Wroński, Sebastian
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nauki fizyczne
inżynieria materiałowa
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Item type:Doctoral Dissertation, Access status: Open Access , Examination of residual stresses in heterogeneous textured materials using diffraction and deformation models(Data obrony: 2007) Wroński, Sebastian
Wydział Fizyki i Informatyki StosowanejThe aim of this work is to propose a methodology for analysis of mechanical behaviour of polycrystalline materials using diffraction methods and deformation models. A new grazing incidence X-ray diffraction method was developed to study the residual stress gradient. Measurement uncertainties in this technique were studied, especially the influence of: absorption, Lorentz-polarization factor, atomic scattering factor and refractive index. The main purpose is to interpret experimental results on the basis of the elasto-plastic models (self-consistent and Leffers-Wierzbanowski models), which describe the mechanisms of the stress field generation in elasto-plastically deformed polycrystalline materials. Special attention has been paid to the explanation of physical origins of the residual stress, to the prediction of stress evolution and to the influence of residual stress on material properties. Presented models and experimental methods were used for stress analysis in single and multi phase materials. Polycrystalline copper and one and two-phase steels after rolling and cross rolling were investigated. The new method of analysis of multi phase materials was applied. It was used for the estimation of residual stresses and their anisotropy in duplex stainless steel.Item type:Article, Access status: Open Access , Evolution of intergranular stresses in titanium studied using grazing incident X-ray diffraction and self-consistent model(2025) Nowak, Sylwia; Wroński, Marcin; Wroński, Sebastian; Baczmański, Andrzej; Marciszko-Wiąckowska, Marianna; Braham, Chedly
Wydział Fizyki i Informatyki StosowanejOne of the important causes for the formation of residual stresses in polycrystalline materials is the anisotropy of the plastic deformation process. Different slip systems activity leads to different plastic deformations of polycrystalline grains. The resulting mismatch (incompatibility) between adjacent grains is a source of the second order incompatibility stresses. These stresses cannot be easily measured directly, but can be predicted by elastoplastic deformation models. In the present work, stresses in deformed titanium alloy are studied. The grazing incidence X-ray diffraction measurements carried out during an "in situ" tensile test and a novel method of interpreting the experimental data allowed us to determine the evolution of macroscopic stresses and second order stresses during elastic-plastic deformation. This work shows that second order stresses, related to microstructure of material, are generated during plastic deformation and remain in the material. It was shown that the distribution of second order stresses in the Euler space correlates with the distribution of the Schmid factor for the non-basal crystallographic systems, especially Pyramidal system P1 <c+a>. This confirms that these systems play a key role in generating intergranular stresses. Comparison of the experimental data with the predictions of the self-consistent model also allowed the determination of the critical resolved shear stresses for slip systems activated during plastic deformation.