Cette thèse s’ajoute aux différents travaux de recherche qui traitent des alliages d’aluminium fortement utilisés dans l’industrie aéronautique et contribue fortement à comprendre le comportement élastoplastique en chargement cyclique à contrainte imposée du 2017A. L’apport essentiel de ce travail est l’étude de l’anisotropie propre du matériau utilisé à travers le suivi de l’évolution des différents paramètres caractérisant la plasticité cyclique de notre matériau. En effet, nous avons caractérisé cette anisotropie en comparant le comportement du matériau en traction-compression avec celui de la torsion alternée selon l’évolution cyclique de la réponse contrainte-déformation, l’évolution de l’état stabilisé, l’évolution des variables d’écrouissages cinématique et isotrope ainsi que l’anisotropie selon le comportement en fatigue et endommagement. Pour mieux affiner la partie expérimentale de ce travail, des investigations microstructurales des faciès de rupture de toutes les éprouvettes utilisées ont été effectuées afin de mieux comprendre les mécanismes d’endommagement cyclique dans notre matériau. Dans la partie numérique de cette thèse, nous avons réalisé des simulations numériques en utilisant la dernière version du modèle multimécanismes qui tient compte de l’anisotropie du matériau. Les résultats de ces simulations, réalisées en considérant les mêmes conditions de nos essais expérimentaux, confirment les capacités de cette nouvelle version à estimer le comportement élastoplastique d’un matériau anisotrope. / The present work is devoted to study the anisotropic behavior of an extruded aluminum alloy under cyclic loading in axial and shear directions. In the first part, we have studied its elastoplastic behavior through the evolution of stress–strain loops, isotropic and kinematic hardening and we have associated this behavior with the evolution of its elastic adaptation (shakedown). We have studied the behavior of the material in fatigue damage using the evolution of stiffness. Microstructural investigations were performed on fractured surfaces using scanning electron microscope (SEM) in orderto understand the evolution of fatigue damage during cyclic loading. In the second part, we have simulated all the tests performed in the experimental part using the new version of multimechanisms model. The obtained results show that this version is able to take into account the anisotropic behavior of the materials under stress controlled tests.

[pt] O fenômeno da fadiga é uma das falhas mais comuns em pavimentos asfálticos e se caracteriza pela aparição e posterior desenvolvimento de micro e macro trincas. As misturas asfálticas são compostas por agregados graúdos e por uma matriz circundante composta por ligante asfáltico, agregados miúdos e fíler, conhecida como Mistura Asfáltica Fina (MAF). Estudos indicam que os fenômenos que afetam as microfissuras se iniciam na mistura asfáltica fina. O presente trabalho investiga o comportamento em relação à fadiga das misturas asfálticas, utilizando como passo intermediário a análise de MAFs. Foram selecionadas três misturas asfálticas, compostas pelo mesmo ligante, porém com agregados distribuídos em três curvas granulométricas diferentes, variando seu tamanho máximo nominal. Para as MAFs, as granulometrias foram proporcionais às encontradas nas respectivas misturas asfálticas. As misturas e as MAFs seguiram programação experimental semelhante, com a caracterização viscoelástica linear e realização de ensaios dinâmicos uniaxiais de fadiga. Para interpretação dos resultados, foi utilizado o modelo simplificado de viscoelasticidade do dano contínuo (S-VECD) e os critérios de ruptura G(R) e D(R), que descrevem satisfatoriamente o comportamento em relação à fadiga das misturas e MAFs estudadas. Foi analisada a resistência ao dano das MAFs, bem como a influência da variação do tamanho máximo nominal no seu desempenho a fadiga. Estudou-se a relação entre as deformações encontradas nas misturas asfálticas e na parcela fina das misturas asfálticas. As misturas com maior presença de mistura asfáltica fina apresentaram melhor desempenho a fadiga e os fatores de proporcionalidade de deformação foram maiores para as misturas com tamanhos máximos nominais maiores. / [en] Fatigue is one of the most common problems in asphalt pavements and it is characterized by the appearance and subsequent development of micro and macro cracks. Asphalt mixtures are composed of large aggregates and a matrix that surrounds these aggregates, composed of asphalt binder, small aggregates and filler, known as Fine Aggregate Mixture (FAM). Studies indicate that the phenomena that affect micro cracks starts in the FAM. Therefore, this work aims to investigate the fatigue behavior of the Asphalt mixtures, using as intermediate means an analysis of the FAM. To achieve this objective, three asphalt mixtures were selected. They are composed of the same binder, but with aggregates distributed according to three different aggregate gradation curves, varying their maximum nominal size. The FAM had gradation curves proportional to that applied in asphalt mixtures. Mixtures and MAFs followed similar experimental programming with linear viscoelastic characterization and dynamic uniaxial fatigue tests. In order to interpret the results it was used the Simplified Viscoelastic Continuum Damage (S-VECD) model, G(R) and D(R) failure criteria, which presented a good prediction of the fatigue behavior of the Mixtures and MAFs studied. The MAF s tolerance to damage was analyzed as well as the influence of the maximum nominal size variation. A relation between strains in the asphalt mixtures and the strain in the fine portion of the asphalt mixtures was studied. The asphalt mixtures with higher content of fine asphalt mixture showed better fatigue performance and the strain proportionality factors were higher for mixtures with larger nominal maximum sizes.

Nowadays, the Norwegian Public Roads Administration plans to replace the ferry connections along the western coast of Norway with fixed road connections through the coastal highway E39 project. Due to the necessity of bridging long distances with considerable depths, non-conventional engineering solutions are being developed. To date, the first fjord planned to be cross is Bjørnafjord, located just in the middle of Trondheim and Kristiansand. In order to bridge the fjord distance, three innovative solutions have been developed: a submerged floating tube bridge, a floating pontoon bridge, and finally, a multi-span suspension bridge. It is known that these structures are affected by periodic environmental forces which may cause significant fatigue problems in some structural components, disturbing their service behaviour. The aim of this master thesis is to deeply analyse the cumulative fatigue damage produced in the mooring lines of a proposed solution for crossing Bjørnafjorden as well as to investigate the influence of the implementation of different mooring line scenarios on the damage. A 3D finite element model of the chosen alternative was conducted and verified. The model provided the stress variations in each mooring line which were processed through Excel software using macros performed as well as Matlab scripts in order to obtain the results. Then, a deep fatigue damage assessment was carried out discussing how different tension-history time period calculations affect to the damage, as well as which fatigue evaluation methodology is adequate for the chosen solution. Moreover, the fatigue damage produced on the initial mooring line system configuration was analysed. It was investigated the repercussions of each direction and the contribution of each environmental load on the total damage. Last but not least, it was researched the influence of different water depths and line configurations on the fatigue damage. The results show that the fatigue damage obtained for the adopted solution remains far from the failure threshold with the worst damage produced in the mooring line chain components. The previous results have been computed employing a 1-hour analysis duration through the rainflow counting method. Also, the worst fatigue damage is produced by environmental states propagating in a westerly direction, corresponding to the maximum fetch. Regarding the load contribution in the fatigue damage, it is proved in this case that the current loads stabilise the mooring lines, reducing the fatigue damage. Finally, investigating the effect of various mooring line scenarios on the damage it has been proved that the fatigue damage is increased as the water depth is decreased and as the lateral mooring lines are separated from the initial configuration.

Le travail abordé dans le cadre de cette thèse constitue une contribution à la compréhension des mécanismes d'endommagement et à l'identification d'un critère de durée de vie du polyamide 6,6 renforcé à 30% en masse de fibres de verre courtes (PA66GF30), obtenu par moulage par injection, en prenant en compte les effets de la température, de la teneur en eau et des orientations de fibres induites par le procédé de fabrication. Ainsi, dans un premier temps, une campagne d'essais de caractérisation du comportement mécanique du PA66GF30, pour différentes orientations de fibres, températures, teneurs en eau et vitesses de sollicitation, a été menée. Ceux-ci ont mis en évidence le rôle de la matrice polyamide 6,6 (PA66) dans la dépendance à la température, à la teneur en eau et à la vitesse de sollicitation du comportement du PA66GF30. Dans ce sens, une triple équivalence Temps-Température-Teneur en eau du comportement du PA66 a été démontrée à l'aide de courbes maîtresses obtenues par DMA. Une nouvelle expression de la vitesse équivalente à une température et une teneur en eau de référence en a alors été déduite, dans l'objectif de pouvoir rendre compte de cette triple sensibilité dans un futur modèle de comportement. Ensuite, une campagne d'essais de fatigue dans des conditions environnementales contrôlées, a permis d'étudier les effets de l'orientation des fibres, de la température et de la teneur en eau, sur la tenue en fatigue d'éprouvettes en PA66GF30. L'analyse mécanique de ces essais a abouti à l'identification d'un critère de durée de vie, tenant compte de l'ensemble des facteurs influents. Enfin, la microtomographie des rayons X sous faisceau synchrotron a été utilisée pour étudier les mécanismes d'endommagement en fatigue présents dans le PA66GF30, suite à des analyses post-mortem et des expériences in-situ. Le dépouillement de ces observations a permis de faire la lumière sur les mécanismes d'endommagement, et de proposer un nouveau scénario d'endommagement en fatigue. / The work discussed in this thesis is a contribution to the understanding of damage mechanisms and identifying a fatigue criterion of polyamide 6,6 reinforced with 30 wt% of short glass-fibres (PA66GF30), obtained by injection molding, taking into account the effects of temperature, water content and fiber orientations induced by the process. Thus, in a first step, the characterization of the mechanical behavior of PA66GF30 for different fiber orientations, temperatures, moisture contents and strain rates, was conducted. They have highlighted the role of the polyamide matrix (PA66) in the temperature, water content and strain rate behavior dependence of PA66GF30. In this sense, Time-Temperature-Water content equivalence of mechanical behaviour of PA66 was demonstrated using master curves obtained by DMA. A new expression of the equivalent strain rate at temperature reference and a water content reference was then deduced, and it is now possible to relay the triple sensitivity to strain rate, temperature and water content in only one term. Then, a fatigue test campaign in controlled environmental conditions, allowed to study the effects of fiber orientation, temperature and water content on the fatigue behaviour of PA66GF30 specimens. The mechanical analysis of these tests has led to the identification of a fatigue life criterion, taking into account all the influencing factors. Finally, the X-ray microtomography under synchrotron beam was used to study the mechanisms in fatigue damage present in the PA66GF30, following post-mortem analysis and in-situ experiments. The analysis of these observations has shed light on the mechanisms damage and, it has been proposed a new fatigue damage scenario.

This diploma thesis is dedicated to mechnical desing, fabrication and assembly of experimental bearing testing rig. First part of the document contains research of current knowlege in the field of bearing testing and desings of currently used machines. In second part is conception of the testing rig described. Third part contains description of design variations that were designed. In Discussion is comented choices of final variants. Last part is dedicated to functional verification of the whole testing rig by first series of the tests.

<div>Despite the advances of analytical and numerical methods for composite materials, it is still challenging to predict the onset and evolution of their different failure mechanisms. Because most failure mechanisms are irreversible processes in thermodynamics, it is beneficial to model them within a unified thermodynamic framework. Noting the advantages of so-called generalized standard models (GSMs) in this regard, the objective of this work is to formulate constitutive models for several main failure mechanisms: brittle fracture, interlaminar delamination, and fatigue behavior for both continuum damage and delamination, in a generalized standard manner.</div><div><br></div><div>For brittle fracture, the numerical difficulties caused by damage and strain localization in traditional finite element analysis will be addressed and overcome. A nonlocal damage model utilizing an integral-type regularization technique will be derived based on a recently developed ``local'' continuum damage model. The objective is to make this model not only rigorously handle brittle fracture, but also incorporate common damage behavior such as damage anisotropy, distinct tensile and compressive damage behavior, and damage deactivation. A fully explicit integration scheme for the present model will be developed and implemented.</div><div><br></div><div>For fatigue continuum damage, a viscodamage model, which can handle frequently observed brittle damage phenomena, is developed to produce stress-dependent fatigue damage evolution. The governing equation for damage evolution is derived using an incremental method. A class of closed-form incremental constitutive relations is derived. </div><div><br></div><div>For interlaminar delamination, a cohesive zone model (CZM) will be proposed. Focus is placed on making the associated cohesive elements capable of displaying experimental critical energy release rate--mode mixture ratio relationships. To achieve this goal, each cohesive element is idealized as a deformable string exhibiting path dependent damage behavior. A damage model having a path dependence function will be developed, which will be constructed such that each cohesive element can exhibit designated, possibly sophisticated mixed-mode behavior. The rate form of the cohesive law will be subsequently derived.</div><div><br></div><div>Finally, a CZM for interlaminar fatigue, capable of handling brittle damage behavior, is developed to produce realistic interlaminar crack propagation under high-cycle fatigue. An implicit integration scheme, which can handle complex separation paths and mixed-mode delamination, is developed. Many numerical examples will be utilized to clearly demonstrate the capabilities of the proposed nonlocal damage model, continuum fatigue damage model, and CZMs for quasi-static and fatigue delamination.</div>

Depuis la restriction de l’utilisation du plomb dans l’électronique, les alliages de brasure de type SnPb ont été remplacés majoritairement par des alliages de type SnAgCu (SAC). Des travaux précédents ont révélé un phénomène de vieillissement de ces alliages, caractérisé par une forte variation des propriétés mécaniques et se stabilisant après plusieurs années à température ambiante. L’objectif de ce travail est d’étudier l’influence du vieillissement thermique sur l’endommagement des assemblages électroniques utilisant l’alliage SAC305 sous chargements mécaniques.L’étude s’est d’abord concentrée sur le comportement mécanique du SAC305, puis sur l’endommagement des joints brasés.L’impact du vieillissement sur le comportement mécanique a été évalué à l’échelle massive ainsi qu’à l’échelle d’un joint brasé. L’évolution de la dureté et du comportement mécanique cyclique à température ambiante a été reliée à un phénomène de grossissement de grain. Des essais de compression sur billes en SAC305, représentatives de la structure réelle, ont montré les mêmes évolutions. Deux modèles de comportement viscoplastique ont été développés à l’échelle d’un joint brasé pour l’alliage dans l’état initial et dans l’état vieilli. Des simulations numériques réalisées à l’aide de ces modèles, ont permis de valider cette approche.L’influence du vieillissement sur l’endommagement des joints brasés en SAC305 a été évaluée à l’aide d’essais de torsion cycliques sur cartes assemblées. Les résultats montrent que le vieillissement induit une diminution du nombre de cycles à la défaillance en fatigue oligocyclique, élément très important pour la gestion du risque dans les équipements électroniques / Since the use of the lead was restricted in electronic assemblies, the electronic market turned on lead-free alloys for electronic assemblies. Most of electronic manufacturers chose SnAgCu (SAC) to replace SnPb alloys. For SAC, former results suggest that high temperature thermal ageing causes a significant drop in mechanical properties, which stabilises after several years at room temperature. The aim of this work is to analyse the impact of thermal ageing on the fatigue damage of SAC305 electronic assemblies under mechanical loadings.This study first focused on the mechanical behaviour of SAC305 alloy. Then, the fatigue damage of SAC305 was analysed on solder joints.The impact of thermal ageing on the mechanical behaviour of SAC305 was evaluated at the bulk scale and at the solder joint scale. Changes in the hardness and in the cyclic mechanical behaviour at room temperature were linked to a grain growth phenomenon. Compression tests on SAC305 solder balls, which are representative of real structure, showed the same changes in the mechanical behaviour. Two viscoplastic constitutive models of mechanical behaviour were identified at the solder joint scale for both initial and aged conditions. Numerical simulations were carried out using these models and led to the validation of the proposed approach.The impact of thermal ageing on the fatigue damage of SAC305 alloy was evaluated thanks to torsion tests on assembled boards. The results of these tests show that the thermal ageing decreases the number of cycles to failure in low cycle fatigue. This observation is very important considering the reliability risk for electronic devices

Diplomová práce popisuje metodiku výpočtů částí náchylných k rozvoji mnoho-ohniskového únavového poškození (WFD). Nejdříve se práce zabývá rozborem předpisů letové způsobilosti souvisejících s WFD pro letadla certifikovaných podle FAR 23 v kategorii commuter. Následuje popis metodiky únavového výpočtu a predikce šíření trhliny. Dále jsou popsány řešení pro výpočet faktoru intenzity napětí pro základné konfigurace trhliny, tam kde to bylo možné v uzavřeném tvaru, jinak ve formě tabulky. Hlavní částí práce je návrh algoritmu AIMA schopného provést kompletní analýzu části náchylné k rozvoji únavového poškození na více místech (MSD). Model se validoval únavovou zkouškou vzorku přeplátovaného spoje dolního panelu křídla. Následně byla analyzována reálná konstrukce spoje dolních panelů křídla letounu L 410 NG.

In the future, hydropower plants are expected to operate more flexibly. This will lead to a more varied operation of the turbine and the generator, such as more start and stop in order to stabilise the frequency in the grid. Studies show that these transient operations are more costly in terms of fatigue degradation, i.e. consumption of fatigue life. Vattenfall has developed a methodology with the aim to analyse fatigue loads, acting on the runner and the rotor in hydropower units during operation. With a numerical model, the loads are assessed with input data gathered from measurements together with given data on several parameters. Some of the input data are bearing structure stiffness, bearing oil properties, and point of action of forces, etc. Several of these input parameters are subject to a degree of uncertainty, which affect the assessed fatigue load, determined with the methodology. This study will focus on analysing one fatigue force component acting on the runner. The aim with this study is to answer the following research questions: (i) Which input parameters, that are subject to a degree of uncertainty, contribute the most to the combined standard uncertainty in the assessed fatigue force? (ii) How much does the combined standard uncertainty in the assessed fatigue force amount to? (iii) How does the uncertainty in the assessed fatigue force affect the fatigue damage?. The combined standard uncertainty in the fatigue force is determined with methods in uncertainty propagation. In order to evaluate the effect from the uncertainty in the fatigue load on the fatigue damage, a statistical analysis of the ratio between the fatigue damage associated with a probability of exceedance and the expected fatigue damage is conducted. From the results it can be observed that the governing uncertainty parameter is the offset of the shaft displacement signal, which amount to 40 % of the combined standard uncertainty in the fatigue force. Of the nine analysed uncertainty parameters, three parameters are bearing properties parameters, i.e. the bearing clearance, the oil film temperature and the point of action of bearing forces, which amount to 47.5 % of the combined standard uncertainty in the fatigue force. Therefore, in order to decrease the uncertainties, focus should be kept on the bearing properties. Given each parameters uncertainty, the ratio between the combined standard uncertainty in the fatigue force and the expected fatigue force amount to 7 %. This corresponds to a ratio between the standard uncertainty in the fatigue damage and the expected fatigue damage of 35 %, due to the value of the index of S-N curve of five. Given the standard uncertainty in the fatigue force together with the index of S-N-curve, the ratio between the fatigue force associated with a probability of exceedance and the expected fatigue force can be assessed, i.e. the fatigue force ratio. Consequently, the fatigue force ratio amount to 1.32 for a probability of 0.0032 %, 1.09 for a probability of 10 % and 1.04 for a probability of 30 %. These probabilities correspond to the fatigue damage ratios, i.e. the ratios between the fatigue damage associated with a probability of exceedance and the expected fatigue damage of 4, 1.56 and 1.20. Thereby, the uncertainty in the fatigue force can greatly affect the uncertainty in the fatigue damage, dependent on the value of the index of S-N-curve. The results from this study imply the importance of considering the uncertainties in fatigue load assessments. These results provide support for assessing load levels for runner dimensioning to finally, be able to derive a correct margin of safety. This in order to not underestimate fatigue damage and thereby decrease the risk for unexpected fatigue failure. / Det finns ett förväntat behov av att kraftproduktionen i vattenkraftverk skall vara mer flexibel i framtiden. Detta leder till mer varierande driftlägen för turbinen och generatorn, såsom fler start och stop med syfte att stabilisera frekvensen i elnätet. Studier påvisar att transienta driftlägen är mer kostsamma i form av utmattningsdegradering, d.v.s. konsumtion av utmattningsliv. Vattenfall har utvecklat en metodik för att analysera inverkan av utmattningslaster verkande på löphjulet och rotorn i vattenkraftsaggregat under drift. Med en numerisk modell kan utmattningslasterna bedömas. Den ingående datan till modellen är bland annat är uppmätta storheter och given data på parameterar. Några av de ingående storheterna är lagerstyvhet, angreppspunkter för lagerkrafter och lageroljans egenskaper, etc. Flera av dessa ingående parametrar innehar osäkerheter, vilket påverkar bedömningen av utmattningslasterna. Denna studie kommer att fokusera på en kraftkomponent verkande på löphjulet. Malet med detta arbete är att svara på följande forskningsfrågor: (i) Vilka ingående parametrar, som innehar en osäkerhet, bidrar med en styrande osäkerhet i den bedömda kraften? (ii) Hur mycket uppgår den kombinerade standardosäkerheten i den bedömda kraften till? (iii) Hur påverkar kraftens osäkerhet utmattningsskadan? Den kombinerade standardosäkerheten i kraften är beräknad med metoder i fortplantning av osäkerheter. För att kunna bedöma påverkan på delskadan givet osäkerheten i kraften, så sker en statistisk analys av förhållandet mellan delskadan sammanhängande med en sannolikhet för överskridande och den förväntade delskadan. Resultatet påvisar att den styrande ingående parametern är offset i signalen för axelförskjutning, vilken uppgår till 40 % av den kombinerade standardosäkerheten i utmattningskraften. Av de nio analyserade parametrarna härrör tre av dessa lageregenskaper, d.v.s. lagerspel, oljetemperatur och angreppspunkter för lagerkrafterna, vilka tillsammans uppgår till 47.5 % av den kombinerade standardosäkerheten i utmattningskraften. Därför, för att reducera den totala osäkerheten bör fokus ligga på lageregenskaperna. Givet alla standardosäkerheter i de analyserade parametrarna så uppgår förhållandet mellan standardosäkerheten i utmattningskraften och den förväntade utmattningskraften på löphjulet till 7 %. Detta motsvarar att förhållandet mellan standardosäkerheten i delskadan och väntevärdet för delskadan uppkommer till 35 %, givet ett index av S-N-kurvan på fem. Givet standardosäkerheten i kraften och index av S-N-kurvan, kan förhållandet mellan utmattningskraften förenad med en sannolikhet för överskridande, och den förväntade utmattningskraften, d.v.s. kvoten av utmattningskraften, utvärderas. Detta resulterar att kvoten av utmattningskraften uppgår till 1.32 för en sannolikhet för överskridande på 0.0032 %, 1.09 för en sannolikhet på 10 % och 1.04 för en sannolikhet på 30 %. Dessa sannolikheter motsvarar att kvoten av delskadan, d.v.s. kvoten mellan delskadan förenad med en sannolikhet för överskridande, och den förväntade delskadan uppgår till 4, 1.56 och 1.20. Därför kan osäkerheten i utmattningskraften påverka osäkerheten i delskadan med en betydande faktor, beroende på värdet på index av S-N-kurvan. Således, resultaten från denna studie påvisar betydelsen att beakta osäkerheterna i de ingående parameterna vid bedömning av utmattningslast. Dessa resultat tillhandahåller stöd vid bedömning av lastnivåer för dimensionering av löphjul, för att slutligen kunna erhålla en korrekt säkerhetsmarginal. Detta för att inte underskatta utmattningsskadan och därmed minska risken oför oväntat utmattningshaveri.

Cette thèse est consacrée au développement d’un outil de pré-dimensionnement par éléments finis pour l’estimation de l’endommagement par fatigue polycyclique de structures linéaires sous chargements multiaxiaux et stationnaires gaussiens. L’état de contraintes atteint dans ces structures étant aléatoire, il devient nécessaire de raisonner en terme de statistique et l’approche spectrale s’avère particulièrement adaptée pour cette situation. Dans ce travail, les méthodes spectrales sont améliorées par la prise en compte des largeurs de bande des spectres de réponses des structures soumises à des chargements nonproportionnels et de moyennes non nulles. Le critère d’endommagement de Sines est retenu. L’étude numérique de la distribution de l’endommagement résultant des incertitudes sur les paramètres matériaux et des applications dans le domaine de l’optimisation des structures sont également abordées. / This dissertation is devoted to the development of a finite element pre-designing tool for the estimation of high cycle fatigue damage for linear structure subject to multiaxial and Gaussian stationary loads. Given the random nature of the stress state, it becomes necessary to look at this problem from a statistical point of view and spectral methods appear to be the best approach. In this work, spectral methods are improved by taking into account the response spectral bandwidths of structures under non proportional and non zero mean loads; the Sines’ damage criterion is employed. The numerical analysis of the fatigue damage distribution resulting from the uncertainties of the material parameters and applications in the field of structural optimisation are also treated.