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Numerical simulation of the hole drilling method for residual stress measurement
Halabuk, Dávid ; Ganev, Nikolaj (referee) ; Pástor,, Miroslav (referee) ; Návrat, Tomáš (advisor)
The doctoral thesis is focused on the investigation of various cases that may occur in the measurement of residual stresses by hole-drilling method and which deviate from the ideal state for which hole-drilling method is derived. In order to assess various stress states, geometries or material properties of the measured body, a computational model simulating the hole-drilling method was created by the finite element method. The first investigated case deals with cylindrical bodies and errors that may occur when the hole-drilling method is used to measure residual stresses in bodies with various surface radii. In addition to the evaluation of errors for different stress states, a procedure for the calculation of uniform residual stresses in cylindrical bodies has been proposed. The next part of the thesis is focused on investigating the influence of the residual stress placed in the perpendicular direction to the measured surface on the error of evaluated residual stresses located in a plane parallel to the surface of a measured body. The last and largest part of the thesis deals with cases in which plastic deformations form in the area around the drilled hole during residual stress measurement. After examining of various parameters influencing the formation of plastic deformations, a correction procedure which is capable to correct the uniform residual stresses for various hole diameters and various strain gauge rosettes independently of the stress state or material properties was proposed. The proposed correction procedure was thoroughly tested to ensure its satisfactory results. Based on the obtained results published in this thesis, it is possible to estimate the influence of various conditions deviating from the ideal case on the accuracy of the evaluated residual stresses and in some cases minimize this influence by the proposed procedures.
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Residual stresses of laser-welded pressure vessel steel determined by X-ray and neutron diffraction
Trojan, K. ; Vlk, A. ; Čapek, J. ; Hervoches, Charles ; Ganev, N.
To gain insight into the quality of the laser weld, information about the residual stress state across the weld is very useful. In this contribution, the residual stress profiles for lowalloy carbon steel plates of P355NL1 grade, which were laser welded from both sides, are presented. To separate the effects of the production of plates from the welding process, the samples were annealed for stress relieving. Using X-ray and neutron diffraction, the surface and bulk RS profiles were obtained. From the obtained data, first, the difference in the character of the longitudinal (parallel to the weld axis) and the transversal component of the RS tensor can be seen. The longitudinal component has a tensile character with a maximum value approximately 500 MPa. Values and character of the transversal component vary strongly with depth and distance from the weld axis.
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Structural study of nanocrystalline titanium oxide films and their temperature stability
Chlanová, Lea ; Kužel, Radomír (advisor) ; Čapková, Pavla (referee) ; Ganev, Nikolaj (referee)
Title: Structural study of nanocrystalline titanium oxide films and their temperature stability Author: Lea Chlanová Department: Department of Condensed Matter Physics Supervisor: Prof. RNDr. Radomír Kužel, CSc., Department of Condensed Matter Physics Abstract: TiO2 thin films can exhibit photocatalytic activity and photoinduced su- perhydrophilicity depending on crystallinity, phase composition and mi- crostructure. These parameters were studied by X-ray diffraction (XRD) and reflectivity (XRR) for magnetron deposited films - nanocrystalline and amorphous, namely their temperature and time evolution. For nanocrystalline films, it was found that higher partial oxygen pressure during the deposition is beneficial. Small anatase crystallites were stable up to about 450 ◦ C. Depth-profiling XRD of some samples revealed that rutile phase was only present close to the substrate. For amorphous films it was found that the crystallization depends strongly on the film thickness and it is slower for very thin films. Evolution of the intensities of anatase diffraction peaks with annealing time could be described by a modified Avrami equation. XRD profile was relatively narrow from the very be- ginning of crystallization (at about 220 ◦ C), which indicated relatively larger crystallites (> 100 nm), and hence, nanocrystalline films...
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