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  • 1.
    Adervall, Mikael
    Malmö högskola, School of Technology (TS).
    Väntmöbel för offentlig inomhusmiljö2011Independent thesis Basic level (professional degree), 10 credits / 15 HE creditsStudent thesis
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  • 2.
    Adnan, Safdar
    Malmö högskola, School of Technology (TS).
    Microstructures and surface roughness of EBM produced Ti-6Al-4V2010Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The work presented in this dissertation is concerned with the microstructures andsurface roughness of test slabs of Ti-6Al-4V produced by one of powder based AdditiveManufacturing (AM) technique namely Electron Beam melting (EBM). The effects of processparameters of a EBM system and geometry factors of a EBM build such as slabs’ thickness andheight etc. on the microstructure and the surface roughness of the EBM produced Ti-6Al-4Vhave being investigated. The processing parameters of the EBM system involved in the presentwork include beam current, scan speed, offset focus and scanning length etc. In this study threedifferent batches of samples were prepared. Microstructures of EBM built Ti-6Al-4V werestudied using Optical Microscopy (OM), Scanning Electron Microscopy (SEM), TransmissionElectron Microscopy (TEM), and X-ray diffraction (XRD). Confocal microscopy and imageanalysis codes ImageJ’s routine SurfCharJ were used to quantify the surface roughness of the testslabs. The microstructures of EBM built Ti-6Al-4V in general consist of columnar grains of priorβ phase. Inside the columnar grains there is a typical (α+β) microstructure of titanium alloyscontaining Widmanstätten α platelets and rod-shaped β phase. Grain boundary α layer has alsobeen observed on the grain boundaries of prior b columnar grains. By using TEM, the β phase inEBM built Ti-6Al-4V has been identified as a rod-like structure located on the grain boundariesof the fine a grains and often grows up along the build direction. The size of the β rods is about200nm and the distance between the β rods is ranged between 0.5 -2μm. Chemical compositionsfor different phases have been measured by TEM/EDX and volume fraction of the β phase in theEBM Ti-6Al-4V has been determined to be 2.7%. The phase transformation sequence in EBMbuilt Ti-6Al-4V has been discussed according to processing history and microstructuresobserved. It has been observed that, the size, number and geometry of prior β columnar graindepend on the sample thickness and other process parameters setting. The diameter of columnargrain varies between 2-70μm. The increase in size, number and regularity of columnar grains hasbeen observed with increase in sample thickness, beam energy density and scanning length.While with increase in height of the build it decreases. The length and smoothness of α plateletsincreases with increase in diameter of prior β columnar grain. The β phase rods are unaffected bysample thickness and process parameter settings. The sample thickness and beam energy densityhas a strong effect on the surface roughness of the test slabs. The value of surface roughnesscoefficient Ra for different test slabs varies between 1-20μm. It is observed that the surfaceroughness increases of the test slab increases with increase in thickness of the slab and beamenergy density. The possible reasons for these variations in microstructures and surfaceroughness have been discussed.

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  • 3.
    Al-Ashraf, Samir Daniel
    et al.
    Malmö högskola, School of Technology (TS).
    Sefedini, Arban
    Malmö högskola, School of Technology (TS).
    Prototyper för NFC implementeringar2010Independent thesis Basic level (professional degree), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Near Field Communication (NFC) is a contactless short distance (approximately 10 centimeters) communication technology, which conveys a more secure connection. NFC is a relatively young technology which is cheap to implement, and user-friendly. NFC is directed to mainly cellphones, where opportunities for implementation of applications are wide. The technology conveys a faster and easier exchange of information, by putting units side by side. At present, the technology is used mostly in Asia. In Europe, no major effort has begun yet, but is expected to. NFC is expected to exist in a majority of cellphones, in the future. This essay treats practical implementation of a “toolbox” with the NFC technology. The goal was to make a “toolbox” with different components. The “toolbox” is intended as a base for implementing NFC applications and for experimenting with the different components. The hardware components are: cellphone, a tag, a RFID module and a microprocessor. The program components consist of a number of code examples. Our work has resulted in three prototypes which together constitute a “toolbox”. The prototypes communicate between any combinations of the components in the “toolbox”: cellphone with tag, reader with tag and reader with cellphone.

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  • 4.
    Alkebro, Jesper
    Malmö högskola, School of Technology (TS).
    Multiphase oxide ceramics in the alumina-yttria system2002Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    As a means of creating dispersed multiphase oxide structures, high-energy milling has been used for pre-treating alumina-yttria powder mixtures before pressing and sintering. Processing was performed in a planetary ball mill with steel or alumina milling tools and measured effects of the treatment have served as data for a modeling study. Subsequent phase development and sintering during heat treatment of the milled powders have been examined. Two compositions likely to result in a minority phase dispersed in another phase in equilibrium were selected and subjected to the milling treatment. The two constituent powders were homogenously mixed and defects were injected into the crystal structures which were gradually destroyed. Subsequently, depending on milling parameters, there was either amorphization of the sample or formation of yttrium aluminum perovskite, an intermediate phase of the alumina-yttria system. Alumina milling tools exhibited a higher milling efficiency, but they were prone to chipping which lead to massive contamination. Steel milling tools were worn in a more controlled manner and the total amount of contamination was much lower. In heat treatment milled powders easily attained phase equilibrium and there was no metastable behavior noted. Transformation temperatures fell as a function of milling time but for longer milling times the effects of prolonged processing decreased. Sintering properties were also improved resulting in higher final density and lower sintering temperatures. Iron contamination from steel milling tools was suspected to be detrimental for the final solidification and to cause large porosity, but when oxidized the effect is inversed leading to very good densification in argon atmosphere. Relative densities as high as 96% were measured after sintering 1 h in 1500°C, but the process was sensitive to the environment resulting in poor sintering for oxidizing (air) or reducing (argon in graphite furnace) atmospheres. A dispersion of a second phase in the dominant matrix phase was observed but further improvement of the process should be needed to make it finer. The grain size could be estimated to be around 5 µm from fracture surface images.

  • 5.
    Allgulander, Jenny
    Malmö högskola, School of Technology (TS).
    Consumer benefits of mechano-active packages2010Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Through research Innventia has successfully invented a mechano-active (motioned) paper. The purpose of the current work was to do a survey of consumer benefits of mechano-active packages, leading to creation of 1-5 simple concepts and (or) prototypes of mechano-active packages based on consumer benefits. This survey is executed for Innventia in order to help them, in their continuing work with developing mechano-active consumer based packages based on real consumer needs. Using three targeting groups answering a questionnaire and participating in workshops have carried out the survey. The targeting groups were divided into three categories: youth of today, older with reduced mobility and parents with small children; each targeting group contained six participants. The results revealed that 89 % of the participants at sometimes find packages difficult to handle. All of the participants believe that the packages of today can improve with mechano-active packages. The participants in this survey were very open-minded towards the prospect of mechano-active packages and the results (helped me come to the conclusion) indicate that there might be (is) a market for mechano-active packaging solutions that fulfil real consumer needs.

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  • 6.
    Alpkvist, Erik
    et al.
    Malmö högskola, School of Technology (TS).
    Bengtsson, Jessica
    Overgaard, Niels
    Malmö högskola, School of Technology (TS).
    Christensson, Magnus
    Heyden, Anders
    Malmö högskola, School of Technology (TS).
    Simulation of nitrification of municipal wastewater in moving-bed biofilm process: approach based on a 2D continuum model for growth and detachment2007In: Water Science and Technology, Vol. 55, no 8-9, p. 247-255Article in journal (Refereed)
    Abstract [en]

    This paper presents a complete mathematical model of a Moving Bed biofilm process for waste-water treatment, in particular for the nitrification process. The model is based on a bottom up approach adopting a multidimensional model for the biofilm growth and metabolism and a global mass balance model for the whole reactor. The model shows that oxygen is limiting the amount of biomass involved in the nitrification process. Furthermore, it suggests the existence of an optimal amount biomass for an optimal reactor turnover rate. Studies of two specific new suspended carriers show that the model output is dependable on the geometry of the carrier, and to a satisfactory extent agreeable with measurements.

  • 7.
    Alpkvist, Erik
    et al.
    Malmö högskola, School of Technology (TS).
    Klapper, Isaac
    Description of mechanical response including detachment using a novel particle model of biofilm/flow interaction2007In: Water Science and Technology, Vol. 55, no 8-9, p. 265-273Article in journal (Refereed)
  • 8.
    Alpkvist, Erik
    et al.
    Malmö högskola, School of Technology (TS).
    Overgaard, Niels
    Malmö högskola, School of Technology (TS).
    Gustafsson, Stefan
    Malmö högskola, School of Technology (TS).
    Heyden, Anders
    Malmö högskola, School of Technology (TS).
    Mathematical modelling of biofilm growth based on a cubic spline representation2003Conference paper (Refereed)
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  • 9.
    Alpkvist, Erik
    et al.
    Malmö högskola, School of Technology (TS).
    Overgaard, Niels
    Malmö högskola, School of Technology (TS).
    Heyden, Anders
    Malmö högskola, School of Technology (TS).
    Cellular Automata Biofilm Modelling including Quorum Sensing2003Conference paper (Refereed)
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  • 10.
    Alpkvist, Erik
    et al.
    Malmö högskola, School of Technology (TS).
    Overgaard, Nils-Christian
    Malmö högskola, School of Technology (TS).
    Gustafsson, Stefan
    Malmö högskola, School of Technology (TS).
    Heyden, Anders
    Malmö högskola, School of Technology (TS).
    A new mathematical model for chemotactic bacterial colony growth2004In: Water Science and Technology, ISSN 0273-1223, E-ISSN 1996-9732, Vol. 49, no 11-12, p. 187-192Article in journal (Refereed)
    Abstract [en]

    A new continuum model for the growth of a single species biofilm is proposed. The geometry of the biofilm is described by the interface between the biomass and the surrounding liquid. Nutrient transport is given by the solution of a semi-linear Poisson equation. In this model we study the morphology of a chemotactic bacterial colony, which grows in the direction of increasing nutrient concentration. Numerical simulations using the level set method and finite difference schemes are presented. The results show rich heterogeneous morphology.

  • 11.
    Amhag, Lisbeth
    et al.
    Malmö högskola, School of Technology (TS). Malmö högskola, School of Teacher Education (LUT), School Development and Leadership (SOL).
    Nilsson, Bengt J
    Malmö högskola, School of Technology (TS). Malmö högskola, School of Teacher Education (LUT), School Development and Leadership (SOL).
    e-Läranderesurser i Sverige2010In: Från didaktik till e-didaktik, Malmö högskola, 2010, p. 397-410Chapter in book (Other academic)
    Abstract [en]

    We give a brief history of distance learning in Sweden. We then present the main electronically available resources that have been established in recent years for learning purposes. We divide the resources into two categories: Administrative resources. These include LMS-systems and other systems to administer applications, student result, course material, etc. We present studera.nu which is the Swedish application website for all university courses and programs, Ladok and Skola24, the student result databases for universities and schools, nationwide. Educational resources. These are mainly web-based systems containing material that can be used for education. We present LIBRIS Uppsök and SwePub, the two Swedish National Libary websites containing all theses and essays published at Swedish universities. We also look at the electronic library search system for Malmö University as an example of an online library system. Finally, we discuss internationally available resources such as Wikipedia, Google search and Google scholar as well as the educational aspects of social networking systems such as Facebook, Myspace and Classroom 2.0.

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  • 12.
    Andersson, Lisa
    Malmö högskola, School of Technology (TS).
    Knowledge Management System och kollaborativt arbete – Wiki som informationshanteringsverktyg2010Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Knowledge Management System and collaborative work - Wiki as an information management tool This report addresses whether Wiki, as information management tools, can meet the requirements of the enterprise information management today. The purpose of the work is that based on theory and a small survey to see what opportunities and disadvantages that exist with the tool for a company. A small interview study with twelve informants has been implemented at the company Agda Lön AB. To create a base, theories in Knowledge Management and Knowledge Management Systems, collaborative and cooperative work, and the Wiki tool are presented. Then describes the study conducted. Further on the various aspects emerging from the theory and empiricism are discussed. Following the discussion presented a conclusion. The report would demonstrate that Wiki can be used as an information management tool, although there are drawbacks in it. However, there are also opportunities, which outweigh the disadvantages. The overwhelming obstacle is whether firms dare to introduce a open system like Wiki.

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  • 13.
    Andersson, Mattias
    Malmö högskola, School of Technology (TS).
    Approximation Algorithms for Geometric Networks2007Doctoral thesis, monograph (Other academic)
    Abstract [en]

    The main contribution of this thesis is approximation algorithms for several computational geometry problems. The underlying structure for most of the problems studied is a geometric network. A geometric network is, in its abstract form, a set of vertices, pairwise connected with an edge, such that the weight of this connecting edge is the Euclidean distance between the pair of points connected. Such a network may be used to represent a multitude of real-life structures, such as, for example, a set of cities connected with roads. Considering the case that a specific network is given, we study three separate problems. In the first problem we consider the case of interconnected `islands' of well-connected networks, in which shortest paths are computed. In the second problem the input network is a triangulation. We efficiently simplify this triangulation using edge contractions. Finally, we consider individual movement trajectories representing, for example, wild animals where we compute leadership individuals. Next, we consider the case that only a set of vertices is given, and the aim is to actually construct a network. We consider two such problems. In the first one we compute a partition of the vertices into several subsets where, considering the minimum spanning tree (MST) for each subset, we aim to minimize the largest MST. The other problem is to construct a $t$-spanner of low weight fast and simple. We do this by first extending the so-called gap theorem. In addition to the above geometric network problems we also study a problem where we aim to place a set of different sized rectangles, such that the area of their corresponding bounding box is minimized, and such that a grid may be placed over the rectangles. The grid should not intersect any rectangle, and each cell of the grid should contain at most one rectangle. All studied problems are such that they do not easily allow computation of optimal solutions in a feasible time. Instead we consider approximation algorithms, where near-optimal solutions are produced in polynomial time. In addition to the above geometric network problems we also study a problem where we aim to place a set of different sized rectangles, such that the area of their corresponding bounding box is minimized, and such that a grid may be placed over the rectangles. The grid should not intersect any rectangle, and each cell of the grid should contain at most one rectangle. All studied problems are such that they do not easily allow computation of optimal solutions in a feasible time. Instead we consider approximation algorithms, where near-optimal solutions are produced in polynomial time.

  • 14. Appelgren, Ester
    et al.
    Leckner, Sara
    Malmö högskola, School of Technology (TS).
    Tröga processer i en snabb medievärld: en introduktion till att förutspå medieutveckling2013In: På väg mot medievärlden 2020: journalistik, teknik, marknad / [ed] Gunnar Nygren, Ingela Wadbring, Studentlitteratur AB, 2013, p. 41-57Chapter in book (Other academic)
    Abstract [en]

    This chapter discusses the extent to which technological change and innovation can be predicted by a demonstration of a number of explanatory models for media development. Furthermore, it discusses how technology change affects media development and diffusion and its impact on society. Specifically, four factors affecting the success of media will be addressed: users, technology, timing and needs.

  • 15. Appelgren, Ester
    et al.
    Leckner, Sara
    Malmö högskola, School of Technology (TS).
    Mejtoft, Thomas
    Mediekonsumentens medvetna och omedvetna val: en nyckel till morgondagens mediekonsumtion2014In: Medie-Sverige 2014: statistik och analys / [ed] Ulla Carlsson, Ulrika Facht, Nordicom, 2014, p. 29-37Chapter in book (Other academic)
    Abstract [en]

    Media Sweden is a publication that provides a wide and updated overview of the Swedish media landscape. This is Nordicom’s tenth edition of the printed edition. The book contains articles in which various research groups and individual researchers at Swedish universities and colleges analyzes and discusses current issues surrounding the media. It also provides a survey of four decades of media development. This is followed by a comprehensive statistical overview of the Swedish media, divided into ten chapters (Media in Sweden, Media companies and ownership, Information & Communication Technology, Newspapers, Magazines, Books, Radio, Audio recordings, Television and Film, Cinema & Video). The goal is to provide an easily accessible knowledge about the media situation in Sweden. The chapter “The media consumers’ conscious and unconscious choices: A key to understanding the news media consumption of tomorrow" discusses the conscious and unconscious choices people make when choosing content in news media and the impact these choices may have on media consumption and the media market. The chapter argues that the choices that are made are strongly related to the production, collection and analysis of data and may increasingly shape the development of communication technologies. It specifically discusses the role of media technology in relation to data, using the Swedish media market as an example. It aims to fill a gap by discussing the interdependency between people’s choices and the market-driven choices made by the media industry.

  • 16. Appelgren, Ester
    et al.
    Leckner, Sara
    Malmö högskola, School of Technology (TS).
    Mejtoft, Thomas
    The media consumers’ conscious and unconscious choices: a key to understanding the news media consumption of tomorrow2014In: Colloque International Communication Électronique Cultures et Identités, 11, 12 & 13 juin 2014, The IUT of Le Havre : Information-Communication Department CIRTAI IDEES (UMR6228) , 2014, p. 1-8Conference paper (Refereed)
    Abstract [en]

    The digital society of today is dramatically different than that of a decade ago. During the past decades computers have gone from being clearly visible and at the center of attention to becoming an integrated and omnipresent part of our everyday lives. Today, individuals are catching up on a reality where homes, workplaces and society to a large extent consist of microprocessors that collect, analyze and present information. With regards to news and information sharing, it may seem that the users, thanks to greater ability to choose content, hold the upper hand in this process. However, since these data are constantly collected and analyzed for various purposes by companies, for example in the media industry, the users’ choices may not be as unconditional as they may think they are. Using the Swedish media market as an example, this exploratory paper discusses the interdependency between people’s choices and the market-driven choices made by the media industry in relation to news, and the impact these choices may have on media consumption and the media market.

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  • 17. Argatov, Ivan
    et al.
    Iantchenko, Alexei
    Malmö högskola, School of Technology (TS).
    Resonance spectrum for a continuously stratified layer: application to ultrasonic testing2013In: Waves in Random and Complex Media, ISSN 1745-5030, E-ISSN 1745-5049, Vol. 23, no 1, p. 24-42Article in journal (Refereed)
    Abstract [en]

    Ultrasound wave propagation in a nonhomogeneous linearly elastic layer of constant thickness immersed between homogeneous fluid and solid media is considered. The resonances (scattering poles) for the corresponding acoustic propagator are studied. It is shown that the distribution of the resonances depends on the smoothness of the coefficients that characterize physical properties of the layer and the ambient media. Namely, if the coefficients have jump discontinuities at the boundaries, then the resonances are asymptotically distributed along a straight line parallel to the real axis on the unphysical sheet of the complex frequency plane. On the contrary, if the coefficients are continuous, then it is shown that the resonances are asymptotically distributed along a logarithmic curve. The developed mathematical model is applied to the ultrasonic testing of the articular cartilage (AC) layer attached to the subchondral bone from one side and being in contact with a solution on the other side. It is conjectured that the spacing between two successive resonances may be sensitive to AC degeneration. The application of the obtained results to the development of ultrasonic testing for quantitative evaluation of AC is discussed.

  • 18. Avdeichikov, V
    et al.
    Helgesson, J
    Malmö högskola, School of Technology (TS).
    Golubev, P
    Jakobsson, B
    Colonna, N
    Tagliente, G
    Kopecky, S
    Kravchuk, V L
    Wilschut, H W
    Anderson, E W
    Nadel-Turonski, P
    Westerberg, L
    Bellini, V
    Sperduto, M L
    Sutera, C
    Ghetti, R
    Chronology of Particle Emission from the E/A = 61 MeV Ar + Al Reaction2003In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 91Article in journal (Refereed)
  • 19.
    Azadian, Saied
    Malmö högskola, School of Technology (TS).
    Aspects of Precipitation in Alloy Inconel 7182004Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    A study was made of the microstructure of the Ni-base alloy Inconel 718 with emphasis on the precipitation and stability of intermetallic phases as affected by heat treatments. In addition the effect of the precipitation on selected mechanical properties namely hardness, creep notch sensitivity and hot ductlity were investigated. The materials studied were a spray-formed version and three wrought versions of the alloy. The spray-formed version of the alloy was of interest since it exhibited a superior compositional homogeneity to more conventional forms of the alloy. To characterise the precipitation kinetics and to determine the associated hardening, a series of isothermal ageing treatments were carried out on both spray-formed and ring rolled material at selected temperatures between 600°C and 1025°C for up to 100h. The results were presented in the form of TTH diagrams for the two alloys. The heat treated specimens were then studied using optical microscopy, scanning electron microscopy and transmission electron microscopy. Where possible these were supplemented with quantitative metallographic measurements of volume fraction and precipitates size.The three main intermetallic precipitation phases in IN 718 are (i) gamma’ having a composition Ni3(Al,Ti), a cubic crystal structure and cubic or spherical particle shape (ii) gamma” having a composition Ni3Nb, a bct crystal structure and a lens-like disc shape (iii)delta having composition Ni3Nb, an orthorhombic crystal structure and forming as grain boundary particles and films as well as thin plates extending long distances into the grains. In thermomechanically processed material the delta-phase can also occur as shorter platelets and particles resulting from fragmentation of the original plates. In this work the rates of precipitation and the temperature ranges of their existence were determined qualitatively. Moreover the coarsening of the ganmma" precipitates was determined quantitatively. The kinetics of precipitation and dimensional coarsening of the delta-phase were also established quantitatively. Similarly, the dissolution kinetics of the delta-phase were measured in the spray-formed and three wrought versions of the alloy leading to a determination of the effect of Nb-content on the delta solvus temperature. After a standard heat treatment, the spray-formed IN 718 was found to be creep notch sensitive according to an SAE-AMS standard rupture test. It was found that notch ductility could be restored to the alloy by inserting a delta-phase precipitation treatment at 875°C-900°C prior to the standard heat treatment. This could be attributed to the formation of a more favourable delta-phase morphology than that formed during the solution treatment at 954°C in the standard heat treatment cycle. A study was made of high temperature tensile properties of a wrought version of IN 718 in particular in relation to the problem of hot cracking in repair welding. Measurements were made of the strength loss temperature on heating and the strength and ductility return temperatures on cooling. These properties provide an indication of the sensitivity of the alloy to hot cracking due to liquation. The tests were made on the alloy after various heat treatments designed to produce microstructures with two different grain sizes with and without delta-phase precipitation. Hot tensile tests were also performed on the in-situ solidified alloy in order to describe the weld metal ductility and properties. The grain size and the presence of large fractions of delta-phase precipitated at 900°C had only small effects on the strength loss temperature and brittle-ductile transition of the alloy. On the other hand, a small fraction of delta-phase precipitated in the grain boundaries at 960°C reduced the brittle-ductile transition temperature significantly. It is proposed that the reduction was associated with interaction between the grain boundary delta-phase and grain boundary boron segregation that was observed in all the heat treated materials.

  • 20. Backlund, Emil
    et al.
    Bolle, Mikael
    Tichy, Matthias
    Olsson Holmström, Helena
    Malmö högskola, School of Technology (TS).
    Bosch, Jan
    Automated User Interaction Analysis for Workflow-Based Web Portals2014In: Software Business: Towards Continuous Value Delivery, Springer, 2014, p. 148-162Conference paper (Refereed)
    Abstract [en]

    Success in the software market requires constant improvement of the software. These improvements however have to directly align with the needs of the users of the software. A recent trend in software engineering is to collect post-deployment data about how users use a software system. We report in this paper about a case study with an industrial partner in which (1) we identified which data has to be collected for a web-based portal system, (2) implemented the data collection, and (3) performed an experiment comparing the collected data with answers of the test subjects in a survey.

  • 21. Bakhtyar, Shoaib
    et al.
    Persson, Jan A.
    Malmö högskola, School of Technology (TS).
    Holmgren, Johan
    Malmö högskola, School of Technology (TS).
    Achieving services when turning a waybill into an e-waybill2011Conference paper (Other academic)
    Abstract [en]

    The focus of this paper is to present potential electronic waybill (e-waybill) solutions for a traditional waybill with the potential for supporting different Intelligent Transport System (ITS) services, such as, identification of freight, automating the exchange of content-related data for regulatory or commercial purposes, etc. At present there are some initiatives, for instance, by the International Air Transport Association (IATA) and the e-Freight framework, for achieving solutions that can handle e-waybills. Both these solutions focus on actor-to-actor communication, however we hypothesize that the storage of a waybill’s data both locally and centrally (i.e. actor-to-actor as well as goods-to-actor communication) can support more services than only central storage of the waybill’s data. Further we look at the information required and possible communication links between different actors in order to identify different ITS services that can be achieved through an e-waybill solution. We then map this information on to the e-waybill solutions that we have proposed, which will allow us to identify which services are supported by the different e-waybill solutions.

  • 22. Banks-Sills, Leslie
    et al.
    Ståhle, Per
    Malmö högskola, School of Technology (TS).
    Svensson, Ingrid
    Eliaz, Noam
    Strain Driven Transport for Bone Modeling at the Periosteal Surface2011In: Mathematical Biosciences, ISSN 0025-5564, E-ISSN 1879-3134, Vol. 230, no 1, p. 37-44Article in journal (Refereed)
    Abstract [en]

    Bone modeling and remodeling has been the subject of extensive experimental studies. There have been several mathematical models proposed to explain the observed behavior, as well. A different approach is taken here in which the bone is treated from a macroscopic view point. In this investigation, a one-dimensional analytical model is used to shed light on the factors which play the greatest role in modeling or growth of cortical bone at the periosteal surface. It is presumed that bone growth is promoted when increased amounts of bone nutrients, such as nitric oxide synthase (NOS) or messenger molecules, such as prostaglandin E2 (PGE2), seep out to the periosteal surface of cortical bone and are absorbed by osteoblasts. The transport of the bone nutrients is assumed to be a strain controlled process. Equations for the flux of these nutrients are written for a one-dimensional model of a long bone. The obtained partial differential equation is linearized and solved analytically. Based upon the seepage of nutrients out of the bone, the effect of loading frequency, number of cycles and strain level is examined for several experiments that were found in the literature. It is seen that bone nutrient seepage is greatest on the tensile side of the bone; this location coincides with the greatest amount of bone modeling

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  • 23. Bengtsson, Peter
    et al.
    Ekman, Jörgen
    Malmö högskola, School of Technology (TS).
    Gustafsson, Stefan
    Malmö högskola, School of Technology (TS).
    Jönsson, Per
    Malmö högskola, School of Technology (TS).
    Karlsson, Lennart
    Malmö högskola, School of Technology (TS).
    Gaigalas, Gediminas
    Energy structure and transition rates in the Ne-like sequence from relativistic CI calculations2012In: Europhysics Conference Abstracts;36C, European Physical Society , 2012, p. 128-128Conference paper (Other academic)
    Abstract [en]

    Atomic data are important in astrophysical applications and transition rates can be used in the determination of element abundances and plasma diagnostics. To provide for the extensive data needs a number of general computer codes such as SUPERSTRUCTURE, CIV3, and ATSP2K have been developed. As an alternative to these codes, which all rely on the Breit-Pauli approximation, the fully relativistic GRASP2K code can be used. GRASP2K is based on the multiconfiguration Dirac-Hartree-Fock method and implements a bi-orthogonal transformation method that permits initial and final states in a transition array to be optimized separately, which, in many cases, leads to more accurate values of the resulting rates. The GRASP2K package also contains modules to compute diagonal and off-diagonal hyperfine interaction constants, isotope shifts, Land´e gJ factors, and splittings of magnetic sub-state in intermediate and strong magnetic fields. In this work, GRASP2K has been applied to provide highly accurate spectroscopic data for ions in the Ne-like sequence between Mg III and Kr XXVII. Valence, core-valence, and core-core correlation effects were accounted for through SD-MR expansions to increasing sets of active orbitals. In Mg III, Al IV, Si V, P VI, S VII, and Ar IX, for which experimental energies are known to high accuracy, the mean error in the calculated energies is only 0.011%. For ions with no available experimental energy levels the calculated values should be most valuable in various applications. The high accuracy of the calculated energies makes it possible, in some cases, to to point out experimental values that are in error. Babushkin (length) and Coulomb (velocity) forms of transition rates are computed and agree to within a few percent for the majority of the allowed transitions. Computed lifetimes for states belonging to the 2p33s and 2p53d configurations are in good agreement with values from beam-foil measurements as well as from accurate MCHF Breit-Pauli calculations.

  • 24. Bergknut, Knut
    et al.
    Dackman, Carin
    Malmö högskola, School of Technology (TS).
    Genus, miljö, migration och etnicitet - om konsten att arbeta med perspektiv2004Book (Other academic)
    Abstract [sv]

    Innehåll: Medborgerlig bildning - Att närma sig miljöperspektivet - Om genusperspektivet - Migrations- och etnicitetsperspektivet - Exempel påhur vi arbetar med perspektiven i utbildningen - Man talar om barn men i själva verrket tänker man flickor och pojkar - Introduktionskursen hälsa och samhälle - Transkulturell omvårdnad i sjukskötyerskeutbildningen - Genus- och etnicitetsperspektiven i en vårdutbildning - Perspektivintegrering i praktiken - Riskbedömning vid laboratoriearbete - Tillämpad globalisering - Mentrosprojektet Näktergalen - Internationalisering på hemmaplan - Perspektivkurs i den högskolepedagogiska utbildningen. Förord: I denna bok har vi samlat ett antal artiklar kring Malmö högskolas perspektiv sedda utifrån en uppfattning om medborgerlig bildning. Grundtanken bakom medborgerlig bildning är enkel. Den högre utbildningen skall bidra till att forma reflekterande och kritiska medborgare. Detta förutsätter att man har goda kunskaper om och ett kritiskt förhållningssätt till centrala frågor i vår egen samtid. Under senare år har frågor som rör miljö och hållbar utveckling, genus samt migration och etnicitet blivit allt viktigare. Insikten har ökat i att vi måste sträva efter att bygga ett hållbart samhälle där vi lämnar över en värld till våra barn, som ger dem minst lika goda förutsättningar som vi fick att utveckla samhället och leva ett gott liv. När vi talar om miljö, genus, migration och etnicitet, måste vi varamedvetna om att dessa skall sättas i relation till frågor som rör makt och demokrati. Det kan kanske tyckas motsägelsefullt att tala om makt och demokrati samtidigt. Men satt i relation till medborgerlig bildning är det självklart att utövande av makt i demokratiska former ställer stora krav på en självkritisk hållning och en prövande attityd från såväl den som utövar makten som den som kritiserar makten. Den bok som du här håller i handen är ett resultat av ett högskolegemensamt samarbete kring att utveckla hur vi skall arbeta med perspektiven. Författarna har haft gemensamma träffar där vi gått genom hur vi skall lägga upp boken. Sedan har de olika författarna kommenterat varandras texter. Därefter har vi lagt ut texterna på nätet och fått in synpunkter från andra medarbetare inom högskolan. Jag vill här passa på att tacka alla dem som har bidragit till denna bok på olika sätt. Ingen nämnd och därmed ingen glömd. Boken består av två delar, en mer allmänt inledande del där vi börjar med att diskutera innebörden i begreppet medborgerlig bildning och vad det kan betyda idag. Därefter följer tre kapitel, ett vardera om varje perspektiv. I dessa ger författarna sin bild av hur de uppfattar respektive perspektiv. Den andra delen består av goda exempel på hur man kan arbeta med perspektiven i olika utbildningar. Man måste utgå från den konkreta situationen och den konkreta utbildningen när man arbetar med perspektiven. Tanken med dessa exempel är att inspirera medarbetare och studenter till hur man kan implementera perspektiven. Vi som arbetat med denna bok ser fram emot många och spännande diskussioner med alla läsare; medarbetare inom högskolan, studenter och alla andra som har ett intresse för de frågor vi diskuterar i denna bok.

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  • 25. Bernstoen, Christian
    et al.
    Heyden, Anders
    Malmö högskola, School of Technology (TS).
    Image analysis for monitoring of crack growth in hydropower concrete structures2009In: Measurement, ISSN 0263-2241, E-ISSN 1873-412X, Vol. 42, no 6, p. 878-893Article in journal (Refereed)
    Abstract [en]

    A digital image analysis technique for crack monitoring using a standard web-camera has been further developed to acquire continuous data sets on crack development in concrete dams. The method is based on an existing robust and straightforward non-contact method for experimental deformation analysis. It allows for the measurement of suspected serious cracks, identified from inspections, through a sequence of images captured at intervals. The crack opening displacements at the surface of investigated objects are obtained by an algorithm that makes it possible to automatically track the motions of discrete markers painted on the object surface markers and compute their centre of mass in a sequence of images. The data acquisition process is straightforward and is well suited for this type of environment. Results from laboratory experiments and a field-test on a commuter bridge in Sweden are presented. The study implies that the technique can be useful for hydropower concrete structure applications.

  • 26. Bieron, Jacek
    et al.
    Brage, Tomas
    Froese Fischer, Charlotte
    Gaigalas, Gediminas
    Godefroid, Michel
    Jönsson, Per
    Malmö högskola, School of Technology (TS).
    Computational Atomic Structure2012In: Program and Abstracts: Eighth International Conference on Atomic and Molecular Data and Their Applications: ICAMDATA 8, 2012, p. 56-56Conference paper (Other academic)
    Abstract [en]

    There is an increasing demand for accurate atomic data due to advancements in experimental techniques and investments in large scale research facilities. In astrophysics the quality and resolution of solar and stellar spectra has so improved that the accuracy of atomic data is frequently a limiting factor in the interpretation. Accurate atomic data are also required in plasma physics and in other emerging areas such as laser spectroscopy on isotope separators, X-ray lithography, and lighting research. The needs include accurate transition energies, fine- and hyperfine structures, isotope shifts as well as parameters related to interaction with external magnetic fields. Also there is a constant need for transition rates between excited states. Data are needed for a wide range of elements and ionization stages. To meet the demands for accurate atomic data the COMPutational Atomic Structure (COMPAS) group has been formed. The group is involved in developing state of the art computer codes for atomic calculations in the non-relativistic scheme with relativistic corrections in the Breit-Pauli approximation [1] as well as in the fully relativistic domain. Here we describe new developments of the GRASP2K relativistic atomic structure code [2, 3]. We present results for a number of systems and properties to illustrate the potential and restriction of computational atomic structure. Among the properties are hyperfine structures and hyperfine quenched rates, Zeeman splittings in intermediate fields, isotope shifts and transition rates [4]. We also discuss plans for future code developments.

  • 27.
    Bjerkén, Christina
    Malmö högskola, School of Technology (TS).
    Branching of a dissolution driven stress corrosion crack2009In: Proceedings of the International Conference on Crack Paths 2009, European Structural Integrity Society , 2009Conference paper (Other academic)
    Abstract [en]

    Stress corrosion cracking occurs due to the synergistic interaction between mechanical load and corrosion reactions. Some types of stress corrosion crack branch heavily. Here, branching during dissolution driven crack growth is studied using an adaptive FE method. A strain-assisted evolution law is used for the inherently blunted crack. No criterion for crack growth is needed as for a sharp crack, neither for the growth direction. Several simulations are performed with different degrees of load biaxiality. It is found that large biaxiality promotes branching, but no conditions for when branching takes place is found. Instead, branching seems to occur rather randomly due to the perturbation sensitivity of a dissolution driven crack. Also crack growth rates for branched cracks are investigated, and it is found that both constant growth rates can be reached, as well as decreasing rates and eventual arrest. The cracks follow a mode I crack path, however local changes may occur due to the perturbation sensitivity.

  • 28.
    Bjerkén, Christina
    Malmö högskola, School of Technology (TS).
    Dissolution Driven Fracture - Simulation of Crack Growth2006In: Proceedings of 19th Nordic Seminar on Computational Mechanics, Structural Mechanics, LTH, Sweden. , 2006, p. 130-134Conference paper (Refereed)
    Abstract [en]

    The growth of a crack subjected to corrosion fatigue is studied using adaptive finite elements. The crack growth is the result of a repeated cycle of dissolution of the material, formation of a protective oxide film and break-down of the oxide film due to straining at the surface. The dissolution rate is assumed to be proportional to this stretching. The growth of a semi-infinite crack lying in an infinite strip subjected to different degrees of mixed-mode loading is studied.

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  • 29.
    Bjerkén, Christina
    Malmö högskola, School of Technology (TS).
    Spänningskorrosion - modellering av utveckling från ytojämnheter via gropar till sprickor2007In: Abstracts Svenska mekanikdagarna, Luleå, Sweden, 2007Conference paper (Other academic)
    Abstract [sv]

    Den kombinerade effekten av mekanisk belastning och en korrosiv miljö kan leda till spänningskorrosion. Vid anodisk spänningskorrosion löses materialet upp och bildar korrosionsprodukter. I vissa fall bildas en ytbeläggning, t ex en oxidfilm, som verkar skyddande och därmed bromsar korrosionsprocessen. Om en dylik film inte skapas, eller om den kontinuerligt bryts ned, kan korrosionsprocessen fortgå. I en plan yta kan gropar bildas, och någon eller några av dessa kan i sin tur utvecklas till en kritisk spricka. I denna studie undersöks utvecklingen av korrosionssprickor med hjälp av en modell där korrosionshastigheten är proportionell mot den elastiska töjningsenergin och kurvaturen i varje punkt på ytan. Det är känt sedan tidigare att kurvaturen påverkar benägenheten för atomer att lossna från eller binda vid en yta, vilket leder till att en obelastad yta planar ut vid t ex etsning. Om ytan däremot är belastad kommer en ytojämnhet med ett specifikt frekvensinnehåll att utvecklas. Vågor med längder kortare än en viss kritisk våglängd kommer att avklinga. På detta sätt leder korrosionen till att gropar bildas i ytan och vissa av dessa fördjupas allt mer tills de blir sprickliknande. Dessa spänningskorrosionssprickor kommer dock att ha en finit radie i spetsen som är given av det lokala spänningstillståndet. Simuleringar är gjorda med en adaptiv metod. För varje tidsinkrement beräknas töjningarna i ytan i en finita element-analys, därefter bestäms ytevolutionen och sedan genereras ett nytt elementnät för den uppdaterade geometrin. Resultat från simuleringarna visar utvecklingen från en plan yta, med en initiell pertubation, via gropbildning till sprickor.

  • 30.
    Bjerkén, Christina
    Malmö högskola, School of Technology (TS).
    The discrete nature of the growth and arrest of microstructurally short fatigue cracks modelled by dislocation technique2005In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 27, no 1, p. 21-32Article in journal (Refereed)
    Abstract [en]

    Growth of a microstructurally short edge crack in the neighbourhood of a grain boundary has been studied using a dislocation technique. Influence of the distance between the crack tip and a high-angle grain boundary was studied for 5000 load cycles. Growth rate was found to change stepwise during crack advance, both accelerating and decelerating, and finally retarding before crack arrest. Crack propagation is ruled by the competition between the shielding effect from the dislocations in the plastic zone and the stress field increase due to crack extension, and clearly shows a discrete behaviour at growth below the fatigue threshold load.

  • 31.
    Bjerkén, Christina
    Malmö högskola, School of Technology (TS).
    The influence of biaxial loading on branching of a dissolution driven stress corrosion crack2010In: Engineering Fracture Mechanics, ISSN 0013-7944, E-ISSN 1873-7315, Vol. 77, no 11, p. 1989-1997Article in journal (Refereed)
    Abstract [en]

    Stress corrosion cracking occurs due to the synergistic interaction between mechanical load and corrosion reactions. In this study, branching during anodic dissolution driven crack growth is studied using an adaptive FE procedure. The crack has an inherent blunt tip due to the dissolution, and the growth is treated as a moving boundary problem with a strain-assisted evolution law. Simulations are performed with different degrees of load biaxiality. It is found that increasing biaxiality promotes branching. No conditions for when branching takes place are found. Crack growth rates for branches are investigated, and it is found that, after an initial acceleration, constant growth rates can be reached, as well as decreasing speed and eventual arrest. The influence of T-stresses and perturbations sensitivity are discussed.

  • 32.
    Bjerkén, Christina
    et al.
    Malmö högskola, School of Technology (TS).
    Kao-Walter, Sharon
    Ståhle, Per
    Malmö högskola, School of Technology (TS).
    Fracture Mechanisms of a Thin Elastic Plastic Laminate2006In: Fracture of Nano and Engineering Materials and Structures: Proceedings of the 16th European Conference of Fracture, Alexandroupolis, Greece, July 3–7, 2006, 2006, p. 927-928Conference paper (Other academic)
  • 33.
    Bjerkén, Christina
    et al.
    Malmö högskola, School of Technology (TS).
    Massih, Ali
    Malmö högskola, School of Technology (TS).
    Nucleation of second-phase near elastic defects in crystalline solids2011In: Proceedings of MS&T'11, TMS , 2011Conference paper (Other academic)
    Abstract [en]

    The problem of heterogeneous nucleation of second-phase in alloys in the vicinity of elastic defects is considered. The defect can be a dislocation line or a crack tip residing in a crystalline solid. We use a compressible Ising-like model, represented by the Ginzburg-Landau equation, to describe the spatiotemporal evolution of the order parameter in the environs of the defect. The model accounts for the elasticity of the solid and the interaction of order parameter field with the elastic field of the defect. A finite volume numerical method is used to solve the governing partial differential equation for the order parameter. We examine the nature of the phase transition and discuss the phase diagram topology near and away from the defect. We discuss our calculations in light of observations of formation of hydrides in zirconium and titanium alloys.

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  • 34.
    Bjerkén, Christina
    et al.
    Malmö högskola, School of Technology (TS).
    Massih, Ali
    Malmö högskola, School of Technology (TS).
    Phase ordering kinetics of second-phase formation near an edge dislocation2014In: Philosophical Magazine, ISSN 1478-6435, E-ISSN 1478-6443, Vol. 94, no 6, p. 569-593Article in journal (Refereed)
    Abstract [en]

    The time-dependent Ginzburg-Landau (TDGL) equation for a single component non-conservative structural order parameter is used to study the spatio-temporal evolution of a second phase in the vicinity of an edge dislocation in an elastic crystalline solid. A symmetric Landau potential of sixth-order is employed. Dislocation field and elasticity modify the second-order and fourth-order coefficients of the Landau polynomial, respectively, where the former makes the coefficient singular at the origin. The TDGL equation is solved numerically using a finite volume method, where a wide range of parameter sets is explored. Computations are made for temperatures both above and below the transition temperature of a defect-free crystal Tc0. In both cases, the effects of the elastic properties of the solid and the strength of interaction between the order parameter and the displacement field are examined. If the system is quenched below Tc0, a steady state is first reached on the compressive side of the dislocation. On the tensile side, the growth is held back. The effect of thermal noise term in the TDGL equation is studied. We find that if the dislocation is introduced above Tc0, thermal noise supports the nucleation of the second phase, and a steady state will be attained earlier than if the thermal noise was absent. For a dislocation-free solid, we have compared our numerical computations for a mean-field (spatially averaged) order parameter versus time with the late time growth of the ensemble-averaged order parameter, calculated analytically, and find that both results follow upper asymptotes of sigmoid curves.

  • 35.
    Bjerkén, Christina
    et al.
    Malmö högskola, School of Technology (TS).
    Melin, Solveig
    Dislocation distribution in the plastic zone and growth of ashort fatigue crack2005In: Zeszyty naukowe / Mechanika;1, Politechnika opolska , 2005, p. 29-36Conference paper (Refereed)
  • 36.
    Bjerkén, Christina
    et al.
    Malmö högskola, School of Technology (TS).
    Melin, Solveig
    Growth of a short fatigue crack - A long term simulation using a dislocation technique2009In: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 46, no 5, p. 1196-1204Article in journal (Refereed)
    Abstract [en]

    In this study, the growth of a short edge crack during more than 14 000 cycles of fatigue loading is investigated in detail. An edge crack, in a semi-infinite body with no pre-existing obstacles present, is modelled in a boundary element approach by a distribution of dislocation dipoles. The fatigue cycles are fully reversed (R = -1), and the load range is well below the threshold for long fatigue cracks. The developing local plasticity consists of discrete edge dislocations that are emitted from the crack tip. The movements of discrete dislocations are restricted to slip along preferred slip planes. The present model is restricted to a 2D plane strain problem with a through-thickness crack, assuming no 3D irregularities. A remote load is applied perpendicular to the crack extension line, and the material parameters are those of a BCC crystal structure. The competition between influence of the global loading on and local shielding of the crack tip governs the crack growth. The growth rate increases in discrete steps with short periods of retardation, from approximately the size of Burgers vector, b, up to 25 b per cycle as the length of the crack is tripled. The plastic zone changes from having an elongated, slender form to include a low angle grain boundary, which, eventually, divides into two parts. The crack growth is found to change from constant acceleration to constant growth rate as the event of the low-angle grain boundary split is approached. ; The results are compared to long crack characteristics, for which linear elastic fracture mechanics and Paris law can be used to predict fatigue crack growth. The exponent in Paris law varies between 1 and 0 in the present study, i.e. smaller than typical values for ductile BCC materials. The ratio between static and cyclic plastic zone sizes is found to increase during crack growth, and the angle of the general plastic zone direction increases, showing a tendency towards long crack values. The characteristics of the simulated crack growth, found in the present study, are typical for below-threshold growth, with slow acceleration, constant growth rate. and, eventually, either arrest or transition to long crack growth behaviour, as reported in the literature.

  • 37.
    Bjerkén, Christina
    et al.
    Malmö högskola, School of Technology (TS).
    Melin, Solveig
    Influence of low-angle grain boundaries on short fatigue crack growth studied by a discrete dislocation method2008In: Proceedings 17th European Conference on Fracture, Brno 2008, VUTIUM Brno, Czech Republic , 2008Conference paper (Other academic)
    Abstract [en]

    The growth of short fatigue cracks in or below the threshold regime are highly influenced by the local microstructure. In the present study, the influence of low-angle boundaries on the growth and arrest of microstructurally short edge cracks in crystalline material is investigated using a discrete dislocation method. The crack is modelled by boundary elements consisting of dislocation dipoles. An external load that is fully reversed during the fatigue cycle is applied to obtain a crack growth rate of a few Burgers vector per cycle. The crack growth and the developing plasticity are given by the emission, and eventual annihilation, of dislocations at the crack tip. The low-angle grain boundary is modelled as an array of aligned dislocations. It is found that the developing local plasticity, is crucial for the growth rates. Different stress ranges are used and both positive and negative low-angle grain boundaries are considered. It is found that depending on sign of the of the grain boundary, different growth behaviour are found. Generally, a positive low-angle grain boundary gives a low, rather stress range independent growth rate. A negative grain boundary results in increasing crack growth when the stress range is increased. The distance between the crack tip and the low-angle boundary is found not to significantly influence the crack growth characteristics, for the geometries and load ranges considered in this study.

  • 38.
    Bjerkén, Christina
    et al.
    Malmö högskola, School of Technology (TS).
    Ortiz, Michael
    Evolution of anodic stress corrosion cracking in a coated material2010In: International Journal of Fracture, ISSN 0376-9429, E-ISSN 1573-2673, Vol. 165, no 2, p. 211-221Article in journal (Refereed)
    Abstract [en]

    In the present paper, we investigate the influence of corrosion driving forces and interfacial toughness for a coated material subjected to mechanical loading. If the protective coating is cracked, the substrate material may become exposed to a corrosive media. For a stress corrosion sensitive substrate material, this may lead to detrimental crack growth. A crack is assumed to grow by anodic dissolution, inherently leading to a blunt crack tip. The evolution of the crack surface is modelled as a moving boundary problem using an adaptive finite element method. The rate of dissolution along the crack surface in the substrate is assumed to be proportional to the chemical potential, which is function of the local surface energy density and elastic strain energy density. The surface energy tends to flatten the surface, whereas the strain energy due to stress concentration promotes material dissolution. The influence of the interface energy density parameter for the solid-fluid combination, interface corrosion resistance and stiffness ratios between coating and substrate is investigated. Three characteristic crack shapes are obtained; deepening and narrowing single cracks, branched cracks and sharp interface cracks. The crack shapes obtained by our simulations are similar to real sub-coating cracks reported in the literature.

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  • 39.
    Bjerkén, Christina
    et al.
    Malmö högskola, School of Technology (TS).
    Rimoli, Julian
    Ortiz, Michael
    Stress corrosion crack growth beneath a stiff coating: influence of chemical potential and interface toughness2009In: Proceedings 12th International Conference on Fracture, Ottawa 2009, ICF12 , 2009Conference paper (Other academic)
    Abstract [en]

    In the present paper we investigate the influence of corrosion driving forces and interfacial toughness for a coated material subjected to mechanical loading. If the protecting coating is cracked, the substrate material may become exposed to a corrosive media. For a stress corrosion sensitive substrate material, this may lead to detrimental crack growth. A crack is assumed to grow by anodic dissolution, inherently leading to a blunted crack tip. The rate of dissolution along the crack surface is assumed to be proportional to the chemical potential, which is function of the local surface energy density and the elastic strain energy density. The surface energy tends to flatten the surface, whereas the strain energy due to stress concentration promotes material dissolution. The evolution of the crack surface is modelled as a moving boundary problem using an adaptive finite element method. The crack shapes obtained by our simulations are remarkably similar to real stress corrosion cracks reported in the literature.

  • 40.
    Bjerkén, Christina
    et al.
    Malmö högskola, School of Technology (TS).
    Ståhle, Per
    Malmö högskola, School of Technology (TS).
    Branching of growing corrosion fatigue cracks2005Conference paper (Other academic)
    Abstract [en]

    Strain-driven corrosion of branching cracks, initiated from a virtually plane surface, has been studied using a moving boundary technique. The material is assumed linear elastic and is subjected to fatigue loading under plain strain conditions. The surface of the material is covered by a protective film. During loading this film can be damaged if it is strained above a threshold value, thus revealing an unprotected surface. Corrosion advances by material dissolution, eventually evolving into cracks. The rate of surface evolution is a function of the degree of protective film damage. During unloading the protective film is assumed to develop and heal the surface. A low frequency cyclic loading is applied to ensure that total healing is assumed. The moving boundary technique, simulating corrosion, results in arc-shaped crack tips, rather than singular crack tip points, thus no crack growth criterion is needed in the analysis. For each load step, the strain distribution is found using the finite element method, followed by required the movement the boundary and then remeshing. The crack growth has been investigated for at least 2000 cycles. A more or less pronounced branching of the cracks is found to develop. The crack branches can be classified in three groups; main cracks that grows with maximum rate and branches further, branch cracks that initially retards and then find a steady state growth rate that is a fraction of maximum speed, and finally, arresting cracks that after a period of retardation stop growing. The crack patterns are realistic, showing a sort of self-similarity with tree-like structure, cf. the picture below that shows a typical finite element result. The width of a crack branch together with the shielding from the applied stresses, caused by the other branches and main cracks, seem to govern the evolution of the crack branch. A steady-state growth rate is achieved during parts of the evolution as the crack width and the strain field surrounding the crack tip is in balance, i.e. the crack widens while the crack grows longer. As the bluntness of the tip reaches an upper limit, branching results.

  • 41.
    Bjerkén, Christina
    et al.
    Malmö högskola, School of Technology (TS).
    Ståhle, Per
    Malmö högskola, School of Technology (TS).
    Simulation of corrosion fatigue crack growth under mixed-mode loading2008In: Engineering Fracture Mechanics, ISSN 0013-7944, E-ISSN 1873-7315, Vol. 75, no 3-4, p. 440-451Article in journal (Refereed)
    Abstract [en]

    The kinking of a corrosion crack due to mixed-mode fatigue loading is studied using an adaptive finite element procedure. The rate of material dissolution is assumed to be proportional to the stretching of the corroding surface. The dissolution of material is governed by a corrosion law, where no criterion is needed for neither crack growth nor growth direction. The problem is treated as a general moving boundary problem. The kink angles are found to be in very good agreement with results for sharp cracks using criteria reported in the literature.

  • 42.
    Bjerkén, Christina
    et al.
    Malmö högskola, School of Technology (TS).
    Ståhle, Per
    Malmö högskola, School of Technology (TS).
    The path of a growing crack - A simulation of the fracture process2006Conference paper (Other academic)
    Abstract [en]

    The growth of a crack subjected to corrosion fatigue is studied using adaptive finite elements. The crack is the image of a deep corrosion pit, and the growth is the result of a repeated cycle of dissolution of the material, formation of a protective oxide film and break-down of the oxide film. The break-down of the film is governed by the strain at the surface and the dissolution rate is assumed to be proportional to this stretching. A threshold strain is assumed to exist below which the oxide film remains intact. With this model, no criterion is needed, neither for crack growth, nor for prediction of the growth direction. The reason is that both are immediate results of the evolution of the body shape. The growth of a semi-infinite crack lying in an infinite strip subjected to different degrees of mixed-mode loading is studied and the results are compared to crack path criteria for sharp cracks. Additionally, the path of a corrosion fatigue crack starting at the surface of an elastic layer attached to a stiff substrate is simulated. The result showed some agreement with experimental results found in the literature.

  • 43.
    Bjerkén, Christina
    et al.
    Malmö högskola, School of Technology (TS).
    Ståhle, Per
    Malmö högskola, School of Technology (TS).
    Gunnars, Jens
    The Path of a Growing Crack - Experiment and Simulation2006In: Proceedings of Optical methods, 2006Conference paper (Other academic)
  • 44.
    Björgvinsson, Erling
    et al.
    Malmö högskola, Faculty of Culture and Society (KS), School of Arts and Communication (K3). Malmö högskola, Faculty of Culture and Society (KS), Medea.
    Birt, Arlene
    Cuartielles, David
    Malmö högskola, Faculty of Culture and Society (KS), School of Arts and Communication (K3). Malmö högskola, Faculty of Culture and Society (KS), Medea.
    Davidsson, Paul
    Malmö högskola, School of Technology (TS). Malmö högskola, Faculty of Culture and Society (KS), Medea.
    Ehn, Pelle
    Malmö högskola, Faculty of Culture and Society (KS), School of Arts and Communication (K3). Malmö högskola, Faculty of Culture and Society (KS), Medea.
    Ginslov, Jeannette
    Gustafsson Friberger, Marie
    Hillgren, Per-Anders
    Malmö högskola, Faculty of Culture and Society (KS), School of Arts and Communication (K3). Malmö högskola, Faculty of Culture and Society (KS), Medea.
    Hobye, Mads
    Malmö högskola, Faculty of Culture and Society (KS), School of Arts and Communication (K3). Malmö högskola, Faculty of Culture and Society (KS), Medea.
    Jacobson, Bob
    Jacobsson, Andreas
    Malmö högskola, School of Technology (TS). Malmö högskola, Faculty of Culture and Society (KS), Medea.
    Kozel, Susan
    Malmö högskola, Faculty of Culture and Society (KS), School of Arts and Communication (K3). Malmö högskola, Faculty of Culture and Society (KS), Medea.
    Linde, Per
    Malmö högskola, Faculty of Culture and Society (KS), School of Arts and Communication (K3). Malmö högskola, Faculty of Culture and Society (KS), Medea.
    Löwgren, Jonas
    Malmö högskola, Faculty of Culture and Society (KS), School of Arts and Communication (K3). Malmö högskola, Faculty of Culture and Society (KS), Medea.
    Nilsson, Elisabet M.
    Malmö högskola, Faculty of Culture and Society (KS), School of Arts and Communication (K3). Malmö högskola, Faculty of Culture and Society (KS), Medea.
    Peterson, Bo
    Malmö högskola, Faculty of Culture and Society (KS), School of Arts and Communication (K3). Malmö högskola, Faculty of Culture and Society (KS), Medea.
    Rosenqvist, Karolina
    Topgaard, Richard
    Malmö högskola, Faculty of Culture and Society (KS), Medea. Malmö högskola, Faculty of Culture and Society (KS), School of Arts and Communication (K3).
    Prototyping Futures2012Report (Other academic)
    Abstract [en]

    Prototyping Futures gives you a glimpse of what collaborating with academia might look like. Medea and its co-partners share their stories about activities happening at the research centre – projects, methods, tools, and approaches – what challenges lie ahead, and how these can be tackled. Examples of highlighted topics include: What is a living lab and how does it work? What are the visions behind the Connectivity Lab at Medea? And, how can prototyping-methods be used when sketching scenarios for sustainable futures? Other topics are: What is the role of the body when designing technology? What is collaborative media and how can this concept help us understand contemporary media practices? Prototyping Futures also discusses the open-hardware platform Arduino, and the concepts of open data and the Internet of Things, raising questions on how digital media and connected devices can contribute to more sustainable lifestyles, and a better world.

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    FULLTEXT01
  • 45.
    Blom, A
    Malmö högskola, School of Technology (TS).
    Cyclic Loading of a Brazed Joint under Stress Concentration2001Report (Other academic)
  • 46. Blomqvist, Jacob
    et al.
    Massih, Ali
    Malmö högskola, School of Technology (TS).
    Bjerkén, Christina
    Malmö högskola, School of Technology (TS).
    A First Principle Atomistic Pre-study of a Multiscale Model of Hydride Induced Embrittlement in Zirconium2010Conference paper (Other academic)
    Abstract [en]

    Hydrogen induced embrittlement and associated cracking effects in Zirconium alloys impose a serious problem, for example, within the nuclear industry where these materials are used in a range of applications, including fuel claddings. To get a fuller understanding of the hydrogen diffusion, hydride formation and phase transformations taking place at conditions of external stress and at elevated temperature it is crucial to augment experimental measurements with multi-level modelling. It is, for example, possible to simulate hydride phase-transformation trough phase-field calculations[1]. In order to get accurate results from these calculations, however, it is important to have basic physical information, such as interfacial energies and elastic constants. The latter were obtained completely from first principle calculations of density functional theory. In pure zirconium, at low hydrogen concentrations and at low temperatures, hydrogen atoms are dissolved into the matrix and preferentially occupy tetrahedral sites within the thermodynamically stable aZr hexagonal closed packed unit cell. At higher concentrations the various face centred cubic and tetragonal hydride phases start to form. Using the plane-wave code DACAPO, within the generalized gradient approximation, the lattice parameters and the ionic positions of bulk aZr, dZrHx and gZrHx were relaxed with respect to total energies. The formation energies as well as bulk moduli were then obtained by fitting total energies as a function of lattice parameters with a 3rd or 4th order polynomial. By comparing the present results with previous calculations and experiments it was possible to validate the methods for further use. The results, thus, comprise a foundation and serves to verify methods and codes. The next step is to compute more complex properties such as surface free energies, or interfacial energies, of bi-phase Zr-H systems, so that the full multiscale model can be implemented. 1. V. Vaithyanathan et al., Acta Materialia 52 (2004) p. 2973

  • 47.
    Blomqvist, Jakob
    et al.
    Malmö högskola, School of Technology (TS).
    Johansson, Johan
    Alvarez, Anna-Maria
    Bjerkén, Christina
    Malmö högskola, School of Technology (TS).
    Structure and Thermodynamical Properties of Zirconium Hydrids from First Principle2011Conference paper (Other academic)
    Abstract [en]

    Zirconium alloys are used as nuclear fuel cladding material due to their mechanical and corrosion resistant properties together with their favorable cross-section for neutron scattering. At running conditions, however, there will be an increase of hydrogen in the vicinity of the cladding surface at the water side of the fuel.The hydrogen will diffuse into the cladding material and at certain conditions, such as lower temperatures and external load, hydrides will precipitate out in the material and cause well known embrittlement, blistering and other unwanted effects. Using phase-field methods it is now possible to model precipitation build-up in metals, for example as a function of hydrogen concentration, temperature and external load, but the technique relies on input of parameters, such as the formation energy of the hydrides and matrix. To that end, we have computed, using the density functional theory (DFT) code GPAW, the latent heat of fusion as well as solved the crystal structure for three zirconium hydride polymorphs: delta-ZrH1.6, gamma-ZrH, and epsilon-ZrH2.

    Download full text (pdf)
    FULLTEXT01
  • 48.
    Blomqvist, Jakob
    et al.
    Malmö högskola, School of Technology (TS).
    Olofsson, Johan
    Alvarez, Anna-Maria
    Bjerkén, Christina
    Malmö högskola, School of Technology (TS).
    Structure and Thermodynamical Properties of Zirconium hydrides from first-principle2012In: Proceedings of the 15th international conference on environmental degradation of materials in nuclear power systems-water reactors, John Wiley & Sons, 2012, p. 671-679Conference paper (Other academic)
    Abstract [en]

    Zirconium alloys are used as nuclear fuel cladding material due to their mechanical and corrosion resistant properties together with their favorable cross-section for neutron scattering. At running conditions, however, there will be an increase of hydrogen in the vicinity of the cladding surface at the water side of the fuel. The hydrogen will diffuse into the cladding material and at certain conditions, such as lower temperatures and external load, hydrides will precipitate out in the material and cause well known embrittlement, blistering and other unwanted effects. Using phase-field methods it is now possible to model precipitation build-up in metals, for example as a function of hydrogen concentration, temperature and external load, but the technique relies on input of parameters, such as the formation energy of the hydrides and matrix. To that end, we have computed, using the density functional theory (DFT) code GPAW, the latent heat of fusion as well as solved the crystal structure for three zirconium hydride polymorphs: \delta-ZrH1.6, \gamma-ZrH, and \epsilon-ZrH2.

  • 49.
    Blomqvist, Jakob
    et al.
    Malmö högskola, School of Technology (TS).
    Olsson, Pär
    Malmö högskola, School of Technology (TS).
    Steuwer, Axel
    Maimaitiyili, Tuerdi
    Malmö högskola, School of Technology (TS).
    Massih, Ali
    Malmö högskola, School of Technology (TS).
    Bjerkén, Christina
    Malmö högskola, School of Technology (TS).
    Towards a multiscale understanding of hydride induced embrittlement in zirconium and titanium: theory and experiments2013In: Thermec' 2013 Rio Hotel Las Vegas USA, Abstract book, 2013, article id 140Conference paper (Other academic)
  • 50. Brodén, Björn
    et al.
    Hammar, Mikael
    Nilsson, Bengt J.
    Malmö högskola, School of Technology (TS).
    Guarding Lines and 2-Link Polygons is APX-hard2001Conference paper (Other academic)
    Abstract [en]

    We prove that the minimum line covering problem and the minimum guard covering problem restricted to 2-link polygons are APX-hard.

    Download full text (pdf)
    FULLTEXT01
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