La compréhension des mécanismes de compaction des roches et des sédiments est importante dans différents domaine des géosciences en particulier pour caractériser la compaction dans les bassins sédimentaires ou le colmatage dans les failles actives. Les objectifs de cette thèse sont d'une part de séparer et de quantifier le rôle respectif de la compaction mécanique et chimique dans les sédiments carbonatés. D'autre part d'obtenir une meilleure compréhension des procédés aboutissant au fluage des roches sédimentaires carbonatées. La perte de porosité par compaction mécanique a été étudiée en réalisant des essais triaxiaux K0 sur des échantillons provenant de plateformes carbonatées. Onze échantillons cimentés par de la calcite faiblement magnésienne et cinq échantillons dolomitisés provenant du Marion Plateau au large de la côte nord-est Australienne (ODP (ocean drilling program) Leg194) ont été compactés de manière uniaxiale à des contraintes effectives allant jusqu'à 70 MPa. La cimentation à faible profondeur à laquelle ces échantillons ont été soumis a créé une structure cimentée stable ayant un fort degré de sur–consolidation et une faible compressibilité. La plupart des échantillons testés étaient tellement cimentés à 30–400 mètres que la perte de porosité à des profondeurs atteignant 4–5 km doit être principalement liée à des procédés chimiques et non à des procédés mécaniques. Pour étudier ces processus chimiques deux autres types d'expériences ont été réalisées. La dissolution sous contrainte est le principal mécanisme responsable du fluage des roches sédimentaires pendant leur enfouissement. Par conséquent la vitesse de déformation de la calcite par dissolution sous contrainte à l'échelle d'un contact a été étudiée. Les résultats obtenus permettent l'identification de l'importance respective de la dissolution sous contrainte résultant de l'application de la contrainte normale et celle de la dissolution au niveau des surfaces 'libres' résultant de l'accumulation de l'énergie élastique ou plastique. Deux mécanismes différents se produisent lors de la dissolution sous contrainte de cristaux de calcite à l'échelle du grain. Dans un premier cas, la diffusion du solide en solution se produit dans le fluide présent à l'interface rugueuse entre la calcite et le poinçon. Dans un deuxième cas, la diffusion se produit le long de fractures qui se propagent du contact vers la partie du cristal soumise à des contraintes plus faibles. Les vitesses de déformation sont plus élevées dans les expériences pour lesquelles la propagation de fractures se produit. De manière générale la vitesse de déformation n'apparait pas comme étant dépendante de la contrainte, mais plutôt de la propagation ou non de fractures. Finalement, les procédés mécaniques et chimiques actifs pendant la compaction ont été étudiés sur des agrégats de cristaux de calcite ou de sables bioclastique. Les expériences montrent que la compaction des sables carbonatés doit être modélisée en prenant en compte à la fois la compaction mécanique et chimique. Dans toutes les expériences la nature du fluide saturant, l'organisation initiale des grains et la taille des grains sont des paramètres important contrôlant la déformation finale ainsi que la vitesse de déformation à une contrainte donnée. La déformation des échantillons saturés avec des fluides non réactifs, e.g. air ou décane, est moins importante qu'avec des fluides réactifs, puisque dans ce cas la compaction est seulement mécanique. Pendant la phase de chargement, la compaction chimique se produit par dissolution sous contrainte, dont la vitesse est augmentée par la présence de petites fractures au niveau des contacts intergranulaires. Cette interprétation est confirmée par l'observation des échantillons en lame-minces. Les vitesses ultrasoniques se propageant dans les agrégats saturés avec des fluides réactifs ont été mesurées et il a pu être montré que la dissolution et le transport de matière affectant la géométrie des contacts au niveau des grains, ainsi que la fracturation des grains sont probablement les raison de cette diminution de vitesse. En conclusion, la perte de porosité dans les sédiments carbonatés est principalement due à la compaction chimique et très peu à la compaction mécanique. Les procédés chimique de la compaction sont d'une part la dissolution sous contrainte, et d'autre part la dissolution sous contrainte assistée par la propagation sous–critique de fissures. La prédominance de l'un ou l'autre de ces procédés est liée à la nature du fluide présent dans l'espace poreux ainsi qu'à la nature des grains.

The thesis is focussed on improving the material yield in closed-die forging and rolling. The former is restricted to the manufacturing of heavy crown wheels and front axle beams and the latter to the hot rolling of steel slabs. To enhance the yield the commercial FE-codes Form2D and Dyna3D are used. Results from forging simulations are strengthened by full scale experiments. The research is carried out in near contact with the Swedish steel and engineering industry. In closed die forging, two bulk forming problems are treated: How to improve the tool design and how to change the pre-form geometry for decreasing the amount of material exiting the flash gap? In slab rolling, two problems related to material defects are considered: How to eliminate existing surface cracks and how to prevent the formation of voids around macro-inclusions embedded in the steel matrix? Internal voids might be the reason for scrapping the whole workpiece. Considering the forging of crown wheels, a new concept is proposed. For making the central hole of the product, the traditional method was forging a thin circular plate which was then sheared off and scrapped. Using the new technique this operation is replaced by forging a conical tap in the centre, which is then discarded. Doing so, the inner scrap material decreased with about 15%. The idea has been used in production for seven years. – Regarding the forging of front axle beams, a quasi-3D method is used comprising full scale measurements of the axial material flow. Here the theoretical material yield increased 2-7%. Regarding rolling, the initial surface cracks in the simulations are V-shaped with a crack angle of 6o and of depth 5-20 mm. The inclusions are cylindrical and either three times harder or three times softer than the matrix. The behaviour of the cracks and the inclusions are studied as influenced by process parameters. Current industrial input data are used as a reference. – It is concluded that longitudinal cracks cannot be totally eliminated. During rolling their V-shape gradually changes to Y-shape and a remaining oxide flake separates the crack bottom surfaces. For minimizing the detrimental influence of the entrapped oxide, an early closure of the crack bottom is important. Throughout the remaining rolling schedule the entrapped oxide is then torn to pieces with large areas of virgin metal in between ensuring a strong bond. The following recommendations are given for the longitudinal cracks: Light drafts/pass at the beginning of the rolling schedule followed by heavy ones. – Contradictory to longitudinal cracks it is concluded that transversal cracks are possible to eliminate. When eliminated, the initial bottom of the crack coincides with the slab surface. No folds are formed. For the transversal cracks light drafts/pass are proposed together with reversal rolling, the latter for avoiding crack folding. – Voids are easiest formed around hard macro-inclusions in the centre of the slab. Large rolls and heavy drafts are recommended to avoid this. / QC 20100720

The main objective of this study is to evaluate mixed mode stress intensity factors for inclined embedded cracks in functionally graded materials. Fracture analysis of inclined cracks requires the calculation of both Mode I and Mode II stress intensity factors ( I K , II K ). In this study, k J -integral is used to calculate I K and II K . Equivalent domain integral approach is utilized to evaluate the k J - integral around the crack tip. The present study aims at developing a finite element model to study inclined crack problems in graded media under thermomechanical loading. A two dimensional finite element model is developed for inclined cracks located in a functionally graded medium. Structural and thermal problems are solved using two dimensional finite elements namely 8- noded triangles. Material properties are sampled directly at the integration points of the elements, as required by the numerical integral evaluation. The main results of the study are the stress intensity factors at the crack tip for functionally graded materials subjected to thermomechanical loading.

In this study, hydrogen induced cracking (HIC) behavior of welded steels used in petroleum lines under sour petroleum environments was investigated. The testing environment in NACE TM0284-2003 standard was used in order to simulate sour petroleum environment. In order to investigate behavior of welding parameters, used in pipe production, on HIC, welds were done with different line energies. Two different API X-65 steels were used in welding operations. The specimens taken from welded zones were tested in testing environment. The specimens were examined metallographically. Crack lengths were measured with a computer program. The results obtained were discussed in view of metallurgical and welding parameters aspects. The result obtained from this investigation led to a general conclusion that, the metallurgical parameters of steels used in pipe production were more important than welding parameters regarding their effect on HIC. It was shown that the composition and microstructural grain size of steels were in direct relation to HIC.

In this study, it is aimed to investigate the mixed-mode fracture behavior of orthotropic functionally graded material (FGM) coatings bonded to a homogeneous substrate through a homogeneous bond-coat. Analytical and computational methods are used to solve the embedded cracking problems under mechanical or thermal loading conditions. It is assumed that the material property gradation of the FGM coating is in the thickness direction and cracks are parallel to the boundaries. The principal axes of orthotropy are parallel and perpendicular to the boundaries. A single embedded crack in the orthotropic FGM coating is investigated analytically assuming that crack surfaces are subjected to either uniform normal or uniform shear stresses. Using Fourier transformations, the problem is reduced to a couple of singular integral equations that are solved numerically to obtain the mixed-mode stress intensity factors, energy release rate and crack opening displacements. To investigate the analytically untractable problems without restrictive assumptions, a computational approach is employed. The adopted computational approach is based on finite element method and displacement correlation technique. Using the computational approach, fracture parameters are obtained considering single and periodic embedded cracking conditions in the orthotropic FGM coatings under mechanical or thermal loads. The results obtained in this study show the effects of material nonhomogeneity, material orthotropy and geometric variables on the fracture behavior of the structure.

An elastic FGM layer bonded to a semi-infinite linear elastic, isotropic, homogeneous half plane is considered. The half plane contains periodic cracks perpendicular to the interface. Mechanical loading is applied through crack surface pressure, resulting in a mode I crack problem. The plane elasticity problem described above is formulated by using Fourier transforms and Fourier series. A singular integral equation is obtained for the auxiliary variable, namely derivative of the crack surface displacement. Solution is obtained, and stress intensity factors are calculated for various values of crack period, crack length, crack location, layer thickness and material gradation.

Zur numerischen Simulation piezoelektrischer Probleme mit linearem Materialgesetz wird die adaptive Finite-Element-Methode genutzt. Bei der Lösung der entstehenden Gleichungssysteme vom Sattelpunktstyp wird auf eine Variante des Bramble-Pasciak-CG zurückgegriffen. Die Einbettung von Projektionstechniken in den Löser erlaubt eine Behandlung von verschiedenen Problembesonderheiten, speziell wird hier auf die Fälle konstanten Potentials auf Teilrändern sowie Kontaktprobleme an wachsenden Rissen eingegangen. Erste numerische Ergebnisse werden an einigen Beispielen demonstriert.

Naudojamų hidrotechnikos statinių konstrukcijos veikiamos įvairių apkrovų ir neigiamo aplinkos poveikio nudėvimos, susiformuoja pažeidos. Ypač pavojingos pažeidos, mažinančios pagrindinių konstrukcijų laikančiąją galią. Netekus laikomosios galios kyla grėsmė statinio patikimumui ir ilgaamžiškumui. Remiantis atsivėrusių plyšių įtakos hidrotechnikos statinių konstrukcijoms tyrėjų darbais nustatėme, kad mokslinėje literatūroje lig šiol nepakankamai aptarta šachtinių perteklinio vandens pralaidų laikomosios galios metodika. Ji pagrįsta pagrindinių betoninių ir gelžbetoninių konstrukcijų fizikinių ir mechaninių savybių kitimo atsiradus plyšiams vertinimu Darbo tikslas – įvertinti gelžbetoninės šachtinės perteklinio vandens pralaidos (toliau– ŠPVP) sienutėje atsiradusių plyšių įtaką jos laikomąjai galiai. Uždaviniai: 1) Natūriniais tyrimais nustatyti šachtinės perteklinio vandens pralaidos gniuždomojo stiprio faktines reikšmes ir vienas iš pagrindinių pažaidų – plyšių geometrinius parametrus. 2) Preliminariai įvertinti ŠPVP techninę būklę pagal (STR.1.12.03:2006) 3) Analitiniais skaičiavimais apskaičiuoti ŠPVP laikomąją galią. 4) Atlikti galutinį ŠPVP būklės vertinimą. 2007–2008 metais tyrinėtos šachtinės perteklinio vandens pralaidos, įrengtos Kauno rajone naudojamose žemių užtvankose. Atliekant tyrimus nustatytos labiausiai pažeistos ŠPVP vietos, pažeidų tipas, plotas ir gylis bei nustatyta pagrindinė tiriamoji charakteristika – gniuždomojo betono stipris. Skaičiavimais... [toliau žr. visą tekstą] / The operating hydraulic structures, which are under the impact of various loads and aggressive environment, are deteriorated and defects are formed during their exploitation. Defects are especially dangerous because they decrease the bearing capacity of main constructions. After loosing bearing capacity the danger arises for the reliability and durability of hydraulic structures. With reference to the works of the investigators on the influence of the crack opening upon the constructions of hydraulic structures we have defined that in scientific literature the method of the bearing capacity of surplus water gatewells has not been discussed enough till now. It is substantiated by the evaluation of the alteration of physical-mechanical properties of main concrete and reinforced concrete constructions after crack opening. The aim of the work is to evaluate the influence of the crack opening in the reinforced concrete wall of the surplus water gatewell upon its bearing capacity. Tasks to be solved: 1) to determine (by natural investigations) factual significance and one of the main defects as well as crack geometrical parameters of the compressive strength of the surplus water gatewell; 2) to tentatively evaluate the technical state of the surplus water gatewell according to STR.1.12.03:2006; 3) to calculate (by analytical calculations) the bearing capacity of the surplus water gatewell; 4) to carry out the final evaluation of the condition state of he surplus water gatewell... [to full text]

The manuscript presents my research on hyperbolic Partial Differential Equations (PDE), especially on conservation laws. My works began with this thought in my mind: ''Existence and uniqueness of solutions is not the end but merely the beginning of a theory of differential equations. The really interesting questions concern the behavior of solutions.'' (P.D. Lax, The formation and decay of shock waves 1974). To study or highlight some behaviors, I started by working on geometric optics expansions (WKB) for hyperbolic PDEs. For conservation laws, existence of solutions is still a problem (for large data, $L^\infty$ data), so I early learned method of characteristics, Riemann problem, $BV$ spaces, Glimm and Godunov schemes, \ldots In this report I emphasize my last works since 2006 when I became assistant professor. I use geometric optics method to investigate a conjecture of Lions-Perthame-Tadmor on the maximal smoothing effect for scalar multidimensional conservation laws. With Christian Bourdarias and Marguerite Gisclon from the LAMA (Laboratoire de \\ Mathématiques de l'Université de Savoie), we have obtained the first mathematical results on a $2\times2$ system of conservation laws arising in gas chromatography. Of course, I tried to put high oscillations in this system. We have obtained a propagation result exhibiting a stratified structure of the velocity, and we have shown that a blow up occurs when there are too high oscillations on the hyperbolic boundary. I finish this subject with some works on kinetic équations. In particular, a kinetic formulation of the gas chromatography system, some averaging lemmas for Vlasov equation, and a recent model of a continuous rating system with large interactions are discussed. Bernard Rousselet (Laboratoire JAD Université de Nice Sophia-Antipolis) introduced me to some periodic solutions related to crak problems and the so called nonlinear normal modes (NNM). Then I became a member of the European GDR: ''Wave Propagation in Complex Media for Quantitative and non Destructive Evaluation.'' In 2008, I started a collaboration with Bruno Lombard, LMA (Laboratoire de Mécanique et d'Acoustique, Marseille). We details mathematical results and challenges we have identified for a linear elasticity model with nonlinear interfaces. It leads to consider original neutral delay differential systems.

Heat of hydration is a source of problem in mass concrete since it causes the difference between the inner and the outer temperatures increase excessively, which leads thermal cracks. The first step in fighting against this problem is to keep the initial temperature of concrete as low as possible. From this point of view, Preplaced Aggregate Concrete (in short PAC) is quite advantageous, because the friction taking place among the coarse aggregates during the mixing operation causes the initial temperature of concrete increase. However, since coarse aggregates are not subjected to the mixing operation in PAC method, comparatively lower initial temperatures can be achieved. On the other hand, making PAC by the conventional injection method is quite troublesome, since it requires special equipment and experienced workmanship. Because of this, it would be very useful to investigate alternative methods for making PAC. In this research, a new method for making PAC has been investigated. The new method is briefly based on increasing the fluidity of the grout by new generation superplasticizers to such an extent that, it fills all the voids in the preplaced coarse aggregate mass when it is poured over, without requiring any injection. In the scope of the study, twelve concrete cube specimens, each with 1 m volume, have been prepared / one of which as conventional concrete, seven of which as PAC by injection method, and four of which as PAC by the new method mentioned above. In order to examine the specimens that have been prepared by three different methods from thermal properties point of view, the difference between the central and the surface temperatures of the specimens have been followed by the thermocouples located in the specimens during preparation. Also, in order to examine the mechanical properties of the specimens, three core specimens have been taken from each specimen at certain ages, compressive strength and modulus of elasticity tests have been carried out on these core specimens. As a result of the experiments it has been observed that, the PAC specimens prepared by injection method performed better from thermal properties point of view, but worse from mechanical properties point of view than conventional concrete. On the other hand, the PAC specimens prepared by the new method have performed both as well as the other PAC specimens from thermal properties point of view, and as well as conventional concrete from mechanical properties point of view.