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Дисертації з теми "Matériaux hybrides – Contraintes (mécanique) – Détérioration"
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
Fredj, Narjes. "Vieillissements de peintures marines anticorrosion sous contraintes physico-chimiques couplées et/ou cycliques." La Rochelle, 2008. http://www.theses.fr/2008LAROS252.
Повний текст джерелаNew formulations of marine organic coatings, with or without solvent, abiding by recent environmental standards, must be studied and compared to classical solvent-borne organic coatings in order to determine their performance and durability. If the main degradation factors of polymers are known (water, temperature, mechanical solicitations and light), the accelerated ageing tests used to assess the organic coatings lifetime do not take into account of these parameters together or their hierarchical effects. This is particularly true when a mechanical stress is applied onto a metallic structure in tidal zone. In this work, we studied the ageing of organic coatings as free films and as attached films onto a steel substrate in natural and synthetic seawater (3% NaCl solution) for different temperatures and different mechanical visco-elastic mechanical stresses. The coating degradation was analyzed by monitoring the glass transition temperature evolution and the mechanical properties modifications after a water uptake that was measured using electrochemical impedance spectroscopy and gravimetry techniques. Our results show that the water uptake is a thermally activated diffusionnal phenomenon, sensitive to a stress state. This latter can lead to antagonist phenomena which favour or not diffusion. A thermodynamic interpretation was proposed in terms of polymer chains rearrangements affecting the number of possible water distribution paths and the energy barrier associated with this move. These two mechanisms are very dependent on the nature of the coating. Moreover, a desorption phenomenon of organic and mineral species, in competition with the water absorption, was identified. Besides, the temperature variation in natural environment, which implies internal stresses in organic coatings, seems to affect significantly the kinetics of water uptake and the degradation of coatings. Finally, synergies between the ageing factors were established: the association of stress leads to a higher degradation kinetic than the sum of individual effects
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 джерелаGougeon, Nicolas. "Rupture et vieillissement des fibres optiques." Rennes 1, 2003. http://www.theses.fr/2003REN10152.
Повний текст джерелаKang, Chi-Hang. "Une famille d'éléments hybrides singuliers pour l'étude des plaques fissurées métalliques et composites." Compiègne, 1991. http://www.theses.fr/1991COMPD362.
Повний текст джерелаMiot, 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
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
Eyer, Gabriel. "Rupture des matériaux composites en compression sens fibre : analyse de l'effet de l'endommagement." Thesis, Aix-Marseille, 2015. http://www.theses.fr/2015AIXM4728/document.
Повний текст джерелаTo design composite structures it is required to access materials properties and to understand mechanisms of failure for different types of load. Shear and tensile tests are quite easy to do. That is why ply properties are well identified for these types of load. Yet in the case of compression, experimental methods are complex and then the knowledge of materials properties remains poor.When the slenderness of the specimen is excessive in compression test, buckling will affect the failure. But when the coupon is smaller, stress concentration generates a failure in the clamped-end. Structural effects are here the reason of the failure. It is then not possible to conclude about the materials properties.That is why an experimental study is proposed. This work is divided in two main parts. The first one talk about the measure of the compressive strength on undamaged samples with different geometries. It is shown that the behavior up to failure is well identified. In a second part it is demonstrated that damage decreases significantly the compressive strength. These results will finally be apply to the global design of laminates for any type of load
Léger, Romain. "Contribution à l'étude de la durabilité des structures collées soumises à des efforts mécaniques après vieillissement humide." Phd thesis, Chasseneuil-du-Poitou, Ecole nationale supérieure de mécanique et d'aéronautique, 2010. http://tel.archives-ouvertes.fr/tel-00518367.
Повний текст джерелаLahoud, Nadine. "Modélisation du vieillissement des isolants organiques sous contrainte électrique : application à la fiabilité des matériaux." Toulouse 3, 2009. http://thesesups.ups-tlse.fr/517/.
Повний текст джерелаThe aim of this study is to improve the description of solid organic insulators or polymers ageing under electrical stress. With this objective in view, the different ageing scenarios existing in the literature were analyzed, compared and improved. This theoretical study showed that many parameters related to their heterogeneous structure and the distribution of their properties were neglected in order to simplify the modelling. This study presents a new approach in the description of solid organic insulators ageing by taking into consideration their experimentally demonstrated structural complexity. In this approach, the polymer material has been assimilated to a set of sites representing different energy states, thereby different properties as well as ageing rates depending on each site. The principal parameters involved during the ageing process, such as the specific volume variation, the dielectric strength evolution and the local value of the electrical field have been defined. The expression of the retardation time specific to each elementary ageing process has been established. Finally, a distributed form of those retardation times has been presented. Our "phenomenological" approach is thus a multi-sites one permitting, along with an experimental study, to establish an equation relating the life time of polymer electrical insulators to the different parameters at play, all along respecting their distribution over the entire set of sites within the polymer
Книги з теми "Matériaux hybrides – Contraintes (mécanique) – Détérioration"
1942-, Baïlon Jean-Paul, Masounave Jacques 1943-, and Dorlot Jean-Marie 1940-, eds. Des matériaux. 2nd ed. Montréal, Qué: École Polytechnique de Montréal, 1986.
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