| 1. |
- Abdikalikova, Zamira
(författare)
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Embedding theorems for spaces with multiweighted derivatives
- 2007
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This Licentiate Thesis consists of four chapters, which deal with a new Sobolev type function space called the space with multiweighted derivatives. This space is a generalization of the usual one dimensional Sobolev space. Chapter 1 is an introduction, where, in particular, the importance to study function spaces with weights is discussed and motivated. In Chapter 2 we consider and analyze some results of L. D. Kudryavtsev, where he investigated one dimensional Sobolev spaces. Moreover, in this chapter we present and prove analogous results by B. L. Baidel'dinov for generalized Sobolev spaces. These results are crucially for the proofs of the main results of this Licentiate Thesis. In Chapter 3 we prove some embedding theorems for these new generalized Sobolev spaces. The main results of Kudryavtsev and Baidel'dinov about characterization of the behavior of functions at a singularity take place in weak degeneration of spaces. However, with the help of our new embedding theorems we can extend these results to the case of strong degeneration. In Chapter 4 we prove some new estimates for each function in a Tchebychev system. In order to be able to study also compactness of the embeddings from Chapter 3 such estimates are crucial. I plan to study this question in detail in my further PhD studies.
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| 2. |
- Adolfsson, Daniel
(författare)
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Steelmaking slags as raw material for sulphoaluminate belite cement
- 2007
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The present work was undertaken as part of the research in the Minerals and Metals Recycling research centre, MiMeR. The course of the thesis is attributed to metallurgical slags from the steelmaking industry and the possible use of such by-products as raw material for sulphoaluminate belite cement (SAB). Implementing steel slags into the production of cement could contribute to the steel industry's possibility of increasing the recirculation. In addition to the previous objective, the introduction of slag into the cement manufacturing can also facilitate the reduction of carbon dioxide emissions as well as lowering the overall energy consumption during the manufacturing. The reason for this is that the SAB system enables the reduction of the lime saturation factor (LSF) which in turn implies that less limestone is needed in the raw meal. Additionally, the firing temperature can be reduced by about 100-150°C, since dicalcium silicate and sulphoaluminate are formed already at approximately 1200-1250°C. In any event, one should remember that this is not intended to be a final solution for the recycling of slag, nor a replacement for already accepted cement materials. A number of applications currently exist where ordinary Portland cement (OPC) is used, but in cases where the OPC could be replaced with other type of cements, e.g. SAB cement, the possibility of using residues material in cement applications is increased. Considering the clinker covered within this work, possible applications are those where slow hydraulic properties are suitable. The behaviour of high temperature reactions of tested mixtures was investigated using thermogravimetric analysis coupled with a quadrupole mass spectrometer. Mineralogical observations were carried out with x-ray powder diffraction (XRD) and scanning electron microscopy (SEM). The results proved that steelmaking slags have the potential to work as raw material, since sulphoaluminate along with polymorphs of dicalcium silicate and ferrite phases were detected after firing at 1200 ºC in an air atmosphere. The hydraulic properties of the specimens were analysed through conduction calorimetry, XRD, differential scanning calorimetry (DSC) as was the mechanical strength of the specimens when hydrated for 2 and 28 days. The compressive strength was in accordance with that suggested in the literature for slow hardening SAB cement. Both mixtures tested behaved the same with regard to heat development as well as the amount of AFt formed during the first 24 hours of the hydration.
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| 3. |
- Ahmadi, Alireza
(författare)
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An assessment of operational consequences of failures to support aircraft scheduled maintenance program development
- 2007
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A majority of the direct and indirect maintenance costs in the life cycle of aircraft stems from the consequences of decisions taken during the initial maintenance program development. In particular, the preventive and corrective maintenance requirements, which greatly influence both the system availability and life cycle cost, need to be defined in order to perform only those preventive actions that are absolutely necessary and costeffective. Reliability-Centered Maintenance (RCM) is a systematic methodology used to identify the preventive maintenance tasks that are necessary to realize the inherent reliability of equipment at the lowest possible cost. Developing a scheduled maintenance program by means of RCM consists of identifying those preventive tasks which are both applicable (technically feasible) and effective (worth doing). An applicable maintenance task must satisfy the requirements of the type of failure to restore the item's initial performance capability. To be effective, a preventive maintenance task must lead to a reduced risk (or expected loss) of the consequence classes to a level which is acceptable to the user. In the design development phase, in order to identify the most cost effective solution, a design trade-off study is needed. This involves choosing the correct balance of the cost of consequences of failure and its correction, with their cost of prevention. However, during initial aircraft maintenance program development, lack of a methodology that supports the assessment of the operational consequences of failures has made the costeffectiveness analysis of maintenance tasks a challenging issue. This might reduce the accuracy of the analysis, which results in higher maintenance costs and may decreases the punctuality of operation, which ultimately increases the total aircraft life cycle cost. The purpose of this study is to develop a methodology for identifying different operational consequences and associated costs caused by aircraft system failure, in order to facilitate and enhance the capability of taking correct and efficient decisions when analyzing the cost-effectiveness of maintenance tasks. Some empirical studies of possible scenarios involving aircraft failures and their operational consequences for a commercial airline have been performed. Empirical data were extracted through document studies and interviews, guided by the application of an Event Tree Analysis (ETA). The analysis was performed together with experienced practitioners from both an aircraft manufacturer and commercial airlines, which contributed to a continuous verification of the outcomes of the study. Finally, the study has also estimated the associated cost of the identified operational consequences of failures. In order to quantify the operational consequences of failures, in the absence of adequate and reliable data, a methodology using pair-wise comparison technique has been applied to extract judgments of experts efficiently
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| 4. |
- Aitomäki, Yvonne
(författare)
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Towards a measurement of paper pulp quality : ultrasonic spectroscopy of fibre suspensions
- 2006
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- For the paper and pulp industry in Sweden and Finland to remain competitive against countries with lower overheads, they have to constantly strive to improve the quality and the efficiency of the manufacturing processes. One of the ways of doing this is to introduce sensors that will provide valuable online feedback on the characteristics of the pulp so that adjustments can be made to optimise the manufacturing process. The measurement method proposed in this thesis is based on ultrasound, since it is rapid, inexpensive, non-destructive and non-intrusive. Thus could be done online. Since ultrasound propagation and attenuation depends on the material properties through which is propagates, it has the potential to provide measurements of material properties such as pulp fibre density and elasticity. The aim of this thesis is to investigate the possibility of using ultrasound to measure pulp fibre material properties. The idea is to solve the inverse problem of estimating these properties from attenuation measurements and to establish the degree of accuracy to which this can be done. Firstly a model is developed and is tested with synthetic fibres to establish is validity. It is then used to solve the inverse problem of estimating material properties from attenuation measurements, again with synthetic fibres, to test the accuracy to which these properties can be estimated. Resonance peaks in the frequency response of the attenuation were found. On closer investigation it was established that the location of these peaks in the frequency domain is sensitive to the diameter of the fibres and their material properties. If the diameter is known, these peaks improve the accuracy of the estimation process. The results of the estimation process for synthetic fibre suspensions show values for the shear modulus are within known ranges but the estimation of Poisson's ratio and Young's modulus is poor. Improving the model or the estimation procedure may lead to better results. For the method as it is to have application in the paper and pulp industry there are certain conditions that need to be fulfilled. These are that we find peaks in the frequency response of the attenuation in pulp, know the diameter distribution of the fibres and the hollow nature of the fibres does not significantly alter the results. We can then, potentially, be able to establish the shear modulus of the pulp fibres. If the shear modulus is a factor in paper quality, we may be close to an online measurement of paper pulp quality using ultrasonic spectroscopy. Improving the model may allow us to estimate further properties and take into account the fibres being hollow. The thesis consists of two parts. The first part includes an overview of the pulp and paper industry and current testing methods, background theory on which the model is based and an overview of the model that is used in predicting ultrasound attenuation. There then follows a summary of the work done, some addition points are raised in the discussion before drawing conclusions. Finally we discuss what needs to be done to take this further. The second part contains a collection of four papers describing the research.
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| 5. |
- Alakangas, Lena
(författare)
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Sulphide oxidation and geochemical processes in mine tailings
- 2003
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The generation of acid mine drainage (AMD) from oxidation of sulphide- bearing waste is a world wide problem, due to low pH levels and the release of metals to recipients. It is therefore important to understand the fundamental geochemical processes occurring in mine waste. The geochemistry of the drainage water from the tailings at the abandoned Laver copper mine in Northern Sweden was studied in 2001 and compared with a previous study performed in 1993. All drainage water is collected in a brook, which means that Laver is a favourable site for mass balance studies. The results show a decrease in the amount of sulphide-associated elements such as S, Cu and Zn in the drainage water, and an increase of the pH level. It has been suggested that this is due to the decrease in the sulphide oxidation rate in the tailings. Modelling the oxidation front movement using the shrinking core model gives similar results. This indicates that the sulphur transported in the drainage water could relatively well reflect the oxidation rate in the tailings. Oxygen sampling was also performed in 2001- 2002 to evaluate whether the flux of oxygen into the tailings was restricted by a vegetation cover. The results show that vegetation does not limit oxygen diffusion into the tailings. There is an atmospheric concentration throughout a profile through oxidised grass covered tailings during the whole sampling period. Oxygen concentrations at depths where sulphide oxidation occurs show seasonal variations, probably due to varying water saturation. Cemented layers were sampled at two locations in the Laver impoundment tailings, where they had been formed in spite of the low sulphide content and lack of carbonates. The aim of the study was to determine the effects of cemented layer formation on metal mobility in the tailings. The cementing agents are jarosite and Fe-oxyhydroxides. Arsenic is strongly enriched and somewhat higher concentrations of Pb, V, Mo and Hg, compared to those in unoxidised tailings, occur in these layers. Sequential extraction shows that these metals are mostly adsorbed/co-precipitated with crystalline iron oxyhydroxides. The enriched metals will probably be remobilised if changes towards more reducing conditions occur, for instance as a result of remediation of the tailings impoundment. An attempt was made to use LA-ICP-SMS to quantify the role of pyrite surfaces as scavengers of metals in oxidising mine tailings. Pyrite grains were collected from a profile through the pyrite-rich tailings at the Kristineberg mine in Northern Sweden. At each spot hit by the laser, the surface layer was analysed in the first shot, and a second shot on the same spot indicated the chemical composition of the pyrite immediately below. The crater diameter for a laser shot is known, and by estimating the crater depth and total pyrite surface, the total enrichment on pyrite grains was calculated. Results are presented for As, Cd, Co, Cu, Ni and Zn. The results clearly show that there is an enrichment of As, Cd, Cu and Zn on the pyrite surfaces below the oxidation front in the tailings, but not of Co and Ni. Arsenic is also enriched on the pyrite grains that survived in the oxidised zone. However, only 1.4 to 3.1% of the Cd and Zn released by sulphide oxidation in the oxidised zone had been enriched on the pyrite surfaces in the unoxidised tailings, but for As and Cu the corresponding figures are about 64 and 43%, respectively. The results should not be taken too literally but allow the conclusion that scavenging to pyrite surfaces is an important process for retention of As and Cu below the oxidation front in pyrite-rich tailings. Although only pyrite grains that appeared to be fresh, without surface coatings, were used in this study, the possibility of a thin layer of Fe-hydroxides occurring must be considered. Both adsorption to the pyrite directly, or to Fe-oxyhydroxides, may explain the enrichment of As, Cd, Cu and Zn on the pyrite surfaces, and, in the case of Cu, also replacement of Fe (II) by Cu(II) in pyrite.
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| 6. |
- Alam, Md. Minhaj
(författare)
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A study of the fatigue behaviour of laser and hybrid laser welds
- 2009
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This licentiate thesis focuses on the fatigue cracking behaviour of laser and hybrid laser-MAG welded structures. Beside the welding process and the resulting weld, several topics related to fatigue of welded structures are treated such as; macro and micro surface geometry, weld defects and their influence on fatigue performance of welded structures, fatigue analysis by the nominal and effective notch stress method, fatigue life prediction using LEFM (Linear Elastic Fracture Mechanics), fatigue testing, metallurgical analysis, elastic and elastic-plastic finite element analysis. The main objective is to gain understanding of the impact of weld defects and weld shape details on the fatigue behaviour of laser and hybrid laser welded joints. The first paper is a literature survey which compiled useful information regarding fracture and fatigue analysis of various welded joints. In the second paper fatigue testing by bending of laser hybrid welded eccentric fillet joints was carried out. The weld surface geometry was measured and studied in order to understand the crack initiation mechanisms. The crack initiation location and the crack propagation path were studied and compared to Finite Element stress analysis, taking into account the surface macro- and micro-geometry. Based on the nominal stress approach, SN-curves were designed for laser hybrid welded eccentric fillet joints. The competing criteria of throat depth and stress raising by the weld toe radii and by the surface ripples are explained, showing that surface ripples can be critical.The third paper is the continuation of the second paper, but studying the fatigue crack propagation of laser hybrid welded eccentric fillet joints. Microscopic analysis was carried out to identify internal weld defects. Nominal and effective notch stress analysis was carried out to compare standardized values. LEFM analysis was conducted for this joint geometry for four point bending load in order to study the effect of LOF on fatigue life. In good agreement between simulation and metallurgy, cracking starts and propagates from the lower toe, but for certain geometries alternatively from the weld bead or upper toe, even in case of Lack of Fusion, as was well be explained. Improved understanding of the crack propagation for these geometrical conditions was obtained and in turn illustrated. Lack of fusion surprisingly was not critical and only slightly lowered the fatigue life. Two dimensional linear elastic finite element analyses is carried out in the fourth paper on laser welding of a beamer in order to study the impact of geometrical aspects of the joint design and of the weld root on the fatigue performance. Critical geometrical aspects were classified and then studied by FE-analysis with respect to their impact on the fatigue behaviour. Stress comparison of full 15 mm and partial 6 mm weld penetration of the beam was done by varying the toe and root geometry to identify the critical details. Generalization of the knowledge by new methods was an important aspect, particularly to apply the findings for other joints. Together the papers provide better understanding of fatigue behaviour for complex geometries and are therefore suitable guidelines for improved weld design.
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| 7. |
- Alberg, Henrik
(författare)
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Material modelling for simulation of heat treatment
- 2003
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Heat treatment of materials is a fundamental metallurgical process. Materials are subjected to heat treatment to relieve internal stresses, reduce brittleness and to improve machinability. The properties of materials can also be altered such as hardness, strength, toughness, and wear resistance to suit particular applications. Nevertheless, heat treatment can generate unwanted stresses and deformations, a fact that has to be taken into consideration when designing or changing the sequence of manufacturing for a given component. One way to decrease cost and reduce time in product development can be to use simulation tools that can reliably predict the final properties and shape of a component caused by the used manufacturing process. A decrease in cost and better knowledge of final properties already in product development can give the company a better market position and competitiveness. The objective of the work presented in this thesis is to develop efficient and reliable methods and models for simulation of heat treatment using the Finite Elements Method. The result of the simulation must be sufficiently accurate and completed within an acceptable time when the manufacturing simulation is to be used in product development. The models would enable us to predict residual stresses, distortion, final shape, and amount material phases after a heat treatment process. The formulation of constitutive equations for elasticity, plasticity, and creep is discussed, along with three unified models, bringing together plasticity/viscoplasticity, and creep into one model. There are many materials models to choose among but material parameters are usually lacking An approach where the same numerical algorithm for the implementation of a constitutive model in the finite element code is also used for material parameter identification is presented. A parameter fitting using a viscoplastic model with nonlinear isotropic hardening is performed. Combined welding and heat treatment simulation is performed on a geometrical complex shaped aerospace component. Efforts to accurately determine the boundary conditions have been made. During the cooling sequence most of the heat transfer is carried out by convective heat transfer. Therefore, a method is developed and a CFD analysis is carried out to obtain this convective heat transfer Moreover, comparisons how the use of different material models affects the response from combined welding and heat treatment on an aerospace component is made. The material models include different effects; rate-independent and viscoplastic models including microstructure calculation and transformation induced plasticity. Different creep models and different ways to apply them has also been investigated.
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| 8. |
- Albing, Malin
(författare)
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Process capability analysis with focus on indices for one-sided specification limits
- 2006
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis some aspects of process capability analysis are considered. Process capability analysis deals with how to assess the capability of manufacturing processes. Based on the process capability analysis one can determine how the process performs relative to its product requirements or specifications. An important part within process capability analysis is the use of process capability indices. This thesis focuses on process capability indices in the situation when the specification limits are one- sided. The thesis consists of a summary and three papers, of which one is already published in an international journal. The summary gives a background to the research area, a short overview of the three papers, and some suggestions for future research. In Paper I, the frequency and use of process capability analysis together with statistical process control and design of experiments, within Swedish companies hiring alumni students are investigated. We also investigate what motivates organisations to implement or not implement these statistical methods, if there are differences in use that can be related to organisational types and what will be needed to increase the use. One conclusion drawn from the results is that the students employed in the Swedish industrial sector witness a modest use of these statistical methods and use in other sectors hiring the alumni is uncommon. In Paper II we present a graphical method useful when doing capability analysis having one-sided specification limits. This is an extension of the process capability plots previously developed for two-sided specification intervals. Under the assumption of normality we suggest estimated process capability plots to be used to assess process capability at a given significance level. The presented graphical approach is helpful to determine if it is the variability, the deviation from target, or both that need to be reduced to improve the capability. In Paper III the situation with non-negative process data having a skew distribution with a long tail towards large values are considered, when an upper specification limit only exists and the target value is 0. No proper indices exist for this specific situation, which is common in practice. We contribute to this area by proposing a new class of indices designed for skew, zero-bound distributions when an upper specification only exists and the target value is 0. This new class of indices is simple and possesses properties desirable for process capability indices. Two estimators of the proposed index are studied and the asymptotic distributions of these estimators are derived. Furthermore, we consider decision procedures, based on the estimated indices, suitable for deeming the process capability or not.
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| 9. |
- Alici, Güler
(författare)
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Integration på arbetsmarknaden : en studie av personer med utländsk bakgrund
- 2007
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- I denna licentiatuppsats redovisar erfarenheter från åtta fallstudier som alla har haft målsätt¬ningen att underlätta arbetsmarknadsintegrationen för personer med utländsk bakgrund. De åtta studierna har alla olika inriktning och innehåller olika aktiviteter som t.ex "starta eget"-program, nätverksbyggande, yrkesutbildning eller praktik. Syftet med licentiatuppsatsen är att identifiera hinder och gynnsamma faktorer i de åtta studier samt identifiera vilka faktorer som underlättar respektive motverkar integrationsprocessen. Studien bygger på ett rikt empiriskt material och metoden har valts beroende på vilket fall som studerats. Fem metoder har varit aktuella, studier av dokument, enkäter, individuella intervjuer, gruppintervjuer och deltagande observationer. En slutsats som kan dras här är att de flesta personer av utländsk bakgrund och som startar eget, blir objektivt integrerade på arbetsmarknaden. Deras företagande är inte en direkt integrationsfrämjande handling, men en bieffekt av företagandet är just att de känner sig integrerade i arbetslivet, även om yrket i sig inte råkar vara det bästa eller mest eftersträvans¬värda alternativet i deras perspektiv. Företagarna visade sig ha tillgång till ett omfattande etniska och informell nätverk bestod av släkt och familj, vänner och både inom och utom den etniska eller nationella gruppen. Däremot fanns inte ett fungerande formellt nätverk i lokalsamhället bland företagare och andra organisationer och näringsliv. Utan att förringa betydelsen av en social och kulturell integration så är i ett första steg en ekonomisk integration av största vikt för den invandrade. En annan slutsats är att är att många aktörer på det lokala planet erbjuder personer med utländsk bakgrund utbildning och praktik som ska gynna deras integrering i det svenska samhället. Valmöjligheterna mellan olika utbildningsalternativ och praktikplatser är dock tämligen begränsade. Man tvingas således till ett mer instrumentellt förhållningssätt som innebär att man väljer sådant som eventuellt kan gynna möjligheterna att få ett arbete utan att man för den skull är intresserad av yrket i sig. Detta påverkar deltagarna att uppleva sina egna val som otillfredsställande vilket också påverkar deras motivation att genomföra utbildningar och praktik och i förlängningen förutsättningarna att integreras, både i arbetsliv och i samhället som helhet. Trots att praktik lett till arbete för flera personer hamnade många deltagare efter utbildning och praktik utanför arbetsmarknaden, vilket ledder till att man går tillbaka till arbetslöshet eller nya utbildningar. Slutligen kan man konstatera att det fanns en stor potential i att engagera engagerade individer och ideella organisationer i arbetet att integrera individer med utländsk bakgrund i det lokala samhället, men det var svårt att finna former för ett konstruktivt samarbete med olika myndigheter.
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| 10. |
- Almqvist, Andreas
(författare)
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Rough surface elastohydrodynamic lubrication and contact mechanics
- 2004
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In the field of tribology, there are numerous theoretical models that may be described mathematically in the form of integro-differential systems of equations. Some of these systems of equations are sufficiently well posed to allow for numerical solutions to be carried out resulting in accurate predictions. This work has focused on the contact between rough surfaces with or without a separating lubricant film. The objective was to investigate how surface topography influences contact conditions. For this purpose two different numerical methods were developed and used. For the lubricated contact between rough surfaces the Reynolds equation were used as a basis. This equation is derived under the assumptions of thin fluid film and creeping flow. In highly loaded, lubricated, non- conformal contacts of surfaces after running-in, the load concentration no longer results in plastic deformations, however large elastic deformations will be apparent. It is the interaction between the hydrodynamic action of the lubricant and the elastic deformations of the surfaces that, in certain applications, enable the lubricant film to fully separate the surfaces. This is commonly referred to as full film elastohydrodynamic (EHD) lubrication. Typical machine elements that operates in the full film EHD lubrication (FL) regime include rolling element bearings, cams and gears. Unfortunately, a cost effective way of machining engineering surfaces seldom results in a surface topography that influence contact conditions in the same way as a surface after running-in. Such topographies may prevent the lubricant from fully separating the surfaces because of deteriorated hydrodynamic action. In this case the applied load is carried in part by the lubricant and in part by surface asperities and/or surface active lubricant additives. This could also be the case in lubricant starved contacts, which is a common situation in not only grease lubricated contacts but also in many liquid lubricated contacts, such as high speed operating rolling element bearings. The load sharing between the highly compressed lubricant and the surface and/or surface active lubricant additives is the reason why this lubrication regime is most commonly referred to as mixed EHD lubrication (ML). Machine elements that while running operate in the FL regime may experience a transition into the ML regime at stops or due to altered operating conditions. It is not possible to simulate direct contact between the surfaces using a numerical method based on Reynolds equation. A parameter study, of elementary surface features passing each other inside the EHD lubricated conjunction, was performed. The results obtained, even though no direct contact could be simulated, does indicate that a transition from the FL to the ML regime would occur for certain combinations of the varied parameters. At start-ups, the contact in a rolling element bearing could be both starved and drained from lubricant. In this case the hydrodynamic action becomes negligible in terms of load carrying capacity. The load is carried exclusively by surface asperities and/or surface active lubricant additives. This regime is referred to as boundary lubrication (BL). Operation conditions could also make both FL and ML impossible to achieve, for example, in the case in a low rpm operating rolling element bearing. The BL regime is in this work modeled as the unlubricated frictionless contact between rough surfaces, i.e., a dry contact approach. A variational principle was used in which the real area of contact and contact pressure distribution are those which minimize the total complementary energy. A linear elastic-perfectly plastic deformation model in which energy dissipation due to plastic deformation is accounted for was used. The dry contact method was applied to the contact between four different profiles and a plane. The variation in the real area of contact, the plasticity index and some surface roughness parameters due to applied load were investigated. The surface roughness parameters of the profiles differed significantly.
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