Dissertationen zum Thema „Fissuration dynamique“
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Célarié, Fabrice. „Dynamique de fissuration à basse vitesse des matériaux vitreux“. Phd thesis, Université Montpellier II - Sciences et Techniques du Languedoc, 2004. http://tel.archives-ouvertes.fr/tel-00007583.
Der volle Inhalt der Quelle1. La propagation de la fissure dans des vitrocéramiques a été étudiée par AFM en fonction de leur degré de dévitrification. Des écarts à la propagation rectiligne ont été mis en évidence. Dans le matériau le plus dévitrifié, la fissure contourne les cristaux nanométriques engendrant des contraintes de torsion et de cisaillement ce qui accroît d'autant la résistance à la rupture du matériau.
2. En utilisant la microscopie AFM, nous avons montré que la propagation de la fissure dans des matériaux vitreux –étudiés à des températures très inférieures à la température de transition vitreuse- se faisait, au devant de la tête de fissure, par un processus de nucléation, croissance et la coalescence de nano-cavités d'endommagement. La mise en évidence expérimentale de ce phénomène de ductilité du verre à l'échelle nanométrique est un résultat novateur faisant un lien entre les mécanismes de fissuration des matériaux ductiles (métaux) et fragiles (verres). La différence se situe au niveau des échelles de longueur des cavités, respectivement micrométriques et nanométriques.
3. Enfin, l'étude de la fissuration d'un verre contenant des ions alcalins révèle une migration, à l'échelle nanométrique, d'espèces chimiques au voisinage immédiat de la fissure. Cette migration s'observe sous la forme d'apparition et de croissance de nodules de dimensions nanométriques. Le champ de contrainte mécanique local, le taux d'humidité relative, ainsi que le temps de séjour de la tête de fissure dans une zone non fissurée du matériau, sont des paramètres essentiels pour le contrôle de ces phénomènes de diffusion à l'échelle nanométrique. Les processus physico-chimiques impliqués (comme la diffusion locale d'ions sodium) ont été étudiés.
L'étude in-situ de la fissuration des matériaux vitreux aux échelles de longueur caractéristiques des hétérogénéités est d'une importance capitale pour comprendre et améliorer les propriétés mécaniques du verre, matériau qui est à l'heure actuelle de plus en plus utilisé dans de multiples domaines.
Maigre, Hubert. „Contribution theorique a d'identification des grandeurs caracteristiques en mecanique de la rupture dynamique“. Palaiseau, Ecole polytechnique, 1990. http://www.theses.fr/1991EPXX0006.
Der volle Inhalt der QuelleMosnier, Martial. „Etude expérimentale de la fissuration dynamique de plaques : application à la fragmentation de réservoirs“. Phd thesis, Université d'Orléans, 2006. http://tel.archives-ouvertes.fr/tel-00115871.
Der volle Inhalt der Quelle· La première a consisté à soumettre des plaques métalliques à des chargements sous forme d'explosions, et à examiner leur mode de fissuration. Les vitesses de fissuration semblent indépendantes du chargement, tandis que la taille des fragments augmente avec la violence de l'explosion.
· La deuxième a consisté à faire exploser des enceintes d'environ vingt litres. Elle a permis de confirmer une partie des tendances observées précédemment.
Menouillard, Thomas Combescure Alain. „Dynamique explicite pour la simulation numérique de propagation de fissure par la méthode des éléments finis étendus“. Villeurbanne : Doc'INSA, 2008. http://docinsa.insa-lyon.fr/these/pont.php?id=menouillard.
Der volle Inhalt der QuellePerales, Frédéric. „Fissuration des matériaux à gradient de propriétés. Application au Zircaloy hydruré“. Phd thesis, Université Montpellier II - Sciences et Techniques du Languedoc, 2005. http://tel.archives-ouvertes.fr/tel-00079015.
Der volle Inhalt der QuelleSapardanis, Hélène. „Fissuration à l’interface d’un revêtement plasma céramique et d’un substrat métallique sous sollicitations dynamique et quasi-statique multiaxiales“. Thesis, Paris Sciences et Lettres (ComUE), 2016. http://www.theses.fr/2016PSLEM033/document.
Der volle Inhalt der QuelleThe work presented in this manuscript aims to investigate the growth of an interfacial flaw, whose geometry is known, under macroscopic shear loading. An experimental methodology is thus developed in which i) a ceramic/metal coated system with controlled interface roughness is processed, ii) an interfacial flaw is introduced using the laser shock technique, iii) a macroscopic shear loading is applied on the coated system using a biaxial in-plane testing device and iv) interfacial crack growth and buckling are measured in situ. Hence, both dynamic and quasi-static loadings are applied on the coated system by respectively the laser shock technique and biaxial testing. The interface roughness, which affects the crack growth, is also considered in the study. A pure alumina coating is deposited by air plasma spraying on a metallic substrate, polycrystalline cobalt base superalloy Haynes 188 and stainless steel 304L substrates, with no bond coat.First, the flaw resulting from the propagation of a laser shock wave has been analyzed according to the laser parameters and the interface roughness. An interfacial flaw is characterized by a circular delamination with a diameter of a few millimeters and a circular blister with a height of a few tens of micrometers. These characteristic dimensions have been measured thanks to non destructive techniques: 3D profilometry and image analysis based on optical observations and infrared thermography. A finite element analysis has been carried out to investigate the crack behavior under laser shock wave propagation using a cohesive contact to account for the interface behavior.The interfacial flaw growth under macroscopic shear loading has been characterized with optical observations and the digital image stereo-correlation technique. The related finite element analysis enabled to identify the local loading along the crack front and gave a first explanation about the shapes of the delaminated area observed experimentally. This analysis relies on a cohesive zone model whose applied boundary conditions are established from the displacements measured by digital image correlation technique. By this way, the delamination growth was revealed to be mostly driven by local shear (mode II and III) and the crack opening (mode I), induced by the buckling of the deposited layer and the macroscopic shear, makes the delamination growth easier. Finally, the influence of the macroscopic shear loading on the interfacial delamination has been studied from three different macroscopic shear loadings. The finite element analysis based on linear elastic fracture mechanics in a homogenous material has allowed to study the influence of the macroscopic shear loading on the local loading along the crack front
Menouillard, Thomas. „Dynamique explicite pour la simulation numérique de propagation de fissure par la méthode des éléments finis étendus“. Lyon, INSA, 2007. http://theses.insa-lyon.fr/publication/2007ISAL0048/these.pdf.
Der volle Inhalt der QuelleNumerical tools are still more efficient and allow a good description of physical phenomena. Moreover these tools are not restricted to linear mechanics, but are a Iso developped for more complex behaviour such as fracture. Dynamic or static loadings can create damage, micro cracks and then fracture of structure. Fast dynamic allows to compute phenomena such as crash, impacts on structure. Application domain is really broad; th us it a Iso concerns resistance and accidents for nuclear reactor tank. Lt is interesting for numerical codes to be able to predict these situations: damage evolution and crack propagation consist in being an essential challenge. Th us the eXtended Finite Element Method allows to avoid remeshing and field projection. The crack is kinematically described by the use of additional degrees of freedom. One can underline the difficulties between the eXtended Finite Element Method and the explicit lime integration: the diagonal mass matrix and the corresponding critical lime step. One presents two lumping techniques based on the conservation of kinetic energy, and critical time steps of enriched elements. One demonstrates thal the critical lime step is almost the same !han the one corresponding to the finite element problem, and is independant of the position of the crack
Croix, Patrick. „Endommagement et rupture des métaux anisotropes pour la dynamique et le crash de véhicules“. Valenciennes, 2002. https://ged.uphf.fr/nuxeo/site/esupversions/35d379a9-0ce7-47e2-b08f-5ae639026583.
Der volle Inhalt der QuelleThe shape and orientation of the microvoids are taken into account in the finite element model developed to improve the prediction of cracks occurrence. The evolution law of porosity due to nucleation is modified to solve the problem of the non-evolution of damage in pure shearing. An identification procedure of damage parameters by the inverse method is developed. This method is based on the correlation of experimental and numerical results, obtained from tensile and Arcan tests. The identification was carried out in the case of an anisotropic aluminium material. To obtain an independence with the mesh size, two strategies are used : by an adaptive meshing based on a damage criterion and/or by the determination of the damage parameters according to the size of the mesh. This work is illustrated by several confrontations of experimental/numerical tests carried out on an extruded aluminium tube
Réthoré, Julien Combescure Alain. „Méthode éléments finis étendus en espace et en temps application à la propagation dynamique des fissures /“. Villeurbanne : Doc'INSA, 2005. http://docinsa.insa-lyon.fr/these/pont.php?id=rethore.
Der volle Inhalt der QuelleAttigui, Mohammed. „Modélisation du comportement dynamique des structures fissurées par la mécanique de rupture“. Limoges, 1997. http://www.theses.fr/1997LIMO0032.
Der volle Inhalt der QuelleChen, Wen. „Fracturation électrique des géomatériaux Etude de l'endommagement et de la perméabilité“. Phd thesis, Université de Pau et des Pays de l'Adour, 2010. http://tel.archives-ouvertes.fr/tel-00577790.
Der volle Inhalt der QuelleLi, Ling. „Etude de la fissuration engendrée par le séchage dans les matériaux cimentaires : influence des inclusions“. Thesis, Lille 1, 2016. http://www.theses.fr/2016LIL10176/document.
Der volle Inhalt der QuelleDrying process of cementitious materials leads to microcracks, which has important consequences on transport and mechanical properties. The aim of this study is to investigate the evolution of microcracking of cementitious materials during drying and better understand the associated mechanisms. This work presents both an experimental study and a numerical simulation of drying shrinkage microcracking. The experiments are performed in order to study the effect of drying and the role of the aggregates. The study of the internal structure and crack propagation is conducted by X-ray microtomography. The influences of the stiffness and the surface roughness of inclusions on the occurrence of cracking are highlighted. Moreover, a series of mechanical tests is performed on the cement paste to understand the mechanical behaviour of this material and to use for identification of the model parameters in the numerical study developed in the framework of this thesis. Numerical models are then proposed to investigate the mechanisms associated with experimentally observed microcracks. These modellings are performed under the framework of poromechanics in partially saturated medium, and the material is considered as biphasic: the inclusions embedded in a porous cement matrix (elastic models, elastoplastic and damage). The results of numerical simulations allow access to the stress distribution and reproduce the observed cracking under microtomography. The influences of matrix behaviour and stiffness of inclusion are studied. Finally, a preliminary modelling based on extended finite element method focusing on the effects of paste-inclusions interface is proposed
Lammens, Bastien. „Caractérisation de la décohésion dynamique des matériaux composites à matrice organique (CMO)“. Electronic Thesis or Diss., Ecole centrale de Nantes, 2024. http://www.theses.fr/2024ECDN0007.
Der volle Inhalt der QuelleOrganic matrix laminated composites are increasingly used in the aeronautical field to reduce the weight of structures. However, during an impact on this type of material, various damage mechanism can occur, such as delamination. This is a process of macroscopic decohesion of the interlaminar environment, which can be characterised by GIC (or KIC ). The literature shows a wide disparity in measurements due to incomplete decoupling of the effects of resin confinement by fibers, nonlinearitiesbehaviour and/or velocity effects. This work proposes to develop an experimental protocol to characterise pure resin usingfullfields measurements to methodically study these couplings. The goal is to evaluate the impact of the crack propagation speed and the structural effects on the fracture behaviour and in particular to extend Griffith's theory to laminated composites. Different specimen geometries are used to reproduce structural effects. Crack propagation speeds ranging from quasi-static to dynamic are studied and all the tests are analysed using linear elastic fracture mechanics and the fracture surfaces. Finally, this work proposes a model to describe the evolution of KIC for the resin HexplyM21 used in aeronautics field, from the non-singularterms of the stress field T-stress, B-stress and also the speed ȧ in the ranges [0 - 15] MPa, [- 200 - 10] MPa.m-0.5 et [10-6, 600] m.s-1 respectively
Akiki, Rana. „Développement d'un outil numérique pour la prévision de la fissuration d’une structure en béton de fibres sous impact“. Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLN056/document.
Der volle Inhalt der QuelleThe research work falls within the framework of the transportation and handling safety of radioactive waste containment packages. The goal is to develop a numerical tool capable of simulating the overall behaviour of a fiber concrete structure subject to a dynamic loading. It also gives access to more local information such as cracking, both in terms of path and opening. To do this, a set of mechanical tests is carried out in order to better understand the mechanisms of damage and cracking of the material under quasi-static and dynamic loading. The model capable of capturing on a global scale the non-linearities related to the cracking of the structure in a continuous framework is detailed. The parameters associated with the material constitutive law are identified via an identification procedure based on the experimental data of the conducted tests. The determination of dynamic cracking energy is investigated and the structural inertial part of this is underlined. Two numerical methods used to post-process the results of the global numerical simulations, giving access to finer information at the local scale, in terms of path and crack opening, are detailed. The study of a fiber-reinforced concrete beam subjected to a dynamic 1-point bending loading, post-processed with the two approaches, is presented. The results of the numerical post-processing are compared with those obtained experimentally by correlation of digital images
Valette, Gilles. „Simulation dynamique spatialisée de l’évolution de la structure de surface des sols cultivés sous l’action de la pluie“. Reims, 2008. http://www.theses.fr/2008REIMS006.
Der volle Inhalt der QuelleThis document is the result of a thesis conducted on the interface between computer science and soil science. This work concerns the modeling and simulation of two types of changes in the structure of a cultivated soil surface: its degradation by the action of rain, and its cracking by the action of dessication. The models we have developed are based on the DEVS formalism, which is dedicated to discrete event systems, and on extended cellular automata principle. The main originality of our simulator of soil degradation is that it aims to reproduce the interaction between the erosion processes and the evolution of the relief and of the soil surface structure. The processes of water transfer are represented, as well as the processes of sediment transfer. A rain simulator experiment permitted to verify that our simulator provides a correct global behavior, producing a realistic crusting on both qualitative and quantitative aspects, which is one of its most original and innovative characteristics. The cracking simulator reproduces the emergence and development of vertical cracks in the surface layer of a dessicating soil. We have introduced the method of hierarchical watershed to obtain a cracks network that can be determined by soil properties, especially the crust thickness. Besides a validation using Minkowski's densities, we have also proposed a generalization of our method to 3D meshes
Nader, Christian. „Stratégie multi-échelles de modélisation probabiliste de la fissuration des structures en béton armé“. Thesis, Paris Est, 2017. http://www.theses.fr/2017PESC1157/document.
Der volle Inhalt der QuelleNo modeling approach exists nowadays that can provide reliable information about the cracking process in large/complex reinforced concrete structures. However, this is an important issue for controlling the lifespan of structures, which is at the heart of the principal of sustainable development. In this work we introduce a new approach to model the cracking processes in large reinforced concrete structures, like dams or nuclear power plants. For these types of structures it is unreasonable, due to calculation time, to explicitly model the rebars and the steel-concrete bond. Nevertheless, access to data about the cracking process is imperative for structural analysis and diffusion problems. So in order to draw the information about cracking in the structure, without resorting to the use of local approaches, we developed a probabilistic macroscopic cracking model based on a multi-scale simulation strategy. The strategy is a sort of a multi-steps process that takes over the whole modelization of the structure in the framework of the finite element method, from meshing, to model creation, and parameter identification. The heart of the strategy is inspired from regression (supervised learning) algorithms: data on the local scale | the training data coupled with working knowledge of the mechanical problem | would shape the macroscopic model. The probabilistic macroscopic model's identification is case-specific because it holds information about the local behavior, obtained in advance via numerical experimentation. This information is then projected to the macroscopic finite element scale via inverse analysis. Numerical experiments are performed using a validated cracking model for concrete and a bond model for the steel-concrete interface, allowing for a fine description of the cracking processes. Although the identification phase can be relatively time-consuming, the structural simulation is as a result, very time-efficient, leading to a sensitive reduction of the overall computational time, with no loss in information/accuracy of results on the macroscopic scale
Bichet, Lionel. „Mécanismes de transports dans la fissuration des matériaux hétérogènes : application à la durée de vie d’exploitation des centrales nucléaires“. Thesis, Montpellier, 2017. http://www.theses.fr/2017MONTS001/document.
Der volle Inhalt der QuelleDuring their confinement in a nuclear power plant, the mechanical properties of the constitutive materials of concrete change as a result of ageing. This is due to the transportation of chemical species at the microscopic level of the media. Firstly, this can be modelled with average equations. The Fick laws represent the evolution of chemical diffusion and the Fourier laws, the transportation of heat at a mesoscopic level. In this research, we will consider thermal evolution on a fractured media.This thermomechanical problem is solved with a staggered method. The mechanical contribution used an approach based on multi-bodies system linked with cohesive zone models. The thermal problem is based on the approximation of the heat transfer equation at the cohesive interface. This approach has been implemented and validated. The description of the heat trough the interface is composed with the definition of an homogenised conductivity and the local damage parameter. In order to optimize the computational cost with a good agreement of the crack propagation, a criterion is proposed for sizing a representative elementary volume (REV). The eigenerosion method is used, validated and extended to heterogeneous media. Two studies are carried out on the morphological properties on a cementious media. As a result of those studies, a minimal size for a REV is defined.Crack spread under thermal loads are investigated on a media representing the concrete of the containment of a nuclear power station. The ageing effect are taken into account as an initial damage between the mortar and the aggregates. These parameters are expressed in terms of rate of initial damage. A study is proposed for different values of this rate. As assumed, the development of multi-cracks is linked with the rate of initial damage and the creation of thermal border is proposed
FAURE, LAURENT KLEPACZKO JANUSH Molinari Alain. „ETUDE EXPERIMENTALE DE LA FISSURATION DYNAMIQUE DES ACIERS 40-NCD-16 ET XC-18 PAR IMPACT ET USINAGE RAPIDE - APPLICATION A L'ANALYSE DES DEFORMATIONS PAR IMAGERIE NUMERIQUE /“. [S.l.] : [s.n.], 1997. ftp://ftp.scd.univ-metz.fr/pub/Theses/1997/Faure.Laurent.SMZ9752.pdf.
Der volle Inhalt der QuelleChen, Wei. „Etude expérimentale de la perméabilité du béton sous conditions thermiques et hydriques variables“. Phd thesis, Ecole Centrale de Lille, 2011. http://tel.archives-ouvertes.fr/tel-00778621.
Der volle Inhalt der QuelleRéthoré, Julien. „Méthode éléments finis étendus en espace et en temps : application à la propagation dynamique des fissures“. Phd thesis, INSA de Lyon, 2005. http://tel.archives-ouvertes.fr/tel-00121172.
Der volle Inhalt der QuelleAnciaux, Guillaume. „Simulation multi-échelles des solides par une approche couplée dynamique moléculaire/éléments finis. De la modélisation à la simulation haute performance“. Phd thesis, Université Sciences et Technologies - Bordeaux I, 2007. http://tel.archives-ouvertes.fr/tel-00263816.
Der volle Inhalt der QuelleWang, Meng. „Dynamic fracture of solar grade single crystalline silicon wafers“. Thesis, Lyon, 2019. http://www.theses.fr/2019LYSEI081.
Der volle Inhalt der QuelleCrystalline silicon has attracted substantial attention for decades because of its large applications in solar cells and microelectromechanical systems. The high brittleness of silicon raises wide concerns since the failure of this semiconductor material increases the manufacturing cost and decreases the efficiency of the utilization of Si-based devices. Crack propagation of crystalline silicon is the main cause of catastrophic failure of silicon components. It has been intensively studied but is not fully understood yet due to intricate dynamic fracture behavior linked to small-scale phenomena. Therefore, the development of feasible methods to study the dynamic fracture, as well as the deeper understanding of fracture mechanism of crystalline silicon, are of paramount importance to improve the reliability and durability of Si-based systems for both industrial and scientific practitioners. In this work, dynamic fracture behavior of solar-grade single crystalline silicon wafers under mechanical loads was studied. We carried out fracture experiments on (001) silicon wafers using three-line or four-line bending apparatus under quasi-static loading. The entire fracture process was captured using a high-speed camera and was analyzed by the high-speed imaging technique. We studied the post-mortem fracture surface using a digital microscope, a laser scanning profilometer, as well as an atomic force microscope. The failure source of the silicon wafer was identified using fractographic analysis. Coupling the crack velocity measurement and fractographic analysis, we determined the crack front during dynamic crack propagation, which exhibits a velocity-dependent shape. We revealed the source of (110)-(111) cleavage plane deflection phenomena during high-speeding crack propagation under line-contact effects. Besides, jointly with the finite element simulations, we demonstrated how dynamics of the crack front is governed by the crystallographic direction-dependent dynamic fracture toughness. Finally, in comparison with the Wallner lines on the fracture surface, generated by linear perturbations of elastic waves on the crack front, we highlight the nucleation and strong nonlinear characteristics of out-of-plane corrugation waves, leaving specific markings that alter the surface roughness of asperity-free material
Soumahoro, Zoumana. „Etude du couplage thermomécanique dans la propagation dynamique de fissure“. Phd thesis, Ecole Polytechnique X, 2005. http://pastel.archives-ouvertes.fr/pastel-00001627.
Der volle Inhalt der QuelleSimon, Samuel. „De la dynamique ferroviaire à l’accommodation microstructurale du rail : Contribution des TTS à la réponse tribologique des aciers : Cas du défaut de squat“. Thesis, Lyon, INSA, 2014. http://www.theses.fr/2014ISAL0028/document.
Der volle Inhalt der QuelleSquats have recently become recognised as one of the major rolling contact fatigue defects in modern railway networks for which there is currently no solution other than preventive grinding operations or costly rail renewal. To better understand the entire damage mechanism of squat, A tribological and metallurgical analysis of the rolling band and the near surface layer was performed close to an incipient squat. This characterization show a significant anisotropy of the rail surface layer associated with developments of Tribological Transformation of Surface. These results reflect some specific wheel/rail contact conditions in this squat area, including an unusual level of shear forces in a straight track. In order to validate this observations, two tests were performed. On the one hand, the contact conditions in a squat area were measured from an instrumented train. On the other hand, the tribological response of the rail steel was studied through regular monitoring of a test site subjected to railway traffic. These tests allow to identify a high imbalance of the traction forces and the presence of local slips at the wheel/rail interface. Several thermomechanical initiation mechanism of squats are then given in a overall diagram of the tribological response of rail steels
Marazzato, Frédéric. „Discrete element and time-integration methods forelasto-plasticity and dynamic cracking“. Thesis, Paris Est, 2020. http://www.theses.fr/2020PESC1001.
Der volle Inhalt der QuelleThe present Ph.D. dissertation proposes contributions to discrete element methods (DEM) and explicit time integration schemes with a view towards dynamic cracking for metallic materials under dynamic loading. DEM, which are usually used to simulate granular materials, are understood through the prism of gradient discretization methods in order to simulate continuous materials. The method has been extended from previous Voronoi meshes to support generalpolyhedral meshes. Material behaviours have been extended from elasto-dynamics to dynamic elasto-plasticity through the addition of a tensorial degree of freedom per mesh cell. The method is robust with respect to the incompressible limit and its parameters only depend on material parameters. Moreover, an explicit pseudo-energy conserving time integration method has been developed, even for nonlinear behaviours and variable time steps, so as to avoid thedissipation of energy available for plastic dissipation and cracking. The method has been coupled to the proposed DEM. Finally, Griffith crack propagation through the mesh facets has been adapted to the present DEM for linear elastic behaviours in two space dimensions. The energy release rate is computed for every cracking mode using the stress intensity factors approximated close to the crack. A criterion of maximization of elastic energy density is used tosimulate kinking
Cortet, Pierre-Philippe. „Croissance lente de fissures : de la fragilité à la complexité“. Phd thesis, Ecole normale supérieure de lyon - ENS LYON, 2007. http://tel.archives-ouvertes.fr/tel-00162873.
Der volle Inhalt der QuelleBenazzouk, Louiza. „Approche du comportement dynamique d'un oxyde liquide dans un matériau composite autocicatrisant " MAC "“. Phd thesis, Université Sciences et Technologies - Bordeaux I, 2013. http://tel.archives-ouvertes.fr/tel-00984446.
Der volle Inhalt der QuellePradille, Christophe. „Vers une meilleure compréhension et caractérisation du comportement des aciers à très haute température“. Phd thesis, École Nationale Supérieure des Mines de Paris, 2011. http://pastel.archives-ouvertes.fr/pastel-00617963.
Der volle Inhalt der QuellePyrzowski, Lukasz. „Analyse visco-plastique de l'endommagement des plaques et coques soumises aux impacts“. Phd thesis, Université d'Orléans, 2010. http://tel.archives-ouvertes.fr/tel-00608054.
Der volle Inhalt der QuelleJoudon, Vincent. „Caractérisation expérimentale de l'initiation et de la propagation de fissure dans une résine époxy sous chargement dynamique“. Thesis, Valenciennes, 2014. http://www.theses.fr/2014VALE0029/document.
Der volle Inhalt der QuelleEpoxy resins toughened with embedded thermoplastic particles are classically used in the aeronautical composites manufacturing. As matrix into laminated composites, epoxy resins determine the delamination resistance of the interlaminar field. The delamination process is a large decohesion that often occurs during impact loadings and it critically compromises the integrity of the light weight composite structures. However, most of the cohesive zone models are not intended to simulate delamination under high rate loadings. In particular, these models do not consider the expected effects of loading rate on fracture behaviour of the resin-rich interlaminar field. Therefore, this research aims at characterizing crack initiation and propagation in epoxy resins under dynamic loadings. For that purpose, we manufacture notched specimens made of pure Hexply RM21 epoxy resin which is mainly used in aeronautics. An experimental procedure is developed and validated in order to estimate initiation and propagation fracture toughness on a 3-points bending test associated to a servo-hydraulic testing machine. Experimental results demonstrate that the dynamic fracture toughness highly increases with the crack propagation speed while the initiation toughness decreases with the impact velocity. These evolutions are consistent with post-mortem micrographic observations that show intensifying fracture mechanisms. Finally, a cohesive law is defined and identified to take into account the dynamic dependency of crack initiation and propagation in the considered epoxy resin
Chantrait, Teddy. „Approche multiéchelle en espace et en temps pour la prévision des endommagements dans les structures composites soumises à un impact de faible énergie“. Thesis, Lyon, INSA, 2014. http://www.theses.fr/2014ISAL0129/document.
Der volle Inhalt der QuelleThe composite laminates are increasingly used in aircraft structural parts which lead to new issues such as the Low Energy Impacts (LEI). Indeed, although they have well mechanical properties relative to their mass, small shocks may be very harmfull for laminates. Controlling such situations is essential for manufacturers that why lot of testing campaigns are currently performed. Yet, they are time consuming and expensive considering the many influential parameters (energy, speed, layup...). Numerical simulations of this phenomenon by practicing the so called “virtual testing” process could be really helpfull to rationalize testing campaigns in order to save money. Yet, this practice remain currently hard to do at the industrial scale due to the excessive CPU time required for fine simulation of damages induced by the LEI. Based on this observation, this work has consisted in taking advantage of the spatial and temporal location of delamination, matrix cracking and fiber breakage that can occur during impact in order to reduce the computational cost. Thus, a space and time multiscale method has been put in place. The impacted structure is split into two areas. One is located around the impacted point, it contains all the non-regularities of the problem (contact, softening law, cohesive zone model). This domain is treated with the explicit dynamics code Europlexus. The other one corresponds to the complementary part. The mechanical problem is much more regular and it is treated with the implicit dynamics code Zset / Zebulon. A low intrusive coupling based on the GC method is carried out between these two codes. It allows to use an adapted model in both regions different time step are in particular used. A time step ratio upper to 1000 can be reach between the one of the explicit code set by the stability condition and the one used in the complementary part. As a results, significant CPU time is saved. This is confirmed by the simulation of a stiffened composite panel impacted. It is also shown that the implicit / explicit allocation can change over the calculation. To do that, a switch mechanism has been established. It thus makes it possible to transit the resolution of a portion of the structure initially solved in the code Zebulon to Europlexus. As a results, further gain is obtained
Zacharopoulos, Marios. „Simulation numérique des fissures et du comportement ductile-fragile de l’aluminium et du fer“. Electronic Thesis or Diss., Paris 6, 2017. http://www.theses.fr/2017PA066038.
Der volle Inhalt der QuelleThe principal aim of the present dissertation is to investigate the role of sharp cracks on the mechanical behaviour of crystals under load at the atomic scale. The question of interest is how a pure crystal, which contains a single crack in mechanical equilibrium, deforms. Two metals were considered: aluminium, ductile at any temperature below its melting point, and iron, being transformed from ductile to brittle upon decreasing temperature below T=77K. Cohesive forces in both metals were modeled via phenomenological n-body potentials. A (010)[001] mode I nano-crack was introduced in the perfect crystalline lattice of each of the studied metals by using appropriate displacements ascribed by anisotropic elasticity. At T=0K, equilibrium crack configurations were obtained via energy minimization with a mixed type of boundary conditions. Both models revealed that the crack configurations remained stable under a finite range of applied stresses due to the lattice trapping effect. The present thesis proposes a novel approach to interpret the intrinsic mechanical behaviour of the two metallic systems under loading. In particular, the ductile or brittle response of a crystalline system can be determined by examining whether the lattice trapping barrier of a pre-existing crack is sufficient to cause the glide of pre-existing static dislocations on the available slip systems. Simulation results along with experimental data demonstrate that, according to the model proposed, aluminium and iron are ductile and brittle at T=0K, respectively
Boukhili, Rachid. „Fissuration par fatigue des polyamides : mécanismes“. Compiègne, 1985. http://www.theses.fr/1985COMPD005.
Der volle Inhalt der QuelleEid, Elie. „Towards a multi-scale analysis of dynamic failure in architectured materials“. Thesis, Ecole centrale de Nantes, 2021. https://tel.archives-ouvertes.fr/tel-03670412.
Der volle Inhalt der QuelleArchitectured materials are a rising class of materials that provide tremendous possibilities in terms of functional properties. Interest is drawn on the failure of architectured materials in which scale separation ceases to exist. This directly translates to strong interactions between a crack tip and the architecture independently of the considered scale. Moreover, under dynamic loadings, stress-waves come into play and interactions between the crack-tip, the microstructure (architecture) and the stress-waves eventually pilot together the structural behaviour. In this thesis, three types of architectured materials are considered: one periodic and two Penrose-type quasi-periodic lattices of holes. The analysis is broken into three parts. To study the influence of the microstructure on crack-propagat ion at different scales, numerical simulations of failure are analysed; they show improved resistance to crack propagation in the quasi-periodic materials. At the core of the work is also the development of a coarse-graining technique that requires no representative volume element. This technique allows for a physically consistent multiscale evaluation of the effective failure properties of the architectures. The inevitability of the consideration of a non-homogeneous effective medium to accurately model microstructural effects at larger scales is highlighted. In dynamics, the influence of the architectures on the stress-wave attenuation shows improved attenuation properties of the quasi-periodic lattices. Moreover, to understand the mechanism(s) governing the dynamic branching phenomenon in a homogeneous material, a criterion based on dynamic fracture mechanics is developed and validated on a novel experimental setup where Ultra-High-Speed-High- Resolution imaging is combined with Digital Image Correlation to capture extraordinary phenomena. The unquestionable role of T-stress in dynamic branching is put forth. This thesis brings forth the necessary tools towards a multi-scale analysis of dynamic failure of architectured materials
Ulm, Franz-Josef. „Modélisation élastoplastique avec endommagement du béton de structure. Application aux calculs statiques et dynamiques de structures en béton armé et béton précontraint“. Phd thesis, Ecole Nationale des Ponts et Chaussées, 1994. http://tel.archives-ouvertes.fr/tel-00529366.
Der volle Inhalt der QuelleAsali, Mehdi. „Modélisation et prévision du comportement thermo-hydro-mécanique d’une paroi en béton : application au cas des enceintes de confinement des bâtiments réacteurs nucléaires“. Thesis, Lille 1, 2016. http://www.theses.fr/2016LIL10143/document.
Der volle Inhalt der QuelleThe containment building represents the third and last protection barrier of nuclear reactors buildings (NRB). Yet ageing mechanisms of prestressed concrete could strongly affect the tightness capacity of the inner containment of a double-wall reactor building over time. That is a major issue considering the long term operation and the possible life extension of NRB while ensuring safety and regulatory requirements. Considering the size of such structures and the complexity of all interacting phenomena, it is very difficult to build an industrial and operational tool modeling all the strong couplings occurring at different scales. In that context, this Ph.D. thesis introduces a numerical strategy aiming at forecasting the leakage rate evolution of inner containments during operation. It is based on an adapted macro-element mesh, on a simple but physically representative chained weakly-coupled thermo-hydro-mechanical modeling and on a 3D finite element specially designed for computing air leakage through unsaturated porous and cracked concrete. The proposed strategy has been applied to the scale 1:3 VeRCoRs mock-up: results are validated with available experimental data until the first internal pressurization test before being extended until the third one.The proposed strategy enables operators to:- Take into account variabilities and uncertainties of main parameters to quantify their impact on the total leak rate;- Numerically introduce defects coming from visual inspections;- Pre-empt and optimize leak mitigation actions to avoid outage extensions and associated losses of income
Grégoire, David. „Initiation, propagation, arrêt et redémarrage de fissures sous impact“. Phd thesis, INSA de Lyon, 2008. http://tel.archives-ouvertes.fr/tel-00418626.
Der volle Inhalt der QuelleDes expériences de rupture dynamique ont donc été réalisées sur du Polyméthacrylate de méthyle (PMMA) durant lesquelles la mixité du chargement varie et des arrêts et redémarrages de fissures se produisent. Deux bancs d'essais différents ont été utilisé, le premier basé sur la technique des barres de Hopkinson (ou barres de Kolsky), le second mettant en jeu un vérin rapide. Le PMMA étant transparent, la position de la fissure au cours de l'essai a été acquise grâce à des caméras rapides mais aussi en utilisant un extensomètre optique (Zimmer), habituellement dédié à la mesure de déplacements macroscopiques d'un contraste noir/blanc. L'utilisation de cet extensomètre pour suivre la fissure au cours de l'essai a permis d'obtenir une localisation très précise de la pointe de la fissure en continu, permettant ainsi l'étude des phases transitoires de propagation. Afin d'étudier le même phénomène dans des matériaux opaques comme les aluminiums aéronautiques (Al 7075), des techniques de corrélation d'images numériques ont été employées en mouchetant les éprouvettes impactées. De nouveaux algorithmes ont été développés afin de traiter les images issues d'une caméra ultra-rapide (jusqu'à 400 000 images par seconde).
Plusieurs géométries ont été envisagées afin d'étudier différents cas de propagation dynamique : initiation en mode I pur, initiation en mode mixte, propagation, arrêt, redémarrage, interaction entre deux fissures, influence d'un trou sur le trajet d'une fissure, branchement dynamique de fissures. Ces expériences ont ensuite été reproduites numériquement afin de valider les algorithmes et les critères de rupture choisis.
Perez, Romero Sergio Alejandro. „Approche experimentale et numérique de la fissuration réflective des chaussées : de la chaussée instrumentée au laboratoire en passant par la modélisation“. Limoges, 2008. https://aurore.unilim.fr/theses/nxfile/default/8a632270-ccc9-4e1d-b0d9-864a330063c7/blobholder:0/2008LIMO4070.pdf.
Der volle Inhalt der QuelleIn the domain of pavement maintenance, a major problem observed is the frequent incidence of reflective cracking over the top asphalted new layer. The object of this work is to determine the internal efforts in this layer in order to define the loading protocols for the reflective cracking testing machine called MEFISTO at the Laboratoire Regional d'Autun (LRA). In a first stage, the phenomenon of reflective cracking was studied on a small track in a full scale test using the Accelerated Pavement Testing (APT) machines FABAC of the LCPC. The experimental results have been compared with numerical calculations made with the CESAR-LCPC FEA software. This comparison has lead into a validation of the calculation hypothesis and into a better comprehension of the reflective cracking failure mechanism reproduced with the LCPC APT equipment. In a second stage, the FEA calculation method was used to define the loading protocols of the MEFISTO equipement
Duplessis, Kergomard Yann. „Etude expérimentale et numérique de la fissuration intralaminaire et de l’initiation du délaminage de bord libre dans les structures stratifiées pseudo-tissées“. Paris, ENMP, 2007. http://www.theses.fr/2007ENMP1508.
Der volle Inhalt der QuelleGlass / Epoxy laminated structures made with pseudo woven prepregs are studied. In this kind of materials, delamination and intralaminar damages are usually observed. The study is divived in five main parts. First, intralaminar fissuration’s characteristics are experimentaly investigated. Many of this characteritics are very like the ones usually observed in non woven laminated composites. Still, the studied material’s pseudo woven structure have great influence on this damage, particularly for the damages’ kinetic evolution and its thickness effect. A second testing program was conducted to investigate on structures’ free egdes delamination initiation. To able to detecte and observe the differents damages developping on specimen’s free edges, an innovative optic method was established. A dye and a suitable lighting are used for this method. We have been able to study both effects of intralaminar damages and the material’s pseudo woven structure on delamination beginning. In addition, intralaminar damages have been modeled and a delamination initiation criterion have been established. Moreover, intralaminar damages modeling could take into account incomplete closing cracks effects. Delamination criterion is a stress criterion. It’s built with the delaminating interface’s stress vector of whom components are averaged on a characteristic distance. At last, the model and the criterion were validated on both non holed and holed specimens
Jaafari, Chaimaa. „Effect of early age drying shrinkage on the seismic response of RC Structures“. Thesis, Lyon, 2020. http://www.theses.fr/2020LYSEI113.
Der volle Inhalt der QuelleReinforced Concrete (RC) structures get damaged over time due to many factors: thermal conditions, chemical attacks, shrinkage, creep, carbonation, corrosion, etc. This damaging process starts at early-age and continues with structure aging. Early age damage can have a significant impact on the dynamic behavior of reinforced concrete structures. In fact, the natural frequency of a structure, which is a design parameter can be highly reduced due to this damage. In order to quantify the impact of early-age damage (0 to 28 days) on the seismic response of a reinforced concrete structure, this thesis combined both numerical modeling and pseudo-dynamic tests on two types of RC portal frames. The first one was kept in endogenous conditions (water exchange with the surrounding environment was prevented) during its early age period in a way to limit drying effects leading to cracks. As for the second one, it was kept in non-endogenous conditions (possibility of water exchange with the surrounding environment) similar to construction site conditions, which induced an initial damage (cracks apparition) due to a more important drying shrinkage. Both types of RC portal frames were subjected after their early age period to the same seismic loading using pseudodynamic tests. On the one hand, this manuscript presents the experimental results obtained through the use of pseudodynamic tests in order to evaluate the behavior of the two types of RC structures under a moderate intensity earthquake. The structures were instrumented using optical fiber sensors, displacement and load sensors, velocimeters and monitored using Digital Image Correlation. On the other hand, the enhanced multifiber beam model that was developed for the portal frames in order to follow their early age damage and to determine their static and dynamic behavior while accounting for their early age effects is presented. In this numerical model, shrinkage and concrete thermal deformations are calculated and then introduced as inputs of a coupled damage model accounting for creep and mechanical deformations. Such model was validated by comparing its results to the ones obtained experimentally, which made it possible to evaluate the evolution of frequency content of the two types of structures during early age and to quantify their difference of behavior in the non-linear domain. Work conducted within this thesis thus allowed proposing a complete model for reinforced concrete structures that can be used in order to follow their damage evolution from casting until being subjected to a seismic load and to quantify their seismic vulnerability
Baglion, Laurent de. „Comportement et endommagement en fatigue oligocyclique d'un acier inoxydable austénitique 304L en fonction de l'environnement (vide, air, eau primaire REP) à 300°C“. Chasseneuil-du-Poitou, Ecole nationale supérieure de mécanique et d'aérotechnique, 2011. https://tel.archives-ouvertes.fr/tel-00623190.
Der volle Inhalt der QuelleNowadays, for nuclear power plants licensing or operating life extensions, various safety authorities require the consideration of the primary water environment effect on the fatigue life of Pressurized Water Reactor (PWR) components. Thus, this work focused on the study of low cycle fatigue damage kinetics and mechanisms, of a type 304L austenitic stainless steel. Several parameters effects such as temperature, strain rate or strain amplitude were investigated in air as in PWR water. Thanks to targeted in-vacuum tests, the intrinsic influence of these parameters and environments, on the fatigue behaviour of the material, was studied. It appears that compared with vacuum, air is already an active environment which is responsible for a strong decrease in fatigue lifetime of this steel, especially at 300°C and low strain amplitude. The PWR water coolant environment is more active than air and leads to increased damage kinetics, independently of the strain amplitude in the elastoplastic domain and without any modifications of the initiation sites or propagation modes. Moreover, the decreased fatigue life in PWR water is essentially attributed to an enhancement of both initiation and micropropagation of "short crack". Finally, the deleterious influence of low strain rates on the 304L austenitic stainless steel fatigue lifetime was observed in PWR water environment, in air and also in vacuum any environmental effects
Zacharopoulos, Marios. „Simulation numérique des fissures et du comportement ductile-fragile de l’aluminium et du fer“. Thesis, Paris 6, 2017. http://www.theses.fr/2017PA066038/document.
Der volle Inhalt der QuelleThe principal aim of the present dissertation is to investigate the role of sharp cracks on the mechanical behaviour of crystals under load at the atomic scale. The question of interest is how a pure crystal, which contains a single crack in mechanical equilibrium, deforms. Two metals were considered: aluminium, ductile at any temperature below its melting point, and iron, being transformed from ductile to brittle upon decreasing temperature below T=77K. Cohesive forces in both metals were modeled via phenomenological n-body potentials. A (010)[001] mode I nano-crack was introduced in the perfect crystalline lattice of each of the studied metals by using appropriate displacements ascribed by anisotropic elasticity. At T=0K, equilibrium crack configurations were obtained via energy minimization with a mixed type of boundary conditions. Both models revealed that the crack configurations remained stable under a finite range of applied stresses due to the lattice trapping effect. The present thesis proposes a novel approach to interpret the intrinsic mechanical behaviour of the two metallic systems under loading. In particular, the ductile or brittle response of a crystalline system can be determined by examining whether the lattice trapping barrier of a pre-existing crack is sufficient to cause the glide of pre-existing static dislocations on the available slip systems. Simulation results along with experimental data demonstrate that, according to the model proposed, aluminium and iron are ductile and brittle at T=0K, respectively
Roux, Stéphane. „Structures et désordres“. Phd thesis, Ecole Nationale des Ponts et Chaussées, 1990. http://tel.archives-ouvertes.fr/tel-00523045.
Der volle Inhalt der QuelleDo, Xuan Nam. „Localized failure in dynamics for brittle and ductile materials“. Thesis, Compiègne, 2017. http://www.theses.fr/2017COMP2356.
Der volle Inhalt der QuelleFailure 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
Giry, Cedric. „Modélisation objective de la localisation des déformations et de la fissuration des structures en béton soumises à des chargements statiques ou dynamiques“. Phd thesis, Université de Grenoble, 2011. http://tel.archives-ouvertes.fr/tel-00697769.
Der volle Inhalt der QuelleGlacet, Arthur. „Study of quasi-periodic architectured materials : Vibrations, dynamic fracture and homogenization“. Thesis, Lyon, 2018. http://www.theses.fr/2018LYSEI062/document.
Der volle Inhalt der QuelleQuasi periodic (QP) structures have shown peculiar properties in the atomistic domain, especially the vibrational one. It could be interesting to be able to transpose these properties in macroscopic meta-materials. Quasi periodic 2D beam lattices are studied in this thesis due to the simplicity of the Euler Bernoulli finite element (FE) model. These beam lattices can easily be produced by additive manufacturing or by laser cutting. It is possible to vary the beam slenderness (i.e the ratio of height over length) that is a interesting parameter to modify the mechanical response of the lattice. Using finite element method, the influence of the beam slenderness over the vibration behavior of the QP beam lattices will be studied. The Kernel Polynomial numerical Method (KPM) is successfully adapted from molecular dynamics simulations in order to study vibrational modes of FE beam lattices without having to fully diagonalize the dynamical matrix. The QP lattices show similar properties as their atomic counterpart e.g mode localization over sub-stuctures and hierarchical dispersion relation. The fracture behavior is also studied, as the special symmetries allowed by the quasi periodicity could result in beam lattices without weak planes for crack propagation. It was proved to be true from static FE simulations with a brittle strain energy breaking criterion. Static simulations were not enough and do not grasp the complex dynamical phenomena taking place in brittle fracture. A dynamic crack propagation model was thus developed. The vibrational properties of quasi periodic structures could also have an impact on the dynamic crack propagation. Several simulations are run in order to study the impact of the slenderness on the energy dissipated by fracture of QP lattices. Finally, a coarse graining method (CG) was developed to identify a continuous Cosserat medium at different scales from the FE beam model. This CG method allows to identify, density, strain, stress and elastic moduli of an equivalent continuous Cosserat. This allows a better understanding of the role of previously identified characteristic sub structures
Lambert, 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.
Der volle Inhalt der QuelleNaït, Oultit Bouchra. „Endommagement des soudures d'aciers à très haute résistance pendant l'essai de traction en croix : analyse mécanique et métallurgique de la fissuration dans la zone fondue“. Saint-Etienne, EMSE, 2008. http://www.theses.fr/2008EMSE0032.
Der volle Inhalt der QuelleResistance spot welding is the most widely used joining process in automotive industry. In order to assess the performances of the spot welds, specific behaviour is recommended after the cross-tension test. Mild and low-alloyed steels show a plug failure occurrence in the base metal or the Heat-Affected Zone (HAZ) and then meet the standards. Newly developed advanced high-strength steels (AHSS, Rm≥800MPa) have to meet also specific requirements of this process. However, Dual-Phase (DP) and TRansformation-Induced Plasticity (TRIP) steels exhibit a completely new behaviour where crack propagates very often partially or totally within the Fusion Zone (FZ) along the joint interface. The obtained plug size is generally rejected after qualitative tests because it is assumed to correspond to a very low mechanical strength. Add to this that the cross-tension strength (CTS) of the joint does not increase with base metal resistance. In this work, a new methodology to analyse the cross-tension test curves is developed and leads to the definition of the damage steps (6 at most). These sequences are highlighted by precise evolutions of the apparent rigidity during the test. Physical interpretations explain the occurrence of each sequence and confirm that CTS level is not directly correlated to a specific failure type. In order to assess CTS, we argue how both mechanical components of the solicitation and local crack resistance have to be considered. Several DP and TRIP steels exhibiting very different failure types are analyzed. Our characterization of local microstructure leads us to understand the variations of the apparent rigidity during a given sequence and hence the impact of base metal or weld microstructures on CTS. It is hence assessed that crack paths responsible for failures within the FZ are not necessarily indicative of a reduced mechanical strength. This approach is capitalized through the Damage Contribution Methodology, DCM. With the help of this new tool, it becomes possible to target the physical factors that steel developers have to act on to reach optimal mechanical behaviour
Yao, Lan. „Experimental and numerical study of dynamic crack propagation in ice under impact loading“. Thesis, Lyon, 2016. http://www.theses.fr/2016LYSEI043/document.
Der volle Inhalt der QuelleThe phenomena relating to the fracture behaviour of ice under impact loading are common in civil engineering, for offshore structures, and de-ice processes. To reduce the damage caused by ice impact and to optimize the design of structures or machines, the investigation on the dynamic fracture behaviour of ice under impact loading is needed. This work focuses on the dynamic crack propagation in ice under impact loading. A series of impact experiments is conducted with the Split Hopkinson Pressure Bar. The temperature is controlled by a cooling chamber. The dynamic process of the ice fracture is recorded with a high speed camera and then analysed by image methods. The extended finite element method is complementary to evaluate dynamic fracture toughness at the onset and during the propagation. The dynamic behaviour of ice under impact loading is firstly investigated with cylindrical specimen in order to obtain the dynamic stress-strain relation which will be used in later simulation. We observed multiple cracks in the experiments on the cylindrical specimens but their study is too complicated. To better understand the crack propagation in ice, a rectangular specimen with a pre-crack is employed. By controlling the impact velocity, the specimen fractures with a main crack starting from the pre-crack. The crack propagation history and velocity are evaluated by image analysis based on grey-scale and digital image correlation. The main crack propagation velocity is identified in the range of 450 to 610 m/s which confirms the previous results. It slightly varies during the propagation, first increases and keeps constant and then decreases. The experimentally obtained parameters, such as impact velocity and crack propagation velocity, are used for simulations with the extended finite element method. The dynamic crack initiation toughness and dynamic crack growth toughness are determined when the simulation fits the experiments. The results indicate that the dynamic crack growth toughness is linearly associated with crack propagation velocity and seems temperature independent in the range -15 to -1 degrees
Oni, Olorunnisola. „Contribution à l'étude des fissures courtes se propageant en fatigue dans les aciers“. Compiègne, 1986. http://www.theses.fr/1986COMPI214.
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