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  • 1. Abbasalizadeh, A.
    et al.
    Sridar, S.
    Chen, Z.
    Sluiter, M.
    Yang, Y.
    Sietsma, J.
    Seetharaman, Seshadri
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Hari Kumar, K. C.
    Experimental investigation and thermodynamic modelling of LiF-NdF3-DyF3 system2018In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 753, p. 388-394Article in journal (Refereed)
    Abstract [en]

    Electrolysis of molten fluorides is one of the promising methods for the recovery and recycling of rare earth metals from used magnets. Due to the dearth of phase equilibria data for molten fluoride systems, thermodynamic modelling of LiF-DyF3-NdF3 system using the CALPHAD approach was carried out. Gibbs energy modelling for LiF-NdF3 and LiF-DyF3 systems was performed using the constitutional data from literature. Ab initio calculations were used to obtain enthalpy of reaction of LiDyF4, an intermediate phase that is found to exist in the LiF-DyF3 system. Differential thermal analysis was carried out for selected compositions in the NdF3-DyF3 system, in order to determine liquidus and solidus temperatures. The Gibbs energy parameters for the limiting binaries determined in this work is used for modelling the Gibbs energy functions of equilibrium phases in the ternary system. Selected compositions of LiF-NdF3-DyF3 were subjected to DTA in order to validate the calculated phase temperatures involving melt.

  • 2.
    Abbasi, Saeed
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements. KTH, School of Engineering Sciences (SCI), Centres, The KTH Railway Group.
    Characterisation of airborne particles from rail traffic2011Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Since the investigation of wear particles in rail transport started in late-1910s, the high mass concentration of these particles has raised worries among researchers concerned with air quality. However, effective action has yet to be taken because of lack of relevant knowledge. This thesis provides applicable information for the airborne wear particles in rail transport. Some aspects of their characteristics such as diameter size, mass concentration, number concentration, and morphology of particles were investigated in field tests and laboratory tests.The effects on particle characterisations from different operational conditions in the field tests, and applying different braking materials, conducting tests in different applied loads or sliding velocities in the laboratory tests were studied. The main advantage of conducting laboratory tests was to focus on studying particles from one source. The possibility of repetition, using high sensitive instruments and conducting tests at low costs are the other advantages of laboratory studies. Paper A describes how a pin-on-disc machine was used to reproduce similar real operational conditions during mechanical braking in a train. The results were validated by comparing the field tests results with the laboratory studies. The particles morphology and size distribution were also studied.Paper B presents a summary of field tests results. The effects of curve negotiating and applying braking in different real conditions were investigated with an on-board measurement.The element composition of the particles and their potential sources were also investigated outside of the particles morphologies.Paper C presents comprehensive results from laboratory studies on airborne particles from different braking materials. The differences in the particle characteristics in similar test conditions were attributable to different material compositions and dominant wear mechanisms. A new index was introduced in this paper and is suggested to be used as a qualitative factor with regard to the airborne wear particle emission rate.Paper D is a review of the recent studies of exhaust emission and non-exhaust emission from rail vehicles. A summary of results, measurements, adverse health effects, and proposed or applied solutions are reviewed in this paper.

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  • 3.
    AbdElKhalek, Y. M.
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS).
    Awad, M. I.
    Abd El Munim, H. E.
    Maged, S. A.
    Trajectory-based fast ball detection and tracking for an autonomous industrial robot system2021In: International Journal of Intelligent Systems Technologies and Applications, ISSN 1740-8865, E-ISSN 1740-8873, Vol. 20, no 2, p. 126-145Article in journal (Refereed)
    Abstract [en]

    Autonomising industrial robots is the main goal in this paper; imagine humanoid robots that have several degrees of freedom (DOF) mechanisms as their arms. What if the humanoid's arms could be programmed to be responsive to their surrounding environment, without any hard-coding assigned? This paper presents the idea of an autonomous system, where the system observes the surrounding environment and takes action on its observation. The application here is that of rebuffing an object that is thrown towards a robotic arm's workspace. This application mimics the idea of high dynamic responsiveness of a robot's arm. This paper will present a trajectory generation framework for rebuffing incoming flying objects. The framework bases its assumptions on inputs acquired through image processing and object detection. After extensive testing, it can be said that the proposed framework managed to fulfil the real-time system requirements for this application, with an 80% successful rebuffing rate. 

  • 4.
    Adolfi, Sofia
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Slag inclusion formation during solidification of steel alloys and in cast iron2007Licentiate thesis, comprehensive summary (Other scientific)
    Abstract [en]

    This thesis explores the formation of segregation and inclusions during solidification of steel and cast iron. A better understanding of the formation mechanism should result in decreasing fraction of defects during solidification of ingot and strand material.

    Density driven macrosegregation was studied both experimentally and theoretically to see the effect of channel segregation on the total segregation. Formation of these pencil-like segregations is due to natural convection in the solidifying metal caused by liquid enrichment of elements with lower density compared to the bulk. It is suggested to change the composition to compensate for this density difference.

    Inclusion precipitation can be finite by limitations in segregation. Saturated liquid is found in the last solidified areas, often between dendrites. Here the enrichment of the liquid is possible due to microsegregation. Meanwhile crystals form and solidify the elements with low solubility in the solid is pushed out in the remaining liquid. Soon the liquid is saturated to the level where spontaneous formation of inclusions occurs. Microstructure studies by aid of SEM and micro-probe measurements are analysed to find at what point during solidification process the inclusions start to form. In steel making this formation has a detrimental effect on the mechanical properties in contrary to the production of nodular cast iron where the inclusions have a beneficial effect on the graphite formation.

    Inoculation of cast iron aims at reaching higher number density of graphite nodules, nodule morphology modification and control of nodule distribution during solidification. Late precipitation of nucleation sites has shown to have a positive impact on preventing chill. To find the most potent inoculation agent different additives were tested. Special effort has been made to analyse the effect of oxides and sulphides as nucleation sites.

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  • 5.
    Afshari, Davood
    et al.
    Univ Zanjan, Zanjan 4537138791, Iran..
    Mirzaahamdi, Soheil
    Univ Zanjan, Zanjan 4537138791, Iran..
    Barsoum, Zuheir
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Residual Stresses in Resistance Spot Welded AZ61 Mg Alloy2019In: CMES - Computer Modeling in Engineering & Sciences, ISSN 1526-1492, E-ISSN 1526-1506, Vol. 118, no 2, p. 275-290Article in journal (Refereed)
    Abstract [en]

    The use of magnesium alloys has been rapidly increased due to their ability to maintain high strengths at light weights. However weldability of steels and aluminum alloys by using resistance spot weld (RSW) process is a major issue, because it cannot be directly utilized for magnesium alloys. In this study, a structural-thermal-electrical finite element (FE) model has been developed to predict the distribution of residual stresses in RSW AZ61 magnesium alloy. Thermophysical and thermomechanical properties of AZ61 magnesium alloy have been experimentally determined, and have been used in FE model to increase the accuracy of the model. X-ray diffraction (XRD) technique has been utilized to measure the residual stresses in welded samples, and its results have been used to validate the FE model. Comparison study shows that the results obtained by using FE model have a good agreement with the experimental XRD data. In specific, the results show that the maximum tensile residual stress occurs at the weld center while decreases towards the nugget edge. In addition, the effects of welding parameters such as electrical current, welding time, and electrode force have been investigated on the maximum tensile residual stress. The results show that the tensile residual stress in welded joints rises by increasing the electrical current; however, it declines by prolonging the welding time as well as increasing the electrode force.

  • 6.
    Agde Tjernlund, Jessica
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Length-scale effects in yielding and damage development in polymer materials2005Licentiate thesis, comprehensive summary (Other scientific)
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  • 7.
    Agde Tjernlund, Jessica
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Gamstedt, Kristofer
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Gudmundson, Peter
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Length-scale effects on damage development in tensile loading of glass-sphere filled epoxy2006In: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 43, no 24, p. 7337-7357Article in journal (Refereed)
    Abstract [en]

    Particle-reinforced polymers are widely used in load-carrying applications. The effect of particle size on damage development in the polymer is still relatively unexplored. In this study, the effect of glass-sphere size on the damage development in tensile loaded epoxy has been investigated. The diameter of the glass spheres ranged from approximately 0.5-50 mu m. The first type of damage observed was debonding at the sphere poles, which subsequently grew along the interface between the glass spheres and epoxy matrix. These cracks were observed to kink out into the matrix in the radial direction perpendicular to the applied load. The debonding stresses increased with decreasing sphere diameter, whereas the length to diameter ratio of the resulting matrix cracks increased with increasing sphere diameter. These effects could not be explained by elastic stress analysis and linear-elastic fracture mechanics. Possible explanations are that a thin interphase shell may form in the epoxy close to the glass spheres, and that there is a length-scale effect in the yield process which depends on the strain gradients. Cohesive fracture processes can contribute to the influence of sphere size on matrix-crack length. Better knowledge on these underlying size-dependent mechanisms that control damage development in polymers and polymer composites is useful in development of stronger materials. From a methodology point of view, the glass-sphere composite test can be used as an alternative technique (although still in a qualitative way) to hardness vs. indentation depth to quantify length-scale effects in inelastic deformation of polymers.

  • 8.
    Agde Tjernlund, Jessica
    et al.
    KTH, Superseded Departments (pre-2005), Solid Mechanics.
    Gamstedt, Kristofer
    KTH, Superseded Departments (pre-2005), Solid Mechanics.
    Xu, Zhi-Hui
    KTH, Superseded Departments (pre-2005), Materials Science and Engineering.
    Influence of molecular weight on strain-gradient yielding in polystyrene2004In: Polymer Engineering and Science, ISSN 0032-3888, E-ISSN 1548-2634, Vol. 44, no 10, p. 1987-1997Article in journal (Refereed)
    Abstract [en]

    Experimental observations have indicated that the presence of strain gradients has an influence on the inelastic behavior of polymers as well as in other materials such as ceramics and metals. The present study has experimentally quantified length-scale effects in inelastic deformations of the polymer material polystyrene (PS) with respect to the molecular length. The experimental technique that has been used is nano-indentation to various depths with a Berkovich indenter. The hardness has been calculated with the method by Oliver and Pharr, and also by direct measurements of the area from atomic force microscopy. The experiments showed that the length-scale effects in inelastic deformations exist in polystyrene at ambient conditions. The direct method gave a smaller hardness than the Oliver-Pharr method. It was also shown that the length-scale parameter according to Nix and Gao increases with increasing molecular weight. For high molecular weights above a critical value of entanglement, there was no pertinent increase in the length-scale parameter. The length-scale parameter for strain-gradient plasticity has a size of around 0.1 μm for polystyrene.

  • 9.
    Aghdam, Araz Sheibani
    et al.
    Sabanci Univ, Fac Engn & Nat Sci, TR-34956 Istanbul, Turkey..
    Ghorbani, Morteza
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Biomedical Engineering and Health Systems. Sabanci Univ, Fac Engn & Nat Sci, Mechatron Engn Program, TR-34956 Istanbul, Turkey;Sabanci Univ, Ctr Excellence Funct Surfaces & Interfaces NanoDi, TR-34956 Istanbul, Turkey..
    Deprem, Gokberk
    Sabanci Univ, Fac Engn & Nat Sci, Mechatron Engn Program, TR-34956 Istanbul, Turkey..
    Cebeci, Fevzi Cakmak
    Sabanci Univ, Fac Engn & Nat Sci, TR-34956 Istanbul, Turkey.;Sabanci Univ, SUNUM Nanotechnol Res & Applicat Ctr, TR-34956 Istanbul, Turkey..
    Kosar, Ali
    Sabanci Univ, Fac Engn & Nat Sci, Mechatron Engn Program, TR-34956 Istanbul, Turkey.;Sabanci Univ, Ctr Excellence Funct Surfaces & Interfaces NanoDi, TR-34956 Istanbul, Turkey.;Sabanci Univ, SUNUM Nanotechnol Res & Applicat Ctr, TR-34956 Istanbul, Turkey..
    A New Method for Intense Cavitation Bubble Generation on Layer-by-Layer Assembled SLIPS2019In: Scientific Reports, E-ISSN 2045-2322, Vol. 9, article id 11600Article in journal (Refereed)
    Abstract [en]

    The importance of surface topology for the generation of cavitating flows in micro scale has been emphasized during the last decade. In this regard, the utilization of surface roughness elements is not only beneficial in promoting mass transportation mechanisms, but also in improving the surface characteristics by offering new interacting surface areas. Therefore, it is possible to increase the performance of microfluidic systems involving multiphase flows via modifying the surface. In this study, we aim to enhance generation and intensification of cavitating flows inside microfluidic devices by developing artificial roughness elements and trapping hydrophobic fluorinated lubricants. For this, we employed different microfluidic devices with various hydraulic diameters, while roughness structures with different lengths were formed on the side walls of microchannel configurations. The surface roughness of these devices was developed by assembling various sizes of silica nanoparticles using the layer-by-layer technique (D2). In addition, to compare the cavitating flow intensity with regular devices having plain surfaces (D1), highly fluorinated oil was trapped within the pores of the existing thin films in the configuration D2 via providing the Slippery Liquid-Infused Porous Surface (D3). The microfluidic devices housing the short microchannel and the extended channel were exposed to upstream pressures varying from 1 to 7.23 MPa. Cavitation inception and supercavitation condition occured at much lower upstream pressures for the configurations of D2 and D3. Interestingly, hydraulic flip, which rarely appears in the conventional conical nozzles at high pressures, was observed at moderate upstream pressures for the configuration D2 proving the air passage existence along one side of the channel wall.

  • 10.
    Akbarnejad, Shahin
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Investigation on static strength of welded joints2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Although high strength steels represent yield strength up to 1300 MPa, welded structures reveal lowerstrength values. The strongest commercially available electrode provides the yield strength of about900 MPa. Therefore, in welded steels with strength above this type of filler metal, achieving anacceptable global strength is a crucial issue.

    In this master thesis, affects of different welding procedures on static strength of welded jointsof Weldox 960 and Weldox 1100 steels, were studied. These steels are produced by SSAB inOxelösund. Meanwhile, finite element method analyses were applied in order to investigatethe static strength behavior of such weldments under uniaxial tension.

    The welding parameters which were selected as variables are:

    •  Heat input
    • Weld joint geometry
    • Filler metal

    When weld metal is undermatching in strength levels than the base material, by applyingtension the soft weld metal begins to deform before parent metal. At that point thedeformation of resulted soft zone, including the weld metal and the heat affected zone, ishindered by high strength parent metal. Thus, uniaxial stress caused by uniaxial load isconverted to multiaxial stress. This conversion in tension results in increase in the staticstrength of weldment. The increase in strength is emphasized by increase in the width of thewelded joint while the thickness of the plate is kept as constant.

    After experiments and performing FEM studies, it was revealed that the static strength ofWeldox 960 welded joints approaches towards the tensile strength of parent metal by increasein the width of the weldment. In Weldox 1100 joints; a slight increase in tensile properties ofthe weldments, when the width of the sample increases, was observed.

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    Investigation on static strength of welded joints
  • 11.
    Akbarnejad, Shahin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Kennedy, M. W.
    Fritzsch, R.
    Aune, R. E.
    An Investigation on Permeability of Ceramic Foam Filters (CFF)2015In: Light Metals 2015, Wiley , 2015, p. 949-954Chapter in book (Other academic)
    Abstract [en]

    CFF s are used to filter liquid metal in the aluminum industry. CFFs are classified in grades or pores per inch (PPI), ranging froml0-100 PPI. Their properties vary in everything from pore and strut size to window size. CFFs of 80-100 PPI are generally not practical for use by industry, as priming of the filters by gravitational forces requires an excessive metal head. Recently, co-authors have invented a method to prime such filters using electromagnetic Lorentz forces, thus allowing filters to be primed with a low metal head. In the continuation of this research work, an improved experimental setup was developed in the present study to validate previous results and to measure the permeability of different filters, as well as a stack of filters. The study of permeability facilitates estimation of the required pressure drop to prime the filters and the head required to generate a given casting rate.

  • 12.
    Akhtar, Suleman
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Material Factors Influencing Crack Initiation and Propagation During Seamless Tube Rolling of Low Carbon Steel Grades2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Lower hot ductility can lead to cracks in steels. Hot ductility is affected by grain boundary sliding at temperatures higher than A3 and by the presence of thin films of ferrite at grain boundaries at temperatures lower than A3. Grain boundary sliding might occur because of the segregation of harmful elements like sulphur, etc. While thin films of ferrite at grain boundaries lead to easy interlinking of MnS precipitates at grain boundaries and ultimately may cause cracks in the material. Also, stress concentration is higher at thin ferrite films at grain boundaries which for being softer as compared to austenite matrix lead to cracks in the material. Elongated  (Fe, Mn)S sulphides are more detrimental for the hot ductility as compared to round ones. Higher aspect ratio of the precipitates is also dependent on sulphur content. The higher the sulphur content, the higher would be the hot ductility. Silicon, being a ferrite stabilizer, causes the volume fraction of ferrite to increase which improves the hot ductility of the steels. Hot ductility can be improved by adding Boron that segregates to grain boundaries instead of sulphur improving the strength of grain boundaries. Increasing silicon content can lead to higher volume fraction of ferrite thus improving ductility because stress would uniformly be distributed across the grain and not merely on the grain boundaries. Apart from that, decreasing the solution treatment temperature and increasing holding time on solution treatment temperature can lead to lower dissolved content of sulphur and coarser MnS precipitates hence improving hot ductility. 

  • 13.
    Alemani, Mattia
    et al.
    Brembo S.p.A, via Europa 2, 20140 Stezzano, BG, Italy.
    Gialanella, S.
    Department of Industrial Engineering, University of Trento, via Sommarive 9, Povo, Trento 38123, Italy.
    Straffelini, G.
    Department of Industrial Engineering, University of Trento, via Sommarive 9, Povo, Trento 38123, Italy.
    Ciudin, R.
    Department of Industrial Engineering, University of Trento, via Sommarive 9, Povo, Trento 38123, Italy.
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Perricone, G.
    Brembo S.p.A, via Europa 2, 20140 Stezzano, BG, Italy.
    Metinoz, I.
    Brembo S.p.A, via Europa 2, 20140 Stezzano, BG, Italy.
    Dry sliding of a low steel friction material against cast iron at different loads: Characterization of the friction layer and wear debris2017In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 376-377, p. 1450-1459Article in journal (Refereed)
    Abstract [en]

    Pin-on-disc testing was used to investigate the sliding behavior and the wear products of a low-steel friction material against a cast iron disc at different applied loads, to investigate the effect of the temperature rise induced by frictional heating. The testing rig was operated in a clean chamber with a purified incoming air flux. The outgoing flux carries the wear particles to an impactor that counted and sorted them by average diameter and weight. At increasing applied loads, corresponding to a proportional increase of the pin-disc contact temperature, the coverage of both the pin and disc surface by a friction layer was found to increase too. The relevant X-Ray diffraction patterns revealed the presence of a large amount of graphite and different compounds originating from the friction material and from the counterface disc, mainly iron oxides, as concerns this latter. After the test at the lowest investigated load, i.e., 1 kg, the disc worn surface exhibited abrasive grooves and a discontinuous friction layer mainly made of compacted iron oxide particles. After the test at higher loads, i.e., 5 and 7 kg, the disc surface was covered by a compact friction layer. As concerns the friction layer on the pins, most of the ingredients from the friction material were detected, in association with the iron oxides from the disc. These results can be interpreted in terms of the temperature stability range of the phenolic resin used as a binder of the friction material. The characterization of the collected airborne wear debris showed that the particles produced by the low temperature (i.e., low load) test were mostly equiaxed; whereas those produced by the high temperature (i.e., high loads) tests, predominantly displayed a plate-like morphology. The mechanisms of their formation in relation to the characteristics of the friction layers are illustrated and discussed.

  • 14.
    Ali, Rashid
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Palm, Björn E.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    Maqbool, Mohammad H.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Applied Thermodynamics and Refrigeration.
    A Visualization Study During Flow Boiling of R134a In A Horizontal Microchannel2010In: ASME 2010 8th International Conference on Nanochannels, Microchannels, and Minichannels Collocated with 3rd Joint US-European Fluids Engineering Summer Meeting, ICNMM2010, 2010, p. 85-94Conference paper (Refereed)
    Abstract [en]

    In this paper, the experimental flow boiling visualization results of a microchannel are presented and discussed. A series of visualization experiments have been conducted in a horizontal, circular, uniformly heated microchannel, to record the two-phase flow patterns evolved during the boiling process and to study the ebullition process. A high speed camera (REDLAKE HG50LE) with a maximum of 100000 fps together with tungsten lights was used to capture the images along the test section. Microchannel was made of circular fused silica tube having an internal diameter of 0.781 mm and a uniformly heated length of 191 mm. Outside of the test tube was coated with a thin, electrically conductive layer of Indium Tin Oxide (ITO) for direct heating of the test section. Refrigerant R134a was used as working fluid and experiments were performed at two different system pressures corresponding to saturation temperatures of 25 degrees C and 30 degrees C. Mass flux was varied from 100 kg/m(2)s to 400 kg/m(2)s and heat flux ranged from 5 kW/m(2) to 45 kW/m(2). Visualization results show that the bubble growth is restricted by the tube diameter which results in very short existence of isolated bubbly flow regime except essentially restricted to a very short length of test tube. Flow patterns observed along the length were: Isolated bubble, elongated bubble, slug flow, semi annular and annular flow. Rigorous boiling and increased coalescence rates were observed with increase in heat flux. Bubble frequency was observed to increase with both heat and mass flux. A comparison with our previous flow boiling visualization studies, carried out for a test tube of 1.33 mm internal diameter, shows that the number of active nucleation sites is less while the bubble frequency is higher for the current study. Mean bubble length and bubble velocity during elongated bubble flow pattern have also been calculated from the images obtained during the tests.

  • 15. Almessiere, M. A.
    et al.
    Slimani, Y.
    Trukhanov, A. V.
    Sadaqat, A.
    Korkmaz, A. D.
    Algarou, N. A.
    Aydın, H.
    Baykal, A.
    Toprak, Muhammet
    KTH, School of Engineering Sciences (SCI), Applied Physics, Biomedical and X-ray Physics.
    Review on functional bi-component nanocomposites based on hard/soft ferrites: Structural, magnetic, electrical and microwave absorption properties2021In: Nano-Structures and Nano-Objects, ISSN 2352-507X, Vol. 26, article id 100728Article in journal (Refereed)
    Abstract [en]

    Bi-component hard (H) (hexaferrite) and soft (S) (spinel) ferrites nanocomposites are gaining interest scientifically and technically, not only for combining the high magnetization of spinel ferrite nanomaterials and the high coercivity of hexaferrite magnetic nanomaterials but also for the outstanding exchange-coupling behavior among hard and soft magnetic phase. The improved magnetic features lead to produce a new nanocomposite with higher microwave absorption capacity in comparison with ferrites with a single absorption mechanism. Exchange-coupled effect has a potential application based on microwave absorption, recording media, permanent magnets, biomedical and other applications. Intensive studies have been conducted on this topic to produce hard/soft (H/S) ferrite nanocomposites with establishment of exchange coupled effect between the two phases. Preparation methods, microstructure, magnetics features, microwave and dielectric properties, and applications are elaborated. Consequently, a comprehensive effort has been made to contain an original reference investigating in detail the precise outcomes of the published papers. 

  • 16.
    Andersson, Albin
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    A novel chitosan-stearic coating with bee-pollen microcapsules for corrosion protection2020Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    In this project a novel chitosan-stearic acid (CS-SA) coating with bee-pollen microcapsules for encapsulation of 2-mecraptobenzothiazole (MBT) as a waterborne formulation for a biocompatible corrosion protection coating was developed and the coating properties was analyzed. Hydrophobic stearic acid (SA) was crosslinked with via a carbodiimide reaction to form micelles and is assembled on the bee- pollen grains and the chitosan matrix was further self-crosslinked using glutaraldehyde (GA). Stearic acid was used to hydrophobically interact with modified pollen and with further crosslinking with the chitosan, which was proven successful by FTIR results. The encapsulation of anticorrosive agent MBT into pollen was successful and examined by UV-Vis spectroscopy, however, the pollen cannot form a fully stable formulation with the chitosan micelle matrix, partially due to its relatively big size (ca. 20 μm), causing problems with forming a proper barrier protection. The size of the grains and the interference of the carbodiimide crosslinking is the most severe problems with the pollen microcapsules. Therefore, no further testing of the corrosive properties could be done, which requires a dense and stable coating to sustain in salty water for the whole measurement period. As the reference coatings without pollen provided much more promising results, especially when crosslinked with GA, the conclusion is that the reactivity of the pollen is proven difficult to crosslink, and choosing a proper size of a microcontainer and the appropriate encapsulation method in the binder matrix is vital and important for developing a corrosion protective coating.

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  • 17.
    Andersson, Daniel
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Brunnberg, André
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Lind, Emil
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Catalytic Graphitization of Biomass: For the Production of Graphite Materials2021Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    In recent years the material graphite has been heavily studied since its use in widespread applications have increased, for example batteries, vehicles, and solar cells. When the need for this type of material increases the efficiency and the sustainability of the production methods must be taken into consideration. This thesis presents an alternative method to produce graphite from biochar which is renewable. Biochar in combination with a catalyst was used rather than the more traditional method, which is known for its high temperatures and time-consuming procedures. The weight ratio of pure iron (catalyst) to biochar was approximately 22.4 wt-% in the graphite production process. The result was analyzed using X-Ray Diffraction and showed that the method managed to produce a high crystalline graphite at a temperature of 1300 °C within 3 hours. The result also showed that by using a catalyst a graphite sample with a high “degree of graphitization” with a moderate crystal size was produced.

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  • 18.
    Andersson, Robin
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Modeling Radiation Induced Degradation of Lattice Thermal Conductivity2020Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Nuclear power technology is currently experiencing a revolutionary development process and its utilization is researched and debated throughout the world whereas sustainability is one of the most important topics in the material science arena. Some components in a nuclear power plant are subject to an irradiating environment which will cause significant damage to the material over time. Thus, it is of utmost importance that the affected materials are well designed for enduring such conditions because of the extensive lifetime of a nuclear power plant. The highly energetic particles that are inherent with nuclear reactions will generate point defects in the microstructure of the material which will alter its macroscopic behavior.

    Managing heat is crucial in a nuclear power plant and therefore this thesis is devoted to modeling the degradation effect on the lattice thermal conductivity as a result of the point defects, and to establish the intervening relation. This is achieved by ab initio simulations on supercells where the quantum-mechanical forces are calculated with density functional theory and with the generalized gradient approximation for the exchange-correlation term. The phonon Boltz- mann equation is solved by linearization and by using the relaxation-time ap- proximation which allows the lattice thermal conductivity to be calculated for the model. The phonon band modes and the phonon density of states is examined as well.

    To date there are no reports currently found in the literature where this topicis approached with similar methods.

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  • 19.
    Andolfi, Riccardo
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Embedding Carbon Nanotubes Sensors into Carbon Fiber Laminates2022Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The use of Fibre Reinforced Polymer (FRP) composite materials in structural applications has increased in the past decades in high­performance sectors, such as in the automotive and aeronautic industries, for weight reduction purposes. However, FRP composite materials can offer more significant innovation potential. The application of CNTs in conjunction with composite material can allow the creation of multifunctional materials, relying on FRP for the structural side and CNT for the sensing ability. In this master thesis, the embedment of a Vertical Aligned Carbon Nanotube (VACNT) layer into the interlaminar region of Carbon Fibre (CF) laminates to provide polyvalent sensing ability to the material was investigated. In order to obtain accurate results, the sensor had to be isolated from the rest of the laminate. For this reason, the main problem to be solved in this project was the electrical isolation on the CNT layer and its contacts from the layers of CF laminate. This study aims to find a suitable isolation technique in order to apply the CNT sensor technology, developed in previous studies, into CF laminate. Although thought for aerospace applications, these sensors could be applied to different structural components in various fields.

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  • 20.
    Andrén, Peter
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Development and results of the Swedish road deflection tester2006Licentiate thesis, monograph (Other scientific)
    Abstract [en]

    A project to construct a high-speed road deflection tester was initiated in the 1991. A mid-sized truck was used as a carrier for the first prototype. The results were promising and it was decided to build a full-size truck system. The new vehicle, based on a Scania R143 ML, was completed in 1997.

    The Road Deflection Tester (RDT) is equipped with two arrays of twenty noncontact laser sensors that collects transversal surface profiles at normal traffic speeds. One profile, placed between the wheel axles, constitutes an unloaded case. The other profile, just behind the rear axle of the vehicle, constitutes the loaded case. By subtracting the front cross profile from the corresponding rear one, the "deflection profile" is assessed. The deflection is assumed to vary with the stiffness of the road.

    In order to produce a large load on the rear wheels the engine was mounted in the back of the vehicle, slightly behind the rear axle. In testing mode the rear axle force is approximately 112 kN, and the front axle force is about 30 kN. An incremental wheel pulse transducer, two force transducers and two accelerometers, an optical speedometer and a gyroscope are also mounted on the RDT.

    The first test programme was carried out in 1998. Due to the careful choice of test sections, data from these sections still produce the best results. A smaller test programme was carried out in 2001, and a larger one in 2002 when the RDT was taken to England and France for demonstration. Promising results, both on an aggregated scale and for individual test sections, have been obtained. The RDT compares favourably with the Falling Weight Deflectometer.

    Short histories of road construction and road research give some historical and cultural background to the more recent developments. A more comprehensive history of rolling deflectographs presents all devices found in the literature from the start in the mid-fifties when the California Traveling Deflectograph and Lacroix Deflectograph were constructed, to the latest laser based High-Speed Deflectograph. Many references are given for further reading.

    The data acquisition hardware on the RDT system consist of sensors, signal converters, signal processing cards, an industrial computer for data communication, and an ordinary PC for operating the equipment and data storage. The software used to evaluate the data is written entirely in Matlab. Many levels of pre-processing make evaluation relatively fast, and the modularised design makes it easy to implement new evaluation algorithms in a clean and efficient way.

    A literature survey on the deformations of solids under static and moving load is presented in Appendix A. The static case started with Boussinesq in 1885, was much developed in the sixties, but since the eighties only a very limited amount of new results have been published. The moving load case, on the other hand, is still an field of active research and development.

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  • 21.
    Anghel, Clara
    KTH, Superseded Departments (pre-2005), Materials Science and Engineering.
    Studies of transport in oxides on Zr-based materials2004Licentiate thesis, comprehensive summary (Other scientific)
    Abstract [en]

    Zr-based materials have found their main application in the nuclear field having high corrosion resistance and low neutron absorption cross-section. The oxide layer that is formed on the surface of these alloys is meant to be the barrier between the metal and the corrosive environment. The deterioration of this protective layer limits the lifetime of these alloys. A better understanding of the transport phenomena, which take place in the oxide layer during oxidation, could be beneficial for the development of more resistant alloys.

    In the present study, oxygen and hydrogen transport through the zirconia layer during oxidation of Zr-based materials at temperatures around 400C have been investigated using the isotope-monitoring techniques Gas Phase Analysis and Secondary Ion Mass Spectrometry. The processes, which take place at oxide/gas and oxide/metal interface, in the bulk oxide and metal, have to be considered in the investigation of the mechanism of hydration and oxidation. Inward transport of oxygen and hydrogen species can be influenced by modification of the surface properties. We found that CO molecules adsorbed on Zr surface can block the surface reaction centers for H2 dissociation, and as a result, hydrogen uptake in Zr is reduced. On the other hand, coating the Zr surface with Pt, resulted in increased oxygen dissociation rate at the oxide/gas interface. This generated enhanced oxygen transport towards the oxide/metal interface and formation of thicker oxides. Our results show that at temperatures relevant for the nuclear industry, oxygen dissociation efficiency decreases in the order: Pt > Zr2Fe > Zr2Ni > ZrCr2 ≥ Zircaloy-2.

    Porosity development in the oxide scales generates easy diffusion pathways for molecules across the oxide layer during oxidation. A novel method for evaluation of the gas diffusion, gas concentration and effective pore size of oxide scales is presented in this study. Effective pore sizes in the nanometer range were found for pretransition oxides on Zircaloy-2.

    A mechanism for densification of oxide scales by obtaining a better balance between inward oxygen and outward metal transport is suggested. Outward Zr transport can be influenced by the presence of hydrogen in the oxide/metal substrate. Inward oxygen transport can be promoted by oxygen dissociating elements such as Fe-containing second phase particles. The results suggest furthermore that a proper choice of the second-phase particle composition and size distribution can lead to the formation of dense oxides, which are characterized by low oxygen and hydrogen uptake rates during oxidation.

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  • 22.
    Annie, Lundberg
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Environmental transformations of Manganese and Manganese oxide nanoparticles2020Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Engineered nanoparticles (NPs) are produced in increased quantities. Due to this increase, itis vital to understand the full lifecycle and fate of these NPs to prevent any possible environmental stress. As a result of their size, NPs may interact differently with their environment compared to bulk materials with the same composition, this both gives NPs their usage as well as risks. The risks often include unwanted interaction with biological systems which may lead to generation of toxicity. This study focused on environmental transformations of manganese and manganese oxide (Mn3O4) NPs. Applications these nanoparticles are often in battery technology and catalysis. A solution intended to mimic  the composition of freshwater was used as the environmental media to study these transformations. Exposure of NPs was performed both with and without added natural organic matter (NOM). Several experiments were preformed such as Atomic absorption spectroscopy (AAS) for dissolution of the NPs, Nanoparticle Tracking Analysis (NTA) for particle size, and Attenuated total reflection Fourier transform infrared spectroscopy (ATR- FTIR) for adsorption studies. The production of reactive oxygen species (ROS) was also investigated, and simulations of metal speciation using Visual MINTEQ were also performed.

    The results from NTA and AAS (for Mn3O4) were not very reliable due to inconsistencies in the results which were probably caused by problems with preparation. However, for both, the results point towards that the dissolution rates of the particles are slightly slowed down when NOM is added. From ATR-FTIR and the simulations it was confirmed that NOM, carbonate, and sulfur will adsorb onto both particles, possibly in multiple layers. As for increased ROS development, no evidence of such an increase was found. However, the method used does not test for increased hydrogen peroxide development so this would in interesting test as well. Other studies which also would contribute to a more nuanced picture of this system is studies regarding zeta potential and studies which furtherinvestigates the type of adsorption mechanism which occurs at the particles surface.

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  • 23.
    Arif, Muhammad Jalil
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    High Temperature Air/Steam Gasification (HTAG) Of Biomass – Influence of Air/Steam flow rate in a Continuous Updraft Gasifier2013Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Biomass is an important source of energy and the most important fuel worldwide after coal, oil and natural gas. Biomass does not add carbon dioxide to the atmosphere as it absorbs the same amount of carbon in growing as it releases when consumed as a fuel. Its advantage is that it can be used to generate electricity with the same equipment or power plants that are now burning fossil fuels. However, the low energy density of the biomass requires developments and advances in conversion technologies in order to increase process efficiency and reduce pollution. One of the most promising converting methods for treatment of biomass and waste feedstock is gasification. In this study a highly preheated air/steam of temperatures >800oC is introduced to the gasifier which is fed with wood pellets’ feeding rate 40-50 kg/h.

    The system is redesigned to work as a continuous type updraft HTAG. The aim of the studies was to test the performance of an Updraft configuration in various operating conditions using Biomass (wood pellets) as the feedstock, and facing primarily technological difficulties and process limitations. Determining the Temperature distribution along the reactor and synthesis gas composition of the process are reported for various operating parameters.

    During the experiment it is observed that the introduction of more steam flow rate increases the LHV (lower heating value) of the synthesis gases. Three case studies (Case1, Case2, and Case3) are conducted, each case having different biomass feeding rate, steam flow rate and process air flow rate. The result show that the amount of LHV of gas varied from 3 to 4.2 MJ/Nm3, the H2: CO ratio is between 0.5-0.9 and the CO/CO2 ratio has range 1.0-1.7.  Case 3, in which 40 kg/h biomass feeding rate and 80 kg/h Steam flow rate is maintained gives High LHV, high H2/CO ratio and more CO/CO2 ratio among the rest case studies.

    Further improvement can be done within the reactor, increase in retention time and variation of more parameters can examine, in order to get the optimum result in future.

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  • 24.
    Armani, Alessandro
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Development of corrosion resistant coatings using natural biopolymer and pollen2020Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Corrosion is a mechanism that highly reduces the lifetime of metals in different environments, especially in water or moisture environment. The worldwide maintenance cost due to corrosion is estimated in billions of dollars per year, and actual solutions in terms of coating usually contains toxic or environmentally harmful species. With an always increasing restriction by environmental restraints and regulations, a sustainable solution is urgently needed.

    Chitosan, easily obtained from chitin, the second most abundant biopolymer on earth, can be the solution to many problems. Crustacean shell waste is one of the major sources of chitin. Its resource efficiency, biocompatibility, and versatile physicochemical properties for chelation and crosslinking make chitosan a promising candidate as matrix material for biobased anticorrosive application.

    The purpose of the Master Thesis is to combine the properties of chitosan with the high porosity of bee pollen as anticorrosive agent carrier to obtain a fully sustainable solution for anticorrosive protection. The objective of this very ambitious project is to produce a composite material with a triple action: anticorrosive protection of metal surfaces, self-healing property of the coating and anti- biofouling activity.

    Results show that a biopolymer composite in forms of suspension or coatings with all desired components could be achieve. Specifically, a biopolymer nanocomposite composed of chitosan matrix, embedded with pollen grains that were loaded with anticorrosion agent 2- mercatobenzothiazole (MBT) in advance, and with zinc oxide nanoparticles have been produced.

    The physicochemical characterization of the biopolymer composite and its coatings, as well as electrochemical impedance spectroscopy (EIS) measurements on stainless steel plate with such coatings, suggest that a uniform and compact coating is obtained. Despite its good hydrophobicity with maximum contact angle 134.32 ± 3.84° with top coating, the chitosan nanocomposite coating is still permeable to water, partially because of the relatively big size of pollen (ca. 20 μm) that introduces gaps and interferes integrity of the coating. Therefore, a full immersion corrosion resistance is not achieved. In conclusion, phase transfer of hydrophobic pollen into hydrophilic chitosan matrix, MBT loading in pollen, ZnO encapsulation in chitosan, as well as crosslinking of chitosan, were successfully carried out. A coating based on such biopolymer nanocomposite is prepared on stainless steel and investigated on its anti-corrosion property. Future work will be choosing a proper sized pollen as a microcontainer to enhance the integrity of the coating, and eventually endow the coating with the three-in-one function, i.e., anticorrosion, antimicrobial, and self-healing.

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  • 25.
    Arvhult, Carl
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Guéneau, C.
    DEN-Service de Corrosion et du Comportement des Matériaux dans leur Environnement (SCCME), CEA, Université Paris-Saclay, Gif-sur-Yvette, F-91191, France.
    Gossé, S.
    DEN-Service de Corrosion et du Comportement des Matériaux dans leur Environnement (SCCME), CEA, Université Paris-Saclay, Gif-sur-Yvette, F-91191, France.
    Selleby, Malin
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Thermodynamic assessment of the Fe–Ni–Te system2019In: Calphad, ISSN 0364-5916, E-ISSN 1873-2984, Vol. 67, article id 101672Article in journal (Refereed)
    Abstract [en]

    For the purpose of modeling internal corrosion of the stainless steel fuel pins in fast nuclear reactors, the present work presents a thermodynamic description of the Fe–Ni–Te system modeled via the Calphad method. The liquid phase was modeled using the ionic 2-sublattice liquid model. Only binary parameters were optimized in the β2, δ and τ solid phases, to fit the isothermal section at 600 °C. The liquid did not require much adjustment from the extrapolation from the binary Fe–Te, Ni–Te and Fe–Ni systems. The paper presents a re-optimization of the Fe–Te liquid description in order to remove inverted liquid miscibility gaps at high temperatures. The resulting phase diagrams reproduce experimental isothermal sections well, and fits liquidus and solidus data very well. The description will be incorporated into the Thermodynamics of Advanced Fuels - International Database (TAF-ID). This will then be coupled with the Germinal system code to model the fission-product induced corrosion in nuclear fuel pins.

  • 26.
    Arvhult, Carl-Magnus
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Modelling the system Cr-Fe-Ni-Te via the CALPHAD method, DFT and experiments: for fast nuclear reactor applications2019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In the pursuit of safer, more environmentally friendly and sustainable forms of energy production for our ever growing demands, a type of nuclear reactor cooled by liquid metal instead of water is under development. Specific to this type of reactor are special forms of corrosion of the material that encapsulates the fuel pins in the reactor core, called Fuel-Clad Chemical Interaction (FCCI) or Fission Product-induced Liquid Metal Embrittlement (FPLME). This is a complicated chemical process which has been observed in the fuel pins of Sodium-cooled Fast neutron Reactors (SFR). In order to predict the consequences and impact of this corrosion, it must be simulated, which requires a description of the thermodynamics of the elements involved, i.e. Cr--Cs--Fe--Ni--Te--O. This thesis covers the development of a thermodynamic description of the Cr--Fe--Ni--Te system by model parameter optimizations supported by first-principles calculations and experimental investigations.

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  • 27.
    Asplund, Maria
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    Conjugated Polymers for Neural Interfaces: Prospects, possibilities and future challenges2009Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Within the field of neuroprosthetics the possibility to use implanted electrodes for communication with the nervous system is explored. Much effort is put into the material aspects of the electrode implant to increase charge injection capacity, suppress foreign body response and build micro sized electrode arrays allowing close contact with neurons. Conducting polymers, in particular poly(3,4-ethylene dioxythiophene) (PEDOT), have been suggested as materials highly interesting for such neural communication electrodes. The possibility to tailor the material both mechanically and biochemically to suit specific applications, is a substantial benefit with polymers when compared to metals. PEDOT also have hybrid charge transfer properties, including both electronic and ionic conduction, which allow for highly efficient charge injection.

     

    Part of this thesis describes a method of tailoring PEDOT through exchanging the counter ion used in electropolymerisation process. Commonly used surfactants can thereby be excluded and instead, different biomolecules can be incorporated into the polymer. The electrochemical characteristics of the polymer film depend on the ion. PEDOT electropolymerised with heparin was here determined to have the most advantageous properties. In vitro methods were applied to confirm non-cytotoxicity of the formed PEDOT:biomolecular composites. In addition, biocompatibility was affirmed for PEDOT:heparin by evaluation of inflammatory response and neuron density when implanted in rodent cortex.

     

    One advantage with PEDOT often stated, is its high stability compared to other conducting polymers. A battery of tests simulating the biological environment was therefore applied to investigate this stability, and especially the influence of the incorporated heparin. These tests showed that there was a decline in the electroactivity of PEDOT over time. This also applied in phosphate buffered saline at body temperature and in the absence of other stressors. The time course of degradation also differed depending on whether the counter ion was the surfactant polystyrene sulphonate or heparin, with a slightly better stability for the former.

     

    One possibility with PEDOT, often overlooked for biological applications, is the use of its semi conducting properties in order to include logic functions in the implant. This thesis presents the concept of using PEDOT electrochemical transistors to construct textile electrode arrays with in-built multiplexing. Using the electrolyte mediated interaction between adjacent PEDOT coated fibres to switch the polymer coat between conducting and non conducting states, then transistor function can be included in the conducting textile. Analogue circuit simulations based on experimentally found transistor characteristics proved the feasibility of these textile arrays. Developments of better polymer coatings, electrolytes and encapsulation techniques for this technology, were also identified to be essential steps in order to make these devices truly useful.

     

    In summary, this work shows the potential of PEDOT to improve neural interfaces in several ways. Some weaknesses of the polymer and the polymer electronics are presented and this, together with the epidemiological data, should point in the direction for future studies within this field.

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  • 28.
    Asplund, Maria
    et al.
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    von Holst, Hans
    KTH, School of Technology and Health (STH), Neuronic Engineering.
    Inganäs, Olle
    Composite biomolecule/PEDOT materials for neural electrodes2008In: Biointerphases, ISSN 1559-4106, Vol. 3, no 3, p. 83-93Article in journal (Refereed)
    Abstract [en]

    Electrodes intended for neural communication must be designed to meet boththe electrochemical and biological requirements essential for long term functionality. Metallic electrode materials have been found inadequate to meet theserequirements and therefore conducting polymers for neural electrodes have emergedas a field of interest. One clear advantage with polymerelectrodes is the possibility to tailor the material to haveoptimal biomechanical and chemical properties for certain applications. To identifyand evaluate new materials for neural communication electrodes, three chargedbiomolecules, fibrinogen, hyaluronic acid (HA), and heparin are used ascounterions in the electrochemical polymerization of poly(3,4-ethylenedioxythiophene) (PEDOT). The resultingmaterial is evaluated electrochemically and the amount of exposed biomoleculeon the surface is quantified. PEDOT:biomolecule surfaces are also studiedwith static contact angle measurements as well as scanning electronmicroscopy and compared to surfaces of PEDOT electrochemically deposited withsurfactant counterion polystyrene sulphonate (PSS). Electrochemical measurements show that PEDOT:heparinand PEDOT:HA, both have the electrochemical properties required for neuralelectrodes, and PEDOT:heparin also compares well to PEDOT:PSS. PEDOT:fibrinogen isfound less suitable as neural electrode material.

  • 29.
    Assuncao, Milton
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Mathematical modelling of vanadium redox batteriesIndependent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Mathematical modelling using differential equations is an important tool to predict the behaviorof vanadium redox batteries, since it may contribute to improve the device performance and leadto a better understanding of the principles of its operation. Modelling can be complementedby asymptotic analysis as a mean to promote reductions or simplifications that make modelsless complex. Such simplifications are useful in this context, whereas these models usuallyaddresses one cell only – the smallest operating unit – while real applications demand tensor hundreds cells implying on larger computational requirements. In this research, severaloptions for asymptotic reductions were investigated and, applied to different models, were ableto speed up the processing time in 2.46× or reduce the memory requirements up to 11.39%. Thecomputational simulations were executed by COMSOL Multiphysics v.4.4, also by in-housecode developed in MATLAB. The validation of results was done by comparing it to experimentalresults available in literature. Additionally, correlating the results provided by COMSOL withthe ones arising from the implemented sub-routines allowed to validate the developed algorithm.Key-words:

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  • 30.
    Axelsson, Gary
    KTH. Skanska Teknik AB, Stockholm.
    Set-up of driven piles in sand - The effect of constrained dilatancy during loading2018In: ISRM International Symposium 2000, IS 2000, International Society for Rock Mechanics , 2018Conference paper (Refereed)
    Abstract [en]

    The increase in bearing capacity over time (i.e. set-up) of driven piles in non-cohesive soils is often substantial. However, the basic mechanisms behind the phenomenon are still not fully understood. In order to investigate the mechanisms related to set-up a comprehensive field test was performed involving a full-scale driven pile. The pile was instrumented with earth pressure cells and piezometers on the shaft, as well as a pressure cell at the pile toe. The pile was static load tested at different points in time during a period of almost two years. During the whole time period the long-term increase in the horizontal stress, due to stress relaxation, was monitored. However, during the actual loading of the pile a large increase in horizontal stress on the shaft was observed, as a result of confined dilatancy. The results showed that this mechanism had a major influence on the pile capacity and was clearly time-dependent. Furthermore, it was concluded that it was the predominant cause behind the observed set-up. The results provide a valuable insight into how piles behave during loading, as well as clarifying the basic mechanisms involved during set-up.

  • 31. Ayedh, H. M.
    et al.
    Iwamoto, N.
    Nipoti, R.
    Hallén, Anders
    KTH, School of Information and Communication Technology (ICT), Electronics, Integrated devices and circuits.
    Svensson, B. G.
    Formation of D-Center in p-type 4H-SiC epi-layers during high temperature treatments2017In: 11th European Conference on Silicon Carbide and Related Materials, ECSCRM 2016, Trans Tech Publications Inc., 2017, Vol. 897, p. 262-265Conference paper (Refereed)
    Abstract [en]

    The current work is devoted to studying the evolution of deep level defects in the lower half of the 4H-SiC bandgap after high temperature processing and ion implantation. Two as-grown and pre-oxidized 4H-SiC sets of samples have been thermally treated at temperatures up to 1950 °C for 10 min duration using RF inductive heating. Another set of as grown samples was implanted by 4.2 MeV Si ions at room temperature (RT) with different doses (1- 4×108 cm-2). The so-called “D-center” at EV+0.6 eV dominates and forms after the elevated heat treatments, while it shows no change after the ion implantations (EV denotes the valence band edge). In contrast, the concentration of the so-called HK4 level at EV+1.44 eV increases with the implantation dose, whereas it anneals out after heat treatment at ≥ 1700 °C.

  • 32.
    Bagampadde, Umaru
    et al.
    Makerere University, Kampala.
    Karlsson, R.
    KTH.
    Laboratory studies on stripping at bitumen/substrate interfaces using FTIR-ATR2007In: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 42, no 9, p. 3197-3206Article in journal (Refereed)
    Abstract [en]

    A technique based on Fourier Transform Infrared Spectroscopy-Attenuated Total Reflectance (FTIR-ATR) was developed and used to study movement of water into bitumen/substrate interfaces, as well as to characterize stripping. Bitumens from different sources were used and applied on various substrates (silicon, germanium and zinc selenide) as thin films. The influence of bitumen type, substrate type, temperature, film thickness and modification with amines, on water damage was studied. The technique gave information on water flow into interfaces and how stripping possibly occurs. It distinguished between stripping and non-stripping bitumens. At least one of three processes occurred, namely water diffusion, film fracture, and bitumen displacement by water, respectively. The diffusion of water did not obey Fick's law. Stripping was influenced by bitumen source when silicon and germanium substrates were used. Notching the films made the process of water entry almost occur immediately. Additives significantly reduced stripping in the moisture-sensitive bitumen on silicon and germanium substrates, even after film notching. Although, good agreement was observed between tests for the bitumens that did not strip, the tests on stripping bitumens showed poor agreement.

  • 33.
    Baghsheikhi, Saeed
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Spinodal Decomposition in the Binary Fe-Cr System2009Independent thesis Advanced level (degree of Master (Two Years)), 30 credits / 45 HE creditsStudent thesis
    Abstract [en]

    Spinodal decomposition is a phase separation mechanism within the miscibility gap. Its importance in case of Fe-Cr system, the basis of the whole stainless steel family, stems from a phenomenon known as the “475oC embrittlement” which results in a ruin of mechanical properties of ferritic, martensitic and duplex stainless steels. This work is aimed at a better understanding of the phase separation process in   the Fe-Cr system.

    Alloys of 10 to 55 wt.% Cr , each five percent, were homogenized to achieve fully ferritic microstructure and then isothermally aged at 400, 500 and 600oC for different periods of time ranging from 30min to 1500 hours. Hardness of both homogenized and aged samples were measured by the Vickers micro-hardness method and then selected samples were studied by means of Transmission Electron Microscopy (TEM).

     It was observed that hardness of homogenized samples increased monotonically with increasing Cr content up to 55 wt.% which can be attributed to solution hardening as well as higher hardness of pure chromium compared to pure iron.  At 400oC no significant change in hardness was detected for aging up to 1500h, therefore we believe that phase separation effects at 400oC are very small up to this time. Sluggish kinetics is imputed to lower diffusion rate at lower temperatures. At 500oC even after 10h a noticeable change in hardness, for alloys containing 25 wt.% Cr and higher, was observed which indicates occurrence of phase separation. The alloy with 10 wt.% Cr did not show change in hardness up to 200h which suggests that this composition falls outside the miscibility gap at 500oC. For compositions of 15 and 20 wt.% Cr only a small increase in hardness was detected even after 200h of aging at 500oC, which could be due to the small amounts of α´ formed. However, it means that alloys of 15 wt.% Cr and higher are suffering phase separation. For compositions inside the miscibility gap, hardening effect is a result of phase separation either by nucleation and growth or spinodal decomposition. To distinguish between these two mechanisms, TEM studies were performed and we found evidence that at 500oC the Fe-25 wt.% Cr sample decomposes by nucleation  and growth  while that of 35 wt.% Cr  shows characteristics of the spinodal mechanism. For compositions inside the miscibility gap, with increasing Cr content up to 40% the change in hardness generally increased and for 45% and higher it always decreased. This suggests that the composition range corresponding to the spinodal region at 500oC is biased towards the Fe-rich side of the phase diagram. At 600oC only samples of 25, 30 and 35 wt.% Cr were studied because according to the previous studies, the spinodal boundary is most probably located in this composition range. However, no change in hardness was observed even up to 24h. We believe that this means the miscibility line lies below 600oC for alloys containing 35 wt.% Cr and lower. Further investigations are needed to confirm and explain this result. 

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  • 34.
    Balafendiev, Rustam
    et al.
    ITMO Univ, Sch Phys & Engn, St Petersburg 197101, Russia..
    Simovski, Constantin
    Aalto Univ, Sch Elect Engn, Dept Elect & Nanoengn, POB 13000, Aalto 0007, Finland..
    Millar, Alexander J.
    Stockholm Univ, Oskar Klein Ctr Cosmoparticle Phys, Dept Phys, Albanova Univ Ctr, SE-10691 Stockholm, Sweden.;Nordita SU.
    Belov, Pavel
    ITMO Univ, Sch Phys & Engn, St Petersburg 197101, Russia..
    Wire metamaterial filled metallic resonators2022In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 106, no 7, article id 075106Article in journal (Refereed)
    Abstract [en]

    In this work we study electromagnetic properties of a resonator recently suggested for the search of axions-a hypothetical candidate to explain dark matter. A wire medium loaded resonator (called a plasma haloscope when used to search for dark matter) consists of a box filled with a dense array of parallel wires electrically connected to top and bottom walls. We show that the homogenization model of a wire medium works for this resonator without mesoscopic corrections, and that the resonator quality factor Q at the frequency of our interest drops versus the growth of the resonator volume V until it is dominated by resistive losses in the wires. We find that even at room temperature metals like copper can give quality factors in the thousands-an order of magnitude higher than originally assumed. Our theoretical results for both loaded and unloaded resonator quality factors were confirmed by building an experimental prototype. We discuss ways to further improve wire medium loaded resonators.

  • 35.
    Banno, Yuki
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics. Gifu University, Gifu, Japan.
    Kinoshita, K.
    Barsoum, Zuheir
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Numerical investigation of crack opening-closing behavior on pre-fatigued welded joints repaired by HFMI2022In: Welding in the World, ISSN 0043-2288, E-ISSN 1878-6669, Vol. 66, no 4, p. 767-781Article in journal (Refereed)
    Abstract [en]

    This study aims to understand crack opening-closing behavior on pre-fatigued welded joints repaired by High Frequency Mechanical Impact (HFMI). Detailed rat-hole specimen models inserting different depths of rectangle slit in the weld toes to simulate initial cracks were used in the HFMI treatment simulation. Induced compressive residual stress, change of slit geometry, and opening-closing behavior of the slit after HFMI treatment simulation were investigated numerically. The amount of induced compressive residual stress around the slit tip is reduced when slit depth becomes larger, and slit size of about 0.4 mm remains when the slit depth is 2.0 mm. The opening-closing behavior of HFMI treated slit was examined based on change of strains along the slit face. The slit is opened from the bottom side prior to its treated surface. Additionally, the crack opening-closing behavior was investigated experimentally using pre-fatigued out-of-plane gusset welded joints repaired by impact crack closure retrofit treatment. Phased array ultrasonic testing system was used to examine the change of echo height from cracks. It could be concluded that similar behavior as the numerical investigation is observed. From both investigations, experimentally and numerically, the behavior on pre-fatigue welded joints repaired by HFMI could be studied successfully. 

  • 36.
    Banno, Yuki
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics. Department of Civil Engineering, Gifu University, Gifu, Japan.
    Kinoshita, K.
    Barsoum, Zuheir
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Numerical investigation of influence of under- and over- treatment on residual stress state induced by HFMI2021In: Welding in the World, ISSN 0043-2288, E-ISSN 1878-6669, Vol. 65, no 11, p. 2135-2146Article in journal (Refereed)
    Abstract [en]

    This study aims to investigate influence of under- and over-treatment on residual stress state induced by HFMI numerically. Finite element simulations were performed using a flat plate model considering S355 where feed rate and the number of hits were varied. To reduce computational time, the mass scaling method was adopted to the simulations. In addition, in order to survey influence of surface removal on residual stress state, electropolishing was conducted after the HFMI simulation. Additional simulations were performed on bead on plate model considering JIS-SM400 in order to investigate applicability of isotropic hardening model for residual stress estimation. From the results, the mass scaling method can result in reducing computational time more than 90% with reasonable good estimation of the residual stresses.The investigations regarding under- and over-treatment reveal that high feed rate mainly influences residual stress state on the treated surface and the number of hits is independent of amount of induced residual stress. Surface removal after the simulation can result in slightly improving the accuracy of the estimated residual stresses. The simulations to bead on plate model give reasonable results in a depth of around 0.2 mm even when the residual stresses due to welding is disregarded. 

  • 37.
    Banno, Yuki
    et al.
    KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
    Kinoshita, K.
    Ishikawa, T.
    Anami, K.
    Influence of grid blast on the fatigue strength improvement by peening2021In: Bridge Maintenance, Safety, Management, Life-Cycle Sustainability and Innovations - Proceedings of the 10th International Conference on Bridge Maintenance, Safety and Management, IABMAS 2020, CRC Press/Balkema , 2021, p. 3165-3173Conference paper (Refereed)
    Abstract [en]

    In this study, to evaluate the influence of grid blast following to the peening process on the fatigue strength improvement, residual stress measurement and fatigue tests have been conducted. Examined peening processes were UIT, PPP and HP with ICR apparatus. For the residual stress measurement, plate and on-bead specimens made of JIS-SM400, SBHS400, SBHS500 and SBHS700 were used, and X-ray diffraction method was applied to the measurement. The results concluded that the differences in the compressive residual stress distribution in the vicinity of peened area with and without blast are not so significant. For the fatigue tests, out-of-plane gusset welded joint specimens made of JIS-SM490 and SBHS500 were used. Fatigue tests were conducted under stress ratio R=0.0 and 0.5. Fatigue tests showed that fatigue strength of peened specimens with blast are almost the same as that of peened specimens without blast, and those results were observed independently of steel grade and of peening methods.

  • 38. Baron-Wiechec, A.
    et al.
    Widdowson, A.
    Alves, E.
    Ayres, C. F.
    Barradas, N. P.
    Brezinsek, S.
    Coad, J. P.
    Catarino, N.
    Heinola, K.
    Likonen, J.
    Matthews, G. F.
    Mayer, M.
    Petersson, Per
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Rubel, Marek
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    van Renterghem, W.
    Uytdenhouwen, I.
    Global erosion and deposition patterns in JET with the ITER-like wall2015In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 463, p. 157-161Article in journal (Refereed)
    Abstract [en]

    A set of Be and W tiles removed after the first ITER-like wall campaigns (JET-ILW) from 2011 to 2012 has been analysed. The results indicate that the primary erosion site is in the main chamber (Be) as in previous carbon campaigns (JET-C). In particular the limiters tiles near the mid-plane are eroded probably during the limiter phases of discharges. W is found at low concentrations on all plasma-facing surfaces of the vessel indicating deposition via plasma transport initially from the W divertor and from main chamber W-coated tiles; there are also traces of Mo (used as an interlayer for these coatings). Deposited films in the inner divertor have a layered structure, and every layer is dominated by Be with some W and O content.

  • 39.
    Barsoum, Imad
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Ductile failure and rupture mechanisms in combined tension and shear2006Licentiate thesis, comprehensive summary (Other scientific)
    Abstract [en]

    This licentiate thesis is generally concerned with the ductile failure and rupture mechanisms encountered under combined tension and torsion loading. In the first part entitled Paper A, an experimental investigation of the rupture mechanisms in a mid-strength and a high strength steel was conducted employing a novel test configuration. The specimen used was a double notched tube specimen loaded in combined tension and torsion at a fixed ratio. The effective plastic strain, the stress triaxiality and the Lode parameter was determined in the centre of the notch at failure. Scanning electron microscopy of the fractured surfaces revealed two distinctively different ductile rupture mechanisms depending on the stress state. At high stress triaxiality the fractured surfaces were covered with large and deep dimples, suggesting that growth and internal necking of voids being the governing rupture mechanism. At low triaxiality it was found that the fractured surfaces were covered with elongated small shear dimples, suggesting internal void shearing being the governing rupture mechanism. In the fractured surfaces of the high-strength steel, regions with quasi-cleavage were also observed. The transition from the internal necking mechanism to the internal shearing mechanism was accompanied by a significant drop in ductility.

    In the second part entitled Paper B, a micromechanics model based on the theoretical framework of plastic localization into a band introduced by Rice is developed. The model employed consists of a planar band with a square array of equally sized cells, with a spherical void located in the centre of each cell. The periodic arrangement of the cells allows the study of a single unit cell for which fully periodic boundary conditions are applied. The micromechanics model is applied to analyze failure by ductile rupture in experiments on double notched tube specimens subjected to combined tension and torsion carried out by the present authors. The stress state is characterized in terms of the stress triaxiality and the Lode parameter. Two rupture mechanisms can be identified, void coalescence by internal necking at high triaxiality and void coalescence by internal shearing at low triaxiality. For the internal necking mechanism, failure is assumed to occur when the deformation localizes into a planar band and is closely associated with extensive void growth. For the internal shearing mechanism, a simple criterion based on the attainment of a critical value of shear deformation is utilized. The two failure criteria capture the transition between the two rupture mechanisms successfully and are in good agreement with the experimental result.

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  • 40.
    Batista, Marine
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Self-assembly of Fatty Acids of Hair at the water-air interface2020Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    18-methyl eicosanoic acid (18-MEA), which is a branched fatty acid, is found at the outermost surface of mammalian hair with other straight-chain fatty acids such as palmitic acid and stearic acid. However, the precise role of 18-MEA is not yet completely understood. 18-MEA on Cadmium chloride subphase forms curvature at the water/air interface, leading to the formation of 3D-domains that can be easily transferred into solid support allowing to create complex and multi-functional structures. This project investigates if a non-toxic subphase would also lead to the formation of 3D-domains or if it is an intrinsic property of Cadmium chloride; and to investigate if the domain properties were tuneable. A combination of the Langmuir trough and the Atomic Force Microscopy is used. It is shown that a toxic subphase is not necessary and a more benign sodium subphase can be used to obtain 3D-domains. It is also shown that different chains length interact dissimilarly with the branched fatty acid. This results in the formation of very various structures. It is also shown that the subphase, the surface pressure of deposition and the composition of the fatty acid in the monolayer affect the properties of the domain, leading to different size of domain but also different morphology in the domain. Circular domains, elongated domains, continuous labyrinthine structures, dendritic centipede-like structures and no domains are obtained.

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  • 41.
    Baykov, Vitaly
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Point defect interactions and structural stability of compounds2007Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    Theoretical studies of point defect interactions and structural stability of compounds have been performed using density functional theory. The defect-related properties, such as activation energy of diffusion, electronic and magnetic structure of selected materials have been studied.

    The major part of the present work is devoted to a very important material for semiconductor industry, GaAs. The formation energies of intrinsic point defects and the solution energies of 3d transitions in GaAs have been calculated from first principles. Based on the calculated energies, we analysed the site preference of defects in the crystal. The tendency of defects to form clusters has been investigated for the intrinsic defects as well as for impurities in GaAs. The magnetic moment of 3d impurities has been calculated as a function of the chemical environment. The possibility of increasing the Curie temperature in (Ga,Mn)As by co-doping it with Cr impurities has been examined on the basis of calculated total energy difference between the disordered local moment and the ferromagnetically ordered spin configurations. We found that, in order to reach the highest critical temperature, GaAs should be separately doped with either Cr or Mn impurities. Also, we have shown that diffusion barrier of interstitial Mn depends on the charge state of this impurity in (Ga, Mn)As. The formation of defect complexes between interstitial and substitutional Mn atoms, and their influence on the value of diffusion barrier for interstitial Mn, has been studied.

    The pair interactions energies between interstitial oxygen atoms in hcp Zr, Hf and Ti have been calculated using first principles. Based on the calculated energies, the oxygen ordering structures in IVB transition metal solid solutions have been explained. A prediction of nitrogen ordering in Hf-N solid solution has been made.

    The thermodynamic description of intermetallic compounds in the Zr-Sn binary system has been obtained. The conclusion has been made that Zr substitution on the Sn sites takes place in the Zr4Sn phase, which accounts for the unusual stoichiometry of this Cr3Si structure type compound.

    The influence of pressure on the phase stability in the Fe-Si system has been investigated. We have found instability of the hcp Fe0.9Si0.1 random alloy with respect to the decomposition onto the Si-poor hcp Fe alloy and the B2 FeSi under high pressure. The tendency of this decomposition becomes stronger with increasing the applied pressure.

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  • 42.
    Baykov, Vitaly
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Isaev, P. A.
    Moscow State Institute of Steel and Alloys.
    Korzhavyi, Pavel A.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Vekilov, Y. K.
    Moscow State Institute of Steel and Alloys.
    Abrikosov, I. A.
    Linköping University.
    Ab Initio Studies of the Energy Characteristics and Magnetic Properties of Point Defects in GaAs2005In: Physics of the solid state, ISSN 1063-7834, E-ISSN 1090-6460, Vol. 47, no 10, p. 1831-1836Article in journal (Refereed)
    Abstract [en]

    The formation energies of intrinsic point defects and solution energies of transition metal impurities in gallium arsenide are determined on the basis of ab initio calculations using the method of a locally self-consistent Green's function, which is a generalization of the coherent potential approximation. Based on the calculated energies, the conclusion is made that the As-Ga antisite defect is the most common intrinsic defect in GaAs. Calculations showed that transition metal impurities, except for Ni, preferentially occupy gallium sites substitutionally. The magnetic moments of impurity atoms are calculated as a function of the chemical environment. It is shown that, in compensated GaAs, Mn atoms tend to form clusters.

  • 43.
    Baykov, Vitaly
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Korzhavyi, Pavel A.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Smirnova, E. A.
    Department of Theoretical Physics of Steel and Alloys, Moscow.
    Abrikosov, I. A.
    Department of Physics and Measurement Technology, Linköping University.
    Johansson, Börje
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Magnetic properties of 3d impurities in GaAs2007In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 310, no 2, p. 2120-2122Article in journal (Refereed)
    Abstract [en]

    Electronic structure, thermodynamic, and magnetic properties of 3d-transition metal (TM) impurities in GaAs have been studied from first principles using Green's function approach. The studied TM impurities (V, Cr, Mn, and Fe) are found to form substitutional alloys on the Ga sublattice. The possibility of raising the Curie temperature TC in (GaMn) As by co-doping it with Cr impurities was examined on the basis of total energy difference between the disordered local moment (DLM) and the ferromagnetically ordered (FM) spin configurations. The calculated Curie temperature and magnetic moment have maxima for GaAs doped with Cr and Mn. The magnetic properties of Mn-doped GaAs are shown to be more sensitive to antisite As defects than those of Cr-doped GaAs. However, the Cr impurities are sensitive to the presence of acceptor defects, such as vacancies on the Ga sublattice. The investigation of the electronic structure of pseudo-ternary alloys (Ga(1-x-y)MnxCry) As has shown a mutual compensation of Mn and Cr impurities. Therefore, in order to reach the highest critical temperature, GaAs has to be separately doped with Cr or Mn impurities. The GaAs doped with Fe is found to be non-ferromagnetic.

  • 44.
    Bechlioulis, C. P.
    et al.
    School of Mechanical Engineering, Control Systems Lab, National Technical University of Athens, Athens, Greece.
    Heshmati Alamdari, Shahabodin
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Decision and Control Systems (Automatic Control).
    Karras, G. C.
    School of Mechanical Engineering, Control Systems Lab, National Technical University of Athens, Athens, Greece.
    Marantos, P.
    School of Mechanical Engineering, Control Systems Lab, National Technical University of Athens, Athens, Greece.
    Kyriakopoulos, K. J.
    School of Mechanical Engineering, Control Systems Lab, National Technical University of Athens, Athens, Greece.
    Sensor-based motion control of autonomous underwater vehicles, part II: Robust motion control strategies2020In: Autonomous Underwater Vehicles, Institution of Engineering and Technology (IET) , 2020, p. 45-78Chapter in book (Other academic)
    Abstract [en]

    The first section of this chapter presents an NMPC strategy for underwater robotic vehicles operating under various constraints. The purpose of the controller is to guide the vehicle towards specific way -points. Various constraints such as obstacles, workspace boundaries and control input saturation as well as predefined upper bound of the vehicle velocity (requirements for several underwater tasks such as seabed inspection scenario and mosaicking) are considered during the control design. The proposed scheme incorporates the full dynamics of the vehicle in which the ocean currents are also involved. The controller is designed in order to find the optimal thrusts required for minimizing the way -point tracking error. Moreover, the controlinputs calculated by the proposed approach are formulated in a way that the vehicle will exploit the ocean currents, when they are in favor of the way -point tracking mission, which results in reduced energy consumption by the thrusters. In the second part of this chapter, novel position- and trajectory -tracking control schemes for AUVs are presented. The proposed controllers do not utilize the vehicle’s dynamic model parameters and guarantee prescribed transient and steady-state performance despite the presence of external disturbances and kinematic constraints for the case of underactuated vehicles. Moreover, through the appropriate selection of certain performance functions, the proposed scheme can also guarantee the satisfaction of motion and performance constraints imposed by the desired task.

  • 45.
    Bergagio, Mattia
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Engineering.
    Fan, Wenyuan
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Engineering.
    Thiele, Roman
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Engineering.
    Anglart, Henryk
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Engineering.
    Large eddy simulation of thermal mixing with conjugate heat transfer at BWR operating conditions2020In: Nuclear Engineering and Design, ISSN 0029-5493, E-ISSN 1872-759X, Vol. 356, article id 110361Article in journal (Refereed)
    Abstract [en]

    Thermal fatigue occurs in most metals under cyclic heat loads and can threaten the structural integrity of metal parts. Detailed knowledge of these loads is of utter importance to prevent such issues. In this study, a large eddy simulation (LES) with wall-adapting local eddy viscosity (WALE) subgrid model is performed to better understand turbulent thermal mixing in an annulus with a pair of opposing cold inlets at a low axial level (z = 0.15 m) and with a pair of opposing hot inlets at a higher axial level (z = 0.80 m). Each inlet pair is 90 degrees from each other in the azimuthal direction. Conjugate heat transfer between fluid and structure is accounted for. The geometry simplifies a control-rod guide tube (CRGT) in a boiling water reactor (BWR). LES results are compared with measurement data. This is one of the first times BWR conditions are met in both experiments and LES: pressure equals 7.2 MPa, while the temperature difference between hot and cold inlets reaches 216 K. LES temperatures at the fluid-structure interface are fairly correlated with their experimental equivalents, with regard to mean values, local variances, and dangerous oscillation modes in fatigue-prone areas (z = 0.65 - 0.67 m). An elastic analysis of the structure is performed to evaluate stress intensities there. From them, cumulative fatigue usage factors (CUFs) are estimated and used as screening criteria in the subsequent frequency analysis of temperature time series at the fluid-structure interface. The likelihood of initiating a fatigue crack is linked to the maximum CUF, which is 3.2 x 10(-5) for a simulation time of similar to 10 s.

  • 46.
    Bergqvist, Lars
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Korzhavyi, Pavel A.
    KTH, Superseded Departments (pre-2005), Materials Science and Engineering.
    Sanyal, B.
    Mirbt, S.
    Abrikosov, I. A.
    Nordstrom, L.
    Smirnova, E. A.
    Mohn, P.
    Svedlindh, P.
    Eriksson, O.
    Magnetic and electronic structure of (Ga1-xMnx)As2003In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 67, no 20, p. 205201-Article in journal (Refereed)
    Abstract [en]

    We present theoretical calculations of the magnetic and electronic structure of Mn-doped GaAs (in the zinc-blende structure). The magnetic properties are shown to be very sensitive to structural defects, in particular, As antisite defects and Mn at interstitial positions. Only when considering such defects can the experimental magnetic moments be reproduced by first-principles theory. We present a simple model for understanding the connection between the magnetic ordering and the As antisites, and the way in which the defects help to stabilize a partial disordered local-moment state. The connection between the energetics of the Mn substitution and the As antisite concentration is also analyzed. In addition, we compare the calculated magnetic properties and electronic structures of Mn situated on substitutional sites (Mn replacing a Ga atom) and on interstitial sites, where in agreement with observations the interstitial site is found to be less favorable. Finally, combining our first-principles calculations of the spin-wave excitation energies with a classical Heisenberg Hamiltonian we have calculated interatomic exchange interactions, and using Monte Carlo simulations we present theoretical values of the critical temperature as a function of Mn concentration.

  • 47.
    Bergstedt, Edwin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Földhazy, Johan
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Lundstjälk, Alexander
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Vibration Analysis on AC Electric Arc Furnace2015Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    A computerized Fast Fourier Transform system has been used to analyse vibration measurements sampled from a 100-ton electric arc furnace. It has been the hypothesis that patterns in the vibration data would correlate to specific events in the electric arc furnace during the melting process. The theory was that the vibration patterns would be most powerful in multiples of 50 Hz, as the electric arcs operate with a frequency of 50 Hz. It was concluded that the multiples of 50 Hz were dominant. Investigation was made regarding how the amount of scrap affects the amplitude in the vibrations after a defined amount of energy input. It was confirmed that the intensity of the vibrations decreased with increasing mass and basket volume. Another discovery was the M-shaped pattern at the beginning of the melting process. This pattern was statistically analysed. It was found that 71 % of the 41 charges showed an M-shaped correlation. The appearance of this M-shape was analysed regarding power usage, and steel-type. It was concluded that the steel type affected the appearance of the M-shape. The occurrence of flat-bath was also investigated. The theory was that the vibration data would be fairly constant with the occurrence of flat-bath. It was discovered that the vibration data experienced a somewhat constant behaviour towards the end of the melting process in approximately 57 % of the 41 charges. Difficulties were encountered regarding detection of patterns, and correlating them to specific conditions, due to the many parameters that affect the vibration measurements from charge to charge. It was concluded that vibration analysis are unlikely to be used as an absolute way to foresee every event in the electric arc furnace during each charge. But can rather serve as a statistical tool, upon which decisions of how the melting process should be conducted could be based on.

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  • 48. Bergström, Lennart
    et al.
    Allibert, Colette
    Ågren, John
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Kostorz, Gernot
    International Symposium on Inorganic Interfacial Engineering 2006, Stockholm, Sweden, June 20–21, 20062008In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 475, no 1-2, p. 1-Article in journal (Other academic)
  • 49.
    Berling, Victor
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Quality evaluation of PVD coatings on cutting tools by micro-blasting2016Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Sandvik Coromant in Gimo is in need of a good quality evaluation method of adhesion for PVD layers; since the existing testing method is located in Sandvik Coromant’s other location in Västberga. Different micro-blasting methods were investigated in this thesis and the results show that some of the methods could potentially be used for evaluation of adhesion, more specifically the wet blasting methods, M1 and M2. The results also show that the investigated geometry received varying adhesion quality when lower etching bias in the PVD process was used and when different sides was pointing upwards in the PVD furnace. Further investigation will have to be made in order to fully implement micro-blasting as a testing method in production. 

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  • 50.
    Bertling, Moa
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Milstig, Agnes
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Electrified Reforming of Biogas to Hydrogen for Industrial Furnaces with Negative Carbon Emissions: A Feasibility Study2022Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    The steel industry emits large amounts of carbon dioxide, the main emissions are produced inthe process of heating up steel in industrial furnaces of electric arc furnaces (EAF). The purposeof this project was to propose and evaluate a process of reforming biogas to hydrogen to use asfuel for industrial furnaces and result in carbon neutral or carbon negative emissions. This hasbeen done through a literature study reviewing current methods of reforming biogas to hydrogengas, computer simulations in a program called Aspen Plus, thermodynamic calculations and acomparison with the combustion of pure methane. The study resulted in a process theoreticallypossible which would produce negative carbon emissions as a result of carbon capture andstorage techniques. The proposed process is not as efficient as the process of burning puremethane, however, because it can offer carbon negative emissions it is still a more beneficialoption environmentally.

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