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  • 251.
    Aune, Ragnhild E.
    et al.
    KTH, Superseded Departments, Materials Science and Engineering.
    Sridhar, S.
    Hayashi, Miyuki
    Viscosities and Gibbs energies: On a common structural base2004In: High Temperature Materials and Processes, ISSN 0334-6455, E-ISSN 2191-0324, Vol. 22, no 5/6, p. 369-378Article in journal (Refereed)
    Abstract [en]

    The present paper reviews the extensive work carried out with respect to the modeling of viscosities of high temperature melts carried out in the Division of Metallurgy, Royal Institute of Technology (KTH), Stockholm, Sweden. This work was inspired to a great extent by a past collaboration with Professor Ken Mills at Imperial College, London, UK. A thermodynamic approach based on Richardson's theory of ideal mixing of silicates, was used to predict the viscosities of binary silicates. The second derivative of In eta with respect to composition was used to predict the setting of ordering in a homogeneous silicate melt during cooling as it approaches the liquidus temperature. The paper clearly demonstrates the powerfulness of the thermodynamic approach to physical properties of high temperature melts.

  • 252.
    Aune, Ragnhild Elizabeth
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
    Seetharaman, Seshadri
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
    Experimental designs toward an understanding of process phenomena in steelmaking2006In: Iron and Steel Technology, ISSN 1547-0423, Vol. 3, no 12, p. 137-146Article in journal (Refereed)
    Abstract [en]

    Various experimental studies towards the understanding of different process phenomena in iron and steelmaking were presented. Thermal diffusivity measurement was carried out at various temperature to monitor the structural changes occurring in coke. X-ray diffraction measurements were carried out to determine the average crystallite size of graphite along the structural c-axis and in the structural ab plane. It was observed that the apparent thermal diffusivity during the cooling cycle is larger than the heating cycle. Many experiments were also conducted in a high-temperature x-ray diffraction unit, to study the rate of graphitization at any given temperature for a given coke sample. An experimental design for the investigation of the mechanism of reduction in the blast furnace shaft, and the role of coke by dynamic x-ray photography was also carried out. The heating and melting of a mold flux during continuous casting were also simulated in specially designed laboratory.

  • 253.
    Aune, Ragnhild Elizabeth
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
    Seetharaman, Seshadri
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Process Science.
    Experimental designs towards an understanding of process phenomena in steel making2005In: ICS 2005: Proceedings of the 3rd International Congress on the Science and Technology of Steelmaking, 2005, p. 381-392Conference paper (Refereed)
  • 254.
    Austrell, Per-Erik
    et al.
    Division of Structural Mechanics, Lund Institute of Technology.
    Kari, LeifKTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, MWL Structural and vibroacoustics.
    Constitutive Models for Rubber IV: proceedings of the 4th European Conference for Constitutive Models for Rubber, ECCMR 2005, Stockholm, Sweden, 27-29 June 20052005Collection (editor) (Refereed)
    Abstract [en]

    The unique properties of elastomeric materials are taken advantage of in many engineering applications. Elastomeric units are used as couplings or mountings between stiff parts. Examples are shock absorbers, vibration insulators, flexible joints, seals and suspensions etc.

     

    However, the complicated nature of the material behavior makes it difficult to accurately predict the performance of these units, using for example finite element modelling. It is therefore necessary that the constitutive model accurately capture relevant aspects of the mechanical behavior.

     

    The latest development concerning constitutive modelling of rubber is collected in these proceedings. It is the fourth ECCMR-European Conference on Constitutive Modelling in a series on this subject.

     

    Topics included in this volume are, Hyperelastic models, Strength, fracture & fatigue, Dynamic properties & the Fletcher-Gent effect, Micro-mechanical & statistical approaches, Stress softening, Viscoelasticity, Filler reinforcement, and Tyres, fiber & cord reinforced rubber.

  • 255. Avazkonandeh-Gharavol, M. H.
    et al.
    Haddad-Sabzevar, M.
    Fredriksson, Hasse
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Analysis of phase diagram and diffusion coefficient for modeling of microsegregation2017In: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 52, no 3, p. 1446-1460Article in journal (Refereed)
    Abstract [en]

    Thermodynamic description of phase diagram and diffusion data are required to model microsegregation during solidification of metallic alloys. Knowledge about non-equilibrium phase diagrams is essential for modeling of microsegregation in practical situations. Therefore, the aim of this study is to theoretically analyze phase diagram and diffusion data for calculation of microsegregation. For this purpose, aluminum-rich part of the Al-Cu phase diagram was recalculated under non-equilibrium conditions. Effect of excess vacancies formed during solidification was considered on both the phase diagram and diffusion coefficient. The results show that by modifying the phase diagram, the calculated results have better consistency with the experimental results, but there is still room for improvement. When the effect of excess vacancies on diffusion coefficient is considered, the modeling results show a much better correlation with the experimental results. The origin of discrepancies between the calculations and experiments are deeply discussed using current theories in solidification.

  • 256. Avazkonandeh-Gharavol, M. H.
    et al.
    Haddad-Sabzevar, M.
    Fredriksson, Hasse
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Casting of Metals.
    Effect of partition coefficient on microsegregation during solidification of aluminium alloys2014In: International Journal of Minerals, Metallurgy and Materials, ISSN 1674-4799, E-ISSN 1869-103X, Vol. 21, no 10, p. 980-989Article in journal (Refereed)
    Abstract [en]

    In the modeling of microsegregation, the partition coefficient is usually calculated using data from the equilibrium phase diagrams. The aim of this study was to experimentally and theoretically analyze the partition coefficient in binary aluminum-copper alloys. The samples were analyzed by differential thermal analysis (DTA), which were melted and quenched from different temperatures during solidification. The mass fraction and composition of phases were measured by image processing and scanning electron microscopy (SEM) equipped with an energy-dispersive X-ray spectroscopy (EDS) unit. These data were used to calculate as the experimental partition coefficients with four different methods. The experimental and equilibrium partition coefficients were used to model the concentration profile in the primary phase. The modeling results show that the profiles calculated by the experimental partition coefficients are more consistent with the experimental profiles, compared to those calculated using the equilibrium partition coefficients.

  • 257. Avazkonandeh-Gharavol, M. H.
    et al.
    Haddad-Sabzevar, M.
    Fredriksson, Hasse
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Experimental analysis of partition coefficient in Al-Mg alloys2016In: Iranian Journal of Materials Science and Engineering, ISSN 1735-0808, Vol. 13, no 2, p. 62-72Article in journal (Refereed)
    Abstract [en]

    Because the partition coefficient is one of the most important parameters affecting microsegregation, the aim of this research is to experimentally analyse the partition coefficient in Al-Mg alloys. In order to experimentally measure the partition coefficient, a series of quenching experiments during solidification were carried out. For this purpose binary Al-Mg alloys containing 6.7 and 10.2 wt-% Mg were melted and solidified in a DTA furnace capable of quenching samples during solidification. Cooling rates of 0.5 and 5 KJmin were used and samples were quenched from predetermined temperatures during solidification. The fractions and compositions of the phases were measured by quantitative metallography and SEM/EDX analyses, respectively. These results were used to measure the experimental partition coefficients. The resultant partition coefficients were used to model the concentration profile in the primary phase and the results were compared with equilibrium calculations and experimental profiles. The results of calculations based on the experimental partition coefficients show better consistency with experimental concentration profiles than the equilibrium calculations.

  • 258. Avazkonandeh-Gharavol, M. H.
    et al.
    Haddad-Sabzevar, M.
    Fredriksson, Hasse
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Casting of Metals.
    On the microsegregation of Al-Mg alloys by thermal analysis and numerical modeling2014In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 610, p. 462-471Article in journal (Refereed)
    Abstract [en]

    Knowledge about solid fraction versus temperature during solidification is crucial for the control of solidification processes. In the present paper solidification sequence and path of Al-Mg binary alloys containing 6.7 and 10.2 wt.% Mg was investigated by a series of DTA and quenching experiments and numerical modeling in 0.5 and 5 K min(-1) cooling rates. Experimental results show that at both cooling rates, Al-6.7 wt.% Mg solidifies with a single phase structure, but Al-10.2 wt.% Mg solidifies with a two phase structure. According to the results of numerical modeling, good agreement between calculated solidification curves and experimental solid fractions, but poor correlation with concentration profiles. The source of discrepancies is discussed according to different theories of microsegregation.

  • 259.
    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.

  • 260.
    Axelsson, Patrik
    et al.
    KTH, Superseded Departments, Pulp and Paper Technology.
    Gellerstedt, Göran
    KTH, Superseded Departments, Pulp and Paper Technology.
    Lindström, Mikael
    KTH, Superseded Departments, Fibre and Polymer Technology.
    Condensation reactions of lignin during birch Kraft pulping as studied by thioacidolysis2004In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 30, no 12, p. 317-322Article in journal (Refereed)
    Abstract [en]

    The influences of kappa number and ionic strength during birch kraft cooking on the extent of lignin condensation have been studied using thioacidolysis and size exclusion chromatography. Thioacidolysis degrades alkyl-aryl ether bonds in lignin while leaving carbon-carbon and diaryl-ether bonds relatively intact. Therefore, the lignin structures not cleaved during thioacidolysis can be considered as relatively stable and may account,, for example,for the slow residual phase delignification in the kraft cook and for differences in bleachability. It was shown that condensed lignin structures are formed in the residual lignin during birch kraft cooking. The relative amount of such structures increased with decreasing kappa number or with increasing sodium ion concentration in the cook. These structures were also found in a xylan-lignin complex isolated from a birch kraft pulp. The condensed structures were only partly reactive during oxygen delignification.

  • 261. Ayedh, H. M.
    et al.
    Bobal, V.
    Nipoti, R.
    Hallén, Anders
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Svensson, B. G.
    Formation and annihilation of carbon vacancies in 4H-SiC2016In: 16th International Conference on Silicon Carbide and Related Materials, ICSCRM 2015, Trans Tech Publications, 2016, p. 331-336Conference paper (Refereed)
    Abstract [en]

    The carbon vacancy (VC) is a major point defect in high-purity 4H-SiC epitaxial layers limiting the minority charge carrier lifetime. In layers grown by chemical vapor deposition techniques, the VC concentration is typically in the range of 1012 cm-3 and after device processing at temperatures approaching 2000 °C, it can be enhanced by several orders of magnitude. In the present contribution, we show that the cooling rate after high-temperature processing has a profound influence on the resulting VC concentration where a slow rate promotes elimination of VC. Further, isochronal annealing of as-grown and as-oxidized epi-layers protected by a carbon-cap was undertaken between 800 °C and 1600 °C. The results reveal that thermodynamic equilibrium of VC is established rather rapidly at moderate temperatures, reaching a VC concentration of only a few times 1011 cm-3 after 40 min at 1500 °C. Hence, the concept of eliminating VC’s by annealing at moderate temperatures under C-rich equilibrium conditions shows great promise and enables reannealing of high-temperature processed wafers, in contrast to the procedures commonly used today to eliminate VC. In-diffusion of carbon interstitials and out-diffusion of VC’s are discussed as the kinetics processes establishing the thermodynamic equilibrium.

  • 262. 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.

  • 263. Ayedh, H. M.
    et al.
    Nipoti, R.
    Hallén, Anders
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Svensson, B. G.
    Controlling the carbon vacancy concentration in 4H-SiC subjected to high temperature treatment2016In: 16th International Conference on Silicon Carbide and Related Materials, ICSCRM 2015, Trans Tech Publications, 2016, p. 414-417Conference paper (Refereed)
    Abstract [en]

    The carbon vacancy (VC) is the major charge carrier lifetime limiting-defect in 4H-SiC epitaxial layers and it is readily formed during elevated heat treatments. Here we describe two ways for controlling the VC concentration in 4H-SiC epi-layer using different annealing procedures. One set of samples was subjected to high temperature processing at 1950 °C for 3 min, but then different cooling rates were applied. A significant reduction of the VC concentration was demonstrated by the slow cooling rate. In addition, elimination of the VC’s was also established by annealing a sample, containing high VC concentration, at 1500 °C for a sufficiently long time. Both procedures clearly demonstrate the need for maintaining thermodynamic equilibrium during cooling.

  • 264.
    Ayedh, H. M.
    et al.
    Norway.
    Nipoti, R.
    Italy.
    Hallén, Anders
    KTH, School of Electrical Engineering and Computer Science (EECS), Electronics, Integrated devices and circuits.
    Svensson, B. G.
    Norway.
    Kinetics modeling of the carbon vacancy thermal equilibration in 4H-SiC2018In: International Conference on Silicon Carbide and Related Materials, ICSCRM 2017, Trans Tech Publications, 2018, p. 233-236Conference paper (Refereed)
    Abstract [en]

    The carbon vacancy (VC) is a major limiting-defect of minority carrier lifetime in n-type 4H-SiC epitaxial layers and it is readily formed during high temperature processing. In this study, a kinetics model is put forward to address the thermodynamic equilibration of VC, elucidating the possible atomistic mechanisms that control the VC equilibration under C-rich conditions. Frenkel pair generation, injection of carbon interstitials (Ci’s) from the C-rich surface, followed by recombination with VC’s, and diffusion of VC’s towards the surface appear to be the major mechanisms involved. The modelling results show a close agreement with experimental deep-level transient spectroscopy (DLTS) depth profiles of VC after annealing at different temperatures.

  • 265. Aygul, Mustafa
    et al.
    Al-Emrani, Mohammad
    Barsoum, Zuheir
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering. Khalifa University of Science Research and Technology, United Arab Emirates.
    Leander, John
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    An investigation of distortion-induced fatigue cracking under variable amplitude loading using 3D crack propagation analysis2014In: Engineering Failure Analysis, ISSN 1350-6307, E-ISSN 1873-1961, Vol. 45, p. 151-163Article in journal (Refereed)
    Abstract [en]

    The distortion-induced fatigue cracks in the welded details of the Soderstrom Bridge are analytically and numerically investigated by performing 3D crack propagation analyses with variable amplitude fatigue loading. In the crack propagation analyses, the effects of bridge loading are defined on the basis of the field measurements in order to simulate crack growth and predict the residual fatigue life of the studied detail as accurately as possible. The effect of crack closure and crack direction while considering the most common criteria is also studied. The results are compared with those obtained from the crack propagation analyses with constant amplitude fatigue loading presented in Ayg l et al. [1]. The results of the crack growth simulations with variable amplitude fatigue loading have generally shown good agreement with the real crack formation and reveal that the crack growth rates are different in different directions. The crack behaviour in the damaged detail is mainly controlled by the loading and geometrical arrangement of the detail components. There is generally a significant difference between constant and variable amplitude fatigue crack growth analyses and the variable amplitude fatigue crack growth analyses yield more conservative results. The main reason for this difference is the bridge loading and the number of stress cycles defined in the analyses. The crack direction criteria studied in this investigation showed basically the same crack formation and crack growth rate.

  • 266. Aygül, M.
    et al.
    Al-Emrani, M.
    Barsoum, Zuheir
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Leander, John
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Investigation of distortion-induced fatigue cracked welded details using 3D crack propagation analysis2014In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 64, p. 54-66Article in journal (Refereed)
    Abstract [en]

    The behaviour of distortion-induced fatigue cracks in welded details in an existing bridge was studied analytically by performing crack propagation analysis based on linear elastic fracture mechanics. The real load history of the bridge was obtained from strain measurements. These loads were utilised to examine the crack growth rate and the residual service life of the cracked detail. Moreover, the effectiveness, accuracy and applicability of the crack propagation analysis on bridge structures were investigated by simulating a complex case of fatigue cracking using several crack propagation analyses. The results of the analyses revealed that the fatigue crack in the studied details had significantly different crack growth characteristics in different directions. In the thickness direction, for instance, the crack was seen to propagate at a certain rate, which increased with the propagated crack from the beginning and, as expected, the crack propagation rate decreased when the crack grew longer. The crack was subsequently arrested half way through the thickness of the plate. In the longitudinal direction, the crack was not, however, arrested in the same way as in the thickness direction and it continued to propagate at a reduced yet constant crack growth rate. The results also revealed that, even though distortion-induced fatigue cracking was usually caused by a mixed-mode condition (i.e. a combination of modes I, II and III), the governing propagation mode is still mode I. Furthermore, it was also observed that the contribution of modes II and III to crack propagation was very little and dependent on the location of the propagated crack front, as well as the geometrical configuration of the cross-beam.

  • 267.
    Aytekin, Kasim
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Characterization of machinability in lead-free brass alloys2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Recent legislation has put focus on the toxic nature of lead as an alloying element in brass products. Watersupply systems are of biggest concern where suspected lead leakages from brass products are threatening human health.

    A comprehensive study has been conducted in order to characterize the machinability of lead-free brass alloys to provide the industry with necessary information to assist a replacement of the leaded alternatives. The characterization has focused on two particular machining processes, namely turning and drilling and has been based on cutting force generation and chip formation. While the turning tests aimed to characterize the machinability by comparing two lead-free alloys (CW511L and AquaNordic®) with a leaded alloy (CW625N), drilling tests aimed to characterize machinability of the lead-free AquaNordic® alloy particularly, with the main focus put on the impact of tool geometry on machinability.

    The results have shown that significantly higher cutting forces are generated during turning of lead-free alloys as compared to the leaded. There was, however, no significant difference between the two lead-free alloys regarding cutting forces while chip formation is improved for AquaNordic®. Drilling tests have shown that the machinability of the lead-free AquaNordic® alloy can be improved by increasing the tool rake angle and decreasing tool diameter.

    Based on the results from this thesis work, it has been concluded that the machinability of lead-free brass alloys is sufficiently good to be able to be adopted by the industry. However, improvement is necessary inorder to fulfill the requirement needed to replace the leaded alternatives.

  • 268.
    Azizi Samir, M. A. S.
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Alloin, F.
    Dufresne, A.
    High performance nanocomposite polymer electrolytes2006In: Composite interfaces (Print), ISSN 0927-6440, E-ISSN 1568-5543, Vol. 13, no 4-6, p. 545-559Article in journal (Refereed)
    Abstract [en]

    Solid lithium-conducting nanocomposite polymer electrolytes based on poly(oxyethylene) (POE) were prepared using high aspect ratio cellulosic whiskers and lithium imide salt, LiTFSI. The cellulosic whiskers were extracted from tunicate - a sea animal - and consisted of slender parallelepiped rods that have an average length around 1 μm and a width close to 15 nm. High performance nanocomposite electrolytes were obtained. The filler provided a high reinforcing effect, despite the favorable cellulose/POE interactions that were expected to decrease the possibility of interwhisker connection and formation of a percolating cellulosic network, while a high level of ionic conductivity was retained with respect to unfilled polymer electrolytes. Cross-linking and plasticizing of the matrix as well as preparation of the composites from an organic medium were also investigated.

  • 269. Babonas, G. J.
    et al.
    Reza, A.
    Simkiene, I.
    Sabataityte, J.
    Baran, M.
    Szymczak, R.
    Karlsson, Ulf O.
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Suchodolski, Arturas
    KTH, School of Information and Communication Technology (ICT), Material Physics, Material Physics, MF.
    Optical properties of Fe-doped silica films on Si2006In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 252, no 15, p. 5391-5394Article in journal (Refereed)
    Abstract [en]

    Optical properties of Fe-doped silica films on Si were investigated by ellipsometric technique in the region 1-5 eV. Samples were produced by sol-gel method. Precursors were prepared by mixing tetraethoxysilane (TEOS) solution in ethanol and water with aqueous solution of Fe-chloride or Fe-acetate. The coating solution was deposited on Si substrates by spin on technique. The size of Fe-containing nanometric-sized particles depended on technology and varied from 20 to 100 nm. Optical response of complex hybrid samples SiO2:Fe/Si was interpreted in a multi-layer model. In the inverse problem, the Maxwell equations were solved by transfer matrix technique. Dielectric function of Fe-doped silica layers was calculated in the model of effective media. Analysis of optical data has shown that various Fe-oxides formed. Experimental data for films obtained from precursors with Fe-acetate and annealed in hydrogen were well described by the model calculations taking into account a small contribution 1-5% of metal Fe imbedded in silica. The Fe/Fe-O contribution to optical response increased for samples grown from FeCl3-precursor. Ellipsometric data for Fe-doped silica films on Si were interpreted taking into account the structural AFM studies as well as the results of magnetic measurements.

  • 270.
    Babu, Prasath
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Indian Institute of Science, Bangalore, India.
    Vamsi, K. V.
    Karthikeyan, S.
    On the formation and stability of precipitate phases in a near lamellar γ-TiAl based alloy during creep2018In: Intermetallics (Barking), ISSN 0966-9795, E-ISSN 1879-0216, Vol. 98, p. 115-125Article in journal (Refereed)
    Abstract [en]

    The formation, evolution and stability of metastable phases observed in the γ-TiAl based alloy Ti-47Al-2Cr-2Nb was studied under creep deformation with stress applied at two different hard orientations in a highly textured as-cast + HIPed material. Previously we have reported that the metastable phase Ti(Al,Cr)2 with C14 Laves phase structure forms at the γ-α2 interface which acts as sink for the alloying elements ejected from the dissolving α2 phase and also expected to effectively control the interface stresses through short range diffusion and modifications in the chemical composition [1]. Ab initio density functional theory based calculations were carried out to evaluate the effect of choice of lattice position and site occupancy of aluminium atoms in the Ti(Al,Cr)2 structure on the lattice parameter variation and thermodynamic stability. C14 with the composition 25 at. % Al was found to have lattice parameter values close to the inter-planar spacing of <110>γ and <10-10>α2 which would have a lower misfit with C14 across the interface. From the cohesive energy calculations, Laves phase C14 with a constrained lattice parameter due to the adjoining phases, exhibits higher stability than the B2 and L10 structures across a range of compositions studied. Electron diffraction simulations of C14 with a composition of 25% Al compared with the experimental data suggest that the structure C14 has taken up either a random site occupancy compared to a specific choice of ordering to minimize the interfacial stress. Though the experimental evidences do not strongly support a long-range ordering theory in C14, short-range ordering could be a tangible choice for alleviating interface misfits. The ability of C14 to assume different lattice parameters at and far from the α2-γ interface also suggest that the C14 acts as buffer layer between α2 and γ phases in the presence of local stresses, although this is not the thermodynamically expected phase at the temperature of creep experiment.

  • 271. Backstrom, Marie
    et al.
    Jensen, Anna
    Brännvall, Elisabet
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Influence of chip presteaming conditions on kraft pulp composition and properties2016In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 70, no 5, p. 393-399Article in journal (Refereed)
    Abstract [en]

    Presteaming is a well-established technique in pulp mills, which improves cooking liquor impregnation by removing air from within and between chips. The aim of the study was to investigate how conditions during steaming affect the subsequent kraft cook and properties of the obtained pulp. It was found that higher pressure and temperature during chip presteaming led to increased degradation and dissolution of hemicelluloses. Lower refinability and tensile index was obtained for pulps cooked after presteaming at high pressure and for a long time.

  • 272.
    Badal Tejedor, Maria
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Surface and Corrosion Science. RISE Res Inst Sweden, Stockholm, Sweden..
    Nordgren, Niklas
    RISE Res Inst Sweden, Stockholm, Sweden..
    Schuleit, Michael
    Novartis Pharma AG, Basel, Switzerland..
    Millqvist-Fureby, Anna
    RISE Res Inst Sweden, Stockholm, Sweden..
    Rutland, Mark W.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemistry, Surface and Corrosion Science. RISE Res Inst Sweden, Stockholm, Sweden..
    AFM colloidal probe measurements implicate capillary condensation in punch-particle surface interactions during tableting2019In: Abstracts of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 257Article in journal (Other academic)
  • 273. Badia, J. D.
    et al.
    Reig-Rodrigo, P.
    Teruel-Juanes, R.
    Kittikorn, Thorsak
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. Prince of Songkla University, Thailand.
    Strömberg, Emma
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Ek, Monica
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Karlsson, Sigbritt
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Ribes-Greus, A.
    Effect of sisal and hydrothermal ageing on the dielectric behaviour of polylactide/sisal biocomposites2017In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 149, p. 1-10Article in journal (Refereed)
    Abstract [en]

    The dielectric properties of virgin polylactide (PLA) and its reinforced composites with different weight amounts of sisal fibres were assessed at broad temperature (from −130 °C to 130 °C) and frequency ranges (from 10−2–107 Hz), before and after being subjected to accelerated hydrothermal ageing. The synergetic effects of both the loading of sisal and hydrothermal ageing were analysed by means of dielectric relaxation spectra. The relaxation time functions were evaluated by the Havriliak-Negami model, substracting the ohmic contribution of conductivity. The intramolecular and intermolecular relaxations were respectively analysed by means of Arrhenius and Vogel-Fulcher-Tammann-Hesse thermal activation models. The addition of fibre increased the number of hydrogen bonds, which incremented the dielectric permittivity and mainly hindered the non-cooperative relaxations of the biocomposites by increasing the activation energy. Hydrothermal ageing enhanced the formation of the crystalline phase at the so-called transcrystalline region along sisal. This fact hindered the movement of the amorphous PLA fraction, and consequently decreased the dielectric permittivity and increased the dynamic fragility.

  • 274.
    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.

  • 275.
    Bagheri, Mehdi
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Stille, Håkan
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Investigation of model uncertainty for block stability analysis2011In: International journal for numerical and analytical methods in geomechanics (Print), ISSN 0363-9061, E-ISSN 1096-9853, Vol. 35, no 7, p. 824-836Article in journal (Refereed)
    Abstract [en]

    The application of probabilistic design, such as FORM, is expanding rapidly in the design of geotechnical structures. The analytical solution proposed by Crawford and Bray for analyzing block stability can be used as a performance function to carry out probabilistic design. The solution benefits from considering both clamping forces and joint stiffness. However, imperfect assumptions and simplifications in the solution generate model uncertainties. The amount of model uncertainty must be considered in order to assess a reliable design. The purpose of this paper is to identify when the analytical solution is applicable and quantify the model uncertainty of the solution. The amount of model uncertainty for the analytical solution has been assessed for different conditions. The results show that at a shallow depth with a low value of in situ stress ratio (horizontal stress/vertical stress), the analytical solution predicts that the block is stable whereas DEM shows that the block is unstable. The results of the analyses indicate that in cases with low stress ratio, cases with high anisotropy of joint stiffness or the case of a semiapical angle close to the friction angle, the accuracy of the analytical solution is low. Neglecting key parameters, such as the absolute value of joint shear and normal stiffness, vertical in situ stress and its influence on joint relaxation generate model uncertainty in the analytical solution. The analyses show that by having more information about the key parameters, the model uncertainty factor could be identified more precisely.

  • 276.
    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. 

  • 277.
    Bai, Haitong
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    A Study of the Swirling Flow Pattern when Using TurboSwirl in the Casting Process2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The use of a swirling flow can provide a more uniform velocity distribution and a calmer filling condition according to previous studies of both ingot and continuous casting processes of steel. However, the existing swirling flow generation methods developed in last decades all have some limitations. Recently, a new swirling flow generator, the TurboSwirl device, was proposed. In this work, the convergent nozzle was studied with different angles. The maximum wall shear stress can be reduced by changing the convergent angle between 40º and 60º to obtain a higher swirl intensity. Also, a lower maximum axial velocity can be obtained with a smaller convergent angle. Furthermore, the maximum axial velocity and wall shear stress can also be affected by moving the location of the vertical runner. A water model experiment was carried out to verify the simulation results of the effect of the convergent angle on the swirling flow pattern. The shape of the air-core vortex in the water model experiment could only be accurately simulated by using the Reynolds Stress Model (RSM). The simulation results were also validated by the measured radial velocity in the vertical runner by the ultrasonic velocity profiler (UVP). The TurboSwirl was reversed and connected to a traditional SEN to generate the swirling flow. The periodic characteristic of the swirling flow and asymmetry flow pattern were observed in both the simulated and measured results. The detached eddy simulation (DES) turbulence model was used to catch the time-dependent flow pattern and the predicted results agree well with measured axial and tangential velocities. This new design of the SEN with the reverse TurboSwirl could provide an almost equivalent strength of the swirling flow generated by an electromagnetic swirling flow generator. It can also reduce the downward axial velocities in the center of the SEN outlet and obtain a calmer meniscus and internal flow in the mold.

  • 278.
    Bai, Haitong
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Ersson, Mikael
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Jonsson, Par
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Effect of TurboSwirl Structure on an Uphill Teeming Ingot Casting Process2015In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 46, no 6, p. 2652-2665Article in journal (Refereed)
    Abstract [en]

    To produce high-quality ingot cast steel with a better surface quality, it would be beneficial for the uphill teeming process if a much more stable flow pattern could be achieved in the runners. Several techniques have been utilized in the industry to try to obtain a stable flow of liquid steel, such as a swirling flow. Some research has indicated that a swirl blade inserted in the horizontal and vertical runners, or some other additional devices and physics could generate a swirling flow in order to give a lower hump height, avoid mold flux entrapment, and improve the quality of the ingot products, and a new swirling flow generation component, TurboSwirl, was introduced to improve the flow pattern. It has recently been demonstrated that the TurboSwirl method can effectively reduce the risk of mold flux entrapment, lower the maximum wall shear stress, and decrease velocity fluctuations. The TurboSwirl is built at the elbow of the runners as a connection between the horizontal and vertical runners. It is located near the mold and it generates a tangential flow that can be used with a divergent nozzle in order to decrease the axial velocity of the vertical flow into the mold. This stabilizes flow before the fluid enters the mold. However, high wall shear stresses develop at the walls due to the fierce rotation in the TurboSwirl. In order to achieve a calmer flow and to protect the refractory wall, some structural improvements have been made. It was found that by changing the flaring angle of the divergent nozzle, it was possible to lower the axial velocity and wall shear stress. Moreover, when the vertical runner and the divergent nozzle were not placed at the center of the TurboSwirl, quite different flow patterns could be obtained to meet to different requirements. In addition, the swirl numbers of all the cases mentioned above were calculated to ensure that the swirling flow was strong enough to generate a swirling flow of the liquid steel in the TurboSwirl.

  • 279.
    Bai, Haitong
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Ersson, Mikael
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Jönsson, Pär
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    The physical and mathematical modelling of swirling flow by turboswirl in an uphill teeming ingot casting process2015In: Proceedings of the 6th International Congress on the Science and Technology of Steelmaking, ICS 2015, Chinese Society for Metals , 2015, p. 473-476Conference paper (Refereed)
    Abstract [en]

    Ingot casting is widely used to produce some certain specialty steel grades. During the process of teeming the liquid steel from the ladle to the mould for a final solidification, the high velocity of the liquid steel can result in an uneven flow pattern either in the vertical and horizontal runners or in the mould. This can cause some serious problems, such as a high erosion of refractory walls or a mould flux entrapment. Here, some research indicate that a swirling flow is beneficial for making the flow pattern even and for reducing turbulence in the runners. Recently, a new swirling flow generation component, TurboSwirl, was applied to improve the flow pattern of the liquid steel as it flows into the mould so that a more stable flow could be obtained. The TurboSwirl is located on the intersection of the horizontal and vertical runners near the mould. It generates a tangential flow that can be used with an expanding nozzle with a flaring angle in order to decrease the vertical flow velocity. Moreover, a mathematical model has been developed to optimize the geometry of the physical model. The results shows that a much more beneficial flow pattern can be obtained by reducing the flaring angle or moving the vertical runner to an off-center position of the TurboSwirl, according to the numerical models. Therefore, a water modelling experiment was built, including the TurboSwirl, one mould and the runners. Tracers will be mixed into the water to detect the flow pattern and the velocity of the fluid would be recorded by a digital motion analysis recorder for later analysis. Firstly, different flaring angles of the expanding nozzle were simulated and compared. The results could supply a good support to the following water modelling experiments and to prove that the TurboSwirl setup produces a much calmer initial filling of the mould, compared to a conventional setup.

  • 280.
    Bai, Haitong
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Ersson, Mikael
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Jönsson, Pär G.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    An Experimental and Numerical Study of Swirling Flow Generated by TurboSwirl in an Uphill Teeming Ingot Casting Process2016In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 56, no 8, p. 1404-1412Article in journal (Refereed)
    Abstract [en]

    A swirling flow has been demonstrated to be beneficial for making the flow pattern even and to reduce turbulence during filling in ingot casting. A new swirling flow generation device, TurboSwirl, was applied to improve the flow pattern of the liquid steel as it flows into the mold so that a more stable flow could be obtained. A water model was built including the TurboSwirl with different flaring angles of the divergent nozzle, according to a former numerical study indicating that a much more beneficial flow pattern could be obtained by reducing the flaring angle. To validate the mathematical model, the air-core vortex formed in the water model experiment was used, and the length of the vortex was measured and compared to the numerical predictions. Different turbulence models including the standard k-epsilon, realizable k-epsilon and Reynolds stress model were tested. It was found that only the Reynolds stress model could most accurately simulate the high swirling flow including a vortex. In addition, the radial velocity of the water around the vortex was measured by an ultrasonic velocity profiler (UVP). The experimental results revealed a high turbulence of the swirling flow and strong fluctuations of the vortex. The radial velocity of the water around the upper part of the vortex could be predicted well compared to the experimental results by the UVP measurements.

  • 281.
    Bai, Haitong
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Ersson, Mikael
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Jönsson, Pär G.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Experimental Validation and Numerical Analysis of the Swirling Flow in a Submerged Entry Nozzle and Mold by using a Reverse TurboSwirl in a Billet Continuous Casting Process2016In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344XArticle in journal (Refereed)
    Abstract [en]

    As an alternative to some traditional methods to generate a swirling flow in the continuous casting process, the use of a new swirling flow generator, TurboSwirl, was studied. Specifically, a reversed TurboSwirl device was designed as part of a submerged entry nozzle (SEN) for a round billet continuous casting process. Mathematical modelling was used to investigate this new design and a water model experiment was carried out to validate the mathematical model. The predicted velocities by the turbulence models: realizable k-ε model, Reynold stress model (RSM) and detached eddy simulation (DES) were compared to the measured results from an ultrasound velocity profile (UVP) method. The DES model could give the best prediction inside the SEN and had a deviation less than 3.1% compared to the measured results. Moreover, based on the validated mathematical model and the new design of the SEN, the effect of the swirling flow generated by the reverse TurboSwirl on the flow field of the SEN and mold was compared to the design of the electromagnetic swirl flow generator (EMSFG). A very strong swirling flow in the SEN and a stable flow pattern in the mold could be obtained by the reverse TurboSwirl compared to the EMSFG. 

  • 282.
    Bai, Haitong
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Ersson, Mikael
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Jönsson, Pär G.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Numerical Study of the Application for the Divergent Reverse TurboSwirl Nozzle in the Billet Continuous Casting ProcessManuscript (preprint) (Other academic)
    Abstract [en]

    The swirling flow is demanded from the submerged entry nozzle (SEN) to the mold for the continuous casting process. A new design of the SEN is applied by using the reverse TurboSwirl. The TurboSwirl has been proved that it can provide a more stable flow pattern of the liquid steel in the mold. It also can supply a strong enough swirling flow compared to other swirling flow generation methods. Furthermore, a divergent nozzle is added to replace the bottom part of the straight SEN. This new divergent reverse TurboSwirl nozzle (DRTSN) could gain a more beneficial flow pattern in the mold compared to the straight nozzle. The numerical results reveals that a stronger swirling flow can be gained at the SEN outlet with a calmer flow field and active meniscus flow. It is also found that the swirl intensity in the SEN is independent of the casting speed. Lower casting speed is more desired due to a lower maximum wall shear stress. The DRTSN is connected to the tundish by an elbow and a horizontal runner. Longer horizontal runner can supply a more uniform velocity profile and symmetrical flow pattern in the mold. 

  • 283.
    Bai, Haitong
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
    Ni, Peiyuan
    Northeastern Univ, Sch Met, Key Lab Ecol Met Multimet Intergrown Ores, Educ Minist, Shenyang 110819, Liaoning, Peoples R China.;Osaka Univ, Grad Sch Engn, Dept Mat & Mfg Sci, 2-1 Yamadaoka, Suita, Osaka 5650871, Japan..
    Ersson, Mikael
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Zhang, Tingan
    Northeastern Univ, Sch Met, Key Lab Ecol Met Multimet Intergrown Ores, Educ Minist, Shenyang 110819, Liaoning, Peoples R China..
    Jönsson, Pär
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Materials Processing.
    Effect of swirling flow tundish submerged entry nozzle outlet design on multiphase flow and heat transfer in mould2019In: Ironmaking & steelmaking, ISSN 0301-9233, E-ISSN 1743-2812Article in journal (Refereed)
    Abstract [en]

    Effect of a swirling flow SEN (submerged entry nozzle) outlet design on the multiphase flow and heat transfer in a mould was investigated by using numerical simulation. It was found that different SEN outlet designs could form different flow patterns and temperature distributions on the upper of the mould. The enlarged outlet SEN design had an effect to decrease the horizontal velocity of liquid steel flowing out the SEN outlet, reducing the steel flow velocity towards the solidification front. Although a higher velocity was found near the slag/steel interface with the enlarged outlet SEN, but the turbulent kinetic energy was lower. The reason was that less circulation flows were formed in the region of the mould top. The weak horizontal flow towards the solidification front with the enlarged outlet SEN induced lower wall shear stresses, at the same time it also formed a lower temperature distribution near the solidified shell.

  • 284. Bai, Q.
    et al.
    Guo, Z.
    Cui, X.
    Yang, X.
    Yanhua, L.
    Jin, L.
    Sun, Y.
    Experimental investigation on the solidification rate of water in open-cell metal foam with copper fins2018In: Energy Procedia, Elsevier Ltd , 2018, p. 210-214Conference paper (Refereed)
    Abstract [en]

    This study focused on the effect of inserting fins into metal foam on the solidification rate. To this aim, a well-designed experimental system with solid-liquid interface visualization was built. Metal foam samples with different fin intervals were prepared for experiments. Solidification process of water saturating in finned metal foam under bottom cooling was experimentally investigated. Results showed that inserting fins into metal foam can make a promotional improvement on solidification rate of water. The solid-liquid interface became curved after inserting fins, compared with metal foam sample without fins. Besides, changing the interval has little effect on the solidification rate. 

  • 285. Bai, Q.
    et al.
    Guo, Z.
    Li, H.
    Yang, Xiaohu
    KTH, School of Chemical Science and Engineering (CHE).
    Jin, L.
    Yan, Jerry
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering, Energy Processes.
    Experimental investigation on the solidification behavior of phase change materials in open-cell metal foams2017In: Energy Procedia, Elsevier Ltd , 2017, Vol. 142, p. 3703-3708Conference paper (Refereed)
    Abstract [en]

    This study presented an experimental investigation on solidification behavior of fluid saturated in highly porous open-cell copper foams. Particular attention has been made on the effect of pore parameters (pore density and porosity) on the solidification behavior. A purposely-designed apparatus was built for experimental observations. Results showed that the copper foam had a great effect on solidification and the full solidification time can be saved up to 50%, especially preventing the decrease in solidification rate during the later stage of phase change. The smaller the porosity is, the faster the solidification rate will be. Pore density was found to have little influence upon the solidification rate. In addition, the local natural convection does exist but it has a slight effect on solidification, leading to the slant of the solid-liquid interface.

  • 286. Bakaev, A.
    et al.
    Terentyev, D.
    Chang, Z.
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Posselt, M.
    Olsson, Pär
    KTH, School of Engineering Sciences (SCI), Physics, Reactor Physics.
    Zhurkin, E. E.
    Effect of isotropic stress on dislocation bias factor in bcc iron: an atomistic study2018In: Philosophical Magazine, ISSN 1478-6435, E-ISSN 1478-6443, Vol. 98, no 1, p. 54-74Article in journal (Refereed)
    Abstract [en]

    The effect of externally applied stress on the dislocation bias factor (BF) in bcc iron has been studied using a combination of atomistic static calculations and finite element integration. Three kinds of dislocations were considered, namely, a0/2〈1 1 1〉{1 1 0} screw, a0/2〈1 1 1〉{1 1 0} edge and a0〈1 0 0〉{0 0 1} edge dislocations. The computations reveal that the isotropic crystal expansion leads to an increasing or constant dislocation bias, depending on the Burgers vector and type of dislocation. On the other hand, compressive stress reduces the dislocation bias for all the dislocations studied. Variation of the dislocation BF depending on dislocation type and Burgers vector is discussed by analysing the modification of the interaction energy landscape and the capture efficiency values for the vacancy and self-interstitial atom. 

  • 287.
    Balieu, Romain
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, Highway and Railway Engineering.
    Lauro, F.
    Bennani, B.
    Matsumoto, T.
    Mottola, E.
    Non-associated viscoplasticity coupled with an integral-type nonlocal damage model for mineral filled semi-crystalline polymers2014In: Computers & structures, ISSN 0045-7949, E-ISSN 1879-2243, Vol. 134, p. 18-31Article in journal (Refereed)
    Abstract [en]

    A non-associated viscoplastic model coupled with nonlocal damage under finite strain framework is developed to simulate the non-isochoric deformation and the damage process exhibiting strain-softening of a 20% mineral filled semi-crystalline polymer. The logarithmic spin tensor properties linking the Eulerian Hencky strain with the Cauchy stress is used thanks to hypoelasticity assuming the additive decomposition of the stretching into elastic and viscoplastic parts. The constitutive model with its nonlocal formulation is implemented in an efficient manner in a commercial implicit finite element code. The proposed model exhibits mesh-independent responses and is in agreement with strain evolution observed experimentally.

  • 288.
    Ballesteros, Antonio
    et al.
    JRC Petten, Holland.
    Hein, Hieronymus
    AREVA Gmbh Germany.
    May, Johannes
    AREVA Gmbh Germany.
    Planman, Tapio
    VTT Finland.
    Todeshini, Patrick
    EdF France.
    Brumowski, Milan
    UJV Czech Republic.
    Roudén, Jenny
    Gillemot, Ferenc
    MTA Hungary.
    Chaouadi, Rachid
    SCK-CEN, Belgium.
    Efsing, Pål
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Altstadt, Eberhard
    Forschung Center Rossendorff, Germany.
    Reactor Pressure vessel surveillance2014In: Nuclear Engineering International, ISSN 0029-5507, Vol. 59, no 12, p. 19-20Article in journal (Refereed)
    Abstract [en]

    This publication summarizes techniques suitable for surveillance program for the objective of  long term operation (LTO) on European NPPs and provides recommendations on reactor pressure vessel (RPV) irradiation surveillance based on the work preformed in the work package 7 "Surveillance guidelines" of the LONGLIFE international project. The LONGLIFE project "treatment of long term irradiation embrittlement effects in RPV safety assessment" was 50% funded by the Euratom 7th framework programme of the European commision. The project coordinated by the Helmholtz-centrum Dresden Rossendorf successfully finalized in 2014.

  • 289. Ban-Ya, S.
    et al.
    Hino, M.
    Hayashi, M.
    Sano, N.
    Fredriksson, Patrik
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Comments on "Evaluation of thermodynamic activity of metallic oxide in a ternary slag from the sulphide capacity of the slag"2005In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 45, no 11, p. 1754-1757Article in journal (Refereed)
  • 290.
    Baradaran, Mohammad Ali
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.). KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Hydrogen Embirttlement in Weldox 1300 and Hardox 5002014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Abstract

    Upon trying to reach higher strengths, when designing steels, inevitably susceptibility to one

    type of cracking known as hydrogen cracking increases. In present work, this complexity with

    regard to high strength structural steel of Weldox 1300 and wear plate of Hardox 500 was

    studied.

    Effect of low temperature tempering (200 ) and hard leveling on hydrogen embrittlement was

    qualitatively explored by fracture toughness testing. Tests were performed on SENB specimens of two types of Weldox 1300 in air and 3.5% NaCl solution. In-situ testing of as-quenched Weldox caused K value for crack growth initiation to drop to almost 20% of that for reference specimen tested in air. However, Weldox 1300 in tempered and leveled condition exhibited considerably improved resistance against hydrogen cracking by almost 50% compared to asquenched condition.

    It is believed that formation of transit carbides acting as strong traps due to tempering, and alteration in dislocations’ structure and level of tensile residual stresses thanks to combined effects of tempering and leveling have considerable impact on crack growth kinetics which results in improved resistance. The influence of tempering and leveling was not investigated separately.

    Additionally, by using four-point-bending test it was attempted to screen a method suitable for study of hydrogen embrittlement. Test variables were tried to be adjusted to meet the failure criteria. Precharged samples were subjected to bending stresses and left in outdoor atmosphere. Hydrogen measurement after passing 41 days on one of the samples containing a stress concentrator showed that hydrogen had been trapped and still present into the sample. Although hydrogen measurement showed the effect of stress fields on hydrogen trapping, test results along with FEM simulation indicated that such a test method might not be practicable for this special combination of materials and expectations.

  • 291.
    Barbier, Christophe
    KTH, Superseded Departments, Solid Mechanics.
    On folding of coated papers2004Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    The mechanical behaviour of coated papers during folding has been investigated. This problem has been studied with experimental techniques and numerical analyses in order to give a better understanding of the folding properties of coated papers pertinent to the mechanical behaviour in general, and particularly cracking along the fold.

    A microscopy investigation has been performed. The surface of the folded paper has been carefully examined to study the event of fracture and related issues. The influence of the grammage on the cracking event has been studied and it was shown that the coating material would not fail if the paper sample was sufficiently thin. It was found that a stress or strain based criterion is sufficient to describe the cracking of the coating layers and that the anisotropy of paper should be taken into account when studying the folding process.

    The finite element method has been used for the numerical analyses remembering that the geometry of the problem is rather complicated, excluding a solution in analytical form. Using different constitutive models for the base stock, it has been shown that the deformation of the coated paper during folding is much governed by the paper substrate. The numerical results also suggested that particular forms of plastic anisotropy can substantially reduce the maximum strain levels in the coating. Furthermore, it has also been shown that delamination buckling, in the present circumstances, has a very small influence on the strain levels in the coating layer subjected to high tensile loading.

    Dynamic effects have also been studied and it has been shown that a quasi-static analysis of the problem is sufficient in order to describe many of the important features related to cracking. An attempt to model strong anisotropy of paper has been presented and the results indicate that the large anisotropy in the thickness direction of coated papers needs to be taken into account in order to fully understand the mechanics of folding.

    Finally, an experimental investigation has been presented in order to study if important mechanical properties of the coating material could be determined by microindentation techniques. The results presented indicate that microindentation can be a powerful tool for characterization of these materials, but only if careful efforts are made in order to account for the influence from plasticity as well as from boundary effects.

    KEYWORDS: folding, coated papers, finite element method, cracking, indentation, anisotropy, plasticity.

  • 292.
    Barbier, Christophe
    et al.
    KTH, Superseded Departments, Solid Mechanics.
    Larsson, Per-Lennart
    KTH, Superseded Departments, Solid Mechanics.
    Östlund, Sören
    KTH, Superseded Departments, Solid Mechanics.
    Experimental investigation of damage at folding of coated papers2002In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 17, no 1, p. 34-38Article in journal (Refereed)
    Abstract [en]

    An experimental investigation of damage occuring at folding of coated paper has been performed. For this purpose an experimental device was constructed in such a way that close resemblance with an industrial situation was achieved. During the experiments the influence on the damage levels in the coating from such features as delamination, humidity and paper thickness have been studied using an optical microscope. The behaviour of two different paper materials has been investigated. A stress (or strain) based fracture criterion is relevant for the present problem but biaxiality of stresses as well as in-plane anisotropy must be taken into account. It was observed that cracking of the coating would not lead to subsequent cracking of the paper substrate and that delamination occurred during folding, in the base stock and not at the paper/coating interface, but its quantitative influence as regards cracking could not be determined. The influence from sheet grammage was investigated and it was found that the only case when (visible) cracks did not appear was at low values. High humidity did not affect the cracking.

  • 293.
    Barbier, Christophe
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Larsson, Per-Lennart
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Östlund, Sören
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Numerical investigation of folding of coated papers2005In: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, Vol. 67, no 4, p. 383-394Article in journal (Refereed)
    Abstract [en]

    Folding of coated paper is examined numerically using the finite element method. Particular emphasis is put on the behaviour of field variables relevant for cracking of the coating layers. In the numerical analysis, the basepaper is modelled as an anisotropic elastic-plastic material (both elastic and plastic anisotropy is accounted for) while the constitutive behaviour of the coating layers are approximated by classical (Mises) elastoplasticity. The numerical results suggest, among other things, that particular forms of plastic anisotropy can substantially reduce the maximum strain levels in the coating. It is also shown that delamination buckling, in the present circumstances, will have a very small influence on the strain levels in the coating layer subjected to high tensile loading.

  • 294.
    Barbier, Christophe
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Larsson, Per-Lennart
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Östlund, Sören
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    On dynamic effects at folding of coated papers2005In: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, Vol. 67, no 4, p. 395-402Article in journal (Refereed)
    Abstract [en]

    Folding of coated papers is examined numerically using the finite element method. The analysis is focused on the influence from dynamic effects on the folding process. In particular, the behaviour of field variables relevant for cracking of the coating layers are studied in some detail. The results presented indicate that dynamic effects are of little importance as regards maximum strain levels in the coating but will influence the stress and strain distributions. Accordingly, a quasi-static analysis of the problem will be sufficient in order to describe many of the important features related to cracking.

  • 295.
    Barbier, Christophe
    et al.
    KTH, Superseded Departments, Solid Mechanics.
    Larsson, Per-Lennart
    KTH, Superseded Departments, Solid Mechanics.
    Östlund, Sören
    KTH, Superseded Departments, Solid Mechanics.
    On the effect of high anisotropy at folding of coated papers2004Report (Refereed)
  • 296.
    Barbier, Christophe
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Larsson, Per-Lennart
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Östlund, Sören
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    On the effect of high anisotropy at folding of coated papers2006In: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, Vol. 72, no 3, p. 330-338Article in journal (Refereed)
    Abstract [en]

    A finite element procedure, developed in order to account for the effect of high anisotropy at folding of coated papers, is presented. The anisotropic behaviour (with very low stiffness in the thickness direction) is modelled using stiff structural elements (trusses and beams). The numerical results indicate that high elastic anisotropy leads to lower strain levels at folding than reported in previous analyses where this effect was not accounted for. High plastic anisotropy, on the other hand, will contradict this result.

  • 297.
    Barbier, Christophe
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Larsson, Per-Lennart
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Östlund, Sören
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Eklund, Johan
    DPC, MidSweden University.
    Folding of Printed Papers: Experiments and Numerical Analysis2003In: Preprints of the 2003 International Paper Physics Conference, 2003, p. 193-196Conference paper (Refereed)
  • 298.
    Barbier, Christophe
    et al.
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.), Solid Mechanics (Div.).
    Larsson, Per-Lennart
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Östlund, Sören
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    Hallbäck, N.
    Karathanasis, M.
    On material characterization of paper coating materials by microindentation testing2005In: Journal of Coatings Technology Research, ISSN 1547-0091, Vol. 2, no 6, p. 463-471Article in journal (Refereed)
    Abstract [en]

    Microindentation as a method for determining important material properties of paper coating materials is studied experimentally and numerically The bulk of the investigation is concentrated upon the short-lived elastic part of a spherical indentation test, but determination of the failure stress of the coating is also discussed. The results indicate that microindentation can be a powerful tool for material characterization of these materials, but only if careful efforts arc, made to account for the influence from plasticity as well as from boundary effects.

  • 299.
    Barkar, Thomas
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. KTH.
    Modelling phase separation in Fe-Cr alloys: A continuum approach2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The formation of Cr-rich and Fe-rich domains upon ageing of an initially homogeneous Fe-Cr alloy at elevated temperatures (300-600 ºC) is commonly referred to as phase separation. The behaviour originates from a miscibility gap in the Fe-Cr phase diagram. The boundary of the miscibility gap is denoted the binodal, and the line where the second derivative of the molar Gibbs energy w.r.t. composition is zero, the spinodal. In the region between the binodal and spinodal lines, the phase separation is said to occur by means of nucleation and growth. Inside the spinodal line, no thermally activated nucleation event is needed, and the initially homogeneous alloy decomposes "spinodally" into Cr-rich and Fe-rich regions. This type of phase transformation can be viewed as a continuous build up of Cr-rich regions, that also are interconnected, forming a microstructure characteristic for alloys decomposed spinodally. Phase separation has been of great interest within the metallurgical community as well as industry, due to its embritteling effect. Phase separation in Cr-rich ferritic steels, and thus embrittlement, sets a practical upper service temperature of ~300 ºC for Cr-containing ferrites. It is desirable to develop understanding and modelling capability for decomposing alloy systems, since such knowledge could be used to relieve the limitation in service temperature. The current work has been focused around the development and use of computer simulations, using thermodynamic and kinetic input from databases, in order to progress towards alloy design where decomposition is minimized. Simulations in this work are based on solving the so called Cahn-Hilliard equation, where an important parameter is the gradient energy, since it influences both the morphology and rate of decomposition in the simulations. An attempt at formulating a general model for the gradient energy coefficients in multi-component systems has been made, but has yet to be properly tried against experimental data. Improvements, and insights, to the initial state used in simulations has also been achieved. The combination of above mentioned efforts is a step towards a predictive tool for decomposition of complex alloys. Such a tool could not only be an aid in future alloy design, but also be used as an aid as a diagnosis tool in life time assessment of critical components already in use and thereby difficult to assess on site by means of in-destructive testing, typically components in nuclear power facilities.

  • 300.
    Barkar, Thomas
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Odqvist, Joakim
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Höglund, Lars
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Ågren, John
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Phase field modeling of spinodal decomposition in Fe-Cr based alloys2015In: PTM 2015 - Proceedings of the International Conference on Solid-Solid Phase Transformations in Inorganic Materials 2015, International Conference on Solid-Solid Phase Transformations in Inorganic Materials , 2015, p. 827-828Conference paper (Refereed)
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