Дисертації з теми "Matériaux hybrides – Contraintes (mécanique) – Endommagement, Mécanique de l' (milieux continus)"
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Miot, Stéphanie. "Rupture de structures composites stratifiées sous chargements statique et de fatigue." Aix-Marseille 1, 2009. http://www.theses.fr/2009AIX11016.
Повний текст джерелаRecent developments in the aeronautics industry have accelerated interest in the use of composites as primary structural materials. This project is based on a collaboration with Eurocopter. The objectives are to experimentally analyse and model the behaviour until failure of laminated composite structures under static and fatigue loadings. To describe the mechanical behaviour of composite materials, several damage mechanisms have to be considered. A model, based on the Continuum Damage Mechanics and recently developed at the LMA, takes into account the effects of transverse and shear damages characterized by the creation of small cracks which run along the fibres. This model was integrated into Abaqus/Standard in order to study the behaviour of laminated structures under static and fatigue loadings. The comparisons between experimental data and numerical simulations have proved that conventional failure criteria do not work if the strain field is inhomogeneous. A non local approach, based on the definition of a Fracture Characteristic Volume, has been developed. This method takes into account the effects of stress concentrations on the failure of laminated structures. Comparisons with experimental data allows to valid thebehaviour model associated to the non local approach for various materials, laminates and geometries in the case of static loading conditions. The application in the case of fatigue loading is in progress and first results are promising
Chihi, Manel. "Étude des performances d’un composite carbone/époxy dopé par des nanocharges sous des sollicitations sévères." Electronic Thesis or Diss., Brest, École nationale supérieure de techniques avancées Bretagne, 2021. http://www.theses.fr/2021ENTA0017.
Повний текст джерелаThis thesis work was carried out in a context of valorization of composite materials based on nanofillers. The knowledge of the mechanical behavior of nanocomposites doped by nanofillers submitted to high dynamic loading is an important data for the designers of composite structures dedicated to civil and military applications. This behavior must be characterized in a wide range of deformation; for strain rates in the range of 10² to 10⁵s⁻¹. Particular attention is devoted to the Hopkinson pressure bar system (SHPB) because of its frequent use in such a wide range of deformation which corresponds to the strain rate deformation range of most industrial applications. In this context, we first conducted a study focused on the effect of nanofillers on the dynamic behavior and damage kinetics of a carbon/epoxy composite. We have chosen two types of nanofillers with similar chemical compositions (based on pure carbon) but two different geometries (quasi-1D for carbon nanotubes (CNT) and 2D for graphene nanoplatelets (GNP). The two series of nanocomposites CNT and GNP were prepared under the same conditions while using common mass fractions (0.5%, 1% and 2%) in order to conduct a comparative study of the two nanocomposite systems. A dynamic compression test (in-plane (IP) and out-of-plane (OP)) and a numerical study were conducted. It has been shown that the dynamic behavior and damage kinetics of the materials are very sensitive to the strain rate and the direction of solicitation. The results of these tests also allowed us to understand the influence of the addition of nanofillers on the response of the materials. The percentage of 1% GNP shows optimal performances in stiffness, maximum stress and resistance to damage. However, nanocomposites can be very sensitive to environmental conditions, in particular to hygrothermal aging that can reduce the mechanical performances. Therefore, the effect of hygrothermal aging (60°C/80%RH) on the lifetime of nanocomposites is studied experimentally (in-plane loading). Decreases of different mechanical properties as a function of time (15, 40 and 100 days) and absorbed water content are highlighted for each mass fraction. However, it was shown that the introduction of nanofillers, except in the case of 0.5% CNT, leads to a more significant degradation of the reference composite
Millot, Thierry. "Etude d'un essai original de flexion-torsion 4 points et application à la modélisation du comportement des matériaux composites en contraintes complexes." Besançon, 1990. http://www.theses.fr/1990BESA2051.
Повний текст джерелаKarami, Mohammad Hassan. "Etude expérimentale du comportement poromécanique d'une roche endommageable." Lille 1, 1998. https://pepite-depot.univ-lille.fr/LIBRE/Th_Num/1998/50376-1998-147.pdf.
Повний текст джерелаGérard, Nicolas. "Etude du comportement des fissures courtes au fond d'une entaille mécanique sous sollicitation en fatigue." Tours, 2003. http://www.theses.fr/2003TOUR4029.
Повний текст джерелаWeber, Bastien. "Fatigue multiaxiale des structures industrielles sous chargement quelconque." Lyon, INSA, 1999. http://theses.insa-lyon.fr/publication/1999ISAL0056/these.pdf.
Повний текст джерелаThe work of thesis deals with multiaxial fatigue. Its purpose is the fatigue life assessment of industrial structures submitted to any kind of solicitations, from the most basic case, which is uniaxial and periodical, to the most general one, which is multiaxial and of variable amplitude. The first part is dedicated to the study of multiaxial fatigue stress-based criteria. 37 criteria issued from the literature are analysed. They are divided into empirical, critical plane and global approaches. 24 criteria are validated through 233 multiaxial fatigue tests issued also from the literature. The second part aims at taking into account the stress gradient effect within the multiaxial criteria formulation. Similarly to some recent work, the stress gradient effect is introduced within the Laboratory's criteria. These propositions are validated through combined bending-torsion tests. A proposition is made to calculate the stress gradient field from finite elements results obtained over any complex industrial structure. The third part describes the evolution of the Laboratory's fatigue life prediction method under multiaxial random loading. The first step presents a plane per plane damage accumulation. The fatigue damage is calculated and cumulated on physical planes. The second step shows the influence of the so-called counting variable on the fatigue life prediction results, and leads to a new concept: the cycle counting and the damage assessment are performed plane per plane. This procedure avoids the dependence of the choice of the counting on the life assessments. A critical plane approach criterion is required for these latter methods. This work is integrated to an industrial software called Sollife allows one to simulate the fatigue behaviour of any complex structure. The first results are in good assessment with experiments. They show the important effect of metal forming process (as stamping) and result in lots of perspectives
Scida, Daniel. "Étude et modélisation du comportement mécanique de matériaux composites à renforts tisses hybrides et non hybrides." Compiègne, 1998. http://www.theses.fr/1998COMP1168.
Повний текст джерелаEl, Hage Christiane. "Modélisation du comportement élastique endommageable de matériaux composites à renfort tridimensionnel." Compiègne, 2006. http://www.theses.fr/2006COMP1642.
Повний текст джерелаThis thesis is dedicated to the modelling of the elastic damage behaviour composite material 3D reinforced. The study is articulated around three essential points: the comprehension of the damage process, analytical modelling and the optimization of architectures of the reinforcements. The studies of carbon architectures are resulting from an orthogonal weaving 3D and 5 Interlock. They are subjected respectively to compression and uniaxial tension tests. The correlation between signals of acoustic emission and the microscopic observations makes it possible to emphasize the effect of architecture on the phenomena of damages. The elastic damage behaviour until the rupture is described with a duality between an analytical model of homogenization and the criterion 3D of Tsai-Wu, coupled to damage criteria. This model takes into account the geometrical characteristic of architectures of the reinforcements. The optimization part is dedicated to minimization of the REV
Risbet-Voitot, Marion. "Influence de l'état métallurgique et d'un gradient de contraintes sur le critère d'endurance (critère de Dang Van) d'un superalliage à base nickel." Compiègne, 2002. http://www.theses.fr/2002COMP1436.
Повний текст джерелаVu, Anh Thang. "Endommagement de stratifiés aéronautiques à fibre de carbone et matrice polymère soumis à des chargements monotones ou cycliques à plusieurs températures : expériences et modélisation." Chasseneuil-du-Poitou, Ecole nationale supérieure de mécanique et d'aéronautique, 2009. http://www.theses.fr/2009ESMA0009.
Повний текст джерелаThe main objective of this study is to investigate the transverse cracking kinetics in [0m/90n]S cross-ply laminates made of IM7/977-2 or IMS/M21 composite systems, which are used in the aeronautic industry, from monotonic or cyclic tensile tests performed at several temperatures. An energetic cracking criterion is used. Several strain energy release rate expressions are compared, in order to obtain a realistic curve of fracture energy versus crack density. The influence of delamination and temperature on the cracking curves (crack density versus applied stress) is also considered. For the IM7/977-2 composite sysstem, the temperature effect can be accounted for using the time-temperature superposition principle, by constructing master curves of equal damage. A transition from monotonic cracking to fatigue cracking is investigated. Experimental results and simulations of transverse crack growth during fatigue tests are presented. The cracking criterion uses a fracture energy expression stemming from an extension of Vinogradov’s model which relies upon a simple assumption regarding the shape of first cracking S-N curves, and takes into account the R-curve effect
Randrianarivo, Bruno. "Prévision de la durée de vie en fatigue d'une structure ou d'un élément de structure sous chargement à amplitudes variables." Compiègne, 1991. http://www.theses.fr/1991COMPD444.
Повний текст джерелаRamond, Bruno. "Analyse des signaux d'émission acoustique sur des structures boulonnées et rivetées soumises à des contraintes de fatigue." Compiègne, 1988. http://www.theses.fr/1988COMP0273.
Повний текст джерелаThe analysis of elastic waves emitted during the damaging of a material under strain can give information as to the nature of the damage and its evolution. The complexity of physical phenomena involved and the limited performances of the instruments available impose the implementation of specific methods for the processing of the information given by the transducers. We suggest to apply factor analysis to the study of acoustic emission signals, which enables the bringing to the fore of the various mechanics involved. A method based on a moving average offers a new possibility of following the evolution of the damaging in real time. Examples of applications on assemblages of structure components in aluminium alloy show how efficient this method is
Cherfaoui, Mohammed. "Étude de l'émission acoustique associée à l'endommagement en fatigue des matériaux sous sollicitations cycliques et par blocs programmés." Compiègne, 1985. http://www.theses.fr/1985COMPD011.
Повний текст джерелаRedjel, Bachir. "Mécanique et mécanismes de rupture dans les matériaux composites SMC (Sheet Molding Compound)." Compiègne, 1987. http://www.theses.fr/1987COMPD067.
Повний текст джерелаLambert, Yvan. "Étude de l'endommagement en pointe de fissure dans le cas de la fissuration en plasticité non confinée." Compiègne, 1986. http://www.theses.fr/1986COMPI230.
Повний текст джерелаTaraf, Modar. "Endommagement par fatigue de contact d'une roue ferroviaire : étude numérique par éléments finis." Thesis, Metz, 2008. http://www.theses.fr/2008METZ021S/document.
Повний текст джерелаThis study by finites elements proposes to estimate the Rolling Contact Fatigue (RCF) strength of a railway wheel. The first part of the thesis presents a critical analysis of the approaches of the literature relatives to the various aspects of the problem of RCF. The second part relates to the two-dimensional modeling of a railway wheel, consist a defect circular, and subjected to a moving hertzian contact pressure .The damage is quantified by a Fatigue Parameter (FP) based on the density of energy and the concept of critical plan. The lifetime is calculated using a law consist of the parameters of low-cycle fatigue. It is shown that the technique of the submodeling is an effective tool to reduce the computing time CPU. The third chapter is a parametric study about the influence over the lifetime, of the loading level, the defect depth, the nature and the size of the defects. The results show that the critical plan of crack initiation is parallel to the contact surface when mode I dominate; it deviates when mode II is dominating. The fourth chapter relates to the influence of the loadings with variable amplitudes and that of friction. We show the beneficial effect of an overload over the lifetime to crack initiation. The harmful incidence of the coefficient of friction over the lifetime is highlighted in the case of a wheel with and without defect. Finally, the last part of this work approaches the effects of inertia in the case of the RCF. The lifetime is over-estimated in the static case and decreases in dynamics with the rolling speed and the loading level
Tang, Sui. "Étude de l'endommagement sous sollicitations monotone et cyclique de matériaux composites à matrices 2024 A1 et 2124 A1 renforcées par des fibres SiCw." Compiègne, 1989. http://www.theses.fr/1989COMPI284.
Повний текст джерелаMyrtja, Erisa. "Comportement des mortiers haute performance sous sollicitations de fatigue en compression." Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPAST017.
Повний текст джерелаThe work in this thesis is related to the durability of high-strength grouts, in a mechanical perspective. Numerous structures are subjected to fatigue loading during their lifetime such as offshore structures, wind turbines, road joints, airport runways or industrial floors.Despite the fact that this phenomenon is well known in steel structures, it can be noticed that for concrete structures and grouts, fatigue loading is rarely explicitly taken into consideration in the design codes. Furthermore, the information available in the literature concerning the phenomena influencing fatigue resistance and which determine the lifetime of structures, such as the number of cycles, the amplitude of stresses before failure, the frequency level applied are quite contradictory, in part because of the heterogeneous nature of the material.Thus, the aim of this thesis is firstly to analyze the damage induced by fatigue loading mainly in compression by means of different experimental methods. An important part of this study consists in identifying the parameters which have an influence on the fatigue life and the strain and stiffness evolution during loading. Among these parameters, the following are predominantly investigated : the loading frequency, the maximum stress applied, the temperature increase. Subsequently, alternative methods are proposed in order to evaluate the endurance limit and the fatigue life of grouts.A second part of this thesis consists in analyzing the influence of different mix components on the fatigue behavior. Different mixes have been developed with different aggregate types, in different grain fractions and an increased porosity level by entrained air and W/B. Therefore, the influence of the microstructure is examined and completed by different measuring techniques such as SEM-EDS, XRD, digital image correlation, infrared camera, mercury intrusion porosimetry and total water porosity
Ben, ameur Mariem. "Caractérisation mécanique et suivi par émission acoustique des mécanismes d’endommagement des composites à fibres hybrides lin/carbone." Thesis, Le Mans, 2019. http://www.theses.fr/2019LEMA1039.
Повний текст джерелаThe use of natural fibers as reinforcement makes it possible to improve the environmental performance of the composite materials as well as their damping properties. Nevertheless, these natural fiber composites have lower mechanical performance than synthetic fiber composites. In this context, this study proposes to develop composite structures with hybrid reinforcement made of flax and carbon fibers. The objective of this hybridization is to find a compromise between the mechanical and dissipative properties. First, the static behavior of flax fiber, carbon fiber and flax/carbon hybrid composites was analyzed. The principal elastic characteristics of a UD ply in plane stresses are thus determined. Moreover, a monitoring and an analysis of the mechanisms of damage were carried out by means of the technique of acoustic emission associated with microscopic observations. In order to better meet industrial needs, the behavior of composites subjected to cyclic fatigue tests must be studied. In fact, the fatigue behavior of these materials with non-hybrid and hybrid reinforcements was analyzed under tensile stress and three-point bending. The influence of hybridization on the fatigue life of these composites has been established. Finally, an experimental study and a finite element modeling of the vibratory behavior of non-hybrid and hybrid composites were carried out. Thus, the role of different fibers, fiber orientations, stacking sequences in vibration damping has been discussed
Le, Viet Dung. "Modélisation et identification du comportement plastique visco-élastique endommageable d'un matériau agrégataire." Tours, 2007. http://www.theses.fr/2007TOUR4044.
Повний текст джерелаThis research is achieved in the general frame work of the study of the thermomechanical behaviour of a quasi-compact aggregate. It has for objective the development of a new behaviour model satisfying to the particular requirements for an industrial exploitation. The model is isotropic and includes only a limited number of parameters. The experimental response shows a behaviour material comparable to concrete, to know the following characteristics : viscoelastic, damageable and sensitive to the hydrostatic pressure. For such materials, existing models were generally developped within the framework of the dynamic and static behaviour. They are not appropriate to simulate completely the material behaviour researched. Consequently, a specific model and an experimental protocol are presented. The model is derived from the tensile tests, the compressive tests and the triaxial compresssion tests under hydrostatic containment. The plastic limit is described by the means of a parabolic criterion with isotropic hardening. The flow rule is non-associated ; an isotropic damage achieves the model. Then, the developed model is implanted in the code of calculation standard abaqus by means of a numeric integration dealed with the shape of a procedure in Fortram. An extension in temperature comes to complete the modelling of the material behaviour. The dependance in temperature of the model parameters is taken into account in the Fortram subroutine. The validation of the model is done on the basis of several homogeneous tests as well as tests on structures by comparisons data/simulation
Chen, Xiao-Ting. "Effet du chauffage sur le comportement mécanique et poro-mécanique de matériaux cimentaires : propriétés hydrauliques et changements morphologiques." Phd thesis, Ecole Centrale de Lille, 2009. http://tel.archives-ouvertes.fr/tel-00577102.
Повний текст джерелаLi, Changle. "Application de la méthode d'analyse simplifiée des structures inélastiques à la fatigue de contact." Lille 1, 2004. https://pepite-depot.univ-lille.fr/RESTREINT/Th_Num/2004/50376-2004-233.pdf.
Повний текст джерелаLi, Li. "Modélisation numérique de l'endommagement des couches en proche surface : application aux systèmes Ni/NiO et Zr/ZrO2." Compiègne, 2011. http://www.theses.fr/2011COMP1929.
Повний текст джерелаIn the context of the prediction of coated materials durability submitted to mechanical loadings, we have developed a numerical model based on damage mechanics able to describe oxide layer fracture for Ni/NiO and Zr/ZrO2 systems (the periodic crack pattern in the oxide layer and the debonding of the oxide layer). A finite element model combining strong discontinuity approach and interface elements has been used. To take into account the initial defects in the material, we consider randomly distributed limit stress in the oxide layer. A statistical analysis is performed to evaluate the “mean inter-crack distance” of the periodic crack pattern in the oxide layer. The developed model is based on an experimental analysis of the oxide layer fracture phenomenon. This analysis focuses on the observation of the oxide layer damage evolution with different levels of mechanical loadings. These observations are performed by scanning electron microscopy (SEM) which allows to determine the “mean inter-crack distance” and by correlation with the numerical results, the model parameters (the limit stress of the metal/oxide interface, the crack energy of the periodic cracks) have been identified and our numerical approach has been validated
Gong, Xiao Lu. "Développement d'une méthodologie expérimentale associée à une approche analytique pour la compréhension du comportement de plaques composites non-trouées et trouées sous chargement simple et combiné de traction-torsion." Compiègne, 1994. http://www.theses.fr/1994COMPD741.
Повний текст джерелаDompierre, Benoît. "Fiabilité mécanique des assemblages électroniques utilisant des alliages du type SnAgCu." Phd thesis, Ecole Centrale de Lille, 2011. http://tel.archives-ouvertes.fr/tel-00604954.
Повний текст джерелаGarcia, Miranda J. Santos. "Développement d'un nouveau modèle d'endommagement et de cumul de dommage en fatigue sous sollicitations variables." Lille 1, 2003. https://pepite-depot.univ-lille.fr/RESTREINT/Th_Num/2003/50376-2003-155.pdf.
Повний текст джерелаLe, Graverend Jean-Briac. "Etude et modélisation des effets d'incursion à très haute température sur le comportement mécanique d'un superalliage monocristallin pour aubes de turbine." Phd thesis, ISAE-ENSMA Ecole Nationale Supérieure de Mécanique et d'Aérotechique - Poitiers, 2013. http://tel.archives-ouvertes.fr/tel-00834830.
Повний текст джерелаVioleau, David. "Une stratégie de calcul pour l'analyse à l'échelle "micro" des endommagements jusqu'à rupture des composites stratifiés." Phd thesis, École normale supérieure de Cachan - ENS Cachan, 2007. http://tel.archives-ouvertes.fr/tel-00254379.
Повний текст джерелаThébaud, Louis. "Etude des relations entre microstructure et propriétés mécaniques du nouveau superalliage base nickel AD730™." Thesis, Chasseneuil-du-Poitou, Ecole nationale supérieure de mécanique et d'aérotechnique, 2017. http://www.theses.fr/2017ESMA0033/document.
Повний текст джерелаIn view of the turbine entry temperature evolution, the main challenge for metallurgists is to elaborate new alloys able to withstand higher temperatures while keeping great mechanical properties. Therefore, knowing the relationships between microstructural parameters and mechanical properties at high temperatures (700°C and more) is mandatory.The creep and dwell-fatigue durability as well as the damage mechanisms of AD730™, a new nickel base superalloy developed for turbine disks, have been analyzed. Several microstructural parameters were studied (grain boundaries, grain size, size and distribution of γ′ precipitates) as well as experimental parameters (temperature, environment, applied stress or dwell period). By using single crystalline specimens having the same chemical composition of the studied alloy, it has been shown unambiguously that single crystalline microstructures do not necessarily present better creep properties compared to polycristalline ones. This result is supposed to be caused by a grain boundary strengthening mechanism. Moreover, in creep at 700°C, it has been shown that the main viscoplasticity controlling parameters are the size and distribution of γ′ precipitates.An unexpected dwell-fatigue behavior has been observed for long hold times and in a specific applied stress window. This phenomena is attributed to a “Bauschinger type” effect, occurring during unloading phases
Sadriji, Besnik. "Analysis and characterization of the damage phenomena occurring from handling and service surface anomalies." Thesis, université Paris-Saclay, 2022. http://www.theses.fr/2022UPAST082.
Повний текст джерелаThis research work concerns the study of the induced physical phenomena by the introduction of handling surface anomalies such as dents or scratches, on high pressure turbine disks. On one hand, they create a geometrical stress concentration at the anomaly root and combined with the severe thermomechanical loadings undergone by the disks, leads to a short crack initiation and propagation. On the other hand, these anomalies induce deformations which lead to hardening and residual stresses in the material. The latter have an important influence on the crack propagation and is necessary to take into account. Thus, the aim is to characterize these phenomena induced by the introduction of surface anomalies, namely the short crack effect and the residual stress field.For the short crack effect characterization, a pioneering experimental campaign has been set up implying uniaxial and multiaxial fatigue tests as well as numerical simulations in crack propagation. This experimental campaign highlights the T-stress effect on the crack propagation first. Then, it gives an experimental protocol to obtain short cracks and characterize their behavior. Finally, it gives a lead to take into account the short crack effect via the T-stress.With the aim of characterizing the residual stress field, Synchrotron X-ray diffraction measurements have been performed at the European Synchrotron Radiation Facility (ESRF) at Grenoble. The determination of the interatomic distances allows to determine the strains and the induced residual stresses by the anomaly. The results show important 3D stress levels, gradients and a substantial in-depths extent, as expected. The numerical model of a dent introduction has been improved to compare the experimental results with.A strategy to take into account these phenomena in the Incremental model is given in the perspectives in order to consider crack propagation from surface anomalies
Manai, Asma. "Sur une approche pragmatique de l'endommagement anisotrope par fatigue basée sur un critère de fatigue et ses gradients." Thesis, Sorbonne université, 2018. http://www.theses.fr/2018SORUS068.
Повний текст джерелаA new practical engineering methodology for the analysis of structures under cyclic loading is proposed in this work . A new anisotropic fatigue damage model is developed. The evolution of material properties degradation depends on a failure criterion and its gradient. The anisotropic material degradation will guide the damage propagation. The propagation of damage is mainly depending on the ridges of the criterion’s « surface » (zero gradients). The proposed approach can describe the initiation and propagation of the damage until the structural failure under fatigue loading. For each finite element, non-homogeneous anisotropic distributions of material properties are associated. Schematically, it seems like a material « surfing » on the criterion’s « surface » and damages follow the crest of the criterion’s « surface » (level and gradient). A global approach criterion, based on invariants of the stress tensor, is adopted. The reduction of material properties is assigned to a number of cycles and a global level of stresses, using an experimental Wöhler curve. Two simplified forms of the model are proposed and results are compared with a cruciform experimental reference example and an industrial case. A mapping with Dang Van criterion is also computed to analyze the numerical results
Mrozowski, Nicolas. "Mécanismes de propagation de fissure dans un superalliage base nickel polycristallin en régime d’interaction fatigue-fluage-oxydation-vieillissement métallurgique Aging of γ′ precipitates at 750°C in the nickel-based superalloy AD730TM: a thermally or thermo-mechanically controlled process?" Thesis, Chasseneuil-du-Poitou, Ecole nationale supérieure de mécanique et d'aérotechnique, 2020. http://www.theses.fr/2020ESMA0010.
Повний текст джерелаThe 750°C crack propagation behavior in the polycristalline nickel-base superalloy AD730TM is studied. This study falls within the overall objectives of optimizing the “microstructure – mechanical properties” relations in nickel-base superalloys used for example in turbine disks. The deceleration of the crack propagation with the increase in ΔK value is specifically at the core of the PhD thesis work. Via a crack propagation test campaign, this phenomenon is systematically identified when dwell-fatigue loading are performed. The influence of the thermomechanical history of the material in investigated by varying several experimental parameters such as the initial microstructural state (γ’ precipitates), the initial value of ΔK, the environment or the dwell durations. The origin of the deceleration phenomenon is therefore shown to be linked with combined and protective effects of stress relaxation, oxide growth and metallurgical aging at the crack tip. To improve the understanding of the crack propagation results, complementary analysis of the 750°C γ’ precipitates aging is performed. One of the main outcomes is that aging kinetics (γ’ growth, carbide precipitation) are enhanced thanks to a cyclic loading. Besides, the more the microstructure is aged, the higher the stress relaxation rate at 750°C
Rial, Djihad. "Modélisation tridimensionnelle des flexibles hydroformés et tressés en statique et en fatigue." Electronic Thesis or Diss., Compiègne, 2015. http://www.theses.fr/2015COMP2184.
Повний текст джерелаHydroformed flexible tubes are essential structures used in several industrial sectors such as the automotive sector, the aviation industry or energy production, such as the production of renewable energy in solar thermal energy farms where the panels must both be supplying fluid along and follow the direction of the sun. These structures serve as connecting parts between the rigid parts different mechanisms, primarily used for damping vibrations and acoustic emissions, and, as their name suggests, they also allow flexibility and pressure expansion, which considerably improves the fatigue strength. The mastery and prediction of the mechanical behavior of these structures are very important from a safety point of view and an economic point of view. Indeed, their accidental breakage can cause very serious consequences due to their use in sensitive areas such as the nuclear industry. In this context, this thesis was launched between Compiegne University of Technology and industrial BOA-group to create digital approaches to behavioral predictions and estimating the life braided hoses that take into account extreme conditions (temperature and pressure) and the forming parameters and properties of the materials used. In terms of use, these products are subject to thermomechanical charge-discharge cycles and vibrations can induce complex deformed piping of wear due to friction and damage by fatigue, The purpose of the study is to develop a numerical approach validated by the experience to certify products and improve the design. This approach will allow to estimate the lifetime of braided wavy taking into account: - the initial state of the product after forming and assembly, - thermomechanical stresses, is defined by the specification, or encountered in specific use cases, - vibrations encountered during use in real cases. The expected results are the life of the products from a calculation model of their behavior using the characteristics of the materials and interaction braid / tube
Cerdan, Florent. "Etude du vieillissement hydrique et des effets de couplages hygro-thermo-mécaniques sur le comportement d'une mousse polyuréthane renforcée par des fibres de verre au sein d'une membrane Mark III." Thesis, Chasseneuil-du-Poitou, Ecole nationale supérieure de mécanique et d'aérotechnique, 2017. http://www.theses.fr/2017ESMA0028/document.
Повний текст джерелаThe insulation of containment membrane of liquid natural gas carrier using the MarkIII membrane system, consists of load-bearing system made of panels in glass fiber reinforced polyurethane foam. The membrane is designed to resist to mechanical and thermal service load cases. As stated by IGC code regulation, and more specifically in some critical safety scenario, it has to be demonstrated that the cargo containment system will keep its integrity and main functions when subjected to water leakage through the inner hull wall (ballast).The challenge of this study is to appreciate the behavior of the reinforced polyurethane foam in immersion, which could widen the understanding of both water diffusion mechanisms and the impact of water penetration on the properties of the material.The setting up of water sorption tests at ambient temperature, according to three conditioning "free", "blocked" and "coupled" has allowed to identify a swelling law, a loading law and a damage law.In "free" conditioning, the cellular structure and the orientation of glass fibers in XY planes induce an anisotropic hygro-mechanical coupling. The swelling of Z direction has an important impact on the water solubility levels.In "blocked" conditioning, the blocking of the displacement of the faces perpendicular to the Z direction induces an increase in the internal stress levels as a function of the progression of the penetration front. In "coupled" conditioning, the sequence of the water aging and the cryogenic aging causes several damages. The damage degree is proportional to the hygroscopic swelling level of the cellular structure.The impact of these different conditionings on the durability of the material mechanical properties has been evaluated
Do, Xuan Nam. "Localized failure in dynamics for brittle and ductile materials." Thesis, Compiègne, 2017. http://www.theses.fr/2017COMP2356.
Повний текст джерелаFailure of engineering materials and structures can be considered as a result of a complex interplay between different physical phenomena such as nucleation of cavities, microcracks,microvoids and other irreversible processes. These micro-defects eventually coalesce into one or more macro-cracks leading to a decrease in the load-bearing capability and finally, to failure of the structure under consideration. Prevention of failure of structures and structural parts has always been a critical subject and a major concern in engineering. This thesis aims to represent localized failure in non linear materials without mesh dependency. Of special interest will be the case of dynamic strain-softening. Localized phenomena are taken into account by using the embedded strong discontinuities approach in which the displacement field is enhanced to capture the discontinuity. Based upon this approach, a one-dimensional model for elasto-plastic bar capable of representing failure for ductile materials with combined hardening in FPZ-fracture process zone and softening with embedded strong discontinuities was first developed. Results comparing the proposed one-dimensional model to (semi-) analytical works are presented. It was shown that the proposed strategy provides mesh independent solutions. Strain increases in the softening domain with a simultaneous decrease of stress. The problem unloads elastically outside the strain softening region. The strain energy is found to vanish. The model was also compared with a one dimensional damage model capable of representing the dynamic fracture for elasto-damage bar with combined hardening in fracture process zone - FPZ and softening with strong embedded discontinuities to find a good agreement between two models. A two-dimensional finite element model was developed, capable of describing both the diffuse damage mechanism accompanied by initial strain hardening and subsequent softening response of the structure. The results of several numerical simulations, performed on classical mechanical tests under slowly increasing loads such as Brazilian test or three-point bending test were analyzed. The proposed dynamics framework is shown to increase computational robustness. It was found that the final direction of macro-cracks is predicted quite well and that influence of inertia effects on the obtained solutions is fairly modest especially in comparison among different meshes. This two-dimensional model was expanded further into the two dimensional continuum viscodamage-embedded discontinuity model to help briefly explore the implementation of the second order mid-point scheme that can provide improved results under limitation of viscous regularization of localized failure damage model
Audibert, Clément. "Contribution à la caractérisation des mécanismes dissipatifs sous sollicitation d'impact de structures composites sandwichs intégrant des fibres naturelles. Proposition d'une zone d'absorption pour siège pilote." Thesis, Chasseneuil-du-Poitou, Ecole nationale supérieure de mécanique et d'aérotechnique, 2017. http://www.theses.fr/2017ESMA0030/document.
Повний текст джерелаThis work is part of the problem of mass reduction, safety inherent in the aeronautical field, it concerns more specifically the seats of pilots of airliner. A new multi-functional sandwich composite seat pan is proposed, composed by a carbon skin, a Nomex honeycomb core and a Kevlar/flax hybrid skin. The assembly of several materials generates complex behaviors and makes the ruin of the structure difficult to predict. An experimental/numerical approach is used to understand the damage mechanism of the seat and to create a pre-dimensioning numerical tool.Firstly, characterization tests allow identifying the mechanical behaviors of each material and constituting a database for the creation of material laws. The hybrid composite shows an elastoplastic-damaging-anisotropic behavior. The honeycomb is represented by a spring network and a law coupling the compression and shear behavior is implemented. Impact tests are used to evaluate the failure modes and the energy dissipated by the different concepts. The impact tests are correlates by numerical simulation using the identified material behaviors. The analysis of the experimental and numerical results makes it possible to identify the coupling between the different mechanisms. Finally, the model is used to design a new composite seat pan. This one is comparable to the existing aluminum seat pan without optimization phase
Dang, Van Truong. "Etude numérique statistique des champs locaux de contraintes en surface de polycristaux cubiques et hexagonaux en élasticité." Thesis, Chasseneuil-du-Poitou, Ecole nationale supérieure de mécanique et d'aérotechnique, 2016. http://www.theses.fr/2016ESMA0003/document.
Повний текст джерелаThe first stages of fatigue damage in metallic polycrystalline materials are governed by local mechanical field at the grain scale. Fatigue crack initiation is often related to the emergence of persistent slip band at surface.Localization of cyclic plasticity occurs within grains of polycristals in which elastic stress field can be highly heterogeneous due to the granular microstructure and crystalline anisotropic elasticity. The main goal of this study is to evaluate and analyse statistically the stress fields in surface grains of polycristals. In this work, the elasticregime only is considered in order to study the subsequent activation of plastic slip and its variability. The possibleconsequences regarding crack formation are also addressed but in a lesser extent. The methodology is based on fullfield finite element numerical simulation of the elastic response of a set of polycrystalline aggregates in which grains orientation is chosen randomly.The two materials chosen for this study exhibit different characteristics regarding crystal elasticity and slip systems.The first one is an austenitic stainless steels 316L (face centered cubic) and the second one a titanium alloy TA6V(hexagonal close packed). The distribution of resolved shear stress within several sets of surface grains, for different classes of crystal orientation, are analysed in relation to local crystallographic configurations in order to identify those which promote - or prevent from - plastic slip activation. For TA6V, the results suggest in particular that basal slip is activated earlier than prismatic slip. In addition, the simulation strategy has been modified tomodel the presence of some sharp band-like crystallographic textures named “macrozones” whose influence has been qualitatively predicted. Plastic slip activation in TA6V is also studied experimentally. In situ tensile test using SEM has shown the earlier activation of basal slip. Experimental data has been combined with simulated distribution of resolved shear stress in order to estimate the critical resolved shear stress of basal and prismatic slip systems
Stanic, Andjelka. "Solution methods for failure analysis of massive structural elements." Thesis, Compiègne, 2017. http://www.theses.fr/2017COMP2383/document.
Повний текст джерелаThe thesis studies: the methods for failure analysis of solids and structures, and the embedded strong discontinuity finite elements for modelling material failures in quasi brittle 2d solids. As for the failure analysis, the consistently linearized path-following method with quadratic constraint equation is first presented and studied in detail. The derived path-following method can be applied in the nonlinear finite element analysis of solids and structures in order to compute a highly nonlinear solution path. However, when analysing the nonlinear problems with the localized material failures (i.e. materialsoftening), standard path-following methods can fail. For this reason we derived new versions of the pathfollowing method, with other constraint functions, more suited for problems that take into account localized material failures. One version is based on adaptive one-degree-of-freedom constraint equation, which proved to be relatively successful in analysing problems with the material softening that are modelled by the embedded-discontinuity finite elements. The other versions are based on controlling incremental plastic dissipation or plastic work in an inelastic structure. The dissipation due to crack opening and propagation, computed by e.g. embedded discontinuity finite elements, is taken into account. The advantages and disadvantages of the presented path-following methods with different constraint equations are discussed and illustrated on a set of numerical examples. As for the modelling material failures in quasi brittle 2d solids (e.g. concrete), several embedded strong discontinuity finite element formulations are derived and studied. The considered formulations are based either on: (a) classical displacement-based isoparametric quadrilateral finite element or (b) on quadrilateral finite element enhanced with incompatible displacements. In order to describe a crack formation and opening, the element kinematics is enhanced by four basic separation modes and related kinematic parameters. The interpolation functions that describe enhanced kinematics have a jump in displacements along the crack. Two possibilities were studied for deriving the operators in the local equilibrium equations that are responsible for relating the bulk stresses with the tractions in the crack. For the crack embedment, the major-principle-stress criterion was used, which is suitable for the quasi brittle materials. The normal and tangential cohesion tractions in the crack are described by two uncoupled, nonassociative damage-softening constitutive relations. A new crack tracing algorithm is proposed for computation of crack propagation through the mesh. It allows for crack formation in several elements in a single solution increment. Results of a set of numerical examples are provided in order to assess the performance of derived embedded strong discontinuity quadrilateral finite element formulations, the crack tracing algorithm, and the solution methods
Doktorska disertacija obravnava: (i) metode za porušno analizo trdnih teles in konstrukcij, ter (ii) končne elemente z vgrajeno močno nezveznostjo za modeliranje materialne porušitve v kvazi krhkih 2d trdnih telesih. Za porušno analizo smo najprej preučili konsistentno linearizirano metodo sledenja ravnotežne poti skvadratno vezno enačbo (metoda krožnega loka). Metoda omogoča izračun analize nelinearnih modelov, ki imajo izrazito nelinearno ravnotežno pot. Kljub temu standardne metode sledenja poti lahko odpovedo,kadar analiziramo nelinearne probleme z lokalizirano materialno porušitvijo (mehčanje materiala). Zatosmo izpeljali nove različice metode sledenja poti z drugimi veznimi enačbami, ki so bolj primerne zaprobleme z lokalizirano porušitvijo materiala. Ena različica temelji na adaptivni vezni enačbi, pri katerivodimo izbrano prostostno stopnjo. Izkazalo se je, da je metoda relativno uspešna pri analizi problemov zmaterialnim mehčanjem, ki so modelirani s končnimi elementi z vgrajeno nezveznostjo. Druge različicetemeljijo na kontroli plastične disipacije ali plastičnega dela v neelastičnem trdnem telesu ali konstrukciji.Upoštevana je tudi disipacija zaradi širjenja razpok v elementih z vgrajeno nezveznostjo. Prednosti inslabosti predstavljenih metod sledenja ravnotežnih poti z različnimi veznimi enačbami so predstavljeni naštevilnih numeričnih primerih. Za modeliranje porušitve materiala v kvazi krhkih 2d trdnih telesih (npr. betonskih) smo izpeljali različne formulacije končnih elementov z vgrajeno močno nezveznostjo v pomikih. Obravnavane formulacije temeljijo bodisi (a) na klasičnem izoparametričnem štirikotnem končnem elementu bodisi (b) na štirikotnem končnem elementu, ki je izboljšan z nekompatibilnimi oblikami za pomike. Nastanek in širjenje razpoke opišemo tako, da kinematiko v elementu dopolnimo s štirimi osnovnimi oblikami širjenja razpoke in pripadajočimi kinematičnimi parametri. Interpolacijske funkcije, ki opisujejo izboljšano kinematiko, zajemajo skoke v pomikih vzdolž razpoke. Obravnavali smo dva načina izpeljave operatorjev, ki nastopajo v lokalni ravnotežni enačbi in povezujejo napetosti v končnem elementu z napetostmi na vgrajeni nezveznosti. Kriterij za vstavitev nezveznosti (razpoke) temelji na kriteriju največje glavne napetosti in je primeren za krhke materiale. Normalne in tangentne kohezijske napetosti v razpoki opišemo z dvema nepovezanima, poškodbenima konstitutivnima zakonoma za mehčanje. Predlagamo novi algoritem za sledenje razpoki za izračun širjenja razpoke v mreži končnih elementov. Algoritem omogoča formacijo razpok v več končnih elementih v enem obtežnem koraku. Izračunali smo številne numerične primere, da bi ocenili delovanje izpeljanih formulacij štirikotnih končnih elementov z vgrajeno nezveznostjo in algoritma za sledenje razpoki kot tudi delovanje metod sledenja ravnotežnih poti
Yu, Xiaoyang. "Dynamic acoustic emission for the characterization of the nonlinear behavior of complex materials." Thesis, Le Mans, 2020. http://www.theses.fr/2020LEMA1019.
Повний текст джерелаAcoustic emission (AE) is well known to be an efficient structural health monitoring technique to detect the creation and propagation of micro-cracks within structural materials such as concrete or composites when submitted to quasi-static stresses. Based on adequate signal processing methods, different research studies have established links between the detected AE hits and the created micro-damages. Other works have shown that it is possible to correlate the relaxation time in composites and the energy of the damage mechanisms measured during the quasi-static loading using the recorded AE hits. This thesis proposes to use an original experimental protocol to probe the nonlinear relaxation of concrete samples at the intact and damaged states. This protocol is based on the use of AE to passively probe the nonlinear relaxation of concrete samples instead of the weak amplitude signal usually used in slow dynamics experiments. Results show that passive and active probing methods lead to equivalent relaxation times. Furthermore, AE probing reveals the existence of a ‘silence period’ during the first minutes of the nonlinear relaxation after which AE hits start to be detected. In addition, the characteristics of AE hits recorded during the passive relaxation showed a clear resemblance to those obtained during the damaging of the same samples, where shear and compression mechanisms are involved. For the clustering of the AE hits, in addition to use of an unsupervised pattern recognition approach to cluster the detected AE hits, this work proposes a novel ‘image- based AE classification’ approach based on continuous wavelet transform (CWT) and convolutional neural network (CNN). Results related to the nonlinear dynamic and quasi-static AE data show that both signal processing approaches have high classification accuracy, which represents a great interest in the development of dynamic AE methods in the presence of micro-cracks
Zinszner, Jean-Luc. "Identification des paramètres matériau gouvernant les performances de céramiques à blindage." Thesis, Université de Lorraine, 2014. http://www.theses.fr/2014LORR0337/document.
Повний текст джерелаSince the sixties, ceramics are commonly used as armour materials. Indeed, thanks to their interesting physical and mechanical properties, they allow a significant weight benefit in comparison to monolithic steel plate armours. However, the microstructure of the ceramic may have a strong influence on its penetration resistance. Based on characterisation tests and on the use of four silicon carbide grades, this work aims to highlight the links between the microstructure and the ballistic efficiency. Experimental compressive and spalling tests are based on the use of the GEPI device. For studying the compressive dynamic behaviour, it allows using the lagrangian analysis method and characterising the yield strength of the material. For studying the tensile dynamic behaviour, it allows assessing the strain-rate sensitivity of the spall strength. An analysis of the fragmentation process is performed based on Edge-On Impact tests. Moreover, an innovating impact test on fragmented ceramics has been designed and performed. The different experimental results allow a better understanding of the influence of the ceramic microstructure on its behaviour under the different loadings. All the experimental data have been compared to numerical results allowing validating the constitutive models. The DFH (Denoual-Forquin-Hild) damage model of brittle materials showed very good capacities to simulate the tensile dynamic behaviour of ceramics (spalling and fragmentation)
Vu, Anh Thang. "Endommagement de stratifiés aéronautiques à fibres de carbone et matrice polymère soumis à des chargements monotones ou cycliques à plusieurs températures. Expériences et modélisation." Phd thesis, 2010. http://tel.archives-ouvertes.fr/tel-00523580.
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