| 11. |
- Broberg, Patrik, 1983-
(författare)
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Towards Automation of Non-Destructive Testing of Welds
- 2011
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- All welding processes can give rise to defects that will weaken the joint and can lead to failure of the welded structure. Because of this, non-destructive testing (NDT) of welds have become increasingly important to ensure the structural integrity when the material becomes thinner and stronger and welds become smaller; all to reduce weight in order to save material and reduce emissions due to lighter constructions.Several NDT methods exists for testing welds and they all have their advantages and disadvantages when it comes to the types and sizes of defects that are detectable, but also in the ability to automate the method. Several methods were compared using common weld defects to determine which method or methods were best suited for automated NDT of welds. The methods compared were radiography, phased array ultrasound, eddy current, thermography and shearography. Phased array ultrasound was deemed most suitable for detecting the weld defects used in the comparison and for automation and was therefore chosen to be used in the continuation of this work. Thermography was shown to be useful for detecting surface defects; something not easily detected using ultrasound. A combination of these techniques will be able to find most weld defects of interest.Automation of NDT can be split into two separate areas; mechanisation of the testing and automation of the analysis, both presenting their own difficulties. The problem of mechanising the testing has been solved for simple geometries but for more general welds it will require a more advance system using an industrial robot or similar. Automation of the analysis of phased array ultrasound data consists of detection, sizing, positioning and classification of defects. There are several problems to solve before a completely automatic analysis can be made, including positioning of the data, improving signal quality, segmenting the images and classifying the defects. As a step on the way towards positioning of the data, and thereby easing the analysis, the phase of the signal was studied. It was shown that the phase can be used for finding corners in the image and will also improve the ability to position the corner as compared to using the amplitude of the signal. Further work will have to be done to improve the signal in order to reliably analyse the data automatically.
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| 12. |
- Carlsson, Henrik, 1979-
(författare)
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Reliable Virtual Commissioning
- 2012
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Virtual commissioning is a technique for programming, optimising and verifying industrial automated production, such as robot controllers and programmable logic controllers (PLC), off-line in a simulated environment. Compared with traditional robot off-line programming and simulation, the scope is wider and can include an entire production cell.Robot simulation is a well-established technique and widely used in industry today, much thanks to the RRS interface that enables simulated robot control systems to be integrated in the simulation software. A more general interface for industrial control system integration is OPC that has been an industrial de facto standard for connection between industrial control systems and regular PCs. State-of-the-art production simulation tools often include the possibility to connect an industrial control system via OPC. However, OPC suffers a major drawback when it comes to production simulation, there is no mechanism that synchronises the industrial control system with the simulation and this could lead to unreliable results from the simulation.Another obstacle for virtual commissioning is the amount of time that needs to be spent during the simulation model building phase, since virtual commissioning includes more signals. This does not only take more time, but it is also an error prone process that might lead to unreliable results.In this thesis problems related to the OPC interface and the modelling process are discussed, and suggestions how these issues can be solved are presented so reliable virtual commissioning can be achieved.
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| 13. |
- Charles, Corinne, 1979-
(författare)
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Modelling microstructure evolution of weld deposited Ti-6Al-4V
- 2008
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The microstructure and consequently the mechanical properties of titanium alloys are highly dependent on the temperature history endured by the material. The manufacturing process of metal deposition induces repetitive cooling and heating in the material determining a specific microstructure. The presented study is devoted to developing and implementing a microstructure model for Ti-6Al-4V intended to be coupled to a thermo- mechanical model of the metal deposition process.Microstructural analysis of the metal deposited samples was first performed to understand the formed microstructure. A set of representative parameters for microstructure modelling were then selected as representative for the known impact of Ti-6Al-4V microstructure on mechanical properties. Evolution equations for these parameters were implemented for thermal finite element analysis of the process. Six representative state variables are modelled: the phase volume fraction of total alpha, beta, Widmanstätten alpha, grain boundary alpha, martensite alpha, and the alpha lath thickness. Heating, cooling and repeated re-heating involved in the process of metal deposition are taken into account in the model. The phase transformations were modelled based on a diffusionnal theory described by a Johnson-Mehl-Avrami formulation, as well as diffusionless transformations for the martensite alpha formation and the beta reformation during reheating. The Arrhenius equation is applied as a simplification to model temperature dependent alpha lath size calculation. Grain growth is not included in the present formulation, but would have to be added for capturing alpha lath coarsening during long term heat treatment.The temperature history during robotised tungsten inert gas deposition welding is simulated together with the microstructure. The implementation of the model handles well the complex cyclic thermal loading from the metal deposition process. A particular banded structure observed in the metal deposited microstructure is partially explained using the proposed microstructure model. It is concluded that although qualitatively interesting results have been achieved, further calibration testing over a wider range of temperature histories must be performed to improve the transformation kinetic parameters for reliable quantitative predictions of the microstructure.
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| 14. |
- Coll Ferrari, María Teresa
(författare)
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Effect of austenitising temperature and cooling rate on microstructures of hot-work tool steels
- 2015
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The average size of hot-work tools has gradually increased over the past years.This affects the effective temperature cycle tools experience during hardening,as large dimensions prevent uniform and rapid cooling, and thereby the resulting microstructures and properties. In order to avoid the formation of coarse structures or cracking during heat treatment it has become common practise to lower the austenitising temperature below that recommended by the steel manufacturer.In this work, therefore, the effects of austenitising at temperatures lower thancommonly recommended are investigated. Three 5% Cr hot-work tool steelsalloyed with Mo and V were heat treated, resulting microstructures andtempering carbides were studied and transformation characteristics determined for different austenitising temperatures and different cooling rates. The temperatures and cooling rates have been chosen to be representative for heat treatments of different sizes of tools. Bainite rather than martensite formed during slow cooling regardless of austenitising temperature. A lowered austenitising temperature produced largeramounts of both bainite and retained austenite while a higher caused graingrowth. Carbon partitioning during the bainitic transformation resulted in anincrease of the carbon content in the retained austenite of at least 0.3 wt.%. The austenitising temperature influences also the type and amount of tempering carbides that precipitate, which affects the properties of the steel. Higher austenitising temperatures favour the precipitation of MC carbides during tempering. The Mo rich M2C type carbides were proven to be more prone to coarsening during service at 560°C-600°C, while V rich MC carbides preserve their fine distribution. A best practice heat treatment needs to balance the increase of grain size with increasing austenitising temperatures, with the possibility to form more tempering carbides. Higher austenitising temperatures also give less retained austenite, which can affect dimensional stability and toughness negatively after tempering
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| 15. |
- Curry, Nicholas, 1984-
(författare)
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Design of Thermal Barrier Coating Systems
- 2012
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Thermal barrier coatings (TBC’s) are used to provide both thermal insulation and oxidation protection to high temperature components within gas turbines. The development of turbines for power generation and aviation has led to designs where the operation conditions exceed the upper limits of most conventional engineering materials. As a result there has been a drive to improve thermal barrier coatings to allow the turbine to operate hotter for longer.The focus of this study has been the development of a new generation of TBC system for industrial implementation. The goal for these new coatings was to achieve lower conductivity and longer lifetime than those coatings used today. The route taken to achieve these goals has been twofold. Firstly an alternative stabiliser has been chosen for the zirconium oxide system in the form of dysprosia. Secondly, Control of the powder morphology and spray parameters has been used to generate coating microstructures with favourable levels of porosity.Samples have been heavily characterised using the laser flash technique for evaluation of thermal properties. Measurements were performed at room temperature and at intervals up to 1200°C. Samples have also been tested in their as produced state and after heat treatments of up to 200 hours.Lifetime evaluation has been performed using the thermo-cyclic fatigue test to expose coating systems to successive cycles of heating and cooling combined with oxidation of the underlying metallic coating.Microstructures have been prepared and analysed using SEM. An image analysis routine has been used to attempt to quantify changes in microstructure features between coating types or coating exposure times and to relate those changes to changes in thermal propertiesResults show that dysprosia as an alternative dopant gives a reduction in thermal conductivity. While small at room temperature and in the as produced state; the influence becomes more pronounced at high temperatures and with thermal exposure time. Overall, the greatest sustained influence on thermal conductivity has been from creating coatings with high levels of porosity.In relation to lifetime, the target of double the thermo-cyclic fatigue life was achieved using a coating with engineered porosity. Introducing a polymer to the spray powder helps to generate large globular pores within the coating together with a large number of delaminations. Such a structure has shown to be highly resistant to TCF testing.
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| 16. |
- De Backer, Jeroen, 1987-
(författare)
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Robotic Friction Stir Welding for Flexible Production
- 2012
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Friction Stir Welding (FSW) is a modern welding process that joins materials by frictional heat, generated by a rotating tool. Unlike other welding processes, the material never melts, which is beneficial for the weld properties. FSW is already widely adopted in several industries but the applications are limited to simple geometries like straight lines or circular welds, mostly in aluminium. The welding operation is performed by rigid FSW machines, which deliver excellent welds but puts limitations on the system in terms of flexibility and joint geometries. Therefore, several research groups are working on the implementation of the FSW process on industrial robots. A robot allows welding of three-dimensional geometries and increases the flexibility of the whole system. The high process forces required for FSW, in combination with the limited stiffness of the robot brings some extra complexity to the system. The limitations of the robot system are addressed in this licentiate thesis.One part of the thesis studies the effect of robot deflections on the weld quality. A sensor-based solution is presented that measures the path deviation and compensates this deviation by modifying the robot trajectory. The tool deviation is reduced to an acceptable tolerance and root defects in the weld are hereby eliminated. The sensor-based method provided better process understanding, leading to a new strategy that uses existing force-feedback for path compensations of the tool. This method avoids extra sensors and makes the system less complex. Another part of this work focuses on the extra complexity to maintain a stable welding process on more advanced geometries. A model is presented that allows control of the heat input in the process by control of the downforce. Finally, the robot’s limitations in terms of maximal hardness of the materials to be welded are investigated. Parameter tuning and implementation of preheating are proposed to allow robotic FSW of superalloys.
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| 17. |
- Detlin, Mia
(författare)
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Work-integrated learning in a hospital ward setting : Exploring the interdependency between the professions and the organization
- 2023
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Introduction:Contemporary hospital settings are a challenging learning and working environment for healthcare professionals. The challenges are largely related to the increasing need for healthcare caused by an ageing population, a lack of personnel resources, and demands for time efficiency. Therefore, it is of interest to study how individuals and teams learn during these working conditions. Nurses are especially exposed when entering working life, why this profession has been of interest to explore further in this thesis. Furthermore, the interprofessional team is significant in providing qualitative care at the hospital wards, which could be affected by the lack of nurses and demands for efficiency. Aim: To explore work integrated learning from an individual nurse and interprofessional team learning perspective in a contemporary hospital ward setting.Methodology:Two qualitative approaches were used in this thesis. Study I was a qualitative content analysis based on individual interviews with 10 nurses within hospital ward care. Study II was an insider action research project (IAR) within a specific hospital ward. Data from the project in Study II were analyzed using the cycle of expansive learning.Results:Study I showed that, during their early working life, newly graduated nurses learned their profession by developing and using different learning strategies. Their initial strategy was to learn how to perform daily tasks as safely and effectively as possible. However, in learning how to provide qualitative care, the nurses realized the importance of participating in bedside care to gain clinical experience. Opportunities to learn from clinical experiences and reflection were essential for developing as a new nurse.Study II explored work integrated learning in an interprofessional ward team. The learning process resulted in the establishment of a digital planning board to illustrate the patients’ recovery process during their stay at the ward. This board opened an opportunity to learn about core values and goals for discharge, but also contributed to boundary awareness between the professionals, which was important for collaboration to improve patient safety in daily work. Discussion: The results reveal that work-integrated learning was manifested in an interdependency between the professionals and the health-care organization. The interdependency was multifaceted as the professionals were dependent on each other to learn as individuals in relation to each other, and to develop their joint work processes. The professionals were also dependent on the organizational prerequisites to learn. This result shows the need for the professionals to develop their own learning strategies to manage daily work, which was associated with the professional’s motivation in leading their own professional development towards qualitative and safe care.Conclusion:The results of this thesis reveal that the professions within a hospital ward setting are largely dependent on each other to create conditions for work integrated learning. The individuals and the team both had strong determination, will, and desire to learn to provide patients with care that was as qualitative and safe as possible. The quality of work-integrated learning was found to be related to the professions’ awareness of boundaries, knowledge, and responsibilities related to each other within the interprofessional team.
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| 18. |
- Devotta, Ashwin Moris
(författare)
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Characterization & modeling of chip flow angle & morphology in 2D & 3D turning process
- 2015
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Within manufacturing of metallic components, machining plays an important role and is of vital significance to ensure process reliability. From a cutting tool design perspective, tool macro geometry design based on physics based numerical modelling is highly needed that can predict chip morphology. The chip morphology describes the chip shape geometry and the chip curl geometry. The prediction of chip flow and chip shape is vital in predicting chip breakage, ensuring good chip evacuation and lower surface roughness. To this end, a platform where such a numerical model’s chip morphology prediction can be compared with experimental investigation is needed and is the focus of this work. The studied cutting processes are orthogonal cutting process and nose turning process. Numerical models that simulate the chip formation process are employed to predict the chip morphology and are accompanied by machining experiments. Computed tomography is used to scan the chips obtained from machining experiments and its ability to capture the variation in chip morphology is evaluated. For nose turning process, chip curl parameters during the cutting process are to be calculated. Kharkevich model is utilized in this regard to calculate the ‘chip in process’ chip curl parameters. High speed videography is used to measure the chip side flow angle during the cutting process experiments and are directly compared to physics based model predictions. The results show that the methodology developed provides the framework where advances in numerical models can be evaluated reliably from a chip morphology prediction capability view point for nose turning process. The numerical modeling results show that the chip morphology variation for varying cutting conditions is predicted qualitatively. The results of quantitative evaluation of chip morphology prediction shows that the error in prediction is too large to be used for predictive modelling purposes.
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| 19. |
- Edstorp, Marcus, 1980-
(författare)
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Weld Pool Simulations
- 2008
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This investigation is devoted to the study of welding and its effect on the workpiece, focusing on the thermo and fluid dynamical phenomena occuring during a autogenous or nonautogenous arc fusion welding process. Its aim is to simulate the behaviour of the weld pool and analyze the consequence of the solid-liquid phase change, thus obtaining a methodology for predicting the appearance of weld defects related to solidification and cooling. In order to accomplish this, we solve equations governing a number of continuum mechanical and electromagnetical quantities, as well as consider the motion of the freely moving boundary of the weld pool. Since the state of these quantities is strongly influenced by phenomena such as arc and droplet impingement, non-isothermal phase change, surface tension, Marangoni forces and Lorentz forces, much effort is necessarily devoted to the modelling of the corresponding fluxes and sources, as well as to the implementation of computationally efficient techniques for simulating the geometrical deformation of the workpiece, which in our setting is entirely determined by the motion of the weld pool surface.Common to all arc fusion welding processes is the employment of a welding arc. Many techniques rely on the arc to clean and shield the workpiece during the process, however in this study we consider it to be its main purpose to cause the local increase of thermal energy that is required for the establishment of the weld pool, and also to exert the mechanical forces that provoke the subsequent fluid flow which enhances heat transfer and facilitates weld penetration. The physics of the welding arc itself is quite intricate, and although the modelling of the arc is not the prime objective of this research project, we conclude that arc forces act on the pool surface, and that the investigation of the arc behaviour is important insofar that it provides input to the pool model and thus enables a more accurate prediction of the quality of the weldment that is created once the pool has solidified
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| 20. |
- Emilsson, Maria, 1966-
(författare)
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Betydelsen av personlighet och uppfattning om läkemedel för följsamhet till astmamedicinering
- 2010
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- En okontrollerad astma kan leda till komplikationer i lungor och luftvägar. Astma kan kontrolleras med läkemedelsbehandling men fullständig astmakontroll uppnås inte alltid. Den vanligaste orsaken till att astmakontrollen inte uppnås är brister i följsamheten till astmamedicinering. Syfte: 1) Att undersöka om personlighetsdrag hos unga vuxna med astma var relaterad till astmakon-troll och hälsorelaterad livskvalitet, samt belysa samband mellan personlighetsdrag och följsamhet till regelbunden a... merstmamedicinering. 2) Att belysa samband mellan personlighetsdrag, uppfattning om läkemedel och följsamhet till astmamedicinering. Material och metod: I Studie I ingick 268 individer (165 kvinnor och 103 män) i åldern 22 år (±1år). I Studie II ingick 35 patienter (25 kvinnor och 10 män) med en medelålder av 52.8 år. I studierna an-vändes frågeformulär för att samla in data om personlighet, följsamhet, astmakontroll, hälsorelaterad livskvalitet och uppfattning om läkemedel. Resultat: Personlighet hade samband med följsamhet till astmamedicinering, uppfattningar om läke-medel, astmakontroll och hälsorelaterad livskvalitet. I Studie I framkom att de som skattade sig mer impulsiva rapporterade lägre följsamhet. Ett negativt samband fanns mellan höga värden i personlig-hetsdraget alexitymi (bristande intresse att förstå och prata om känslor) och följsamhet till astmamedi-cinering hos unga vuxna män. Likaledes framkom ett negativt samband mellan personlighetsdraget antagonism och följsamhet hos unga vuxna män. Hos båda könen var personlighetsdraget negativ af-fektivitet relaterat till dåligt kontrollerad astma. Det indikerades att personlighet kan påverka den men-tala hälsan hos både unga kvinnor och män, medan den fysiska hälsan hade samband med astmakon-troll och fysisk aktivitet. I Studie II framkom att fyra av fem personlighetsdrag hade samband i olika riktningar med uppfattningar om läkemedel. Högt värde i Specefikt-nödvändighetsskalan (uppfattning om nödvändigheten av förskrivna läkemedel) var relaterat till hög grad av följsamhet. Personlighets-draget målmedvetenhet var relaterat till hög följsamhet hos män. Känslomässig instabilitet hade sam-band med lägre värden i följsamhet också hos män. Konklusion: Kunskapen om personlighetens betydelse behöver fördjupas, men uppsatsens resultat indikerar behovet av att identifiera individuella skillnader i personlighet för att öka patienternas följ-samhetsbeteende, stärka deras uppfattning om nödvändigheten av läkemedelsbehandling och minska deras oro för läkemedelsbehandling, vilket har betydelse för både astmakontroll och hälsorelaterad livskvalitet.
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