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  • 251.
    Li, Xiaoqing
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik. Uppsala University, Sweden.
    Schönecker, Stephan
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
    First-principles prediction of the stacking fault energy of gold at finite temperature2017Ingår i: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 135, s. 88-95Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The intrinsic stacking fault energy (ISFE) γ is a material parameter fundamental to the discussion of plastic deformation mechanisms in metals. Here, we scrutinize the temperature dependence of the ISFE of Au through accurate first-principles derived Helmholtz free energies employing both the super cell approach and the axial Ising model (AIM). A significant decrease of the ISFE with temperature, −(36–39) % from 0 to 890 K depending on the treatment of thermal expansion, is revealed, which matches the estimate based on the experimental temperature coefficient dγ/dT closely. We make evident that this decrease predominantly originates from the excess vibrational entropy at the stacking fault layer, although the contribution arising from the static lattice expansion compensates it by approximately 60%. Electronic excitations are found to be of minor importance for the ISFE change with temperature. We show that the Debye model in combination with the AIM captures the correct sign but significantly underestimates the magnitude of the vibrational contribution to γ(T). The hexagonal close-packed (hcp) and double hcp structures are established as metastable phases of Au. Our results demonstrate that quantitative agreement with experiments can be obtained if all relevant temperature-induced excitations are considered in first-principles modeling and that the temperature dependence of the ISFE is substantial enough to be taken into account in crystal plasticity modeling.

  • 252.
    LI, Xinmin
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.).
    Olofsson, Ulf
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.).
    FZG gear efficiency and pin-on-disc frictional study of sintered and wrought steel gear materials2015Ingår i: Tribology letters, ISSN 1023-8883, E-ISSN 1573-2711, Vol. 60, nr 9Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Load-dependent power loss is a major contributor to power loss in gear transmission systems. In this study pin-on-disc frictional and FZG efficiency experiments were conducted with powder metallurgy (Distaloy AQ+0.2%C) and wrought material (16MnCr5) combinations. The gear mesh torque loss from gear efficiency tests and the friction coefficient from the pin-on-disc tests were then compared. The trend for both test series was the same. The combination of 16MnCr5 in contact with Distaloy AQ+0.2%C shows the lowest coefficient of friction and gear mesh torque loss, followed by the combination of Distaloy AQ+0.2%C in contact with itself, and finally the combination of 16MnCr5 in contact with itself.

  • 253.
    Li, Zhou
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Mao, H.
    Selleby, Malin
    Binary cases of the third generation of thermodynamic databases: Co-Cr, Co-C, Cr-C systemsManuskript (preprint) (Övrigt vetenskapligt)
  • 254.
    Li, Zhou
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Mao, H.
    Selleby, Malin
    Thermodynamic evaluation of the Co-Cr-C system within the framework of the third generation of thermodynamic databasesManuskript (preprint) (Övrigt vetenskapligt)
  • 255.
    Lind, Martin
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Improvement in the forming process of support brackets vulnerable to cracking: Problem solving in the field of  sheet metal forming2013Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Denna rapport har skrivits för att sammanfatta mitt arbete med syfte att förbättra tillverkningen av bärok som används till kabelstegar. Det i projektet berörda företaget har under årens lopp upplevt ett flertal problem med svår sprickbildning i en kragad radie. Huvuduppgiften har därför varit att identifiera vad som skulle kunna vara problemet, samt att komma fram till några förslag på hur dessa problem skulle kunna undvikas framöver.   Kragningstest, åtföljda av finita element analyser med hjälp av MSC Marc har utförts för att utvärdera arbetsmaterialets formbarhet. Skicket på den berörda klippkanten, liksom klippverktyget, har också studerats i såväl ljusoptiskt mikroskop (LOM) som svepelektronmikroskop (SEM).   Resultaten visar att kragningsoperationen i dagsläget avsevärt överskrider materialets kritiska kragningsförhållande. Problem med galling kan också fastställas då plåtmaterial tenderar att smeta fast på verktygsytorna under produktionsförloppet. För att förbättra tillverkningen med avseende på tillförlitlighet och en förbättrad produkt, bör företaget överväga lösningar såsom att byta smörjmedel eller att fokusera på en ytbehandling av klippverktyget eller att investera i ett helt nytt verktyg tillverkat av högkvalitativt verktygsstål vilket antagligen skulle vara den mest fördelaktiga lösningen på lång sikt.

  • 256.
    Lind, Martin
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Johansson, Cecilia
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Evaluation of the η (Eta) nitride with three laboratory melts2015Självständigt arbete på avancerad nivå (magisterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    η (eta) nitride, Cr3Ni2SiN, is a precipitate found in high temperature austenitic stainless steel and is not yet included in Thermo-Calc steel database TCFE7. The aim of this thesis is to collect thermodynamic data to enable the addition of η nitride in the databases. Three laboratory melts with varying levels of silicon, chromium and nickel have been aged at 700-1000 °C for 75 h, 300 h and 1200 h and examined by Light Optical Microscopy, Scanning Electron Microscopy, Energy Dispersive Spectroscopy, Wavelength Dispersive Spectroscopy, Electron Backscattered Diffraction and X-ray Powder Diffraction.

    η nitride is in the studied alloys an equilibrium phase stabilized with nitrogen. Presence of η nitride was confirmed by Energy Dispersive Spectroscopy and X-ray Powder Diffraction. It was found to precipitate in four different ways, at primary grain boundaries, intragranularly, as a "skeleton-like" precipitate and as a border around the occurring Cr2N precipitates. The area fraction of η nitrides increases with longer aging times and is favored by silicon and nickel. The composition of η nitride is not changing regardless of material composition, aging temperature and aging time. The composition of η nitride in all three materials are 8.7-9.7 wt.% silicon, 47-54 wt.% chromium, 1.4-4.1 wt.% iron and 33-36 wt.% nickel. The nitrogen content 2

    determined by Wavelength Dispersive Spectroscopy is 2.8-3.2 wt.%. No complete equilibrium was achieved and together with incomplete mixing of the alloying elements during melting, the microstructure is difficult to evaluate. Other precipitates found are Cr2N, π nitride, σ phase and two unidentified phases, M and N. Of these phases at least Cr2N is not an equilibrium phase as it dissolves during aging. Further aging to achieve complete equilibrium is necessary.

  • 257. Linder, Jan
    Corrosion fatigue of austenitic and duplex stainless steels in 3% NaCl1993Ingår i: Proc. Fatigue under spectrum loading and in corrosive environments , A.F. Blom Ed. 26-27 August 1993, Ljungby, Denmark, 1993Konferensbidrag (Refereegranskat)
  • 258.
    Linder, Jan
    KTH, Skolan för industriell teknik och management (ITM), Industriell ekonomi och organisation (Inst.).
    Corrosion fatigue of duplex and austenitic stainless steels in 3% NaCl at 80 degrees C and room temperatur1994Ingår i: Proc. Duplex Stainless Steels, Glasgow, Scotland, 13-16 November 1994, 1994Konferensbidrag (Refereegranskat)
  • 259.
    Linder, Jan
    KTH, Skolan för industriell teknik och management (ITM), Industriell ekonomi och organisation (Inst.).
    Fatigue strength of engineering materials: the influence of environment and porosity2006Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    The objective of this work was to use LEFM in order to assess the detrimental influence of surrounding chloride-containing environments for stainless steels, hardened steel as well as for a cast aluminium alloy. An additional aim was also to use LEFM to assess the influence of porosity on the fatigue properties for different commercial cast aluminium alloys and manufacturing methods. The environmental influence on fatigue performance was mainly evaluated from fatigue crack growth measurements using compact tension (CT) specimens. In addition, fatigue performance in the high cycle regime was studied using spot welded specimens and smooth specimens.

    Corrosion fatigue tests for stainless steels were performed in different chloride-containing aqueous solutions and compared to the behaviour in air. Variables, which have been investigated, included temperature, redox potential and fatigue test frequency. The environmental influence on fatigue performance has also been compared to localised corrosion properties. Fatigue crack propagation rates were found to be higher in 3% NaCl than in air for all stainless steels investigated. The highest alloyed austenitic steel, 654SMO, showed the least influence of the environment. For duplex stainless steels the environment enhanced fatigue crack propagation rate to a higher degree than for austenitic stainless steels. This is explained by a material-dependent corrosion fatigue mechanism.

    In the high cycle regime, fatigue properties for spot welded stainless steels specimens were found to be decreased between 30%-40% due to the presence of 3% NaCl. For the hardened steel 100CrMnMo8 a fracture mechanics approach was employed for prediction of corrosion fatigue properties. In this model corrosion pit growth rate and the threshold stress intensity factor for fatigue crack propagation are needed as input parameters.

    For the high pressure die cast aluminium alloy the environmental influence of fatigue initiation through pre-exposure of smooth specimens was studied. Depending on environment used for pre-exposure, fatigue strength was found to be reduced by up to 50 % compared to the fatigue strength in air. Fatigue strength reduction was clearly associated to corrosion pits in the aluminium material. A fracture mechanics model was further successfully used to predict the environmental influence.

    The influence of porosity on the fatigue strength for the cast aluminium alloys tested has been described by a Kitagawa diagram. In design, the Kitagawa diagram can be used to predict the largest allowable pore size if the load situation in the component is known. The size of the porosity could either be evaluated directly from x-ray images or from metallographic prepared cross-sections using a method of extreme value analysis

  • 260. Linder, Jan
    The influence of surrounding environment on the fatigue properties for a high pressure die cast AlSi9Cu3 alloy2007Ingår i: Fatigue & Fracture of Engineering Materials & Structures, ISSN 8756-758X, E-ISSN 1460-2695, Vol. 30, nr 8, s. 759-765Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The influence of mechanical strength for aluminium castings is often correlated in the literature to the occurrence of cast defects like porosity. However, because aluminium castings in the automotive industry are often used without surface treatment such as painting etc., the influence of corrosion and its effect on fatigue properties are required. Basically a surrounding environment can affect fatigue strength either by enhancing initiation or by increasing fatigue crack propagation properties. In this study, the influence of pre-exposure prior to fatigue testing has been evaluated. This implies that environmental enhancement of fatigue initiation due to corrosion has been studied. Two different environments [seawater acidified test (SWAAT) and Volvo Indoor Corrosion Test (VICT)] often employed for assessment of corrosive properties in the automotive industry have been used for pre-exposure of specimens. Based on experimental results, it is shown that fatigue strength is reduced by approximately 50% for specimens pre-exposed to SWAAT environment, while insignificant influence was found for specimens pre-exposed to VICT environment. The degradation of fatigue strength was found to be due to localized corrosive attacks. Propagation of these corrosive attacks takes place preferably in the eutectic phase and especially at the borderline between primary aluminium dendrites and the cutectic phase.

  • 261. Linder, Jan
    et al.
    Arvidsson, A
    Kron, J
    The influence of porosity on the fatigue strength of high-pressure die cast aluminium2006Ingår i: Fatigue & Fracture of Engineering Materials & Structures, ISSN 8756-758X, E-ISSN 1460-2695, Vol. 29, nr 5, s. 357-363Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Aluminium is a lightweight material with high strength and good corrosion resistance among other beneficial properties. Thanks to these properties, aluminium is more extensively used in the vehicle industry. High-pressure die casting of aluminium is a manufacturing process that makes it possible to attain complex, multi-functional components with near-net shape. However, there is one disadvantage of such castings, that is, the presence of various defects such as porosity and its effect on mechanical properties. The aim of this work was to investigate the influence of porosity on the fatigue strength of high-pressure die cast aluminium. The objective was to derive the influence of defect size with respect to the fatigue load, and to generate a model for fatigue life in terms of a Kitagawa diagram. The aluminium alloy used in this study is comparable to AlSi9Cu3. Specimens were examined in X-ray prior to fatigue loading and classified with respect to porosity level and eventually fatigue tested in bending at the load ratio, R, equal to -1. Two different specimen types with a stress concentration factor of 1.05 and 2.25 have been tested. It has been shown that the fatigue strength decreases by up to 25% as the amount of porosity of the specimen is increased. The results further showed that the influence of defects was less for the specimen type with the higher stress concentration. This is believed to be an effect of a smaller volume being exposed to the maximum stress for this specimen type. A Kitagawa diagram was constructed on the basis of the test results and fracture mechanics calculations. A value of 1.4 Mpa m(1/2) was used for the so-called stress intensity threshold range. This analysis predicts that defects larger than 0.06 mm(2) will reduce the fatigue strength at 5 x 10(6) cycles for the aluminium AlSi9Cu3 material tested.

  • 262. Linder, Jan
    et al.
    Axelsson, Markus
    Nilsson, Henrik
    The influence of porosity on the fatigue life for sand and permanent mould cast aluminium2006Ingår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 28, nr 12, s. 1752-1758Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The automotive industry always strives to achieve light weight components to reduce fuel consumption and to meet environmental requirements. One way to obtain weight reduction is to replace steel components with components made of aluminium or other light weight materials. Aluminium has good corrosion properties and a high strength to weight ratio which makes it favourable in many applications. The increased use of aluminium castings in the automotive industry does also imply that the need for design data for aluminium, increases. Especially for castings, the influence of casting defects are always an issue. For this reason fatigue properties for as-cast sand and permanent mould specimens with different contents of porosity have been studied. Sand cast and permanent mould cast aluminium specimens of two different geometries were fatigue tested in cyclic bending at R= -1. Prior to fatigue test specimens were examined by X-ray and sorted into three quality groups depending on the porosity level. The aim of this work was to investigate the fatigue life for sand cast and permanent mould cast AlSi10Mg with different amounts of porosity. An additional aim was to predict the largest defect contained in a specified volume of a component, by using a statistical analysis of extreme values, and relate it to the fatigue life. The results showed that fatigue strength for a smooth specimen geometry decreases by up to 15% with increased porosity. For specimens with a notched geometry, no influence of porosity on the fatigue strength was found. This is believed to be due to a much smaller volume subject to high stress than for specimens with low stress concentration.

  • 263. Linder, Jan
    et al.
    Blom, R
    Development of a method for corrosion fatigue life prediction of structurally loaded bearing steels2001Ingår i: Corrosion, ISSN 0010-9312, E-ISSN 1938-159X, Vol. 57, nr 5, s. 404-412Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this study a simplified method to predict corrosion fatigue properties for the Cr-alloyed bearing steel 100CrMnMo8 is proposed. With this method corrosion pits are assumed to act as defects, which could initiate fatigue cracks. A linear elastic fracture mechanics (LEFM) model was used to evaluate the critical corrosion pit size when mechanical fatigue crack propagation occurred. The unknown parameters in the prediction model were corrosion pit growth rate and the threshold stress intensity factor (DeltaK(th)) for fatigue crack growth. In this study corrosion pit growth rate was determined for 100CrMnMo8 in a chloride-containing water solution by aid of a statistical method. Corrosion pit growth rate was found to be approximately proportional to the square root of time. The time dependence of corrosion pit growth Zed also to the conclusion that characterization of corrosion fatigue strength must be made with respect to both exposure time in a corrosive environment and the number of cycles to a runout level. DeltaK(th) fatigue crack growth was estimated from interrupted rotating bending fatigue tests in the corrosive environment in question. Since only the corrosion pit growth rate and DeltaK(th), are needed as input in the proposed corrosion fatigue prediction model, much effort can be saved since this can reduce the amount of fatigue testing. Corrosion pit growth rate can be determined on unloaded test coupons In the desired environment. Hence, for materials selection, exposure tests followed by a corrosion pit size analysis can indicate the corrosion fatigue performance in a given environment.

  • 264. Linder, Jan
    et al.
    Melander, Åke
    Fatigue strength of spot welded stainless sheet steels exposed to 3% NaCl solution1998Ingår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 20, nr 5, s. 383-388Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Fatigue properties of spot welded stainless sheets steels have been investigated in a 3% NaCl solution and, for comparison, also in air at ambient temperature. Corrosion fatigue tests have been conducted both for one austenitic Stainless steel type AISI304, and for one duplex (similar to 50% austenite, 50% ferrite) stainless steel SAF2304. For the duplex steel, the effect of preexposure of unloaded specimens to a 3%NaCl solution before corrosion fatigue testing was also investigated. Corrosion fatigue strength in 3% NaCl for the stainless steels investigated was found to be reduced by approximately 30-40% compared to fatigue strength in air. Preexposure of unloaded specimens prior to fatigue testing was shown not to reduce fatigue strength further.

  • 265.
    Lindgren, Gustav
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Canalias, Carlota
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Domain wall conductivity in KTiOPO4 crystals2017Ingår i: APL Materials, ISSN 2166-532X, Vol. 5, nr 7, artikel-id 076108Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We study the local ionic conductivity of ferroelectric domain walls and domains in KTiOPO4 single-crystals. We show a fourfold increase in conductivity at the domain walls, compared to that of the domains, attributed to an increased concentration of defects. Our current-voltage measurements reveal memristive-like behavior associated with topographic changes and permanent charge displacement. This behavior is observed for all the voltage sweep-rates at the domain walls, while it only occurs for low frequencies at the domains. We attribute these findings to the redistribution of ions due to the applied bias and their effect on the tip-sample barrier.

  • 266.
    Lindholm, Per
    KTH, Tidigare Institutioner, Maskinkonstruktion.
    Wear resistant low friction coatings for engine components2004Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Engine development today is driven by cost, performance and government regulations. Customers want cars and trucks to consume less fuel, last longer, pollute less and be safer. Several of the requirements have tribological associations. For example, product longevity can be improved by lowering friction and using more wear-resistant components. In recent decades, the use of new coating application procedures and techniques has produced remarkably advances in relation to cutting tools. The process temperature at which coatings are applied has been lowered to below 200 oC. Thus it is now possible to coat low-alloy temper-sensitive steels, which are widely used in the automotive industry in machine elements such as gears, bearings and cam followers.

    The aim of this work has been to investigate the possibility of using sputtered amorphous carbon coatings to reduce friction and prevent wear in engine components, and specifically in valve train components. Test equipment simulating near-normal running conditions for the valve mechanism has been developed and used to test standard and coated valve components. The mechanism has also been analysed and simulated numerically. The results show a low velocity difference between the injector cam lobe and the roller, except for a short interval at the top dead centre of the rocker arm. In that region the slip increases significantly at higher speeds due to inertial forces.

    A three-dimensional finite element parameter study of the coating thickness, elastic modulus, asperity contact size and wavelength has shown that tensional stresses at the coating surface increase significantly when asperity contacts approach and interact. Testing of different thicknesses in rolling contact, together with finite element stress analysis, showed that a higher tensional stress level through the coating thickness increases the possibility of cracks propagating down to the interlayer and causing delamination of the coating. Tests with a rapid load increase on two carbon coatings show no transition from mild to more severe wear. Instead the contact is dimensioned by the plastic deformation of the underlying substrate.

  • 267.
    Lindström, Anders
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    In-plane Compressive Response of Sandwich Panels2009Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    The high specific bending stiffness of sandwich structures can with advantage be used in vehicles to reduce their weight and thereby potentially also their fuel consumption. However, the structure must not only meet the in-service requirements but also provide sufficient protection of the vehicle passengers in a crash situation. The in-plane compressive response of sandwich panels is investigated in this thesis, with the objective to develop a methodology capable of determining if the structural response is likely to be favourable in an energy absorption perspective. Experiments were conducted to identify possible initial failure and collapse modes. The initial failure modes of sandwich panels compressed quasi-statically in the in-plane direction were identified as global buckling, local buckling (wrinkling) and face sheet fracture. Global buckling promotes continued folding of the structure when compressed beyond failure initiation. Face sheet fracture and wrinkling can promote collapse in the form of unstable debond crack growth, stable end-crushing or ductile in-plane shear collapse. Both the unstable debond crack propagation and the stable end-crushing are related to debond crack propagation, whereas the ductile in-plane shear mode is related to microbuckling of the face sheets.

    The collapse behaviour of sandwich configurations initially failing due to wrinkling or face sheet fracture was investigated, using a finite element model. The model was used to determine if the panels were likely to collapse in unstable debond propagation or in a more stable end-crushing mode, promoting high energy absorption. The collapse behaviour is mainly governed by the relation between the fracture toughness of the core and the bending stiffness and strength of the face sheets. The model was successfully used to design sandwich panels for different collapse behaviour. The proposed method could therefore be used in the design process of sandwich panels subjected to in-plane compressive loads.During a crash situation the accelerations on passengers must be kept below life threatening levels. The extreme peak loads in the structure must therefore be limited. This can be achieved by different kind of triggering features.Panels with either chamfered face sheets or with grooves on the loaded edges were investigated in this thesis. The peak load was reduced with panels incorporating either of the two triggering features. Another positive effect was that the plateau load following failure initiation was increased by the triggers. This clearly illustrates that triggers can be used to promote favourable response in sandwich panels.

    Vehicles are harmful to the environment not only during in-serve use, but during their entire life-cycle. By use of renewable materials the impact on the environment can be reduced. The in-plane compressive response of bio-based sandwich panels was therefore investigated. Panels with hemp fibre laminates showed potential for high energy absorption and panels with a balsa wood core behaved particular well. The ductile in-plane shear collapse mode of these panels resulted in the highest energy absorption of all investigated sandwich configurations.

     

  • 268.
    Lindström, Anders
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Hallström, Stefan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Energy absorption of sandwich panels containing bio-based materials2010Manuskript (preprint) (Övrigt vetenskapligt)
  • 269.
    Lindström, Anders
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Hallström, Stefan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Energy absorption of SMC/balsa sandwich panels with geometrical triggering features2010Ingår i: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, Vol. 92, nr 11, s. 2676-2684Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The influence of triggering topologies on the peak load and energy absorption of sandwich panels loaded in in-plane compression is investigated. Sandwich panels with different geometrical triggering features are manufactured and tested experimentally. The damage initiation in panels with grooves is investigated using finite element models. As expected the investigated triggering features reduce the extreme load peaks. A less expected result is that the plateau load following peak load tends to be higher for panels with triggering features. Both results are favourable for the crash performance of panels in vehicle applications. For panels containing no or few grooves the peak load seems to be governed by principles of fracture mechanics while initial failure in panels with a higher number of grooves appears to be controlled by the average stress.

  • 270.
    Lindström, Fredrik
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.).
    Ångström, Hans-Erik
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.).
    Kalgathgi, Gautam
    Elmqvist Möller, Christel
    An empirical SI combustion model using laminar burning velocity correlations2005Ingår i: SAE transactions, ISSN 0096-736X, Vol. 114, nr 4, s. 833-846Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Predictive simulation models are needed in order to exploit the full benefits of 1-D engine simulation. Simulation model alterations such as cam phasing affect the gas composition and gas state in the cylinders and have an effect on the combustion. Modelling of these effects is particularly important when the engine is knock limited. A knock model, able to phase the combustion towards the knock limit, was previously developed by the authors. A major challenge in such knock models is to predict the pressure and temperature evolution in the end-gas accurately through an adequate combustion model. The Wiebe function is often used to model the combustion in Sl engine simulations, owing to its ease of use and computational efficiency. The Wiebe function simply imposes a curve shape for the fuel burn rate and the parameters are easily determined from calculated heat release. Detailed models of turbulent combustion also exist which require more knowledge or assumptions about combustion chamber turbulence. The combustion model proposed in this paper uses existing correlations of laminar burning velocity to predict the parameters of the Wiebe function relative to a base operating condition. The model aims at predicting combustion at high load operation. Experimental and simulation data from a gasoline fuelled 4-cylinder turbo charged port injected spark ignition engine are used to correlate the Wiebe function parameters dependence on laminar burning velocity.

  • 271.
    Linnarsson, Margareta K.
    et al.
    KTH.
    Ayedh, H. M.
    Hallén, Anders
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektronik, Integrerade komponenter och kretsar.
    Vines, L.
    Svensson, B. G.
    Surface erosion of ion-implanted 4H-SiC during annealing with carbon cap2018Ingår i: International Conference on Silicon Carbide and Related Materials, ICSCRM 2017, Trans Tech Publications Inc., 2018, Vol. 924, s. 373-376Konferensbidrag (Refereegranskat)
    Abstract [en]

    The stability/ erosion of the interface between a C-cap and 4H-SiC have been studied by secondary ion mass spectrometry (SIMS). Aluminum implantation has been used to monitor the position of the moving interface as well as to investigate the influence on the interface stability by the crystal quality of the 4H-SiC. After Al implantation a C-cap has been deposited by pyrolysis of photoresist. Subsequent annealing has been performed at 1900 and 2000 °C with durations between 15 minutes and 1 hour. SIMS measurements have been performed without removal of the C-cap. The surface remains smooth after the heat treatment, but a large amount of SiC material from the uppermost part of the wafer is lost. The amount of lost material is related to for instance annealing temperature, ambient conditions and ion induced crystal damage. This contribution gives a brief account of the processes governing the SiC surface decomposition during C-cap post implant annealing.

  • 272.
    Lissel, Linda
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Modeling the microstructural evolution during hot working of C-Mn and Nb microalloyed steels using a physically based model2006Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Recrystallization kinetics, during and after hot deformation, has been investigated for decades. From these investigations several equations have been derived for describing it. The equations are often empirical or semi-empirical, i.e. they are derived for certain steel grades and are consequently only applicable to steel grades similar to these. To be able to describe the recrystallization kinetics for a variety of steel grades, more physically based models are necessary.

    During rolling in hot strip mills, recrystallization enables the material to be deformed more easily and knowledge of the recrystallization kinetics is important in order to predict the required roll forces. SSAB Tunnplåt in Borlänge is a producer of low-carbon steel strips. In SSAB’s hot strip mill, rolling is conducted in a reversing roughing mill followed by a continuous finishing mill. In the reversing roughing mill the temperature is high and the inter-pass times are long. This allows for full recrystallization to occur during the inter-pass times. Due to the high temperature, the rather low strain rates and the large strains there is also a possibility for dynamic recrystallization to occur during deformation, which in turn leads to metadynamic recrystallization after deformation. In the finishing mill the temperature is lower and the inter-pass times are shorter. The lower temperature means slower recrystallization kinetics and the shorter inter-pass times could mean that there is not enough time for full recrystallization to occur. Hence, partial or no recrystallization occurs in the finishing mill, but the accumulated strain from pass to pass could lead to dynamic recrystallization and subsequently to metadynamic recrystallization.

    In this work a newly developed physically based model has been used to describe the microstructural evolution of austenite. The model is based on dislocation theory where the generated dislocations during deformation provide the driving force for recrystallization. The model is built up by several submodels where the recrystallization model is one of them. The recrystallization model is based on the unified theory of continuous and discontinuous recovery, recrystallization and grain growth by Humphreys.

    To verify and validate the model, rolling in the hot strip mill was modeled using process data from SSAB’s hot strip mill. In addition axisymmetric compression tests combined with relaxation was modeled using experimental results from tests conducted on a Gleeble 1500 thermomechanical simulator at Oulu University, Finland. The results show good agreement with measured data.

  • 273. Litnovsky, A.
    et al.
    Hellwig, M.
    Matveev, D.
    Komm, M.
    van den Berg, M.
    De Temmerman, G.
    Rudakov, D.
    Ding, F.
    Luo, G. -N
    Krieger, K.
    Sugiyama, K.
    Pitts, R. A.
    Petersson, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Optimization of tungsten castellated structures for the ITER divertor2015Ingår i: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 463, s. 174-179Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In ITER, the plasma-facing components (PFCs) of the first wall and the divertor armor will be castellated to improve their thermo-mechanical stability and to limit forces due to induced currents. The fuel accumulation in the gaps may significantly contribute to the in-vessel fuel inventory. Castellation shaping may be the most straightforward way to minimize the fuel inventory and to alleviate the thermal loads onto castellations. A new castellation shape was proposed and comparative modeling of conventional (rectangular) and shaped castellation was performed for ITER conditions. Shaped castellation was predicted to be capable to operate under stationary heat load of 20 MW/m(2). An 11-fold decrease of beryllium (Be) content in the gaps of the shaped cells alone with a 7-fold decrease of carbon content was predicted. In order to validate the predictive capabilities of modeling tools used for ITER conditions, the dedicated modeling with the same codes was made for existing tokamaks and benchmarked with the results of multi-machine experiments. For the castellations exposed in TEXTOR and DIII-D, the carbon amount in the gaps of shaped cells was 1.9-2.3 times smaller than that of rectangular ones. Modeling for TEXTOR conditions yielded to 1.5-fold decrease of carbon content in the gaps of shaped castellation outlining fair agreement with the experiment. At the same time, a number of processes, like enhanced erosion of molten layer yet need to be implemented in the codes in order to increase the accuracy of predictions for ITER.

  • 274.
    Liu, Chunxin
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Alternative binder phases for WC cemented carbides2014Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    WC cemented carbides are composites consisting of WC and a binder phase. WC/Co is widely used as cutting tools due to its excellent combination of hardness and toughness. This thesis work was performed at the R&D department of Sandvik Coromant and aimed to find the alternative binder phase to substitute cobalt. Several compositions of Fe-Ni and Fe-Ni-Co binder have been investigated in this study. The WC/Co reference samples were also prepared. The initial compositions were decided by the CALPHAD method. The samples were then produced by the means of powder metallurgy. The producing conditions, especially the sintering conditions, were manipulated to achieve full dense and uniform samples. The samples were analyzed by XRD, LOM, SEM, and EDS. Mechanical properties test has also been performed.The results showed that adjustment on carbon content is necessary to attain desirable structure. Increasing Fe content in the binder tends to make the materials harder. For Fe-Ni and Fe-Ni-Co, the martensitic transformation is essential to the mechanical performance. The induced “transformation toughening” in 72Fe28Ni and 82Fe18Ni binders significantly promoted the toughness. Furthermore, the grain growth inhibition by Fe was confirmed. The relations between sintering temperature, grain size and mechanical properties have been discussed. Compared with the WC/Co references, several compositions showed close and even superior mechanical performance which might provide solutions for the future alternative binder phase.

  • 275.
    Liu, Jiewei
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Fysiokemisk strömningsmekanik.
    Do-Quang, Minh
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Fysiokemisk strömningsmekanik.
    Amberg, Gustav
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Fysiokemisk strömningsmekanik.
    Thermohydrodynamics of boiling in binary compressible fluids2015Ingår i: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics, ISSN 1539-3755, E-ISSN 1550-2376, Vol. 92, nr 4, artikel-id 043017Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We numerically study the thermohydrodynamics of boiling for a CO2 + ethanol mixture on lyophilic and lyophobic surfaces in both closed and open systems, based on a diffuse interface model for a two-component system. The corresponding wetting boundary conditions for an isothermal system are proposed and verified in this paper. New phenomena due to the addition of another component, mainly the preferential evaporation of the more volatile component, are observed. In the open system and the closed system, the physical process shows very different characteristics. In the open system, except for the movement of the contact line, the qualitative features are rather similar for lyophobic and lyophilic surfaces. In the closed system, the vortices that are observed on a lyophobic surface are not seen on a lyophilic surface. More sophisticated wetting boundary conditions for nonisothermal, two-component systems might need to be further developed, taking into account the variations of density, temperature, and surface tension near the wall, while numerical results show that the boundary conditions proposed here also work well even in boiling, where the temperature is nonuniform.

  • 276. Loyola, C.
    et al.
    Davis, Sergio
    Universidad de Chile, Chile.
    Peralta, J.
    Gutiérrez, G.
    Onset of failure in argon by the effect of a shockwave: A molecular dynamics study2010Ingår i: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 49, nr 3, s. 582-587Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Molecular dynamic simulations of shockwaves in solid argon were performed. The simulation cell contains 51,840 atoms at 5 K interacting by means of a pairwise potential. The shockwave itself was introduced explicitly in the simulation by a piston hitting the sample from one side of the simulation box, at speeds ranging from 1.2 to 1.3 times the speed of sound in solid argon at the chosen density. In order to characterize the sample in terms of both structural and dynamic properties, we determine the density and temperature profiles according the advance of the shockwave, evaluating, for different slabs, the pair-distribution function, coordination number as well as performing a common neighbor analysis for the atoms. Our simulations reproduce the experimental Hugoniot curve and show how the material is break due to rarefaction waves. The picture that emerges is that when the shockwave starts, a local melting is produced in a region of the sample. Then, as the shockwave travels through the sample, a high density disordered phase is identified. When the piston stops, a rarefaction wave develops, producing a large tensile stress, which finally causes the failure of the sample.

  • 277. Lu, Yiping
    et al.
    Gao, Xiaoxia
    Dong, Yong
    Wang, Tongmin
    Chen, Hai-Lin
    Mao, Huahai
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Termodynamisk modellering.
    Zhao, Yonghao
    Jiang, Hui
    Cao, Zhiqiang
    Li, Tingju
    Guo, Sheng
    Preparing bulk ultrafine-microstructure high-entropy alloys via direct solidification2018Ingår i: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 10, nr 4, s. 1912-1919Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In the past three decades, nanostructured (NS) and ultrafine-microstructure (UFM) materials have received extensive attention due to their excellent mechanical properties such as high strength. However, preparing low-cost and bulk NS and UFM materials remains to be a challenge, which limits their industrial applications. Here, we report a new strategy to prepare bulk UFM alloys via the direct solidification of high-entropy alloys (HEAs). As a proof of concept, we designed AlCoCrxFeNi (1.8 <= x <= 2.0) HEAs and achieved a complete UFM in bulk materials. The compositional requirements for obtaining the formation of the UFM are highly demanding, necessitating the coupling of near eutectic alloy composition and the high temperature decomposition of supersaturated primary and secondary phases. Our strategy provides a low-cost and highly efficient method to prepare bulk UFM alloys, with great potential to accelerate the engineering application of these materials.

  • 278.
    Lu, YiYao
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Theoretical and Experimental Study of the Co-Cr-Mo System2011Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    The thermodynamic properties of the Co-Cr-Mo ternary system have been described. Available experimental data on the system have been assessed and applied to optimize the parameters used in the thermodynamic models within the Calphad method.

    Meanwhile, samples were made by the powder metallurgical process and heat treated (sintered) at 1573 K to investigate the phase diagram data related to the intermetallic phases, such as σ, μ and R phases present in the system.

    With the optimized thermodynamic description, we are able to fit most of the experimental data in the literature and from this work. However, the one phase field of R is too narrow in the present description. Furthermore, at 1573 K the extension of the phase boundary of σ toward the Co corner needs to be improved. In addition, the calculated phase diagram at 1573 K shows a fcc-bcc-σ three-phase equilibrium near the Co-Cr binary side. This is not shown in the experimentally determined ternary phase diagram but is necessary in order to match the recent data on the Co-Cr binary system.

  • 279.
    Luberry, Claire
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Keramteknologi.
    Morphological control of Ceria particles by precipitation method2011Självständigt arbete på avancerad nivå (magisterexamen), 30 poäng / 45 hpStudentuppsats (Examensarbete)
  • 280.
    Ma, Luyao
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Optimization of experimental conditions of hot wire method in thermal conductivity measurements2012Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    This work studied the hot wire method in measuring thermal conductivity at room temperature. The purpose is to find the optimized experimental conditions to minimize natural convection in liquid for this method, which will be taken as reference for high temperature thermal conductivity measurement of slag. Combining room temperature experiments and simulation with COMSOL Multiphysics 4.2a, the study on different experimental parameters which may influence the accuracy of the measured thermal conductivity was conducted. The parameters studied were the diameter of crucible, the position of wire in the liquid, including z direction and x-y plane position, diameter of the hot wire, and current used in the measurement. In COMSOL simulations, the maximum natural convection velocity value was used to evaluate the natural convection in the liquid. The experiment results showed after 4~5 seconds of the measuring process, the natural convection already happened. Also when current was fixed, the thinner the hot wire, the larger convection it would cause. This is because thinner wire generates more heat per unit surface area. Using higher current in measuring, more heat generation improved accuracy of result but also had earlier and larger effect on convection. Both simulation and experiments showed that with the height of the liquid fixed, the smaller diameter of the crucible (not small to the level which is comparable with hot wire diameter), the higher the position in z direction (still covered by liquid), the less natural convection effect existed. But the difference was not significant. The radius-direction position change didn’t influence the result much as long as the wire was not too close to the wall.

  • 281.
    Makaya, Advenit
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Materialens processvetenskap.
    On the effect of nitrogen, hydrogen and cooling rate on the solidification and pore formation in Fe-base and Al-base alloys2007Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Experiments on the production of porous metallic materials were performed on Fe-base and Al-base alloys. The method involves dissolution of gases in the liquid state and solidification at various cooling rates. The alloy compositions were selected to induce solidification of primary particles intended to control the pore distribution. For the Fe-base alloys, nitrogen was introduced into the melt by dissolution of chromium nitride powder. Fe-Cr-Mn-Si-C alloys featuring M7C3 carbide particles were selected. For the Al-base alloys, hydrogen gas was dissolved into the melt by decomposition of water vapor. Al-Ti and Al-Fe alloys featuring primary Al3Ti and Al3Fe intermetallic particles, respectively, were considered. In the Fe-base alloys, a homogeneous distribution of gas pores through the specimens’ volume was obtained at high cooling rate (water quenching) and after introduction of external nucleating agents. In the case of the Al-base alloys, a good pore distribution was observed at all cooling rates and without addition of nucleating agents. Calculations of the variation of nitrogen (respectively hydrogen) solubility based on Wagner interaction parameters suggest that pore nucleation and growth occur during precipitation of the primary particles (M7C3 carbides, Al3Ti or Al3Fe intermetallics), due to composition changes in the melt and resultant supersaturation with gas atoms. Microscopic analyses revealed that the primary particles control the pore growth in the melt and act as barriers between adjacent pores, thereby preventing pore coalescence and promoting a fine pore distribution. Uniaxial compression testing of the porous Al-Ti and Al-Fe materials showed the typical compressive behavior of cellular metals. Further work is needed to improve the quality and reproducibility of the porous structures which can possibly be used in energy absorption or load-bearing applications.

    As a corollary result of the quenching of hypereutectic Fe-Cr-Mn-Si-C alloys in the experiments of synthesis of porous metals, a homogeneous featureless structure was observed in some parts of the samples, instead of the equilibrium structure of M7C3 and eutectic phases. Subsequent investigations on rapid solidification of Fe-base alloys at various alloy compositions and cooling rates led to the formation of a single-phase structure for the composition Fe-8Cr-6Mn-5Mo-5Si-3.2C (wt.%), at relatively low cooling rates (≈103 K/s) and for large sample dimensions (2.85 mm). The single phase, which is likely to be the hcp ɛ-phase, was found to decompose into a finely distributed structure of bainite and carbides at ≈600 °C. The annealed structure showed very high hardness values (850 to 1200 HV), which could be exploited in the development of high-strength Fe-base materials.

  • 282.
    Makaya, Advenit
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Fredriksson, Hasse
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Production of Fe-Cr-C base foam: theoretical considerations and partical fabrication2005Ingår i: Proceedings of the Symposium on "Cellular Metals and Polymers" / [ed] Singer,R.F., Körner, C., Altstädt, V., Münstedt, H., Zürich: Trans Tech Publications , 2005, s. 49-52Konferensbidrag (Refereegranskat)
  • 283.
    Makaya, Advenit
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Fredriksson, Hasse
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Study on the production of Fe–Cr–Mn–C–Si foam by nitrogen solubility difference between the liquid and solid phases2005Ingår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 413-414, s. 533-537Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The feasibility of the production of Fe-base metallic foam by using the nitrogen solubility difference between the liquid and austenite phases has been studied in the Fe-Cr-Mn-C-Si system. Compositions showing a suitable solubility gap for precipitation of gas pores upon solidification have been derived by thermodynamic calculations of the nitrogen solubility in the liquid and solid phases, using the interaction parameters of nitrogen. Small amount of foams were produced for different compositions. The foaming involved dissolution of chromium nitrides into the melt and subsequent quenching. Four different compositions were tested: by varying the C content between 2 and 6 wt.%, the effect of the primary carbides on the foam microstructure could be studied. The presence of those carbides appears as an important element for the promotion of the pore nucleation and the prevention of pore coalescence. The addition of SiO2 powder in some experiments illustrated the beneficial effect of a nucleating agent to reach a homogeneous distribution of the gas pores.

  • 284.
    Makaya, Advenit
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Fredriksson, Hasse
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Synthesis and structural characterisation of porous Al-Fe and Al-Ti materials obtainted by hydrogen solubility variation2007Rapport (Övrigt vetenskapligt)
  • 285.
    Makaya, Advenit
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Fredriksson, Hasse
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Uniaxial compression testing of porous Al-Fe and Al-Ti materials synthesized by water vapor dissolution2007Rapport (Övrigt vetenskapligt)
  • 286.
    Makaya, Advenit
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Fredriksson, Hasse
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Variation of nitrogen solubility and mechanism of pore formation during production of porous Fe-Cr-Mn-Si-C material2007Ingår i: International Journal of Cast Metals Research, ISSN 1364-0461, E-ISSN 1743-1336, Vol. 20, nr 2, s. 73-83Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Experiments regarding the synthesis of porous metallic materials were performed by dissolution of nitrogen into molten hypereutectic 77Fe-8Cr-6Mn-5Si-4C (wt-%) and hypoeutectic 79Fe-8Cr-6Mn-5Si-2C alloys, and water quenching. A uniform pore distribution was obtained only for the hypereutectic alloy. To study the effect of the alloy composition and microstructure on the pore distribution, the variation of nitrogen solubility during primary solidification was calculated for both alloys, taking into account the phase composition changes. A mechanism of pore formation is proposed. In the hypereutectic alloy, an increasing nitrogen supersaturation in the melt during primary carbide growth is believed to fuel the growth of nucleated N-2 pores. The primary M7C3 carbides play an essential role in preventing pore coalescence. In the hypoeutectic alloy, a decreasing nitrogen solubility gap between the austenite dendrites and the liquid does not allow extensive pore growth. The absence of primary carbides favours the formation of a single large pore.

  • 287.
    Malmgren, C.
    et al.
    Engineering Physics, Mid Sweden University.
    Hummelgård, M.
    Engineering Physics, Mid Sweden University.
    Bäckström, J.
    Permascand AB.
    Cornell, Ann
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Olin, H.
    Engineering Physics, Mid Sweden University.
    Nanoscale characterization of crystallinity in DSA (R) coating2008Ingår i: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 100, nr Part 5, s. 052026-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Dimensionally Stable Anodes (DSA (R)) are used for industrial production of e. g. chlorine and chlorate. It is known that the superior electrocatalytical properties of DSA (R) is due to the large effective area of the porous coating. However, this knowledge is mainly found from in situ electrochemical measurements. Here, we used ex situ methods, AFM, TEM and gas porosimetry, for characterization at the nanoscale. The DSA (R) coating was found to consist of mono-crystalline grains with a size of 20-30 nm and with pores of about 10 nm in diameter. Using a simple geometrical model an effective area was calculated. For a typical coating thickness, an increase of about 1000 times in the effective surface area was found, which is consistent with in situ estimations. These results suggest that the dominating source of surface enlargement is due to nano-crystallinity.

  • 288.
    Manda, Krishnagoud
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Finite Element Simulations of Biphasic Articular Cartilages With Localized Metal Implants2010Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Articular cartilage is a specialized connective soft tissue that resides onthe ends of long-bones, transfers the load smoothly between the bones in diarthrodialjoints by providing almost frictionless, wear resistant sliding surfacesduring joint articulation. Focal chondral or osteochondral defects in articularcartilage are common and show limited capacity for biological repair. Furthermore,changes in the bio-mechanical forces at the defect site may makethe tissue more susceptible to continued degeneration. Alternatively, the contouredfocal resurfacing metal implant can be used to treat such full thicknesscartilage defects. Physiological and biomechanical studies on animal modelswith metal implant have shown good clinical outcomes. However, the mechanicalbehavior of cartilage surrounding the implant is not clearly known withrespect to the joint function after treating such defects with metal implantsand also to improve the implant design. We developed a simple 3-dimensionalfinite element model by approximating one of the condyles of the sheep kneejoint. Parametric study was conducted in the simulations to verify differentprofiles for the implant, positioning of the implant with respect to cartilagesurface, defect size and to show the mechanical sealing effect due to the wedgeshape of the implant. We found the maximal deformations, contact pressuresand stresses which constitute the mechanical behavior of cartilages. We alsoconfirmed that using a metal implant to fill the full thickness chondral defectsis more beneficial than to leave the defect untreated from mechanical point ofview. The implant should be positioned slightly sunk into the cartilage basedon the defect size, in order to avoid damage to the opposing surface. The largerthe defect size, the closer the implant should be to the flush. We also simulatedthe time dependent behavior of the cartilages. In all the simulations, a staticaxial loading was considered. The wedge shape of the implant provided themechanical sealing of the cartilage surrounding the implant. The determineddeformations in the cartilages immediately surrounding the implant are instrumentalin predicting the sticking-up of the implant into the joint cavity whichmay damage opposing soft tissues.

  • 289.
    Manda, Krishnagoud
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Eriksson, Anders
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Time-dependent behavior of cartilage surrounding a metal implant for full-thickness cartilage defects of various sizes: a finite element study2012Ingår i: Biomechanics and Modeling in Mechanobiology, ISSN 1617-7959, E-ISSN 1617-7940, Vol. 11, nr 5, s. 731-742Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Recently, physiological and biomechanical studies on animal models with metal implants filling full-thickness cartilage defects have resulted in good clinical outcomes. The knowledge of the time-dependent macroscopic behavior of cartilage surrounding the metal implant is essential for understanding the joint function after treating such defects. We developed a model to investigate the in vivo time-dependent behavior of the tibiofemoral cartilages surrounding the metal implant, when the joint is subjected to an axial load for various defect sizes. Results show that time-dependent effects on cartilage behavior are significant, and can be simulated. These effects should be considered when evaluating the results from an implant. In particular, the depth into the cartilage where an implant is positioned and the mechanical sealing due to solidification of the poroelastic material need a time aspect. We found the maximal deformations, contact pressures and contact forces in the joint with time for the implant positioned in flush and sunk 0.3 mm into the cartilage. The latter position gives the better joint performance. The results after 60 s may be treated as the primary results, reflecting the effect of accumulation in the joint due to repeated short-time loadings. The wedge-shaped implant showed beneficial in providing mechanical sealing of cartilages surrounding the implant with time.

  • 290.
    Manda, Krishnagoud
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Ryd, Leif
    Department of Orthopaedics, Karolinska University Hospital/Huddinge and Department of Clinical Science, Intervention and Technology, Karolinska Institutet, Sweden.
    Eriksson, Anders
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Finite element simulations of a focal knee resurfacing implant applied to localized cartilage defects in a sheep model2011Ingår i: Journal of Biomechanics, ISSN 0021-9290, E-ISSN 1873-2380, Vol. 44, nr 5, s. 794-801Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Articular resurfacing metal implants have recently been tested in animal models to treat full thickness localized articular cartilage defects, showing promising results. However, the mechanical behavior of cartilage surrounding the metal implant has not been studied yet as it is technically challenging to measure in vivo contact areas, pressures, stresses and deformations from the metal implant. Therefore, we implemented a detailed numerical finite element model by approximating one of the condyles of the sheep tibiofemoral joint and created a defect of specific size to accommodate the implant. Using this model, the mechanical behavior of the surrounding of metal implant was studied. The model showed that the metal implant plays a significant role in the force transmission. Two types of profiles were investigated for metal implant. An implant with a double-curved profile, i.e., a profile fully congruent with the articular surfaces in the knee, gives lower contact pressures and stresses at the rim of the defect than the implant with unicurved spherical profile. The implant should be placed at a certain distance into the cartilage to avoid damage to opposing biological surface. Too deep positions, however, lead to high shear stresses in the cartilage edges around the implant. Mechanical sealing was achieved with a wedge shape of the implant, also useful for biochemical sealing of cartilage edges at the defect.

  • 291.
    Manuilov, Sergey
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Integrerade komponenter och kretsar.
    Ferromagnetic resonance in films with growth induced anisotropy2011Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    This thesis discusses two different magnetic materials: epitaxial yttrium iron garnet (YIG) and heteromorphous CoFeB-SiO2 films.

    YIG films were grown by pulse laser deposition (PLD) techniques onto gadolinium gallium garnet (GGG) substrates of (111) and (001) crystal orientations. Using stoichiometric and overstoichiometric ablative targets, we developed two types of YIG submicron films. The films grown from overstoichiometric targets have magnetic properties slightly different from standard liquid phase epitaxy (LPE) YIGs. They also demonstrate good substrate matching and approximately 6% nonstoichiometry. In contrary, films grown from stoichiometric targets posses surprisingly high values of uniaxial anisotropy, meanwhile cubic anisotropy is reduced several times. These films also reveal strong lattice distortions and nonstoichiometry around 17%.

    Employing Weiss molecular field theory and single-ion anisotropy model we determined the preferential occupancy of the octahedral [a] positions in the YIG cubic lattices by Fe3+ vacancies. The vacancies were found to be preferentially oriented along the growth direction perpendicular to the film surface. We called this effect “deformation blockade”.

    Different magnetostatic surface wave (MSSW) filters were also demonstrated. The filters employ high uniaxial anisotropy in YIG submicron films with magnetic losses ΔH ~ 1 Oe.

     Heteromorphous CoFeB-SiO2 films were deposited onto glass substrates employing carrousel magnetron sputtering. This novel technique allows amorphous films fabrication with record high in-plane anisotropy. The induced anisotropy fields here are approximately dozen times greater the values achieved using conventional growth technique when external bias field is applied during deposition process.

    Interesting observations were made studying CoFeB-SiO2 magnetization dynamics in the wide frequency range from 500 kHz up to 15 GHz.  Two different anomalies of the magnetic susceptibility were found at the field of in-plane anisotropy Hp and critical field Hcr (0 < Hcr < Hp). We explained the anomalies appearance by sequence of the domain walls transformations so that Néel-Bloch-Néel domain wall transition stands for the instability at H = ±Hcr and transition from the uniformly magnetized state to the domain state with Néel domain wall and vice versa is responsible for the instability at H = ±Hp.

  • 292.
    Manzo, Michele
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Denning, Denise
    Rodriguez, Brian J.
    Gallo, Katia
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Laserfysik.
    Piezoresponse force microscopyon proton exchanged LiNbO3 layers2012Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    We use piezoresponse force microscopy for high-resolution investigations on protonexchanged LiNbO3 surfaces. We also quantify the reduction of the d33 nonlinear coefficientinduced by proton exchange in congruent LiNbO3 substrates with and without Mg-doping.

  • 293.
    Marquis, Gary
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner. Aalto University, School of Engineering, Espoo, 00076, Finland .
    Barsoum, Zuheir
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    A guideline for fatigue strength improvement of high strength steel welded structures using high frequency mechanical impact treatment2013Ingår i: Procedia Engineering, Elsevier, 2013, s. 98-107Konferensbidrag (Refereegranskat)
    Abstract [en]

    In the past decade, high frequency mechanical impact (HFMI) has significantly developed as a reliable, effective and userfriendly method for post-weld fatigue strength improvement technique for welded structures. This paper presents a proposed fatigue design and assessment guideline for HFMI improved welded joints. Stress analysis methods based on nominal stress, structural hot spot stress and effective notch stress are discussed. The document especially considers the observed extra benefit that has been experimentally observed for HFMI treated high strength steels. The proposal is considered to apply to steel structures from plate thickness 5 to 50 mm and for yield strengths ranging from 235 MPa to 960 MPa. Several fatigue assessment examples are also provided. Lessons learned concerning appropriate HFMI procedures and quality assurance measures are presented. Due to differences in the HFMI tools and the wide variety of potential applications, certain details of a proper treatment procedures and quantitative quality control measures are presented generally. It is proposed that specific details should be documented in a HFMI Procedure Specification for each structure being treated. It is hoped that this guideline proposal will provide a stimulus to researchers working in the field.

  • 294. Martinez, L. L.
    et al.
    Barsoum, Zuheir
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Paradowska, A.
    State-of-the-art: Fatigue life extension of offshore installations2012Ingår i: Proceedings of the ASME 31st International Conference on Ocean, Offshore and Arctic Engineering--2012: presented at ASME 2012 31st International Conference on Ocean, Offshore and Arctic Engineering, July 1-6, 2012, Rio de Janeiro, Brazil, ASME Press, 2012, s. 9-20Konferensbidrag (Refereegranskat)
    Abstract [en]

    The use of fatigue life improvement techniques and specifically ultrasonic peening treatment to extend the service life of offshore structures has become an accepted practice during the last five years. The understanding of the process as well as equipment's upgrading for treatment in-situ including quality control and assurance have been developed up to a level that it has become a current practice in many parts of the world. However, the efficiency of the ultrasonic peening is strictly dependent on the deep understanding of significant fatigue parameters as weld defects, stress concentrations and residual stresses and their interaction. In this paper we attempt to present the current knowledge and the physical reasons why the ultrasonic peening treatment is able to improve the fatigue life of welded joints. The local weld geometry or stress concentration, weld imperfections as well as welding residual stresses are all modified and improved by the application of ultrasonic peening. Local weld geometry and weld process inherent weld imperfections are the factors primarily influencing the fatigue strength in welded joints. Comprehensive studies have been carried out during the last 20 years in order to detect and document the weld defects as well as to understand their origin and effect on the fatigue strength of welds. Analogous efforts have been dedicated to understand and document the influence of local weld geometries on the stress concentrations and its influence on endurance and structural integrity. Similarly, efforts have been done to understand the influence of the relaxation by external loads of the by the ultrasonic peening treatment induced compressive stresses. Fatigue test results of ultrasonic peening treated relevant weld details have been used to assess the potential life extension. The results showed four to six times fatigue life extension. The spectrum fatigue test was designed to confirm that relaxation by service loads of the induced compressive stresses during ultrasonic peening treatment would not diminish the benefit.

  • 295.
    Masood, Ansar
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Teknisk materialfysik.
    Afridi, A. A.
    Ström, Valter
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Teknisk materialfysik.
    Belova, Lyubov
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Teknisk materialfysik.
    Rao, K. Venkat
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Teknisk materialfysik.
    Spin-Reorientation Transition in Fe-Ni-B-Nb thin filmsManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    Spontaneous perpendicular magnetization manifested by transcritical loops and stripe domain magnetic pattern have been observed for nanocrystalline film (~408nm) of Fe-Ni-B-Nb alloy grown by pulse laser deposition (PLD) which, otherwise, could not be seen for thinner films (≤100 nm) and at low temperatures (≤225K). Thermal treatment of thicker films (408nm) was found to affect the global magnetic behaviors by transforming transcritical loops to simple square type. Temperature dependence of magnetization M (T) and AC susceptibility measurement revealed that intergranular amorphous matrix gets magnetically order/disorder as a function of temperature by giving rise to different global magnetic behaviors at different temperatures.    

  • 296.
    Masood, Ansar
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Teknisk materialfysik.
    Oak, J. J
    Mao, H.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Ågren, John
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    Belova, Lyubov
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Teknisk materialfysik.
    Inoue, A.
    Rao, K. V.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Teknisk materialfysik.
    Distinct Plasticity of Biocompatible Ti-Zr-Cu-Pd-Sn Bulk Metallic GlassManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    We have developed Ti-Zr-Cu-Pd-Sn bulk metallic glass without toxic elements which exhibits distinct plasticity (~12.6%) by revealing strain hardening before failure. Specimens performed under compression tests do not show any crystalline phases which usually enhance plasticity by branching or restricting the rapid propagation of shear bands. Along with excellent mechanical properties alloy exhibits appreciably high bulk forming ability, GFA, with large supercooled regime (~56K) and as a consequence cylindrical rods of at least 7mm were fabricated directly by Cu-mold casting. The combination of such mechanical properties and appreciably high bulk forming ability makes it a potential candidate for biomedical applications.   

  • 297.
    Masood, Ansar
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Teknisk materialfysik.
    Ström, Valter
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Teknisk materialfysik.
    Belova, Lyubov
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Teknisk materialfysik.
    Rao, K. V.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Teknisk materialfysik.
    Low temperature magnetic hardening in nanocrystalline Fe-Ni-B-Nb thin filmsManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    Low temperature magnetic properties of nanocrystalline FeNiBNb thin films grown by Pulse Laser Deposition (PLD) were investigated. Temperature dependence of magnetization M (T) revealed that weak ferromagnetic amorphous matrix gets magnetically order/disorder and as a consequence, system inters into different state of magnetization by giving rise to interesting global magnetic behaviors. Sample exhibits threefold coercive behavior with the evolution of temperature (5-300K).  Magnetic hardening was observed below 25K and attributed to evolution of spin-glass like state of the system. 

  • 298.
    Masood, Ansar
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Teknisk materialfysik.
    Tamaki, T.
    Ström, Valter
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Teknisk materialfysik.
    Belova, Lyubov
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Teknisk materialfysik.
    Rao, K. V.
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Teknisk materialfysik.
    Magneto-Optical properties of amorphous Fe-B-Nbthin filmsManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    Optically highly transparent, soft ferromagnetic thin films of Fe-B-Nb alloy grown on quartz by Pulse Laser Deposition (PLD) were investigated for structural, optical and magneto-optical properties.  All deposited films revealed fully amorphous structure with very uniform thickness and surface morphology.  Optical transmittance of 8 and 11nm thick films were found more than 60% over the entire visible regime (400-700nm). Verdet constant (V) and saturation Faraday rotation angle (θf) of studied films were increased linearly as a function of wavelength (λ) and  considered appreciably high as compared to the reported  magneto-optic materials, for example, 11nm thick film showed θf = 11.8deg/μm and V=21.4deg/Oe cm at λ=611nm. The combination of optical and magneto-optical properties with state of art fabrication process makes this kind of amorphous films interesting for optical telecommunication technology. 

  • 299.
    Mattsson, Tuve
    et al.
    KTH, Skolan för kemivetenskap (CHE), Centra, Wallenberg Wood Science Center. Department of Chemical Engineering, University of Bath, Claverton Down, Bath, United Kingdom.
    Lewis, W. J. T.
    Chew, Y. M. J.
    Bird, M. R.
    In situ investigation of soft cake fouling layers using fluid dynamic gauging2015Ingår i: Food and Bioproducts Processing, ISSN 0960-3085, E-ISSN 1744-3571, Vol. 93, s. 205-210Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Cake fouling is a phenomenon contributing to flux decline during cross-flow filtration. Its behaviour is also difficult to predict, especially for challenging separations where organic materials often form compressible cakes with a high resistance. In this study Kraft lignin was used as a model material for organic foulants in cross-flow microfiltration experiments, and a non-contact fluid dynamic gauging (FDG) technique in pressure-mode configuration was used to study the cake fouling layers in situ. A new and enhanced FDG equipment was used; enabling an increased accuracy of the fouling layer thickness measurements and capable of producing higher fluid shear stresses on the surface of the cake layer for strength measurements. Using FDG, very thin fouling layers were observed; in addition, FDG was used to investigate their cohesive and adhesive strengths, showing that over a 10-fold increase in fluid shear stress was required to remove foulant closer to the membrane compared with that on the surface of the cake.

  • 300.
    Melin, Niklas
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    The modified iosipescu shear test for measuring strengths and constitutive behavior of composites2006Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
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