This thesis deals with measurement of residual stress by hole drilling method. This method is based on drilling a hole and measurement of deformation in the area around this hole. Measured deformations are then converted to residual stresses by using calibration coefficients. The deformation around the drilled hole is measured by optical non contact method called digital image correlation (DIC). First part of the thesis is focused on current state of research. The thesis contains evaluation of residual stresses by using different methods and evaluation of used methods.

This thesis work is concerned with effect of material grade on fatigue strength of welded joints. Fatigue strength evaluation of welded joints in as welded and post weld treated condition was carried out with effective notch method. Results of peak stress method have also been compared with those of effective notch method for as welded joints. In addition, using the results of effective notch method, the effect of important weld and global geometry factors on notch stress concentration factor has been studied with 2-level design of experiment and a mathematical relation among stress concentration factor and the geometric factors has been proposed. Overall, thickness of the base plate and toe radius is found to be the most important factors determining fatigue strength of the joint. Welding induced residual stresses have also been predicted using 2D and 3D FEM analysis to see their effect on fatigue strength of the joints. Also, transversal residual stresses were measured using X-ray diffraction method to assess the accuracy of predicted results. Based on simulation results, effect of geometric factors on maximum value of transversal residual stress was also investigated.

The correlatioin between residual stresses and the global properties from an indentation test, i.e. hardness and size of the contact area, has been studied frequently in recent years. The investigations presented have been based on experimental, theoretical and numerical methods and as a result, the basic features of the problem are fairly well understood in the case of residual equi-biaxial surface stresses. The more general case, when the principal surface stresses are not necessarily equi-biaxial, has received nuch less attention and it is therefore the aim of the present study to remedy this shortcoming. In doing so, qualitative results are of immediate interest in this initial study but possible ways of quantitative descriptions are also discussed for future purposes. The present analysis is based on numerical methods and in particular the finite element method (FEM) is relied upon. Classical Mises elastoplastic material behavior is assumed throughout the investigation.

This dissertation presents an approach to use blade tip timing measurements with finite element analysis to predict the fatigue life of a low pressure steam turbine last stage blade under high backpressure and low flow conditions. Material fatigue properties were determined through the extended universal material law for FV566 material, along with different temper scenarios. A finite element model of a blade with damping pins was developed, using the principle of cyclic symmetry for a perfectly tuned model. Pre-stress modal analysis was conducted, incorporating damping via friction and plasticity for initial 20% overspeed test. The finite element model was verified by two experimental tests: the first being a blade impact test and the second a telemetry strain gauge test in a balance pit. Fatigue life analysis was conducted under the assumption that non-synchronous vibration is experienced by the blade and that only one mode is dominant in the vibration. The results from the fatigue analysis corresponded to the location of the cracks experienced on the blades. The results show twelve orders of magnitude lower life at low load, high backpressure conditions, compared to high load high pressure conditions. The research was further extended to check the same vibratory response on the first three modes, up to their tenth nodal diameters. This was done to analyse fatigue life in a case that a different mode was excited. / Dissertation (MEng)--University of Pretoria, 2020. / Eskom Rotek Industries / Mechanical and Aeronautical Engineering / MEng / Unrestricted

Denna rapport behandlar restspänning i stålet 16MnCrS5 som uppkommer efter sätthärdning med traditionell uppkolning med släckning i olja och lågtrycksuppkolning med släckning i gas. Rapporten har ett fokus på restspänningar men behandlar även materialegenskaper generellt. I rapporten utförs en karaktärisering av materialet där författarna tittar på, kolhalt, kolprofil, ythårdhet (Rockwell C), kärnhårdhet (Vickers10kg) och hårdhetsprofil (Vickers 1kg) samt analys av mikrostruktur. Även resultat för FWHM kommer tas upp som visat sig kunna relateras till hårdheten hos materialet. Diskussionen handlar om att förklara restspänningen i materialet med hjälp av resultatet från karaktäriseringen. Lågtrycksuppkolning har visat sig inte ge inre oxidation vid sätthärdning, medan provbitar som sätthärdats med traditionell sätthärdning har uppvisat inre oxidation. Den inre oxidationen kan bidra till tryckrestspänningar vid ytan på materialet. Hög andel restaustenit har generellt visat sig vara en bidragande faktor till dragrestspänningar främst vid ytan men även inne i sätthärdningsskiktet. Resultatet har också visat att prover som värmebehandlats med lågtrycksuppkolning och har hög halt restaustenit vid ytan kan också ha hög nivå av dragrestspänning vid ytan. / This report addresses residual stress in the steel 16MnCrS5 that occurs after carburization with traditional carburization with quenching in oil and low-pressure carburization with quenching in gas. The report focuses on residual stresses but also deals with material properties in general. The report characterizes the material by looking at the, carbon content, carbon profile, surface hardness (Rockwell C), core hardness (Vickers10kg) and hardness profile (Vickers 1kg) as well as analysis of the microstructure. Low pressure carburization has been shown not to produce internal oxidation, but samples heat treated with traditional carburization has exhibited internal oxidation. High proportion of residual austenite has also been shown to be a contributing factor to tensile residual stresses, mainly at the surface but also within the curing layer. The result have also shown that residual austenite at the surface have been associated with high levels of tensile residual stress at the surface.

京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第18459号 / 医博第3914号 / 新制||医||1005(附属図書館) / 31337 / 京都大学大学院医学研究科医学専攻 / (主査)教授 木村 剛, 教授 坂田 隆造, 教授 戸口田 淳也 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DGAM

No description available.

No description available.

The first part of this dissertation employs a three-dimensional elastic-plastic finite element model of straight-through crack growth to correlate four well-known methodologies characterizing fatigue crack closure. The compliance offset and the adjusted compliance ratio (ACR) are experimental methods, whereas the node displacement and the contact stress methods are numerical approaches. Evolutions of crack closure from all four methodologies are compared for a numerical model of a single edge-cracked tension specimen subjected to different levels of constant amplitude cyclic loading. In the second part, a detailed two dimensional stress analysis is conducted for a single pin-joint under plane stress conditions. This study investigates the influence of material nonlinearity, friction, and pre-existing residual stresses from cold-working process on the local radial and hoop stress levels around the pin-loaded hole. Next, the beneficial influence of cold working process is quantified by computing the Mode I stress intensity factors style='mso-bidiont-style:normal'>KI for a single radial crack eanating from a side of a loaded hole. Two different loading configurations are considered: (a) an open hole in tension, (b) a pin-loaded hole. The stress intensity factors are computed using the J integral solutions and the weight functions specific to the crack configuration. The reductions in KI values due to different levels of cold-working process are presented for a range of crack lengths. The final part of the research involves a numerical investigation of an on-line crack compliance technique that is used for experimental measurements of residual stress fields along the crack growth path. A finite rectangular sheet is considered with a single crack emanating from a side of a central hole. The residual stress field is introduced around the hole by cold-working simulation. As part of validation, the normalized residual stress intensity factors computed using the on-line crack compliance technique are compared with those from the style='mso-bidiont-style:normal'>J-integral approach for the case of elastic crack growth. The influence of crack tip plasticity on the performance of the on-line crack compliance technique is studied by comparing the solutions of the elastic and elastic-plastic crack growth models.

A thermo-mechanical finite element model is developed to determine the temperature history and residual stresses in a Cu-H13 thin-walled plate deposited by the Laser Engineered Net Shaping (LENSTM) process. The same model is also applied to a H13-H13 sample to compare the results. The input laser power is adjusted to maintain a steady molten pool size and depth. For a constant scanning speed the laser power decreases with the addition of more layers, and with the increase of scanning speed the laser power needs to be increased. The Z-component of residual stresses is greater than the other components, and is compressive near the center of the wall and tensile at the free edges. The residual stress levels near the free edges are higher in the H13-H13 sample than in the Cu-H13 sample. In these regions, the use of unidirectional scanning results in a higher stress accumulation than the alternating scanning.