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La finalité de ce travail est de développer un modèle thermomécanique 2D pour analyser en détails les effets de la dissipation visqueuse et de l'hydratation du coin de manteau sur l’état thermique et la dynamique dans les zones de subduction. L’état thermique et la dynamique résultant des modèles prenant en compte la dissipation visqueuse et/ou l'hydratation du manteau sont comparés aux modèles ne les prenant pas en compte (Marotta and Spalla, 2007), afin d’analyser leurs effets sur la viscosité et sur la vitesse de déformation. Notre nouveau modèle démontre l’activation de la convection du manteau à courte longueur d’onde en fonction de l'hydratation et de la serpentinisation du coin de manteau. Il en résulte un recyclage des croûtes continentales et océaniques subduites. En outre, les effets de la vitesse de subduction sur l’ampleur de la région hydratée ont été analysés. Les évolutions des conditions P-T des marqueurs de crustaux et l'état thermique enregistré dans les différentes portions du complexe de subduction sont utilisés pour avoir une meilleure compréhension de la distribution et de l'évolution, dans le temps et dans l'espace, de conditions métamorphiques caractérisées par des rapports P/T contrastés. Une fois ces modèles établis, les évolutions P-T prédites par les modèles sont comparées aux données métamorphiques naturelles observées dans la chaine varisque, plus particulièrement dans les Alpes et le Massif Central français. Afin de prendre en compte l’exhumation de croûte subduite jusqu’aux niveaux les plus superficiels, le modèle prend en compte le rôle de l'atmosphère et donc des mécanisme d’érosion et de sédimentation. / The aim of this work was to develop a 2D thermo-mechanical model to analyse in detail the effects of the shear heating and mantle wedge hydration on the thermal state and dynamics of an ocean/continent subduction system. The thermal setting and dynamics that result from models with shear heating and/or mantle hydration are directly compared to a model that does not account for either (Marotta and Spalla, 2007) to analyse their effects on both the strain rate and the viscosity. The new model show the activation of short-wavelength mantle convection related to the hydration and the serpentinisation of the mantle wedge, with the consequent recycling of oceanic and continental subducted material. The effects of the subduction velocities on the size of the hydrated area are also analysed, andpredictions of the pressure-temperature evolutions of crustal markers and the thermal field, which affect different portions of subduction systems, are used to infer the thermal regimes that affect the models. Similarly, the model can help to understand extensively both the distribution and the evolution, in time and space, of metamorphic conditions characterised by contrasting P/T ratios in subduction systems. In a second phase, P-T predicted by the model has been compared with natural P max -T estimates related to the Variscan metamorphism, from both the present domains of the Alps and from the French Central Massif. However, the model did not allow to compare simulated P-T paths with successive metamorphic stages recorded and preserved by the rocks during their metamorphic evolution, because of the lack of exhumation of subducted material up to the shallowest portion of the crust.

The management of radioactive wastes is a significant environmental issue facing the international nuclear community today. The current international consensus is for disposal of higher activity waste from a variety of sources in deep geological disposal facilities (GDFs). Hydraulic seals, often planned to consist of compacted bentonite-sand blocks, are an important part of the closure phase of a GDF. As such, an understanding of the hydro-mechanical (HM) behaviour of these seals, and the ability to model and predict their behaviour is fundamental to support many planned safety cases and licence applications. Bentonite is well suited for use as a hydraulic seal due to its high swelling capacity that enables it to swell into voids while maintaining a low permeability sealed barrier to advective flow, and to provide structural support by generating a swelling pressure on the excavation walls. The hydro-mechanical process of bentonite hydration is a highly non-linear problem. As such, coupled process models that are able to account for the strong inter-dependence of the hydraulic and mechanical processes are employed to simulate the behaviour of bentonite under repository conditions. This thesis reports the development of an HM coupled model in the open source finite element code OpenGeoSys (OGS), and its application to the simulation of a range of hydraulic seal test conditions. The developed model couples Richards’ equation for unsaturated flow to a new strain dependent non-linear elastic mechanical model that incorporates a Lagrangian moving finite element mesh to inform the material non-linearity. Stress and volumetric dependent water retention behaviour are incorporated through the implementation of the Dueck suction concept extended to take into account non-recoverable strains during consolidation. A number of permeability functions are implemented and tested against experimental data. The mechanical model is extended to account for wetting-induced collapse behaviour by the definition of a failure curve derived from experimental results. Similar in definition to the Loading-Collapse curve in elasto-plastic models, this failure curve triggers the application of a source term to account for wetting-induced collapse. Coupling between the hydraulic and mechanical processes is achieved through the stress dependency of the water retention behaviour, the inclusion of a new coupling factor for the hydraulic contribution to the mechanical process, and the dependency of numerical convergence criteria on net mean stress. An explicit iterative calculation approach is employed. As a result, the hydraulic and mechanical moving meshes are decoupled to allow volumetric dependent parameters to be updated within process iterations. The model is calibrated and compared to experimental data from the SEALEX experiments conducted by the Institut de Radioprotection et de S ˆ uret´e Nucl´eaire (IRSN) at the Tournemire URL, France. The experimental programme comprises standardised laboratory tests, a 1/10th scale mock-up of a hydraulic seal with a uniform technological void, and a full scale in situ performance test with a non-uniform technological void due to its horizontal geometry. Using a model with 5 hydraulic parameters, 8 mechanical parameters with an experimentally defined failure curve, and one coupling parameter, the major trends of behaviour in all the SEALEX experiments can be recreated, including axial stress build up, water uptake, and final deformation. However, the elastic method employed leads to an over prediction of the rebound on loss of axial confinement in the 1/10th scale mock-up test. Simulations suggest that the non-symmetric technological void in the full scale performance test could have lasting effects on the development of heterogeneity in the hydraulic seal. The development of heterogeneity does not adversely affect the permeability with respect to the design criteria, but may have significant consequences for the development of a heterogeneous swelling pressure.

<p>Failure of bi-material interfaces is studied with the aim to quantify the influence of the induced stress concentrations on the strength of the interfaces. A simple point-stress criterion, used in conjunction with finite element calculations, is evaluated to provide strength predictions for bi-material bonded joints and inserts in polymer foam. The influence of local stress concentrations on the initiation of fracture at open and closed wedge bi-material interfaces is investigated. The joint combinations are analysed numerically and the strength predictions obtained from the point-stress criterion are verified in experiments. </p><p>The predictions are made using a simple point-stress criterion in combination with highly accurate finite element calculations. The point-stress criterion was known from earlier work to give accurate predictions of failure at cracks and notches but had to be slightly modified to become applicable for the studied configurations. The criterion showed to be generally applicable to the bi-material interfaces studied herein. Sensible predictions for the tendentious strength behaviour could be made with reasonable accuracy, including the prediction of crossover from local, joint-induced failure to global failure. </p><p>To study the micromechanical properties of a cellular solid with arbitrary topology, various models of a closed-cell foam are created on the basis of random Voronoi tessellations. The foam models are analysed using the finite element method and the effective elastic properties of the model cellular solids are determined. The calculated moduli are compared to the properties of a real reference foam and the numerical results show to be in very good agreement. </p><p>The mechanical properties of closed-cell, low-density cellular solids are governed by the stiffnesses of the cell edges and the cell faces. Models of idealised foam models with planar cell faces, cannot account for the curved faces found on some metal and polymer foams. Finite element models of closed-cell foams were created to analyse the influence of cell face curvature on the stiffness of the foam. By determining the elastic modulus for foams with non-planar cell faces, the effect of cell face curvature could be analysed as a function of the relative density and the distribution of solid material between cell edges and faces. </p><p>Foam models were generated from disturbed point distribution lattices and compared to models obtained from random distributions. The aim was to analyse if and how the geometry of the cells and their spatial arrangement influences the mechanical properties of a foam. The results suggest that the spatial arrangement and the geometry of the cells have significant influence on the properties of a foam. The elastic properties calculated for models from disturbed foam structures underestimated the elastic moduli of the foam, whereas models from random structures provided results which were in very good agreement with a reference foam.</p>

Failure of bi-material interfaces is studied with the aim to quantify the influence of the induced stress concentrations on the strength of the interfaces. A simple point-stress criterion, used in conjunction with finite element calculations, is evaluated to provide strength predictions for bi-material bonded joints and inserts in polymer foam. The influence of local stress concentrations on the initiation of fracture at open and closed wedge bi-material interfaces is investigated. The joint combinations are analysed numerically and the strength predictions obtained from the point-stress criterion are verified in experiments. The predictions are made using a simple point-stress criterion in combination with highly accurate finite element calculations. The point-stress criterion was known from earlier work to give accurate predictions of failure at cracks and notches but had to be slightly modified to become applicable for the studied configurations. The criterion showed to be generally applicable to the bi-material interfaces studied herein. Sensible predictions for the tendentious strength behaviour could be made with reasonable accuracy, including the prediction of crossover from local, joint-induced failure to global failure. To study the micromechanical properties of a cellular solid with arbitrary topology, various models of a closed-cell foam are created on the basis of random Voronoi tessellations. The foam models are analysed using the finite element method and the effective elastic properties of the model cellular solids are determined. The calculated moduli are compared to the properties of a real reference foam and the numerical results show to be in very good agreement. The mechanical properties of closed-cell, low-density cellular solids are governed by the stiffnesses of the cell edges and the cell faces. Models of idealised foam models with planar cell faces, cannot account for the curved faces found on some metal and polymer foams. Finite element models of closed-cell foams were created to analyse the influence of cell face curvature on the stiffness of the foam. By determining the elastic modulus for foams with non-planar cell faces, the effect of cell face curvature could be analysed as a function of the relative density and the distribution of solid material between cell edges and faces. Foam models were generated from disturbed point distribution lattices and compared to models obtained from random distributions. The aim was to analyse if and how the geometry of the cells and their spatial arrangement influences the mechanical properties of a foam. The results suggest that the spatial arrangement and the geometry of the cells have significant influence on the properties of a foam. The elastic properties calculated for models from disturbed foam structures underestimated the elastic moduli of the foam, whereas models from random structures provided results which were in very good agreement with a reference foam. / QC 20101011

Dans cette thèse, les changements de propriétés mécaniques des argiles riches en matière organique sont étudiés afin d'en déduire si leur enfouissement peut déclencher l'écaillage tectonique. Ce travail multidisciplinaire s'organise selon trois axes : une étude de terrain, une étude en laboratoire et une étude de modélisation numérique. L'étude de coupes géologiques équilibrées à travers les chaînes plissées Méditérranéennes montre l'importance de l'interprétation mécanique pour les thématiques de restaurations et pour valider les scénarios d'évolution structurale. Sur les Posidonia Schist Albanais, une caractérisation en laboratoire et à haute résolution de la formation roche-mère permet d'observer l'évolution verticale des paramètres minéralogiques, géochimiques et mécaniques qui contrôle le comportement rhéologique des roches-mères. En utilisant les modèles de bassin TEMISFlow, j'analyse les conditions pour créer des surpressions au sein d'un niveau de décollement roche-mère localisé sous un chevauchement. Au travers de modélisations géo-mécaniques FLAMAR, j'étudie les conditions mécaniques nécessaires pour développer des géométries de plis idéales au sein d'une stratigraphie mécanique. Une hiérarchisation des paramètres qui permettent d'activer un décollement au sein d'une roche-mère intégrée dans une stratigraphie mécanique est proposée. Au travers d'une analyse couplant ces deux aspects géo-mécanique et hydro-mécanique, ce travail est une contribution à la recherche d'une loi de comportement rhéologique permettant de prendre en compte l'adoucissement mécanique thermo-dépendant des argiles et des roches-mères dans les modélisations géo-mécaniques. / In this thesis, changes in the mechanical properties of organic-rich shales, when they mature, are studied in order to deduce if burial may mechanically activate tectonic imbrication and control the folding style. This multidisciplinary work is organized according to three axes: a field study, a laboratory study and a thermo-mechanical modeling study. In the first part, the study balanced geological cross-sections through the Mediterranean fold-and-thrust belts shows the importance of the mechanical interpretation for structural restorations and to validate structural evolution scenarios. The Albanian Posidonia Schist laboratory characterization allows discussing the vertical evolution of mineralogical, geochemical and mechanical parameters in a source-rock formation that control the rheological behavior of source rocks. Both geological cases serve as input data for modeling designed to simulate the evolution of a source rock during its burial. Two aspects are examined: Using TEMISFlow Arctem basin models, I analyze the conditions necessary to create overpressure in a source-rock detachment located in the footwall of a thrust. Through geo-mechanical modeling, I study the mechanical conditions necessary to develop ideal fold geometries within a mechanical stratigraphy. A hierarchy of parameters to activate a detachment within source rocks embedded in a mechanical stratigraphy is thus proposed. Through an analysis of the coupling between these two aspects, geo-mechanical and hydro-mechanical, this thesis is a contribution to the search of a rheological law that takes into account the thermo-dependent softening of shale and source rocks in geo-mechanical modeling.

Deployable structures made from ultra-thin composite materials can be folded elastically and are able to self-deploy by releasing the stored strain energy. Their lightness, low cost due to smaller number of components, and friction insensitive behaviour are key attractions for space applications. This dissertation presents a design methodology for lightweight composite booms with multiple tape-spring hinges. The whole process of folding and deployment of the tape-spring hinges under both quasi-static and dynamic loading has been captured in detail through finite element simulations, starting from a micro-mechanical model of the laminate based on the measured geometry and elastic properties of the woven tows. A stress-resultant based six-dimensional failure criterion has been developed for checking if the structure would be damaged. A detailed study of the quasi-static folding and deployment of a tape-spring hinge made from a two-ply plain-weave laminate of carbon-fibre reinforced plastic has been carried out. A particular version of this hinge was constructed and its moment-rotation profile during quasi-static deployment was measured. Folding and deployment simulations of the tape-spring hinge were carried out with the commercial finite element package Abaqus/Explicit, starting from the as-built, unstrained structure. The folding simulation includes the effects of pinching the hinge in the middle to reduce the peak moment required to fold it. The deployment simulation fully captures both the steady-state moment part of the deployment and the final snap back to the deployed configuration. An alternative simulation without pinching the hinge provides an estimate of the maximum moment that could be carried by the hinge during operation. This moment is about double the snap-back moment for the particular hinge design that was considered. The dynamic deployment of a tape-spring hinge boom has been studied both experimentally and by means of detailed finite-element simulations. It has been shown that the deployment of the boom can be divided into three phases: deployment; latching, which may involve buckling of the tape springs and large rotations of the boom; and vibration of the boom in the latched configuration. The second phase is the most critical as the boom can fold backwards and hence interfere with other spacecraft components. A geometric optimisation study was carried out by parameterising the slot geometry in terms of slot length, width and end circle diameter. The stress-resultant based failure criterion was then used to analyse the safety of the structure. The optimisation study was focused on finding a hinge design that can be folded 180 degrees with the shortest possible slot length. Simulations have shown that the strains can be significantly reduced by allowing the end cross-sections to deform freely. Based on the simulations a failure-critical design and a failure-safe design were selected and experimentally verified. The failure-safe optimised design is six times stiffer in torsion, twice stiffer axially and stores two and a half times more strain energy than the previously considered design. Finally, an example of designing a 1 m long self-deployable boom that could be folded around a spacecraft has been presented. The safety of this two-hinge boom has been evaluated during both stowage and dynamic deployment. A safe design that latches without any overshoot was selected and validated by a dynamic deployment experiment.

Continuous casting represents 96% of all steel products made worldwide. To cast new alloys, optimal process parameters must be determined that reduce quality issues. Traditionally, this is a time-consuming and expensive process due to the need to run multiple casting trials. Alternatively, numerical models can be used to help guide development of optimal process parameters. In this thesis, a 3D thermal-solute-mechanical finite element model has been created using the THERCAST software to simulate the casting process of a new advanced high strength steel grade at Stelco’s Lake Erie Works facility. The model represents the caster from mould to exit, and takes into account heat transfer from the mould, sprays, rolls, and ambient air. The model has been extensively validated using plant measurements from steel shim trials and pyrometer data. The model is used to investigate the evolution of temperature and shell thickness along the cast length, and the effect of spray cooling and casting speed on the surface temperature at unbending to predict transverse cracking during secondary cooling. It was found that the susceptibility to cracking increased with lower casting speed and increased water spray cooling. Increasing the casting speed had a negligible effect, and it was found to decrease with decreasing water spray cooling. This decreased water spray cooling is also accompanied by an increase in metallurgical length, so further work is required to determine appropriate safety factors to ensure the steel is completely solidified. However, preliminary results of solute and mechanical models are also presented. Further work is required to improve the predictions made by these simulations. / Thesis / Master of Applied Science (MASc)

Magnetic ordering of dopants in diamond holds the prospect of exploiting diamond’s unique properties in the emerging field of spintronics. Several transition metal defects have been reported to order ferromagnetically in various semiconductors, however, low Curie temperatures and lack of other fundamental material properties have hindered practical implementation in room temperature spintronic applications. In this Thesis, we consider the energetic stability of 3d transition metal doped-diamond and its magnetic ordering properties at various lattice sites and charge states using ab initio Density Functional Theory methods. We find the majority of 3d transition metal impurities in diamond at any charge state to be energetically most stable at the divacancy site compared to substitutional or interstitial lattice sites, with the interstitial site being highly unstable (by ~8 - 10 eV compared to the divacancy site). At each lattice site and charge state, we find the formation energies of transition metals in the middle of the 3d series (Cr, Mn, Fe, Co, Ni) to be considerably lower compared to those early or late in the series. The energetic stability of transition metal impurities across the 3d series is shown to be strongly dependent on the position of the Fermi level in the diamond band gap, with the formation energies at any lattice site being lower in p-type or ntype diamond compared to intrinsic diamond. Further, we show that incorporation of isolated transition metal impurities into diamond introduces spin polarised impurity bands into the diamond band gap, while maintaining its semiconducting nature, with band gaps in both the spin-up and spin-down channels. These impurity bands are shown to originate mainly from s, p-d hybridization between carbon sp 3 orbitals with the 3d orbitals of the transition metal. In addition, the 4p orbitals contribute significantly to hybridization for transition metal atoms at the substitutional site, but not at the divacancy site. In both cases, the spin polarisation and magnetic stabilization energies are critically dependent on the lattice site and charge state of the transition metal impurity. By allowing magnetic interactions between transition metal atoms, we find that ferromagnetic ordering is likely to be achieved in divacancy Cr+2, Mn+2, Mn+1 and Co0 as well as in substitutional Fe+2 and Fe+1, indicating that transition metal-doped diamond is likely to form a diluted magnetic semiconductor which may successfully be considered for room temperature spintronic applications. In addition, these charge states correspond to p-type diamond, except for divacancy Co0, suggesting that co-doping with shallow acceptors such as B ( will result in an increase of charge concentration, which is likely to enhance mediation of ferromagnetic spin coupling. The highest magnetic stabilization energy occurs in substitutional Fe+1 (33.3 meV), which, also exhibits half metallic ferromagnetic ordering at the Fermi level, with an induced magnetic moment of 1.0 μB per ion, thus suggesting that 100 % spin polarisation may be achieved in Fe-doped diamond. / Physics / D. Litt. et Phil. (Physics)

Afin de répondre aux besoins du marché de l’acier, le procédé de cokéfaction du charbon doit s’adapter. Cependant, changer les paramètres de cokéfaction du charbon, tels que la température du four, le temps de cuisson ou la composition de la pâte à coke enfournée, peut générer un endommagement prématuré de la maçonnerie des fours. En effet, la transformation du charbon en coke s’accompagne d’une poussée sur les parois du four fortement dépendantes d’un grand nombre de paramètres. Afin d’anticiper ce problème, un projet européen nommé « Swelling PRessure In a coke oven, Transmission on oven walls and COnsequences on wall » a été mis en place. Cette thèse s’inscrit dans ce programme et vise à déterminer la poussée maximale pouvant être admise par un piédroit de cokerie lors de la pyrolyse du charbon. Pour modéliser ces structures composées de plusieurs centaines de milliers de briques, le point de vue macroscopique est le plus approprié. La maçonnerie est remplacée par un matériau homogène équivalent dont le comportement varie en fonction de l’état d’endommagement de la maçonnerie, ramené localement à un état d’ouverture des joints de mortier. Afin de détecter ces ouvertures, un critère de type Mohr-Coulomb en contraintes est utilisé. Il repose sur la comparaison des limites à rupture d’un sandwich brique-Mortier déterminé expérimentalement à haute température avec les contraintes mésoscopiques issues de la simulation. Un protocole expérimental novateur a été développé pour caractériser la tenue en traction du sandwich brique / mortier / brique jusqu’à 1000°C. Les limites à rupture issues de cet essai de traction directe ont été comparées à celles obtenues par des essais de fendage réalisés à l’université de Leoben. Les résultats sont concordants et confirment l’importance de l’état de surface avant maçonnage. Selon l’état d’endommagement considéré, les contraintes mésoscopiques sont obtenues grâce à un tenseur de localisation ou grâce à une sous-Structuration. Cette étape de sous-Structuration consiste à simuler localement une cellule à l’échelle mésoscopique en lui appliquant le champ de déplacement macroscopique obtenu grâce à la simulation. L’outil numérique a été validé par confrontation avec un cas test de référence. Pour finir, l’outil numérique développé a été utilisé pour caractériser l’influence de différents paramètres tels que la prise en compte de la thermique, la mise en compression de la structure…. Enfin, la simulation de cuissons sur des piédroits complets (sains ou initialement endommagés) a été réalisée. L’importance de l’endommagement initial est clairement soulignée par les résultats. Enfin, un nouveau modèle, appelé « deux carneaux avec poutres», est proposé pour réduire le coût de calcul. Plus complet que le modèle « deux carneaux » utilisé au CPM, il donne accès à de très bons résultats pour un coût nettement moindre que celui du piédroit complet avec homogénéisation et sous-Structuration. / To face coke and steel market requirements, the coking process has to be more flexible. Changing process parameters such as coking temperature, blend composition and cooking time can damaged coke oven battery heating wall. Indeed, the coking process generates a swelling pressure on wall which depends on a lot of parameters. To study this point, a European project named « Swelling PRessure In a coke oven, Transmission on oven walls and COnsequences on wall » has been set up. This work is a part of it and aims to determine the admissible pushing pressure for the coke oven heating walls to prevent crack formation. To model large masonries composed of numerous bricks, a mesoscopic point of view is more appropriate. Bricks and mortar are replaced by a Homogeneous Equivalent Material (HEM) whose behaviour depends on the joint state. In order to represent joint opening mechanism, a Mohr-Coulomb criterion in stress is used. This criterion compares the level of stress to the ultimate tensile or shear stress at mesoscopic scale. Ultimate stresses are obtained thanks to an experimental campaign using a new protocol developed at PRISME Laboratory. The brick-Mortar behaviour is experimentally characterised at high temperature (20°C to 1000°C). To validate the tensile test developed, a second experimental campaign using “wedge splitting tests” has been done at Leoben University. Results are similar and confirm the importance of the brick surface state. Depending on the initial damage of the structures, mesoscopic stresses are obtained by localization tensor or by sub-Modelling. The sub-Modelling step aims to simulate a local part of the masonry at the mesoscopic scale. This step aims to simulate with a mesoscopic point of view a local part of the global model. This numerical tool has been validated thanks to a literature test. Finally, the numerical tool has been used to characterise the influence of some parameters (thermal, force due to the cross tie rod,..). Next, the simulation of the whole coke oven heating wall has been performed (undamaged or initially damaged masonry). These FE simulations show the influence of initial damage on the final masonry damage. Finally, a two flues model with beams is proposed to take into account compression due to cross tie rod and to limit computational cost. It permits to obtain better results than the existing two flues model used at CPM with a lower cost compared to the whole coke oven heating wall model.