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Дисертації з теми "Matériaux hybrides – Essais dynamiques – Barres de Hopkinson"
Chihi, Manel. "Étude des performances d’un composite carbone/époxy dopé par des nanocharges sous des sollicitations sévères." Electronic Thesis or Diss., Brest, École nationale supérieure de techniques avancées Bretagne, 2021. http://www.theses.fr/2021ENTA0017.
Повний текст джерелаThis thesis work was carried out in a context of valorization of composite materials based on nanofillers. The knowledge of the mechanical behavior of nanocomposites doped by nanofillers submitted to high dynamic loading is an important data for the designers of composite structures dedicated to civil and military applications. This behavior must be characterized in a wide range of deformation; for strain rates in the range of 10² to 10⁵s⁻¹. Particular attention is devoted to the Hopkinson pressure bar system (SHPB) because of its frequent use in such a wide range of deformation which corresponds to the strain rate deformation range of most industrial applications. In this context, we first conducted a study focused on the effect of nanofillers on the dynamic behavior and damage kinetics of a carbon/epoxy composite. We have chosen two types of nanofillers with similar chemical compositions (based on pure carbon) but two different geometries (quasi-1D for carbon nanotubes (CNT) and 2D for graphene nanoplatelets (GNP). The two series of nanocomposites CNT and GNP were prepared under the same conditions while using common mass fractions (0.5%, 1% and 2%) in order to conduct a comparative study of the two nanocomposite systems. A dynamic compression test (in-plane (IP) and out-of-plane (OP)) and a numerical study were conducted. It has been shown that the dynamic behavior and damage kinetics of the materials are very sensitive to the strain rate and the direction of solicitation. The results of these tests also allowed us to understand the influence of the addition of nanofillers on the response of the materials. The percentage of 1% GNP shows optimal performances in stiffness, maximum stress and resistance to damage. However, nanocomposites can be very sensitive to environmental conditions, in particular to hygrothermal aging that can reduce the mechanical performances. Therefore, the effect of hygrothermal aging (60°C/80%RH) on the lifetime of nanocomposites is studied experimentally (in-plane loading). Decreases of different mechanical properties as a function of time (15, 40 and 100 days) and absorbed water content are highlighted for each mass fraction. However, it was shown that the introduction of nanofillers, except in the case of 0.5% CNT, leads to a more significant degradation of the reference composite
Régal, Xavier. "Caractérisation du comportement en traction du béton sous fortes sollicitations : essais de flexion trois points aux barres de Hopkinson." Thesis, Orléans, 2016. http://www.theses.fr/2016ORLE2003/document.
Повний текст джерелаThe concrete is one of the most widely used constructional materials. However, its tensile behavior in dynamic is yet not perfectly known. In order to design concrete structures and predict their collapse in the case of industrial accidents, it is mandatory to know its tensile strength. This property depends on the different solicitations to which the concrete can be exposed. In order to characterize the tensile strength of a R30A7 concrete and its dependence on the strain rate, three points bending tests are performed in static and dynamic cases. For this purpose, the most recent standards are used in the static tests. The dynamic ones are carried out with the split Hopkinson pressure bars. This device allows to perform dynamic tests with both the speed and effort loading measurements. Moreover a high speed camera is used to record these experiments in order to acquire full-field displacement measurements with the help of the digital image correlation. Tools using these fields are created to detect the apparition of the crack in one hand, and to follow the crack propagation in the other hand. All these experimental devices and the use of different models, some of which take in account the sample damage, make it possible to determinate the evolution of the tensile strength depending on the strain rate. This work brings forward the fact that ignoring the material damage increases the tensile strength obtain from the tests
Saletti, Dominique. "Mesures de champs hétérogènes dans un alliage à mémoire de forme de Nickel-Titane sous sollicitations dynamiques." Phd thesis, École normale supérieure de Cachan - ENS Cachan, 2011. http://tel.archives-ouvertes.fr/tel-00669701.
Повний текст джерелаElnasri, Ibrahim. "Comportement des matériaux cellulaires sous impact et de panneaux sandwichs sous perforation dynamique." Phd thesis, École normale supérieure de Cachan - ENS Cachan, 2006. http://tel.archives-ouvertes.fr/tel-00136104.
Повний текст джерелаPenin, Arnaud. "Étude sous chargement dynamique biaxial d'une tôle en acier DP450 : influence sur le comportement et la formabilité." Lorient, 2010. http://www.theses.fr/2010LORIS196.
Повний текст джерелаTeel sheets are subject to multi-axial and dynamic loading during automobile crashes or even stamping. However, there are few experimental techniques that are able to test the material properties for both types of loading. This study presents a new stress technique for steel sheets under biaxial and dynamical loading. The aim of the work is to compare the strain rate sensitivity of steel under uniaxial and biaxial loading. The test was conducted with different strain rates from quasi-static 10-3/s to dynamic at 103/s. The first study was to identify strain rate sensitivity under uniaxial loading so as to obtain a reference behavior. This experimental part highlighted the difficulty of studying behavior under a wide range of strain rates, thus requiring the use of various experimental techniques. Biaxial loading was obtained through an expansion test or bulge test. The bulge test was performed under quasi-static loading rate and using a digital image correlation to measure displacement and the strain field, thus enabling optimization of the test through the calculation of the stress-strain relationship. A Hopkinson apparatus was used to increase the strain rate for dynamic bulge testing. For this device, the strain rate sensitivity of the sample was studied by using an inverse approach. Finally, a punch test was used to study formability for both quasi-static and dynamic strain rates. The sample geometry was optimized to control the strain path in expansion. In the quasi-static mode, DIC ( digital image correlation) was used to detect the beginning of necking. However, in the dynamic mode, we only had the load and displacement relationship. Therefore, the beginning of necking was detected through a new method based on the decrease of load evolution due to necking as compared to the load calculated by simulation. This method is used for both quasi-static to dynamic modes and validated with the DIC results
Ilyas, Muhammad. "Modélisation de l'endommagement de composites stratifiés carbone époxy sous impact." Toulouse, ISAE, 2010. http://www.theses.fr/2010ESAE0009.
Повний текст джерелаMartinez, Figueroa Jésus. "Ténacité dynamique comme indicateur de dommage en fatigue." Thesis, Lille 1, 2015. http://www.theses.fr/2015LIL10142/document.
Повний текст джерелаDamage evaluation and safety assessment of the structural integrity of vehicles and civil structures have been subject of increased attention in recent years. Nowadays the precise knowledge of dynamic fracture parameters is essential for safe design of components. The special arrangement of Three Point Bending Split Hopkinson Bar has been adopted as a convenient means of measuring the dynamic fracture toughness. In this work, an analysis of this arrangement is presented by means of Finite Element Analysis whose results are compared with the theoretical background and the experimental results. A number of important aspects are approached. Among them, the history of the mechanical force actually transmitted from the bars to the specimen and the evolution of the dynamic Stress Intensity Factor (SIF) during the tests. Instead of obtaining the force, the velocity on the bar’s end is proposed to feed the Finite Element model. Experimentally, the arrangement is used to measure the dynamic fracture toughness of AISI 304 TIG welding specimens. The results of a number of fatigue damage-free specimens are compared with those of specimens previously subject to fatigue damage. The technique is also used to measure the dynamic fracture toughness of a carbon-epoxy woven composite material, considered as transversely isotropic media. Simplified formulae to obtain this parameter compared with isotropic materials are proposed along with the precise follow of the SIF evolution during the tests
Al, Baida Halim. "Contribution à l'identification du comportement des matériaux à partir d'essais de micro-impact répétés." Thesis, Belfort-Montbéliard, 2015. http://www.theses.fr/2015BELF0274/document.
Повний текст джерелаThe behavior law is an essential element of the mechanical characterization of materials. To identify the material behavior several experimental methods can be used such as (static traction, Hopkinson bars ...) that allow to obtain mechanical laws applied under well-defined conditions, i.e. on homogeneous and bulk materials. However, do to the rising cost of these tests and their specific sample geometry, their use is limited and does not allow to probe and measure all types of materials (like coatings or porous materials....). Moreover, a broad knowledge of their properties allows a more accurate simulation of their behavior in working process. Behavior laws appropriate for bulk material do not always fit to process modeling shot peening, due to surface deformation. The main objective of this study is to develop a simple, rapid method for identifying the local behavior of materials under dynamic conditions, in order to characterize surfaces under impact loading. An inverse method has been developed to identify the behavior of materials using a combination of numerical and experimental approaches of repeated impact tests. The behavior laws obtained by the inverse method must be further investigated due to missing comparison data in literature. A comparison with an analytical method based on the theory of indentation must be carried out for more accuracy. In order to validate the efficiency of the inverse method and the analytical method, numerical blind tests wereconducted, then applications on industrial and ideal materials have been carried out to determine the limits
Grégoire, David. "Initiation, propagation, arrêt et redémarrage de fissures sous impact." Phd thesis, INSA de Lyon, 2008. http://tel.archives-ouvertes.fr/tel-00418626.
Повний текст джерелаDes 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.
Croteau, Jean-François. "Single crystal and polycrystalline niobium and OFE copper for SRF cavities applications : mechanical characterization at low to high strain rates and microstructural investigations." Thesis, Brest, École nationale supérieure de techniques avancées Bretagne, 2021. http://www.theses.fr/2021ENTA0006.
Повний текст джерелаManufacturing of superconducting radiofrequency (SRF) cavities with high performances is paramount to increase the collision energy in new particle accelerators. The use of high-speed sheet forming techniques, such as electro-hydraulic forming, can be beneficial, but requires a detailed understanding of the mechanical properties of the materials being deformed and the consequence on their microstructure. This thesis focuses on the characterization of high-purity niobium single crystals, polycrystalline niobium sheets, and polycrystalline OFE copper sheets. The results from this study are separated in two parts. In Part I, the characterization of niobium single crystals focused on the mechanical properties in tension and compression at strain rates of 10-4 to 103 s-1 and on the microstructure (analyzed using SEM, EBSD, TEM, and nanoindentation) of the deformed specimens. The effect of crystal orientation, strain rate, and loading direction on the mechanical properties, the crystal rotation, and the dislocation substructures are presented. In Part II, the forming limit diagram (FLD) of polycrystalline niobium sheets and OFE copper sheets were measured at a quasi-static strain rate. The FLDs of those materials should provide important data for manufacturers using conventional techniques, such as deep-drawing and spinning. The second part also presents the mechanical properties of electron beam (EB) welded polycrystalline niobium sheets and OFE copper sheets deformed in tension and compression at strain rates of 10-3 to 103 s-1