| 1. |
- Isaksson, Per
(författare)
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On crack growth under compressive stresses
- 2001
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis concerns fractures subjected to compressive stresses. In the four papers appended fracture behavior in brittle as well as ductile materials is studied. In the first paper, an expression for the mode II stress intensity factor at a straight extended kink has been calculated under the condition that crack opening is suppressed during crack growth. The expression has been found as a function of the mode II stress intensity factor K2 at the parent crack, the direction and length of the kink, and the difference between the remote compressive normal stresses perpendicular to, and parallel with, the plane of the parent crack. Crack growth directions have been suggested based on the result. At a sufficiently high non-isotropic compressive normal stress, so that the crack remains closed, the crack will propagate along a curved path maximizing the mode II stress intensity factor. Only at an isotropic compressive normal stress will the crack continue straight ahead in its original plane without directional change. By analyzing experimental crack growth patterns in paper two, the conclusion is that crack paths experimentally observed indicate that mode II crack growth under compression in some brittle materials follow a propagation path described by a function y=gx^b. In fact, the agreement between the experiments and the propagation path prescribed by the model, in which b=3/2, is astonishingly good since b was found in the interval [1.43-1.58] in all the experiments studied. Further, the investigation of the curvature parameter g has revealed that g also agree with the simplified model, even though not as good as the exponent b. However, the experimentally observed g differs in general less than 15% from the theoretical value predicted by the analytical model discussed in paper I. In paper three, a directional crack growth criterion in a compressed elastic perfectly-plastic material is considered. A slip-line solution is derived for evaluation of the stresses at the crack tip, which considers hydrostatic pressure and friction between the crack surfaces. Based upon the slip-line solution a projection stress based model is discussed for prediction of the direction of initiated crack growth. The opening displacement of an extended kink has been examined in paper four, using a finite element procedure. The conclusion is that an over-critical pressure in the plastic zone surrounding the crack tip suppresses crack opening regardless the direction of crack growth. The only possibility seems to be shear mode crack growth, which occur straight ahead in the crack plane if the crack is assumed to follow the plane of maximum shear stress. At a sub-critical hydrostatic pressure, or lower friction between the crack surfaces, the crack can extend via a kink subjected to local opening mode. An expression for the critical value determining fracture mode has been found as a function of hydrostatic pressure and friction between the crack surfaces assuming the fracture process to be predominantly controlled by local tensile stresses at the crack tip. The crack growth directions predicted by the projection stress based criterion in paper three are comparable with the directions maximizing the opening displacement of an extended kink computed in paper four.
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| 2. |
- Kristén, Lars
(författare)
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Possibilities offered by interventional sports programmes to children and adolescents with physical disabilities : an explorative and evaluative study
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Today, sport is a topic that interests and engages many people. However, pursuing sporting activities and being a member of a sports club is not a matter of course for children and adolescents with physical disabilities. The overall aim of this thesis is to study the possibilities offered by interventional sports programmes to children and adolescents with physical disabilities and to describe in what way they can be offered meaningful physical activities as well as active participation in sport clubs, with a view to improving their health and socialisation through sport. The thesis includes three descriptive and one evaluative study. The results of the thesis rest on a combination of methods: practical- empirical experiences based on theoretical reasoning, interviews in line with a method inspired by phenomenography, and data from questionnaires analysed by descriptive and analytical statistics. The results are also based on a variety of data sources i.e. children, young people and parents as well as theory triangulation i.e. socialisation and health. According to the findings, sports programmes offered possibilities to children and adolescents with physical disabilities for improving their health and socialisation. An important component of the sports programmes were sports clubs that offered meaningful physical activities as well as active participation. Guidelines for co-operation in and the organisation of sports programme for children and adolescents with physical disabilities were of great importance and should involve the families as well as sports organisations and local authorities. The children and adolescents regarded sport as a form of social arena to enhance their participation in society and as a means for achieving better health. They also stressed the importance of knowledge and experiencing nature as factors that promote an active and healthy lifestyle. The parents regarded sport as a form of health education and as a means for their children to achieve increased participation in society. The parents also stressed the fact that the learning process was important for empowering the children to influence their life situation. The findings also illustrate the importance of building co-operation between the habilitation centre, sports clubs and families of children with physical disabilities by means of a working team, as well as the importance of the sports movement opening up its activities to children and adolescents with functional disabilities and each sports club appointing a contact person with special responsibility for this target group. Continued external support was regarded as necessary in order to assist the sports clubs in implementing permanent and well-functioning activities in partnership with a personal sport and health counsellor, who advises and supports the children and adolescents to participate in physical activity.
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| 3. |
- Barth, Henrik, 1971-
(författare)
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Barriers to growth and development in small firms
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The purpose of the extended summary is to develop the understanding of the existence and reasons behind barriers to growth and development in small firms. More specifically, four questions are addressed: (1) What do we know about the term barrier, how can it be defined? (2) What types of barriers to growth and development have been identified? (3) How can barriers to growth and development be addressed in a framework? and (4) How do the results of the appended papers (Papers I-V) contribute to the research field of barriers to growth and development?A literature review was undertaken to answer the first two questions. The literature review was conducted in two phases. The conceptual and operational definition of barriers was addressed in the first phase. The results reveal diverse ways of focusing on barriers, which made it necessary to address similar terms, such as problem and causes of business failure in the second phase of the literature review. The different terms used in the papers of the literature review are discussed in order to determine whether or not the understanding of their content is coherent and conceptual. Based on the conceptual understanding and definition of barriers, the different aspects focused on in the literature were discussed, which led to the second question, What are the various aspects of barriers to growth and development?The knowledge gained from the literature review and the development of the understanding of the barrier concept led to the third question, Can barriers to growth and development be addressed in a framework? The discussion takes its starting point in the studies identified in the literature review and is related to some of the appended papers (Papers I and II). Similarities and differences between frameworks used in the papers identified in the literature review are discussed and, based on this knowledge, a framework for barriers to growth and development in small firms is presented. The framework distinguishes two types of barriers, namely internal/external barriers and tangible/intangible barriers.The knowledge available in the reviewed papers within the field of barriers to growth and development in small firms in combination with the results from the appended papers (Papers I-V) resulted in the fourth question. Part of the contribution of the appended papers concerns the operational definition, for example that barriers to innovation should be categorised as either occurring or preventing firms from innovating (Paper II), while other contributions concern specific types of barriers, for example the importance of managerial skills (Paper V). Overall, the contribution focuses on conditional factors, such as strategy and planning, organisation and management, and institution and policy factors, in relation to growth and development.
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| 4. |
- Dahlén, Leon
(författare)
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Numerical and experimental study of performance of a hydraulic motor
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The aim of this study was to develop an understanding of the fluid properties that influence the efficiency of hydraulic systems in a steady-state, especially components in hydrostatic transmission systems under different running conditions. The aim has also been to investigate and model the sources of losses in hydraulic machines, in order to estimate the losses, taking fluid properties into account. Finally, the technique of optimization has been introduced in order to improve the efficiency of a distributor valve in a radial piston hydraulic motor, Marathon M200. From an experimental field-test, which was performed on a belt conveyer using a hydrostatic transmission system, the overall efficiency of the hydrostatic transmission was compared when using a mineral oil, Shell Tellus TX 68, a synthetic fluid, Mobil SHC 526, and a vegetable fluid, Binol Hydrap II. The experimental field-test showed that vegetable and synthetic fluids improve the efficiency compared to mineral oil. The three fluids have the same viscosity but experimental tests showed that the temperature ()- and pressure() -viscosity coefficient differs between them. It was also found that the pressure-viscosity coefficient () of mineral oil was higher compared to vegetable and synthetic fluids. The proposed steady-state model gives greater accuracy regarding overall efficiency than the Wilson model, when examining fluid properties that differ in other aspects than their viscosity. The study has focused on losses in lubricated sliding contacts within a radial piston hydraulic motor, Marathon M200, and an analysis of the losses has been made using the finite element method (FEM). A FEM software package, Solvia, which takes into account fluid properties, such as temperature- and pressure- viscosity coefficient, heat conduction and specific heat, has been used to simulate the behaviour and to estimate the losses in tribological contact. This approach of simulation has been applied to two different tribological contact within the hydraulic motor: to a journal bearing contact and to a hydrostatic annular multi-recess plane thrust bearing. By using an FEM software package linked to an optimization algorithm, the losses in the tribological contact in a distributor valve were reduced significantly. The study shows that the optimized geometry of the distributor valve in the motor can successfully be improved, with regard to losses, by small changes in the geometry. Combining an FEM software package with the optimization routine offers an effective tool for designers to simulate and improve the efficiency of a hydraulic unit.
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| 5. |
- Grönlund, Erik
(författare)
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Microalgae at wastewater pond treatment in cold climate : an ecological engineering approach
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Three types of wastewater ponds in subarctic climates were investigated, each of them highly dependent on microalgae. They were fellingsdams, i.e. wastewater stabilization ponds complemented with chemical precipitation, high-rate algal ponds (HRAPs), and a type of aquaculture interface ponds between a wastewater treatment plant and the natural surrounding. From a microalgae taxa perspective green algae and cryptophytes were dominant in the wastewater ponds. Green algae and cryptophytes were also, together with chryso- and haptophytes, dominating the hypereutrophic and eutrophic stages of the natural lakes. Biomasses in the different types of ponds were of very different order of magnitude. From 100-1000 mg/l in the stabilization ponds during summer and 10-100 mg/l in spring and autumn, 70- 90 mg/l in a HRAP in autumn, to 5-30 mg/l in the most hypereutrophic stage in the natural ponds, 1-10 mg/l in the eutrophic stage, and below 1 mg/l in the oligotrophic stage. The connection between wastewater pond treatment and the field of ecological engineering was recognized. Future development of pond technology may benefit from a stronger connection to the theoretical framework of systems ecology developed in collaboration with the field of ecological engineering and ecotechnology.
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| 6. |
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| 7. |
- Fredriksson, Maria
(författare)
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From Customer Satisfaction to Citizen Interaction : a cooperation model for community development based on Total Quality Management
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Current problems with unemployment and the consequences of cut-down in the public sector need appropriate solutions, where private citizens perhaps take on more active roles than today, individually or in groups. The aim with this doctoral thesis is to contribute to one such solution, which is a cooperation model for societal development in local communities, based on Total Quality Management (TQM) and on the participation of many residents. The model is gradually developed with the help of collected experiences and opinions from three stakeholder groups in two different Swedish communities, as well as from general theories and literature. These groups are the quality-project initiators, the community residents and the local politicians. The disposition of the thesis is accordingly. The thesis contains two case studies. The first one concerns the use of TQM as a support of societal development in a local community. The improvement work is conducted within a non-profit organisation built on voluntary engagement. These experiences have then been compared, in the second case study, to the ones in another community where TQM is not used, but where the ambitions are the same. Here the framework for the improvement work is both a non-profit organisation and a for-profit one. The analyses indicate that TQM can be used with success within societal development, even if some of its tools or methodologies are interpreted in new ways, or not used at all. As TQM should be applied with regard to the type of organisation and its purpose, a certain flexibility is both expected and helpful. As far as management is concerned, the leadership needs to be “softer” and more diplomatic when managing unpaid volunteers, as compared to the situation in a commercial enterprise. Another observation is that the societal work is best conducted within groups, defined by situations or activities in life or in the society. An active resident can join a group according to interest. This is a modified version of the “quality circles” inherent to TQM. In a separate, and more theoretical study, the issue of adopting TQM to new sectors in society is discussed. In both the studied societies, there are difficulties to get residents involved or active, which puts into question the mandate with a large community project that aims at improving the quality of life for all residents. There are also difficulties with finding and renewing the leadership, and with communication with, above all, local politicians. Nevertheless, these politicians are in general positive to private initiatives like the ones in the two communities, and consider such projects very important for the future development of rural areas. They think that the experienced weaknesses can be reduced if the improvement work is distinctly defined and organised, if information and communication improve, and if the active residents become more educated about the procedures and limitations of the political governing of the communities. These and other observations of the two communities lead to a model where a cooperation between societal stakeholders develop in three phases; the start-up, the establishment and the continuation of the work. Each phase is discussed separately, and advice is given how to avoid, or meet, various problems that are likely to appear along the way.
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| 8. |
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| 9. |
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| 10. |
- Alkebro, Jesper
(författare)
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Multiphase oxide ceramics in the alumina-yttria system
- 2002
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- As a means of creating dispersed multiphase oxide structures, high-energy milling has been used for pre-treating alumina-yttria powder mixtures before pressing and sintering. Processing was performed in a planetary ball mill with steel or alumina milling tools and measured effects of the treatment have served as data for a modeling study. Subsequent phase development and sintering during heat treatment of the milled powders have been examined. Two compositions likely to result in a minority phase dispersed in another phase in equilibrium were selected and subjected to the milling treatment. The two constituent powders were homogenously mixed and defects were injected into the crystal structures which were gradually destroyed. Subsequently, depending on milling parameters, there was either amorphization of the sample or formation of yttrium aluminum perovskite, an intermediate phase of the alumina-yttria system. Alumina milling tools exhibited a higher milling efficiency, but they were prone to chipping which lead to massive contamination. Steel milling tools were worn in a more controlled manner and the total amount of contamination was much lower. In heat treatment milled powders easily attained phase equilibrium and there was no metastable behavior noted. Transformation temperatures fell as a function of milling time but for longer milling times the effects of prolonged processing decreased. Sintering properties were also improved resulting in higher final density and lower sintering temperatures. Iron contamination from steel milling tools was suspected to be detrimental for the final solidification and to cause large porosity, but when oxidized the effect is inversed leading to very good densification in argon atmosphere. Relative densities as high as 96% were measured after sintering 1 h in 1500°C, but the process was sensitive to the environment resulting in poor sintering for oxidizing (air) or reducing (argon in graphite furnace) atmospheres. A dispersion of a second phase in the dominant matrix phase was observed but further improvement of the process should be needed to make it finer. The grain size could be estimated to be around 5 µm from fracture surface images.
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