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Rozprawy doktorskie na temat "Facteur d’intensité des contraintes critiques"
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.
Pełny tekst źródłaOrganic 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
Maamar, Fatouma. "Méthode pour un calcul rapide des facteurs d’intensité de contrainte en bord de joint collé subissant un chargement mécanique et cryogénique : exploitation en vue de prédire la tenue en rupture adhésive". Toulouse 3, 2011. http://thesesups.ups-tlse.fr/4867/.
Pełny tekst źródłaThe work focuses on methods for predicting the adhesive failure strength of a bonded joint, that is to say the resistance to delamination at an interface between a substrate and the adhesive layer. It attempts to define a method to quickly calculate a criterion for the failure initiation to serve a particular application domain: space construction where assemblies undergo thermal loading at low temperatures, the studied materials being structural adhesive Scotch-Weld DP490, invar and silicon carbide. The conventional criterion of the stress intensity factor has been chosen a priori, its formulation being "K < KC” where K is an indicator of the peeling stress intensity at the end of the interface, and KC is a critical value beyond which the rupture occurs. The main objective being to develop a simple and quick method to calculate K, an approach using influence parameters is proposed. It is based on four reference stresses, three of them being obtained at a well defined point of a specific mesh, from a very few detailed finite element analysis, the fourth being the homogeneous peel stress which appears in the entire singular zone in thermal loading conditions. The identification of the four influence parameters is based on a numerical experiments plan where three different types of loads are considered. The gap between the results obtained and reference values remains low. The proposed method is then applied to various concrete configurations corresponding to tests performed by an industrial partner. It is shown that the calculation of K is reliable, but that, cons, the criterion appears not to be suitable for application area considered here
Boussattine, Zaid. "Consequences of the thermal effects generated during fatigue crack growth on the mode one stress intensity factor". Thesis, Paris, ENSAM, 2018. http://www.theses.fr/2018ENAM0047/document.
Pełny tekst źródłaBy subjecting a cracked specimen to a cyclic loading, thermal effects take place and create a heterogeneous temperature field around the crack tip. Those thermal effects are associated with coupling and dissipative heat sources, namely: (i) the heat source due to thermoelastic coupling generated by the hydrostatic part of the stress tensor related to cyclic mechanical loading; (ii) the heat source due to intrinsic dissipation associated with the self-heating phenomena originating from plasticity at the microscopic scale; (iii) and the heat source due to cyclic plasticity, at the macroscopic scale, which occurs in the reverse cyclic plastic zone ahead of the crack tip, and dissipates into heat. The overall heterogeneous temperature field resulting from the heat sources induces a heterogeneous stress field due to thermal expansion phenomena. As a consequence, the stress state over the crack is modified and leads to modify the stress intensity factor, which is a key parameter in modeling fatigue crack growth. Therefore, the aim of this PhD thesis is to quantify the consequences of the heat sources on the stress intensity factor, in the case of a long propagating fatigue crack
Pannemaecker, Alix de. "Etude du phénomène d'arrêt de propagation des fissures au travers d'un couplage multi-échelles fretting, fretting fatigue et essai fatigue C(T)". Thesis, Ecully, Ecole centrale de Lyon, 2015. http://www.theses.fr/2015ECDL0010/document.
Pełny tekst źródłaAircraft structures such as blade/disk, rivet/sheet and fretted or bolted assembly contacts are subjected to fatigue fretting damage caused by vibratory loads. These loads combining fretting (alternating micro displacements) and fatigue contact loading can induce cracks. The objective of this thesis is to identify the propagation and crack arrest mechanisms for different configurations involving fretting and fatigue loads. Various aspects will be studied : - Simple fretting, fatigue fretting and fatigue tests will be correlated in a way to measure some material mechanical properties. A reverse approach allowing to identify the long and short fatigue crack propagation thresholds from simple fretting and fretting fatigue will be introduced. - A new closure model taking into account the effect of loading ratio on crack closure in fretting and fretting fatigue tests will be proposed. - The scaling effect will be studied thanks to the development of a new fretting fatigue machine allowing for in-situ monitoring of the propagation of small scale cracks. The behavior of fretting short cracks has been observed for the first time in a fretting fatigue test. The main idea behind the current work is the consideration that for a simple fretting test, the crack will always lead to a crack propagation arrest condition. Threshold stress intensity factors can thus be extracted from fretting tests using a reverse method. The methodology used consists in measuring the longest fretting crack corresponding to a crack propagation arrest condition. Short and long crack regimes are studied by varying fretting loads and geometries. The corresponding threshold stress intensity factor is calculated for each arrest condition. A complete description of fatigue crack arrest thresholds can be obtained from a plot depicting the evolution of the stress intensity factor range as a function of crack length. This methodology has been applied on multiple simple fretting configurations and was extended to fretting fatigue tests allowing to study a large range of loading ratios. Conventional fatigue crack propagation tests were carried out on C(T) specimens in order to validate the reverse method used for crack arrest conditions. The present thesis is divided into six main chapters. Chapter 1 provides a complete literature review on short and long crack propagation in metallic materials introducing crack closure. It provides a treatment for both fretting and fretting fatigue including a comparative analysis. Chapter 2 provides an overview of the different techniques and methodologies used as part of this research project. The reverse method used for the identification of crack propagation arrest conditions as well as a numerical analysis are presented in Chapter 3. The following Chapters provide a treatment of the various results obtained. Chapter 4 focuses on simple fretting tests carried out on different metallic materials. A correlation between simple fretting and long fatigue crack arrest conditions was obtained for negative loading ratios. This analysis is extended to positive loading ratios in Chapter 5 combining simple fretting, prestressed fretting and C(T) fatigue tests. Finally, scaling effects and fretting fatigue crack propagation kinetics are studied in Chapter 6
Roux-Langlois, Clément. "Simulation de fissures courbes en trois dimensions avec extraction directe des facteurs d'intensité des contraintes : En vue de l'identification de lois de propagation de fatigue". Thesis, Lyon, INSA, 2014. http://www.theses.fr/2014ISAL0112/document.
Pełny tekst źródłaIt is necessary to understand the behavior of structures up to their failure to enhance their design. The mechanisms and phenomena undergoing failure vary according to the considered material and boundary conditions. We consider homogeneous materials for which cracks propagate in a context where behavior nonlinearities are not dominants. These conditions are matched for brittle and quasi-brittle materials and for some fatigue cracks. For the former, the main source of dissipation is the crack propagation which can be seen as the generation of a new free-surface. For the later, there is many applications where, in one loading cycle, the nonlinearities remains confined around the crack tip. The linear elastic fracture mechanics theory is then a pertinent model to approximate the structure behavior. Under such hypotheses, a singularity appears in the crack tip vicinity. The Williams' series expansion is computed from the asymptotic study of plane and anti-plane states. The stress is singular at the crack tip and the order of this singularity is one out of two. The singularity amplitude is quantified by the stress intensity factors (SIF), one for each of the three loading modes. In 3D, the crack shape is potentially complex (front curvature and non-planar crack), and no general asymptotic series expansion exists. In this PhD thesis, the 2D Williams' series in displacements are used and regularized with a finite element evolution along the front. From this 3D definition of the asymptotic fields in the crack tip vicinity, a numerical method for direct estimation of the SIF (DEK-FEM) is extended to 3D. This method is based on domain decomposition, the two domains are bounded in a weak sense on their interface. In the crack tip vicinity, the mechanical fields are approximated by a truncation of the asymptotic series expansion. Therefore, appropriate fields are used to deal with the singularity, and the associated degrees of freedom are directly the asymptotic coefficients. Among these coefficients are the SIF and the T-stresses. To bridge the scales between the structure and the crack front singularity and to increase the numerical efficiency, this method is embedded in a localized X-FEM multigrids approach. The proposed method is shown to provide an accurate evaluation of the SIF and T-stresses evolution. This approach has been developed in combination of an experimental post-processing method (full field displacement measurement through image correlation) based on the same asymptotic series expansion. The 3D images can be obtained for in situ fatigue experiments by X-ray microtomography and reconstruction. The crack geometry and the SIF are then provided by image correlation and regularization based on Williams series expansion. These data can be used for identifying a 3D fatigue crack growth law. The efficiency of the method is illustrated in 2D
Taillebot, Virginie. "Contribition à l'étude de la rupture des alliages à mémoire de forme". Thesis, Besançon, 2012. http://www.theses.fr/2012BESA2026/document.
Pełny tekst źródłaMajor player among functional materials, Shape Memory Alloys (SMA) may undergo verylarge reversible strain. SMA exhibit a Martensitic Phase Transformation (MPT) when they aresubmitted to mechanical or thermal actions, and that gives them some specific characteristics.The thermomechanical behavior of SMA is now well controlled. However, the knowledge of theSMA fracture behavior is a major challenge for their design and sizing for their sustainableindustrialization. This research project has focused on the understanding, describing and quantifyingof the phenomenon of localization at the crack tip due to stress-induced MPT. The study includestwo main aspects: the development of an analytical model and its experimental correlation bysimultaneous field’s measurements during tests on cracked NiTi specimens. Two analytical modelsbased on the linear fracture mechanics and those introduce the asymmetrical nature of the SMAbehavior in tension/compression, were developed for the prediction of transformation zones in thevicinity of the crack tip, taking into account the fracture mode (elementary and mixed ones)and the radii of curvature of the crack tip. A testbench with the measurement of simultaneouskinematic field with Digital Image Correlation (DIC) and thermal field with infrared thermographywas designed for mapping the experimental fields during fracture tests in mode I on pre-crackedspecimen. This good correlation of analytical models opens up many perspectives on the analysisof thermomechanical coupling associated with the MPT at the crack tip, the enrichment of the initialanalytical models, and comparison with experimental results for more complex failure modes (II andmixed I+II)
Pindra, Nadjime. "Etude de l'évolution de la déformation du front d'une fissure". Phd thesis, Université Pierre et Marie Curie - Paris VI, 2009. http://tel.archives-ouvertes.fr/tel-00710029.
Pełny tekst źródłaLachambre, Joël. "Développement d'une méthode de caractérisation 3D des fissures de fatigue à l'aide de la corrélation d'images numériques obtenues par tomographie X". Thesis, Lyon, INSA, 2014. http://www.theses.fr/2014ISAL0050/document.
Pełny tekst źródłaThis manuscript describes a methodology used to compute Stress Intensity Factor values along the curved front of a fatigue crack inside a nodular cast iron. An artificial defect is introduced at the surface of a small sample. The initiation and growth of a fatigue crack from this defect during constant amplitude cycling is monitored in situ by laboratory x-ray tomography. The method for processing the 3D images in order to compute SIF values is described in detail. The results obtained show variations of the stress intensity factor values along the crack front