| 1. |
- Bergström, Anders, 1971
(författare)
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In-situ testing of floating thermal piles in soft sensitive clay
- 2017
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Thermal piles are structural piles with additional function of working as geothermal heat exchangers towards the soil volume. Heating and cooling process of soft soils is known to affect the stress state and soil structure, with potential consolidation settlements and creep as undesired consequences. The aim of this thesis is to investigate the effects of static mechanical and cyclic thermal loading of floating piles in soft clay. A test site with soft sensitive clay is selected and the soil properties are characterised in an extensive field and laboratory test program. A full scale thermal pile and the surrounding soil volume is instrumented with a set of sensors. A thermal loading rig, together with the thermal pile installed, has been successfully designed to absorb and extract energy to the ground. The thermal properties of the clay have been evaluated in the field using a Thermal Response Test (TRT). The field test setup is found to be capable of capturing changes in displacements, pore pressures and temperatures caused by the cyclic thermal loading. The change in pore pressures is strongly linked to the measured change in temperature in the clay. It has been shown that the thermal loading applied neither lead to significant pile head displacements, nor vertical deformations in the soil. The pile bearing capacity, recorded in a maintained loading test, has been found to be similar for both the thermal and the reference test piles. The test is adding novel data on the response from a driven floating thermal pile in soft sensitive clay.
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| 2. |
- Gåård, Anders, 1977-
(författare)
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Wear in sheet metal forming
- 2008
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The general trend in the car body manufacturing industry is towards low-series production and reduction of press lubricants and car weight. The limited use of press lubricants, in combination with the introduction of high and ultra-high strength sheet materials, continuously increases the demands of the forming tools. To provide the means of forming new generations of sheet material, development of new tool materials with improved galling resistance is required, which may include tailored microstructures, introducing of specific(MC, M(C,N))carbides and nitrides, coatings and improved surface finish. In the present work, the wear mechanisms in real forming operations have been studied and emulated on a laboratory scale by developing a test equipment. The wear mechanisms identified in the real forming process, were distinguished into a sequence of events consisting of initial local adhesive wear of the sheets resulting in transfer of sheet material to the tool surfaces. Successive forming operations led to growth of the transfer layer and initiation of scratching of the sheets. Finally, scratching changed into severe adhesive wear, associated with gross macroscopic damage. The wear process was repeated in the laboratory test-equipment in sliding between several tool materials, ranging from cast iron to conventional ingot cast tool steels to advanced powder metallurgy tool steel, against dual-phase carbon steel sheets. By use of the test-equipment, selected tool materials were ranked regarding wear resistance in sliding against ferritic-martensitic steel sheets at different contact pressures. Wear in sheet metal forming is mainly determined by adhesion; initially between the tool and sheet surface interaction and subsequently, after initiation of material transfer, between a sheet to sheet contact. Atomic force microscopy force curves showed that adhesion is sensitive to both chemical composition and temperature. By alloying of iron with 18wt.% Cr and 8wt.% Ni, alloying in itself, or changes in crystal structure, led to an increase of 3 times in adhesion at room temperature. Hence, alloying may be assumed a promising way for control of adhesive properties. Additionally, frictional heating should be controlled to avoid high adhesion as, generally, adhesion was found to increase with increasing temperature for all investigated materials.
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| 3. |
- Kihlberg, Johan, 1972-
(författare)
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Vällingby och kulturarvet : Att bevara och förnya ett centrum
- 2012
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The focus of this case study is the renewal of Vällingby Centre which took place between 2004 and 2008. With its scale, ambition and content, Vällingby represented something completely new in Swedish urban development when the town district came into being in the early 1950s. The community centre also had an important role to play, it not only had a commercial function it also had a social and cultural function. Despite the fact that community centres appeared in great numbers, few of them remain as they once were. Many have undergone major changes including alterations and, quite often rather careless intervention, both with regard to their interior and exterior. New shop types, consumption patterns and increasingly fierce competition are just some of the factors that have led to the original values contained within this area being on the verge of disappearing. The entire town of Vällingby was nominated in 1987 by the National Heritage Board as a clear and well preserved example of an ABC city with regard to it structure and the planning ideals of the 1950s. An expression of such conservation ambitions signifies, however, a potential conflict situation with other interested parties and areas of interest, not least when it comes to buildings and environments that are for commercial use. The main purpose of this study is to deal with the renewal of Vällingby centre from a cultural heritage perspective. The first chapter will provide a background as to why Vällingby came about and present a picture of post-war town planning and the emergence of Vällingby Centre; while the second chapter will examine the decision-making process behind the renewal, where Välingby's town centre regeneration offers an interesting example of how areas which are classed as being of national interest are dealt with during the planning process. Vällingby Centre is an example of one of our modern national interests and of the maintenance and conservation problems post-war developments are associated with. The central parts of the town are also associated with a largely unexplored field of study, despite the increased diversity conservation intentions have received over the past few decades.
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| 4. |
- Tofique, Muhammad Waqas, 1986-
(författare)
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Very high cycle fatigue of duplex stainless steels and stress intensity calculations
- 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Very high cycle fatigue (VHCF) is generally considered as the domain of fatigue lifetime beyond 10 million (107) load cycles. Few examples of structural components which are subjected to 107-109 load cycles during their service life are engine parts, turbine disks, railway axles and load-carrying parts of automobiles. Therefore, the safe and reliable operation of these components depends on the knowledge of their fatigue strength and the prevalent damage/failure mechanisms. Moreover, the fatigue life of materials in the VHCF regime is controlled by the fatigue crack initiation and early growth stage of short cracks.This study was focussed on the evaluation of fatigue properties of duplex stainless steels in the VHCF regime using the ultrasonic fatigue testing equipment. The ultrasonic fatigue tests were conducted on the cold rolled duplex stainless strip steel and hot rolled duplex stainless steel grades. Two different geometries of ultrasonic fatigue test specimens were tested. Considerable attention was devoted to the evaluation of fatigue crack initiation and growth mechanisms using the high resolution scanning electron microscopy. The fatigue crack initiation was found to be surface initiated phenomena in all the tested grades, albeit different in each case.The second part of this thesis work was the development of a distributed dislocation dipole technique for the analysis of multiple straight, kinked and branched cracks in an elastic half plane. Cracks with dimensions much smaller than the overall size of the domain were considered. The main goal of the development of this technique was the evaluation of stress intensity factor at each crack tip. The comparison of results from the stress intensity factor evaluation by the developed procedure and the well-established Finite Element Method software ABAQUS showed difference of less than 1% for Jacobi polynomial expansion of sixth order in the dipole density representation.
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| 5. |
- Zhang, Qing
(författare)
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Mechanical Properties of Semi-Solid Al Castings : Role of Stirring
- 2022
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Semi-solid metal (SSM) casting has been widely used in automotive industries to reduce the weight. In RheoMetalTM process which is one of the variations of SSM, the slurry fabrication can be finished within 30 second and can the slurry making process can be integrated into a high pressure die casting (HPDC) route without significant adjustments, making the process a promising alternative for industrial application. However, the application of SSM is still limited due to the semi-solid deformation-induced casting defects, such as macrosegregation and large pores. Due to the short stirring duration, the inefficient stirring is the leading cause of defects formation. Another critical issue in the RheoMetalTM process is the oxidation during the stirring process, which results in the increase of oxides in the castings, reducing the mechanical properties.This study aims to investigate the ductility and the fatigue performance of SSM castings. The main focuses were on the role of the stirring and oxides. The quenched slurry was analyzed to evaluate the effect of the stirring on the particle distribution in the slurry, and its effect on the formation of pores and segregation was discussed. To investigate the oxidation during the slurry making process, two alloys with different Mg content were cast. Scanning electron microscopy (JEOL JSM-7001F SEM) equipped with Energy-dispersive X-ray spectroscopy (EDS) was used to identify the oxides on the fracture surface. Tensile test and fatigue test accompanied with direct current potential drop (DCPD) were performed to investigate the ductility and fatigue performance, respectively.The results suggest that the intensive stirring can avoid the formation of the large clusters, making the particle distribution homogeneous in the slurry. The Mg contents determined the types of the oxides formed in the slurry making process. For alloys with sufficient Mg, the oxides would be MgAl2O4, which exist as small films with numerous cracks, while a large oxides film will be formed in the case of low Mg content.The combined influence of porosity and oxides was concluded. In the 42000 alloy, because of the low Mg content, the ductility was dominated by the large oxide films. In contrast, in the Magsimal 59 alloy, the presence of small oxides (less than 0.2 mm in majority) leads to the influence of oxides on the elongation negligible. However, a good correlation was obtained between the largest pores and ductility.The fatigue test shows that the surface liquid segregation (SLS) determined the fatigue strength under cyclic bend loading, due to its higher hardness. The effect of the inner pores on the fatigue performance was negligible, as the maximum stress was applied on the surface.
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