No description available.

Automation of "contour method" for cliff drawing Abstract This thesis deals with the design of automated creation of cartographic representation of rocks - specifically contour methods. Based on the study of the rules of this method and its use on analog maps, rules for its processing in digital cartography were designed and an algorithm for automated creation of this representation was designed and implemented. The algorithm is based on the design of the contour method described in the study Topographic mapping of rock formations with the use of airborne laser scanning data by J. Lysák (2016) and the output data of the study Sandstone landscapes in GIS by M. Tomková (2015). The algorithm was implemented in the form of Python scripts using the arcpy library. The thesis also includes testing the algorithm on data from sandstone areas in the Czech Republic. key words: rocks formations, visualization of hypsography , digital cartography, contour method

Stationary shoulder friction stir welding (SSFSW) is a recently developed variant of conventional friction stir welding (FSW). Recent studies have shown that SSFSW can join high strength aluminum alloys with improved mechanical strength and reduced distortion as a result of a narrower and more uniform thermal profile. However, a lack of understanding on the residual stress development in the SSFSW process makes it difficult to assess the structural integrity and delays a widespread application of this technique to industry. This dissertation reports the first systematic investigation into the development of residual stress induced by the SSFSW process and comparison between SSFSW and FSW techniques. Welding residual stresses were experimentally assessed with both the contour method and neutron diffraction. The weld microstructure and hardness distributions were characterized and used to understand the formation of residual stresses during the welding process. The results have shown that for both FSW and SSFSW processes, the residual stresses distribute in the form of ‘M’ shaped profile while the magnitude and size of tensile residual stress zone were effectively reduced (by 25%) in the SSFSW process, even when input welding power was identical. Other improvements seen in the SSFSW process include a reduction in the heat affected zone width, an increase in the minimum hardness and a more uniform through-thickness microstructure and hardness. The dominating welding process parameter affecting the welding residual stress was travel speed as compared to rotation speed and tool downforce. With a 90 degree shaped shoulder, SSFSW has been shown to produce defect-free T-sections by dual fillet welds. For these components, an asymmetrical distribution of microstructure, hardness and residual stresses were found as a consequence of the thermal effects induced by second weld on the first weld. The material softening caused by the first weld provides the potential of utilizing a lower heat input on the subsequent pass so as to optimize the welding parameters.

Residual stresses are the stresses which are present within a component without any external load. They can be introduced through any number of manufacturing processes and in-service conditions, meaning that they are almost ubiquitous in engineering components. The characterisation of residual stress is an important field of research particularly in an engineering context since the effects of residual stress sum with the loads. As a result, the performance of a component can be greatly enhanced, or significantly reduced, by the presence of residual stress depending on the sign of the stress and the applied load. In this EngD thesis the focus has been on the development of residual stress through the manufacturing processes of aero-engine forgings, specifically the turbine disc. The forgings studied were sub-scale geometries of the disc, forged from the nickel-base superalloy RR1000. The overall aim of this work is to improve the understanding of the residual stress generation and relaxation through implementation of advanced experimental characterisation techniques, with a view to improving current stress predicting process modelling capabilities. With this in mind the work has focussed on the use of neutron diffraction and the contour method to characterise residual stress experimentally, while residual stress predictions have been made using finite element modelling. The findings of this research indicated that very large residual stresses were generated as a result of the quenching process, and that these stresses were then relaxed and redistributed by ageing heat treatments and material removal by machining. The results obtained through the two experimental techniques exhibited very strong agreement, indicated a robust experimental process. Comparisons to the finite element predictions highlighted some issues with the current model; in particular it was found that the simulation of quenching could be improved by better definition of the heat transfer at the surface. Furthermore, the level of stress relaxation during ageing was consistently over predicted in the model. This result is thought to be the result of an over-prediction of the level primary creep in the alloy. Subsequent studies will investigate this behaviour further using the newly developed in-situ heat treatment capabilities which have developed as part of this research.

The worldwide preferred method for rail joining is welding; flash butt welding (FBW) and thermite welding (TW) are the two main welding methods used for joining continuous welded rail (CWR) tracks. However, the welds still represent a discontinuity in the track structure due to variations in microstructure, mechanical properties and residual stress levels with respect to the parent rail. These variations can play significant roles in increasing the risk of weld failure under service conditions. In order to better understand how FBW parameters affect these variations, the two main parameters; number of preheating cycles and upsetting forces were varied in three 56E1 rail welds, welded by a stationary FBW machine. Besides, these variations were systematically compared with those that occur in a standard thermite 60E2 rail weld. The thermite weld showed a heat affected zone (HAZ) extent much greater than those measured in the flash butt welds. The flash butt rail weld with a greater upsetting force (Standard Crushed) showed a HAZ extent larger than those in the other two welds (Standard Uncrushed and Narrow-HAZ Crushed), while the weld with fewer preheating cycles (Narrow-HAZ Crushed) showed a smaller extent of the HAZ.All welds showed pearlite colonies with proeutectoid ferrite at the prior austenite grain boundaries in the weld centre, and in the thermite weld zone. The rest zones across the welds exhibited almost fully pearlitic microstructures, but the pearlite at nearly the visible HAZ extents was partially spheroidised. The partially spheroidization zone had the minimum hardness across each of the thermite and flash butt welds. The Narrow-HAZ Crushed weld showed hardness in the weld centre, on average, higher than that of the parent metal. Moreover, the averaged hardness levels in this weld were significantly higher than those in the other two welds. However, these levels in the Standard Crushed weld were slightly lower than those in the Standard Uncrushed weld. Although the visible HAZ extent coincided with the point of minimum hardness, the residual stresses arising from the welds seem to extend much further. Contour Method and laboratory X-ray diffraction techniques were used together to measure the residual stress components across the thermite and flash butt rail welds. The longitudinal residual stress distribution showed tension in the web region along with compression in the head and foot regions of the rail welds. The vertical stress distribution across the flash butt welds was generally similar, and the maximum tensile stress values were comparable to those in the longitudinal direction. While the maximum values of the longitudinal tensile stress increased with decreasing the HAZ widths, these values in the vertical direction were significantly unaffected. However, the longitudinal and vertical tensile residual stresses typically promote the vertical straight-break and horizontal split web failure modes respectively.

Les travaux effectués au cours de cette thèse ont pour objectif d’étudier et de modéliser une opération de soudage multipasse d’un acier à haute limite d’élasticité utilisé en construction navale. Dans ce cadre il s’agit de prédire les conséquences métallurgiques et mécaniques du procédé et tout particulièrement la répartition et l’intensité des contraintes résiduelles post- soudage nécessaires pour analyser l’intégrité de la structure navale en service. Deux maquettes représentatives d’un joint d’angle en Té ont permis de caractériser l’évolution des cycles thermiques, de la microstructure et des contraintes résiduelles (estimées par les méthodes du contour et du trou profond) après chaque passe de soudage. La suite de l’étude concerne la caractérisation et la modélisation du comportement thermo-métallurgique et thermo- mécanique des différentes phases apparaissant au cours du soudage. La dernière partie porte sur l’implémentation des modèles retenus dans le code de calcul élément finis Abaqus à l’aide de sous-programmes spécifiques. Une étape de transition d’échelle a permis de décrire le comportement thermomécanique multiphasé de cet acier. Des calculs préliminaires ont été conduits pour valider l’implémentation des modèles sur des cas simples. Différents couplages ont été réalisés, soit une analyse thermique puis thermo-métallurgique, pour estimer la dureté après chaque passe et enfin métallurgique-mécanique pour prédire les contraintes résiduelles pour le procédé de soudage multipasse. Les résultats des calculs éléments finis ont été discutés et comparés aux résultats expérimentaux obtenus dans la première partie de cette étude. / This thesis aims at studying and modeling a multipass welding operation of a high strength steel used in shipbuilding. In this framework, work focus on predicting the metallurgical and mechanical consequences of the process and, in particular, the residual stress distribution after welding. Since residual stresses can be detrimental to the performance of the welded product, their estimation is essential and numerical modelling is useful to predict them. Two welding mock-ups which are representative of a T- joint were used to characterize the evolution of thermal cycles, microstructure and residual stresses (measured by contour method and deep hole drilling) after each welding pass. Metallurgical and mechanical behaviors were thoroughly characterized in order to feed numerical models with reliable constitutive equations. The last part deals with the implementation of the models in the finite element calculation code Abaqus using specific subroutines. A scale transition procedure has been added to describe the thermomechanical multiphase behavior of the steel. Preliminary calculations were carried out for simple cases to validate the implementation of models. Different numerical couplings were made. First a thermal analysis then a thermo-metallurgical analysis, to estimate the hardness after each welding pass. Finally, a metallurgical-mechanical analysis is achieved for the prediction of residual stresses due to multipass welding. The results of the finite element calculations were discussed and compared with the experimental results obtained in the first part of this work.

La méthode du contour est une technique récente pour la mesure de contraintes résiduelles dans des structures mécaniques. Elle permet d'obtenir un champ de contraintes résiduelles en 2D. Dans la méthode du contour, l'échantillon est découpé en deux parties. Les contraintes résiduelles normales aux faces découpées se détendent, ce qui cause leur déformation. Le profil de déformation des faces coupées est mesuré, puis utilisé pour le calcul de contraintes résiduelles. La méthode du contour est basée sur le principe de superposition élastique. Sa théorie assume que la détente de contraintes résiduelles est entièrement élastique. Cependant, en pratique, la détente élastique de contraintes résiduelles peut être accompagnée d'une détente plastique, ce qui induit des erreurs dans les contraintes mesurées. Ce projet se concentre sur l'étude et le contrôle des erreurs de plasticité dans la méthode du contour. Les résultats de cette recherche fournissent d'importantes informations sur la façon dont les déformations plastiques affectent les résultats de la méthode du contour. Par ailleurs une nouvelle technique de coupe pour l'atténuation des erreurs de plasticité a été développée. Des outils de calcul et des instructions sont proposés pour l'estimation des erreurs de plasticité. Enfin des instructions pour la minimisation des erreurs de plasticité sont proposées et appliquées à la mesure de contraintes résiduelles dans un échantillon. / The contour method has emerged as a promising technique for residual stress measurement in relatively large, thick and complex engineering components. The method involves making a cut in the sample of interest, measuring the subsequent relaxed deformation of the cut face and using this profile to back-calculate the original residual stress field by FE modelling. The method is based on the theory of elasticity in that the stress relaxation during test specimen cutting is assumed to be entirely elastic. However, when measuring residual stresses close to the material yield stress, plasticity can occur and affect the measurements.The main aim of this thesis was to develop methods of mitigating and estimating plasticity-induced errors in the contour method. The outcomes of this research provide a valuable insight into how accumulation of plasticity affects the performance of the contour method. A novel cutting strategy that aims at mitigating the plasticity-induced errors has been developed. Furthermore, procedures are developed to estimate the plasticity-induced errors. Finally guidelines are proposed and applied to a case study for mitigating the plasticity-induced errors in the contour method.