Dissertations / Theses on the topic 'Milieux continus'
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Alavi, Seyed Ehsan. "Homogénéisation de milieux architecturés périodiques et quasi-périodiques vers des milieux continus généralisés." Electronic Thesis or Diss., Université de Lorraine, 2021. http://www.theses.fr/2021LORR0305.
Full textThis thesis aims to revisit higher-order homogenization schemes towards higher-order or higher gradient continua, successively for periodic and quasi-periodic architected materials and composites, based on variational principles and an extension of Hill macrohomogeneity condition. Continuous homogenization methods are exposed in Part I for micropolar and micromorphic media, followed by an exposition of the alternative discrete homogenization method.We have extended these theoretical developments to the situation of quasi-periodic materials, which still have a regular microstructure. The common idea to the proposed periodic homogenization methods of continuous or discrete nature is to split the microscopic displacement into a homogeneous part representative of the kinematics of the adopted effective continuum and a fluctuation evaluated from a variational principle. In substance, the theoretical developments allow the elaboration of enriched continua (generalized continua) of micromorphic type and all sub continua obtained using suitable degeneration conditions. Numerical applications have been made for architected materials and inclusion-based composites prone to higher-order effects due to their inner architecture. On the theoretical framework, the performed developments remedy many existing limitations of existing higher-order homogenization schemes.In Part II, repetitive lattice materials' effective classical and higher-order mechanical properties have been evaluated based on discrete homogenization schemes. Following the idea of a phenomenological approach, consistent couple stress models of repetitive beam lattices have been elaborated. Enriched Cosserat media have been derived in the spirit of micromechanics, adopting Timoshenko beam models at a microlevel, and applying a continualization method towards a Cosserat effective substitution medium. The proposed continualization method proves to be accurate and computationally efficient compared to continuous homogenization schemes and fully resolved finite element simulations. One key outcome of the performed analyses is the quantification of edge effects in the response of lattice structures, relying on the surface formulation of the extended Hill macrohomogeneity condition.The theoretical background underlying quasi-periodic asymptotic homogenization in the framework of linearized anisotropic elasticity deserves the development of Part III. Different methodologies for evaluating the effective quasi-periodic properties have been elaborated, leading to the emergence of strain gradient effective media. Conformal transformations define a specific class of geometrical mappings, allowing for designing compatible architected materials with inner porosity gradient, making them suitable bone biomechanics candidates
Cubisol, Gouin Françoise. "Contribution à une étude thermomécanique des milieux continus." Aix-Marseille 3, 1987. http://www.theses.fr/1987AIX30080.
Full textCubisol, Françoise. "Contribution à une étude thermomécanique des milieux continus." Grenoble 2 : ANRT, 1987. http://catalogue.bnf.fr/ark:/12148/cb376055468.
Full textElyoussoufi, Tamaa Lai͏̈la. "Contact unilatéral avec frottement sec en milieux continus discrétisés." Montpellier 2, 1991. http://www.theses.fr/1991MON20103.
Full textFressengeas, Claude. "Analyse de la stabilité des milieux élastiques et méthodes numériques." Metz : Université Metz, 2008. ftp://ftp.scd.univ-metz.fr/pub/Theses/1974/Fressengeas.Claude.SMZ7405.pdf.
Full textBugel, Mathilde. "Couplage entre la dynamique moléculaire et la mécanique des milieux continus." Thesis, Bordeaux 1, 2009. http://www.theses.fr/2009BOR13849/document.
Full textHybrid atomistic-continuum methods allow the simulation of complex flows, depending on the intimate connection of many spatiotemporal scales : from the nanoscale to the microscale and beyond. By limiting the molecular description within a small localized region, for example near fluid/fluid or fluid/solid interfaces (breakdown of the continuum), these methods are useful to study large systems for reasonable times. Besides, there is a wide variety of applications for such hybrid methods, ranging from the micro- or nano-scale devices, and other industrial processes such as wetting, droplet formation, and biomolecules near interfaces. In this work, we present one scheme for coupling the Navier-Stokes set of equations with Molecular Dynamics. Among the existing alternatives to couple these two approaches, we have chosen to implement a domain decomposition algorithm based on the alternating Schwarz method. In this method, the flow domain is decomposed into two overlapping regions : an atomistic region described by molecular dynamics and a continuum region described by a finite volume discretization of the incompressible Navier-Stokes equations. The fundamental assumption is that the atomistic and the continuum descriptions match in the overlapping region, where the exchange of information is performed. The information exchange, requires the imposition of velocity from one sub-domain in the form of boundary conditions (Dirichlet)/constraints on the solver of the other subdomain and vice versa. The spatial coupling as well as the temporal coupling of the two approaches has been investigated in this work. To show the feasibility of such a coupling, we have applied the multiscale method to a classical fluid mechanics problems
Bosia, Stefano. "Sur certain problèmes multi-phase en mécanique des milieux continus." Phd thesis, Ecole Polytechnique X, 2013. http://pastel.archives-ouvertes.fr/pastel-00923691.
Full textFuthazar, Grégory. "Ondes en milieux hétérogènes discrets et continus : propagation, diffusion, cloaking." Phd thesis, Université Rennes 1, 2013. http://tel.archives-ouvertes.fr/tel-00988910.
Full textAndrieux, Florence. "Sur les milieux visco-hyperélastiques endommageables." Compiègne, 1996. http://www.theses.fr/1996COMPD895.
Full textBuisson, Manuel Molinari A. "Sur les lois constitutives des matériaux thermoélastiques hétérogènes." Metz : Université Metz, 2008. ftp://ftp.scd.univ-metz.fr/pub/Theses/1984/Buisson.Manuel.SMZ8403.pdf.
Full textBassout-Lellich, Maarouf. "Sur la théorie des milieux viscoélastiques standards." Metz, 1986. http://docnum.univ-lorraine.fr/public/UPV-M/Theses/1986/Bassout_Lellich.Maarouf.SMZ8602.pdf.
Full textJeannet, Bernard. "Autour de l'usage de méthodes probabilistes en mécanique des milieux continus." Paris 13, 1992. http://www.theses.fr/1992PA132002.
Full textRuimy, Charles. "Chargements axisymétriques sur un milieu à anisotropie tétragonale." Besançon, 2002. http://www.theses.fr/2002BESA2002.
Full textJazzar, Mohamad Fadl. "Modélisation du comportement hyperélastique quasi incompressible de structures acier-élastomères et validation expérimentale." Aix-Marseille 2, 1993. http://www.theses.fr/1993AIX22085.
Full textVallée, Claude. "Lois de comportement des milieux continus dissipatifs compatibles avec la physique relativiste." Poitiers, 1987. http://www.theses.fr/1987POIT2007.
Full textRakotomanana, Ravelonarivo Lalaonirina. "Analyse théorique et numérique des grandes déformations en mécanique des milieux continus /." [S.l.] : [s.n.], 1986. http://library.epfl.ch/theses/?nr=610.
Full textHammoud, Mohammad. "Modélisation et simulation numérique du couplage entre les milieux discrets et continus." Phd thesis, Ecole Nationale des Ponts et Chaussées, 2009. http://tel.archives-ouvertes.fr/tel-00469475.
Full textFomethe, Anaclet. "Contribution a la theorie des defauts dans les milieux continus ferromagnetiques deformables." Paris 6, 1996. http://www.theses.fr/1996PA066145.
Full textVallée, Claude. "Lois de comportement des milieux continus dissipatifs compatibles avec la physique relativiste." Grenoble 2 : ANRT, 1987. http://catalogue.bnf.fr/ark:/12148/cb376105139.
Full textDaguerre, Jean-Pierre. "Conséquences d'un critère de stabilité pour quelques problèmes d'endommagement de structures." Paris 13, 1993. http://www.theses.fr/1993PA132025.
Full textGest, Jean-Patrick. "Application de la méthode de superposition de maillages (MSM) à l'étude de la localisation dans les milieux endommageables." Poitiers, 1999. http://www.theses.fr/1999POIT2332.
Full textFougeron, Gabriel. "Contribution to the improvement of meshless methods applied to continuum mechanics." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLC068/document.
Full textThis thesis introduces a general framework for the study of nodal meshless discretization schemes. Itsfundamental objects are the discrete operators defined on a point cloud : volume and boundary integration, discretegradient and reconstruction operator. These definitions endow the point cloud with a weaker structure than thatdefined by a mesh, but share several fundamental concepts with it, the most important of them being integrationdifferentiationcompatibility. Along with linear consistency of the discrete gradient, this discrete analogue of Stokes’sformula is a necessary condition to the linear consistency of weakly discretized elliptic operators. Its satisfaction, atleast in an approximate fashion, yields optimally convergent discretizations. However, building compatible discreteoperators is so difficult that we conjecture – without managing to prove it – that it either requires to solve a globallinear system, or to build a mesh. We dub this conjecture the "meshless curse". Three main approaches for theconstruction of discrete meshless operators are studied. Firstly, we propose a correction method seeking the closestcompatible gradient – in the least squares sense – that does not hurt linear consistency. In the special case ofMLS gradients, we show that the corrected gradient is globally optimal. Secondly, we adapt the SFEM approachto our meshless framework and notice that it defines first order consistent compatible operators. We propose adiscrete integration method exploiting the topological relation between cells and faces of a mesh preserving thesecharacteristics. Thirdly, we show that it is possible to generate each of the meshless operators from a nodal discretevolume integration formula. This is made possible with the exploitation of the functional dependency of nodal volumeweights with respect to node positions, the continuous underlying space and the total number of nodes. Consistencyof the operators is characterized in terms of the initial volume weights, effectively constituting guidelines for thedesign of proper integration formulae. In this framework, we re-interpret the classical stabilization methods of theSPH community as actually seeking to cancel the error on the discrete version of Stokes’s formula. The example ofSFEM operators has a volume-based equivalent, and so does its discrete mesh-based integration. Actually computingit requires a very precise description of the geometry of cells of the mesh, in particular in the case where its facesare not planar. We thus fully characterize the shape of such cells, only as a function of nodes of the mesh andtopological relations between cells, allowing unambiguous definition of their volumes and centroids. Finally, wedescribe meshless discretization schemes of elliptic partial differential equations. We propose several alternatives forthe treatment of boundary conditions with the concern of imposing as few constraints on nodes of the point cloudas possible. We give numerical results confirming the crucial importance of verifying the compatibility conditions,at least in an approximate fashion. This simple guideline systematically allows the recovery of optimal convergencerates of the studied discretizations
Darrieulat, Michel. "Prévision du comportement plastique anisotrope des polycristaux texturés par la mécanique des milieux continus." Paris, ENMP, 1993. http://www.theses.fr/1993ENMP0435.
Full textCazes, Fabien. "Construction et implémentation de lois cohésives extrinsèques." Lyon, INSA, 2010. http://theses.insa-lyon.fr/publication/2010ISAL0075/these.pdf.
Full textThis thesis deals with the common use of continuous models (damage, plasticity) and discontinuous models (cohesive zone models, Griffith theory) in rupture calculations. Two types of models are retained to modelize the diffuse phase of rupture as well as the localized phase appearing when the behaviour law becomes softening: - continuous models regularized with the implicit gradient method, - mixt continuous/discontinuous models associating a continuous hardening model to a cohesive zone model that takes into account the softening behaviour. The main objective of the thesis was the construction of a mixt continuous/discontinuous model from a continuous regularized model used as a reference model. The method used is based on the equivalent crack concept developed by Mazars which says that two models can be considered equivalent if the same quantity of energy is dissipated for a same problem. The numerical implementation of the method is done by realizing two successive calculations : a first calculation using a reference continuous model allows to extract the quantity of energy dissipated at each time step, then a second calculation allows to calculate incrementally the cohesive law of the equivalent model by using the dissipated energy increments calculated during the first calculation. On the other hand, a damage model for which the regularization only begins from the moment when the behaviour becomes softening has been developed. This model has two damage variables, which permits to make the difference between the diffuse and the localized damage. Finally, two formulations have been proposed for the implementation of cohesive laws with an infinite initial stiffness (extrinsic laws)
Doghri, Issam. "Etude de la localisation de l'endommagement." Paris 6, 1989. http://www.theses.fr/1989PA066151.
Full textDancette, Sylvain. "Comportement mécanique des soudures par points : mécanismes et stratégies de prédiction dans le cas des tôles en acier pour automobile." Lyon, INSA, 2009. http://theses.insa-lyon.fr/publication/2009ISAL0039/these.pdf.
Full textPredicting the strength of Advanced High Strength Steels resistance spot welds is a huge challenge in the automotive industry. Indeed, the crash properties of a car body structure depends on the performance of the welded joints. A first step in the PhD work consisted in a statistical analysis of experimental spot welding data available at ArcelorMittal in order to get insights into spot welds mechanical behaviour. An empirical model was proposed for the prediction of spot welds strength. An experimental protocol was developed to overcome the limits of such a model and obtain a better understanding of failure mechanisms. Interrupted Cross Tension and Tensile Shear tests were performed and spot welds failure was investigated with optical micrographs, SEM fractography and 3D-tomography in order to follow the three-dimensional crack paths due to the complex loading modes. A limited number of failure zones and damage mechanisms could be distinguished. Next, a Finite Elements model of spot welds behaviour was developed, requiring an appropriate description of Heat Affected Zones mechanical properties. This has been obtained by experimental simulations of the spot welding thermal cycles with a Gleeble machine followed by classical mechanical tests. Spot welds strength and failure type could be predicted as a function of the geometrical features the weld assembly and the loading mode
Aymard-Vinet, Corinne. "Modèles tridimensionnels d'endommagement de matériaux composites à matrice céramique en dynamique rapide." Bordeaux 1, 1997. http://www.theses.fr/1997BOR10561.
Full textLoizeau, Thierry. "Analyse des sources acoustiques dues aux transferts convectifs instationnaires : application à l'étude des auto-oscillations thermoacoustiques dans le tube de Rijke." Poitiers, 1995. http://www.theses.fr/1995POIT2258.
Full textRivet, Jean-Pierre. "Hydrodynamique par la méthode des gaz sur réseaux." Nice, 1988. http://www.theses.fr/1988NICE4215.
Full textLienard, Catherine. "Plasticité couplée à l'endommagement en conditions quasi-unilatérales pour la prévision de l'amorçage des fissures." Paris 6, 1989. http://www.theses.fr/1989PA066317.
Full textDumont, Christian. "Endommagement de métaux à matrice ductile en traction quasi statique et dynamique." Paris, ENMP, 1991. http://www.theses.fr/1991ENMP0267.
Full textDiener, Karsten. "Etude de l'influence d'un rayonnement laser ND:YAG a1. 3 um sur les paramètres thermo-mécano-optiques du matériau germanium." Mulhouse, 2004. http://www.theses.fr/2004MULH0766.
Full textTardif, Fabrice. "Analyse des mécanismes d'endommagement dans les composites 3D C/C : mesures optiques des champs de déformation par corrélation d'image." Bordeaux 1, 1998. http://www.theses.fr/1998BOR10671.
Full textPhilip, Armelle. "Endommagement en plasticité anisotrope : une contribution mécanique et physique." Grenoble INPG, 1989. http://www.theses.fr/1989INPG0149.
Full textMellouki-Filali, Chaakir. "Problème des milieux continus en contact avec frottement : stabilité et convergence des algorithmes numériques." Montpellier 2, 1988. http://www.theses.fr/1988MON20109.
Full textMellouki-Filali, Chaakir. "Problème des milieux continus en contact avec frottement stabilité et convergence des algorithmes numériques /." Grenoble 2 : ANRT, 1988. http://catalogue.bnf.fr/ark:/12148/cb37616251g.
Full textDutta, Nilankur. "Biomécanique du développement par l'analyse d'images : La dynamique de l'actomyosine pulsatile pendant la fermeture dorsale de la Drosophile." Thesis, Université Grenoble Alpes (ComUE), 2019. http://www.theses.fr/2019GREAI087.
Full textMechanics has emerged as a necessary discipline to understand embryogenesis. The effect of mechanical forces in tissue development and cell fate determination has been demonstrated, showing that cells respond to forces and mechanical cues.The Drosophila melanogaster is a model organism to study mechanics, with studies showing the mechanical control of cell shape and morphogenesis. Recently, the actomyosin cortex has attracted attention as a key regulator of cell mechanics. In this work, the morphogenetic process of dorsal closure is chosen to study the mechanical effect of actomyosin pulsations during development.Dorsal closure involves the closing of an epidermal gap in the embryo by the contraction of the amnioserosa, the extra-embryonic tissue covering the gap. During this time, cells delaminate from the amnioserosa, but there are no intercalations, migrations or divisions, making it an ideal system to study pulsatile actomyosin, or foci. Biophysical modelling suggests various modes of focus' motion such as advection or diffusion, but the kinetics of these foci are poorly understood. Thus, this work offers the mechanistical quantification of focus behaviour with a stress on kinetic properties.To that end, we use image analysis to create a tracking algorithm for travelling Myosin pulses. In four chapters, the thesis describes data processing tools which characterize focus behaviour, analysing a set of amnioserosa time-lapse movies.In chapter 1, the dataset of two channel (E-cadherin and Myosin II) time-lapse movies of the amnioserosa are described. Using the first channel, the cell membranes are identified. On the second channel, a method of pre-processing is defined, necessary for uniform focus identification over the whole dataset. Through this, the focus static properties, such as characteristic sizes and distribution on cell surface, are quantified.In chapter 2, the introduction of tracking algorithm enables temporal linkages among the identified foci. Merging and splitting behaviour of foci is seen. Under a point-particle ansatz, focus' kinematic properties, such as speeds, durations and angles of deviations between subsequent steps, are described. It is noted that the angles of deviation are non-isotropic, indicating directional motion. It is observed that foci always have non-zero speed between frames, suggesting motion that is not purely diffusive.In chapter 3, through further point-particle analysis of the trajectories of foci, their mean-squared-distances are quantified. Fitting a power-law, the median exponent is found to be in the super-diffusive regime of motion. Though impeded by the small duration of trajectories, this is consistent with the hypothesis of a self-avoiding motion. Measuring the mean direction of trajectory, it is seen that the orientation of the individual steps is preferentially aligned according to this direction. This is found to be linked to cellular confinement due to anisotropy in cell shapes.In chapter 4, the continuous Myosin signal is analysed, and the apical features of florescence in the known spatio-temporal neighbourhoods of foci are visualized through kymographs. These are then averaged to look at the properties of the apical Myosin signal in the regions where a focus has been, and will be. We find the average kinetics of a focus is followed by the phenomenon of Myosin depletion around it. We also note the presence of high Myosin signal across cell-membranes from foci.The work posits a model of self-avoidance due to substrate refractoriness as a mechanism for focus propagation and death. High myosin concentration at a sub-cellular region would be followed by a local refractor
Fick, Michel. "Etude de la fermentation acétonobutylique cinétique et morphologie en réacteur discontinu, mise en oeuvre du réacteur continu sur milieux synthétique et complexe, modélisation en réacteurs discontinus, continus et semi-continus." Grenoble 2 : ANRT, 1986. http://catalogue.bnf.fr/ark:/12148/cb375976143.
Full textEtcheverry, Philippe. "Etude théorique du comportement non linéaire de milieux poreux globalement isotropes." Paris 6, 1998. http://www.theses.fr/1998PA066731.
Full textRharbal, Jamal. "Contribution théorique à l'étude du comportement des milieux endommagés initialement anisotropes et simulations numériques." Dijon, 1998. http://www.theses.fr/1998DIJOS003.
Full textAmmiar, Belkacem. "Microstructure et effet d'échelle dans les essais de micro-indentation sur les roches." Marne-la-vallée, ENPC, 2003. http://www.theses.fr/2003ENPC0004.
Full textAboutayeb, Sidi Mohamed. "Comportement à l'endommagement des matériaux métalliques hétérogènes : simulation et expérience." Lille 1, 2000. http://www.theses.fr/2000LIL10175.
Full textLes modeles presentes sont implementes dans un code de calcul par elements finis. Les calculs sont effectues en grandes deformations en formulation lagrangienne reactualisee. L'etude experimentale a ete realisee sur des eprouvettes axisymetriques entaillees. Elle a pour but d'evaluer les mecanismes de degradation progressive du materiau (nucleation de cavites, croissance et coalescence) et determiner, a partir de ces mecanismes, les parametres constitutifs des modeles d'endommagement. Le couplage du modele de thomason avec les autres modeles montre une nouvelle possibilite de representer le stade de coalescence. Les resultats obtenus illustrent les complementarites entre l'approche locale et l'approche globale et la pertinence de cette derniere pour l'etude de l'influence de la triaxialite et de la deformation plastique equivalente sur l'endommagement
Aboutayeb, Sidi Mohamed Weichert Dieter. "Comportement à l'endommagement des matériaux métalliques hétérogènes." [S.l.] : [s.n.], 2000. http://www.univ-lille1.fr/bustl-grisemine/pdf/extheses/50376-2000-414-415.pdf.
Full textLecoutre, Gautier. "Etude de la fléxoélectricité de nanosystèmes par le développement d'algorithmes mêlant approche atomistique et mécanique des milieux continus." Thesis, Bourgogne Franche-Comté, 2018. http://indexation.univ-fcomte.fr/nuxeo/site/esupversions/a3ff4c82-e0dc-4c31-879b-e12ea6812264.
Full textThe flexoelectricity tensor of a material characterizes its ability to polarize under the action of a deformation gradient. The phenomenon is still rarely used though it exists in every material, because the effects are usually very weak. However, for nanoscale systems, flexoelectricity can be largely enhanced because of a possibly much greater gradient. Thus, the aim of this PHD thesis is to build a model that would allow us to compute the characteristic tensors of flexoelectricity in order to design a nanosytem in which huge flexoelectric effects could be used for energy conversion. For that purpose, we have studied the flexion of several semi-conducting Single-Wall Carbon NanoTubes (SWCNT), considered either as continuous cylinders or as a discrete network of carbon atoms. In the continuum point of view, we have applied the principle of virtual powers and classical thermodynamics to systematically obtain the constitutive equations of a semi-conducting, electro-magnetic deformable continuum, including the effects of the deformation, polarization and magnetization gradients. Meanwhile, we have improved an atomistic model with distributed permanent and induced dipoles to simulate the inverse flexoelectric effect on the SWCNTs. Using homogenization hypothesis, we have coupled these two approaches by obtaining the equations binding the atomistic quantities computed in the numerical simulations, with the corresponding macroscopic quantities used in the previously obtained constitutive equations. The first numerical results seem to show a notable variation of the elements of the flexoelectric tensors as a function of the radius and length of the SWCNT
Forster, Charles. "Contribution à l'étude de la rupture ductile des structures élastoplastiques." Compiègne, 1995. http://www.theses.fr/1995COMPD784.
Full textSuffis, Arnaud. "Développement d'un modèle d'endommagement à taux de croissance contrôlé pour la simulation robuste de ruptures sous impacts." Lyon, INSA, 2004. http://theses.insa-lyon.fr/publication/2004ISAL0033/these.pdf.
Full textNumerical simulation is today a usual practice for the design of industrial pieces and structures. In this context, the description of the damage of metals represents a new challenge. But damage models have to face a major difficulty: an abusive mesh dependency of the results which is called localization. In order to solve this problem, a damage model whose rate is limited, also called delayed damage model, was developed. Recent studies showed its aptitudes in dynamic to prevent localization. Its use in dynamic finite element codes implies however new problems to which an answer is proposed. An analytical expression of the size of the fully damaged zone, also called characteristic length, is given initially. This allows to evaluate a priori the adequate mesh size. Coupled to an original convergence analysis of the model, it should allow in the future to reduce considerably computation cost by using appropriate numerical techniques as remeshing, multi-grips methods or domain decomposition. For an industrial application, the length of the calculation remains too large. Furthermore, two ways of identification of the two delayed damage parameters using plates impact experiment are proposed. These two protocols are then applied successively for the first time to an aluminium alloy on the one hand and to an titanium ally on the other. Lastly, the implementation of the model was achieved in the fast dynamic finite element code Europlexus, some simulations are proposed. In the mean time, they allow the application and the validation of the various developments carried out previously
Sabar, Hafid. "Problèmes d'inclusions à frontière mobile et applications." Metz, 1990. http://docnum.univ-lorraine.fr/public/UPV-M/Theses/1990/Sabar.Hafid.SMZ9022.pdf.
Full textEl, khaoulani El idrissi Rachid. "Prédiction fiable de l'endommagement ductile par la méthode des éléments finis mixtes : endommagement non local et adaptation de maillage." Paris, ENMP, 2010. http://pastel.archives-ouvertes.fr/pastel-00566805.
Full textThe aim of this thesis is to develop an accurate numerical model to predict damage growth and failure in ductile solids. These developments are done within a parallel finite element library called CIMLib. To deal with the incompressibility of plastic deformations, a mixed velocity-pressure finite element approximation with a stabilized discretization P1+/P1 is used to solve mechanical equations. The numerical analysis of an elastic-plastic damage law in this approximation has been widely discussed. An enhanced Lemaitre damage evolution law is considered. Coupled dissipative phenomena, influence of stress triaxiality ratio, and crack-closure effects under compressive conditions are taken into account in this formulation. A nonlocal damage approach, based on an implicit gradient formulation, is used. This nonlocal approach enables to avoid the localization phenomenon and the associated mesh dependency. The well-known physical plastic strain localization in shear bands is modelled to prove that the proposed approach gives reliable and physical results. An another main focus of this thesis is the anisotropic mesh adaptation to the damage phenomenon. An anisotropic adaptive meshing scheme has been applied to increase the accuracy of the damage variable with minimum computing time. Moreover the numerical tests have proven that this mesh adaptation strategy allows our approach to predict accurately the expected damaged and fractured areas. The last contribution of this work is the implementation of a geometric multigrid preconditioner in order to allow an efficient computation for large linear systems from a FE approximation. The first validations have shown a quasi-linear growth of the cpu-time as a function of the number of degrees of freedom. The developed numerical model can be used to simulate sheet metal joining processes based on material plastic deformation and to study their mechanical strength. In the future, these developments will also useful for other cold metal forming processes, such as forging, stamping, cutting. .
Aublive-Conil, Nathalie. "Modélisation du comportement mécanique des argiles raides avec prise en compte de l'endommagement : application aux argilites de l'Est." Cergy-Pontoise, 2003. http://www.theses.fr/2003CERGA001.
Full textThe storage in deep geological formation is one of the solutions retained by France for the management of highly long life radioactive waste. The retained host rock is a claystone named East argillite located in the departments of Meuse and Haute-Marne. A thermodynamic formulation is used to propose a rheological model, which reproduces the mechanical behavior of claystones. Initially, an anisotropic damage plastic model was formulated in order to describe material degradations. Then, the damage plastic model is reformulated in order to taken into account the damage influence on the hydraulic behavior of porous material. The numerical simulations correctly reproduce the mechanical behavior of East Argillites but also the anisotropy of the hydraulic behavior introduced by the damage effect
Notta-Cuvier, Delphine. "Méthode des Champs Virtuels pour la caractérisation de comportements viscoplastiques et d'endommagement, à partir de mesures de champs mécaniques hétérogènes." Valenciennes, 2011. http://ged.univ-valenciennes.fr/nuxeo/site/esupversions/845b29c3-db42-4fa3-ad43-c6d172e0eda1.
Full textThe behaviour of materials subjected to high-energy dynamic loadings (impacts, blasts…) is usually sensitive to strain-rate (viscoplastic) and/or damage. Conventional procedures for the characterization of corresponding models of behaviour use statically determined tests requiring restrictive hypotheses. So, it is impossible to deal with heterogeneous mechanical fields and the exploitation of tests is limited to small levels of strain. Moreover, several tests have to be performed, at constant strain rate, to characterize viscoplasticity. However, these limitations do not allow to take advantage of the large amount of information available thanks to full-field measurements. One solution is to use statically undetermined tests to deal with heterogeneous fields. Among available tools, the Virtual Fields Method (VFM) has undeniable advantages compared to classic FEMU methods. This study focuses on the development of the VFM for the characterization of Johnson-Cook's viscoplastic model of behaviour. An asset of the VFM is that it makes possible the characterization of the viscoplastic part of the model with only one testing, under dynamic conditions, thanks to a statically undetermined exploitation of heterogeneous strain and strain-rate fields. A short-term prospect is to use the VFM to identify parameters of elastoplastic models of behaviour coupled with damage (e. G. Lemaitre). The feasibility was demonstrated for numerical data