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  • 151.
    Ngaruye, Innocent
    et al.
    Linköping University, Department of Mathematics, Mathematical Statistics . Linköping University, Faculty of Science & Engineering.
    Nzabanita, Joseph
    Department of Mathematics, University of Rwanda.
    von Rosen, Dietrich
    Linköping University, Department of Mathematics, Mathematical Statistics . Linköping University, Faculty of Science & Engineering.
    Singull, Martin
    Linköping University, Department of Mathematics, Mathematical Statistics . Linköping University, Faculty of Science & Engineering.
    Small Area Estimation under a Multivariate Linear Model for Repeated measures Data2017In: Communications in Statistics - Theory and Methods, ISSN 0361-0926, E-ISSN 1532-415X, Vol. 46, no 21, p. 10835-10850Article in journal (Refereed)
    Abstract [en]

    In this article, Small Area Estimation under a Multivariate Linear model for repeated measures data is considered. The proposed model aims to get a model which borrows strength both across small areas and over time. The model accounts for repeated surveys, grouped response units and random effects variations. Estimation of model parameters is discussed within a likelihood based approach. Prediction of random effects, small area means across time points and per group units are derived. A parametric bootstrap method is proposed for estimating the mean squared error of the predicted small area means. Results are supported by a simulation study.

  • 152.
    Nordqvist, Joel
    Linköping University, Department of Management and Engineering, Machine Design. Linköping University, The Institute of Technology.
    Applicering av temperaturgivare2011Independent thesis Basic level (university diploma), 10,5 credits / 16 HE creditsStudent thesis
    Abstract [sv]

    Examensarbetets mål är att ta fram en ny konstruktion för montering av temperaturgivare i värmepumpar. Arbetet begränsas till att omfatta de givare som idag är monterade på rör och den nya konstruktionen är tänkt att användas med en givare från en ny leverantör.

    En undersökning av hur givarna är monterade idag har genomförts i Boschs egna värmepumpar men även i konkurrenters värmepumpar. Dessa undersökningar har varit till stor hjälp för att bättre förstå problemet och för att planera till de tester som sedan utförts.

    För att på ett bra sätt avläsa temperaturen med givarna krävs att de monteras på ett bra sätt. En testrigg har byggts för att på ett bra sätt kunna jämföra och utvärdera olika lösningar mot varandra. De lösningar som har testats är bland annat de som hittades i undersökningen av värmepumparna men också några egna idéer.

    Efter testerna har resultaten utvärderats och med detta som grund har förbättringar av existerande lösningar eller nya lösningar arbetats fram i form av skisser.

    Ett clips som en konkurrent använder har efter testerna uppvisat relativt bra resultat men den stora fördelen med clipset är att det är väldigt lätt att montera och kräver inga verktyg. På grund av tidsbrist har vissa tester inte kunnat utföras för att säkerställa att detta clips uppfyller alla krav som ställs på ett nytt monteringssätt.

  • 153.
    Norman, Oskar
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Anisotropic material modeling and impact simulation of a brush cutter casing made of a short fiber reinforced plastic2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    A popular way to reduce weight in industrial products without compromising the strength or stiffness is to replace components made of metal by plastics that have been reinforced by glass fibers. When fibers are introduced in a plastic, the resulting composite usually becomes anisotropic, which makes it much more complex to work with in simulation software. This thesis looks at modeling of such a composite using the multi-scale material modeling tool Digimat.

    An injection molding simulation of a brush cutter casing made of a short fiber reinforced plastic has been performed in order to obtain information about the glass fiber orientations, and thus the anisotropy, in each material point. That information has then been transferred over from the injection mesh to the structural mesh via a mapping routine. An elasto-viscoplastic material model with failure has been employed and calibrated against experimental data to find the corresponding material parameters. Lastly, a finite element analysis simulating a drop test has been performed. The results from the analysis have been compared with a physical drop test in order to evaluate the accuracy of the methodology used. The outcome has been discussed, conclusions have been drawn and suggestions for further studies have been presented.

  • 154.
    Norman, Viktor
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Calmunger, Mattias
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    On the micro- and macroscopic elastoplastic deformation behaviour of cast iron when subjected to cyclic loading2019In: International journal of plasticity, ISSN 0749-6419, E-ISSN 1879-2154, Vol. 115, p. 200-215Article in journal (Refereed)
    Abstract [en]

    The complicated constitutive behaviour of cast iron, involving a non-linear elastic regime, tension-compression stress asymmetry, varying elastic modulus and an inflection in the tension-to-compression hardening curve, is investigated using a micromechanical modelling approach. In this way, it is demonstrated that the abnormalities observed in the constitutive behaviour are qualitatively and quantitatively explained by the interaction behaviour between the matrix and graphite constituents. In initial tension, the absence of linearity is rationalised by the successive loss in load-carrying capacity of the graphite phase due to debonding, which in subsequent cycling, results in the opening and re-contact of the matrix-graphite interface. This effect is demonstrated to result in tension-compression asymmetry in stress and elastic modulus, as well as the inflection in tension-to-compression loading. The given model of explanation is validated by comparison to the experimentally acquired microscopic strain field in EN-GJV-400 at locations where stress concentrations are generated due to the matrix-graphite debonding, using high-resolution digital image correlation of scanning electron images.

  • 155.
    Olofsson, Erik
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Chassis calculations for Frame design2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This is a Masters Thesis report of a project carried out at Scania AB in Södertälje. The project concerns rationalizing Chassis calculations for use in truck Frame design. The subject for analysis is a six-wheeled articulated truck, and the load cases under study is Lateral Loading, Frame Torsion and Vertical Load on Kingpin. Making robust deformation and stress models with a calculation time sufficiently short and accuracy consistently high for efficient design work is an arduous task. This report presents several approaches to tackle this type of problem. By means of simplifying contemporary modeling approaches and methods and automating the setup process, a method that enables short calculation iterations on a chassis frame of a truck is achieved. This is done using the Catia GAS framework in conjunction with several other licences commonly used by designers.

  • 156.
    Palmert, Frans
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Crack growth in single crystal nickel base superalloys under isothermal and thermomechanical fatigue2019Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    This work concerns the fatigue crack growth behaviour of nickel base single crystal superalloys. The main industrial application of this class of materials is in gas turbine blades, where the ability to withstand severe mechanical loading in combination with high temperatures is required. In order to ensure the structural integrity of gas turbine blades, knowledge of the fatigue crack growth behaviour under service-like conditions is of utmost importance. The aim of the present work is both to improve the understanding of the crack growth behaviour of single crystal superalloys and also to improve the testing and evaluation methodology for crack propagation under thermomechanical fatigue loading conditions. Single crystal superalloys have anisotropic mechanical properties and are prone to localization of inelastic deformation along the close-packed planes of the crystal lattice. Under some conditions, crystallographic crack growth occurs along these planes and this is a complicating factor throughout the whole chain of crack propagation life simulation; from material data generation to component calculation. Fatigue crack growth testing has been performed, both using conventional isothermal testing methods and also using thermomechanical fatigue crack growth testing. Experimental observations regarding crystallographic crack growth have been made and its dependence on crystal orientation and testing temperature has been investigated. Quantitative crack growth data are however only presented for the case of Mode I crack growth under isothermal as well as thermomechanical fatigue conditions. Microstructural investigations have been undertaken to investigate the deformation mechanisms governing the crack growth behaviour. A compliance based method for the evaluation of crack opening force under thermomechanical fatigue conditions was developed, in order to enable a detailed analysis of the test data. The crack opening force evaluation proved to be of key importance in the understanding of the crack driving force under different testing conditions.

    List of papers
    1. Fatigue crack growth behaviour of an alternative single crystal nickel base superalloy
    Open this publication in new window or tab >>Fatigue crack growth behaviour of an alternative single crystal nickel base superalloy
    2018 (English)In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 109, p. 166-181Article in journal (Refereed) Published
    Abstract [en]

    The fatigue crack growth behaviour of a single crystal nickel base superalloy was studied at three different temperatures (20 degrees C, 500 degrees C and 750 degrees C) and three different crystallographic orientations. At the highest testing temperature, the influence of hold time at maximum load was also evaluated. Under some of the testing conditions, crystallographic crack growth occurred along {1 1 1} planes, which were non-perpendicular to the loading direction. The propensity for crystallographic cracking was observed to be strongly temperature dependent with a maximum occurring at the intermediate testing temperature of 500 degrees C. During non-crystallographic, Mode I crack growth the crack tended to avoid the gamma particles and propagated preferentially through the gamma matrix.

    Place, publisher, year, edition, pages
    ELSEVIER SCI LTD, 2018
    Keywords
    Single crystal superalloy; Fatigue; Crack growth; Crystallographic crack growth; Temperature dependence; Orientation dependence; Hold time influence
    National Category
    Applied Mechanics
    Identifiers
    urn:nbn:se:liu:diva-145431 (URN)10.1016/j.ijfatigue.2017.12.003 (DOI)000425073100017 ()
    Note

    Funding Agencies|Siemens Industrial Turbomachinery AB in Finspang, Sweden; Swedish Energy Agency, via the Research Consortium of Materials Technology for Thermal Energy Processes [KME-702]

    Available from: 2018-04-03 Created: 2018-04-03 Last updated: 2019-09-23
    2. Thermomechanical fatigue crack growth in a single crystal nickel base superalloy
    Open this publication in new window or tab >>Thermomechanical fatigue crack growth in a single crystal nickel base superalloy
    2019 (English)In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 122, p. 184-198Article in journal (Refereed) Published
    Abstract [en]

    Thermomechanical fatigue crack growth in a single crystal nickel base superalloy was studied. Tests were performed on single edge notched specimens, using in phase and out of phase thermomechanical fatigue cycling with temperature ranges of 100-750°C and 100-850°C and hold times at maximum temperature ranging from 10s to 6h. Isothermal testing at 100°C, 750°C and 850°C was also performed using the same test setup. A compliance-based method is proposed to experimentally evaluate the crack opening stress and thereby estimate the effective stress intensity factor range ΔKeff for both isothermal and nonisothermal conditions. For in phase thermomechanical fatigue, the crack growth rate is increased if a hold time is applied at the maximum temperature. By using the compliance-based crack opening evaluation, this increase in crack growth rate was explained by an increase in the effective stress intensity factor range which accelerated the cycle dependent crack growth. No significant difference in crack growth rate vs ΔKeff was observed between in phase thermomechanical fatigue tests and isothermal tests at the maximum temperature. For out of phase thermomechanical fatigue, the crack growth rate was insensitive to the maximum temperature and also to the length of hold time at maximum temperature. The crack growth rate vs ΔKeff during out of phase thermomechanical fatigue was significantly higher than during isothermal fatigue at the minimum temperature, even though the advancement of the crack presumably occurs at the same temperature. Dissolution of γ′ precipitates and recrystallization at the crack tip during out of phase thermomechanical fatigue is suggested as a likely explanation for this difference in crack growth rate.

    Place, publisher, year, edition, pages
    Elsevier, 2019
    Keywords
    single crystal superalloy, thermomechanical fatigue, crack growth, crack closure
    National Category
    Materials Engineering Applied Mechanics Manufacturing, Surface and Joining Technology Metallurgy and Metallic Materials Infrastructure Engineering
    Identifiers
    urn:nbn:se:liu:diva-154074 (URN)10.1016/j.ijfatigue.2019.01.014 (DOI)000462110100017 ()
    Note

    Funding agencies: Siemens Industrial Turbomachinery AB in Finspang, Sweden; Swedish Energy Agency, via the Research Consortium of Materials Technology for Thermal Energy Processes [KME-702]

    Available from: 2019-01-28 Created: 2019-01-28 Last updated: 2019-04-08
  • 157.
    Palmert, Frans
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Gustafsson, David
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Thermomechanical fatigue crack growth in a single crystal nickel base superalloy2019In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 122, p. 184-198Article in journal (Refereed)
    Abstract [en]

    Thermomechanical fatigue crack growth in a single crystal nickel base superalloy was studied. Tests were performed on single edge notched specimens, using in phase and out of phase thermomechanical fatigue cycling with temperature ranges of 100-750°C and 100-850°C and hold times at maximum temperature ranging from 10s to 6h. Isothermal testing at 100°C, 750°C and 850°C was also performed using the same test setup. A compliance-based method is proposed to experimentally evaluate the crack opening stress and thereby estimate the effective stress intensity factor range ΔKeff for both isothermal and nonisothermal conditions. For in phase thermomechanical fatigue, the crack growth rate is increased if a hold time is applied at the maximum temperature. By using the compliance-based crack opening evaluation, this increase in crack growth rate was explained by an increase in the effective stress intensity factor range which accelerated the cycle dependent crack growth. No significant difference in crack growth rate vs ΔKeff was observed between in phase thermomechanical fatigue tests and isothermal tests at the maximum temperature. For out of phase thermomechanical fatigue, the crack growth rate was insensitive to the maximum temperature and also to the length of hold time at maximum temperature. The crack growth rate vs ΔKeff during out of phase thermomechanical fatigue was significantly higher than during isothermal fatigue at the minimum temperature, even though the advancement of the crack presumably occurs at the same temperature. Dissolution of γ′ precipitates and recrystallization at the crack tip during out of phase thermomechanical fatigue is suggested as a likely explanation for this difference in crack growth rate.

    The full text will be freely available from 2021-01-25 17:11
  • 158.
    Palmert, Frans
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering. Siemens Ind Turbomachinery AB, Sweden.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Gustafsson, David
    Siemens Ind Turbomachinery AB, Sweden.
    Busse, Christian
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Fatigue crack growth behaviour of an alternative single crystal nickel base superalloy2018In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 109, p. 166-181Article in journal (Refereed)
    Abstract [en]

    The fatigue crack growth behaviour of a single crystal nickel base superalloy was studied at three different temperatures (20 degrees C, 500 degrees C and 750 degrees C) and three different crystallographic orientations. At the highest testing temperature, the influence of hold time at maximum load was also evaluated. Under some of the testing conditions, crystallographic crack growth occurred along {1 1 1} planes, which were non-perpendicular to the loading direction. The propensity for crystallographic cracking was observed to be strongly temperature dependent with a maximum occurring at the intermediate testing temperature of 500 degrees C. During non-crystallographic, Mode I crack growth the crack tended to avoid the gamma particles and propagated preferentially through the gamma matrix.

  • 159.
    Palmér, Martin
    et al.
    Linköping University, Department of Management and Engineering, Machine Design.
    Meijer, Jacob
    Linköping University, Department of Management and Engineering, Machine Design.
    Utveckling av fettdoseringsenhet: förbättrad indikering och justering2016Independent thesis Basic level (university diploma), 10,5 credits / 16 HE creditsStudent thesis
    Abstract [en]

    The work consists of a construction process in order to improve the adjustment and indication of a grease dosing unit used in a dual-line lubrication system. The work is performed on behalf of and in consultation with Assalub AB in Åtvidaberg.

    The grease dosing unit is a part of a dual-line central lubrication system and is often used in exposed and strenuous environments. Therefor it is important that the unit’s function and adjustment is easy and trustworthy and that the indication is clear and facilitates functional checks. The adjustment device used for adjustment and indication today does not cater Assalubs requirements. The present construction has no reliable adjustment, can give rise to leakage and has an indication which is difficult to see from some angles. This work therefor aims to develop and improve the design of the adjustment device so that the reliability and life expectancy increases and functional checks is simplified.

    The work resulted in a concept with a reliable adjustment unit with well visible flags for indication and a simple adjustment unit was developed. Based on this concept CAD-models and production drawings was produced and delivered, and a prototype was made for function testing.

  • 160.
    Pannetier, Romain
    et al.
    Renault SAS, Service Facteur Humain, Conduite et Vie Abord, 1 avenue du Golf, Guyancourt, France.
    Robert, Thomas
    Université de Lyon, F-69622, Lyon, France, Ifsttar, UMR_T9406, LBMC, Université Lyon1, France.
    Holmberg, Joakim
    Linköping University, Department of Management and Engineering, Mechanics. Linköping University, The Institute of Technology.
    Wang, Xuguang
    Université de Lyon, F-69622, Lyon, France, Ifsttar, UMR_T9406, LBMC, Université Lyon1, France.
    Optimization-based muscle force scaling for subject specific maximum isometric torque estimation2011In: Proceedings of the XXIIIth Congress of the International Society of Biomechanics, 2011Conference paper (Refereed)
  • 161.
    Pavlovic, Srdan
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Andersson, Magnus
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Lantz, Jonas
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Karlsson, Matts
    Linköping University, Center for Medical Image Science and Visualization (CMIV). Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Reduced Aerodynamic Drag for Truck-Trailer Configurations Using Parametrized CFD Studies2012In: ASME 2012 International Mechanical Engineering Congress and Exposition, Volume 7: Fluids and Heat Transfer Parts A, B, C, and D, New York, NY, USA: American Society of Mechanical Engineers , 2012, p. 1213-1220Conference paper (Refereed)
    Abstract [en]

    In the presented work, two studies using ComputationalFluid Dynamics (CFD) have been conducted on a generictruck-like model with and without a trailer unit at a speed of 80km/h. The purpose is to evaluate drag reduction possibilitiesusing externally fitted devices. A first study deals with a flapplaced at the back of a rigid truck and inclined at seven differentangles with two lengths. Results show that it is possible todecrease drag by 4%. In a second study, the flap has been fittedon the tractor and trailer units of a truck-trailer combination.Four settings were surveyed for this investigation, one of whichproved to decrease drag by up to 15%. A last configurationwhere the gap between the units has been closed has also beenevaluated. This configuration offers a 15% decrease in drag.Adding a flap to the closed gap configuration decreases drag by18%. New means of reducing aerodynamic drag of heavy-duty(HD) vehicles will be important in the foreseeable future inorder to improve the fuel economy. The possibilities of reducingdrag are prevalent using conceptual design.

  • 162.
    Pelosi, Matteo
    et al.
    Öhlins Racing AB, Jönköping, Sweden.
    Subramanya, Kashyap
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Lantz, Jonas
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Investigation on the Dynamic Behavior of a Solenoid Hydraulic Valve for Automotive Semi-Active Suspensions Coupling 3D and 1D Modeling2013In: 13th Scandinavian International Conference on Fluid Power / [ed] Petter Krus, Magnus Sethson and Liselott Ericson, Linköping University Electronic Press, 2013, p. 241-250Conference paper (Refereed)
    Abstract [en]

    The aim of this paper is to investigate the influence of the internal fluid flow characteristics of a special hydraulic solenoid valve, developed by Öhlins Racing AB, on its overall dynamic behavior. This valve is a two stage hydraulic pressure control valve and is typically mounted on each shock absorber of an on-road vehicle, allowing the implementation of semi-active suspension functionality. This technology is referred as CES (Continuously Controlled Electronic Suspension). The CES valve allows continuously controlling the vehicle shock absorbers damping characteristic by proportionally adjusting the metering geometry offered to its damping element, i.e. hydraulic oil. The electronic valve actuation and control, obtained through an electromagnetic solenoid, is based on the input from several vehicle dynamics sensors, such as accelerometers, gyroscopes and other displacement sensors. The CES valve’s unconventional design significantly influences the fluid flow, making the use of numerical modeling essential to discover its physical behavior and to support further product development. In this paper, a CFD (Computational Fluid Dynamics) analysis on the main and pilot stages of the hydraulic valve is discussed. This 3D numerical analysis is used to extract critical physical variables, affecting the valve behavior, such as flow coefficients and pressure distributions on the moving elements, i.e. flow forces. This information is coupled with a detailed lumped parameter model of the hydraulic valve, which solves for the valve moving element dynamics considering the action of the main external forces. Moreover, the 1D model allows predicting the valve critical pressure/flow characteristics. It is shown how the coupling of 3D modeling results with the CES valve 1D model strongly improves the whole valve dynamics numerical predictions over traditional methods for considering the effect of fluid inertia and discharge in lumped parameter simulations. Comparisons with measurement both on single regions of the CES hydraulic valve and on the entire valve are discussed in order to validate the various phases of numerical modeling.

  • 163.
    Petersson, Jens
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    CFD-analysis of buoyancy-driven flow inside a cooling pipe system attached to a reactor pressure vessel2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In this work a cooling system connected to a reactor pressure vessel has been studied using the CFD method for the purpose of investigating the strengths and shortcomings of using CFD as a tool in similar fluid flow problems within nuclear power plants. The cooling system is used to transport water of 288K (15°C) into a nuclear reactor vessel filled with water of about 555K (282°C) during certain operating scenarios. After the system has been used, the warm water inside the vessel will be carried into the cooling system by buoyancy forces. It was of interest to investigate how quickly the warm water moves into the cooling system and how the temperature field of the water changes over time.

    Using the open source CFD code OpenFOAM 2.3.x and the LES turbulence modelling method, a certain operating scenario of the cooling system was simulated. A simplified computational domain was created to represent the geometries of the downcomer region within the reactor pressure vessel and the pipe structure of the cooling system. Boundary conditions and other domain properties were chosen and motivated to represent the real scenario as good as possible. For the geometry, four computational grids of different sizes and design were generated. Three of these were generated using the ANSA pre-processing tool, and they all have the same general structure only with different cell sizes. The fourth grid was made by the OpenFOAM application snappyHexMesh, which automatically creates the volume mesh with little user input.

    It was found that for the case at hand, the different computational grids produced roughly the same results despite the number of cells ranging from 0,14M to 3,2M. A major difference between the simulations was the maximum size of the time steps which ranged from 0,3ms for the finest ANSA mesh to 2ms for the snappy mesh, a difference which has a large impact on the total time consumption of the simulations.

    Furthermore, a comparison of the CFD results was made with those of a simpler 1D thermal hydraulic code, Relap5. The difference in time consumption between the two analyses were of course large and it was found that although the CFD analysis provided more detailed information about the flow field, the cheaper 1D analysis managed to capture the important phenomena for this particular case. However, it cannot be guaranteed that the 1D analysis is sufficient for all similar flow scenarios as it may not always be able to sufficiently capture phenomena such as thermal shocks and sharp temperature gradients in the fluid.

    Regardless of whether the CFD method or a simpler analysis is used, conservativeness in the flow simulation results needs to be ensured. If the simplifications introduced in the computational models cannot be proved to always give conservative results, the final simulation results need to be modified to ensure conservativeness although no such modifications were made in this work.

  • 164.
    Polák, Jaroslav
    et al.
    Institute of Physics of Materials, Academy of Sicences of Czech Republic, Brno.
    Petrás, Roman
    Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Brno.
    Heczko, Milan
    Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Brno.
    Kruml, Tomás
    Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Brno.
    Chai, Guocai
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering. Sandvik Materials Technology, Sandviken, Sweden.
    Evolution of the Cyclic Plastic Response of Sanicro 25 Steel Cycled at Ambient and Elevated Temperatures2016In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 83, no 1, p. 75-83Article in journal (Refereed)
    Abstract [en]

    Cyclic plastic response of the austenitic heat resistant steel Sanicro 25 has been studied during strain controlled low cycle fatigue tests performed at ambient and at elevated temperature. Simultaneously with the cyclic hardening/softening curves hysteresis loops during cyclic loading were analyzed using generalized statistical theory of the hysteresis loop. The probability density distribution function of the internal critical stresses, the effective saturated stress and their evolution during cycling were derived for various strain amplitudes. The internal dislocation structure and the surface relief at room and at elevated temperature were studied and correlated with the cyclic stress–strain response and the evolution of the probability density function of the internal critical stresses.

  • 165.
    Rashid, Asim
    et al.
    Tekniska Högskolan, Högskolan i Jönköping, JTH. Forskningsmiljö Produktutveckling - Simulering och optimering.
    Strömberg, Niclas
    Tekniska Högskolan, Högskolan i Jönköping, JTH. Forskningsmiljö Produktutveckling - Simulering och optimering.
    An Efficient Sequential Approach for Simulation of Thermal Stresses in Disc Brakes2012Conference paper (Other academic)
    Abstract [en]

    In this paper an ecient approach to simulate thermal stresses due to tem-perature variations in disc brakes is presented. In the approach thermal and stress analysis are performed sequentially. The frictional heat analysis is based on the Eulerian method, which requires signicantly low computational time as compared to the Lagrangian approach. The nodal temperature history is recorded at each time step and is used in a sequentially coupled stress analysis, where a temperature dependent elasto-plastic material model is used to compute the stresses in the disc brake. The results show that during hard braking, high compressive stresses are generated on the disc surface in circumferential direction which cause plastic yielding. But when the disc cools down, the compressive stresses transform to tensile stresses. Such thermoplastic stress history may cause cracks on disc surface after a few braking cycles. These results are in agreement with experimental observations available in the literature.

  • 166.
    Rashid, Asim
    et al.
    Tekniska Högskolan, Högskolan i Jönköping, JTH. Forskningsmiljö Produktutveckling - Simulering och optimering.
    Strömberg, Niclas
    Tekniska Högskolan, Högskolan i Jönköping, JTH. Forskningsmiljö Produktutveckling - Simulering och optimering.
    Sequential simulation of thermal stresses in disc brakes for repeated braking2013In: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 227, no 8, p. 919-929Article in journal (Refereed)
    Abstract [en]

    In this paper, an efficient sequential approach for simulating thermal stresses in brake discs for repeated braking is presented. First, a frictional heat analysis is performed by using an Eulerian formulation of the disc. Then, by using the temperature history from the first step of the sequence, a plasticity analysis with temperature dependent material data is performed in order to determine the corresponding thermal stresses. Three-dimensional geometries of a disc and a pad to a heavy truck are considered in the numerical simulations. The contact forces are computed at each time step taking the thermal deformations of the disc and pad into account. In such manner, the frictional heat power distribution will also be updated in each time step, which in turn will influence the development of heat bands. The plasticity model is taken to be the von Mises yield criterion with linear kinematic hardening, where both the hardening and the yield limit are temperature dependent. The results show that during hard braking, high compressive stresses are generated on the disc surface in the circumferential direction which cause yielding. But when the disc cools down, these compressive stresses transform to tensile residual stresses. For repeated hard braking when this kind of stress history is repeated, we also show that stress cycles with high amplitudes are developed which might generate low cycle fatigue cracks after a few braking cycles.

  • 167.
    Rasmussen, John
    et al.
    M-Tech, Aalborg University, Denmark.
    Holmberg, L. Joakim
    Linköping University, Department of Management and Engineering, Mechanics. Linköping University, The Institute of Technology.
    Sörensen, K.
    M-Tech, Aalborg University, Denmark.
    Kwan, M.
    M-Tech, Aalborg University, Denmark.
    Andersen, M.S.
    M-Tech, Aalborg University, Denmark.
    de Zee, M.
    Department of Health Science and Technology, Aalborg University, Denmark.
    Performance optimization by musculoskeletal simulation2012In: Movement & Sport Sciences – Science & Motricité, ISSN 2118-5735, Vol. 75, p. 73-83Article in journal (Refereed)
    Abstract [en]

    This paper uses two examples, from cross country skiing and badminton, to illustrate the idea of using musculoskeletal simulation as a tool to understand and ultimately optimize sports performance. The results show that the analysis provides insight into the performances that cannot be obtained by other means, and it is advocated that this insight ultimately can lead to better coaching. The importance of “know-why” over “know-how” is stressed, and it is hypothesized that this may enable athletes to learn difficult techniques faster.

  • 168.
    Rasmussen, John
    et al.
    M-Tech, Aalborg University, Denmark.
    Holmberg, L. Joakim
    Linköping University, Department of Management and Engineering, Mechanics. Linköping University, The Institute of Technology.
    Sørensen, K.
    M-Tech, Aalborg University, Denmark.
    Kwan, M.
    M-Tech, Aalborg University, Denmark.
    Andersen, M.S.
    M-Tech, Aalborg University, Denmark.
    de Zee, Mark
    Department of Health Science and Technology, Aalborg University, Denmark.
    Performance optimization by musculoskeletal simulation: Erratum2012In: Movement & sport sciences, ISSN 2118-5735, Vol. 76, p. 75-75Article in journal (Other academic)
  • 169.
    Renner, Johan
    et al.
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Ghavami Nejad, Mehdi
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Nadali Najafabadi, Hossein
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Loyd, Dan
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Skoog, Pontus
    SAPA Heat Transfer AB.
    Abrahamsson, David
    SAPA Heat Transfer AB.
    Karlsson, Matts
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Conduction and convection heat transfer for aluminum ingot in preheating furnace2011In: Proceedings of 6th Baltic Heat Transfer Conference 2011 / [ed] Reijo Karvinen & Matti Lindstedt, 2011Conference paper (Refereed)
    Abstract [en]

    Aluminium is a widely used material, which is found in a number of products e.g. thin aluminium bands that is the base material in many heat exchangers. Rolling processes are used to produce these thin aluminium bands, in order to get the right properties and to get the aluminium easier to roll, heat treatment is needed. This heat treatment of aluminium ingots prior to the rolling is in focus in this work, where computational fluid dynamics and computational heat transfer techniques is used to predict the heating process in a hot air pre-heating furnace. The used approach includes steady state computational fluid dynamics simulations combined with transient computational heat transfer simulations. The simulation results in form of spatial and temporal distributed aluminium ingot temperature was compared with temperature measurement in a thermocouple prepared ingot in the actual pre-heating furnace. Simulation results correspond well with the measurements and there are small differences. Results of the described simulation approach open the possibility to predict spatial and temporal temperature distribution in these kinds of pre-heating processes.

  • 170.
    Ryberg, Ann-Britt
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering. Combitech AB, Trollhättan, Sweden.
    Metamodel-Based Multidisciplinary Design Optimization of Automotive Structures2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Multidisciplinary design optimization (MDO) can be used in computer aided engineering (CAE) to efficiently improve and balance performance of automotive structures. However, large-scale MDO is not yet generally integrated within automotive product development due to several challenges, of which excessive computing times is the most important one. In this thesis, a metamodel-based MDO process that fits normal company organizations and CAE-based development processes is presented. The introduction of global metamodels offers means to increase computational efficiency and distribute work without implementing complicated multi-level MDO methods.

    The presented MDO process is proven to be efficient for thickness optimization studies with the objective to minimize mass. It can also be used for spot weld optimization if the models are prepared correctly. A comparison of different methods reveals that topology optimization, which requires less model preparation and computational effort, is an alternative if load cases involving simulations of linear systems are judged to be of major importance.

    A technical challenge when performing metamodel-based design optimization is lack of accuracy for metamodels representing complex responses including discontinuities, which are common in for example crashworthiness applications. The decision boundary from a support vector machine (SVM) can be used to identify the border between different types of deformation behaviour. In this thesis, this information is used to improve the accuracy of feedforward neural network metamodels. Three different approaches are tested; to split the design space and fit separate metamodels for the different regions, to add estimated guiding samples to the fitting set along the boundary before a global metamodel is fitted, and to use a special SVM-based sequential sampling method. Substantial improvements in accuracy are observed, and it is found that implementing SVM-based sequential sampling and estimated guiding samples can result in successful optimization studies for cases where more conventional methods fail.

    List of papers
    1. Multidisciplinary design optimisation methods for automotive structures
    Open this publication in new window or tab >>Multidisciplinary design optimisation methods for automotive structures
    2017 (English)In: International Journal of Automotive and Mechanical Engineering, ISSN 2229-8649, Vol. 14, no 1, p. 4050-4067Article in journal (Refereed) Published
    Abstract [en]

    Multidisciplinary design optimisation (MDO) can be used as an effective tool to improve the design of automotive structures. Large-scale MDO problems typically involve several groups who must work concurrently and autonomously in order to make the solution process efficient. In this article, the formulations of existing MDO methods are compared and their suitability is assessed in relation to the characteristics of automotive structural applications. Both multi-level and single-level optimisation methods are considered. Multi-level optimisation methods distribute the design process but are complex. When optimising automotive structures, metamodels are often required to relieve the computational burden of detailed simulation models. The metamodels can be created by individual groups prior to the optimisation process, and thus offer a way of distributing work. Therefore, it is concluded that a single-level method in combination with meta-models is the most straightforward way of implementing MDO into the development of automotive structures. If the benefits of multi-level optimisation methods, in a special case, are considered to compensate for their drawbacks, analytical target cascading has a number of advantages over collaborative optimisation, but both methods are possible choices.

    Place, publisher, year, edition, pages
    Pekan, Malaysia: Universiti Malaysia Pahang Publishing, 2017
    Keywords
    Multidisciplinary design optimisation, single-level optimisation methods, multilevel optimisation methods, automotive structures
    National Category
    Production Engineering, Human Work Science and Ergonomics
    Identifiers
    urn:nbn:se:liu:diva-140876 (URN)10.15282/ijame.14.1.2017.17.0327 (DOI)
    Available from: 2017-09-14 Created: 2017-09-14 Last updated: 2018-02-26Bibliographically approved
    2. A metamodel-based multidisciplinary design optimization process for automotive structures
    Open this publication in new window or tab >>A metamodel-based multidisciplinary design optimization process for automotive structures
    2015 (English)In: Engineering with Computers, ISSN 0177-0667, E-ISSN 1435-5663, Vol. 31, no 4, p. 711-728Article in journal (Refereed) Published
    Abstract [en]

    Automotive companies continuously strive to design better products faster and more cheaply using simulation models to evaluate every possible aspect of the product. Multidisciplinary design optimization (MDO) can be used to find the best possible design taking into account several disciplines simultaneously, but it is not yet fully integrated within automotive product development. The challenge is to find methods that fit company organizations and that can be effectively integrated into the product development process. Based on the characteristics of typical automotive structural MDO problems, a metamodel-based MDO process intended for large-scale applications with computationally expensive simulation models is presented and demonstrated in an example. The process is flexible and can easily fit into existing organizations and product development processes where different groups work in parallel. The method is proven to be efficient for the discussed example and improved designs can also be obtained for more complex industrial cases with comparable characteristics.

    Place, publisher, year, edition, pages
    Springer, 2015
    Keywords
    Multidisciplinary design optimization (MDO); metamodel-based design optimization (MBDO); automotive structures
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-88135 (URN)10.1007/s00366-014-0381-y (DOI)000360859000004 ()
    Available from: 2013-01-30 Created: 2013-01-30 Last updated: 2017-12-06Bibliographically approved
    3. Spot weld reduction methods for automotive structures
    Open this publication in new window or tab >>Spot weld reduction methods for automotive structures
    2016 (English)In: Structural and multidisciplinary optimization (Print), ISSN 1615-147X, E-ISSN 1615-1488, Vol. 53, no 4, p. 923-934Article in journal (Refereed) Published
    Abstract [en]

    Spot welds are commonly used to join steel sheets in automotive structures. The number and layout of these spot welds are vital for the performance of the structure. However, reducing the number of spot welds will cut both production time and cost. This article presents three different methods of reducing the number of spot welds in automotive structures: ranking-based selection, topology optimization and size optimization of a parameterized model. The methods are compared in a simple example and it is found that the latter two methods have the best potential of reducing the number of spot welds. Topology optimization requires less preparation and computational effort as compared to size optimization of a parameterized model. However, the method is primarily suitable for studies where load cases involving linear systems are judged to be most important. Otherwise, size optimization of a parameterized model is probably a better choice. The topology optimization approach is successfully demonstrated in a full-scale industrial application example and confirms that the method is useful within contemporary product development.

    Place, publisher, year, edition, pages
    SPRINGER, 2016
    Keywords
    Spot weld optimization; Multidisciplinary design optimization (MDO); Topology optimization; Size optimization; Metamodels; Automotive structures
    National Category
    Mechanical Engineering
    Identifiers
    urn:nbn:se:liu:diva-127430 (URN)10.1007/s00158-015-1355-4 (DOI)000373023800018 ()
    Note

    Funding Agencies|Vinnova FFI project

    Available from: 2016-05-01 Created: 2016-04-26 Last updated: 2017-11-30
  • 171.
    Ryberg, Ann-Britt
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Domeij Bäckryd, Rebecka
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Nilsson, Larsgunnar
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Metamodel-Based Multidisciplinary Design Optimization for Automotive Applications2012Report (Other academic)
    Abstract [en]

    When designing a complex product, many groups are concurrently developing different parts or aspects of the product using detailed simulation models. Multidisciplinary design optimization (MDO) has its roots within the aerospace industry and can effectively improve designs through simultaneously considering different aspects of the product. The groups involved in MDO need to work autonomously and in parallel, which influence the choice of MDO method. The methods can be divided into single-level methods that have a central optimizer making all design decisions, and multi-level methods that have a distributed decision process.

    This report is a comprehensive summary of the field of MDO with special focus on structural optimization for automotive applications using metamodels. Metamodels are simplified models of the computationally expensive detailed simulation models and can be used to relieve some of the computational burden during MDO studies. The report covers metamodel-based design optimization including design of experiments, variable screening, metamodels and their validation, as well as optimization methods. It also includes descriptions of several MDO methods, along with a comparison between the aerospace and automotive industries and their applications of MDO.

    The information in this report is based on an extensive literature survey, but the conclusions drawn are influenced by the authors’ own experiences from the automotive industry. The trend goes towards using advanced metamodels and global optimization methods for the considered applications. Further on, many of the MDO methods developed for the aerospace industry are unsuitable for the automotive industry where the disciplines are more loosely coupled. The expense of using multi-level optimization methods is then greater than the benefits, and the authors therefore recommend single-level methods for most automotive applications.

  • 172.
    Rydberg, Karl-Erik
    Linköping University, Department of Management and Engineering, Fluid and Mechatronic Systems. Linköping University, Faculty of Science & Engineering.
    Hydraulic Servo Systems: Dynamic Properties and Control2016Book (Other academic)
    Abstract [en]

    When closed-loop hydraulic control systems first began to appear in industry, the applications were generally those in which very high performance was required. While hydraulic servo systems are still heavily used in high-performance applications such as the machine-tool industry, they are beginning to gain wide acceptance in a variety of industries. Examples are material handling, mobile equipment, plastics, steel plants, mining, oil exploration and automotive testing

    Closed loop servo drive technology is increasingly becoming the norm in machine automation, where the operators are demanding greater precision, faster operation and simpler adjustment. There is also an expectation that the price of increasing the level of automation should be contained within acceptable limits.

  • 173.
    Sandgren, Emil
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Fatigue design of tensile loaded bolted joints2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Bolted joints are frequently used in aeroplanes, but there is no commonly accepted method for how to carry out fatigue calculations for tensile loaded bolted joints. In this master thesis, the effect of various parameters on the fatigue life of bolted joint will be studied. An important part of the thesis is to investigate what data is currently available at the company, and which tests that is required to fill up the gaps in the fatigue database.

    A literature survey of different models for performing fatigue calculations for tensile loaded bolted joints showed, as mentioned above, that no common method exists. In general, the method to solve the problem is based on advice and guidance from various experts at the company, and usage of data etc. from different articles in the subject.

    The parametric study showed that methods could be formulated for some parameters, while others parameters needed more testing before methods could be formulated with confidence. These gaps in the fatigue database need to be filled by more testing before the methodology to be implemented for calculating the fatigue life for tensile loaded bolted joints. A continuation study, for further investigating of factors that may influence the fatigue life, is also proposed.

  • 174.
    Satha, Ganarupan
    Linköping University, Department of Management and Engineering, Mechanics.
    Nutrient Driven Topology Optimization2010Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The aim of this thesis is to investigate how a biological structure changes its shape and boundary under different cases of load if flow of nutrients is included, since nutrient flow has not been taken into account in previous studies.

    In order to simulate such a scenario we construct a model by using topology optimization (the SIMP model) and a balance law which is suitable for biological structures. Moreover, the model is derived by using an analogy with the dissipation inequality and Coleman-Noll’s procedure. The model can be interpreted as bone or some other biological structure, where the growth and remodeling partly occurs due to nutrient flow.

    The theory is first investigated by selecting an MBB beam with a special boundary condition for the nutrient concentration and inflow of nutrients, and then with a bone-like model.

    For the analysis with different loads we have observed that the structure becomes thicker were the load is applied. Parameters like beta (β) (reflecting the relation between nutrients and material) and nutrient concentration (c) seem to play an important role in nutrient transport and building of the structure. The result for larger values of β and nutrient concentration (c) gives a thicker structure in the entire domain. We also made an assumption of Fick’s law of diffusion. Fick’s law of diffusion describes the flux from high concentration to low concentration. This phenomenon is observed in analysis with different nutrient concentrations (c): we can see that the structure tends to be built up where the concentration is high and continues to be built in the direction from high to low concentration. In analyses with mu-value (μ), which represents cost of material, the result gives a thinner structure for larger values of μ.

  • 175.
    Satha, Ganarupan
    et al.
    Linköping University, Department of Management and Engineering, Mechanics. Linköping University, The Institute of Technology.
    Lindström, Stefan B.
    Linköping University, Department of Management and Engineering, Mechanics. Linköping University, The Institute of Technology.
    Klarbring, Anders
    Linköping University, Department of Management and Engineering, Mechanics. Linköping University, The Institute of Technology.
    Growth and remodeling of arterial tissue: One-dimensional constrained mixture theory2012In: 8th European Solid Mechanics Conference, 2012Conference paper (Other academic)
  • 176.
    Sato, Atsushi
    et al.
    University of Birmingham, United Kingdom.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Hasselqvist, Magnus
    Siemens Industrial Turbomachinery AB, Finspång, Sweden.
    Reed, Roger C.
    University of Birmingham, United Kingdom.
    On the Mechanical Behavior of a New Single-Crystal Superalloy for Industrial Gas Turbine Applications2012In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 43A, no 7, p. 2302-2315Article in journal (Refereed)
    Abstract [en]

    The mechanical behavior of a new single-crystal nickel-based superalloy for industrial gas turbine (IGT) applications is studied under creep and out-of-phase (OP) thermomechanical fatigue (TMF) conditions. Neutron diffraction methods and thermodynamic modeling are used to quantify the variation of the gamma prime (γ′) strengthening phase around the γ′ solvus temperature; these aid the design of primary aging heat treatments to develop either uniform or bimodal microstructures of the γ′ phase. Under creep conditions in the temperature range 1023 K to 1123 K (750 °C to 850 °C), with stresses between 235 to 520 MPa, the creep performance is best with a finer and uniform γ′ microstructure. On the other hand, the OP TMF performance improves when the γ′ precipitate size is larger. Thus, the micromechanical degradation mechanisms occurring during creep and TMF are distinct. During TMF, localized shear banding occurs with the γ′ phase penetrated by dislocations; however, during creep, the dislocation activity is restricted to the matrix phase. The factors controlling TMF resistance are rationalized.

  • 177.
    Schlauer, C.
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials .
    Simonsson, K.
    Linköping University, Department of Management and Engineering, Solid Mechanics .
    Moverare, J.
    Linköping University, Department of Management and Engineering, Engineering Materials .
    The effect of machining on residual stresses and low cycle fatigue life of Inconel 718 gas turbine discs2002Report (Other academic)
  • 178.
    Schlauer, Christian
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Simonsson, Kjell
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    The effect of machining on residual stresses and low cycle fatigue life of Inconel 718 gas turbine discs2002Report (Other academic)
  • 179.
    Serbenta, V. A.
    et al.
    National Research Tomsk State University, Russia.
    Skripnyak, Natalia
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. National Research Tomsk State University, Russia.
    Skripnyak, V. A.
    National Research Tomsk State University, Russia.
    Skripnyak, E. G.
    National Research Tomsk State University, Russia.
    Numerical Simulation of the Mechanical Behavior of Ultrafine- and Coarse-Grained Zr-Nb Alloys over a Wide Range of Strain Rates2017In: PROCEEDINGS OF THE INTERNATIONAL CONFERENCE ON ADVANCED MATERIALS WITH HIERARCHICAL STRUCTURE FOR NEW TECHNOLOGIES AND RELIABLE STRUCTURES 2017 (AMHS17), AMER INST PHYSICS , 2017, Vol. 1909, article id UNSP 020190Conference paper (Refereed)
    Abstract [en]

    This paper presents the results on the development of theoretical methods of evaluation and prediction of mechanical properties of Zr-Nb alloys over a range of strain rates from 10(-3) to 10(3) s(-1). The mechanical behavior of coarse-and ultrafine-grained Zr-1Nb (E110) was investigated numerically. The ranges of strain rates and temperatures in which the mechanical behavior of Zr-1Nb alloy can be described using modified models of Johnson-Cook and Zerilli-Armstrong were defined. The results can be used in engineering analysis of designed technical systems for nuclear reactors.

  • 180.
    Sharifimajd, Babak
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    A Continuum Framework for Modeling the Excitation–Contraction Coupling of Smooth Muscle2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Excitation-contraction coupling of smooth muscle refers to a chain of coupled physiological processes which convert a stimulus to a mechanical response. These processes can be disassociated into ionic transport during cell membrane excitation, activation of myosin light chains, and muscle contraction caused by actin-myosin interaction (filament sliding). This thesis concerns the development of a framework which allows to model the smooth muscle excitation-contraction coupling constitutively by applying the principle of virtual power and dissipation inequality. In doing so, the transport of ions through membrane channels is characterized by an ionic flux and an ionic supply, both governed by an electrochemical potential energy. By letting the Helmholtz free energy to be dependent on the myosin light chain configurations during contraction, the myosin light chain activation process, i.e., myosin phosphorylation, is included. The activation process links the membrane excitation to the filament sliding. A contractile element is presented to replicate the active deformation caused by the filament sliding within the smooth muscle cell. This deformation is coupled to the overall deformation of the muscle tissue by assuming a distinct principal alignment for the contractile elements.

    By employing this framework, an electro-chemo-mechanical model is derived by which the mechanical response of smooth muscle to an electrical stimulus is determined. This model is evaluated by comparing the model response to the experimental isometric stress data obtained from rat uterine smooth muscle tissue. By implementing this model in a finite element program, human uterine contractions during labor are simulated. This simulation determines important clinical factors, e.g., intrauterine pressure and provides the opportunity to investigate the effect of physiological and structural parameters on the uterine contractility.

    Finally, a methodology to accommodate individualized parameters from intrauterine pressure measurements is established. This methodology allows to develop models with potentials of being used clinically to diagnose difficulties during labor and delivery.

    List of papers
    1. A continuum model for skeletal muscle contraction at homogeneous finite deformations
    Open this publication in new window or tab >>A continuum model for skeletal muscle contraction at homogeneous finite deformations
    2013 (English)In: Biomechanics and Modeling in Mechanobiology, ISSN 1617-7959, E-ISSN 1617-7940, Vol. 12, no 5, p. 965-973Article in journal (Refereed) Published
    Abstract [en]

    The contractile force in skeletal muscle models is commonly postulated to be the isometric force multiplied by a set of experimentally motivated functions which account for the muscle’s active properties. Although both flexible and simple, this approach does not automatically guarantee a thermodynamically consistent behavior. In contrast, the continuum mechanical model proposed herein is derived from fundamental principles in mechanics and guarantees a dissipative behavior. Further, the contractile force is associated with a friction clutch which provides a simple and well-defined macroscopic model for cycling cross-bridges. To show the performance of the model, it is specialized to standard experiments for rabbit tibialis anterior muscle. The results show that the model is able to capture important characteristics of skeletal muscle.

    Place, publisher, year, edition, pages
    Springer, 2013
    Keywords
    Skeletal muscle, Contractile element, Dissipation inequality, Strain-energy function, Continuum model
    National Category
    Other Mechanical Engineering
    Identifiers
    urn:nbn:se:liu:diva-85805 (URN)10.1007/s10237-012-0456-x (DOI)000324378900008 ()
    Funder
    Swedish Research Council
    Available from: 2012-11-28 Created: 2012-11-28 Last updated: 2018-01-03Bibliographically approved
    2. A continuum model for excitation–contraction of smooth muscle under finite deformations
    Open this publication in new window or tab >>A continuum model for excitation–contraction of smooth muscle under finite deformations
    2014 (English)In: Journal of Theoretical Biology, ISSN 0022-5193, E-ISSN 1095-8541, Vol. 355, p. 1-9Article in journal (Refereed) Published
    Abstract [en]

    The main focus in most of continuum based muscle models is the muscle contraction dynamics while other physiological processes governing muscle contraction, e.g., the cell membrane excitation and the activation, are ignored. These latter processes are essential to initiate contraction and to determine the amount of generated force, and by excluding them, the developed model cannot replicate the true behavior of the muscle in question. The aim of this study is to establish a thermodynamically and physiologically consistent framework which allows to model smooth muscle contraction by including cell membrane excitability and kinetics of myosin phosphorylation, along with dynamics of smooth muscle contraction. The model accounts for these processes through a set of coupled dissipative constitutive equations derived by applying the first principles. To show the performance of the derived model, it is evaluated for two different cases: a mechanochemical study of pig taenia coli cells where the excitation process is excluded, and a complete excitation–contraction process of rat myometrium. The results show that the model is able to replicate important aspects of the smooth muscle EC process acceptably.

    Place, publisher, year, edition, pages
    Elsevier, 2014
    Keywords
    Smooth muscle excitation–contraction, Smooth muscle continuum model, The membrane model, Hodgkin-Huxley model, Hai-Murphy model
    National Category
    Other Mechanical Engineering
    Identifiers
    urn:nbn:se:liu:diva-100778 (URN)10.1016/j.jtbi.2014.03.016 (DOI)000337865100001 ()
    Available from: 2013-11-12 Created: 2013-11-12 Last updated: 2018-01-03Bibliographically approved
    3. Simulating uterine contraction by using an electro-chemo-mechanical model
    Open this publication in new window or tab >>Simulating uterine contraction by using an electro-chemo-mechanical model
    2016 (English)In: Biomechanics and Modeling in Mechanobiology, ISSN 1617-7959, E-ISSN 1617-7940, Vol. 15, no 3, p. 497-510Article in journal (Refereed) Published
    Abstract [en]

    Contractions of uterine smooth muscle cells consist of a chain of physiological processes. These contractions provide the required force to expel the fetus from the uterus. The inclusion of these physiological processes is, therefore, imperative when studying uterine contractions. In this study, an electro-chemo-mechanical model to replicate the excitation, activation, and contraction of uterine smooth muscle cells is developed. The presented modeling strategy enables efficient integration of knowledge about physiological processes at the cellular level to the organ level. The model is implemented in a three-dimensional finite element setting to simulate uterus contraction during labor in response to electrical discharges generated by pacemaker cells and propagated within the myometrium via gap junctions. Important clinical factors, such as uterine electrical activity and intrauterine pressure, are predicted using this simulation. The predictions are in agreement with clinically measured data reported in the literature. A parameter study is also carried out to investigate the impact of physiologically related parameters on the uterine contractility.

    Place, publisher, year, edition, pages
    Springer, 2016
    Keywords
    Excitation-contraction model of uterine smooth muscle; Uterus contraction; Intrauterine pressure; Uterine electrical activity
    National Category
    Applied Mechanics
    Identifiers
    urn:nbn:se:liu:diva-121013 (URN)10.1007/s10237-015-0703-z (DOI)000376014800002 ()26162461 (PubMedID)
    Available from: 2015-09-02 Created: 2015-09-02 Last updated: 2018-01-03Bibliographically approved
    4. Identification of the mechanical parameters for the human uterus in vivo using intrauterine pressure measurements
    Open this publication in new window or tab >>Identification of the mechanical parameters for the human uterus in vivo using intrauterine pressure measurements
    2017 (English)In: International Journal for Numerical Methods in Biomedical Engineering, ISSN 2040-7939, E-ISSN 2040-7947, Vol. 33, no 1, p. 1-11Article in journal (Refereed) Published
    Abstract [en]

    There are limited experimental data to characterize the mechanical response of human myometrium. A method is presented in this work to identify mechanical parameters describing the active response of human myometrium from the in vivo intrauterine pressure measurements. A finite element model is developed to compute the intrauterine pressure during labor in response to an increase in the intracellular calcium ion concentration within myometrial smooth muscle cells. The finite element model provides the opportunity to tune mechanical parameters in order to fit the computed intrauterine pressure to in vivo measurements. Since the model is computationally expensive, a cheaper meta-model is generated to approximate the model response. By fitting the meta-model response to the in vivo measurements, the parameters used to determine the active response of human myometrial smooth muscle are identified.

    Place, publisher, year, edition, pages
    John Wiley & Sons, 2017
    Keywords
    human uterine smooth muscle mechanics, intrauterine pressure, parameter identification, response surface methodology
    National Category
    Applied Mechanics Mechanical Engineering
    Identifiers
    urn:nbn:se:liu:diva-121014 (URN)10.1002/cnm.2778 (DOI)000393964900001 ()26915913 (PubMedID)2-s2.0-84962638845 (Scopus ID)
    Note

    At the time of the thesis presentation this publication was in status Manuscript.

    Available from: 2015-09-02 Created: 2015-09-02 Last updated: 2018-01-03Bibliographically approved
  • 181.
    Sharifimajd, Babak
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Thore, Carl-Johan
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Stålhand, Jonas
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Simulating uterine contraction by using an electro-chemo-mechanical model2016In: Biomechanics and Modeling in Mechanobiology, ISSN 1617-7959, E-ISSN 1617-7940, Vol. 15, no 3, p. 497-510Article in journal (Refereed)
    Abstract [en]

    Contractions of uterine smooth muscle cells consist of a chain of physiological processes. These contractions provide the required force to expel the fetus from the uterus. The inclusion of these physiological processes is, therefore, imperative when studying uterine contractions. In this study, an electro-chemo-mechanical model to replicate the excitation, activation, and contraction of uterine smooth muscle cells is developed. The presented modeling strategy enables efficient integration of knowledge about physiological processes at the cellular level to the organ level. The model is implemented in a three-dimensional finite element setting to simulate uterus contraction during labor in response to electrical discharges generated by pacemaker cells and propagated within the myometrium via gap junctions. Important clinical factors, such as uterine electrical activity and intrauterine pressure, are predicted using this simulation. The predictions are in agreement with clinically measured data reported in the literature. A parameter study is also carried out to investigate the impact of physiologically related parameters on the uterine contractility.

  • 182.
    Sharifimajd, Babak
    et al.
    Institute of Solid Mechanics, Department of Mechanical Engineering, Braunschweig University of Technology, Braunschweig, Germany.
    Ölvander, Johan
    Linköping University, Department of Management and Engineering, Machine Design. Linköping University, Faculty of Science & Engineering.
    Stålhand, Jonas
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Identification of the mechanical parameters for the human uterus in vivo using intrauterine pressure measurements2017In: International Journal for Numerical Methods in Biomedical Engineering, ISSN 2040-7939, E-ISSN 2040-7947, Vol. 33, no 1, p. 1-11Article in journal (Refereed)
    Abstract [en]

    There are limited experimental data to characterize the mechanical response of human myometrium. A method is presented in this work to identify mechanical parameters describing the active response of human myometrium from the in vivo intrauterine pressure measurements. A finite element model is developed to compute the intrauterine pressure during labor in response to an increase in the intracellular calcium ion concentration within myometrial smooth muscle cells. The finite element model provides the opportunity to tune mechanical parameters in order to fit the computed intrauterine pressure to in vivo measurements. Since the model is computationally expensive, a cheaper meta-model is generated to approximate the model response. By fitting the meta-model response to the in vivo measurements, the parameters used to determine the active response of human myometrial smooth muscle are identified.

  • 183.
    Shetty, Sandeep
    Linköping University, Department of Management and Engineering. Linköping University, Faculty of Science & Engineering.
    Optimization of Vehicle Structures under Uncertainties2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Advancements in simulation tools and computer power have made it possible to incorporate simulation-based structural optimization in the automotive product development process. However, deterministic optimization without considering uncertainties such as variations in material properties, geometry or loading conditions might result in unreliable optimum designs. 

    In this thesis, the capability of some established approaches to perform design optimization under uncertainties is assessed, and new improved methods are developed. In particular, vehicle structural problems which involve computationally expensive Finite Element (FE) simulations, are addressed.

    The first paper focuses on the evaluation of robustness, given some variation in input parameters, the capabilities of three well-known metamodels are evaluated. In the second paper, a comparative study of deterministic, reliability-based and robust design optimization approaches is performed. It is found that the overall accuracy of the single-stage (global) metamodels, which are used in the above study, is acceptable for deterministic optimization. However, the accuracy of performance variation prediction (local sensitivity) must be improved. In the third paper, a decoupled reliability-based design optimization (RBDO) approach is presented. In this approach, metamodels are employed for the deterministic optimization only while the uncertainty analysis is performed using FE simulations in order to ensure its accuracy.

    In the fifth paper, two new sequential sampling strategies are introduced that aim to improve the accuracy of the metamodels efficiently in critical regions. The capabilities of the methods presented are illustrated using analytical examples and a vehicle structural application.

    It is important to accurately represent physical variations in material properties since these might exert a major influence on the results. In previous work these variations have been treated in a simplified manner and the consequences of these simplifications have been poorly understood. In the fourth paper, the accuracy of several simple methods in representing the real material variation has been studied. It is shown that a scaling of the nominal stress-strain curve based on the Rm scatter is the best choice of the evaluated choices, when limited material data is available.

    In this thesis work, new pragmatic methods for non-deterministic optimization of large scale vehicle structural problems have been developed. The RBDO methods developed are shown to be flexible, more efficient and reasonably accurate, which enables their implementation in the current automotive product development process.

    List of papers
    1. Robustness study of a hat profile beam made of boron steel subjected to three point bending
    Open this publication in new window or tab >>Robustness study of a hat profile beam made of boron steel subjected to three point bending
    2016 (English)In: International Journal of Vehicle Systems Modelling and Testing, ISSN 1745-6436, E-ISSN 1745-6444, no 3, p. 252-270Article in journal (Refereed) Published
    Abstract [en]

    It is essential to account for variations in the manufacturing process and in loading conditions when improving the robustness and reliability of a product’s design. A finite element study of the robustness of a hat profile beam made from boron steel subjected to a three point bending load is presented, and an approach to incorporate the variations investigated is demonstrated. Fracture risk factors and the maximum deflection of the beam are the measured responses. Spatial variation of the sheet thickness is considered in the forming simulations, along with other input variations. Stress-strain relations from tensile tests have been used in the robustness analyses to represent the variation in material properties. Furthermore, validations of four metamodels have been performed. Both the responses measured were found to be sensitive to input variations. Separate metamodels were created for each risk prone zone in order to improve the performance of the metamodels for risk factor responses.

    Place, publisher, year, edition, pages
    Bucks: InderScience Publishers, 2016
    Keywords
    Robustness analysis; Monte Carlo analysis; metamodel; boron steel; fracture risk factor
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-103690 (URN)10.1504/IJVSMT.2016.080880 (DOI)
    Available from: 2014-01-23 Created: 2014-01-23 Last updated: 2017-12-06Bibliographically approved
    2. Multiobjective reliability-based and robust design optimisation for crashworthiness of a vehicle side impact
    Open this publication in new window or tab >>Multiobjective reliability-based and robust design optimisation for crashworthiness of a vehicle side impact
    2015 (English)In: International Journal of Vehicle Design, ISSN 0143-3369, E-ISSN 1741-5314, Vol. 67, no 4, p. 347-367Article in journal (Refereed) Published
    Abstract [en]

    Optimisation of vehicle design is necessary to meet increased safety requirements, new emission regulations, and to deal with competition in the global market, etc. However, optimised design using classical optimisation techniques with deterministic models might not meet the desired performance level or might fail in extreme events in real life owing to uncertainties in the design parameters and loading conditions. Consequently, it is essential to account for uncertainties in a systematic manner to generate a robust and reliable design. In this paper, an approach to perform multiobjective, reliability-based, and robust design optimisation is presented using a vehicle side impact crashworthiness application. Metamodels have been used in the optimisation process to decrease computational effort. Variations in material properties, thicknesses, loading conditions, and B-pillar heat-affected zone material strength have been considered for the stochastic optimisation. A comparative study of deterministic, reliability-based, and robust optimisation approaches is performed.

    Place, publisher, year, edition, pages
    InderScience Publishers, 2015
    Keywords
    Multiobjective optimisation; robust optimisation; reliabilitybased optimisation; crashworthiness; Monte Carlo analysis; metamodel; boron steel; fracture risk factor
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-103691 (URN)10.1504/IJVD.2015.070410 (DOI)000359461500002 ()
    Available from: 2014-01-23 Created: 2014-01-23 Last updated: 2017-12-06Bibliographically approved
    3. Efficient reliability-based optimization using a combined metamodel and FE-based strategy
    Open this publication in new window or tab >>Efficient reliability-based optimization using a combined metamodel and FE-based strategy
    2014 (English)In: Engineering Optimization IV - Proceedings of the 4th International Conference on Engineering Optimization, ENGOPT 2014 / [ed] Rodrigues H.C., Herskovits J., Soares C.M.M., Guedes J.M., Araujo A.L., Folgado J.O., Moleiro F., Madeira J.F.A., Leiden, The Netherlands: CRC Press, 2014, p. 471-478Conference paper, Published paper (Refereed)
    Abstract [en]

    It is essential to consider the uncertainties in design variables of an optimization process in order to create a reliable design. The computational effort required to perform reliability-based optimization of complex engineering problems is very high and most recent studies have used metamodels in order to reduce the computational effort.An efficient decoupled sequential reliability-based optimization using the combination of metamodel-based strategy and FE-based strategy is presented in this paper. Optimization loop and stochastic analysis loops are completely decoupled. Stochastic analysis is performed at the end of each optimization iteration and at the beginning of the first iteration only. In each optimization iteration, the standard deviation of constraint functions from the previous iteration is used. The stochastic analysis is performed using an FE-based Monte Carlo method,whereas metamodels have been utilized for the optimization. This approach is demonstrated using two engineering examples.

    Place, publisher, year, edition, pages
    Leiden, The Netherlands: CRC Press, 2014
    National Category
    Control Engineering Computational Mathematics Communication Systems Telecommunications Computer Engineering
    Identifiers
    urn:nbn:se:liu:diva-133197 (URN)2-s2.0-84941985436 (Scopus ID)
    Conference
    ENGOPT 2014 - 4th International Conference on Engineering optimization, 8-11 September, Instituto Superioe Tecnico, Lissabon, Portugal
    Available from: 2016-12-14 Created: 2016-12-14 Last updated: 2018-01-13Bibliographically approved
    4. An evaluation of simple techniques to model the variation in strain hardening behavior of steel
    Open this publication in new window or tab >>An evaluation of simple techniques to model the variation in strain hardening behavior of steel
    2017 (English)In: Structural and multidisciplinary optimization (Print), ISSN 1615-147X, E-ISSN 1615-1488, Vol. 55, no 3, p. 945-957Article in journal (Refereed) Published
    Abstract [en]

    It is important to consider variations in material parameters in the design of automotive structures in order to obtain a robust and reliable design. However, expensive tests are required to gain complete knowledge of the material behavior and its associated variation. Consequently, due to time and cost constraints, simplified material scatter modeling techniques based on scatter data of typical material properties provided by the material suppliers are used at early design stages in simulation-based robustness studies. The aim of this paper is to study the accuracy of the simplified scatter modeling methods in representing the real material variation. The simplified scatter modeling methods are evaluated by comparing the material scatter obtained by them to the scatter obtained by complete tensile tests, which are obtained after detailed timeconsuming experimental investigations. Furthermore, an accuracy assessment is carried out based on selected responses from an axially-crushed, square tube made from DP600 steel.

    Place, publisher, year, edition, pages
    Bonn: Springer, 2017
    Keywords
    Flow curve, Material scatter, Stochastic simulation, Tensile test
    National Category
    Aerospace Engineering Building Technologies Composite Science and Engineering Applied Mechanics Other Materials Engineering
    Identifiers
    urn:nbn:se:liu:diva-133198 (URN)10.1007/s00158-016-1547-6 (DOI)000398114200014 ()
    Note

    Funding agencies: Robust and multidisciplinary optimization of automotive structures Project - Vinnova FFI; Volvo Car Corporation

    Available from: 2016-12-14 Created: 2016-12-14 Last updated: 2017-04-20Bibliographically approved
  • 184.
    Shetty, Sandeep
    et al.
    Linköping University, Department of Management and Engineering. Linköping University, Faculty of Science & Engineering. Painted Body and Closures, Volvo Car Corporation.
    Nilsson, Larsgunnar
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    An evaluation of simple techniques to model the variation in strain hardening behavior of steel2017In: Structural and multidisciplinary optimization (Print), ISSN 1615-147X, E-ISSN 1615-1488, Vol. 55, no 3, p. 945-957Article in journal (Refereed)
    Abstract [en]

    It is important to consider variations in material parameters in the design of automotive structures in order to obtain a robust and reliable design. However, expensive tests are required to gain complete knowledge of the material behavior and its associated variation. Consequently, due to time and cost constraints, simplified material scatter modeling techniques based on scatter data of typical material properties provided by the material suppliers are used at early design stages in simulation-based robustness studies. The aim of this paper is to study the accuracy of the simplified scatter modeling methods in representing the real material variation. The simplified scatter modeling methods are evaluated by comparing the material scatter obtained by them to the scatter obtained by complete tensile tests, which are obtained after detailed timeconsuming experimental investigations. Furthermore, an accuracy assessment is carried out based on selected responses from an axially-crushed, square tube made from DP600 steel.

  • 185.
    Simonsson, Kjell
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Sjöström, Sören
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Micromechanical modelling of the constitutive behaviour of a material during a martensitic transformation2002In: IUTAM Symposium on Micro- and Macrostructural Aspects of Thermoplasticity: Proceedings of the IUTAM Symposium held in Bochum, Germany, 25–29 August 1997, 2002, Vol. 62, p. 345-354Conference paper (Refereed)
  • 186.
    Singh, Subrat
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics.
    Veditherakal Shreedhara, Sreehari
    Linköping University, Department of Management and Engineering, Solid Mechanics.
    CAE modelling of cast aluminium in automotive structures2019Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In the automobile industry, there is a big push for the automotive car manufacturers to base engineering decisions on the results of Computer Aided Engineering (CAE) solutions, and to transform the prototyping and testing, from a costly iterative process to a final verification and validation step. The variability in components material properties and environmental conditions together with the lack of knowledge about the underlying physics of complex systems often make it impractical to make reliable predictions based on only deterministic CAE models. One such area is the CAE modelling of cast aluminium components. These cast aluminium components have gained a huge relevance in the automobile industries due to their commendable mechanical properties. The advantage of the cast aluminium alloys are being a well-established alloy system in manufacturing processes, their functional integrity and relatively low weight. However, the presence of pores and micro-voids obtained during the manufacturing process constitutes a specific material behaviour and establishes a challenge in modelling of the cast materials. Furthermore, the low ductility of the materialdemands for the advanced numerical model to predict the failure.

    The main focus of this master thesis work is to investigate modelling technique of a cast aluminium alloy component, a spring tower, for a drop tower test and validate the predicted behaviour with the physical test results. Volvo Car Corporation currently uses a material model provided by MATFEM for cast aluminium parts which are explored in this thesis work, to validate the material model for component level testing.

    The methodology used to achieve this objective was to develop a boundary condition to perform component level tests in the drop tower and to correlate these with the obtained results found by using various modelling techniques in the explicit solver LS-DYNA. Therefore, precise and realistic modelling of the drop tower is crucial because the simulation results can be influenced by major design changes. A detailed finite element model for the spring tower has been developed from the observations made during the physical testing. The refined model showed good agreement with the existing model for the spring tower and observations from physical tests.

  • 187.
    Sjölinder, Emil
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Spray and Wall Film Modeling with Conjugate Heat Transfer in OpenFOAM2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This master thesis was provided by Scania AB. The objective of this thesis was to modify an application in the free Computational Fluid Dynamics software OpenFOAM to be able to handle spray and wall film modeling of a Urea Water Solution together with Conjugate Heat Transfer. The basic purpose is to widen the knowledge of the vaporization process of a Urea Water Solution in the exhaust gas after treatment system for a diesel engine by using OpenFOAM. First, urea has been modeled as a very viscous liquid at low temperature to mimic the solidication process of urea. Second, the development of the new application has been done. At last, test simulations of a simple test case are performed with the new application. The results are then compared with simplied hand calculations to verify a correct behavior of certain exposed source terms. The new application is working properly for the test case but to ensure the reliability, the results need to be compared with another Computational Fluid Dynamics software or more preferable, real experiments. For more advanced geometries, the continued development presented last in this thesis is highly recommended to follow.

  • 188.
    Sjöström, Sören
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Brodin, Håkan
    Siemens Industrial Turbomachinery, FINSPÅNG.
    Influence of TBC end geometry on the TMF life of an APS TBC2010In: Procedia Engineering, ISSN 1877-7058, E-ISSN 1877-7058, Vol. 2, p. 1363-1371Article in journal (Refereed)
    Abstract [en]

    A TBC subjected to TMF loading may spall off after a sufficiently large number of cycles. This is a consequence of a combination of general fatigue damage growth and strong internal stresses caused by oxidation in the bondcoat/topcoat interface. Further, at the ends of the coating there are stress singularities, at which early fatigue cracks tend to develop. This can, however, be avoided or delayed by making the coating end chamfered. This work investigates the influence of coating end chamfer on the fatigue life of an APS TBC.

  • 189.
    Skoglund, Peter
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology. Scania CV.
    Sjögren, Torsten
    SP Technical Research Institute of Sweden.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Fatigue and strength of new grey iron alloys for break discs2013In: Seventh International Conference on Low Cycle Fatigue / [ed] T. Beck, E. Charkaluk, Berlin: Deutscher Verband für Materialforschung und -Prüfung E.V. , 2013, p. 45-50Conference paper (Refereed)
    Abstract [en]

    The static and low cycle fatigue properties of four pearlitic grey iron alloys intended for brake discs are investigated. The effect of alloying a base composition with 0.1 wt% and 0.3 wt% niobium is compared to a 0.3 wt% addition of the more conventional alloying element molybdenum. The results show that the static properties remain unaffected for an Nb content of 0.1 wt% while an addition of 0.3 wt% Nb or 0.3 wt% Mo increases the strength compared to the base alloy without Nb and Mo. The fatigue life on the other hand remains more or less unaffected by the alloying, although the stress levels are substantially higher for the compositions with 0.3 wt% Mo or 0.3 wt% Nb. Thus, the experiments show that graphite is very important for the low cycle fatigue life. It is also seen that crack propagation controls more than 90% of the life. Full scale brake dynamometer crack tests also gave a similar fatigue life of the different brake disc alloys independent of the composition.

  • 190.
    Skripnyak, Natalia
    et al.
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. National Research Tomsk State University, Russia.
    Emelyanova, E. S.
    National Research Tomsk State University, Russia.
    Skripnyak, V. A.
    National Research Tomsk State University, Russia.
    Skripnyak, E. G.
    National Research Tomsk State University, Russia.
    Damage of High-Chromium Steels under Deformation in a Wide Temperature Range2017In: PROCEEDINGS OF THE INTERNATIONAL CONFERENCE ON ADVANCED MATERIALS WITH HIERARCHICAL STRUCTURE FOR NEW TECHNOLOGIES AND RELIABLE STRUCTURES 2017 (AMHS17), AMER INST PHYSICS , 2017, Vol. 1909, article id UNSP 020200Conference paper (Refereed)
    Abstract [en]

    High-chromium steels have high strength properties, corrosion properties and resistance to neutron irradiation, thereby are considered as promising steels for nuclear reactors of generation IV. The deformation and damage of high chromium steels in a wide temperature range was studied by numerical simulation method. A model was proposed to predict the deformation and damage of high chromium steels under quasi-static loading within the temperature range from 295 to 1100 K. It is shown that the ductility of high-chromium steels increases proportionally to temperature in the range from 750 to 1100 K due to the growth of alpha-phase precipitates.

  • 191.
    Skripnyak, Vladimir A.
    et al.
    National Research Tomsk State University of TSU, Russia; Russian Academic Science, Russia; National Research Tomsk Polytech University of TPU, Russia.
    Skripnyak, Natalia
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. National Research Tomsk State University of TSU, Russia.
    Skripnyak, Evgeniya G.
    National Research Tomsk State University of TSU, Russia.
    Skripnyak, Vladimir V.
    National Research Tomsk State University of TSU, Russia; Russian Academic Science, Russia; National Research Tomsk Polytech University of TPU, Russia.
    Influence of Grain Size Distribution on the Mechanical Behavior of Light Alloys in Wide Range of Strain Rates2017In: SHOCK COMPRESSION OF CONDENSED MATTER - 2015: Proceedings of the Conference of the American Physical Society Topical Group on Shock Compression of Condensed Matter, AMER INST PHYSICS , 2017, Vol. 1793, article id UNSP 110001Conference paper (Refereed)
    Abstract [en]

    Inelastic deformation and damage at the mesoscale level of ultrafine grained (UFG) light alloys with distribution of grain size were investigated in wide loading conditions by experimental and computer simulation methods. The computational multiscale models of representative volume element (RVE) with the unimodal and bimodal grain size distributions were developed using the data of structure researches aluminum and magnesium UFG alloys. The critical fracture stress of UFG alloys on mesoscale level depends on relative volumes of coarse grains. Microcracks nucleation at quasi-static and dynamic loading is associated with strain localization in UFG partial volumes with bimodal grain size distribution. Microcracks arise in the vicinity of coarse and ultrafine grains boundaries. It is revealed that the occurrence of bimodal grain size distributions causes the increasing of UFG alloys ductility, but decreasing of the tensile strength.

  • 192.
    Skripnyak, Vladimir A.
    et al.
    Natl Res Tomsk State Univ, Russia.
    Skripnyak, Vladimir V.
    Natl Res Tomsk State Univ, Russia.
    Skripnyak, Evgeniya G.
    Natl Res Tomsk State Univ, Russia.
    Skripnyak, Natalia
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering. Natl Res Tomsk State Univ, Russia.
    MODELLING OF THE MECHANICAL RESPONSE OF Zr-Nb AND Ti-Nb ALLOYS IN A WIDE TEMPERATURE RANGE2018In: IRF2018: PROCEEDINGS OF THE 6TH INTERNATIONAL CONFERENCE ON INTEGRITY-RELIABILITY-FAILURE, INEGI-INST ENGENHARIA MECANICA E GESTAO INDUSTRIAL , 2018, p. 855-862Conference paper (Refereed)
    Abstract [en]

    This article presents the results of modelling of the mechanical behaviour of biocompatible Zr-Nb and Ti-Nb alloys in the range of strain rates from 10(-3) to 10(3) s(-1) at temperatures from 297 K to 1273 K. Modification of the micro-dynamical model was proposed for the description of Zr-1Nb ultrafine grained and coarse grained alloys. It was shown that the phase transition HCP -amp;gt; BCC alloy Zr-Nb at elevated temperatures leads to a sharp changing in the resistance to plastic flow and kinetics of growth of damage. The results can be used for engineering analysis of designed constructive elements of technical and biomedical applications.

  • 193.
    Spagnoli, A.
    et al.
    University of Parma, Parma, Italy.
    Terzano, M.
    University of Parma, Parma, Italy.
    Klarbring, Anders
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Barber, J. R.
    University of Michigan, AnnArbor, MI, USA.
    Shakedown in an elastic-plastic solid with a frictional crack2016In: Procedia Structural Integrity vol. 2 / [ed] Francesco Iacoviello, Elsevier, 2016, Vol. 2, p. 2667-2673Conference paper (Refereed)
    Abstract [en]

    When subjected to periodic loading, elastic systems containing contact interfaces might exhibit frictional slip which ceases after some loading cycles. In such cases, it is said that the system shakes down. For elastic discrete systems presenting complete contacts, it has been proved that Melan’s theorem, originally proposed for elastic-plastic problems, offers a sufficient condition for the system to shake down, provided that the contact is of an uncoupled type. In the present paper, the application of Melan’s theorem is speculated for systems involving plasticity and friction. A finite element example of an elastic-plastic solid containing a frictional crack is discussed.

  • 194.
    Spagnoli, A.
    et al.
    University of Parma, Italy.
    Terzano, M.
    University of Parma, Italy.
    Barber, J. R.
    University of Michigan, MI 48109 USA.
    Klarbring, Anders
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Non-linear programming in shakedown analysis with plasticity and friction2017In: Journal of the mechanics and physics of solids, ISSN 0022-5096, E-ISSN 1873-4782, Vol. 104, p. 71-83Article in journal (Refereed)
    Abstract [en]

    Complete frictional contacts, when subjected to cyclic loading, may sometimes develop a favourable situation where slip ceases after a few cycles, an occurrence commonly known as frictional shakedown. Its resemblance to shakedown in plasticity has prompted scholars to apply direct methods, derived from the classical theorems of limit analysis, in order to assess a safe limit to the external loads applied on the system. In circumstances where zones of plastic deformation develop in the material (e.g., because of the large stress concentrations near the sharp edges of a complete contact), it is reasonable to expect an effect of mutual interaction of frictional slip and plastic strains on the load limit below which the global behaviour is non dissipative, i.e., both slip and plastic strains go to zero after some dissipative load cycles. In this paper, shakedown of general two-dimensional discrete systems, involving both friction and plasticity, is discussed and the shakedown limit load is calculated using a non-linear programming algorithm based on the static theorem of limit analysis. An illustrative example related to an elastic-plastic solid containing a frictional crack is provided. (C) 2017 Elsevier Ltd. All rights reserved.

  • 195.
    Spinks, Geoffrey M.
    et al.
    Univ Wollongong, Australia.
    Bakarich, Shannon E.
    US Army, MD 20783 USA; Cornell Univ, NY 14850 USA.
    Aziz, Shazed
    Linköping University, Department of Physics, Chemistry and Biology, Sensor and Actuator Systems. Linköping University, Faculty of Science & Engineering.
    Salahuddin, Bidita
    Univ Wollongong, Australia.
    Xin, Hai
    Univ Wollongong, Australia.
    Using force-displacement relations to obtain actuation parameters from artificial muscles2019In: Sensors and Actuators A-Physical, ISSN 0924-4247, E-ISSN 1873-3069, Vol. 290, p. 90-96Article in journal (Refereed)
    Abstract [en]

    Many different test methods are currently used to characterise the output of artificial muscle materials but few studies report the full range of possible force and displacements that can be generated by a given material when activated with a given input stimulus but when operated against different external loads. The measurement of the loading and unloading force extension curves in tension in both the un-activated and activated states is investigated as a means for efficiently characterising the full range of outputs for three different types of artificial muscles: pneumatically operated braided muscle and thermally operated shape memory alloy spring and twisted / coiled polymer fiber. A graphical method of analysis was applied whereby the force-extension curves obtained before and after actuator activation were plotted on the same axes. By overlaying the external loading conditions, the graphical method provided the equilibrium starting and finishing forces and displacements and successfully predicted the isotonic strokes, isometric forces and combined force and displacement generated when the actuator was operated against an external spring. Complications in the interpretation of the force-stroke curves were encountered as all three artificial muscles displayed a degree of loading-unloading hysteresis and non-ideal mechanical behavior. (C) 2019 Elsevier B.V. All rights reserved.

  • 196. Spånberg, Anders
    et al.
    Terio, Hikki
    Enberg, Anders
    Ask, Per
    Linköping University, Department of Biomedical Engineering, Physiological Measurements. Linköping University, The Institute of Technology.
    QUANTIFICATION OF URETHRAL FUNCTION BASED ON GRIFFITHS MODEL OF FLOW THROUGH ELASTIC TUBES1989In: Neurourology and Urodynamics, ISSN 0733-2467, E-ISSN 1520-6777, Vol. 8, no 1, p. 29-52Article in journal (Refereed)
    Abstract [en]

    Griffiths' model of flow-through elastic tubes makes it possible to relate the elastic properties of the flow-controlling zone to the pressure/flow relation of the urethra. In this work the pressure function p(A) = Pmo + Kn An, where A is cross-sectional area, Pmo the minimal opening pressure, and Kn and n parameters describing urethral distensibility, describes the elastic properties of the flow-controlling zone. By curve-fitting in the pressure/flow plot, the three parameters pmo, Kn, and n can be estimated analytically. Using this model it is possible to identify three different biomechanical changes that may cause obstruction. First, pmo may be elevated. Second, the urethra can be distended to a certain area only, corresponding to high values of Kn and n. Third, the urethra can be distended but a higher-than-normal pressure increase above Pmo is needed, Kn is high, and n is low. With this model it is possible to quantify urethral function for both scientific and clinical purposes.

  • 197.
    Storgärds, Erik
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    High Temperature Fatigue Crack Growth in a Ni-based Superalloy: Modelling Including the Interaction of Dwell Times2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Safe life of gas turbines is always of major concern for manufacturers in order to ensure passenger safety and stable continuous power output. An increasing amount of resources have been put into research and development to assure that all safety aspects are covered in the design of new turbines and to ensure that enough frequent service intervals are scheduled to avoid complications. Many of these issues require good knowledge of material properties and of how to use these in the design process. Some of these relate to fatigue which is of major concern in all parts of a development programme. However, while some fatigue problems have been extensively studied, some have not. One example is crack growth with influence of dwell times at elevated temperature in combination with cyclic loading. Such loading conditions have been shown to give a different cracking behaviour compared to rapid cyclic loading, increasing the growth rate significantly with respect to the number of load cycles. Improved models for predicting this behaviour is therefore of major interest for gas turbine manufacturers, and could substantially increase the reliability. As a result, more research is needed in order  solve these problems.

    The work presented in this dissertation has focused on how to predict life under the above-mentioned circumstances. The materials used in high temperature gas turbine applications are often nickel-based superalloys, and in this work the most common one, Inconel 718, has been studied. Mechanical experiments have been performed under operation like conditions in order to receive material data for the subsequent modelling work. The modelling approach was chosen such that the underlying physics of the dwell time cracking have been incorporated on a phenomenological basis, creating a model which can be physically motivated as well as used for industrial applications. The main feature of the modelling work has been to track material damage which is received from dwell times, how this interacts with cyclic loading and how it affects the crack growth rate, thus creating a load history dependent model.

    The outcome of this work has resulted in a model which is both easy to use and which has shown to give good correlation to available experimental data. Key components such as calibration for cheap and easy parameter determination, validation on complex engine spectra loadings, three dimensional crack growth, overload influences, material scatter, thermo-mechanical fatigue crack growth and the impact of high cycle fatigue loadings, are all covered in the presented work, both as experimental findings and as continuous development of the modelling concept.

    The dissertation consists of two parts. In the first an introduction with the theory and background to crack growth with dwell times is given, while the second part consists of 10 papers.

    List of papers
    1. High temperature fatigue crack growth behaviour of Inconel 718 under hold time and overload conditions
    Open this publication in new window or tab >>High temperature fatigue crack growth behaviour of Inconel 718 under hold time and overload conditions
    2013 (English)In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 48, p. 178-186Article in journal (Refereed) Published
    Abstract [en]

    Inconel 718 is a frequently used material for gas turbine applications at temperatures up to 650°C. For such components, the main load cycle is typically defined by the start-up and shut-down of the engine. In this main loading cycle, hold times at high temperature are commonly present in critical components. These high temperature hold times may greatly increase the fatigue crack growth rate with respect to the number of cycles unless other beneficial factors such as for example initial overloads are present. The latter can be caused by abnormal service conditions but can also occur on a more regular basis and are then typically observed in components with strong thermal transients during engine start-up. In this paper, focus has been placed on the effect of overloads on the hold time fatigue crack growth behaviour and its subsequent description. More specifically, crack propagation in Inconel 718 has been studied at the temperatures 550°C and 650°C with and without an overload at the start of the cycle. The effect of initial overloads was found to be substantial. A simple model for describing the effect of these loading conditions has also been developed based on the concept of the damaged zone, present around the crack tip. Irregular crack fronts and unbroken ligaments left on the fracture surfaces seen in complementary microscopy studies seem to support this approach. Furthermore, the stress state in front of a crack tip in a 2D model was investigated both with and without an initial overload. The results were related to the observed crack growth retardation behaviour found in the material testing.

    Place, publisher, year, edition, pages
    Elsevier, 2013
    Keywords
    Nickel-base superalloys, fatigue crack propagation, Inconel 718, hold times, grain boundary embrittlement, crack propagation modelling, Finite Element modelling
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-85931 (URN)10.1016/j.ijfatigue.2012.10.018 (DOI)000315617500020 ()
    Available from: 2013-03-13 Created: 2012-12-03 Last updated: 2017-12-07Bibliographically approved
    2. Modelling of high temperature fatigue crack growth in Inconel 718 under hold time conditions
    Open this publication in new window or tab >>Modelling of high temperature fatigue crack growth in Inconel 718 under hold time conditions
    2013 (English)In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 52, p. 124-130Article in journal (Refereed) Published
    Abstract [en]

    Inconel 718 is a frequently used material for gas turbine applications at temperatures up to 650 °C. The main load cycle for such components is typically defined by the start-up and shut-down of the engine. It generally includes hold times at high temperatures, which have been found to have a potential for greatly increasing the fatigue crack growth rate with respect to the number of load cycles. However, these effects may be totally or partly cancelled by other load features, such as overloads or blocks of continuous cyclic loading, and the actual crack propagation rate will therefore depend on the totality of features encompassed by the load cycle. It has previously been shown that the increased crack growth rate found in hold time experiments can be associated with a damage evolution, where the latter is not only responsible for the rapid intergranular crack propagation during the actual hold times, but also for the increased crack growth during the load reversals. In this paper, modelling of the hold time fatigue crack growth behaviour of Inconel 718 has been carried out, using the concept of a damaged zone as the basis for the treatment. With this conceptually simple and partly novel approach, it is shown that good agreement with experimental results can be found.

    Place, publisher, year, edition, pages
    Elsevier, 2013
    Keywords
    Nickel-base superalloys, fatigue crack propagation, Inconel 718, hold times, grain boundary embrittlement, crack propagation modelling
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-85933 (URN)10.1016/j.ijfatigue.2013.03.004 (DOI)000318831300013 ()
    Available from: 2012-12-03 Created: 2012-12-03 Last updated: 2017-12-07Bibliographically approved
    3. A load history dependent model for fatigue crack propagation in Inconel 718 under hold time conditions
    Open this publication in new window or tab >>A load history dependent model for fatigue crack propagation in Inconel 718 under hold time conditions
    2014 (English)In: Engineering Fracture Mechanics, ISSN 0013-7944, E-ISSN 1873-7315, Vol. 118, p. 17-30Article in journal (Refereed) Published
    Abstract [en]

    Modelling of high temperature fatigue crack growth in Inconel 718 under the interaction of fast cyclic loading and hold times at maximum load has been conducted. A model, based on the concept of a damaged zone in front of the crack tip has been applied for three different temperatures, 550, 600 and 650 ◦C, with good agreement for both calibration and validation tests. A statistical evaluation of 22 tests in total was also conducted, which shows that the developed model gives a reasonable scatter factor at a probability of failure of 0.1 %.

    Place, publisher, year, edition, pages
    Elsevier, 2014
    Keywords
    Fatigue crack propagation, Inconel 718, Hold time effects, Crack growth modelling, Statistics
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-104809 (URN)10.1016/j.engfracmech.2014.02.005 (DOI)000334819600002 ()
    Available from: 2014-02-27 Created: 2014-02-27 Last updated: 2017-12-05Bibliographically approved
    4. Modelling of fatigue crack growth in Inconel 718 under hold time conditions - application to a flight spectrum
    Open this publication in new window or tab >>Modelling of fatigue crack growth in Inconel 718 under hold time conditions - application to a flight spectrum
    2014 (English)In: Advanced Materials Research, ISSN 1662-8985, Vol. 891-892, p. 759-764Article in journal (Refereed) Published
    Abstract [en]

    Gas turbine operating cycles at high temperatures often consist of load reversals mixed with hold times; the latter occurring either as cruise for aero engines or at continuous power output for land based turbines, but also at low frequency loading conditions, e.g. slow “ramp up” of engine thrust. The hold time conditions cause the crack to grow by intergranular fracture due to material damage near the crack tip, thus rapidly increasing the crack growth rate. Since the damaged zone will affect the crack propagation rate due to cyclic loadings as well, the complete load history of a component therefore has to be considered. The crack propagation model presented in this paper is based on the damaged zone concept, and considers the history effect in the form of damaged zone build up during hold times, and subsequent destruction as the crack propagates onwards by rapidly applied load reversals. By incorporating crack closure for handling different R-values, an aero engine component spectrum is evaluated for a surface crack at 550 C. The result shows a good correlation to model simulation, despite the complexity of the load spectrum.

    Place, publisher, year, edition, pages
    Trans Tech Publications Inc., 2014
    Keywords
    Fatigue crack propagation, Inconel 718, Hold time effects, Crack growth modelling
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-104812 (URN)10.4028/www.scientific.net/AMR.891-892.759 (DOI)000337767700118 ()
    Available from: 2014-02-27 Created: 2014-02-27 Last updated: 2016-05-18Bibliographically approved
    5. Crack Length Evaluation for Cyclic and Sustained Loading at High Temperature Using Potential Drop
    Open this publication in new window or tab >>Crack Length Evaluation for Cyclic and Sustained Loading at High Temperature Using Potential Drop
    2015 (English)In: Experimental mechanics, ISSN 0014-4851, E-ISSN 1741-2765, Vol. 55, no 3, p. 559-568Article in journal (Refereed) Published
    Abstract [en]

    Crack length evaluations for cyclic loading and sustained loading at high temperature and a mix of both have been conducted on Inconel 718 surface crack specimens at 550 C-a similar to. The choice of method for evaluating the crack length is seen to have a non-negligible impact on the resulting crack propagation rate values. In this paper, some aspects regarding how to evaluate such testing when using the potential drop technique are presented, with the aim of giving a firm explanation on how to proceed for the best possible result.

    Place, publisher, year, edition, pages
    Society for Experimental Mechanics (SEM), 2015
    Keywords
    Fatigue crack propagation; Fatigue test evaluation; Sustained load; Dwell time effects; Crack length evaluation; Potential drop
    National Category
    Mechanical Engineering
    Identifiers
    urn:nbn:se:liu:diva-117241 (URN)10.1007/s11340-014-9963-2 (DOI)000351444300007 ()
    Note

    Funding Agencies|Swedish Energy Agency; Siemens Industrial Turbomachinery AB; GKN Aerospace Engine Systems; Royal Institute of Technology through the Swedish research programme TURBO POWER

    Available from: 2015-04-22 Created: 2015-04-21 Last updated: 2017-12-04
    6. Three-dimensional crack growth modelling of a Ni-based superalloy at elevated temperature and sustained loading
    Open this publication in new window or tab >>Three-dimensional crack growth modelling of a Ni-based superalloy at elevated temperature and sustained loading
    2016 (English)In: Theoretical and applied fracture mechanics (Print), ISSN 0167-8442, E-ISSN 1872-7638Article in journal (Refereed) Published
    Abstract [en]

    High temperature materials subjected to elevated temperature have been shown to be sensitive to dwell times, giving an increased crack growth rate. The interaction between these dwell times and rapid cyclic loads have been shown to constitute a complex problem. Many models have been developed for 1D conditions, but the application to general 3D conditions has seldom been seen, although this is the most common case in most structures. In this paper a model for taking care of the interaction between these load modes in general 3D crack growth has been developed. The model uses 1D results for extension to general 3D, thus providing for local crack front evolution with a minimum of numerical simulations. The model has been implemented for usage with finite element calculations and several different tests are simulated and compared with experimental results for the nickel based superalloy Inconel 718 at 550◦C. The simulation results show crack shapes in agreement with experimental fracture surfaces and time to failure.

    Keywords
    Sustained load, Crack growth modelling, Crack tunnelling, Ni-based superalloy, High temperature
    National Category
    Applied Mechanics Materials Engineering
    Identifiers
    urn:nbn:se:liu:diva-121004 (URN)10.1016/j.tafmec.2015.11.008 (DOI)000369204600002 ()
    Note

    Funding agencies:  Swedish Energy Agency; Siemens Industrial Turbomachinery AB; GKN Aerospace Engine Systems; Royal Institute of Technology through the Swedish research programme TURBO POWER

    Vid tiden för disputation förelåg publikationen som manuskript

    Available from: 2015-09-02 Created: 2015-09-02 Last updated: 2017-12-04Bibliographically approved
    7. Modeling of Crack Growth With Dwell Time for Aero-engine Spectra Loadings in a Ni-Based Superalloy
    Open this publication in new window or tab >>Modeling of Crack Growth With Dwell Time for Aero-engine Spectra Loadings in a Ni-Based Superalloy
    Show others...
    2016 (English)In: Journal of engineering for gas turbines and power, ISSN 0742-4795, E-ISSN 1528-8919, Vol. 138, no 1, p. 012501-012501Article in journal (Refereed) Published
    Abstract [en]

    Testing and simulation of aero-engine spectra with dwell times are reported in this paper. The modeling concept used is built on linear elastic fracture mechanics (LEFM) and provides a history-dependent evolution description of dwell damage and its interaction with cyclic load. The simulations have been carried out for three spectra: (1) cyclic loads, (2) combined sustained load and cyclic loads, and (3) slow load ramps and cyclic loads, all for surface cracks at 550 °C for Inconel 718. All simulations show reasonable good agreement with experimental results. Prediction of multiple tests of several batches is also provided to show statistical scatter.

    Place, publisher, year, edition, pages
    ASME Press, 2016
    National Category
    Applied Mechanics Mechanical Engineering Materials Engineering
    Identifiers
    urn:nbn:se:liu:diva-121005 (URN)10.1115/1.4031155 (DOI)000371127900012 ()
    Note

    Funding agencies: Swedish Energy Agency; Siemens Industrial Turbomachinery AB; GKN Aerospace Engine Systems; Royal Institute of Technology through Swedish Research Programme TURBO POWER

    Available from: 2015-09-02 Created: 2015-09-02 Last updated: 2017-12-04Bibliographically approved
    8. Scatter in Dwell Time Cracking for a Ni-Based Superalloy in Combination With Overloads
    Open this publication in new window or tab >>Scatter in Dwell Time Cracking for a Ni-Based Superalloy in Combination With Overloads
    Show others...
    2016 (English)In: Journal of engineering for gas turbines and power, ISSN 0742-4795, E-ISSN 1528-8919, Vol. 138, no 1, p. 012502-012502Article in journal (Refereed) Published
    Abstract [en]

    In this paper, scatter in crack growth for dwell time loadings in combination with overloads has been investigated. Multiple tests were performed for surface cracks at 550 °C in the commonly used high temperature material Inconel 718. The test specimens originate from two different batches which also provide for a discussion of how material properties affect the dwell time damage and overload impact. In combination with these tests, an investigation of the microstructure was also carried out, which shows how it influences the growth rate. The results from this study show that, in order to take overloads into consideration when analyzing spectrum loadings containing dwell times, one needs a substantial amount of material data available as the scatter seen from one batch to the other are of significant proportions.

    Place, publisher, year, edition, pages
    ASME Press, 2016
    National Category
    Mechanical Engineering Materials Engineering Applied Mechanics
    Identifiers
    urn:nbn:se:liu:diva-121007 (URN)10.1115/1.4031157 (DOI)000371127900013 ()
    Note

    Funding agencies: Swedish Energy Agency; Siemens Industrial Turbomachinery AB; GKN Aerospace Engine Systems; Royal Institute of Technology through Swedish research programme TURBO POWER

    Available from: 2015-09-02 Created: 2015-09-02 Last updated: 2017-12-04Bibliographically approved
    9. Thermomechanical Fatigue Crack Growth Modeling in a Ni-Based Superalloy Subjected to Sustained Load
    Open this publication in new window or tab >>Thermomechanical Fatigue Crack Growth Modeling in a Ni-Based Superalloy Subjected to Sustained Load
    2016 (English)In: Journal of engineering for gas turbines and power, ISSN 0742-4795, E-ISSN 1528-8919, Vol. 138, no 1, p. 012503-012503Article in journal (Refereed) Published
    Abstract [en]

    Thermomechanical fatigue (TMF) crack growth modeling has been conducted on Inconel 718 with dwell time at maximum load. A history dependent damage model taking dwell damage into account, developed under isothermal conditions, has been extended for TMF conditions. Parameter determination for the model is carried out on isothermal load controlled tests at 550–650 °C for surface cracks, which later have been used to extrapolate parameters used for TMF crack growth. Further, validation of the developed model is conducted on a notched specimen subjected to strain control at 50–550 °C. Satisfying results are gained within reasonable scatter level compared for test and simulated number of cycles to failure.

    Place, publisher, year, edition, pages
    ASME Press, 2016
    National Category
    Mechanical Engineering Materials Engineering Applied Mechanics
    Identifiers
    urn:nbn:se:liu:diva-121008 (URN)10.1115/1.4031158 (DOI)000371127900014 ()
    Note

    Funding agencies: Swedish Energy Agency; Siemens Industrial Turbomachinery AB; GKN Aerospace Engine Systems; Royal Institute of Technology through Swedish research programme TURBO POWER

    Available from: 2015-09-02 Created: 2015-09-02 Last updated: 2017-12-04Bibliographically approved
    10. Impact of high cycle fatigue on dwell time crack growth in a Ni-based superalloy
    Open this publication in new window or tab >>Impact of high cycle fatigue on dwell time crack growth in a Ni-based superalloy
    Show others...
    2015 (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    Sustained load have been shown to give rise to increased crack growth rate at elevated temperature. Such loads generate a history dependent fatigue problem due to weakening and cracking of grain boundaries during dwell times, later broken apart during subsequent load cycles. So far most studies have focused on sustained load and the interaction of load cycles, overloads, and temperature, but few studies have been carried out for vibrations and how these affect the dwell time crack growth. Vibrations of different kinds are frequently seen in engine components, and present in combination with sustained loads a more realistic loading situation than the latter itself. An investigation of how a vibrational load affects the dwell time cracking and how to incorporate it in a modelling context is therefore of importance. In this paper a study of the most frequently used gas turbine material, Inconel 718, has been carried out. Mechanical testing has been conducted at 550◦C for surface cracks with and without the interaction of engine vibrations on sustained load, here represented by a superimposed high cycle fatigue (HCF) load. Subsequent investigation of the fracture behaviour was performed by Scanning Electron Microscope (SEM) and the modelling work has been conducted by incorporating the HCF load description within a history dependent crack growth law. The obtained results show reasonable accuracy with respect to the mechanical tests.

    Keywords
    Hold time effects, Dwell times, Sustained load, Crack growth modelling, Inconel 718, High temperature
    National Category
    Mechanical Engineering Materials Engineering Applied Mechanics
    Identifiers
    urn:nbn:se:liu:diva-121009 (URN)
    Available from: 2015-09-02 Created: 2015-09-02 Last updated: 2015-09-02Bibliographically approved
  • 198.
    Storgärds, Erik
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Saarimäki, Jonas
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Simonsson, Kjell
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Sjöström, Sören
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Gustafsson, David
    Siemens Industrial Turbomachinery AB, Finspång, Sweden.
    Månsson, Tomas
    GKN Aerospace Engine Systems, Trollhättan, Sweden.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Scatter in Dwell Time Cracking for a Ni-Based Superalloy in Combination With Overloads2016In: Journal of engineering for gas turbines and power, ISSN 0742-4795, E-ISSN 1528-8919, Vol. 138, no 1, p. 012502-012502Article in journal (Refereed)
    Abstract [en]

    In this paper, scatter in crack growth for dwell time loadings in combination with overloads has been investigated. Multiple tests were performed for surface cracks at 550 °C in the commonly used high temperature material Inconel 718. The test specimens originate from two different batches which also provide for a discussion of how material properties affect the dwell time damage and overload impact. In combination with these tests, an investigation of the microstructure was also carried out, which shows how it influences the growth rate. The results from this study show that, in order to take overloads into consideration when analyzing spectrum loadings containing dwell times, one needs a substantial amount of material data available as the scatter seen from one batch to the other are of significant proportions.

  • 199.
    Storgärds, Erik
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Saarimäki, Jonas
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Simonsson, Kjell
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Sjöström, Sören
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Månsson, Tomas
    GKN Aerospace Engine Systems, Trollhättan, Sweden.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Impact of high cycle fatigue on dwell time crack growth in a Ni-based superalloy2015Manuscript (preprint) (Other academic)
    Abstract [en]

    Sustained load have been shown to give rise to increased crack growth rate at elevated temperature. Such loads generate a history dependent fatigue problem due to weakening and cracking of grain boundaries during dwell times, later broken apart during subsequent load cycles. So far most studies have focused on sustained load and the interaction of load cycles, overloads, and temperature, but few studies have been carried out for vibrations and how these affect the dwell time crack growth. Vibrations of different kinds are frequently seen in engine components, and present in combination with sustained loads a more realistic loading situation than the latter itself. An investigation of how a vibrational load affects the dwell time cracking and how to incorporate it in a modelling context is therefore of importance. In this paper a study of the most frequently used gas turbine material, Inconel 718, has been carried out. Mechanical testing has been conducted at 550◦C for surface cracks with and without the interaction of engine vibrations on sustained load, here represented by a superimposed high cycle fatigue (HCF) load. Subsequent investigation of the fracture behaviour was performed by Scanning Electron Microscope (SEM) and the modelling work has been conducted by incorporating the HCF load description within a history dependent crack growth law. The obtained results show reasonable accuracy with respect to the mechanical tests.

  • 200.
    Storgärds, Erik
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Saarimäki, Jonas
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Simonsson, Kjell
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Sjöström, Sören
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Månsson, Tomas
    GDN Aerospace Engine Systems, Trollhättan.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Influence of Superimposed Vibrational Load on Dwell Time Crack Growth in a Ni-Based Superalloy2016In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 87, p. 301-310Article in journal (Refereed)
    Abstract [en]

    Sustained loads have for some Ni-based superalloys been shown to give rise to increased crack growth rate at elevated temperature. Such loads generate a history dependent fatigue problem due to weakening and cracking of grain boundaries during dwell times, later broken apart during subsequent load cycles. So far most studies have focused on the interaction of load cycles, overloads, and temperature. However, vibrations of different kinds are to some extent always present in engine components, and an investigation of how such loads affect the dwell time cracking, and how to incorporate them in a modelling context, is therefore of importance. In this paper a study of the most frequently used gas turbine material, Inconel 718, has been carried out. Mechanical crack propagation testing has been conducted at 550 °C for surface cracks with and without the interaction of superimposed vibrational loads. Subsequent investigation of the fracture behaviour was performed by scanning electron microscopy and the modelling work has been conducted by incorporating the vibration load description within a history dependent crack growth law. The obtained results show reasonable accuracy with respect to the mechanical test results.

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