<div>Additive manufacturing (AM) or 3D printing has gained significant advancement in recent years. However the potential of 3D printed metals still has not been fully explored. A main reason is the lack of accurate knowledge of the load capacity of 3D printed metals, such as fatigue behavior under cyclic load conditions, which is still poorly understood as compared with the conventional wrought counterpart.</div><div><br></div><div>The goal of the thesis is to advance the knowledge of fatigue behavior of 15-5 PH stainless steel manufactured through laser powder bed fusion process. To achieve the goal, a combined numerical and experimental study is carried out. First, using a rotary fatigue testing experiment, the fatigue life of the 15-5 PH stainless steel is measured. The strain life curve shows that the numbers of the reversals to failure increase from 13,403 to 46,760 as the applied strain magnitudes decrease from 0.214\% from 0.132\%, respectively. The micro-structure analysis shows that predominantly brittle fracture is presented on the fractured surface. Second, a finite element model based on cyclic plasticity including the damage model is developed to predict the fatigue life. The model is calibrated with two cases: one is the fatigue life of 3D printed 17-4 stainless steel under constant amplitude strain load using the direct cyclic method, and the other one is the cyclic behavior of Alloy 617 under multi-amplitude strain loads using the static analysis method. Both validation models show a good correlation with the literature experimental data. Finally, after the validation, the finite element model is applied to the 15-5 PH stainless steel. Using the direct cyclic method, the model predicts the fatigue life of 15-5 PH stainless steel under constant amplitude strain. The extension of the prediction curve matches well with the previously measured experimental results, following the combined Coffin-Manson Basquin Law. Under multi-amplitude strain, the kinematic hardening evolution parameter is incorporated into the model. The model is capable to capture the stresses at varied strain amplitudes. Higher stresses are predicted when strain amplitudes are increased. The model presented in the work can be used to design reliable 3D printed metals under cyclic loading conditions.</div>

Better understanding and control of crack growth direction during hydraulic fracturing are essential for enhancing productivity of geothermal and petroleum reservoirs. Structural analysis of fracture propagation and impact on fluid flow is a challenging issue because of the complexity of rock properties and physical aspects of rock failure and fracture growth. Realistic interpretation of the complex interactions between rock deformation, fluid flow, heat transfer, and fracture propagation induced by fluid injection is important for fracture network design. In this work, numerical models are developed to simulate rock failure and hydraulic fracture propagation. The influences of rock deformation, fluid flow, and heat transfer on fracturing processes are studied using a coupled thermo-hydro-mechanical (THM) analysis. The models are used to simulate microscopic and macroscopic fracture behaviors of laboratory-scale uniaxial and triaxial experiments on rock using an elastic/brittle damage model considering a stochastic heterogeneity distribution. The constitutive modeling by the energy release rate-based damage evolution allows characterizing brittle rock failure and strength degradation. This approach is then used to simulate the sequential process of heterogeneous rock failures from the initiation of microcracks to the growth of macrocracks. The hydraulic fracturing path, especially for fractures emanating from inclined wellbores and closed natural fractures, often involves mixed mode fracture propagation. Especially, when the fracture is inclined in a 3D stress field, the propagation cannot be modeled using 2D fracture models. Hence, 2D/3D mixed-modes fracture growth from an initially embedded circular crack is studied using the damage mechanics approach implemented in a finite element method. As a practical problem, hydraulic fracturing stimulation often involves fluid pressure change caused by injected fracturing fluid, fluid leakoff, and fracture propagation with brittle rock behavior and stress heterogeneities. In this dissertation, hydraulic fracture propagation is simulated using a coupled fluid flow/diffusion and rock deformation analysis. Later THM analysis is also carried out. The hydraulic forces in extended fractures are solved using a lubrication equation. Using a new moving-boundary element partition methodology (EPM), fracture propagation through heterogeneous media is predicted simply and efficiently. The method allows coupling fluid flow and rock deformation, and fracture propagation using the lubrication equation to solve for the fluid pressure through newly propagating crack paths. Using the proposed model, the 2D/3D hydraulic fracturing simulations are performed to investigate the role of material and rock heterogeneity. Furthermore, in geothermal and petroleum reservoir design, engineers can take advantage of thermal fracturing that occurs when heat transfers between injected flow and the rock matrix to create reservoir permeability. These thermal stresses are calculated using coupled THM analysis and their influence on crack propagation during reservoir stimulation are investigated using damage mechanics and thermal loading algorithms for newly fractured surfaces.

O presente trabalho de pesquisa está relacionado à análise do progresso do fraturamento na zona tracionada de fundações rochosas de barragens de concreto e suas conseqüências nas avaliações de estabilidade global. Tomou-se como exemplo a barragem de Porto Primavera de propriedade da CESP (Companhia Energética de São Paulo), situada entre os estados de São Paulo e Mato Grosso do Sul, Brasil. Com a ajuda de modelos elaborados com elementos finitos e sob a ótica da mecânica da fratura não linear e da mecânica do dano, analisa-se o desenvolvimento da fratura mediante uma avaliação iterativa tensão-deformação e carga hidráulica. Devido ao carregamento progressivo de água, realiza-se a análise iterativa baseada no avanço da fratura e na aplicação de pressão hidráulica, até quando a fratura deixa de progredir. A simulação numérica proposta tem o objetivo de estudar o desenvolvimento de fraturas, determinar as deformações ocorridas sob a ação das forças de empuxo d'água, de subpressão, do peso próprio e das pressões de água na fratura do maciço rochoso fraturado. As deformações calculadas são comparadas com registros da instrumentação na fundação efetuados durante o enchimento do reservatório, o que permitirá o ajuste dos parâmetros adotados na simulação, assim como estabelecer as reais características da fundação / This study is related to the analysis of crack propagation in the tensioned zone of concrete dam foundation. The example of Porto Primavera dam owned by CESP (São Paulo State Power Company) Brazil is presented. Fracture growth is analyzed by mean iterative stress-strain and hydraulic head analysis with codes based on finite elements incorporating non-linear fracture mechanics and damage models. Due to progressive load of water, a step-by-step analysis is performed, based on the development of fracture and application of forces due of hydraulic pressure. The proposed numerical simulation has the purpose of studying the development of fracture, determining deformations due to the action of uplift pressure, self-weight and hydraulic pressure on the fracture walls. The computed deformations are compared with instrumentation data, obtained during the impoundment of the reservoir, from devices installed in the foundation, which will allow to adjust the adopted parameters in the simulation and to determine the real characteristics of the foundation

No description available.

There are various distresses arising from traffic loads and the surrounding environment to whichan asphalt pavement is subjected during its life span. The environment-associated damages aremore severe during winter when abundant moisture and freezing temperature are presentsimultaneously. Damage caused by frost heave is one of the important winter-related damagesresulting in severe cracks and bumpy road surfaces. Since the frost heave-induced cracks areusually wide, they can make the pavement more prone to other types of damage by leaving theopen space for water and moisture penetration. Simulating the response of the pavement whenit is subjected to frost heave is the aim of this licentiate thesis. Attaining this objective requirescoupling a frost heave model with a damage model representing the mechanistic behavior ofthe asphalt material. With regard to the brittle behavior of the asphalt at cold temperatures, aviscoelastic damage model for asphalt material is coupled with a thermomechanical frost heavemodel. The thermomechanical approach couples the physical processes involved in frost actioninside the soil. To elucidate more, in this method the thermal and mechanical fields are coupledby the porosity evolution function which implicitly takes into account the effect of the hydraulicfield. On the other hand, the continuum viscoelastic damage model for asphalt material isdeveloped within the infinitesimal strain context by applying the thermodynamical restrictionsof irreversible processes. The suggested framework was employed in different finite elementmodels to simulate damages caused by frost heave in asphalt pavements. The results indicatethat it predicts the damage distribution and evolution in the asphalt. Furthermore, it was shownthat the uneven frost heave and physical processes taking place in the soil during frost actionsuch as cryogenic suction force creation, porosity evolution, ice formation, etc., can also besimulated. / Det finns olika typer av påfrestningar som uppstår från trafikbelastningar och den omgivandemiljön som en asfaltbeläggning utsätts för under sin livslängd. De miljörelaterade skadorna ärallvarligare under vintern när fukt och kalla temperaturer är närvarande samtidigt. Skadororsakade av tjällyft är en av de allvarliga vinterrelaterade skadorna som resulterar i sprickor ochskadade vägsytor. Eftersom de tjällyftsinducerade sprickorna vanligtvis är breda kan de görabeläggningen mer utsatt för andra typer av skador genom vatten- och fuktinträngning. Syftetmed denna licentiatavhandling är att simulera beläggningens reaktion när den utsätts för tjällyft.För att uppnå detta mål krävs att en tjällyftsmodell kopplas till en skademodell somrepresenterar asfaltmaterialets mekanistiska beteende. När det gäller asfaltens spröda beteendevid kalla temperaturer, är en viskoelastisk skademodell för asfaltmaterial kopplad till entermomekanisk tjällyftsmodell. Det termomekaniska tillvägagångssättet kopplar de fysiskaprocesserna som är involverade i frostverkan inuti jorden. För att klarlägga detta mer, är determiska och mekaniska fälten kopplade med porositetsutvecklingsfunktionen som implicit tarhänsyn till effekten av det hydrauliska fältet. Å andra sidan är den kontinuumviskoelastiskaskademodellen för asfaltmaterial utvecklad inom det oändliga töjningssammanhanget genomatt tillämpa de termodynamiska begränsningarna av irreversibla processer. Det föreslagnaramverket användes i olika finita elementmodeller för att simulera skador orsakade av tjällyft iasfaltbeläggningar. Resultaten indikerar att den förutsäger skadefördelningen och utvecklingeni asfalten. Dessutom har det visat sig att det ojämna tjällyft och fysiska processer som äger rumi marken under frostpåverkan, såsom skapande av kryogen sugkraft, porositetsutveckling,isbildning, etc., också kan simuleras. / <p>QC 20221124</p>

As estruturas de concreto armado são um dos tipos de estrutura mais utilizados no mundo e quando localizadas em ambientes não agressivos, respeitam a vida útil para a qual foram projetadas. Entretanto, a durabilidade dessas estruturas pode ser fortemente reduzida por processos de degradação de origens ambientais e/ou funcionais. Dentre esses processos, destacam-se aqueles que desencadeiam a corrosão das armaduras, sendo a difusão de cloretos um dos fatores de maior importância no desencadeamento do processo corrosivo. Apesar da robustez de diversos modelos propostos na literatura, abordagens determinísticas frequentemente falham ao prever o tempo de início da corrosão devido à enorme e à inerente aleatoriedade envolvida nesse processo. Neste contexto, a durabilidade pode ser mais realisticamente representada por meio de modelos probabilísticos. Este trabalho apresenta uma formulação numérica, baseada no Método dos Elementos Finitos (MEF), para a determinação de cenários de falha de vigas de concreto armado submetidas à penetração de cloretos. Nessa formulação, a não linearidade física do concreto é descrita pelo modelo de dano de Mazars e a variação da concentração de cloretos no interior do concreto é determinada por meio da segunda lei de Fick. Além disso, as leis de corrosão de Faraday são adotadas para a determinação da taxa de redução das áreas de aço ao longo do tempo. A partir das cargas de colapso calculadas pelo modelo mecânico, as probabilidades de falha são determinadas utilizando o algoritmo de confiabilidade FORM. Os resultados obtidos mostram a influência da corrosão na segurança estrutural de estruturas de concreto armado ao longo do tempo, assim como, seu impacto na durabilidade dessas estruturas. / Reinforced concrete structures are one of the most commonly used types of structures in the world and when these structures respects the structural life predicted when it is located in non-aggressive environments. However, the durability of these structures can be strongly reduced by degradation processes caused by environmental and/or functional origins. Among these processes, those related to reinforcement\'s corrosion are more outstanding, being the chloride diffusion one of most important factors that triggers the corrosion process. Despite the robustness of several models proposed in literature, deterministic approaches often fail to predict the time of corrosion initiation due to the huge inherent randomness involved in the process itself. In this context, the durability can be more realistically represented by probabilistic models. This work presents a numerical formulation based on the Finite Element Method (FEM) to determine the failure configuration of reinforced concrete beams subjected to chloride penetration. In this formulation, the non-linearity of the concrete is described by Mazars damage model and the variation of chloride concentration along concrete cover is determined by Fick\'s second law. Moreover, Faraday\'s law concerning corrosion is adopted in order to determine the reduction rate of steel areas over a period of time. The probabilities of failure are determined using the reliability algorithm FORM, which accounts the collapse Sloads calculated by the mechanical model. The results showed the influence of corrosion phenomenon on the structural safety of reinforced concrete along time as well as its impact on the structural durability.

As estruturas de concreto armado são um dos tipos de estrutura mais utilizados no mundo e quando localizadas em ambientes não agressivos, respeitam a vida útil para a qual foram projetadas. Entretanto, a durabilidade dessas estruturas pode ser fortemente reduzida por processos de degradação de origens ambientais e/ou funcionais. Dentre esses processos, destacam-se aqueles que desencadeiam a corrosão das armaduras, sendo a difusão de cloretos um dos fatores de maior importância no desencadeamento do processo corrosivo. Apesar da robustez de diversos modelos propostos na literatura, abordagens determinísticas frequentemente falham ao prever o tempo de início da corrosão devido à enorme e à inerente aleatoriedade envolvida nesse processo. Neste contexto, a durabilidade pode ser mais realisticamente representada por meio de modelos probabilísticos. Este trabalho apresenta uma formulação numérica, baseada no Método dos Elementos Finitos (MEF), para a determinação de cenários de falha de vigas de concreto armado submetidas à penetração de cloretos. Nessa formulação, a não linearidade física do concreto é descrita pelo modelo de dano de Mazars e a variação da concentração de cloretos no interior do concreto é determinada por meio da segunda lei de Fick. Além disso, as leis de corrosão de Faraday são adotadas para a determinação da taxa de redução das áreas de aço ao longo do tempo. A partir das cargas de colapso calculadas pelo modelo mecânico, as probabilidades de falha são determinadas utilizando o algoritmo de confiabilidade FORM. Os resultados obtidos mostram a influência da corrosão na segurança estrutural de estruturas de concreto armado ao longo do tempo, assim como, seu impacto na durabilidade dessas estruturas. / Reinforced concrete structures are one of the most commonly used types of structures in the world and when these structures respects the structural life predicted when it is located in non-aggressive environments. However, the durability of these structures can be strongly reduced by degradation processes caused by environmental and/or functional origins. Among these processes, those related to reinforcement\'s corrosion are more outstanding, being the chloride diffusion one of most important factors that triggers the corrosion process. Despite the robustness of several models proposed in literature, deterministic approaches often fail to predict the time of corrosion initiation due to the huge inherent randomness involved in the process itself. In this context, the durability can be more realistically represented by probabilistic models. This work presents a numerical formulation based on the Finite Element Method (FEM) to determine the failure configuration of reinforced concrete beams subjected to chloride penetration. In this formulation, the non-linearity of the concrete is described by Mazars damage model and the variation of chloride concentration along concrete cover is determined by Fick\'s second law. Moreover, Faraday\'s law concerning corrosion is adopted in order to determine the reduction rate of steel areas over a period of time. The probabilities of failure are determined using the reliability algorithm FORM, which accounts the collapse Sloads calculated by the mechanical model. The results showed the influence of corrosion phenomenon on the structural safety of reinforced concrete along time as well as its impact on the structural durability.

Als Großdemonstrator des Sonderforschungsbereichs 532 soll auf dem Gelände der Fakultät für Bauingenieurwesen der RWTH Aachen ein Ausstellungspavillon mit einer Dachkonstruktion aus Textilbeton errichtet werden. Der Beitrag zeigt die automatisierte Bemessung dieser komplexen Tragstruktur mit Hilfe eines hierfür entwickelten numerischen Bemessungsstools. Die Auswertung erfolgt für alle Lastfallkombinationen nach DIN 1055-100 und unter Berücksichtigung der Reduktion der Tragfähigkeit der textilen Bewehrung infolge einer Umlenkung im Riss sowie einer Erhöhung der aufnehmbaren Textilspannungen infolge Biegebeanspruchung. Zur Ermittlung der Tragfähigkeit der Textilbetonschale wurden am Institut für Massivbau Dehnkörper- und Biegeversuche durchgeführt, die in Bewehrungsgrad und Dicke dem realen Bauwerk am Schalenrand entsprachen. / Within the collaborate research center 532 at RWTH Aachen University the construction of an exposition hall with a double-curved roof structure consisting of textile reinforced concrete is currently planned. A numerical tool has been developed to calculate the necessary number of reinforcement layers. Further, the tool evaluates the characteristic stresses of the load case combinations in the ultimate limit state taking into account a reduction of the load-bearing capacity of the textile reinforcement due to alignment of the rovings in the crack bridge and a better activation of the inner filaments for bending induced tension. The resistance of the material has been determined in experimental investigations of tensile and bending specimens of the same thickness and reinforcement ratio as the planned shell structure.

Les travaux présentés dans ce mémoire s'inscrivent dans l'étude et l'amélioration des modèles d'endommagement continus régularisés (non locaux), l'objectif étant d'étudier la transition entre un champ d'endommagement continu défini sur l'ensemble d'une structure et un modèle discontinu de fissuration macroscopique.La première étape consiste en l'étude semi-analytique d'un problème unidimensionnel (barre en traction) visant à identifier une famille de lois d'interface permettant de basculer d'une solution non homogène obtenue avec un modèle continu à gradient d'endommagement vers un modèle discontinu de fissuration cohésive. Ce passage continu / discontinu est construit de telle sorte que l'équivalence énergétique entre les deux modèles soit assurée, et reste exacte quelque soit le niveau de dégradation atteint par le matériau au moment où cette transition est déclenchée.Cette stratégie est ensuite étendue au cadre 2D (et 3D) éléments finis dans le cas de la propagation de fissures rectilignes (et planes) en mode I. Une approche explicite basée sur un critère de dépassement d'une valeur « critique » de l'endommagement est proposée afin de coupler les modèles continus et discontinus au sein d'un même calcul quasi-statique par éléments finis. Enfin, plusieurs résultats de simulations menées avec cette approche couplée sont présentés. / The present work deals with the study and the improvement of regularized (non local) damage models. It aims to study the transition from a continuous damage field distributed on a structure to a discontinuous macroscopic failure model.First, an analytical one-dimensional study is carried out (on a bar submitted to tensile loading) in order to identify a set of interface laws that enable to switch from an inhomogeneous solution obtained with a continuous gradient damage model to a cohesive zone model. This continuous / discontinuous transition is constructed so that the energetic equivalence between both models remains ensured whatever the damage level reached when switching.This strategy is then extended to the bi-dimensional (and tri-dimensional) case of rectilinear (and plane) crack propagation under mode I loading conditions, in a finite element framework. An explicit approach based on a critical damage criterion that allows coupling both continuous and discontinuous approaches is then proposed. Finally, results of several simulations led with this coupled approach are presented.

Dans le cadre de la sécurité routière, les essais de choc ne permettent pas la prédiction des blessures internes, notamment aux organes abdominaux. La simulation numérique apparaît comme un outil prometteur pour évaluer le risque lésionnel d'une configuration d'impact en permettant de décrire les sollicitations relatives aux différents organes. Afin de quantifier le risque de blessure, il est nécessaire de connaître le comportement à rupture des tissus du corps humain. L'objet de cette étude est le foie, dont les blessures sont souvent graves. L'attention s'est portée sur les lacérations surfaciques, qui impliquent le parenchyme et la capsule hépatiques. L'objectif de cette thèse est de caractériser et modéliser le comportement et la rupture de ces deux tissus. L'étude expérimentale s'est progressivement focalisée sur les tissus impliqués dans la lacération surfacique. Un protocole de compression de foie entier pressurisé a mis en évidence le mécanisme d'apparition des lésions, liées à une sollicitation de traction biaxiale. Une série d'essais de traction uniaxiale sur parenchyme et capsule a permis la quantification des propriétés à rupture de ces tissus. Enfin, les essais de gonflement de capsule ont permis la caractérisation indépendante de celle-ci sous une sollicitation plus réaliste. La mesure de champ par corrélation d'images 2D puis 3D a été utilisée dans ces deux derniers protocoles, révélant les phénomènes locaux tels que la localisation de la déformation avant rupture. Le module élastique du parenchyme a été évalué ; un modèle linéaire puis hyperélastique a été identifié pour le comportement de la capsule. Lors de ces campagnes d'essais, les influences de l'origine biologique -porc ou humain - et de la congélation sur les propriétés mécaniques des tissus ont été évaluées par des tests statistiques. Le travail de modélisation s'est porté sur l'endommagement et la rupture d'un tissu fibreux membranaire initialement isotrope. Les fibres sont supposées élastiques linéaires fragiles. L'endommagement est modélisé comme le résultat de la rupture des fibres à l'échelle microscopique. Deux méthodes d'homogénéisation issues de la littérature sont utilisées et comparées. Le modèle obtenu permet de décrire l'endommagement par deux variables scalaires macroscopiques. Plusieurs phénomènes observés expérimentalement - dépliement progressif des fibres, fibres endommageables, propriétés variables d'une fibre à l'autre - constituent des extensions au modèle. Construit dans un cadre très général, ce modèle est identifié sur les essais de gonflement de la capsule hépatique. La simulation des essais est réalisée en appliquant les conditions aux limites expérimentales ; le module élastique et la déformation à rupture des fibres sont identifiés par un algorithme d'optimisation. Les modèles et propriétés mécaniques à rupture ainsi définis peuvent être inclus dans un modèle de foie entier en vue de la simulation d'un choc. / In the field of road safety, internal injuries including abdominal injuries cannot be predicted through crash-tests using dummies. Numerical simulation is a promising tool to evaluate the risk of injury of a given impact configuration by descripting the loadings on the organs. Quantifying the risk of failure requires knowledge about the mechanical behaviour and the failure properties of the tissues of the human body. As the liver injuries account for a large amount of the serious injuries, the present study is focused on this organ and more specifically on the surface laceration. The aim of this study is to characterize and model the failure behaviour of the two tissues involved in the surface laceration : the parenchyma and the hepatic capsule. The experimental study includes three protocols which range from the organ scale to the tissue scale. Compression tests on whole perfused porcine and human livers enhanced the failure mechanism of the liver surface ; surface laceration seems to be caused by multiaxial tension. Uniaxial tensile tests on parenchyma and capsule samples from human and porcine livers allowed the determination of the failure properties of these two tissues. Independent characterization of the human liver capsule was conducted through inflation tests, which correspond to a more realistic loading than uniaxial tension. Full-strain fields were computed by digital image correlation and stereocorrelation on the second and third protocols ; local phenomena such as the localization of the strain field before failure or material heterogeneities were observed. The linear modulus of the parenchyma was determined. The capsule behaviour was modeled as linear first, then as hyperelastic. Statistical tests based on the results of the uniaxial tests assessed the influence of the biological origin of the tissues - porcine or human - and the preservation method - keeping fresh of freezing. The modeling part of this study is focused on the damage and rupture of an isotropic fibrous membrane. The fibers are linear elastic and brittle. The failure of the fibers at the microscopic scale creates macroscopic damage in the tissue which can be described by two scalars. The homogenization of the behaviour is conducted through two methods available in the literature ; they can therefore be compared. Several phenomena observed on biological fibrous tissues - damageable fibers, crimped fibers, random mechanical properties of the fibers - have been included in the model. This damage model is finally identified on the inflation tests of the capsule which are simulated using the experimental boundary conditions catched by stereocorrelation. The elastic modulus as well as the ultimate strain of the fibers are determined by an optimization algorithm. The material and failure properties as well as the damage model determined in this study can be included in a liver model to simulate a crash. The occurence of surface laceration could then be predicted.