Dissertations / Theses on the topic 'Croissance des fissures de fatigue'
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Demulsant, Xavier. "Facteurs microstructuraux gouvernant l'amorçage et la croissance des fissures de fatigue dans les alliages de titane." Poitiers, 1994. http://www.theses.fr/1994POIT2367.
Full textHaddar, Nader. "Fatigue thermique d'un acier inoxydable austénitique 304L : simulation de l'amorçage et de la croissance des fissures courtes en fatigue isotherme et anisotherme." Phd thesis, École Nationale Supérieure des Mines de Paris, 2003. http://tel.archives-ouvertes.fr/tel-00005750.
Full textLa deuxième partie sintéresse au calcul de durées de vie. À travers une représentation énergétique des résultats, nous avons discuté la validité du modèle de durée de vie en nous basant sur une analyse assez simplifiée. Deux approches sont présentées, avec pour chaque cas une comparaison des durées de vie expérimentales aux durées de vie obtenus expérimentalement en fatigue isotherme à 90 et 165°C et en fatigue mécano-thermique. Le modèle de durée de vie retenu a été validé en fatigue isotherme à 90 et 165°C ainsi quen fatigue mécano-thermique.
Ouarabi, Mohand Ouramdane. "Influence de la fréquence de chargement sur la résistance à l'amorçage et la croissance des fissures de fatigue dans des aciers utilisés dans des applications mécaniques exigeantes." Thesis, Paris 10, 2018. http://www.theses.fr/2018PA100034.
Full textFatigue tests can be performed in a similar frequency range, but the higherfrequencies are generally preferable to reduce the test time and obtain results within areasonable time. The question remains whether a frequency effect exists. This study dealswith the effect of the loading frequency on fatigue strength and crack growth of 3 steels(M800HY, CP1000 and DP1180) used in automotive industry. Two load ratios (R = -1 and0.1) and five load frequencies (25 Hz, 30 Hz, 150 Hz and 20 kHz) were studied. First, weperformed dynamics finite element method to calculate the dimensions of the specimens(to vibrate with a resonance at 20 kHz), and, the stress intensity range as a function of the length of crack. Then, we have done some test on fatigue crack initiation and propagation. Whatever the loading frequency, the initiation of the fatigue crack is always on the surfacebecause of the stress concentrations due to the rolling process or the electro-galvanization.The observation with SEM of fracture surface of the specimens tested at 30 Hz and 20 kHzshows that the mode of propagation is transgranular with some locations of intergranularfailure or by cleavage on DP1180 grade. The fatigue striation on fracture surface arepresent on the M800HY and absent on the other two materials. The grade DP1180 has abetter resistance to the initiation and propagation of the crack. Regarding the effect ofloading frequency, overall the initiation of the fatigue crack is dependent on the loadingfrequency, however, the propagation is independent of the loading frequency
Lieurade, Henri-Paul. "Comportement mécanique et métallurgique des aciers dans le domaine de la fatigue oligocyclique étude des phénomènes et application à la croissance des fissures /." Metz : Université de Metz, 2008. ftp://ftp.scd.univ-metz.fr/pub/Theses/1978/Lieurade.Henri_Paul.SMZ7805.pdf.
Full textUribe, Suarez Diego Alejandro. "Combinaison d’éléments cohésifs et remaillage pour gérer la propagation arbitraire du chemin de fissure : des matériaux fragiles à l’analyse de fatigue thermique des petits corps du système solaire." Thesis, Université Côte d'Azur, 2021. http://www.theses.fr/2021COAZ4047.
Full textThe present PhD thesis aims at providing a better modeling of fracture phenomenon in brittle materials, with special attention focused on fracture processes taking place in astronomical bodies. One of the most challenging issues in computational fracture mechanics is the propagation of a crack through a finite element mesh for arbitrary crack paths. In this work, this problem is approached by means of an advanced remeshing technique that propagates a crack using cohesive elements through arbitrary directions (mesh-independent). The crack direction is computed using the maximal energy release rate criterion which is implemented using finite elements and the Gθ method. The effects of different numerical and physical parameters regarding the crack path and fracture energy have been investigated. Even though it has been shown that temperature cycles on airless bodies of our Solar System can cause damaging of surface materials (Thermal cracking), propagation mechanisms in the case of space objects are still poorly understood. Thermal cracking of surface rocks, in addition to the impact of micrometeorties, can eventually lead to rocks’ breakup and produce fresh regolith, the latter being the layer of unconsolidated material that covers planetary surfaces. For this reason, the present work combines a thermoelasticity model together with linear elastic fracture mechanics theory to predict fracture propagation in the presence of thermal gradients generated by diurnal temperature cycling and under conditions similar to those existing on asteroid (101955) Bennu. Using the implemented methodologies, it is found that in asteroid Bennu, cracks preferentially propagate in the North to South (N-S), in the North-East to South-West (NE-SW) and in the North-West to South-East (NW-SE) directions. Finally, thermal fatigue analysis was performed in order to estimate the crack growth rate.Aforementioned methodologies have been implemented in Cimlib, a C++ in-house finite element library developed at CEMEF. Inside Cimlib, a methodology allowing two-dimensional crack propagation through arbitrary directions with the option of handling multiple cracks in the domain and inside a parallel environment was developed. Regarding three-dimensional scenario, a first approach where a crack front was propagated through an arbitrary direction was achieved. Concerning numerical modeling of crack propagation, the developed framework opens new possibilities for various applications such as composites cracking at the meso-scale
Didych, Iryna. "Estimation of structural integrity and lifetime of important structural elements." Electronic Thesis or Diss., Université Clermont Auvergne (2021-...), 2021. http://www.theses.fr/2021UCFAC116.
Full textThis work has been performed under co-tutelle supervision between Ternopil IvanPuluj National Technical University in Ternopil (Ukraine) and UniversityClermont Auvergne, CNRS, SIGMA Clermont, Institut Pascal in Clermont-Ferrand (France).This thesis solves the scientific task of responsible structural elements strength andlifetime evaluation. The aim of the thesis is to evaluate the strength and residuallifetime of structural elements by machine learning methods.Most parts of machines and structural elements while being in service are under theinfluence of loads of various nature. Such forces are applied either directly to theelement or transmitted through neighbor elements connected to it. For the normaloperation of the responsible structures parts, each element must have certain sizeand shape that will withstand the loads acting on it. In particular, it must haveappropriate strength properties, not deform significantly under the action ofstresses, be rigid, and preserve its original shape.The calculated residual lifetime of machines and structures can be predicted usingfatigue crack growth (FCG) diagrams. Often, the experimental data have a certainspread, which should be taken into account in their analysis. The experimentalmethod often takes a lot of time and human resources. Therefore, it is advisable tolearn how to calculate the residual lifetime using machine learning methods,particularly, neural networks, boosted trees, random forests, support-vectormachines and the method of k–nearest neighbors
Tamine, Tawfik. "Amorçage de fissures par fatigue-contact." Metz, 1994. http://docnum.univ-lorraine.fr/public/UPV-M/Theses/1994/Tamine.Tawfik.SMZ9418.pdf.
Full textThe present thesis is a contribution to the knowledge of the shelling process caused by a contact fatigue. This phenomenon appears under a surface submitted to a quasi punctual loading and initiates at an inclusion which is the most probable site for crack initiation. The direction of propagation is associated with the stress distribution resulting from a complex loading. To understand this phenomenon, we present : a bibliographical study to collect the different works related to stress concentration, crack initiation criteria and the stress distribution in the vicinity of a defect. An experimental study for the simulation of crack initiation under the three modes of loading. A finite element calculation from which we have derived new initiation criteria. We have shown that they best fit the experimental results by comparison with those given in the literature
TAMINE, TAWFIK Pluvinage Guy. "AMORCAGE DE FISSURES PAR FATIGUE CONTACT /." [S.l.] : [s.n.], 1994. ftp://ftp.scd.univ-metz.fr/pub/Theses/1994/Tamine.Tawfik.SMZ9418.pdf.
Full textBignonnet, André. "Sur la propagation des fissures de fatigue." Paris, ENSAM, 1991. http://www.theses.fr/1991ENAM0021.
Full textNguedjio, Fouepe Calvin. "Amorçage des fissures de fatigue et probabilisation." Compiègne, 1989. http://www.theses.fr/1989COMPD196.
Full textZeghloul, Abderrahim. "Comparaison de la propagation en fatigue des fissures courtes et des fissures longues." Grenoble 2 : ANRT, 1988. http://catalogue.bnf.fr/ark:/12148/cb37619253w.
Full textCortet, Pierre-Philippe. "Croissance lente de fissures : de la fragilité à la complexité." Phd thesis, Ecole normale supérieure de lyon - ENS LYON, 2007. http://tel.archives-ouvertes.fr/tel-00162873.
Full textDesforges, Jean-Robert. "Propagation en fatigue des fissures courtes dans les alliages d'aluminium." Poitiers, 1996. http://www.theses.fr/1996POIT2293.
Full textNguyen, Hoang-Phuong. "Model-based and data-driven prediction methods for prognostics." Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPASC021.
Full textDegradation is an unavoidable phenomenon that affects engineering components and systems, and which may lead to their failures with potentially catastrophic consequences depending on the application. The motivation of this Thesis is trying to model, analyze and predict failures with prognostic methods that can enable a predictive management of asset maintenance. This would allow decision makers to improve maintenance planning, thus increasing system availability and safety by minimizing unexpected shutdowns. To this aim, research during the Thesis has been devoted to the tailoring and use of both model-based and data-driven approaches to treat the degradation processes that can lead to different failure modes in industrial components, making use of different information and data sources for performing predictions on the degradation evolution and estimating the Remaining Useful Life (RUL).The Ph.D. work has addressed two specific prognostic applications: model-based prognostics for fatigue crack growth prediction and data-driven prognostics for multi-step ahead predictions of time series data of Nuclear Power Plant (NPP) components.Model-based prognostics relies on the choice of the adopted Physics-of-Failure (PoF) models. However, each degradation model is appropriate only to certain degradation process under certain operating conditions, which are often not precisely known. To generalize this, ensembles of multiple degradation models have been embedded in the model-based prognostic method in order to take advantage of the different accuracies of the models specific to different degradations and conditions. The main contributions of the proposed ensemble of models-based prognostic approaches are the integration of filtering approaches, including recursive Bayesian filtering and Particle Filtering (PF), and novel weighted ensemble strategies considering the accuracies of the individual models in the ensemble at the previous time steps of prediction. The proposed methods have been validated by case studies of fatigue crack growth simulated with time-varying operating conditions.As for multi-step ahead prediction, it remains a difficult task of Prognostics and Health Management (PHM) because prediction uncertainty tends to increase with the time horizon of the prediction. Large prediction uncertainty has limited the development of multi-step ahead prognostics in applications. To address the problem, novel multi-step ahead prediction models based on Long Short- Term Memory (LSTM), a deep neural network developed for dealing with the long-term dependencies in the time series data have been developed in this Thesis. For realistic practical applications, the proposed methods also address the additional issues of anomaly detection, automatic hyperparameter optimization and prediction uncertainty quantification. Practical case studies have been considered, concerning time series data collected from Steam Generators (SGs) and Reactor Coolant Pumps (RCPs) of NPPs
Malesys, Nicolas. "Modélisation probabiliste de formation de réseaux de fissures de fatigue thermique." Phd thesis, École normale supérieure de Cachan - ENS Cachan, 2007. http://tel.archives-ouvertes.fr/tel-00319993.
Full textMalésys, Nicolas. "Modélisation probabiliste de formation de réseaux de fissures de fatigue thermique." Cachan, Ecole normale supérieure, 2007. http://tel.archives-ouvertes.fr/tel-00319993/fr/.
Full textThermal superficial crack networks have been detected in mixing zone of cooling system in nuclear power plants. Numerous experimental works have already been led to characterize initiation and propagation of these cracks. The random aspect of initiation led to propose a probabilistic model for the formation and propagation of crack networks in thermal fatigue. In a first part, uniaxial mechanical test were performed on smooth and slightly notched specimens in order to characterize the initiation of multiple cracks, their arrest due to obscuration and the coalescence phenomenon by recovery of amplification stress zones. In a second time, the probabilistic model was established under two assumptions : the continuous cracks initiation on surface, described by a Poisson point process law with threshold, and the shielding phenomenon which prohibits the initiation or the propagation of a crack if this one is in the relaxation stress zone of another existing crack. The crack propagation is assumed to follow a Paris’ law based on the computation of stress intensity factors at the top and the bottom of crack. The evolution of multiaxial cracks on the surface can be followed thanks to three quantities : the shielding probability, comparable to a damage variable of the structure, the initiated crack density, representing the total number of cracks per unit surface which can be compared to experimental observations, and the propagating crack density, representing the number per unit surface of active cracks in the network. The crack sizes distribution is also computed by the model allowing an easier comparison with experimental results
Malésys, Nicolas. "Modélisation probabiliste de formation de réseaux de fissures de fatigue thermique /." Gif-sur-Yvette : CEA Saclay, Direction des systèmes d'information, 2008. http://catalogue.bnf.fr/ark:/12148/cb413925972.
Full textNotice réd. d'après la couv. La couv. porte en plus : "Direction de l'énergie nucléaire, Direction des activités nucléaires de Saclay" Bibliogr. p. 171-177. Résumé en français et en anglais.
Noyel, Jean-Philippe. "Analyse de l’initiation de fissures en fatigue de contact : Approche mésoscopique." Thesis, Lyon, INSA, 2015. http://www.theses.fr/2015ISAL0126/document.
Full textContact fatigue is the predominant mode of failure of components subjected to a repeated contact pressure, like rolling element bearings or gears. This phenomenon is known as rolling contact fatigue (RCF). A large number of models have been developed to predict RCF, but there is today no complete predictive life model, and understanding RCF failure mechanism remains a significant challenge. RCF failure mechanisms are known to be very sensitive to a large number of parameters linked to contact conditions (roughness, lubrication) or materials (inclusions, gradients properties, residual stresses…). To improve knowledge about the influence of these parameters on failure mechanisms and life, a numerical model is developed to simulate the progressive damage of a component subject to rolling contact fatigue. Mechanisms associated with the initiation stage of failure process are located at a scale lower than the macroscopic scale. The proposed approach is to develop a grain level model (mesoscopic scale) in order to focus on initiation mechanisms. A Voronoi tessellation is used to represent the material microstructure. The progressive deterioration is simulated by applying the concept of damage mechanics at grain boundaries represented by cohesive elements. This approach has been first applied to a 2D isotropic model. The numerical behaviour of cohesive elements has been investigated: the influence of cohesive stiffness has been analysed and singularities at the triple junctions has been highlighted. The representativeness of the original model was improved by modelling crystal anisotropy. A cubic elasticity model was used to represent the behaviour of grains. Finally, a thorough analysis of the application of the damage concept at grain boundaries highlighted that the initial formulation results in a very low influence of the damage on the intergranular shear stress. A new formulation leading to a direct influence of the damage on the intergranular shear stress has been proposed. This new formulation has resulted in (i) a change in the distribution of micro-cracks, with coalescence between the different micro-cracks, and (ii) a large increase in the RCF life estimated by the model. The order of magnitude of the number of cycles corresponding to the first micro-cracks is comparable to that given by experiments
Biavant, Guerrier Kristell Le. "Etude de l'amorçage de fissures de fatigue dans le Ti-6A1-4V." Châtenay-Malabry, Ecole centrale de Paris, 2000. https://tel.archives-ouvertes.fr/tel-00466425.
Full textCoppin, Patrick. "Amorçage et propagation des fissures courtes de fatigue dans des alliages aluminium-lithium." Châtenay-Malabry, Ecole centrale de Paris, 1991. http://www.theses.fr/1991ECAP0203.
Full textLesne, Pierre-Marie. "Amorçage et propagation de fissures sous gradients thermiques cycliques." Lille 1, 1985. http://www.theses.fr/1985LIL10111.
Full textLe, Biavant-Guerrier Kristell. "Etude de l'amorçage de fissures de fatigue dans le Ti-6Al-4V." Phd thesis, Ecole Centrale Paris, 2000. http://tel.archives-ouvertes.fr/tel-00466425.
Full textSeyedi, Seyed Mohammad. "Formation, propagation et coalescence dans un réseau de fissures en fatigue thermique." Phd thesis, École normale supérieure de Cachan - ENS Cachan, 2004. http://tel.archives-ouvertes.fr/tel-00133778.
Full textAmargier, Rémi. "Amorçage de fissures et gradient de contrainte en fretting et en fatigue." Phd thesis, Ecole Centrale de Lyon, 2011. http://tel.archives-ouvertes.fr/tel-00728236.
Full textSalapete, Raphael. "Propagation des fissures de fatigue dans les culasses automobiles : expériences et modélisation." Paris, ENMP, 2012. http://www.theses.fr/2007ENMP1566.
Full textJiang, Zhen Dong. "Modélisation numérique de l'intéraction mécanique entre fissures parallèles et application en fatigue." Poitiers, 1991. http://www.theses.fr/1991POIT2288.
Full textToumi, Ahmed. "Etude du processus de propagation de fissures par fatigue dans le beton." Toulouse 3, 1998. http://www.theses.fr/1998TOU30197.
Full textSeyedi, Seyed Mohammad. "Formation, propagation et coalescence dans un réseau de fissures en fatigue thermique /." Cachan : LMT-Cachan, 2004. http://catalogue.bnf.fr/ark:/12148/cb39914632m.
Full textDenarié, Emmanuel. "Etude expérimentale des couplages viscoélasticité-croissance des fissures dans les bétons de ciment /." [S.l.] : [s.n.], 2000. http://library.epfl.ch/theses/?nr=2195.
Full textAncelet, Olivier. "Etude de l'amorçage et de la propagation des fissures sous chargement thermique cyclique 3D." Poitiers, 2005. http://www.theses.fr/2005POIT2308.
Full textThe incident which has occurred on the Civaux power plant has shown the nocivity of thermal loading and the difficulty to take into account at design level. The objective of this paper is to study the initiation and the propagation of crack under thermal loading. In this aim the CEA developed a new experiment named FAT3D. The various experiments carried out showed the harmfulness of a thermal loading, which makes it possible to rapidly initiate a network of cracks and to propagate one (or some) cracks through the totally thickness of the component under certain conditions. These experimental results associated with a mechanical analysis put at fault the usual criteria of damage based on the variations of the equivalent strain. In addition, the study of the propagation stage shows the importance of the plasticity which, in the case of a thermal loading, slows down the propagation of the crack
Trollé, Benoît. "Simulation multi-échelles de la propagation des fissures de fatigue dans les rails." Thesis, Lyon, INSA, 2014. http://www.theses.fr/2014ISAL0033.
Full textTo optimize the rail grinding strategy, the prediction of crack growth rates has a vital role. Contact, with friction between the crack faces, notably occurs in rolling contact fatigue (RCF) problems. These time-dependent, multi-axial, non proportional loadings may lead to a crack initiation and propagation, and sometimes to the development of very complex 3D crack network. Numerical simulations of frictional fatigue crack are efficiently performed using the eXtended Finite Element Method (X-FEM). Within this method, the mesh does not need to conform to the crack geometry. Most difficulties associated to complex mesh generation around the crack and the re-meshing steps during the propagation are hence avoided. A 3D two-scale frictional contact fa-tigue crack model developed within the X-FEM framework is presented. It allows the use of a refined discretization of the crack interface independent from the underlying finite element mesh and adapted to the frictional contact crack scale. The model is used here to analyze the crack propagation, rate and direction, under rolling contact fatigue. The wheel-rail contact loading is modeled as a traveling hertzian load. The stress intensity factors are computed at the crack tips during the wheel passage. Criteria for determining crack growth direction under multiaxial non proportional conditions and mixed mode Paris’ law are used. Actual residual stresses are accounted for in the simulation. They are determined thanks to a dedicated model used at SNCF in which the asymptotic mechanical state of the rail is computed when submitted to cyclic loads. A non-uniform elastic-plastic stabilized state is calculated and introduced, by projection of the mechanical fields onto the finite element mesh, in the crack propagation simulation. All this strategy has been implemented in CAST3M and is now used to model 3D frictional crack growth under RCF
Benguediab, Mohamed. "Etude de propagation des fissures de fatigue sous spectres de chargement réduitsTexte imprimé." Poitiers, 1989. http://www.theses.fr/1989POIT2298.
Full textJohnson, Philippe. "Propagation des fissures en fatigue par chocs : développement d'une méthodologie et étude experimentale." Vandoeuvre-les-Nancy, INPL, 1989. http://www.theses.fr/1989NAN10415.
Full textOni, Olorunnisola. "Contribution à l'étude des fissures courtes se propageant en fatigue dans les aciers." Compiègne, 1986. http://www.theses.fr/1986COMPI214.
Full textOni, Olorunnisola. "Contribution à l'étude des fissures courtes se propageant en fatigue dans les aciers." Grenoble 2 : ANRT, 1986. http://catalogue.bnf.fr/ark:/12148/cb37600148n.
Full textChevalier, Jérôme. "Etude de la propagation des fissures dans une zircone 3Y-TZP pour applications biomédicales." Lyon, INSA, 1996. http://www.theses.fr/1996ISAL0129.
Full textThe Slow Crack Growth (SCG) behavior of different 3Y-TZP is investigated under bath static and cyclic solicitations, in different media, by the double torsion method and by flexural tests on indented bars. After a preliminary study of the testing methods themselves (validity conditions), we have studied the materials properties. Crack propagation under static conditions is related to stress corrosion at the crack tip by water molecules. Indeed, crack propagation is limited under vacuum conditions and accelerated in water. A typical three stage law is obtained in air, with the presence of a well-defined threshold under which no propagation occurs. An activation energy of about 70 KJ/mol. Has been calculated by measurements from crack velocity measurements from 3°C to 85°. The role of crack tip phase transformation on crack propagation has been investigated. It appears that 3Y-TZP with the largest grain size exhibit the best resistance to crack propagation as a direct consequence of transformation toughening. Crack propagation under cyclic conditions is due to stress corrosion assisted by mechanical degradation. Crack velocity are one or two order of magnitude higher under cyclic fatigue than that predicted by SCG laws under static fatigue as a consequence of crack bridging and/or crack tip shielding degradation. A stress intensity factor threshold is still observed under cyclic solicitations. Its value depends on the loading conditions and the amount of crack tip degradation
Jung, Olivier. "Influence du grenaillage sur la propagation des fissures." Poitiers, 1997. http://www.theses.fr/1997POIT2315.
Full textLebaillif, David. "Fissuration en fatigue des structures mécano-soudées soumises à un environnement mécanique complexe." Phd thesis, Université Blaise Pascal - Clermont-Ferrand II, 2006. http://tel.archives-ouvertes.fr/tel-00695047.
Full textAlexandre, Franck. "Aspects probabilistes et microstructuraux de l'amorçage des fissures de fatigue dans l'alliage Inco 718." Phd thesis, École Nationale Supérieure des Mines de Paris, 2004. http://tel.archives-ouvertes.fr/tel-00161472.
Full textJunet, Arnaud. "Étude tridimensionnelle de la propagation en fatigue de fissures internes dans les matériaux métalliques." Thesis, Lyon, 2021. http://www.theses.fr/2021LYSEI006.
Full textFatigue is the main phenomenon causing the failure of mechanical structures. For very long service lives the initiation of cracks leading to the failure of in service mechanical parts changes from surface to volume. Due to experimental difficulties the propagation of internal cracks has only been studied to a limited extent in situ and in 3D. However, it is crucial from a dimensional point of view to know the behaviour of such cracks. In this work, in situ monitoring of the initiation and propagation of internal cracks was carried out by X-ray tomography (synchrotron source). Firstly, a method for manufacturing specimens was developed to enable systematic, non-destructive, and 3D visualization of the propagation of internal cracks in a titanium alloy (Ti-6Al-4V) at 20 Hz. For this purpose, an artificial defect was drilled on the surface of a rolled sheet of this material. A second sheet, placed on top of the first one, was diffusion bonded by spark plasma sintering, making it possible to make the defect volumetric. In situ fatigue tests showed the crucial role of the environment (vacuum) and, to a lesser extent, that of the crystallographic texture on the internal crack propagation rates. Secondly, an ultrasonic fatigue machine (cycling frequency of 20 kHz) allowing in situ testing at the synchrotron was used to study the 3D propagation of internal cracks in A357-T6 aluminium alloy specimens containing an artificial internal defect. The 3D grain distribution obtained by Diffraction Contrast Tomography (DCT) was used to study the interaction mechanisms between the microstructure and the 3D crack path
Erny, Carole. "Prévision de l'amorçage de fissures de fatigue dans des assemblages soudés pour applications navales." Brest, 2010. http://www.theses.fr/2010BRES2063.
Full textShip structures are usually built by using welding process and are submitted to some variable and complex loadings. The welding process induces specific geometries at the weld toe where local stress concentrations are generated and also creates various mechanical properties in the heat affected zone. Accordingly, welded joints could be a critical area for fatigue damage. In a previous work, a methodology to predict fatigue life has been developed and tested on butt-welded joints. To go further, the present work focuses on more complex assemblies in order to validate this strategy and be able to estimate the fatigue life of representative ship structures. First, the methodology consists of the elastic shakedown study of the structure and then of a post-treatment which predicts the fatigue crack initiation. A comparison between experimental and numerical results is proposed in order to present the accuracy of the proposed strategy to predict fatigue life time of welded assemblies typical of shipbuilding applications
Welsch, Markus Theodor. "Formation des micro fissures aux joints des grains : influence de l'orientation sur les contraintes locales et sur la formation des micro fissures." Thesis, Metz, 2011. http://www.theses.fr/2011METZ044S.
Full textFor the case of damaging the anisotropic elastic material behaviour causes additional stresses due to elastic misalignments and the local orientation differences at boundary surfaces. These additional stresses can act as additional driving force for the local damage process. The amount of these additional stresses is strongly dependent on the alignment of the grain boundary with respect to the loading direction and the orientation difference between the two adjacent grains. The influence of microstructural inhomogeneities on the local stresses within the boundary areas during bending and fatigue was investigated by experiments and simulations of Fe-3%Si and Ni specimen. The alignment of the grain boundaries was measured by optical microscopy (LM) and the local crystallographic orientations by electron backscatter diffraction (EBSD). The use of this data for three-dimensional finite element method calculations (FEM) for specimens close to reality obtained as a result, the places with the highest incompatibility stresses at grain boundaries. The use of electron channelling contrast imaging (ECCI) enables to observe characteristics in the dislocation structures at these specific positions and permits to reproduce the damage evolution up to the crack propagation. The nanoindentation technique (NI) and for the first time the magnetic force microscopy (MFM) were both adopted in addition to the local characterization with the objective to contribute to the understandings of crack initiation and crack propagation
Bei der Schädigung bedingen die lokalen Orientierungsunterschiede an Grenzflächen und das anisotrop-elastische Materialverhalten durch elastische Fehlpassungen Zusatzspannungen. Diese können als zusätzliche treibende Kraft für die lokalen Schädigungsvorgänge wirken. Die Stärke der Zusatzspannungen hängt stark von der Lage der Korngrenze in Bezug zur Belastungsrichtung und dem Orientierungsunterschied der angrenzenden Körner ab. Der Einfluss von Inhomogenitäten auf die lokalen Spannungen im Bereich der Grenzflächen bei Biegung und Ermüdung wurde mittels Experimenten und Simulationen an Proben aus Fe-3%Si und Ni untersucht. Die Lage der Korngrenzen wurde durch Lichtmikroskopie (LM) und die lokale kristallographische Orientierung durch Electron Backscatter Diffraction (EBSD) gemessen. Die Nutzung dieser Daten für dreidimensionale Finite-Elemente-Methode-(FEM)-Rechnungen der lokalen Spannungen realitätsnaher Proben ergibt als Ergebnis die Orte mit den höchsten Inkompatibilitätsspannungen an Korngrenzen an. Mittels Electron Channelling Contrast Imaging (ECCI) konnten an diesen Orten Besonderheiten in den Versetzungsstrukturen festgestellt werden, und der Schädigungsverlauf bis zum Risswachstum nachvollzogen werden
Le, Gorju Jago Karine. "Influence de la cristallisation sous contrainte sur l'endurance et la propagation des fissures de fatigue dans les élastomères." Châtenay-Malabry, Ecole centrale de Paris, 1998. http://www.theses.fr/1998ECAP0699.
Full textCerveny, Radim. "Etude de la propagation des fissures de fatigue dans l'alliage d'aluminium 7010-T7651 : fermeture et influence de la microstructure et de la géométrie des éprouvettes." Châtenay-Malabry, Ecole centrale de Paris, 1994. http://www.theses.fr/1994ECAP0368.
Full textAgbessi, Komlan. "Approches expérimentales et multi-échelles des processus d'amorçage de fissures en fatigue sous chargements complexes." Phd thesis, Paris, ENSAM, 2013. http://pastel.archives-ouvertes.fr/pastel-00867947.
Full textLamacq, Valérie. "Amorcage et propagation de fissures de fatigue sous conditions de fretting : Approches theorique et experimentale." Lyon, INSA, 1997. http://www.theses.fr/1997ISAL0037.
Full textThis research work aimed to understand and then model, at a macroscopic scale, the mechanisms governing cracking under Fretting Fatigue loading on a Pre-Stressed sample (FFPS). Cracks are thus submitted to mixed mode and Non Proportional Conditions (NPC). The classical concepts of the Elastic Linear Fracture Mechanic can hardly account for these conditions. It was then necessary to propose a new approach. That is why, an experimental and a theoretical approach were conducted in parallel. Two experimental complementary sets of tests were conducted to study cracking under FFPS. Firstly, three aeronautical aluminum alloys were tested. Experimental observations were performed at the end of each test through a destructive manner. The surface degradations were first related to the applied running conditions. Then, crack location and propagation directions during stage I and II were defined. The second experimental set of tests was conducted on photoelastic samples. The evolution of the isochromatic fringe pattern along crack faces was directly observed during test. It informed us on crack behaviour and displacements during loading cycles. Crack initiation and propagation were also directly recorded. Thanks to the analysis of crack growth rate curves and observations of crack face feature, different propagation stages were defined under FFPS. The aim of the theoretical approach was to identify the macroscopic parameters governing crack life under FFPS. First of all, initiation and propagation mechanisms during stage I were defined and analysed. Crack location in or out the contact area and the corresponding initial crack growth directions were predicted under various fretting conditions. The conditions governing crack transition from stage I to stage II were then defined. Finally, propagation modes and directions during stage II were determined. In order to account for the NPC, a criterion adapted to the loading conditions and material was selected. This first analysis was then completed by analysing the stress field at the crack tip. Crack propagation modes were then clearly identified under FFPS
Baietto, Marie-Christine. "Le contact unilatéral avec frottement le long de fissures de fatigue dans les liaisons mécaniques." Lyon, INSA, 1989. http://www.theses.fr/1989ISAL0088.
Full textZhang, Xiao Ping. "Modélisation de la vitesse de propagation des fissures de fatigue sous chargement à amplitude variable." Vandoeuvre-les-Nancy, INPL, 1991. http://www.theses.fr/1991INPL087N.
Full textGérard, Nicolas. "Etude du comportement des fissures courtes au fond d'une entaille mécanique sous sollicitation en fatigue." Tours, 2003. http://www.theses.fr/2003TOUR4029.
Full textGibert, Gaël. "Propagation de fissures en fatigue par une approche X-FEM avec raffinement automatique de maillage." Thesis, Lyon, 2019. http://www.theses.fr/2019LYSEI088.
Full textTo guarantee the high level of safety of industrial components under fatigue cycles it is essential to be able to predict the initiation and growth of cracks during their entire lifetime. However the numerical cost of a propagation simulation on engineer-sized problems with non-linear behavior may be prohibitive, with the classical techniques. Here, a new approach combining the eXtended Finite Element Method (X-FEM) and automatic Adaptive Mesh Refinement (AMR) is presented taking advantage of both methods. The X-FEM, developed over the past two decades by a large community, have proven its efficiency to handle evolving discontinuities in a variety of fracture analysis. Since this method enables to describe the crack and its propagation independently of the mesh of the structure, a simple hierarchical mesh refinement procedure can be applied. Automatic adaptive re-meshing is a valuable method for elastic-plastic crack propagation analysis since it permits a locally fine mesh and then an accurate description of physical quantities in a limited area around the crack front. This is particularly important when local fracture criteria are concerned. Moreover local refinement saves computational effort, particularly when the propagation path is not a priori known. In the present work, it is shown that both methods combine with minimal effort: the kinematic continuity relations and the field transfer process, needed for history-dependent material, must include in a proper way the enrichment of the model. If this requirement is not fulfilled, numerical error may be introduced. Implementation of this combined X-FEM/AMR approach in the finit elements code Cast3M is presented in detail. In particular, an innovative field transfer strategy is proposed in 2D and 3D. Numerical applications of crack propagation in elastic-plastic media demonstrate accuracy, robustness and efficiency of the technique. Moreover, an experimental study has been conducted on a example propagation with notable impact of confined plasticity. This study provides experimental data to compare with the numerical results obtained with the developed method. This validates our modelization choices. It also is the opportunity to test the developed method robustness on a realistic case of utilization. This study showed the interest of the proposed modelization taking into account plasticity induced crack closure during the fatigue propagation