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  • 1.
    Abbondanza, Giuseppe
    et al.
    Lund Univ, Div Synchrotron Radiat Res, S-22100 Lund, Sweden.;Lund Univ, NanoLund, S-22100 Lund, Sweden..
    Larsson, Alfred
    Lund Univ, Div Synchrotron Radiat Res, S-22100 Lund, Sweden.;Lund Univ, NanoLund, S-22100 Lund, Sweden..
    Linpe, Weronica
    Lund Univ, Div Synchrotron Radiat Res, S-22100 Lund, Sweden..
    Hetherington, Crispin
    Lund Univ, nCHREM, S-22100 Lund, Sweden..
    Carla, Francesco
    Diamond Light Source, Didcot OX11 0DE, Oxon, England..
    Lundgren, Edvin
    Lund Univ, Div Synchrotron Radiat Res, S-22100 Lund, Sweden..
    Harlow, Gary
    Malmö University, Faculty of Technology and Society (TS), Department of Materials Science and Applied Mathematics (MTM).
    Templated electrodeposition as a scalable and surfactant-free approach to the synthesis of Au nanoparticles with tunable aspect ratios2022In: Nanoscale Advances, E-ISSN 2516-0230, Vol. 4, no 11, p. 2452-2467Article in journal (Refereed)
    Abstract [en]

    A high-throughput method for the fabrication of ordered arrays of Au nanoparticles is presented. It is based on pulsed electrodeposition into porous anodic alumina templates. In contrast to many synthesis routes, it is cyanide-free, prior separation of the alumina template from the aluminium substrate is not required, and the use of contaminating surfactants/capping agents often found in colloidal synthesis is avoided. The aspect ratio of the nanoparticles can also be tuned by selecting an appropriate electrodeposition time. We show how to fabricate arrays of nanoparticles, both with branched bases and with hemispherical bases. Furthermore, we compare the different morphologies produced with electron microscopies and grazing-incidence synchrotron X-ray diffraction. We find the nanoparticles are polycrystalline in nature and are compressively strained perpendicular to the direction of growth, and expansively strained along the direction of growth. We discuss how this can produce dislocations and twinning defects that could be beneficial for catalysis.

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  • 2.
    Abdelmajid, Ehab
    et al.
    Malmö University, Faculty of Technology and Society (TS).
    Abouelkhair, Mohammad
    Malmö University, Faculty of Technology and Society (TS).
    Analys av länkarm till transportcykel2020Independent thesis Basic level (university diploma), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    This work has been performed at Starke Cycles and its purpose is to analyze the control arm of the MacPherson's suspension system for their new prototype of transport cycles. To analyze the control arm, the work is divided into different parts. The parts consists of mechanical calculations, material production, CAD modulation, structural mechanics and FEM analyzes. Material production is carried out using the material database CES-EduPack. The CAD program Solidworks is used to obtain a CAD model of the control arm. To analyze the control arm, SolidWorks simulation tools are used to obtain stress concentration and are presented.

    Starke Cycles is a private bicycle manufacturing company. Their idea is to manufacture and develop environmentally friendly electric bicycles for the transport of goods. A normal way of transporting goods is by means of trucks. The disadvantage of transporting goods in a truck compared to transport cycles is that it causes toxic gases, high risk of traffic accidents and delays because it is restricted in traffic where certain roads and roads prevent it from reaching its destination. These disadvantages are a major reason why Starke Cycles has invested in the production of transport bicycles. The electric motors used in the transport bicycles do not emit exhaust gases. The size of the transport bicycles is considerable smaller, which means more space for fellow drivers on roads and ways and the risk of traffic accidents is reduced. Delays rarely occur because the transport bicycles are allowed to drive on cycle tracks and this makes the transport of goods smoother and faster.

    The work results in a 3D model and the control arm reaches the goals that were set at the project. The material selection for the control arm was made of low-alloy steel of the AISI 4340 normalized. FEM analyzes in Solidworks show that the stress concentrations in the link arm can handle the maximum static load with a good safety factor of 200 at maximum load of the transport cycle.

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    E.Abdelmajid_M.Abou El Khair
  • 3.
    Agetorp, Maria
    Malmö University, Faculty of Technology and Society (TS), Department of Materials Science and Applied Mathematics (MTM).
    Gasdysa till brännugn - driftförhållanden och materialval2023Independent thesis Basic level (professional degree), 10 credits / 15 HE creditsStudent thesis
  • 4.
    Albertin, S.
    et al.
    Lund Univ, Div Synchrotron Radiat Res, Box 118, S-22100 Lund, Sweden..
    Gustafson, J.
    Lund Univ, Div Synchrotron Radiat Res, Box 118, S-22100 Lund, Sweden..
    Zhou, J.
    Lund Univ, Div Combust Phys, SE-22100 Lund, Sweden..
    Pfaff, S.
    Lund Univ, Div Combust Phys, SE-22100 Lund, Sweden..
    Shipilin, M.
    Stockholm Univ, Div Phys Chem, SE-10691 Stockholm, Sweden..
    Blomberg, S.
    Lund Univ, Dept Chem Engn, SE-22100 Lund, Sweden..
    Merte, Lindsay R.
    Malmö University, Faculty of Technology and Society (TS), Department of Materials Science and Applied Mathematics (MTM).
    Gutowski, O.
    Deutsch Elektronen Synchrotron DESY, D-22607 Hamburg, Germany..
    Dippel, A-C
    Deutsch Elektronen Synchrotron DESY, D-22607 Hamburg, Germany..
    Zetterberg, J.
    Lund Univ, Div Combust Phys, SE-22100 Lund, Sweden..
    Lundgren, E.
    Lund Univ, Div Synchrotron Radiat Res, Box 118, S-22100 Lund, Sweden..
    Hejral, U.
    Lund Univ, Div Synchrotron Radiat Res, Box 118, S-22100 Lund, Sweden..
    Surface optical reflectance combined with x-ray techniques during gas-surface interactions2020In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 53, no 22, article id 224001Article in journal (Refereed)
    Abstract [en]

    High energy surface x-ray diffraction (HESXRD), x-ray reflectivity (XRR), mass spectrometry (MS) and surface optical reflectance (SOR) have been combined to simultaneously obtain sub-second information on the surface structure and morphology from a Pd(100) model catalyst during in situ oxidation at elevated temperatures and pressures resulting in Pd bulk oxide formation. The results show a strong correlation between the HESXRD and SOR signal intensities during the experiment, enabling phase determination and a time-resolved thickness estimation of the oxide by HESXRD, complemented by XRR measurements. The experiments show a remarkable sensitivity of the SOR to changes in the surface phase and morphology, in particular to the initial stages of oxidation/reduction. The data imply that SOR can detect the formation of an ultrathin PdO surface oxide layer of only 2-3 angstrom thickness.

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  • 5.
    Albertin, Stefano
    et al.
    Division of Synchrotron Radiation Research, Lund University, SE-22100 Lund, Sweden.
    Merte, Lindsay R.
    Malmö University, Faculty of Technology and Society (TS), Department of Materials Science and Applied Mathematics (MTM).
    Lundgren, Edvin
    Division of Synchrotron Radiation Research, Lund University, SE-22100 Lund, Sweden.
    Martin, Rachel
    Department of Chemical Engineering, University of Florida, Gainesville, Florida 32611, United States.
    Weaver, Jason F.
    Department of Chemical Engineering, University of Florida, Gainesville, Florida 32611, United States.
    Dippel, Ann-Christin
    Deutsches Elektronen-Synchrotron (DESY), 22603 Hamburg, Germany.
    Gutowski, Olof
    Deutsches Elektronen-Synchrotron (DESY), 22603 Hamburg, Germany.
    Hejral, Uta
    Division of Synchrotron Radiation Research, Lund University, SE-22100 Lund, Sweden.
    Oxidation and Reduction of Ir(100) Studied by High-Energy Surface X-ray Diffraction2022In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 126, no 11, p. 5244-5255Article in journal (Refereed)
    Abstract [en]

    The oxidation and reduction of an Ir(100) surface using 2.5, 5, and 10 mbar O2 partial pressure and a sample temperature of 775 K have been studied by using high-energy surface X-ray diffraction (HESXRD) which allowed to record large volumes of reciprocal space in short time periods. The complex 3D diffraction patterns could be disentangled in a stepwise procedure. For the 2.5mbar experiment the measurements indicate the formation of an Ir(100)-O c(2 × 2) oxygen superstructure along with the onset of epitaxial IrO2(110) bulk oxide formation. For the 5 and 10 mbar O2 partial pressures the formation of additional IrO2 bulk oxide epitaxies with (100) and (101) orientations as well as of polycrystalline IrO2 was observed. Upon CO reduction, we found the IrO2 islands to be reduced into epitaxial and metallic Ir(111) and (221) oriented islands.

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  • 6.
    Al-Hussein, Hussein
    Malmö University, Faculty of Technology and Society (TS), Department of Materials Science and Applied Mathematics (MTM). mau.
    Theoretical investigation of α-iron chromium carbide (α-Fe/Cr7C3) interfaces2023Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This master thesis presents a theoretical investigation of the energy and stability of interfaces in iron-carbide compounds, specifically focusing on the α-Fe/Cr7C3 system. The study aims to fill the gap in knowledge regarding the surface energetics of these interfaces using Density Functional Theory (DFT). Six different α-Fe/Cr7C3 interfaceswere constructed α-Fe(001)/Cr7C3(024), α-Fe(001)/Cr7C3(202), α-Fe(001)/Cr7C3(040),α-Fe(110)/Cr7C3(024), α-Fe(110)/Cr7C3(202) and α-Fe(110)/Cr7C3(040). Due to limited computational resources, only one of them was computationally analyzed to determine its interfacial energy value. The results revealed that the interfacial energy of the α-Fe(001)/Cr7C3(040) interface falls within the range of incoherent interfaces, indicating its stability. The computed interfacial energy values ranged from 0.94 to 3.39 J/m2, consistent with similar studies on other iron interfaces. The simulations also identified minimum and local minimum points in the interface energy curve, representing stable configurations at specific interface separation distances. The presence of a minimum point at an interface separation value of d = 1.3551 Å with an interfacial energy of 0.94 J/m2 indicates the most stable configuration, while a local minimum point at d = 2.27 Å with an interfacial energy of 2.12 J/m2 suggests another stable configuration for the interface. The conclusion that the computations were correctly performed with an interfacial energy value of 0.94 J/m2 for the most stable configuration at a supercell length (aSupercell ) of 22.23 Å is drawn. The findings of this research have significant implications for future investigations and applications. Firstly, this study fills the gap of the unresearched ferrite-carbide interfaces with theoretical data. Secondly, the knowledge gained from studying these interfaces contributes to understanding hydrogen interactions, which is fundamental for the transition towards a hydrogen economy. Additionally, the incoherent nature of the interface introduces challenges in understanding material behavior and properties, necessitating further investigations for designing efficient systems. Future work includes experimental validation of the α-Fe/Cr7C3 interface to compare the theoretical and experimental energies and stability. Investigating the remaining interfaces and examining the effects of introducing hydrogen atoms in these interfaces, along with calculating the corresponding hydrogen trapping energies, are important research areas. Further advancements in understanding these interfaces can be achieved through interface engineering, multiscale modeling, and studying other iron-carbide systems. 

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    Theoretical investigation of alpha-iron chromium carbide interfaces
  • 7.
    Alhussein, Hussein
    et al.
    Malmö University, Faculty of Technology and Society (TS).
    Muradi, Mostafa
    Malmö University, Faculty of Technology and Society (TS).
    Lösningsalternativ för våtblock2021Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    In recent times, people have begun to reduce the use of environmentally hazardous materials, as the negative effects have become more and more clear. This knowledge has led to a new environmental thinking where individuals and companies have reduced the use of environmentally hazardous materials and started investing in more environmentally friendly alternatives. One such material that has been reduced in use is plastic. Plastic is used in large quantities as the material is cheap and easy to massproduce. But the negative effects of plastics are clearly visible, which has led to an uproar, especially in the florist market. Florists use floral foam for their flower arrangements that create microplastics. Unfortunately, the floral foam mostly consists of phenol formaldehyde, a non-compostable material. These microplastics have easy access to the cell membranes of marine organisms. Intake of microplastics can lead to reduced somatic and reproductive growth in animals by affecting the animals' antioxidant systems. This can lead to various injuries where some of them are fatal. An affected ecosystem leads to several problems that affects many more organisms. The Church of Sweden has also drawn attention to this problem and decided to remedy it by finding a compostable solution alternative for the floral foam that florists can use instead, which this project deals with. The purpose of this project is to reduce the environmental impact caused by florists, companies and congregations that use flowers in larger quantities. The goal is to find a solution that will be able to replace the floral foam in the market that fulfills the purpose. The solution sought should meet a number of requirements, such as that the material has a good absorbency and with the help of that ability preserve and provide plants with nutritions for at least 24 hours. The material should be permeable so it is possible to insert the flower. A material selection process was done using EduPack to know which material meets the requirements. These materials became cotton fiber and wool fiber. An external search was made on cellulosic materials and cellulosic fungi was found. Several experiments were done on these three materials to know how long the roses will live after water has been added to the material. The material candidates were also compared with Oasis, a brand name for floral foam. The result was that the roses lived the longest in the cellulose fungus and the fungus was sufficiently permeable to the roses.

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  • 8.
    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.

  • 9.
    Areitioaurtena, Maialen
    et al.
    Basque Res & Technol Alliance BRTA, Ikerlan Technol Res Ctr, Paseo JM Arizmendiarrieta 2, Arrasate Mondragon 20500, Spain..
    Segurajauregi, Unai
    Basque Res & Technol Alliance BRTA, Ikerlan Technol Res Ctr, Paseo JM Arizmendiarrieta 2, Arrasate Mondragon 20500, Spain..
    Fisk, Martin
    Malmö University, Faculty of Technology and Society (TS), Department of Materials Science and Applied Mathematics (MTM). Lund Univ, Div Solid Mech, POB 118, S-22100 Lund, Sweden..
    Cabello, Mario J.
    Basque Res & Technol Alliance BRTA, Ikerlan Technol Res Ctr, Paseo JM Arizmendiarrieta 2, Arrasate Mondragon 20500, Spain..
    Ukar, Eneko
    Univ Basque Country, Dept Mech Engn, Alameda Urquijo S-N, Bilbao 48013, Spain..
    Numerical and experimental investigation of residual stresses during the induction hardening of 42CrMo4 steel2022In: European journal of mechanics. A, Solids, ISSN 0997-7538, E-ISSN 1873-7285, Vol. 96, article id 104766Article in journal (Refereed)
    Abstract [en]

    The usage of induction hardening in the industry has increased in the last years due to its efficiency and repeatability. Induction hardening produces a hard martensitic layer on the specimen surface, which is accompanied by the generation of compressive residual stresses in the hardened case and tensile stresses in the untreated core. Residual stresses generated by induction hardening greatly impact on fatigue performance, as they act as crack growth retardants. In this work, a multiphysical coupled finite element model is developed to simulate induction hardening and compute the final residual stress state of the specimens along the microstructural transformations and hardness evolution. The impact of the transformation induced plasticity strain in the stress-state of the specimen during the process is also studied. The experimental validation shows that considering the transformation induced plasticity in induction hardening simulations improves the residual stress predictions, concluding that this effect should be included to achieve good residual stress predictions, especially in the subsurface region.

  • 10.
    Areitioaurtena, Maialen
    et al.
    Ikerlan Technology Research Centre, Basque Research and Technology Alliance (BRTA). Paseo J.M. Arizmendiarrieta 2, 20500 Arrasate-Mondragon, Spain.
    Segurajauregi, Unai
    Ikerlan Technology Research Centre, Basque Research and Technology Alliance (BRTA). Paseo J.M. Arizmendiarrieta 2, 20500 Arrasate-Mondragon, Spain.
    Urresti, Iker
    Ikerlan Technology Research Centre, Basque Research and Technology Alliance (BRTA). Paseo J.M. Arizmendiarrieta 2, 20500 Arrasate-Mondragon, Spain.
    Fisk, Martin
    Malmö University, Faculty of Technology and Society (TS), Department of Materials Science and Applied Mathematics (MTM).
    Ukar, Eneko
    Department of Mechanical Engineering. University of the Basque Country. Alameda Urquijo s/n, 48013 Bilbao, Spain.
    Predicting the induction hardened case in 42CrMo4 cylinders2020In: Procedia CIRP, ISSN 2212-8271, E-ISSN 2212-8271, Vol. 87, p. 545-550Article in journal (Refereed)
    Abstract [en]

    Induction hardening has the potential to produce favorable surface integrity that can improve fatigue performance and extend the lifetime of a component. The localized superficial heating provided by induction is the main advantage of this process, as it allows the core to remain intact and, therefore, ductile, while the surface is hardened. Achieving favorable characteristics in the hardened case is of great importance, as this process is usually applied to load bearing and wear-susceptible metallic components. The simulation of the hardening process by induction heating is a complex and challenging task at which many efforts have been directed in the last years. Due to the numerous interactions of the many physics that take part in the process (electromagnetic, thermal, microstructural and mechanical), a highly coupled finite element model is required for its numerical simulation. In this work, a semi-analytical induction heating model is used to compute the induction hardening process, predicting the size and shape of the hardened layer and the distribution of the hardness. Using the semi-analytical model allows the computational time to be much faster compared to a fully coupled model using a commercial software, where the time consumption for the presented 2D case is reduced by 20 %. Experimental validation is presented for cylindrical 42CrMo4 billets heated by a short solenoidal inductor, which shows good agreement with the predicted results, reaching an average error of 3.2 % in temperature estimations.

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  • 11.
    Asbjørn Sörensen, Charlotte
    Lund University.
    A Material Framework for Product Design2018Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    A new paradigm is slowly making its way into society, affecting our material practice as designers. Materials selection in design and product development has for a long time been dominated by a purely technical approach, mainly focusing on properties and performance. With the increasing evidence of climate change, waste and pollution, environmental effects, we are slowly realizing that unsustainable consumption of materials is no longer an alternative. Previous studies of material practices, both within design educations and the design profession, has primarily dealt with the development of material related methods. This thesis has focused on gaining an in-depth understanding of material practices within design processes, in order to develop a pedagogical framework that facilitates the development of reflective material practices in design education. There are four primary aims of the research presented in this licentiate thesis: (1) ascertain obstacles in the traditional ways of teaching materials to design students, (2) to bridge the differences in language, research culture and pedagogic approaches in design education, (3) to investigate current professional material practices in industrial design, and (4) to develop a new material framework for teaching reflective material practices for design students. During the project, the material framework has been tested and evaluated in two mandatory material courses with first and second year bachelor students from Product Design education over a period of four academic years. A comparative case study was conducted with five design consultancies. The qualitative interviews were transcribed and analysed using category zooming. The outcomes of this research are: (1) a new pedagogic framework for teaching materials to Product Design students in higher education, and (2) insights into professional practices of selecting and designing with materials. The pedagogic model A Material Framework for Product Design is designed to facilitate the development of reflective material practices in design education. The Framework consist of four levels: (1) a pedagogical foundation based on Experiential Learning theory that provide a framework for how to approach teaching and learning, (2) designing and structuring learning activities, (3) creating learning environments that facilitate learning activities, and (4) defining learning objectives, assessment of learning outcomes and detecting signs of learning. The main insights from the study of professional practices suggest: (1) that risk management has a major influence on the material selection process, (2) that negotiations of project boundaries in the ‘fuzzy’ pre-design phase has crucial influence on the risk management aspect of the material criteria activities, and (3) a lack of awareness, that design briefs usually outline material criteria expressed as sensorial characteristics, which are later translated by engineering into final material criteria used for the material selection process. The findings implies that design students would benefit from developing reflective material practices in design education.

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    FULLTEXT01
  • 12.
    Asbjørn Sörensen, Charlotte
    et al.
    Malmö University, Faculty of Culture and Society (KS), School of Arts and Communication (K3).
    Thyni, Emma
    Malmö University, Faculty of Culture and Society (KS), School of Arts and Communication (K3).
    A Qualitative Study of the challenges faced by Material Designers when developing DIY-materials2020In: DS 104: Proceedings of the 22nd International Conference on Engineering and Product Design Education : The Value of Design & Engineering Education in a Knowledge Age / [ed] Buck, L; Bohemia, E; Grierson, H, Herning, Denmark: Design Society , 2020, Vol. DS104, article id 1280Conference paper (Refereed)
    Abstract [en]

    The recent academic literature on material practices within design has revealed the emergence of a new design discipline, DIY-materials or material design. Designers educated in DIY-materials and the Material Driven Design method, applied in design courses in major European universities are beginning to identify themselves as material designers. This paper presents a qualitative case study of the challenges faced by material designers and design students developing DIY-materials from the stage of a small sample with promising experiential qualities and technical properties, towards a more viable material. A comparative case study of twenty-eight material driven design projects and four explorative semi-structured interviews were conducted with designers. The result suggest: (a) that designers have a tendency to focus more on the experiential attributes and aesthetical qualities rather than the technical attributes in the early stages of material development, (b) projects that are situated in specific contexts or systems have a higher success rate, (c) bio-based DIY-materials are in general sensitive to moist and high temperatures, (d) a systematic approach during tinkering combined with analytic skills are crucial for the development of DIY-materials. In this paper we also build on our previous research, regarding the development of reflective material practices for design students in higher education. It is hoped that this research can contribute to the further development of material design as a new design discipline.

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    Asbjorn Sorensen_Thyni_EPDE2020
  • 13.
    Awala, Ibrahim
    Malmö University, Faculty of Technology and Society (TS).
    Influence of strain and point defects on the Seebeck coefficient of thermoelectric CoSb3: Inverkan av töjnings och punktdefekter på Seebeck-koefficienten för termoelektrisk CoSb32021Independent thesis Advanced level (degree of Master (Two Years)), 80 credits / 120 HE creditsStudent thesis
    Abstract [en]

    Many studies and experiments have been conducted over the years to find solutions to the electricity problem. This issue is not just related to how fossil fuels are dispensed. Also, the environmental concerns associated with using fossil fuels have become a severe issue, which is a major cause of environmental pollution and ozone layer damage. As such, the need for energy becomes one of the essential goals. Therefore, research has begun to revolve around thermoelectrics, which is a straightforward approach for generating energy, by converting heat directly into electricity.

    Cobalt antimonide (CoSb3) belongs to a broad family of materials with the skutterudite structure, which have been recently identified as potential new thermoelectric materials with high performance. The CoSb3 is one of the numerous promising thermoelectric materials in the intermediate temperature range. The binary CoSb3 is a narrow bandgap semiconductor with a relatively flat band structure and excellent electrical performance. The thermoelectric performance efficiency of binary CoSb3 is measured by its figure of merit. The figure of merit is important for thermoelectric materials and is primarily governed by the Seebeck coefficient because it exhibits a square dependence. The Seebeck coefficient of the CoSb3 can be affected by many factors that can either increase or decrease it. Strain is an important aspect for the transport properties, including the Seebeck coefficient. The goal of this thesis project is to study the effect of point defects and strain on the Seebeck coefficient of skutterudite CoSb3.

    The binary CoSb3 skutterudite was explored through density functional theory (DFT) to calculate the ground-state properties, in particular the Seebeck coefficient. Two different CoSb3 structures were considered, an ideal one (without any defects) and the other was termed real (containing defects). In both cases, the Seebeck coefficient and its response were studied while strain was applied by changing the volume of the structure. The non-equilibrium Green's function was used within a DFT simulation to get a transmission distribution, where it was essential for calculating the Seebeck coefficient. Moreover, oxygen molecules were placed over the (001) surface of 2 × 2 × 1 CoSb3 supercell to establish if oxidation leads to point defect formation. These simulations were carried out by DFT-based molecular dynamics.

    It is found that the strain affects the Seebeck coefficient in the ideal structure. At compression, the absolute value of the Seebeck coefficient increases.  By contrast, the Seebeck coefficient changed its sign from negative to positive and increased to 894 μVK−1at tension, which was unexpected. The electron density distribution map was explored to explain the behavior of the Seebeck coefficient at equilibrium, compression, and tension. It can be seen that the electron distribution between Co and Sb is increased at compression, implying an increased orbital overlap (covalent interaction). By contrast, the tension reduces the electron distribution between Sb and Co.

    The real structure induced by oxidation exhibits Sb vacancies. The See-beck coefficient is affected differently than that of the ideal structure. At equilibrium, the Seebeck coefficient increases to 151 μVK−1. The electron density distribution between Sb and Co is enhanced in the real structure compared to the ideal one. The most drastic change is found at tension, where the Seebeck coefficient reaches−270 μVK−1. It may be speculated that this occurs due to O which increases the orbital overlap. The strategy introduced in this work, an interplay of defects and strain effects, may be beneficial for other thermoelectric materials.

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  • 14.
    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.

  • 15. Barjosef, David
    et al.
    Austen Öhrn, Alexander
    Fracture analysis of tensile- and fatigue failure for perforated and wedge wire structures2022Independent thesis Basic level (university diploma), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    In the effort to produce more durable filters and understand their mechanical failure, this study presents distinctive indicators on the cause of failure for welded perforated- and wedge wire sheets in 316L stainless steel, super duplex UR52N stainless steel and grade 2 titanium. The study achieves this by fracture analysis on specimens from tensile strength- and fatigue testing. These tests are performed to an extent to ensure the highest authenticity and accommodate for the loads and strains on the actual filter structure. The fractured specimens are analysed using industrially applicable methods. 

     The analysis shows numerous macro and microscopical indicators differentiating between tensile- and fatigue fractures. Observable in the materials are, among other things, distinctions in cracking and void formations. The study shows that a subsequent conclusion to the type of failure a fractured filter has exhibited is achievable with these indicators. Through these conclusions, the study contributes to developing more durable filters and a more comprehensive understanding of the failure of welded perforated and wedge wire sheets.

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  • 16. 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.

  • 17.
    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.

  • 18.
    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.

  • 19.
    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)
  • 20.
    Blom, A
    Malmö högskola, School of Technology (TS).
    Cyclic Loading of a Brazed Joint under Stress Concentration2001Report (Other academic)
  • 21. 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

  • 22.
    Carlsson, Axel
    Malmö University, Faculty of Culture and Society (KS), School of Arts and Communication (K3).
    Produktdesign för ett ekologiskt hållbart sportfiske2023Independent thesis Basic level (degree of Bachelor), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Fishing occurs throughout the entire planet, but it occurs for different reasons. It could be a profession, a hobby or a livelihood. Regardless, the bait can break, get stuck or get loose. In the North we lose around 28 million baits every year. The fact that lures is not something that everyone can influence or avoid. However, something that can be changed, is which lures we use and which materials they are made of. There are a variety of anglers who could benefit from new research in this field, and it is about time we embrace a more sustainable sport fishing. This study examines how an ecologically sustainable fishing lure in the shape of a jig, can be produced through a material centered design process. With material driven design and user centered design, this study investigates the possibilities of replacing synthetic plastics with bioplastics in a soft plastic bait. Several design methods were used to research and confirm the problem of lost fishing lures. Market analyses, participant observations and interviews were done with people active in sport- and hobby fishing. These methods gave a broader perception of the problem and which opportunities there are. Different prototypes were sketched and then made by bioplastics. The prototypes were evaluated through different tests, to ensure that the products will live up to the requirements presented by the users. This study provides knowledge about which materials work, and which do not when manufacturing soft plastic features. It also shows how mass-produced molds could encourage hobby anglers to make their own lures. It’s also shown how you can make your own fishing lures from scratch, through a DIY project. The study also results in two biodegradable products. One product for perch fishing and one for pike fishing.

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  • 23.
    Chen, Leilei
    et al.
    Key Laboratory for Precision and Non-Traditional Machining Technology of Ministry of Education, Dalian University of Technology, Dalian, 116024, China; Key Laboratory of Marine Materials and Related Technologies, Zhejiang, Key Laboratory of Marine Materials and Protective Technologies, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo, 315201, China.
    Zhang, Zhenyu
    Key Laboratory for Precision and Non-Traditional Machining Technology of Ministry of Education, Dalian University of Technology, Dalian, 116024, China.
    Lou, Ming
    Key Laboratory of Marine Materials and Related Technologies, Zhejiang Key Laboratory of Marine Materials and Protective Technologies, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo, 315201, China.
    Xu, Kai
    Key Laboratory of Marine Materials and Related Technologies, Zhejiang Key Laboratory of Marine Materials and Protective Technologies, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo, 315201, China.
    Wang, Lu
    Key Laboratory of Marine Materials and Related Technologies, Zhejiang Key Laboratory of Marine Materials and Protective Technologies, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo, 315201, China.
    Meng, Fanning
    Key Laboratory for Precision and Non-Traditional Machining Technology of Ministry of Education, Dalian University of Technology, Dalian, 116024, China.
    Music, Denis
    Malmö University, Faculty of Technology and Society (TS), Department of Materials Science and Applied Mathematics (MTM).
    Chang, Keke
    Key Laboratory of Marine Materials and Related Technologies, Zhejiang Key Laboratory of Marine Materials and Protective Technologies, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo, 315201, China.
    High-temperature wear mechanisms of TiNbWN films: Role of nanocrystalline oxides formation2023In: Friction, ISSN 2223-7690, E-ISSN 2223-7704, Vol. 10, article id 40544Article in journal (Refereed)
    Abstract [en]

    Refractory high/medium entropy nitrides (HENs/MENs) exhibit comprehensive application prospects as protective films on mechanical parts, particularly those subjected to sliding contacts at elevated temperatures. In this study, a new MEN system TiNbWN, forming a single fcc solution, is designed and its wear performance at temperatures ranging from 25 to 750 °C is explored. The wear mechanisms can be rationalized by examining the subsurface microstructural evolutions using the transmission electron microscopy as well as calculating the phase diagrams and interfacial adhesion behavior employing calculation of phase diagram (CALPHAD) and density functional theory (DFT). To be specific, increased wear losses occur in a temperature range of 25–600 °C, being predominantly caused by the thermally-induced hardness degradation; whereas at the ultimate temperature (750 °C), the wear loss is refrained due to the formation of nanocrystalline oxides (WnO3n−2, TiO2, and γTiOx), as synergistically revealed by microscopy and CALPHAD, which not only enhance the mechanical properties of the pristine nitride film, but also act as solid lubricants, reducing the interfacial adhesion. Thus, our work delineates the role of the in situ formed nanocrystalline oxides in the wear mechanism transition of TiNbWN thin films, which could shed light on the high-temperature wear behavior of refractory HEN/MEN films.

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  • 24.
    de Hoop, Maarten V. V.
    et al.
    Rice Univ, Simons Chair Computat & Appl Math & Earth Sci, Houston, TX 77005 USA..
    Iantchenko, Alexei
    Malmö University, Faculty of Technology and Society (TS), Department of Materials Science and Applied Mathematics (MTM). Malmö University, Biofilms Research Center for Biointerfaces.
    Inverse problem for the Rayleigh system with spectral data (vol 63, 031505, 2022)2022In: Journal of Mathematical Physics, ISSN 0022-2488, E-ISSN 1089-7658, Vol. 63, no 4, article id 049901Article in journal (Refereed)
  • 25.
    Digaitis, Ramūnas
    et al.
    Malmö University, Biofilms Research Center for Biointerfaces. Malmö University, Faculty of Health and Society (HS), Department of Biomedical Science (BMV).
    Falkman, Peter
    Malmö University, Faculty of Health and Society (HS), Department of Biomedical Science (BMV). Malmö University, Biofilms Research Center for Biointerfaces.
    Oltner, Viveca
    Magle Chemoswed AB, Malmö, Sweden.
    Briggner, Lars-Erik
    Magle Chemoswed AB, Malmö, Sweden; Adroit Science AB, Lund, Sweden.
    Kocherbitov, Vitaly
    Malmö University, Faculty of Health and Society (HS), Department of Biomedical Science (BMV). Malmö University, Biofilms Research Center for Biointerfaces.
    Hydration and dehydration induced changes in porosity of starch microspheres2022In: Carbohydrate Polymers, ISSN 0144-8617, E-ISSN 1879-1344, Vol. 291, p. 119542-119542, article id 119542Article in journal (Refereed)
    Abstract [en]

    Characterization and tuning of the porosity of amorphous starch materials are important for many applications, including controlled release of encapsulated proteins. The porosities of these materials in dry and hydrated states can have different physicochemical origins and properties. Here, porosities of dry cross-linked starch microspheres and their hydration-induced transformations were characterized by small angle X-ray scattering, scanning electron and optical microscopies, thermogravimetric analysis, sorption calorimetry, nitrogen sorption, and helium-pycnometry. The analyses revealed that dry microspheres consist of porous cores with pore diameters below 100 nm and shells which appeared to be denser but contained wider pores (100–300 nm). The outer crust of the microspheres shell is non-porous, which restricts diffusion of nitrogen, water, and ethanol. Partial hydration triggered an irreversible collapse of dry porosity at 12 wt% water. Further hydration resulted in interfacial changes and promoted wet porosity, related to characteristic distances between polymer chains.

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  • 26.
    Eneberg, Victor
    et al.
    Malmö University, Faculty of Technology and Society (TS).
    Linby, Johannes
    Malmö University, Faculty of Technology and Society (TS).
    Heat transfer analysis on LED-board in closed environment2022Independent thesis Basic level (university diploma), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Motorcyclists are more often involved in accidents with severe harm or even fatal outcome compared to other road users. An experienced motorcycle driver is well familiar with the problem when the day light is reduced. The visibility is of course highly decreased. Allight International develops a light bulb that through a gyroscopic feature allows the light image to always be projected in the same axi-symmetric plane. The low beam head light usually accompanies the drivers movement when cornering, creating a black void ahead that leads to decreased vision. The light bulb has not yet been tested in a headlight and the LED is assumed to have high working temperature, which can lead to a shortened service life and technical errors due to the heat. By comparing empirical tests such as infrared camera and thermocouples on the prototype with theoretical tests such as computer aided design, finite element method, and computational fluid dynamics, a better understanding of how the model can be adapted to counteract the high temperature has achieved. Empirical analysis show that at a lower current of where the light bulb produces a brightness around the lower region of an automotive low beam headlight, the existing solution seems to work with the help of the fan creating forced convection. The improved and evaluated prototype, makes it possible to increase the current for the light bulb when more of the generated heat dissipates from the heat source.

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  • 27.
    Ericsson, A.
    et al.
    Division of Solid Mechanics, Lund University, PO Box 118, Lund, SE 22100, Sweden.
    Pacheco, V.
    Department of Chemistry, Ångström Laboratory, Uppsala University,Box 523, Uppsala, SE 75120, Sweden.
    Marattukalam, J. J.
    Department of Physics & Astronomy, Materials Physics, Uppsala University, Box 516, Uppsala, SE 75121, Sweden.
    Dalgliesh, R. M.
    ISIS Pulsed Neutron and Muon Source, Science and Technology Facilities Council, Rutherford Appleton Laboratory, Harwell Science and Innovation Campus, Didcot OX11 0QX, UK.
    Rennie, A. R.
    Centre for Neutron Scattering, Uppsala University, Box 516, Uppsala, SE 75121, Sweden.
    Fisk, Martin
    Malmö University, Faculty of Technology and Society (TS), Department of Materials Science and Applied Mathematics (MTM). Division of Solid Mechanics, Lund University, PO Box 118, Lund, SE 22100, Sweden.
    Sahlberg, M.
    Department of Chemistry, Ångström Laboratory, Uppsala University,Box 523, Uppsala, SE 75120, Sweden.
    Crystallization of a Zr-based metallic glass produced by laser powder bed fusion and suction casting2021In: Journal of Non-Crystalline Solids, ISSN 0022-3093, E-ISSN 1873-4812, Vol. 571, article id 120891Article in journal (Refereed)
    Abstract [en]

    The crystallization behaviour during low temperature annealing of samples of the Zr59.3Cu28.8Al10.4Nb1.5 (at%) bulk metallic glass produced by suction casting and the laser powder bed fusion (LPBF) process were studied with small angle neutron scattering (SANS), X-ray diffraction and scanning electron microscopy. The in-situ SANS measurements during isothermal annealing reveals that the phase separation in the LPBF processed material proceeds at a smaller characteristic length-scale than the cast material. Quantitative analysis of the SANS data shows that, while the crystallization process in both materials proceed through rapid nucleation followed by diffusion limited growth, the LPBF processed material crystallizes with a smaller cluster size and at a higher rate. The smaller cluster size is attributed to the elevated oxygen content in the LPBF processed material which reduces the nucleation barrier and thus the thermal stability.

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  • 28.
    Ericsson, Anders
    et al.
    Lund Univ, Div Solid Mech, POB 118, SE-22100 Lund, Sweden..
    Fisk, Martin
    Malmö University, Faculty of Technology and Society (TS), Department of Materials Science and Applied Mathematics (MTM). Lund Univ, Div Solid Mech, POB 118, SE-22100 Lund, Sweden.;Malmö Univ, Dept Mat Sci & Appl Math, SE-20506 Malmö, Sweden..
    Modeling of Diffusion-Controlled Crystallization Kinetics in Al-Cu-Zr Metallic Glass2022In: Metals, ISSN 2075-4701, Vol. 12, no 5, p. 1-16, article id 867Article in journal (Refereed)
    Abstract [en]

    Crystallization is a major challenge in metallic glass production, and predictive models may aid the development of controlled microstructures. This work describes a modeling strategy of nucleation, growth and the dissolution of crystals in a multicomponent glass-forming system. The numerical model is based on classical nucleation theory in combination with a multicomponent diffusion-controlled growth model that is valid for high supersaturation. The required thermodynamic properties are obtained by coupling the model to a CALPHAD database using the Al-Cu-Zr system as a demonstrator. The crystallization of intermetallic (Al, Cu)(m)Zr-n phases from the under-cooled liquid phase were simulated under isothermal as well as rapid heating and cooling conditions (10(-1)-10(6) Ks(-1)). The obtained time-temperature transformation and continuous-heating/cooling transformation diagrams agree satisfactorily with the experimental data over a wide temperature range, thereby, demonstrating the predictability of the modeling approach. A comparison of the simulation results and experimental data is discussed.

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  • 29.
    Eriksson, Berth
    Malmö högskola, School of Technology (TS).
    Residual stress in a T-butt joint weld Cylinder versus plane plate geometry2004Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The welding process introduces residual stress originating from the heating, melting and cooling of the material. From the point of view of fatigue and stress corrosion cracking, the weld residual stress perpendicular to the weld axis is of particular interest. When qualifying weld parameters for welds in large cylinders having a ratio of radius to plate thickness larger than say approximately 100; reference to plane plates are often made for the sake of simplicity. However, the weld residual stress perpendicular to the weld axis is severely underestimated in the plane plate compared with the cylindrical structure. This observation is especially pronounced in connection with preheating. The source of the differences is probably due to the radial constraint of the cylinder, compared with that of a plane plate. A plane test specimen will underestimate the weld residual stress perpendicular to the weld axis in a cylinder, even if the radius of the cylinder is very large. However, a test specimen for an 8 m diameter cylinder with a plate thickness of 35 mm needs only to have a segment width of approximately 1.3 m to reflect the stress in the real structure. The weld residual stress perpendicular to the weld axis in the vicinity of the weld toe is governed by the depositing of the weld bead adjacent to the weld toe, neglecting the accumulated strain from the previous deposited weld beads in the multi-pass joint weld. Introducing tensile straining perpendicular to the weld axis during the entire welding procedure reduces the weld–induced residual stress after completed welding. The plastic zone of the weld area will be subjected to compressive strain after completed welding, which in turn will reduce the weld residual stress. This can be achieved by cooling the weld area, which in this case is not recommended since the material is sensitive to hydrogen cracking, or by pre-stretching or modifying the locations for preheating, all aimed to impose a tensile axial straining around the weld area during the entire welding process.

  • 30.
    Everbring, Adam
    et al.
    Malmö University, Faculty of Technology and Society (TS), Department of Materials Science and Applied Mathematics (MTM).
    Larsson, Robin
    Malmö University, Faculty of Technology and Society (TS), Department of Materials Science and Applied Mathematics (MTM).
    Momentmätare för lossning av distansskruvar2023Independent thesis Basic level (degree of Bachelor), 180 HE creditsStudent thesis
    Abstract [en]

    Maintenance of dental implants is time-consuming and can be painful for thepatient. For this reason, it is desirable to maximize the time between return visits. One factor that affects the revisit time is how much the abutment screw in a dental implant has loosened over time. In order to further research on this, a torque wrench is needed that can measure the maximum torque required to loosen the abutment screw. To achieve this, a systematic product development process has been carried out. Strength theory calculations and FEM analyses have been carried out to ensure that the prototype's mechanical properties meet the requirements. To produce the prototype, 3D printing has been used, measurements, calibration and programming has been done to ensure that the torque wrench can measure the maximum torque. The work resulted in a prototype made of carbon fiber composite and titanium for measuring the maximum torque required to loosen a abutment screw.

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    A.Everbring, R.Larsson
  • 31.
    Fierro Tobar, Raul
    et al.
    Malmö University, Faculty of Technology and Society (TS).
    Yuku, Marius
    Malmö University, Faculty of Technology and Society (TS).
    Atomic wear mechanisms of hard chrome against Al2O32021Independent thesis Basic level (university diploma), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Hard chrome exhibit hardness of about 70 HRC and lubricity that prevents seizing and galling and is therefore the common first choice for engineers to reduce friction and minimize wear. These properties enable engineering applications such as cutting and drilling, especially in manufacturing, production and consumer good industries. Hard chrome has a wide set of functions as being decorative, corrosion resistant and ease cleaning procedures. Hence, electroplating is a common process to synthesize hard chrome butthis process is banned by EU due to the rise of hazardous components. However, the need for alternative material is at rise but, fundamental issues for hard chrome are yet to be solved.

    The purpose of the work is to develop atomic structures for two systems using different programs such as OpenMX, VESTA and Ovito. The goal is to identify atomic wear mechanisms of hard chrome in an ideal system (Al2O3- Cr) and a real system (Al2O3 - Cr2O3) using density functional theory (DFT). These two systems are analyzed since every surface oxidises in air (real system) and under increased mechanical loads the pristine surface of hard chrome (ideal system) can be exposed to the counter body (Al2O3). DFT based molecular dynamics simulations are carried out at a temperature of 300 K and a sliding speed of 10 ms−1. The simulation interval is 0-15000 fs and radial distribution function (RDF) is employed to analyse the atomic wear mechanisms. Both systems start to show adhesive wear due to amorphization, mixed with signs of abrasive wear on the atomic scale. The systems are further analyzed using electron density distribution (EDD), that plots electronic structures enhancing the analyse of different type of bondstaking place. The bulk structures mainly show covalent bonds with ionic and metallic bonds less represented. Furthermore, same observations have been made for the interfaces of the ideal and real system.

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  • 32.
    Gajdek, Dorotea
    et al.
    Malmö University, Faculty of Technology and Society (TS), Department of Materials Science and Applied Mathematics (MTM). NanoLund, Lund University, Box 118, 211 00, Lund, Sweden.
    Jensen, Lucy Idowu Ajakaiye
    Department of Chemical Engineering, Lund University, Box 118, 221 00, Lund, Sweden.
    Briois, Valérie
    Synchrotron SOLEIL, UR1-CNRS, L’Orme des Merisiers, Saint-Aubin, BP 48, 91192, Gif-sur-Yvette Cedex, France.
    Hulteberg, Christian
    Department of Chemical Engineering, Lund University, Box 118, 221 00, Lund, Sweden.
    Merte, Lindsay R.
    Malmö University, Faculty of Technology and Society (TS), Department of Materials Science and Applied Mathematics (MTM). NanoLund, Lund University, Box 118, 211 00, Lund, Sweden.
    Blomberg, Sara
    NanoLund, Lund University, Box 118, 211 00, Lund, Sweden; Department of Chemical Engineering, Lund University, Box 118, 221 00, Lund, Sweden.
    Sulfidation of Supported Ni, Mo and NiMo Catalysts Studied by In Situ XAFS2023In: Topics in catalysis, ISSN 1022-5528, E-ISSN 1572-9028, Vol. 66, no 17-18, p. 1287-1295Article in journal (Refereed)
    Abstract [en]

    Active sites in Mo-based hydrotreating catalysts are produced by sulfidation. To achieve insights that may enable optimization of the catalysts, this process should be studied in situ. Herein we present a comparative XAFS study where the in situ sulfidation of Mo/δ-Al2O3 and Ni/δ-Al2O3 is compared to that of δ-Al2O3 supported NiMo catalysts with different NiMo ratios. The study also covers the comparison of sulfidation of Ni and Mo using different oxide supports as well as the sulfidation conditions applied in the reactor. The XAFS spectra confirms the oxide phase for all catalysts at the beginning of the sulfidation reaction and their conversion to a sulfidized phase is followed with in situ measurements. Furthermore, it is found that the monometallic catalysts are less readily sulfidized than bimetallic ones, indicating the importance of Ni-Mo interactions for catalyst activation. Mo K-edge XAFS spectra did not show any difference related to the support of the catalyst or the pressure applied during the reaction. Ni K-edge XAFS spectra, however, show a more complete sulfidation of the Ni species in the catalyst when SiO2 is used as a support as compared to the Al2O3. Nevertheless, it is believed that stronger interactions with Al2O3 support prevent sintering of the catalyst which leads to its stabilization. The results contribute to a better understanding of how different parameters affect the formation of the active phase of the NiMo catalysts used in the production of biofuel.

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  • 33.
    Gajdek, Dorotea
    et al.
    Malmö University, Faculty of Technology and Society (TS), Department of Materials Science and Applied Mathematics (MTM). NanoLund, Lund University, Box 118, SE-221 00 Lund, Sweden.
    Olsson, Pär A T
    Malmö University, Faculty of Technology and Society (TS), Department of Materials Science and Applied Mathematics (MTM). Division of Mechanics, Lund University, Box 118, SE-221 00 Lund, Sweden.
    Blomberg, Sara
    NanoLund, Lund University, Box 118, SE-221 00 Lund, Sweden;Department of Chemical Engineering, Lund University, Box 118, SE-221 00 Lund, Sweden.
    Gustafson, Johan
    Division of Synchrotron Radiation Research, Lund University, Box 118, SE-221 00 Lund, Sweden.
    Carlsson, Per-Anders
    Department of Chemistry and Chemical Engineering, Chalmers University of Technology, SE-412 96 Göteborg, Sweden;Competence Centre for Catalysis, Chalmers University of Technology, SE-412 96 Göteborg, Sweden.
    Haase, Dörthe
    MAX IV Laboratory, Lund University, Box 118, SE-221 00 Lund, Sweden.
    Lundgren, Edvin
    NanoLund, Lund University, Box 118, SE-221 00 Lund, Sweden;Division of Synchrotron Radiation Research, Lund University, Box 118, SE-221 00 Lund, Sweden.
    Merte, Lindsay R.
    Malmö University, Faculty of Technology and Society (TS), Department of Materials Science and Applied Mathematics (MTM). NanoLund, Lund University, Box 118, SE-221 00 Lund, Sweden.
    Structural Changes in Monolayer Cobalt Oxides under Ambient Pressure CO and O2 Studied by In Situ Grazing-Incidence X-ray Absorption Fine Structure Spectroscopy2022In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 126, no 7, p. 3411-3418Article in journal (Refereed)
    Abstract [en]

    We have used grazing incidence X-ray absorption fine structure spectroscopy at the cobalt K-edge to characterize monolayer CoO films on Pt(111) under ambient pressure exposure to CO and O2, with the aim of identifying the Co phases present and their transformations under oxidizing and reducing conditions. X-ray absorption near edge structure (XANES) spectra show clear changes in the chemical state of Co, with the 2+ state predominant under CO exposure and the 3+ state predominant under O2-rich conditions. Extended X-ray absorption fine structure spectroscopy (EXAFS) analysis shows that the CoO bilayer characterized in ultrahigh vacuum is not formed under the conditions used in this study. Instead, the spectra acquired at low temperatures suggest formation of cobalt hydroxide and oxyhydroxide. At higher temperatures, the spectra indicate dewetting of the film and suggest formation of bulklike Co3O4 under oxidizing conditions. The experiments demonstrate the power of hard X-ray spectroscopy to probe the structures of well-defined oxide monolayers on metal single crystals under realistic catalytic conditions.

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  • 34.
    Garcia-Martinez, Fernando
    et al.
    Centro de Física de Materiales CSIC/UPV-EHU-Materials Physics Center, Manuel Lardizabal 5, 20018 San Sebastian, Spain.
    Dietze, Elisabeth
    Department of Physics and Competence Centre for Catalysis, Chalmers University of Technology, 41296 Göteborg, Sweden.
    Schiller, Frederik
    Centro de Física de Materiales CSIC/UPV-EHU-Materials Physics Center, Manuel Lardizabal 5, 20018 San Sebastian, Spain.
    Gajdek, Dorotea
    Malmö University, Faculty of Technology and Society (TS), Department of Materials Science and Applied Mathematics (MTM).
    Merte, Lindsay R.
    Malmö University, Faculty of Technology and Society (TS), Department of Materials Science and Applied Mathematics (MTM). Synchrotron Radiation Research, Lund University, 22100 Lund, Sweden.
    Gericke, Sabrina M
    Combustion Physics, Lund University, Box 118, 22100 Lund, Sweden.
    Zetterberg, Johan
    Combustion Physics, Lund University, Box 118, 22100 Lund, Sweden.
    Albertin, Stefano
    Synchrotron Radiation Research, Lund University, 22100 Lund, Sweden..
    Lundgren, Edvin
    Synchrotron Radiation Research, Lund University, 22100 Lund, Sweden..
    Grönbeck, Henrik
    Department of Physics and Competence Centre for Catalysis, Chalmers University of Technology, 41296 Göteborg, Sweden.
    Ortega, J Enrique
    Centro de Física de Materiales CSIC/UPV-EHU-Materials Physics Center, Manuel Lardizabal 5, 20018 San Sebastian, Spain; Departamento Física Aplicada, Universidad del País Vasco, 20018 San Sebastian, Spain; Donostia International Physics Centre, 20018 San Sebastian, Spain.
    Reduced Carbon Monoxide Saturation Coverage on Vicinal Palladium Surfaces: the Importance of the Adsorption Site2021In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 12, no 39, p. 9508-9515Article in journal (Refereed)
    Abstract [en]

    Steps at metal surfaces may influence energetics and kinetics of catalytic reactions in unexpected ways. Here, we report a significant reduction of the CO saturation coverage in Pd vicinal surfaces, which in turn is relevant for the light-off of the CO oxidation reaction. The study is based on a systematic investigation of CO adsorption on vicinal Pd(111) surfaces making use of a curved Pd crystal. A combined X-ray Photoelectron Spectroscopy and DFT analysis allows us to demonstrate that an entire row of atomic sites under Pd steps remains free of CO upon saturation at 300 K, leading to a step-density-dependent reduction of CO coverage that correlates with the observed decrease of the light-off temperature during CO oxidation in vicinal Pd surfaces.

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  • 35. Garcia-Martinez, Fernando
    et al.
    Schiller, Frederik
    Blomberg, Sara
    Shipilin, Mikhail
    Merte, Lindsay R.
    Malmö University, Faculty of Technology and Society (TS), Department of Materials Science and Applied Mathematics (MTM).
    Gustafson, Johan
    Lundgren, Edvin
    Enrique Ortega, J.
    CO Chemisorption on Vicinal Rh(111) Surfaces Studied with a Curved Crystal2020In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 124, no 17, p. 9305-9313Article in journal (Refereed)
    Abstract [en]

    Curved crystal surfaces enable the systematic and accurate comparison of physical and chemical processes for a full set of vicinal crystal planes, which are probed in the very same environment. Here, we examine the early stages of the CO chemisorption on vicinal Rh(111) surfaces using a curved Rh crystal that exposes a smoothly variable density of {100} (A-type) and {111} (B-type) steps. We readily identify and quanti step and terrace species by resolving their respective core-level lines using X-ray photoelectron spectroscopy at different locations on the curved surface. Uptake experiments show similar sticking probabilities at all surface planes, subtle asymmetries between A- and B-type steps, and significantly lower saturation coverage at densely stepped surfaces as compared to the (111) plane. The analysis of the C is intensity variation across the curved sample allows us to discuss the adsorption geometry around the step edge.

  • 36.
    Gericke, Sabrina Maria
    et al.
    Division of Combustion Physics, Lunds University, P.O. Box 118, 221 00 Lund, Sweden.
    Rissler, Jenny
    RISE—Research Institutes of Sweden, P.O. Box 857, 501 15 Borås, Sweden; NanoLund, Lund University, P.O. Box 188, 221 00 Lund, Sweden; Ergonomics and Aerosol Technology, Faculty of Engineering, Lund University, P.O. Box 118, 221 00 Lund, Sweden.
    Bermeo, Marie
    NanoLund, Lund University, P.O. Box 188, 221 00 Lund, Sweden; Solid State Physics, Lund University, 221 00 Lund, Sweden.
    Wallander, Harald J.
    Malmö University, Faculty of Technology and Society (TS), Department of Materials Science and Applied Mathematics (MTM).
    Karlsson, Hanna
    Department of Chemical Engineering, Lund University, 221 00 Lund, Sweden.
    Kollberg, Linnéa
    Department of Chemical Engineering, Lund University, 221 00 Lund, Sweden.
    Scardamaglia, Mattia
    MAX IV Laboratory, Lund University, 221 00 Lund, Sweden.
    Temperton, Robert
    MAX IV Laboratory, Lund University, 221 00 Lund, Sweden.
    Zhu, Suyun
    MAX IV Laboratory, Lund University, 221 00 Lund, Sweden.
    Sigfridsson Clauss, Kajsa G. V.
    MAX IV Laboratory, Lund University, 221 00 Lund, Sweden.
    Hulteberg, Christian
    Department of Chemical Engineering, Lund University, 221 00 Lund, Sweden.
    Shavorskiy, Andrey
    MAX IV Laboratory, Lund University, 221 00 Lund, Sweden.
    Merte, Lindsay Richard
    Malmö University, Faculty of Technology and Society (TS), Department of Materials Science and Applied Mathematics (MTM).
    Messing, Maria Elise
    NanoLund, Lund University, P.O. Box 188, 221 00 Lund, Sweden; Solid State Physics, Lund University, 221 00 Lund, Sweden.
    Zetterberg, Johan
    Division of Combustion Physics, Lunds University, P.O. Box 118, 221 00 Lund, Sweden.
    Blomberg, Sara
    Department of Chemical Engineering, Lund University, 221 00 Lund, Sweden.
    In Situ H2 Reduction of Al2O3-Supported Ni- and Mo-Based Catalysts2022In: Catalysts, E-ISSN 2073-4344, Vol. 12, no 7, p. 1-15Article in journal (Refereed)
    Abstract [en]

    Nickel (Ni)-promoted Molybdenum (Mo)-based catalysts are used for hydrotreatment processes in the chemical industry where the catalysts are exposed to high-pressure H2 at elevated temperature. In this environment, the catalyst transforms into the active phase, which involves the reduction of the oxide. Here, we report on the first in situ study on the reduction of alumina supported Ni- and Mo-based catalysts in 1 mbar H2 using ambient-pressure X-ray photoelectron spectroscopy (APXPS). The study confirms that mixing Ni and Mo lowers the reduction temperature of both Ni- and Mo-oxide as compared to the monometallic catalysts and shows that the MoO3 reduction starts at a lower temperature than the reduction of NiO in NiMo/Al2O3 catalysts. Additionally, the reduction of Ni and Mo foil was directly compared to the reduction of the Al2O3-supported catalysts and it was observed that the reduction of the supported catalysts is more gradual than the reduction of the foils, indicating a strong interaction between the Ni/Mo and the alumina support.

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  • 37.
    Ghanavi, Sasha
    et al.
    Malmö University, Faculty of Odontology (OD).
    Malmberg, Natali
    Malmö University, Faculty of Odontology (OD).
    Bond strength between resin cements and yttria-stabilized zirconia (YSZ) materials with different yttria content2021Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Aim: To evaluate how yttria content and different 10-MDP utilization affect the shear bond strength between resin cements and zirconia. 

    Materials and methods: 120 pairs of cubical and cylindrical specimens were manufactured from yttria-stabilized zirconia blocks. The specimens were divided into 12 groups (n=10) according to yttria content (3-YSZ, 4-YSZ and 5-YSZ) and cement system. Two adhesive cements (Panavia FTM2.0 and Panavia V5) and two primers (Clearfil Ceramic Primer Plus and Alloy Primer) were included. The cementation surfaces were air-abraded with aluminum oxide particles, treated with a primer and cemented. After 72 hours of storage in a heating cabinet in a humid environment at 37°C and subsequent artificial aging for 5000 thermocycles, shear bond strength test and failure mode analysis were conducted. 

    Results: No statistical differences in shear bond strength were found between different yttria containing zirconia, nor within each zirconia group, irrespective of cement and primer. 

    Conclusion: Within the limitations of the study, it can be concluded that the bond strength between resin cements used in combination with MDP-containing primers and 3-YSZ, 4-YSZ or 5-YSZ, are sufficient. Thus, the yttria content of zirconia does not seem to affect the adhesion. Furthermore, it was found that a universal silane and MDP-primer gives the same bond strength as an MDP-primer. Lastly, similar bond values can be achieved regardless of MDP-primers being used together with non-MDP or MDP-containing resin cements. 

  • 38. Hagman, Benjamin
    et al.
    Posada-Borbon, Alvaro
    Schaefer, Andreas
    Shipilin, Mikhail
    Zhang, Chu
    Merte, Lindsay Richard
    Malmö University, Faculty of Technology and Society (TS), Department of Materials Science and Applied Mathematics (MTM).
    Hellman, Anders
    Lundgren, Edvin
    Grönbeck, Henrik
    Gustafson, Johan
    Steps Control the Dissociation of CO2 on Cu(100)2018In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 140, no 40, p. 12974-12979Article in journal (Refereed)
    Abstract [en]

    CO2 reduction reactions, which provide one route to limit the emission of this greenhouse gas, are commonly performed over Cu-based catalysts. Here, we use ambient pressure X-ray photoelectron spectroscopy together with density functional theory to obtain an atomistic understanding of the dissociative adsorption of CO2 on Cu(100). We find that the process is dominated by the presence of steps, which promote both a lowering of the dissociation barrier and an efficient separation between adsorbed O and CO, reducing the probability for recombination. The identification of steps as sites for efficient CO2 dissociation provides an understanding that can be used in the design of future CO2 reduction catalysts.

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  • 39. Hansson, T
    et al.
    Warren, Richard
    Malmö högskola, School of Technology (TS).
    Particle and whisker reinforced brittle matrix composites2000In: Carbon/Carbon, Cement, and Ceramic Matrix Composites, Elsevier, 2000, p. 579-609Chapter in book (Other academic)
  • 40.
    Hasholt, Marianne Tange
    et al.
    Tech Univ Denmark, Lyngby, Denmark..
    Fridh, Katja
    Malmö University, Faculty of Technology and Society (TS), Department of Materials Science and Applied Mathematics (MTM).
    Spoerel, Frank
    Fed Waterways Engn & Res Inst, Karlsruhe, Germany..
    Lahdensivu, Jukka
    Tampere Univ, Tampere, Finland..
    Helsing, Elisabeth
    RISE Res Inst Sweden, Gothenburg, Sweden..
    Mueller, Matthias
    Bauhaus Univ Weimar, Weimar, Germany..
    Faheem, Abdul
    Tech Univ Denmark, Lyngby, Denmark..
    Sleiman, Sara Al Haj
    Cent Nantes, Nantes, France..
    Jacobsen, Stefan
    Norwegian Univ Sci & Technol, Trondheim, Norway..
    Nordic Concrete Research workshop: "Accelerated freeze-thaw testing of concrete", Lyngby, 20th April 20222022In: Nordic Concrete Research, ISSN 0800-6377, Vol. 66, no 1, p. 113-133Article in journal (Refereed)
    Abstract [en]

    A one-day Nordic Concrete Research workshop on "Accelerated freeze-thaw testing of concrete" attracted approx. 30 participants. The workshop included presentations on various aspects, such as observed frost damage in the field and the importance of the temperature curve during testing as well as other interactions with the surroundings of the concrete. The workshop also included examples of recent research, which can improve our knowledge about the frost damage mechanism and therefore provide input to improving the standardised test methods. The present paper is a summary of the nine presentations and the discussion arising from the presentations.

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  • 41.
    Havir, Jiri
    Institutionen för maskinteknologi, Lunds universitet.
    Om kantbuckling av pappersbanan vid pappersproduktion2005Licentiate thesis, monograph (Other academic)
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  • 42.
    Hejman, Ulf
    Malmö högskola, School of Technology (TS).
    On initiation of chemically assisted crack growth and crack propagation paths of branching cracks in polycarbonate2010Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Stress corrosion, SC, in some cases gives rise to stress corrosion cracking, SCC, which differs from purely stress intensity driven cracks in many aspects. They initiate and grow under the influence of an aggressive environment in a stressed substrate. They grow at low load and may branch. The phenomenon of SCC is very complex, both the initiation phase and crack extension itself of SCC is seemingly associated with arbitrariness due to the many unknown factors controlling the process. Such factors could be concentration of species in the environment, stress, stress concentration, electrical conditions, mass transport, and so on.In the present thesis, chemically assisted crack initiation and growth is studied with special focus on the initiation and branching of cracks. Polycarbonate plates are used as substrates subjected to an acetone environment. Experimental procedures for examining initiation and branching in polycarbonate are presented. An optical microscope is employed to study the substrate.The attack at initiation is quantified from pits found on the surface, and pits that act as origin for cracks is identified and the distribution is analysed. A growth criterion for surface cracks is formulated from the observations, and it is used to numerically simulate crack growth. The cracks are seen to coalesce, and this phenomenon is studied in detail. Branching sites of cracks growing in the bulk of polycarbonate are inspected at the sample surface. It is found that the total width of the crack branches are approximately the same as the width of the original crack. Also, angles of the branches are studied. Further, for comparison the crack growth in the bulk is simulated using a moving boundary problem based algorithm and similar behaviour of crack branching is found.

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  • 43.
    Hejman, Ulf
    et al.
    Malmö högskola, School of Technology (TS).
    Bjerkén, Christina
    Malmö högskola, School of Technology (TS).
    Environmentally assisted initiation and growth of multiple surface cracks2010In: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 47, no 14-15, p. 1838-1846Article in journal (Refereed)
    Abstract [en]

    The initial stages of stress corrosion on an amorphous polymer is investigated. This is done by exposing stressed specimens of polycarbonate to an acetone and water solution. The surface develops two distinct features of degradation that appear on different length scales when subjected to tensile stress. Small pits form on the surface and make it rough. These pits are in the order of micrometers, and are found to be randomly distributed. They occur even without load and seem to slightly increase in number with increasing stress. In the millimeter domain, visible to the bare eye, surface cracks are formed transverse to the direction of loading. The occurrence of cracks is seen to have a positive stress threshold value, exceeding which, a linear increase of number of cracks with stress is found. The manners in which the cracks grow and coalesce on the surface are examined. It is seen that they do not meet crack tip to crack tip. Instead, they avoid each other initially and coalesce crack tip to crack side. The results are discussed in the light of mechanical considerations. A stress analysis for a few configurations of meeting cracks supports the experimental observations. With assumptions of stress corrosion crack growth and coalescence, a simulation of cracks growing from randomly distributed initiation sites is performed. Similar crack patterns as obtained in the experiments are found.

  • 44.
    Hejman, Ulf
    et al.
    Malmö högskola, School of Technology (TS).
    Ståhle, Per
    Malmö högskola, School of Technology (TS).
    Bjerkén, Christina
    Malmö högskola, School of Technology (TS).
    Experiment och simulering av materialupplösningsspricka2007In: Abstracts Svenska mekanikdagarna, Luleå, Sweden, Luleå tekniska universitet, 2007Conference paper (Other academic)
    Abstract [sv]

    Sprickväg och sprickgrening studeras under brottmekaniska experiment i polykarbonat. Detta material är spänningsoptiskt och fotoelastiska analyser utförs. Sprickväg och sprickgrening beräknas också med hjälp av en adaptiv finit element-metod. Spricktillväxten är ett resultat av spänningsunderstödd, kemiskt eller biologiskt aktiverad, materialupplösning, som helt bestämmer provkroppens geometri inklusive sprickans form och längd. På så sätt är de processer som leder till sprickpropagering inkluderade i en allmän materialupplösningsprocess. Som en konsekvens av detta behövs varken brottkriterium eller sprickvägshypotes. Den fotoelastiska undersökningen jämförs med de numeriska resultaten. Avsaknaden av brottkriterium gör att sprickpropageringsprocessen saknar längdskala. Därmed följer att sprickans bredd skalar med kvadraten på den pålagda lasten medan spricktillväxthastigheten blir oberoende av pålagd last. Förhållandet gör vidare att sprickan förgrenas och att alla grenar fortsätter att växa utan att förlora fart.

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  • 45.
    Hiremath, Praveenkumar
    et al.
    Division of Mechanics, Lund University.
    Melin, Solveig
    Division of Mechanics, Lund University.
    Bitzek, Erik
    Friedrich-Alexander-Universität Erlangen-Nürnberg, Germany ; Computational Materials Design, Düsseldorf, Germany.
    Olsson, Pär A T
    Malmö University, Faculty of Technology and Society (TS), Department of Materials Science and Applied Mathematics (MTM). Division of Mechanics, Lund University.
    Effects of interatomic potential on fracture behaviour in single- and bicrystalline tungsten2022In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 207, p. 1-18, article id 111283Article in journal (Refereed)
    Abstract [en]

    In the present work, we have evaluated the performance of different embedded atom method (EAM) andsecond-nearest neighbour modified embedded atom method (2NN-MEAM) potentials based on their predictive capabilities for modelling fracture in single- and bicrystalline tungsten. As part of the study, a new 2NN-MEAM was fitted with emphasis on reproducing surface, unstable stacking fault and twinning energies as derived fromdensity functional theory (DFT) modelling. The investigation showed a systematic underestimation of surfaceenergies by most EAM potentials, and a significant variation in unstable stacking and twinning fault energies.Moreover, the EAM potentials in general lack the ability to reproduce the DFT traction–separation (TS) curves. The shorter interaction length and higher peak stress of the EAM TS curves compared to the 2NN-MEAM and DFT TS curves result in one order of magnitude higher lattice trapping than for cracks studied with 2NN-MEAM. These differences in lattice trapping can lead to significant qualitative differences in the fracture behaviour. Overall, the new 2NN-MEAM potential best reproduced fracture-relevant material properties and its results were consistent with fracture experiments. Finally, the results of fracture simulations were compared with analytical predictions based on Griffith and Rice theories, for which emerging discrepancies were discussed.

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  • 46. Holmberg, Kenneth
    et al.
    Ronkainen, Helena
    Laukkanen, Anssi
    Wallin, Kim
    Hogmark, Sture
    Jacobson, Staffan
    Wiklund, Urban
    Souza, Roberto M
    Ståhle, Per
    Malmö högskola, School of Technology (TS).
    Residual stresses in TiN, DLC and MoS2 coated surfaces with regard to their tribological fracture behaviour2009In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 267, no 12, p. 2142-2156Article in journal (Refereed)
    Abstract [en]

    Thin hard coatings on components and tools are used increasingly due to the rapid development in deposition techniques, tribological performance and application skills. The residual stresses in a coated surface are crucial for its tribological performance. Compressive residual stresses in PVD deposited TiN and DLC coatings were measured to be in the range of 0.03–4 GPa on steel substrate and 0.1–1.3 GPa on silicon. MoS2 coatings had tensional stresses in the range of 0.8–1.3 on steel and 0.16 GPa compressive stresses on silicon. The fracture pattern of coatings deposited on steel substrate were analysed both in bend testing and scratch testing. A micro-scale finite element method (FEM) modelling and stress simulation of a 2 μm TiN-coated steel surface was carried out and showed a reduction of the generated tensile buckling stresses in front of the sliding tip when compressive residual stresses of 1 GPa were included in the model. However, this reduction is not similarly observed in the scratch groove behind the tip, possibly due to sliding contact-induced stress relaxation. Scratch and bending tests allowed calculation of the fracture toughness of the three coated surfaces, based on both empirical crack pattern observations and FEM stress calculation, which resulted in highest values for TiN coating followed by MoS2 and DLC coatings, being KC = 4–11, about 2, and 1–2 MPa m1/2, respectively. Higher compressive residual stresses in the coating and higher elastic modulus of the coating correlated to increased fracture toughness of the coated surface.

  • 47.
    Holmberg-Kasa, Jacob
    Malmö University, Faculty of Technology and Society (TS), Department of Materials Science and Applied Mathematics (MTM).
    Modeling of Precipitation by Structural Phase-Field Crystal Method2021Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Nickel-based alloys are used in components such gas turbines within the aerospace industry and electric power generation due to its high tensile, rapture and creep strength. Increasing the efficiency of gas turbines are crucial to reduce emissions within the aerospace industry and increasing power gain for electric power generation. Innovation to increase the efficiency relies in part on the development of new nickel-based alloys with beneficial material properties. But also on stable and predictable material behavior during processing and post-processing of the components in the gas turbine. In two prominent material processing fields of precipitation hardened nickel-based alloys, additive manufacturing and welding, strain-age cracking (SAC) is a common phenomenon. SAC is a solid state phenomenon that generally occurs in alloys strengthened with 𝛾′, L12(Pm3m), or 𝛾′′, D022(I4/mmm), phase precipitates during post weld heat treatment or reheating where it manifests as intergranular cracking. Even though the existence of SAC has been known for several decades, its dominant mechanisms are still under considerable debate and the undertaken modeling efforts to gain insight on the phenomenon are virtually non-existent. This study aims to clarify the dominant mechanisms behind strain-age cracking. Breaching this gap would allow for new development for nickel-based alloys within both additive manufacturing and welding. To that extent the goal of this study is to provide tools to aid in clarifying the dominant mechanisms behind strain-age cracking. This is done by implementing the recently developed structural phase-field crystal (XPFC) model and examining the capabilities to model a precipitation event during reheating for a reference binary alloy in two dimensions. To evaluate the strain because of precipitation, a simple method based on the principles of neutron and synchrotron strain scanning is outlined and tested on the limited precipitation event achieved within the study. The XPFC model is capable of modeling precipitation with some restrictions that need further development with extended computational recourses. Lastly, the possibilities to extend the implemented XPFC model to cover nickel-based alloys is discussed.

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  • 48.
    Holzapfel, Damian M.
    et al.
    Rhein Westfal TH Aachen, Mat Chem, Kopernikusstr 10, D-52074 Aachen, Germany..
    Music, Denis
    Malmö University, Faculty of Technology and Society (TS), Department of Materials Science and Applied Mathematics (MTM).
    Hans, Marcus
    Rhein Westfal TH Aachen, Mat Chem, Kopernikusstr 10, D-52074 Aachen, Germany..
    Wolff-Goodrich, Silas
    Max Planck Inst Eisenforsch GmbH, Max Planck Str 1, D-40237 Dusseldorf, Germany..
    Holec, David
    Univ Leoben, Dept Mat Sci, A-8700 Leoben, Austria..
    Bogdanovski, Dimitri
    Rhein Westfal TH Aachen, Mat Chem, Kopernikusstr 10, D-52074 Aachen, Germany..
    Arndt, Mirjam
    Oerlikon Balzers Coating Germany GmbH, Hohe Hum Str 22, D-79650 Schopfheim, Germany..
    Eriksson, Anders O.
    Oerlikon Surface Solut AG, Oerlikon Balzers, Iramali 18, LI-9496 Balzers, Liechtenstein..
    Yalamanchili, Kumar
    Oerlikon Surface Solut AG, Oerlikon Balzers, Iramali 18, LI-9496 Balzers, Liechtenstein..
    Primetzhofer, Daniel
    Uppsala Univ, Dept Phys & Astron, Lagerhyddsvagen 1, S-75120 Uppsala, Sweden..
    Liebscher, Christian H.
    Max Planck Inst Eisenforsch GmbH, Max Planck Str 1, D-40237 Dusseldorf, Germany..
    Schneider, Jochen M.
    Rhein Westfal TH Aachen, Mat Chem, Kopernikusstr 10, D-52074 Aachen, Germany..
    Enhanced thermal stability of (Ti,Al)N coatings by oxygen incorporation2021In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 218, article id 117204Article in journal (Refereed)
    Abstract [en]

    Thermal stability of protective coatings is one of the performance-defining properties for advanced cutting and forming applications as well as for energy conversion. To investigate the effect of oxygen incorporation on the high-temperature behavior of (Ti,Al)N, metastable cubic (Ti,Al)N and (Ti,Al)(OxN1-x) coatings are synthesized using reactive arc evaporation. X-ray diffraction of (Ti,Al)N and (Ti,Al)(OxN1-x) coatings reveals that spinodal decomposition is initiated at approximately 800 degrees C, while the subsequent formation of wurtzite solid solution is clearly delayed from 1000 degrees C to 1300 degrees C for (Ti,Al)(OxN1-x) compared to (Ti,Al)N. This thermal stability enhancement can be rationalized based on calculated vacancy formation energies in combination with spatially-resolved composition analysis and calorimetric data: Energy dispersive X-ray spectroscopy and atom probe tomography data indicate a lower O solubility in wurtzite solid solution compared to cubic (Ti,Al)(O,N). Hence, it is evident that for the growth of the wurtzite, AlN-rich phase in (Ti,Al)N, only mobility of Ti and Al is required, while for (Ti,Al)(O,N), in addition to mobile metal atoms, also non-metal mobility is required. Prerequisite for mobility on the non-metal sublattice is the formation of non-metal vacancies which require larger temperatures than for the metal sublattice due to significantly larger magnitudes of formation energies for the non-metal vacancies compared to the metal vacancies. This notion is consistent with calorimetry data which indicate that the combined energy necessary to form and grow the wurtzite phase is larger by a factor of approximately two in (Ti,Al)(O,N) than in (Ti,Al)N, causing the here reported thermal stability increase. (C) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

  • 49.
    Holzapfel, Damian M.
    et al.
    Materials Chemistry, RWTH Aachen University, Kopernikusstr. 10, DE-52074 Aachen, Germany.
    Music, Denis
    Malmö University, Faculty of Technology and Society (TS), Department of Materials Science and Applied Mathematics (MTM). Materials Chemistry, RWTH Aachen University, Kopernikusstr. 10, DE-52074 Aachen, Germany.
    Mráz, Stanislav
    Materials Chemistry, RWTH Aachen University, Kopernikusstr. 10, DE-52074 Aachen, Germany.
    Karimi Aghda, Soheil
    Materials Chemistry, RWTH Aachen University, Kopernikusstr. 10, DE-52074 Aachen, Germany.
    Etter, Martin
    Deutsches Elektronen-Synchrotron DESY, Notkestr. 85, DE-22607 Hamburg, Germany.
    Ondračka, Pavel
    Materials Chemistry, RWTH Aachen University, Kopernikusstr. 10, DE-52074 Aachen, Germany.
    Hans, Marcus
    Materials Chemistry, RWTH Aachen University, Kopernikusstr. 10, DE-52074 Aachen, Germany.
    Bogdanovski, Dimitri
    Materials Chemistry, RWTH Aachen University, Kopernikusstr. 10, DE-52074 Aachen, Germany.
    Evertz, Simon
    Materials Chemistry, RWTH Aachen University, Kopernikusstr. 10, DE-52074 Aachen, Germany.
    Patterer, Lena
    Materials Chemistry, RWTH Aachen University, Kopernikusstr. 10, DE-52074 Aachen, Germany.
    Schmidt, Paul
    Materials Chemistry, RWTH Aachen University, Kopernikusstr. 10, DE-52074 Aachen, Germany.
    Schökel, Alexander
    Deutsches Elektronen-Synchrotron DESY, Notkestr. 85, DE-22607 Hamburg, Germany.
    Eriksson, Anders O.
    Oerlikon Balzers, Oerlikon Surface Solutions AG, Iramali 18, LI-9496 Balzers, Liechtenstein.
    Arndt, Mirjam
    Oerlikon Balzers Coating Germany GmbH, Hohe-Flum-Straße 22, DE-79650 Schopfheim, Germany.
    Primetzhofer, Daniel
    Department of Physics and Astronomy, Uppsala University, Lägerhyddsvägen 1, SE-75120 Uppsala, Sweden.
    Schneider, Jochen M.
    Materials Chemistry, RWTH Aachen University, Kopernikusstr. 10, DE-52074 Aachen, Germany.
    Influence of ion irradiation-induced defects on phase formation and thermal stability of Ti0.27Al0.21N0.52 coatings2022In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 237, article id 118160Article in journal (Refereed)
    Abstract [en]

    The influence of changes induced by ion irradiation on structure and thermal stability of metastable cubic (Ti,Al)N coatings deposited by cathodic arc evaporation is systematically investigated by correlating experiments and theory. Decreasing the nitrogen deposition pressure from 5.0 to 0.5 Pa results in an ion flux-enhancement by a factor of three and an increase of the average ion energy from 15 to 30 eV, causing the stress-free lattice parameter to expand from 4.170 to 4.206 Å, while the chemical composition of Ti0.27Al0.21N0.52 remains unchanged. The 0.9% lattice parameter increase is a consequence of formation of Frenkel pairs induced by ion bombardment, as revealed by density functional theory (DFT) simulations. The influence of the presence of Frenkel pairs on the thermal stability of metastable Ti0.27Al0.21N0.52 is investigated by scanning transmission electron microscopy, differential scanning calorimetry, atom probe tomography and in-situ synchrotron X-ray powder diffraction. It is demonstrated that the ion flux and ion energy induced formation of Frenkel pairs increases the thermal stability as the Al diffusion enabled crystallization of the wurtzite solid solution is retarded. This can be rationalized by DFT predictions since the presence of Frenkel pairs increases the activation energy for Al diffusion by up to 142%. Hence, the thermal stability enhancement is caused by a hitherto unreported mechanism - the Frenkel pair impeded Al mobility and thereby retarded formation of wurtzite solid solution.

  • 50.
    Huaizhi, He
    et al.
    Malmö University, Faculty of Technology and Society (TS), Department of Materials Science and Applied Mathematics (MTM). Harbin Inst Technol, State Key Lab Adv Welding & Joining, Harbin 150001, Peoples R China; Harbin Elect Corp, Cent Acad, Harbin 150028, Peoples R China.
    Adnan, Safdar
    Malmö University, Faculty of Technology and Society (TS), Department of Materials Science and Applied Mathematics (MTM).
    Wei, Liu-Ying
    Malmö University, Faculty of Technology and Society (TS), Department of Materials Science and Applied Mathematics (MTM).
    Effect of Process Parameter Settings and Thickness on Microstructures of EBM Produced Ti-6AI-4V Alloy2021In: Xiyou jinshu cailiao yu gongcheng, ISSN 1002-185X, Vol. 50, no 2, p. 408-415Article in journal (Refereed)
    Abstract [en]

    The effect of sample dimensions and process parameters (beam current, scan speed, offset focus and scan length) of electron beam melting (EBM) system on microstructure of the EBM built Ti-6A1-4V alloy was investigated. The microstructure of EBM built Ti-6A1-4V alloy consists of columnar grains of prior beta phase. Inside the columnar grain, typical (alpha+beta) structures, namely Widmanstatten alpha platelets and rod-like beta phase formed on the interfaces of the fine alpha grains, are observed. Grain boundary a layer forms along grain boundary of prior beta columnar grain. With the increase of thickness of the test slab, beam energy density and scanning length, the prior beta columnar grain grows along the build direction and diameter of which increases. The columnar grain diameter also decreases with the increase in height of the test slab. With increasing the thickness of the test slab and beam energy density, alpha platelets get coarser.

12345 1 - 50 of 224
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