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- Calmunger, Mattias
(författare)
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High-Temperature Behaviour of Austenitic Alloys : Influence of Temperature and Strain Rate on Mechanical Properties and Microstructural Development
- 2013
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The global increase in energy consumption and the global warming from greenhouse gas emission creates the need for more environmental friendly energy production processes. Biomass power plants with higher efficiency could generate more energy but also reduce the emission of greenhouse gases, e.g. CO2. Biomass is the largest global contributor to renewable energy and offers no net contribution of CO2 to the atmosphere. One way to increase the efficiency of the power plants is to increase temperature and pressure in the boiler parts of the power plant.The materials used for the future biomass power plants, with higher temperature and pressure, require improved properties, such as higher yield strength, creep strength and high-temperature corrosion resistance. Austenitic stainless steels and nickel-base alloys have shown good mechanical and chemical properties at the operation temperatures of today’s biomass power plants. However, the performance of austenitic stainless steels at the future elevated temperatures is not fully understood.The aim of this licentiate thesis is to increase our knowledge about the mechanical performance of austenitic stainless steels at the demanding conditions of the new generation power plants. This is done by using slow strain rate tensile deformation at elevated temperature and long term hightemperature ageing together with impact toughness testing. Microscopy is used to investigate deformation, damage and fracture behaviours during slow deformation and the long term influence of temperature on toughness in the microstructure of these austenitic alloys. Results show that the main deformation mechanisms are planar dislocation deformations, such as planar slip and slip bands. Intergranular fracture may occur due to precipitation in grain boundaries both in tensile deformed and impact toughness tested alloys. The shape and amount of σ-phase precipitates have been found to strongly influence the fracture behaviour of some of the austenitic stainless steels. In addition, ductility is affected differently by temperature depending on alloy tested and dynamic strain ageing may not always lead to a lower ductility.
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| 2. |
- Johansson, Elisabeth, 1983-
(författare)
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Managing Quality in a Service Context
- 2013
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In recent years, service organizations have had to increase the number of offerings they provide. These organizations face difficulties in changing their internal processes to provide high-quality offerings. With the increase in demand for delivered services and competitive organizations from low-cost countries, service organizations currently face several issues. Today’s service organizations combine products and services into a solution to improve their competitiveness. These organizations experience changes in customer expectations depending on what they offer. That is, expectations, demands, and wishes change depending on the offering that a customer uses. Thus, service organizations need to know how expectations for quality change based on offerings and how they can work to change certain emphasized quality aspects. Hence, the aim of this licentiate thesis is to contribute to the knowledge of how to manage quality in a service context.This licentiate thesis is based on three different studies. One study is based on a number of self-assessment studies conducted at 138 Swedish service organizations using a total of more than 5,000 respondents. In the second study, data was collected over a five-year period through a literature review, interviews, a document study, and observations to capture the quality profile and associated interventions. The second study was conducted in a service organization in the public transportation industry. In the third study, a literature review was performed to provide theoretical propositions for developing a conceptual model. The conceptual model was built on theories from product quality, service quality, service logic, and solutions.The findings revealed that a service organization could change the performance level of a quality principle if the correct interventions are used. Furthermore, a service organization immature in quality management emphasizes one or two quality principles and, after the initial phase focuses on other principles as well. Therefore, if a service organization wants to change its quality profile pattern, it must change its emphasis on certain norms and principles. A further finding is the proposed solution’s quality concept and its six quality dimensions: (i) reliability, (ii) flexibility, (iii) consistency, (iv) empathy, (v) approachability, and (vi) tangibility. Furthermore, a model connecting the empirical findings in a quality concepts model is proposed. This model shows that the need exists to change work activities if the service organization changes strategic direction, that is, changes the number of offerings offered.
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| 3. |
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| 4. |
- Lundberg, Mattias
(författare)
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Residual Stresses and Fatigue of Shot Peened Cast Iron
- 2013
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The complex geometry of cylinder head in heavy-duty diesel engine makes grey cast iron or compact graphite iron a perfect material choice due to its castability, thermal conductivity and damping capacity. To increase the efficiency of the engine, the fatigue property of the material needs to be improved. Shot peening is often used to increase the fatigue strength of components. The benefits are associated with the compressive stresses induced and with surface hardening. In this research project, these effects on grey and compact iron have been analyzed for different shot peening parameters using XRD, SEM and fatigue testing methods. The ultimate aim of the project is to increase the fatigue strength of cast irons by optimization of residual stresses.The XRD measurements and SEM examinations revealed that the shot peening parameters including shot size and peening intensity had significant influences on the resulted residual stresses and strain hardening while changing the coverage made little difference. Also differences in the peening results between the two materials were observed, which were ascribed to an effect of the different graphite morphology. Nevertheless, a residual stress profile similar to the one general considered to improve the fatigue strength in steels could be obtained in both grey and compact iron after shot peening.The axial fatigue testing with R=-1 on the grey iron showed that peening using large shot size and high peening intensity (heavy shot peening) resulted in a fatigue strength reduction of 15-20% in comparison with the mechanically polished surface. The negative effects are likely related to surface damage and relatively high tensile residual stresses in subsurface induced by the heavy peening. Grey cast iron has low ductility in tension and therefore tensile residual stresses may promote multiple cracking and crack networking during cyclic loading.Shot peening using much smaller shots and lower intensity (gentle shot peening) which resulted in a much smaller residual stress field gave no significant changes in fatigue strength. However, a short time annealing at 285°C of specimens being gently shot peened increased the fatigue strength roughly by 10%. The improvement could be an effect of precipitates formed due to the heat treatment, which lock the dislocation movement under cyclic loading.
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| 5. |
- Vesterlund, Mattias
(författare)
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District heating system analysis within the urban transformation of Kiruna
- 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The urban transformation that is taking place in Kiruna, a Swedish town well above the Arctic Circle in the sub-arctic climate, is due to the ground deformation caused by iron ore mining and it is affecting all the infrastructures of the town. This thesis focuses on the studies about the district heating for the town of Kiruna. In the field of district heating it is important to have a good knowledge about network behavior, especially if network structure is meshed, in order to understand how the flow is distributed in each pipe within the network. This thesis describes the development of a method for the simulation of district heating networks that makes it possible to analyze and study complex networks with meshed structure, something that has not been possible before. The thermal losses for each pipe type are required as a fundamental input for the simulation. A fictitious pipe series has been created so that its loss matches the losses in the real network. It has been found that the created series is close to the series with the highest losses that is manufactured today. When redesigning the network structure to deal with the urban transformation, an investigation is performed regarding how new low energy building can be heated. This investigation shows that the only heating system that fulfills the guidelines stated by the Swedish authorities about indoor climate is the floor heating. A techno-economical evaluation shows that the cheapest heating technology is an air to air heat pump. In order to make district heating attractive as a heating source for house owners a vigorous price reduction is needed.
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