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Etude des micro-contraintes dans les matériaux texturés hétérogènes par diffraction et modèles de comportement

Abstract : The aim of this work is to develop the methodology of stress measurement using theoretical models describing elasto-plastic behaviour of polycrystalline materials. The main purpose is to interpret experimental results on the basis of the self-consistent model which describes the mechanisms of stress field generation in deformed polycrystalline materials. Special attention has been paid to the explanation of the physical origins of stresses and to the prediction of their evolution and influence on material properties. In Chapter 1 the classical method of stress measurement called sin2y was described. The new stress analysis – multi-reflection method - based on strain measurements using a few reflections hkl is introduced (in this method all peaks are analysed simultaneously). Also the methods of calculation of the diffraction elastic constants, which play a crucial role in the stress analysis, were presented. The determination of these constants is essential in explanation of many experimental results. New methods for the calculation of diffraction elastic constants using the self-consistent model have been elaborated and tested. These methods were used for textured samples. In Chapter 2 two models (self-consistent and Leffers-Wierzbanowski models) were presented. They enable the prediction of macroscopic material properties (e.g., texture, stressstrain curves, plastic flow surfaces, dislocation density, final state of residual stress, etc.) basing on the micro-structural characteristics (crystallography of slip systems, hardening law, initial texture, initial residual stress state, etc.). In Chapter 3 a special attention has been paid to the explanation of physical origins of the stresses and to the prediction of the stress evolution and their influence on material properties. The internal stresses were divided into three types in function of the scale. The deformation models were used to analyse the stresses present in grains (the second order stresses). Quantitave estimation of this kind of stresses is possible only by means of models; they cannot be measured directly. Interpretation of experimental data for multiphase material is more complex than for a single phase one, because it is necessary to consider interaction between phases. For this reason, the new method of investigation of multiphase materials was developed and applied for duplex stainless steel. 4 The methods of estimation of the first and the second order stresses which were presented in the third chapter are used to study the residual stresses in materials after cross rolling (Chapter 4). The cross-rolling is applied in order to symmetrize the crystallographic texture and consequently, to decrease the sample anisotropy. The results for series of copper and steel samples are presented. Finally, in Chapter 5 a new method of stress estimation using a constant and low incident beam angle (grazing angle incidence X-ray diffraction technique) was presented. In this method, the penetration depth is almost constant on the contrary to classical method. For this reason, the grazing incidence diffraction technique can be used to investigate materials with a significant stress gradient. Measurement uncertainties in this method were considered; especially the influence of absorption, Lorentz-polarization, atomic scattering factor and refractive index were studied.
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Submitted on : Thursday, December 20, 2007 - 8:00:00 AM
Last modification on : Thursday, January 11, 2018 - 6:20:30 AM
Long-term archiving on: : Wednesday, September 8, 2010 - 5:44:37 PM

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Sebastian Wronski. Etude des micro-contraintes dans les matériaux texturés hétérogènes par diffraction et modèles de comportement. Sciences de l'ingénieur [physics]. Arts et Métiers ParisTech, 2007. Français. ⟨NNT : 2007ENAM0017⟩. ⟨pastel-00003210⟩

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