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Determination of residual stresses by hole-drilling method considering finite body boundaries
Began, Jakub ; Ščerba, Bořek (referee) ; Halabuk, Dávid (advisor)
The diploma thesis analyses the impact of the finite dimensions of a body on residual stresses by means of the hole-drilling method which was derived for bodies of dimensions large enough not to affect the measurement. To assess the impact of the finite dimensions of a body on measured residual stresses, a computational model simulating the hole drilling method was created using the finite element method. The assumptions made during the creation of the computational model included a desired geometric shape and an uniform residual stresses along the depth of the drilled hole. The computational model was subsequently parameterised so that it could be used to simulate different combinations of the finite dimensions of a body, whose impact on measured residual stresses was analysed. In the next part of the thesis, the impact of the biaxiality of residual stresses on the accuracy of their measurement was assessed. Subsequently, three correction algorithms were proposed to minimise the errors of measured residual stresses caused by the finite dimensions of a body. The first correction algorithm is supposed to correct calibration coefficients, the second one to correct input strains, and the third one to correct the assessed residual stresses. In the last part of the thesis, the individual correction algorithms were tested and compared. The outcomes of the diploma thesis suggest the possibility to correct the errors in the analysed residual stresses due to finite dimensions of a body, on the condition of a desired geometric shape and an uniform stresses along the depth of the drilled hole.
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Application of the digital image correlation in the measurement of residual stresses by the hole-drilling method
Plucnar, Tomáš ; Horák, Richard (referee) ; Halabuk, Dávid (advisor)
The thesis focuses on the measurement of residual stresses using digital image correlation (DIC). The work describes residual stresses and also derives an analytical description of the deformation around a drilled hole, which is essential for evaluating the experiment. The largest part of the thesis is dedicated to the measurement and evaluation of residual stresses. Within the framework of the thesis, measurements of residual stresses were conducted for samples with pre-drilled holes and also for solid samples into which holes were drilled. These measurements were then used to evaluate the effects of various DIC software settings on the assessed residual stress. Measurements on samples with pre-drilled holes were used to determine the impact of the random pattern density and the influence of the camera on the evaluated residual stress.
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Numerical modelling of residual stress in metallic materials
Rakušan, Jakub ; Vosynek, Petr (referee) ; Hutař, Pavel (advisor)
The presented master thesis is focused on residual stresses, more precisely on the implementation of residual stresses in simulations using the finite element method (FEM), experimental determination of residual stresses and the influence of residual stresses on fatigue crack propagation. In this thesis, the found approaches of implementing residual stresses in FEM are tested and the most suitable of the tested approaches is then used in the simulation experiment. By comparing the FEM simulation and experimentally measured data determined by the modified slotting method, the residual stress values on an induction hardened railway axle specimen are determined. This is followed by the verification of the determined residual stress values by X-ray diffraction and the determination of the effect of residual stress on the rate of propagation of long fatigue cracks.
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Processing of Inconel 939 alloy using laser powder bed fusion at elevated temperatures
Hertl, David ; Dočekalová, Kateřina (referee) ; Malý, Martin (advisor)
The thesis deals with the problem of Inconel 939 alloy processing by SLM technology using base plate preheating. The main objective of the work is to verify the effect of base plate preheating on residual stresses. The problem was solved by two approaches: process simulation, and subsequent experimental verification. The process simulation with preheating temperature of 400 °C achieved the highest agreement with the experiment with a deviation of 4.1 %. Based on the experiment, a suitable base plate preheating temperature of 100 °C was determined to reduce the deformation and residual stresses. By processing Inconel 939 using preheating temperatures of 100 °C and 400 °C, static mechanical properties comparable to those of the standard components processed by SLM technology from Inconel 939 after the heat treatment were achieved. These results offer the potential for significant reductions in overall production time and costs associated with manufacturing Inconel 939.
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Machining of hardened parts
Heiserová, Sofia ; Sliwková, Petra (referee) ; Polzer, Aleš (advisor)
The usage of quenched materials in industrial production leads to the application of hard machining. Higher requirements for machines and cutting tools are needed during hard machining than during conventional machining. Quenched materials carry problem of volume and geometric changes after quenching and after machining as well. It is necessary to think about volumetric compensation in advance, before quenching of the workpiece. An experiment is suggested for optimalisation of longitudinal turning of steels 42CrMo4 and 50CrMo4. Hard turning has notable benefits such as flexibility of cutting tools and elimination of coolants, which provides ecological benefits. However, the disadvantages are higher tool wear and high prices of tools.
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Age forming of aluminium alloys
Stanislav, Filip ; Petrásek, Miloslav (referee) ; Klement, Josef (advisor)
The diploma thesis is focused on the description and the verification of a relatively young creep age forming method. This method is based on a relaxation of stress and a creep of material, which occur by forming a part in the clamping tool during the artificial precipitation heat treatment at elevated temperature. After removing from the tool, the spring back and the residual stresses in the part are smaller compared to the conventional forming methods. This is mainly reflected in the increased fatigue resistance of the structure. The creep aging is only applicable to the precipitation heat treatable alloys. This thesis is focused on aluminium alloys, which are typical for the aerospace industry. The first part of the thesis describes principles of technology, its use in the aviation and material processes in the aluminium precipitation heat treatable alloys during the creep age forming. In the second part, there is a methodology of the verification of technology on samples made of the aluminium alloys ČSN EN AL-P 7075 and ČSN 424203 (approximate equivalent of ČSN EN AL-P 2024). Furthermore, a forming tool is designed, and experiments are performed according to the proposed methodology. At the end of the thesis, the experiments are evaluated and changes in the spring back of the samples are compared for three different methods of forming: the conventional cold clamping forming, the creep age forming and the creep age forming with an overaging.
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Determination of residual fatigue lifetime of railway axle after surface treatment
Pánek, Ondřej ; Poduška, Jan (referee) ; Náhlík, Luboš (advisor)
This master thesis deals with prediction of residual fatigue lifetime of railway axle. In the first part of this thesis, theoretical introduction to the issue based on research of available literature is elaborated. The second part is dedicated to numerical modelling of actual railway axle with crack, which serves to obtain the necessary parameters entering estimation of the residual fatigue lifetime. At first, a finite element model of cylindrical body with crack loaded by bending moment was created and compared with analytical solution for verification purposes. The second step was the creation of separate models of railway axle with crack for three types of loading – bending moment, press fit of wheel and residual stresses, respectively. Furthermore, the shape of various crack propagation stages was determined, according to the methodology developed at IPM CAS. Using the determined crack shape, stress intensity factors were calculated separately from all types of loads for various crack depths. Dependence of stress intensity factor on the crack length was then used to calculate residual fatigue life for real loading spectrum.
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Influence of the residual stresses on the contact failure of ceramic laminates
German, Roman ; Majer, Zdeněk (referee) ; Ševeček, Oldřich (advisor)
The presence of the compressive or tensile thermal residual stresses in layers of a ceramic laminate induced due to different volume change of each layer´s material during the cooling from the sintering temperature can considerably affect resistivity of ceramics against contact damage. Within this work 2D parametric FEM models were created, in order to study the effect of the surface layer thickness, residual stress values and indenting body dimension on the initiation and propagation of the cone crack in the surface layer of the laminate. For the analysis of the critical conditions for the crack initiation, the coupled stress-energy criterion was used and for the determination of the direction of crack propagation we used the maximum tangential stress criterion. The results show that compressive thermal stresses in the surface layer increase the critical force for the crack initiation, shorten the crack distance from the contact area and shorten the occurred crack itself. Moreover, the compressive stresses enlarge the angle of the crack declination during the propagation process which cause an earlier crack arrest. The tensile thermal stresses have exactly the opposite effect. Results of simulations were compared to experimental results but due to lack of available measurements, the verification is partially limited.
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Computational Modelling of Welding and Heat Treatment Process of Steel with Application of Elastic-Viscoplastic Material Model
Jarý, Milan ; Daněk, Ladislav (referee) ; Dymáček, Petr (referee) ; Junek, Lubomír (advisor)
This dissertation thesis deals with the improvement of computational approaches for prediction of residual stresses in welded joints of welded structures in order to ensure greater compliance of the calculated results with the real conditions of welding and heat treatment. The improvement of computational approaches is based on application of elastic-viscoplastic material models which are able (compared with elastic-plastic material models) to take into account the viscoplastic processes ongoing during welding and heat treatment. This leads to more accurate calculated results which enter into further assessment of limit states and directly decide on the safety and lifetime of welded structures. Performed computational and experimental works, confronted with results published in the world, confirm the influence and benefit of application of elastic-viscoplastic material models in the frame of welding and heat treatment numerical analyses. Therefore elastic-viscoplastic material model is further applied in solution of practical project solved by IAM Brno. Solution of this project, whose aim is the development of repair of dissimilar metal welds (without post-weld heat treatment) in Dukovany and Temelin nuclear power plants using "Weld overlay method", has confirmed that application of elastic-viscoplastic material model leads to more accurate calculated results. For this reason the elastic-viscoplastic computational approach will be included into all future tasks of IAM Brno.
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