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Academic literature on the topic 'Matériaux – Fatigue – Dissertation universitaire'
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Dissertations / Theses on the topic "Matériaux – Fatigue – Dissertation universitaire"
Manaii, Racha. "Étude du comportement mécanique en fatigue et à l'impact du composite lin/ Elium." Electronic Thesis or Diss., Paris, HESAM, 2021. http://www.theses.fr/2021HESAE027.
Full textThe advantages brought by natural fibers in the composite materials sector are multiple: lightness, good specific mechanical properties, competitive cost and reduced environmental impact. In view of these advantages, the interest for these fibers has multiplied the scientific studies concerning them, in particular with regard to the objectives of a sustainable development. However, the use of these materials in structural parts is subject to the knowledge of their long-term behavior and in front of the various dynamic and repetitive loads. In this context, the objective of this thesis is to study the mechanical behavior of a flax fiber composite and Elium® matrix in fatigue and impact. In a first step, this study allowed to determine the mechanical properties of the material in traction and to follow the induced damage by means of microscopic observations and acoustic emission analysis. Then, in order to answer the problem related to the resistance and endurance in fatigue, the experimental campaign carried out allowed an estimation of the LCF/HCF limit and to study the damage in repetitive loading of the material. Finally, the response to low speed impact was studied. Different tools were used to study the impact response. The results also showed a strong potential of repair after impact of the composite, in the absence of fiber rupture, and this thanks to the thermoplastic resin Elium®
Subramanian, girija Rahul. "Durabilité de l'aciers inoxydables obtenu par fabrication additive en situation de couplage Fatigue-Hydrogène." Electronic Thesis or Diss., Paris, HESAM, 2024. http://www.theses.fr/2024HESAE006.
Full textSelective Laser Melting (SLM) process has the potential to fabricate complex parts which can find applications in hydrogen-based systems, due to their improved strength-ductility trade-off and inherent austenite phase traditionally resistant to Hydrogen Embrittlement (HE). Knowledge on the HE resistance of these new class of SLM materials is crucial. In this context, the goal of this work is to experimentally assess and understand the susceptibility of additive manufactured stainless steels (SS) to HE under coupled mechanical testing conditions.For this purpose, three grades of SLM fabricated SS are chosen : austenitic 316L and 304L and martensitic 17-4PH. Heat treatments are performed to modify the dislocation sub-structure and the consequent impact on hydrogen diffusion is studied under both electrochemical and high-pressure hydrogen gas charging conditions. Slower diffusion of hydrogen in the dislocation-rich microstructure and a localisation of hydrogen within 100 µm from the charging surface were observed. The dominant role of defects impedes the evaluation of the impact of hydrogen on both ductility and fatigue crack initiation in SLM-316L samples fabricated through a ‘No Rotation’ laser strategy and SLM-304L.Insitu electrochemical mechanical tests affect the strength and ductility of the chosen materials more than the high-pressure hydrogen gas condition. H-dislocation interaction varies depending on the severity of H-charging and the nature of the dislocations. Complex phenomena are evidenced during insitu electrochemical fatigue tests on SLM-316L, and the observed loss of fatigue properties are explained through complementary evidence. Fatigue crack growth rates increase in the presence of hydrogen supported through observations of fatigue striation spacing, indicating that SLM-fabricated austenitic stainless steels are susceptible to HE under adverse H-charging conditions. Severe HE is observed in SLM-17-4PH subjected to H900 heat treatment both in tension and fatigue
Landron, Thomas. "effets des gradients de porosité et de contrainte sur le comportement en fatigue à grand nombre de cycles de l’alliage d’aluminium AlSi9Cu3 coulé sous pression." Electronic Thesis or Diss., Paris, HESAM, 2023. http://www.theses.fr/2023HESAE091.
Full textThis research deals with the effect of porosity and stress gradients on the high-cycle fatigue behavior (HCF) of the high-pressure die-cast (HPDC) aluminum alloy AlSi9Cu3 used by the automotive industry. The components produced by HPDC are characterized by a high level of porosity compared to other casting processes. In addition, the porosity or defect distribution within a component is highly heterogeneous and the existence of a porosity gradient between the surface and the in-bulk material is notable. Defects of different nature and size are present, including defects formed by complex three-dimensional pore networks.To study the effects of the porosity and stress gradients on the HCF behavior, a test methodology based on reducing the thickness of as-cast specimens by machining was developed. Four geometries machined from the same as-cast specimens were tested in HCF under different loading modes: plane bending and tension-compression with a load ratio R=-1. The analysis of the fatigue failure surfaces, combined with fatigue results in the form of Wöhler curves shows that fatigue behavior is controlled by the interaction between the porosity gradient and the stress gradient. The position of the crack initiation site (surface or in-bulk), the nature of the critical defects, as well as the fatigue strength are entirely determined by these two gradients.The effect of defects on the fatigue behavior was analyzed using an approach based on the Kitagawa-Takahashi diagram and the stress intensity factor threshold (Kth). This analysis shows that the fatigue strength of the material is controlled by the size of the defects in terms of the Murakami parameter (√area). The wide range of defect size and the variety of defect types makes it possible to characterize the behavior of the material in both the short crack and long crack regimes. It is observed that the position of the crack initiation site (surface or in-bulk) has only a small effect on the fatigue behavior. Thanks to a comparison between the studied alloy and other gravity-cast aluminum alloys, it is shown that both the fatigue strength and the crack propagation behavior, is partly controlled by (a) the microstructural characteristics of alloys (grain size and secondary dendrite arm spacing (SDAS)) and by (b) the monotonic and cyclic mechanical behavior of the materials.The complexity of the defect distribution (type, size and spatial distribution) complicates the characterization and modeling of the kinetics of crack propagation and their interactions with defects. To investigate this, in-situ image correlation was used to monitor crack growth during fatigue tests, with the aim of observing the crack interaction with natural defects, in bending at R=-1. The analysis of the crack growth kinetics and the fatigue failure surfaces reveals a strong interaction between fatigue cracks and defects. These interactions cause rapid crack accelerations, which drastically reduce the fatigue life. A HCF crack propagation model is proposed using an averaging approach with the Paris law. The coefficients are adjusted using the crack monitoring tests. The comparison between the simulated Wöhler curves at initial iso-defect-size and the experimental Wöhler curves shows that the propagation approach is not sufficient to account for all the stages leading to fatigue failure. It is clearly highlighted that the initiation phase must be taken into account and that the fatigue damage mechanisms, associated with defects comprised of complex three-dimensional pore networks, are extremely complex.Keywords: High cycle fatigue (HCF), microstructural heterogeneity, porosity gradient, stress gradient, aluminum alloy, high-pressure die-casting, porosity networks, fatigue life, crack – defect interaction
Bremaud, Luc. "Contribution à la modélisation de l’endommagement sous sollicitations dynamiques de céramiques." Electronic Thesis or Diss., Paris, HESAM, 2023. http://www.theses.fr/2023HESAE092.
Full textCeramics play a crucial role in both the industrial and military sectors due to their unique thermomechanical properties. However, their behavior under dynamic loading is complex, with significantly lower tensile strength compared to compression, leading to cracking, damage, and multi-fragmentation. The pursuit of advanced technology necessitates continuous development of the ballistic properties of ceramics. The high cost and technical complexity of dynamic experiments have given rise to simulation programs that seek to digitally replicate the dynamic fracture behavior of these materials.This thesis explored the application of the Discrete Element Method (DEM) to enhance the reproduction of dynamic phenomena in brittle ceramics, with a focus on representing cracking and the evolution of stress at fracture with strain rate. Alumina was chosen as the study material due to the abundance of experimental data available in the literature.The third chapter dealt with the representation of the material in the elastic regime, while the fourth chapter examined the incorporation of different damage models within the discrete approach. Comparisons between experimental and numerical rear face velocity profiles from Gas Gun Projectile Impact (GEPI) tests showed that the use of the Denoual-Forquin-Hild (DFH) and Kachanov laws provided good correlation with experimental data.The fifth chapter presents various types of experimental dynamic fragmentation tests on AL23 alumina: Rockspall tests, edge-on impact tests (from the literature), and laser shock experiments. DEM numerical simulations, using the previously identified damage law as the one that best reproduces GEPI spall tests, were conducted to represent the damage mechanisms, simple and multiple fragmentation of AL23 alumina targets subjected to extreme loading conditions.Finally, to obtain experimental data on dynamic tests of a new ceramic with a more complex behavior, an experimental campaign was conducted on plasma-sprayed yttria-stabilized zirconia. Impact-on-edge and Rockspall tests were carried out to study simple and multi-fragmentation of this ceramic with a complex microstructure. This provided experimental data that will be used in future modeling efforts.In summary, this thesis contributes to improving the replication of the behavior of brittle ceramics subjected to dynamic loading such as impacts or shocks. It highlights the potential of the DEM method to represent multi-fragmentation phenomena and identifies relevant damage models for simulating dynamically observed effects. These results have significant implications for representing the dynamic fracture behavior of high-performance armor materials in various industrial and military applications
Azria, David. "Matériaux fonctionnels par assemblage de microsphères composites de chitosane/collagène pour l’ingénierie tissulaire." Thesis, Paris Sciences et Lettres (ComUE), 2018. http://www.theses.fr/2018PSLEP043.
Full textInjury of the peripheral nerve leads to local degeneration at the damaged site. If the injury results in a large nerve gap, spontaneous regeneration does not lead to functional recovery of the nerve. Among the several therapeutic strategies available, autograft is currently the most efficient technique but is associated with morbidity at the donor site. In the tissue engineering approach that we have investigated, nerve guides are typically elaborated with biocompatible materials to orient nerve outgrowth and regeneration. In this context, we have evaluated materials assembled with functionalized microspheres to form a gradient of neurotrophic factors with the aim of guiding nerve regeneration in the lumen of tubular conduits. We have studied the elaboration of chitosan and collagen microspheres from an emulsion generated in a controlled manner using a microfluidic technology. The solidification of the emulsion droplets was then achieved by the diffusion of ammonia vapors. The microspheres functionalization has been investigated and characterized using model fluorescent molecules, namely FITC (Fluorescein Isothiocyanate) and a protein (BSA, Bovine Serum Albumin) labeled with FITC. These functionalized microspheres were then assembled in the form of membranes with typical dimensions in the centimeter range, and exhibiting a functionalization gradient. Finally, preliminary experiments have demonstrated the possibility of animal implantation by rolling and suturing the membranes to a sectioned sciatic nerve. This work has allowed us to establish the proof of concept of this approach to elaborate functional nerve conduits and will need to be followed by complete study of functional nerve regeneration
Li, Jiayi. "Methodological developments in imaging and new physico-chemical understanding of archaeological flax-based textiles from the ancient East (3rd and 2nd millennium BC)." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLV031.
Full textArchaeological textile remains from the ancient East are rare. In Mesopotamia, most of the knowledge about textiles comes from cuneiform texts. Made from animal or vegetable fibres, textiles are perishable in most archaeological environments. One of the main processes of exceptional preservation of archaeological fibres involves contact with a metallic artefact, this phenomenon is called "mineralization". Very little work has been done on the in-depth study of the mineralization processes of cellulosic textiles. This PhD work consisted of a multi-scale study of the interaction between copper-base substrate and ancient textiles, based on samples from the archaeological sites of Tello, Nausharo and Gonur-Depe (3rd and 2nd millennium BC). The work made it possible to implement a new imaging methodology using synchrotron-based semi-quantitative X-ray microtomography to describe the composition of these complex, heterogeneous and reactive systems in 3d. These developments have allowed us to deepen the archaeological description of these textiles and their burial context in relation to the question of their production and use in past times. Finally, we discussed the description of the hybrid system of fibre-corrosion product and the presence of organic signatures in these altered hybrid systems in order to describe the mechanisms underlying their exceptional conservation
Fahs, Amin. "Modeling of naturel convection in porous media : development of semi-analytical and spectral numerical solutions of heat transfer problem in special domains." Thesis, Strasbourg, 2021. https://publication-theses.unistra.fr/restreint/theses_doctorat/2021/Fahs_Amin_2021_ED269.pdf.
Full textThe problem of the porous square cavity is extensively used as a common benchmark case for Natural convection (NC) problem in porous media. It can be used for several numerical, theoretical, and practical purposes. All the existing high accurate solutions are developed under steady-state conditions. However, it is well known that the processes of NC in porous media occurs naturally in a time-dependent procedure, as boundary conditions can be variable in time. Also, the convergence of the steady-state solution is known to be difficult. To overcome this difficulty, the steady-state solution is often simulated as a transient solution that evolves until reaching the steady-state condition. These time-dependent modes are very efficient to detect the effects of the parameter variations on the physical process of NC, especially for the subject of interest in this thesis: the domain inclination level and hot wall temperature variation in time. For this purpose, three goals are identified in this Thesis: 1. Developing a time-dependent solution of natural convection in porous media using the Darcy model in two modes: Transient and unsteady. 2. Investigating the time-dependent behavior of natural convection in porous media having the domain inclination level as a variable parameter in two modes: Transient and unsteady. 3. Developing a time-dependent solution of natural convection in porous media using the Darcy-Lapwood-Brinkman model in two modes: Transient and unsteady. To do so, according to the high accuracy in the simply connected domains, one of the Galerkin spectral weighted residual method is chosen to develop a space-time dependent solution for NC problem in a square porous cavity. Applying the Fourier-Galerkin (FG) procedure, two configurations dealing with transient and unsteady regimes are considered where each solution is derived for a wide range of Rayleigh numbers with other special conditions. This work of thesis is explained in details as five chapters.The NC physical process with the time-dependent variations is described in the transient mode to reach the steady-state solution and for the unsteady mode during a one period using periodic sinusoidal boundary conditions on the cavity hot wall. Finally, the work of this thesis is described in details in five chapters; while the sixth and last chapter is devoted to the summary and conclusion.The results in this thesis work provide a set of high-accurate data that are published in three papers to be used for testing numerical codes of heat transfer in time-dependent configurations
Zhang, Luqiong. "Magnetic Molecular-based Materials Assembled on Metallic Substrates : Experimental X-ray Absorption Spectroscopy and Ligand Field Multiplet Calculations." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLS587.
Full textThis thesis is focused on the investigation of the magnetic properties of magnetic nanoparticles and spin crossover complexes assembled as monolayers on different metallic substrates by X-ray Absorption Spectroscopy (XAS) at the L₂,₃ edges of the metal atoms. We use X-ray Magnetic Circular Dichroism (XMCD) and X-ray Natural Linear Dichroism (XNLD) to do so. The simulation of the experimental data is carried out by Ligand Field Multiplet (LFM) calculations. This thesis is divided into two parts.The first part aims at studying the magnetic anisotropy of Prussian blue analog magnetic coordination nanoparticles that were assembled as a single layer on Highly Oriented Pyrolytic Graphite. XAS, XNLD and XMCD measurements disclose the presence of electronic and magnetic anisotropy by the opening of a magnetic hysteresis loop at low temperature. Combining experimental data with LFM calculations, we propose a structural model of the surface of the particles that allows accounting for electronic and magnetic anisotropy and that is proposed to be due to the single layer/vacuum interface.In the second part, thermal and light-induced spin crossover behavior of Fe(II) containing molecules have been assembled as a sub-monolayer on metallic substrates. Complementary LFM calculations and experimental XAS data allow unravelling the nature and the magnitude of the spin crossover as a function of the external stimuli (temperature, X-rays, blue and red light). An anomalous blue light effect allowing a crossover at low temperature from the high to low spin states is discovered and analyzed as being due to the interface between the molecules and the metallic substrates