Letteratura scientifica selezionata sul tema "Hyperdéformations"
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Tesi sul tema "Hyperdéformations":
Chen, Cai. "Textures et microstructures dans l'aluminium, le cuivre et le magnésium après hyperdéformation". Thesis, Université de Lorraine, 2016. http://www.theses.fr/2016LORR0061.
Severe plastic deformation (SPD) is an efficient technique to transform the microstructure of bulk metals into ultra fine grained structure with grain sizes less than 1 µm or even into nanostructure with nano-grains of less than 100 nm in diameter. The very small grain size attributes excellent mechanical properties to the material. In present thesis work, two recently developed SPD techniques, namely, High Pressure Tube Twisting (HPTT) and Cyclic Expansion and Extrusion (CEE) were performed on different metallic materials at room temperature. Details of fragmentation of microstructure and metallographic texture evolution were investigated by electron backscattered diffraction (EBSD), transmission electron microscopy (TEM), transmission kikuchi diffraction (TKD) and X-ray diffraction (XRD). Shear strain gradient across the thickness of the HPTT deformed Al tube sample was found by a local shear measurement method. This shear strain gradient induced the inhomogeneity of microstructure and texture in HPTT deformed pure Al, solid solution alloy Al-4%Mg and pure Mg. The microhardness and average grain size in different zones as a function of shear strain were measured. The limiting steady grain sizes in the steady state for these different materials produced by HPTT were 700 nm, 100 nm and 900 nm, respectively. The texture evolution of pure Mg in HPTT up to a shear strain of 16 was simulated in simple shear using the self-consistent (VPSC) polycrystal model and showed good agreements with the experimental results measured by XRD. Based on the measured disorientation distribution function in HPTT deformed Al, a new technique for the magnitude of local shear strain in SPD was proposed. This new technique was applied to a protrusion produced in twist extrusion (TE) and to an Al sample deformed in free-end torsion. Cu and pure Al samples were intensively deformed by the CEE SPD technique. The microstructure and texture evolutions were measured by EBSD, showing a gradient from the center-zone to the edge part of the rod sample. The texture evolution of CEE deformed Cu was simulated by the VPSC polycrystal model using a flow line function. The simulation results confirmed the experimental texture features observed in the CEE process. The tensile testing behavior of large strain torsion pre-processed Cu was examined. In spite of the shear strain gradient existing in the bar, a technique was proposed to obtain the tensile stress-strain curve of such gradient material
Sauvage, Xavier. "Contribution à l'étude des transformations structurales dans des alliages métalliques nanostructurés par hyperdéformation". Habilitation à diriger des recherches, Université de Rouen, 2010. http://tel.archives-ouvertes.fr/tel-00526513.
Arzaghi, Mandana. "Nouveau procédé d'hyperdéformation pour les tubes". Thesis, Metz, 2010. http://www.theses.fr/2010METZ031S.
The new severe plastic deformation (SPD) technique, designated as high pressure tube twisting (HPTT), is a continuous process for grain refinement in bulk metallic materials with tubular geometry. It consists of placing a mandrel into the tube before applying an axial compression directly on the tube confined on both sides to produce high hydrostatic pressure. The tube is then twisted by an external torque with the help of the friction force genrated by the hydrostatic pressure. The ultra-fine grained structures produced with HPTT were confirmed using transmission electron microscopy and their microstructure and mechanical properties were evaluated. The value of yield stress is increased monotonically with the deformation imposed by HPTT. Meanwhile, the inverse deformation path is proved to be less advantageous. Microstructural evolution is studied by EBSD technique and texture measurements were carried out using X-ray. Deformed samples have simple shear texture with relatively low intensities and the effect of the initial texture on the final texture persists up to shear strain of nearly 6. Grain-to-grain misorientation distribution functions are bimodal and the second pick become higher with increasing strain. Industrial application of this new SPD technique requires advanced modelling in terms of texture evolution and grain fragmentation process. For this purpose, the new grain refinement model proposed by Toth and al. was used. Grain refinement improves the texture simulation results significantly and gives information on the average grain size, grain size distribution and misorientation distribution function that can be directly compared to experimental results
Franoux, Chloé. "Contribution expérimentale au frottement sec dans les procédés d’hyperdéformation : application au couple cuivre/acier". Electronic Thesis or Diss., Université de Lorraine, 2023. http://www.theses.fr/2023LORR0007.
Understanding tribological properties is an important issue in forming processes, especially in hyperdeformation processes. In these processes, materials are subjected to severe plastic deformation (SPD) under low feed rates in order to obtain ultrafine grain materials. Some of these processes require a high coefficient of friction such as the high pressure torsion (HPT) process. In other cases, friction is not beneficial as in the Equal-Channel Angular Pressing (ECAP) process where it opposes the relative movement of the sample in the channel. Nevertheless, the friction is generally a fitting parameter to correlate the results from the model and the experimental tests. For this reason, it is important to carry out experimental tests in order to know precisely the friction coefficient and the parameters that influence it in these processes. Devices to obtain friction results are called tribometers. Depending on the study to be carried out, different hard points can be identified and can complicate the use of an already commercialized tribometer. Therefore, despite a wide variety of tribometers available, researchers continue to build new devices, designed to be the most suitable for the tests they want to perform. Tribometers offering the possibility to characterize friction under conditions similar to those of the ECAP process (confined sample) are rare. A first device specifically designed to meet SPD specifications was designed in 2013. This tribometer allowed to study the evolution of dry friction under high pressures, from 200 MPa to 1 GPa, for low sliding velocities and for different initial surface roughness of the matrices. Nevertheless, the possible sliding distance is unfortunately too small to make an analogy with the ECAP process. One of the objectives of this thesis is to improve the existing prototype tribometer so that it can reproduce conditions as close as possible to those of the ECAP. The possible sliding distance has been increased from 1 to 30 millimeters and the development of an intermediate part now allows the post-friction analysis of the samples. Calibration tests were carried out and analyzed in order to show the capacity of this new bench to meet the needs of this study. Following these first tests, different tests were carried out on copper samples rubbing against steel matrices with different roughness, different sliding distances and different pressures from 200 MPa to 1 GPa. The results of these tests are described and analyzed
Velard, Corentin. "Influence de paramètres microstructuraux sur les propriétés de corrosion d'un alliage de magnésium biorésorbable hyperdéformé". Thesis, Université Grenoble Alpes, 2021. http://www.theses.fr/2021GRALI037.
Magnesium alloys are promising candidates for bioresorbable implant applications. In this context, understanding the link between microstructure and corrosion/degradation mechanisms of magnesium alloys is an important issue. The objective of this work was to study the influence of the microstructure on the degradation of a biocompatible Mg-2%Ca alloy. For this purpose, two hyper-deformation processes (Friction Stir Processing and to a lesser extent Equal Channel Angular Pressing) were used to modify the microstructural parameters. These two processes proved to be particularly effective in reducing the grain size (micron-sized grains could be produced), modifying the spatial distribution and size of the second phases present in the alloy and developing specific crystallographic textures. Finally, despite these important microstructural variations, the impact on the degradation rate remains quite limited. The analysis of the electrochemical behaviour helped to decorrelate the influence of these microstructural parameters on the degradation rate; some of them compensating each other. If grain refinement seems to improve the corrosion resistance, due to a coverage of corrosion products probably more coherent with the metal, the role of the second phases appears more complex: the spatial dispersion of the second phase particles has little effect on the electrochemical behaviour whereas the refinement of these particles seems to significantly influence the layer of corrosion products. Finally, as observed on pure Mg and other Mg alloys, crystallographic texture also plays a significant role in corrosion resistance. This work has hence contributed to the improvement of the understanding of the influence of the microstructure on the electrochemical behavior of a magnesium-calcium alloy