| 1. |
- Andersson, Ninnie
(författare)
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Communication and Shared Understanding of Assessment : A phenomenological study of assessment in Swedish upper secondary dance education
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The aim of this study is to describe and explore the phenomenon of assessment in dance education within the Swedish upper secondary schools’ dance orientation. The phenomenon was researched based on teachers’ experiences of assessment in dance education and formulations in the syllabi for upper secondary school. Life-world phenomenology constituted a base for the study. The methods used in the investigation were document analysis, observations, teachers’ written and verbal reflections and interviews. Documentation of observations was made through field notes, video recordings and sound recordings. The generated material was analysed based on Spiegelberg’s (1960) seven stages of phenomenological analysis. Syllabi from Lpf94 and Gy11 were researched to describe and analyse in what ways dance knowledge becomes visible. In total, five teachers and three schools were involved in the study. Within the framework of the course Dance technique 1, observations of dance education in ballet, contemporary- and jazz dance were made as well as of ten grade conferences. The teachers read the field notes and were able to change formulations in case something was misunderstood or it needed to be commented on in the form of teachers’ written or verbal reflections. Interviews with four of the observed teachers were made and the conversations related to what appeared in the observations. Comprehension of teachers’ experiences resulted in a description of the phenomenon and answers to the research questions. The study is communicated through four intertwined papers. The result reveals various conditions for assessment in dance education. Two themes appeared in the overall findings of the study, namely: The design of the assessment practice and Communication within the assessment practice. The syllabi appeared as one condition among others for dance education in upper secondary school including views of dance knowledge that appeared through analysis of the syllabi. In the assessment practice, it was seen that teachers’ conduct of assessment involved conditions for formative assessment to emerge. Conditions in order for communicated assessment to become meaningful for the students also emerged, including shared understanding. The teachers expressed various conditions for the assessment practice to became visible, namely the students’ participation, their own actions, as well as the overall school context. The study contributes to the dance educational research field through making teachers’ experiences of assessment in Swedish dance education visible. The thesis discusses dance teachers’ various approaches to syllabi, how the teachers’ conceptions of quality influence the assessment practice, and finally the importance of shared understanding of communicated assessment is emphasised. Furthermore, collegiate discussions are brought to the attention as a way to improve and reflect upon assessment.Keywords: upper secondary school, dance education, assessment, life-world phenomenology
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| 2. |
- Charles Murgau, Corinne
(författare)
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Microstructure model for Ti-6Al-4V used in simulation of additive manufacturing
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is devoted to microstructure modelling of Ti-6Al-4V. The microstructure and the mechanical properties of titanium alloys are highly dependent on the temperature history experienced by the material. The developed microstructure model accounts for thermaldriving forces and is applicable for general temperature histories. It has been applied to study wire feed additive manufacturing processes that induce repetitive heating and cooling cycles.The microstructure model adopts internal state variables to represent the microstructure through microstructure constituents' fractions in finite element simulation. This makes it possible to apply the model efficiently for large computational models of general thermomechanical processes. The model is calibrated and validated versus literature data. It is applied to Gas Tungsten Arc Welding -also known as Tungsten Inert Gas welding-wire feed additive manufacturing process.Four quantities are calculated in the model: the volume fraction of phase, consisting of Widmanstätten, grain boundary, and martensite. The phase transformations during cooling are modelled based on diffusional theory described by a Johnson-Mehl-Avrami-Kolmogorov formulation, except for diffusionless martensite formation where the Koistinen-Marburger equation is used. A parabolic growth rate equation is used for the to transformation upon heating. An added variable, structure size indicator of Widmanstätten, has also been implemented and calibrated. It is written in a simple Arrhenius format.The microstructure model is applied to in finite element simulation of wire feed additive manufacturing. Finally, coupling with a physically based constitutive model enables a comprehensive and predictive model of the properties that evolve during processing.
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| 3. |
- Dagbro, Ola
(författare)
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Studies on Industrial-Scale Thermal Modification of Wood
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Wood as a raw material is useful for many purposes even though some properties are less than optimal, for example, dimensional stability and durability. These characteristics can however be improved by different treatment methods. Environmental awareness has led to an increased demand for environmentally friendly processes like thermal modification that does not add any chemicals to the wood in contrast to, for example, CCA-impregnated wood.This thesis mainly focuses on thermally modified wood from species such as pine, spruce and birch. The thesis present studies of physical attributes such as color, and chemical analysis of water-soluble compounds and degradation products. Treatment intensity is compared between two different industrial processes referred as Thermowood and WTT, which use respectively superheated steam and pressurized steam as heating media.Thermal modification processes darken the color of wood throughout its cross-section. The formation of darker color is related to a degradation processes that takes place during thermal modification. During thermal modification wood is exposed to temperatures between 160 - 220°C, and the temperature causes physical and chemical transformations that change some of the wood properties. Dimensional stability and durability are typically improved, but mechanical strength properties are usually negatively affected by the treatment.The studied wood species were Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies L.) and Birch (Betula pendula L.). Treatments using pressurized steam were carried out under temperatures of 160°C, 170°C and 180°C, and treatments using superheated steam at normal air pressure were carried out at temperatures of 190°C and 212°C. Results showed that similar L* (lightness) can be reached at lower temperatures using pressurized steam compared to superheated steam. The residual moisture content after completed thermal modification was approximately 10% higher in wood treated with the pressurized steam process. It was found that despite an approximately 25°C lower treatment temperature, birch modified in pressurized steam was more acidic compared to birch modified in superheated steam. This will likely have further consequences, requiring more research concerning surface treatment and fixation.The thesis also includes the development of an industrial-quality control procedure based on nondestructive color measurements verified in industrial environment. Treatment intensity in industry is today certified by inspection of documented process schedule and measuring the temperature and time of the process. Quality control in this context refers to the measurement of wood color as an indirect measure of treatment intensity. The color in our study was measured using L*C*H color space. The study shows that it is possible for quality control purposes to measure the color of thermally modified wood from the surfaces of planed boards instead of sawdust or board cross sections that have been used in other studies.The thesis has a final section about academia-industry collaboration that describes how trust building was established through a fruitful relationship involving academia and regional wood products industry in northern Sweden. The study presents an example of a successful research and development alliance between university and a group of small- and medium-sized enterprises (SMEs). This alliance has been a great example on international collaboration involving researchers originating from Finland, China, Bangladesh, Spain, Russia and Sweden. Through an in-depth multi-year study of how the research cooperation developed, the paper describes how the involved companies successfully entered into a new segment of the market.
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| 4. |
- Gama, Fabio, 1980-
(författare)
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Managing the Collaborative Front End of Innovation in Manufacturing Firms : Requirements, Capabilities, and Conditions
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The front end of innovation is critical to innovative efforts in firms yet it remains to be poorly understood. This especially important since innovation efforts in the front end are becoming increasingly open in line with the era of open innovation. Although the literature on the front end of innovation is well developed, prior studies have largely focused on bilateral agreements and have overlooked conditions for collaborations with science-based partners (universities and research institutes). This is especially true for manufacturing firms, for which a continuous stream of new product ideas are a key source of competitiveness. To make things worse, the front end of innovation in this setting is often characterized by incongruent practices by partners, different magnitudes of fuzziness, and high risks in revealing new ideas. Developing new product definitions with different partners is thus a risky endeavor that may seriously compromise competitive advantages if mishandled. Therefore, there is a need for greater knowledge to facilitate the collaborative front end with different types of partners. Accordingly, the purpose of this dissertation is to understand how to manage the collaborative front end in manufacturing firms, with a particular focus on requirements, capabilities, and conditions.To fulfill this research purpose, data on manufacturing firms were collected through four case studies and one survey. In total, this dissertation is based on empirical data from 81 interviews with R&D members across 10 medium-sized and large manufacturing firms, as well as a survey of 146 small and medium-sized manufacturing firms. Respondents were based in Brazil or Sweden. The key theories and literatures covered in this dissertation include coordination modes, control mechanisms, organizational routines, the resource-based view, and appropriability mechanisms.This dissertation makes numerous theoretical contributions to the front-end literature. First, it extends the front-end literature by presenting the concepts of systematic idea generation and fuzziness assessment as a prerequisite for improving front-end performance. Second, this dissertation extends the front-end literature by listing the collaboration conditions that help firms cooperate with science-based partners. By collaborating with science-based partners, firms can access (unpublished) codified and tacit scientific knowledge, enabling them to rapidly build on the latest research findings. The findings suggest particular practices that can be applied to reduce cultural differences and diminish goal divergence among project members. Third, the findings in this dissertation enrich the front-end literature by describing a set of detailed practices to streamline the involvement of different types of partners using diverse protective practices. Fourth, it suggests a theoretical framework that describes how to manage the collaborative front end of innovation. The theoretical framework explains how manufacturing firms can use their organizational capabilities to develop new product ideas efficiently and safely. In particular, the framework discerns the capabilities that are necessary to explore mechanisms, practices, and routines in terms of divergent thinking, external expertise, and multiple opinions. Altogether, these contributions assist firms to better manage collaborative front end.
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| 5. |
- Ghasemi, Yahya, 1982-
(författare)
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Flowability and proportioning of cementitious mixtures
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Understanding the role of constituents of cementitious mixtures as the most globally used human-made material and their effect on the flowability of the blends is of great importance. A comprehensive understanding of the ingredients of mixtures allows for optimized proportioning of constituents and can lead to a reduction in cement and water demand of the blends.The thesis focuses on relating the flow of mixtures to the specific surface area of the particles through the concepts of excess water layer theory by assuming that the particles are enveloped by a thin film layer that separates the grains and lubricates their surfaces. However, in order to study the film thickness, it is inevitable to consider packing density and specific surface area of the particles. Both of the mentioned parameters and their influence on water requirement of mixtures were investigated as a part of the project.The theoretical part of the thesis includes background and explanation of the concepts and theories used in conducting the research including particle packing theory, specific surface area, and excess layer theories. In addition, the thesis attempts at defining and formulating terms and parameters such as representative shape, mixer efficiency, and optimal packing.The experimental part of the thesis consists of laboratory measurements of packing density in the loose state, estimation of specific surface area using microtomography and slump tests for mortar and concrete.The results of the thesis indicate that the available packing models can estimate the packing density with acceptable accuracy. In addition, it was shown that it is possible to estimate flowability of mixtures based on information about the specific surface area of the constituents. A mix design approach is introduced which predicts flow spread of slump test, a measure that is often used in laboratories and at the building sites.Moreover, the research revealed that the estimation of the specific surface area of particles can be improved by assuming a platonic solid shape for the particles instead of spheres. Furthermore, the mixer efficiency was quantified and optimization of mixtures against packing density and water requirement was explained.The finding of the project lays a foundation for a simple workability based mix design approach.
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| 6. |
- Gustafsson, Emil
(författare)
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Design and application of experimental methods for steel sheet shearing
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Shearing is the process where sheet metal is mechanically cut between two tools. Various shearing technologies are commonly used in the sheet metal industry, for example, in cut to length lines, slitting lines, end cropping etc. Shearing has speed and cost advantages over competing cutting methods like laser and plasma cutting, but involves large forces on the equipment and large strains in the sheet material. The constant development of sheet metals toward higher strength and formability leads to increased forces on the shearing equipment and tools.Shearing of new sheet materials imply new suitable shearing parameters. Investigations of the shearing parameters through live tests in the production are expensive and separate experiments are time consuming and requires specialized equipment. Studies involving a large number of parameters and coupled effects are therefore preferably performed by finite element based simulations. Accurate experimental data is still a prerequisite to validate such simulations. There is, however, a shortage of accurate experimental data to validate such simulations.In industrial shearing processes, measured forces are always larger than the actual forces acting on the sheet, due to friction losses. Shearing also generates a force that attempts to separate the two tools with changed shearing conditions through increased clearance between the tools as result. Tool clearance is also the most common shearing parameter to adjust, depending on material grade and sheet thickness, to moderate the required force and to control the final sheared edge geometry.In this work, an experimental procedure that provides a stable tool clearance together with accurate measurements of tool forces and tool displacements, was designed, built and evaluated. Important shearing parameters and demands on the experimental set-up were identified in a sensitivity analysis performed with finite element simulations under the assumption of plane strain. With respect to large tool clearance stability and accurate force measurements, a symmetric experiment with two simultaneous shears and internal balancing of forces attempting to separate the tools was constructed.Steel sheets of different strength levels were sheared using the above mentioned experimental set-up, with various tool clearances, sheet clamping and rake angles. Results showed that tool penetration before fracture decreased with increased material strength. When one side of the sheet was left unclamped and free to move, the required shearing force decreased but instead the force attempting to separate the two tools increased. Further, the maximum shearing force decreased and the rollover increased with increased tool clearance.Digital image correlation was applied to measure strains on the sheet surface. The obtained strain fields, together with a material model, were used to compute the stress state in the sheet. A comparison, up to crack initiation, of these experimental results with corresponding results from finite element simulations in three dimensions and at a plane strain approximation showed that effective strains on the surface are representative also for the bulk material.A simple model was successfully applied to calculate the tool forces in shearing with angled tools from forces measured with parallel tools. These results suggest that, with respect to tool forces, a plane strain approximation is valid also at angled tools, at least for small rake angles.In general terms, this study provide a stable symmetric experimental set-up with internal balancing of lateral forces, for accurate measurements of tool forces, tool displacements, and sheet deformations, to study the effects of important shearing parameters. The results give further insight to the strain and stress conditions at crack initiation during shearing, and can also be used to validate models of the shearing process.
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| 7. |
- Khodadad, Davood
(författare)
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Multiplexed Digital Holography incorporating Speckle Correlation
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In manufacturing industry there is a high demand for on line quality control to minimize the risk of incorrectly produced objects. Conventional contact measurement methods are usually slow and invasive, meaning that they cannot be used for soft materials and for complex shapes without influencing the controlled parts. In contrast, interferometry and digital holography in combination with computers become faster, more reliable and highly accurateas an alternative non-contact technique for industrial shape evaluation. For example in digital holography, access to the complex wave field and the possibility to numerically reconstruct holograms in different planes introduce a new degree of flexibility to optical metrology. With digital holography high resolution and precise three dimensional (3D) images of the manufactured parts can be generated. This technique can also be used to capture data in asingle exposure, which is important when doing measurements in a disturbed environment. The aim of this thesis is devoted to the theoretical and experimental development of shape and deformation measurements. To perform online process control of free-form manufactured objects, the measured shape is compared with the CAD-model to obtain deviations. To do this, a new technique to measure surface gradients and shape based onsingle-shot multiplexed dual-wavelength digital holography and image correlation of speckle displacements is demonstrated. Based on an analytical relation between phase gradients and speckle displacements it is shown that an object is retrieved uniquely to shape, position and deformation without the unwrapping problems that usually appear in dual-wavelength holography. The method is first demonstrated using continues-wave laser light from twotemperature controlled laser diodes operating at 640 nm. Then a specially designed dual core diode pumped fiber laser that produces pulsed light with wavelengths close to 1030 nm is used. In addition, a Nd:YAG laser with the wavelength of 532 nm is used for 3D deformation measurements. One significant problem when using the dual-wavelength single-shot approach is that phase ambiguities are built in to the system that needs to be corrected. An automatic calibration scheme is therefore required. The intrinsic flexibility of digital holography gives a possibility to compensate these aberrations and to remove errors, fully numerically without mechanical movements. In this thesis I present a calibration method which allows multiplexed singleshotonline shape evaluation in a disturbed environment. It is shown that phase maps and speckle displacements can be recovered free of chromatic aberrations. This is the first time that a multiplexed single-shot dual-wavelength calibration is reported by defining a criteria tomake an automatic procedure. Further, Digital Speckle Photography (DSP) is used for the full field measurement of 3D deformations. In order to do 3D deformation measurement, usually multi-cameras and intricate set-up are required. In this thesis I demonstrate the use of only one single camera torecord four sets of speckle patterns recorded by illuminating the object from four different directions. In this manner, meanwhile 3D speckle displacement is calculated and used for the measurement of the 3D deformations, wrapping problems are also avoided. Further, the same scale of speckle images of the surface for all four images is guaranteed. Furthermore, a need for calibration of the 3D deformation measurement that occurs in the multi-camera methods,is removed. By the results of the presented work, it is experimentally verified that the multiplexed singleshot dual wavelength digital holography and numerically generated speckle images can be used together with digital speckle correlation to retrieve and evaluate the object shape. Usingmultidirectional illumination, the 3D deformation measurements can also be obtained. The proposed method is robust to large phase gradients and large movements within the intensity patterns. The advantage of the approach is that, using speckle displacements, shape and deformation measurements can be performed even though the synthetic wavelength is out of the dynamic range of the object deformation and/or height variation.
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| 8. |
- Pocorni, Jetro, 1988-
(författare)
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Laser cutting and piercing: Experimental and theoretical investigation
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis concerns experimental investigations of laser cutting and piercing, with theoretical and practical discussions of the results. The thesis is made up of an introduction to laser cutting and six scientific Papers. These Papers are linked in such a way that each of them studies a different aspect of laser cutting: process efficiency in Paper I, morphology and melt flow on the laser cut front in Papers II, III and IV and laser piercing in Papers V and VI.Paper I investigates the effect of material type, material thickness, laser wavelength, and laser power on the efficiency of the cutting process for industrial state-of-the-art CO2 and fibre laser cutting machines. Here the cutting efficiency is defined in its most fundamental terms: as the area of cut edge created per Joule of laser energy.In Paper II a new experimental technique is presented which has been developed to enable high speed imaging of laser cut fronts produced using standard, commercial parameters. The results presented here suggest that the cut front produced when cutting 10 mm thick medium section stainless steel with a fibre laser and a nitrogen assist gas is covered in humps which themselves are covered in a thin layer of liquid. Paper III presents numerical simulations of the melt flow on a fibre laser ablation-driven processing front during remote fusion cutting, RFC. The simulations were validated with high speed imaging observations of the processing front. The simulation results provide explanations of the main liquid transport mechanisms on the processing front, based on information on the temperature, velocity and pressure fields involved. The results are of fundamental relevance for any process governed by a laser ablation induced front. In Paper IV cutting fronts created by CO2 and fibre lasers in stainless steel at thicknesses between 2 mm and 10 mm have been ‘frozen’ and their geometry has been measured. The resulting three-dimensional shapes have been curve fitted as ninth order polynomials. Various features of the cutting front geometry are discussed, including the lack of correlation of the cut front inclination with either the relevant Brewster angle or the inclination of the striations on the cut edge. In this paper, mathematical descriptions of the cutting fronts are obtained, which can be used as input parameters by any researcher in the field of laser cutting simulations.Paper V investigates the subject of laser piercing. Before any cut is started the laser needs to pierce the material. In this paper the laser piercing process is investigated using a wide range of laser pulse parameters, for stainless steel using a fibre laser. The results reveal the influence of pulse parameters on pierce time and pierced hole diameter. A high speed imaging camera was used to time the penetration event and to study the laser-material interactions involved in drilling the pierced holes. In Paper VI a ‘dynamic’ or ‘moving beam’, laser piercing technique is introduced for processing 15 mm thick stainless steel. One important aspect of laser piercing is the reliability of the process because industrial laser cutting machines are programmed for the minimum reliable pierce time. In this work a comparison was made between a stationary laser and a laser which moves along a circular trajectory with varying processing speeds. High speed imaging was employed during the piercing process to understand melt behavior inside the pierce hole.Throughout this work experimental techniques, including advanced high speed imaging, have been used in conjunction with simulations and theoretical analysis, to provide new knowledge for understanding and improving laser beam cutting and its associated piercing process.
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| 9. |
- Ma, Charlie
(författare)
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Aspects of Ash Transformations in Pressurised Entrained-Flow Gasification of Woody Biomass : Pilot-scale studies
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Pressurised entrained-flow gasification (PEFG) of woody biomass has the potential to produce high purity syngas for the production of vital chemicals, e.g., biofuels. However, ash-related issues such as reactor blockages and refractory corrosion need to be addressed before this potential can be realised from a technical perspective. These undesirable consequences can be brought about by slag formation involving inorganic ash-forming elements and the chemical transformations that they undergo during fuel conversion. The objective of this study was to elucidate the ash transformations of the major ash-forming elements and the slag formation process. A pilot-scale PEFG reactor was used as the basis of the study, gasifying different woody biomass-based fuels including wood, bark, and a bark/peat mixture. Different ash fractions were collected and chemically analysed. Reactor slags had elemental distributions differing from that of the fuel ash, indicating the occurrence of fractionation of ash material during fuel conversion. Fly ash particles from a bark campaign were also heterogeneous with particles exhibiting differing compositions and physical properties; e.g., molten and crystalline formations. Si was consistently enriched in the reactor slags compared to other major ash-forming elements, while analyses of other ash fractions indicated that K was likely volatilised to a significant extent. In terms of slag behaviour, near-wall temperatures of approximately 1050-1200 °C inside the reactor were insufficient to form flowing ash slag for continuous extraction of ash material during firing the woody biomass fuels alone. However, fuel blending of a bark fuel with a silica-rich peat changed the chemical composition of the reactor slags and bulk slag flow behaviour was evident. Thermochemical equilibrium calculations supported the importance of Si in melt formation and in lowering solidus and liquidus temperatures of Ca-rich slag compositions that are typical from clean wood and bark. Viscosity estimations also showed the impact that solids have upon slag flow behaviour and corresponded qualitatively to the experimental observations. Corrosion of reactor refractory was observed. The mullite-based refractory of the reactor formed a slag with the fuel ash slag, which caused the former to flux away. Reactor blockages were also resultant because of the high viscosity of this slag near the outlet. A preliminary study into the corrosion of different refractories was also carried out, based on firing a bark/peat mixture. Alumina-rich refractories consisting of corundum, hibonite, mullite, and andalusite tended to form anorthite and exhibited varying degrees of degradation. Infiltration of slag was evident for all the samples and was a severe mode of degradation for some refractories. For fused-cast periclase and spinel-based refractories, slag infiltration was limited to voids and no extensive signs of refractory dissolution were found. This is also supported by a thermochemical equilibrium calculations mimicking slag infiltration that incorporated viscosity estimations. The findings from this thesis contribute towards the development of woody biomass PEFG by highlighting issues concerning ash fractionation, slag behaviours and ash\slash refractory interaction that should be investigated further.
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| 10. |
- Abiri, Olufunminiyi
(författare)
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Non-local models in manufacturing simulations
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Ductile fracture presents challenges with respect to material modelling andnumerical simulations of localization. The strain and damage localization maybe unwanted as it indicates a failure in the process or, as in the case ofmachining and cutting, a wanted phenomenon to be controlled. The latterrequires a higher accuracy regarding the modelling of the underlying coupledplastic and fracturing/damage behaviour of the material, metal in the currentcontext as well as the stability and robustness of the simulation procedure.This aim of this work is to develop, evaluate and implement formulations thatcan efficiently and reliably handle localization problems in machiningsimulations. The focus is on non-local models. The non-local models extendthe standard continuum mechanics theory by using non-local continuumtheory in order to achieve mesh independent results when simulating fractureor shear localization.The non-local damage model is implemented and various formulations areevaluated in a Matlab™ based finite element code. The chosen algorithm wasthen implemented in commercial software. The implementations remedy themesh sensitivity problem and gives convergent solution for metal cuttingsimulations with reasonable cost. The length scale associated with the nonlocalmodels are in the current context considered as a numericalregularization parameter. The model has been applied in machiningsimulations and compared with measurements from industry.Keywords: Finite element simulation; Non-local damage; Plasticity; Machining
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