.e. les terranes archéennes et protérozoïques) dans la lithosphère, un modèle numérique thermo-mécanique 2D est proposé. Les facteurs de forçage du premier et du second ordre, respectivement caractérisés par de faible taux de subsidence et par leurs déviations cycliques pendant de longues durées (250 Ma), sont bien contraint par le modèle réconciliant aussi l’architecture tectono-stratigraphique singulière en Arches-Basins. Les différentes simulations ont montré l’importance des anomalies thermiques, de la tectonique (faible taux de déformation) et de l’apport externes en sédiments sur la dynamique de ces bassins intracratoniques. Le flux sédimentaire contrôle la vitesse et la durée de remplissage du bassin jusqu'à l'équilibre isostatique (…).

Titanyum malzeme hafif, dayanıklı, korozyon direnci yüksek ve biyo-uyumlu olması nedeniyle havacılık, medikal, savunma vb. sektörlerde yaygın olarak kullanılmaktadır. Lazer ile işlenmesi sırasında, mekanik yöntemlere göre temassız olması avantaj sağlarken, işlem gören parçaları ısıl girdilere maruz bırakır. Bu ısıl girdiler titanyum vb. ısıl iletimi zayıf malzemelerin imalat süreçlerinde kalıcı deformasyonlara sebep olabilmektedir. Bu tezde CP Titanyum Grade 2 malzemenin lazer ile işlenmesi sırasında oluşabilecek deformasyonlar deneysel olarak incelenmiş ve termomekanik sayısal analizi gerçekleştirilmiştir. Titanyum malzemenin lazer ile işlenmesinde çarpılma, lazer ile şekil verilmesinde şekillendirmeye neden olan bu deformasyonlar ilişkilendirilerek deneyler yapılmış ve FEM analizi gerçekleştirilmiş, deneysel sonuçlarla karşılaştırılmıştır. Oluşturulan model ve yapılan deneyler ile lazer işlemede deformasyonların araştırılmasına ve ön görülebilmesine yönelik çalışmalara katkı sunmak amaçlanmış ve elde edilen sonuçların uyumu hesaplanmıştır., Titanium material is lightweight, durable, high in corrosion resistance and biocompatible, thus it is widely used in the aviation, medical, defense etc. sectors. In these applications, laser processing is advantageous as it's non-contacting compared to mechanical methods, at the same time it causes thermal input in the processed parts. The thermal inputs may cause permanent deformations in manufacturing processes of materials with poor thermal conduction as titanium and so on. In this thesis, the deformations that occur during laser processing of CP Titanium Grade 2 material are investigated experimentally and numerically with thermo-mechanical analysis. Experiments were carried out by correlating these deformations which caused distortion in laser processing and forming in laser forming of titanium material and FEM analysis were performed and compared with experimental results. It was aimed to contribute to the studies of deformations and their prediction in laser processing and the corelation of the obtained results was calculated with the model and experiments.

A commonly held view in the turbomachinery community is that finite element methods are not well-suited for very large-scale thermomechanical simulations. We seek to dispel this notion by presenting performance data for a collection of realistic, large-scale thermomechanical simulations. We describe the necessary technology to compute problems with $O(10^7)$ to $O(10^9)$ degrees-of-freedom, and emphasise what is required to achieve near linear computational complexity with good parallel scaling. Performance data is presented for turbomachinery components with up to 3.3 billion degrees-of-freedom. The software libraries used to perform the simulations are freely available under open source licenses. The performance demonstrated in this work opens up the possibility of system-level thermomechanical modelling, and lays the foundation for further research into high-performance formulations for even larger problems and for other physical processes, such as contact, that are important in turbomachinery analysis., The support of Mitsubishi Heavy Industries is gratefully acknowledged. CNR is supported by EPSRC Grant EP/N018877/1.