| 61. |
- Eriksson, Magnus
(författare)
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Modelling of forming and quenching of ultra high strength steel components for vehicle structures
- 2002
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The doctoral thesis deals with modelling and simulations in integrated product and process development. The research concerns with development of models and methods for simulation of component manufacturing and product functionality. One aim of the research project is to enable the introduction of tubular high strength components in vehicle structures. The new type of structure components requires changes in the product development process in order to closely couple the design with the development of the manufacturing tools and process parameters. The coupling is performed with the development and introduction of new modelling and simulation methods and tools for the analysis of thermomechanical forming of tubular high strength components. In this work the requirements for the numerical models are studied and evaluated by comparisons with experimental results. A set of tests are defined, performed and evaluated for establishing the required material parameters for the analysis of the manufacturing process. An inverse modelling method has been developed for evaluation of continuous cooling and deformation experiments performed in Gleeble 1500 thermomechanical simulator equipment. Spray cooling experiments have been designed for the modelling of the cooling effects of different types of spray nozzles. A model and an algorithm for the introduction of water spray cooling from a set of water spray nozzles has been developed and implemented in to a thermomechanical analysis code. A tool and a set of experiments are used for the verification of thermomechanical analyses of the component forming and quenching process.
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| 62. |
- Fagerström, Birgitta
(författare)
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IT-användning : en analysmodell för IT-nytta
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Den möjliga IT-användningen har med tiden utökat sina domäner och det är i dag möjligt att använda tekniken som stöd för de flesta funktioner i en verksamhet. Frågan om ekonomisk avkastning och praktisk realisering av potentialen i tekniken är emellertid ifrågasatt och debatterad. I avhandlingen studeras IT-användning ur individperspektiv. Syftet har varit att analysera och förstå vilka faktorer som bidrar respektive motverkar upplevd IT-nytta. Analysen tar sin utgångspunkt i individerna som använder IT-systemen och i det arbete som utförs i verksamheten. I det empiriska underlaget ingår tre kvalitativt genomförda fallstudier, där faktorer som bidrar till IT-nytta undersökts med hjälp en analysmodell som utvecklats inom ramen för avhandlingsarbetet. I det empiriska underlaget ingår även en studie som belyser implementation och användning ur införarperspektiv. Förklaringar till upplevd nytta eller icke-nytta, den teoretiska referensramen, har varit områdena IT-strategier/IT-management, systemutveckling och systemförvaltning. Positivt verkande faktorer för IT-nytta är, enligt genomförda undersökningar, sådant som bidrar positivt till den egna effektiviteten och till utförandet av de egna arbetsuppgifterna. Negativt verkande faktorer är, när det uppfattas som obekvämt eller ologiskt att arbeta med systemen. Saknad funktionalitet upplevs också som en brist liksom bristande integration mellan olika system. Analysmodellen som användes i undersökningarna var ändamålsenlig, men undersökningen av implementation ur införarperspektiv indikerade, att det fanns ytterligare faktorer som var relevanta för IT-användning och nytta. Avhandlingsarbetet har av det skälet givit ett resultat även i detta avseende - en utvecklad analysmodell.
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| 63. |
- Ferm, Cecilia
(författare)
-
Öppenhet och medvetenhet : en fenomenologisk studie av musikdidaktisk interaktion
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- My interest in the problem I have chosen has grown from my practise as a music teacher in Swedish compulsory schools. My ontological and epistemological standpoints belong to a life-world-phenomenological way of thinking. By this I mean that the world is around us and in us, we are in the world, but experience it in different ways from our earlier experiences. An assumption in the study is that method and theory can hardly be separated from each other. When it comes to my view on teaching and learning, I have a holistic perspective. I don’t think you can separate content and methods. I think that the development of an individuals’ music experience and music knowledge needs to be in focus. With that foundation of understanding as a startingpoint, I believe that learning is constituted by our experiences in the world. I will also stress that learning does not arise nor is it formed in a vacuum, it is instead found in a complex context. The aim of the study is to describe, analyse and try to understand music teaching and learning interaction between teachers and pupils at music lessons in years 4-6 of compulsory school. There is a focus on the teacher’s words, actions and reflections. In what ways do teachers interact with pupils in musical learning processes? What aspects of the teaching and learning interaction are important when the aim is to offer the pupils, musical experience? How do the teachers reflect upon the interaction? According to a phenomenological way of looking at the world, the mean is to find a method that makes it possible to understand individuals and social groups from the lived relations they have to their environments, the world they live and participate in. The purpose is not solely to enlighten the things that already exist, but to see new connections between what is already existing. I followed three teachers for one semester, observed them and let them reflect via e-mail on the notes I wrote them every week. The generated written material was analysed by a method inspired by phenomenology. The results are presented in two parts. The first part is based on the observations. It is presented as themes and aspects that through the analysis seemed to be important and represent different sides of the phenomenon. The themes focus the following; How the teachers related to the incorporated musical knowledge of the pupils, in which way the teachers were open to the initiatives of the pupils, how musical experience was made possible, how the acts of the pupils were handled and finally which symbols were used in the interaction. The second part is based on the teachers’ reflections and is presented in two themes; Conditions that influence the quality of the interaction, and balance. Each theme is commented, related to practise and earlier research, and put into a broader context. In the last chapter some pervading characteristics such as inter-subjective creation of meaning, and distribution of responsibility are discussed.
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| 64. |
- Fernberg, Patrik
(författare)
-
Toughness of short fiber composites : an approach based on crack-bridging
- 2002
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The presented work considers how to properly characterize fracture properties of short fiber composites (SFC). Associated with fracture of SFC is the creation of a comparably widespread fracture process zone. This zone develops since a number of inelastic failure mechanisms (e.g. debonding, microcracking, fiber failure and fiber pull-out) take place in the vicinity of an advancing crack. In the present approach, a bridging law (or cohesive zone law) approach is adopted in order to characterize the fracture toughness of the material. Conventional fracture toughness measures, such as KIC were in most cases found not to be applicable. This was because fundamental small-scale yielding geometry requirements could not be fulfilled in experiments. The bridging law approach captures previously mentioned mechanisms in terms of a closure stress (bridging stress). This stress acts between two fictitious crack planes. The relation between crack opening displacement and bridging stress is governed by the bridging law. Parts of the presented work consider determination of bridging laws from experiments (Paper I and Paper III). Different experimental configurations, double cantilever beam (DCB) specimens loaded with pure moments and double edge notched tension (DENT) specimens, were used in the two studies. A main conclusion from Paper I is that the large differences in fracture characteristics between two sheet molding compound (SMC) composites could be explained on the basis of bridging laws and their influence on fracture energy. Similar observations were made in Paper III. In Paper III, it also was evident that the intrinsic non-linearity of bulk SMC material has to be considered separately in the data reduction of experimental results, in order to capture the bridging law. Bilinear approximations of decreasing bridging laws were obtained as a result from the study. A closer investigation on the mechanical behavior of SMC with varied composition was performed in Paper II. Various mechanical tests, including tension, compression, in situ studies, DCB and stiffness degradation measurements through quasi-static cyclic loading-unloading experiments, were employed. The purpose was to characterize and understand observed differences between conventional and toughened SMC with low density additives. The applicability of the proposed bridging law approach is confirmed by the work presented in Paper IV and Paper V. In these papers, the previously measured (Paper I and Paper III) bridging relations are used as a constitutive property in predictions of structural behavior of specimens with varied geometry. Paper IV considers that bridging law parameters can be used to predict and explain the change in notch-sensitivity observed on SMC DENT-specimens with varied geometry. A comparably simple analytical route (neglecting non-linear bulk behavior and shape of bridging law) is employed with satisfactory results. In Paper V, the use of the finite element method (FEM) in conjunction with measured bilinear bridging laws, allows reconstruction of experimentally measured compact tension (CT) specimen load vs. displacement curves with good accuracy. Three different CT specimen geometries are considered. Modeling and experimental results from Paper V also shows that compression failure often is of equal importance as tensile, in real structures and loading conditions.
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| 65. |
- Forsman, Arne
(författare)
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Skolans texter mot mobbning : reella styrdokument eller hyllvärmare?
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The aim of this doctoral thesis is to describe, analyse and interpret what is expressed in the comprehensive school’s texts against peer bullying. Express in this study means how international conventions, laws and school documents, research in the field and organisations against peer bullying, influence the content of the school texts against peer bullying. Texts consisting of plans, program methods and models against bullying from the school boards in the municipalities of the county of Norrbotten and one school district’s and a local school’s text in every municipality are objects for the analysis. The concept of bullying is discussed and the nature of measure program and how researchers construct these is shown. The analysis and the interpretation are based on a hermeneutic approach. Theories of attribution and coping are discussed in order to explain and understand the nature and the underlying mechanisms within the victim, the perpetrator and the school system that enable bullying to occur and continue. In some municipalities, contrary to legislation, texts about bullying are missing. Deficiencies in authority control are noted. Some texts have clear connections to overall ruling documents and research in the topic and a few of them could be useful tools in the school’s preventive and proceeding mission against bullying. Just in some texts the possibility to use the organisations in society, which struggle against peer bullying, is mentioned. The texts have an instrumental and individualistic view of bullying and consist in many cases of more or less brief manuals. In order to make the school’s preventive and measure task against peer bullying more efficient development of the school staff competencies and skills is needed in the fields of psychology, sociology and special education.
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| 66. |
- Forsman, Tomas
(författare)
-
Laser welding of aluminium alloys
- 2000
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis treats laser welding of aluminium alloys from a practical perspective with elements of mathematical analysis. The theoretical work has in all cases been verified experimentally. The aluminium alloys studied are from the 5xxx and 6xxx groups which are common for example in the automotive industry. Aluminium has many unique physical properties. The properties which more than others have been shown to influence the welding process is its high reflection, high thermal conductivity, low melting point, low viscosity and the alloying elements used. The most important physical properties have been described and studied experimentally as well as theoretically. The high surface reflectivity was shown to be of little importance when welding has initiated because the deep and narrow gas/plasma filled 'keyhole' captures the incident light which leads to considerably higher total absorption. The high thermal conductivity was shown to lead to a large weld width compared to the condition of other common metals. In addition the thermal conductivity together with low melting point and high boiling point was shown to yield a relatively large weld melt pool. A large melt pool together with the low viscosity has been shown to result in instability of the melt during welding. A number of defects can occur when laser welding aluminium alloys. The defects considered to be most important to try to avoid include porosity, edge effects and instability problems. Porosity has been shown to consist of spherical (gas filled) and cylindrical voids with different origins. Edge effects were found to be of different types when welding thin and thick material respectively. Common for both is that the heat distribution in the workpiece determines the result and that it can be theoretically predicted. Instability problems include random blowholes, smoke, spatter and weld depth variations. Natural variations exist but they can be controlled by the process parameters. The one most important cause of spatter from the melt is the amount of magnesium as an alloying element. The strength of the welded joints has been tested in static as well as dynamic loading. In normal tensile tests the best joints reached 90% of the strength of the parent material. Using wire as a filler a strength close to 100% was realised but this was due to a larger weld cross section. In fatigue tests the laser welds have performed better than other melt welding processes such as TIG and MIG. A fast and user friendly model predicting the weld dimensions was developed to cover laser welding with CO2 and Nd:YAG lasers of a range of common materials including aluminium alloys. The conclusion of this work is that welding of aluminium alloys is a challenge. It is predicted that methods such as riveting and clinching in the future in many cases will be replaced by the more cost effective laser welding. Laser welding of aluminium alloys will be increasingly used in automated industry as knowledge of the process continues to grow. In cases where thin aluminium alloys are to be joined at high speed lasers are expected to dominate.
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| 67. |
- Frenne, Nicklas
(författare)
-
Acoustic time histories of vibrating partial sources
- 2004
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The research in this thesis evaluates a method designed for separation of individual or partial sounds from multiple sounds generated by a sound source (e.g. a diesel engine). The sound of sound sources can be recorded to reproduce a sound event in an environment, just like a photo or moving picture can be used to illustrate a visual impression. By modifying the recordings, desired sounds can be described as targets of an improved sound environment. Furthermore, the reproduced sounds of the recordings can form the basis for improvements on sources, sound paths and sound environments which affect the cause and the perception of the sound. This is the founding idea of sound design and work that strives to bring about improved product sound quality. In cases when the sound comes from a multipart product, questions may arise about which parts produce which sound. With knowledge about which sound is caused by which part, modification of the right part and hence the sound is achievable. After the different sound signals are separated from each other, the components of a multipart sound source can be identified and then appropriately tested. For example, the sound of the separate parts of a heavy vehicle engine may be assessed in listening positions around the vehicle or in its cabin. Time signals of the parts of the engine and the sound paths from the engine to the listening positions are calculated and measured separately. The sound of similar engines can therefore be determined in different cabins regardless as to whether an engine actually had been positioned there. The foundation for this research originates from signal processing and inverse problems, in the aspect of calculated time histories from sources, and methods for empirical measurements of transfer functions between sources and microphones. The method used consists of six steps: Recording of sound pressure signals, measurement of transfer functions, measurement of source strength, calculation of source strength matrix, calculation of filters and filtering of recorded sound pressure signals. The first four steps of the method can be used for automated sound source quantification of the sources' source strength or sound power; the subsequent steps are needed to determine the acoustic time histories of the sources as source strength at the source or as sound pressure in the listening positions. The results of the research demonstrated that this approach is a viable method for the detection and isolation of partial sound sources. As the research used two types sound source it is also apparent that additional research is needed before the model can be widely applied to other types of sources. In particular, the effect of the positioning of fictitious monopoles needs to be better understood and also the effect of distance on the positioning of microphones from a partial source.
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| 68. |
- Gabra, Mohamed
(författare)
-
Study of possibilities and some problems of using cane residues as fuel in a gas turbine for power generation in the sugar industry
- 2000
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The potential of cane residuals as a source of energy could help many developing countries to improve their balance of payments by decreasing fossil fuels imports and increasing the electrical power production. A substantial increase of the electricity output in the sugar industry could be achieved by using a combined gas turbine/steam turbine integrated with gasifier supplying combustible gas to the gas turbine combustor. The problem is to find a way to avoid those ash-forming elements in the solid fuel that cause erosion, corrosion and deposits in the gas turbine. A method for avoiding excessive amounts of alkali compounds and particles in producer gas from gasification of cane residues has been studied and evaluated. Powderised cane residue is gasified in a cyclone gasifier. The cyclone gasifier works as a particle separator as well. The advantage with this technique is that the gasification temperature might be kept at a level where the volatilisation of corrosive elements such as sodium and potassium will not occur which could be separated from the product gas in the cyclone. A comparative study between the cyclone gasifier and a bench-scale fluidised bed gasifier have been conducted to evaluate which gasification process is most attractive as regards alkali separation/retention, and to try to elucidate the mechanisms responsible for the retention.
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| 69. |
- Gao, Chuansi
(författare)
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Slip and fall risk on ice and snow : identification, evaluation and prevention
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Slip and fall accidents and associated injuries on ice and snow are prevalent among outdoor workers and the general public in winter in many regions of the world. To understand and tackle this multi-factorial problem, a multidisciplinary approach was used to identify and evaluate slip and fall risks, and to propose recommendations for prevention of slips and falls on icy and snowy surfaces. Objectives were to present a systems perspective of slip and fall accidents and related risk factors; to evaluate the integration of slip resistance, thermal insulation, and usability of footwear by subjective trials. Further, to study the interaction mechanisms between footwear soling material and ice; to investigate and describe the relationship of ice and snow living experience and participation in winter sports with slips and falls; and to explain the role and mechanisms of lower extremity muscles in maintaining gait dynamic balance on inclined icy surface. The following methods were applied: 1) a systematic analysis of multiple risk factors through literature review; 2) direct observation; 3) videotaping; 4) subjective evaluations of slipperiness, thermal comfort and usability using rating scales; 5) a tribological study of the Coefficient of Friction (COF); 6) a questionnaire survey to identify and evaluate risk factors related to slips and falls; 7) a biomechanical study of human locomotion on ice. A systematic analysis of slips and falls on icy and snowy surfaces made it possible to use a multi-faceted approach to evaluation and prevention. The slip resistance, thermal insulation and usability of footwear tested were not suitably integrated, indicating the need of improving anti-slip properties and usability of footwear for use in cold environments. The artificially abrasive wear of soling materials improved slip resistance on hard ice, but not on melting ice. When comparing hard ice, melting ice and lubricated steel surfaces, the highest slip resistance was observed on hard ice, then on lubricated steel plate. Melting ice was most slippery. Curling footwear with crepe rubber soling showed significantly higher COF than other types. The footwear tested included winter footwear, professional footwear, safety footwear, and footwear considered to be slip resistant by manufacturers did not provide adequate protection against slips and falls on melting ice. Thus, additional measures should be taken to reduce slip and fall risk on melting ice. Slip and fall events declined with increased living experience in cold environments and winter sports participation. Biomechanical studies showed both increased and decreased magnitudes of gait muscle activities (EMG) at different gait phases and a generating of cautious gait strategies with an anticipated icy surface. These findings provided insights into how the proactive kinetic and kinematic adjustments of gait are achieved and the control mechanisms of stabilizing gait and posture through certain muscle activities when ascending on an icy slope. The mechanisms identified may be applied to develop intervention, rehabilitation and training techniques, which prevent slip and fall risks and associated injuries on icy surfaces and to improve performance in human locomotion, e.g., for winter sports. Measurement methods of slipperiness on ice and snow, related standards, task-related factors, slip resistant footwear, and intervention programs should be further studied and developed.
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| 70. |
- Gardelli, Åsa
(författare)
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"Det handlar om ett värdigt liv" : människor med funktionshinder införlivar IKT i sina vardagliga liv
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Studien fokuserar på människor med funktionshinder och hur de kan påverka sin livssituation med informations- och kommunikationsteknologin (IKT) som verktyg. Människor med funktionshinder ses i många sammanhang som om de vore en enhetlig grupp utan att man beaktar att funktionshinder är en av de samhälleliga skillnader som, liksom ålder, kön, klass, geografisk region etc., påverkar människors livssituation. Människor med funktionshinder är, liksom alla andra, individer med likheter och olikheter. Den svenska handikappolitiken bygger på målsättningar som full delaktighet, jämlikhet och alla människors lika värde. Levnadsvillkor för enskilda och för grupper av individer påverkas av hur samhället är organiserat, och ju större behov av stöd och särskilda insatser som en människa har, desto viktigare blir frågan om hur de samhälleliga strukturerna ser ut för att möta behovet av insatser. I såväl forskningsrapporter som statliga utredningar framhålls ofta IKT som ett kraftfullt verktyg för att stärka demokratin. Samtidigt ifrågasätts i rapporter, om den nya tekniken är en teknik för alla. Studiens syfte är att beskriva och analysera, och därigenom utveckla kunskap om, huruvida människor med funktionshinder kan påverka sina vardagliga liv med IKT som verktyg, och om så är fallet, på vilket sätt de kan göra detta och vad det i så fall får för betydelse för deras liv. Vidare belyses på vilka villkor människor med funktionshinder införlivar IKT i sina vardagliga liv - vilka möjligheter och vilka hinder som har funnits när det gäller IKT-användandet. Under närmare åtta år, 1996-2004, har olika forskningsprojekt pågått på Luleå tekniska universitet, där människor med funktionshinder har använt IKT i hemmen, i sina vardagliga liv. Från projekten finns omfattande material insamlat och en stor del av avhandlingen bygger på erfarenheterna från projekten - dels egna erfarenheter som doktorand och projektledare i dessa projekt, dels erfarenheter från de människor med funktionshinder som deltagit i den longitudinella studien kring projekten. Deltagarna från det ursprungliga projektet har följts under närmare åtta år och ytterligare deltagare med funktionshinder har tillkommit. Avhandlingen är en utveckling av den licentiatuppsats som huvudsakligen hade ett av projekten, som pågick 1996-1998, som grund. Studien vilar på en empirisk bas. Arbetet och angreppssättet är utpräglat tvärvetenskapligt och flera olika metoder har kombinerats för att få en mer heltäckande bild av livssituationen för människor med funktionshinder och deras IKT-användande. I studien ligger fokus på att den omfattande mängden empiri som ligger till grund för studien får tala, för att ge röst åt människor med funktionshinder och låta deras erfarenheter komma fram. Detta görs delvis med utgångspunkt från den narrativa kunskapstraditionen, med hjälp av livsberättelser kring några av de personer med funktionshinder som deltagit i projekten. Alla deltagarna i studien införlivade IKT i sina vardagliga liv på olika sätt. Det visade sig samtidigt att det fanns problem och hinder som överskuggade nyttan med att använda IKT för några av deltagarna i studien. De flesta av deltagarna använde IKT varje dag och de blev mycket vana IKT-användare. För dem blev IKT ett näst intill omistligt verktyg som användes i mycket stor omfattning till många nödvändiga göromål. För andra blev hindren svåra att överbrygga och de blev mer av icke-användare under tiden som studien pågick. Skillnaderna mellan deltagarna ökade under den longitudinella studien.
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