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  • 1.
    Ahlbert, Gabriella
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Method Evaluation of Global-Local Finite Element Analysis2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    When doing finite element analysis upon the structure of Saab’s aeroplanes a coarse global model of mainly shell elements is used to determine the load distribution for sizing the structure. At some parts of the aeroplane it is however desirable to implement a more detailed analysis. These areas are usually modelled with solid elements; the problem of connecting the fine local solid elements to the coarse global model will shell elements then arises.

     

    This master thesis is preformed to investigate possible Global-Local methods to use for the structural analysis on Gripen. First a literature study of current methods on the market is made, thereafter a few methods are implemented on a generic test structure and later on also tested on a real detail of Gripen VU. The methods tested in this thesis are Mesh refinement in HyperWorks, RBE3 in HyperWorks, Glue in MSC Patran/Nastran and DMIG in MSC Nastran. The software is however not evaluated in this thesis, and a further investigation is recommended to find the most fitting software for this purpose. All analysis are performed with linear assumptions.

     

    Mesh refinement is an integrated technique where the elements are gradually decreasing in size. Per definition, this technique cannot handle gaps, but it has almost identical results to the fine reference model.

     

    RBE3 is a type of rigid body elements with zero stiffness, and is used as an interface element. RBE3 is possible to use to connect both Shell-To-Shell and Shell-To-Solid, and can handle offsets and gaps in the boundary between the global and local model.

     

    Glue is a contact definition and is also available in other software under other names. The global respectively the local model is defined as contact bodies and a contact table is used to control the coupling. Glue works for both Shell-To-Shell and Shell-To-Solid couplings, but has problem dealing with offsets and gaps in the boundary between the global and local model.

     

    DMIG is a superelement technique where the global model is divided into smaller sub-models which are mathematically connected. DMIG is only possible to use when the nodes on the boundary on the local model have the same position as the nodes at the boundary of the global model. Thus, it is not possible to only use DMIG as a Global-Local method, but can advantageously be combined with other methods.

     

    The results indicate that the preferable method to use for Global-Local analysis is RBE3. To decrease the size of the files and demand of computational power, RBE3 can be combined with a superelement technique, for example DMIG.

     

    Finally, it is important to consider the size of the local model. There will inevitably be boundary effect when performing a Global-Local analysis of the suggested type, and it is therefore important to make the local model big enough so that the boundary effects have faded before reaching the area of interest.

  • 2.
    Almroth, Per
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Solid Mechanics . Linköping University, The Institute of Technology.
    Hasselqvist, M.
    Demag Delaval Indust. Turbomach. AB, Finspång.
    Simonsson, Kjell
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Solid Mechanics .
    Sjöström, Sören
    Linköping University, Department of Management and Engineering, Solid Mechanics . Linköping University, The Institute of Technology.
    Viscoplastic-plastic modelling of IN7922004In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 29, no 4, p. 437-445Article in journal (Refereed)
    Abstract [en]

    At high temperatures metallic materials behave in a viscous manner exemplified by strain rate dependence, stress relaxation and creep deformation. At low temperatures however, these effects are extremely small, and the behaviour is strain rate independent and shows no or very small relaxation effects. Finally there exists an intermediate region, in which the material behaviour is close to strain rate independent for high strain rates but at the same time shows time dependent inelastic effects, such as stress relaxation and creep. For IN792 this occurs at temperatures around 650 °C. The article describes the extension of a power-law viscoplastic model describing the behaviour of IN792 at 850 °C, also to describe the behaviour at 650 °C, by bounding the elastic-viscoplastic stress-space by a plastic yield surface. The model parameters have been estimated using data from creep test and tailored step relaxation tests, and the model fits well to both the step relaxation data aimed at resembling relevant component conditions and long term creep data. © 2003 Published by Elsevier B.V.

  • 3.
    Arkman, Jonas
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Boo, Christofer
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Design och dimensionering av momentskärmsstativ för provflygning av JAS39 Gripen: Konceptverifiering med hjälp av handberäkningar och FEM2013Independent thesis Basic level (degree of Bachelor), 10,5 credits / 16 HE creditsStudent thesis
    Abstract [sv]

    Det här projektet har genomförts på uppdrag av Saab, med syftet att designa och dimensionera ett stativ för infästning av en momentskärm. Denna momentskärm används vid provflygning av JAS39 Gripen för att vid behov upphäva ett okontrollerat tillstånd som kan inträffa vid tester av spinnfall och högalfaflygningar.

    Det arbete som presenteras i den här rapporten är en del av ett större projekt där målet har varit att ta fram ett stativ. I den här rapporten presenteras analyser som har gjorts dels med handbokslösningar och klassisk hållfasthetslära, dels med FE-programmet Ansys för att kontrollera att det slutgiltiga konceptet uppfyller samtliga givna krav.

    Vid dimensioneringen har ett iterativt arbetssätt använts, det har byggt på att först ta fram ett grundläggande koncept och sedan förbättra detta under projektets gång. Efter varje iteration har analyser gjorts av resultatet för att verifiera stativets funktion. För att inte påverka flygegenskaperna mer än nödvändigt har det även varit viktigt att minimera stativets vikt. Projektet har resulterat i ett koncept av titanlegeringen Ti-6Al-4V med en vikt på 67,7 kg.

  • 4.
    Aspenberg, David
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Robust optimisation of structures: Evaluation and incorporation of variations in simulation based design2011Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis concerns the robustness of structures considering various uncertainties. The overall objective is to evaluate and develop simulation based design methods in order to find solutions that are optimal both in the sense of handling typical load cases and minimising the variability of the response, i.e. robust optimal designs. Conventionally optimised structures may show a tendency of being sensitive to small perturbations in the design or loading conditions. These variations are of course inevitable. To create robust designs, it is necessary to account for all conceivable variations (or at least the influencing ones) in the design process. The thesis is divided into two parts. The first part serves as a theoretical background for this work. It includes introductions to the concept of robust design, basic statistics, optimisation theory and metamodelling. The second part consists of five appended papers on the topic.

    The first and third papers focuse on the evaluation of robustness, given some dispersions in the input data. Established existing methods are applied, and for paper three, comparisons with experimentally evaluated dispersions on a larger system are made.

    The second and fourth paper introduce two new approaches to perform robust optimisation, i.e. optimisations where the mean performance and the robustness in the objectives are simultaneously optimised. These methods are demonstrated both on an analytical example and on a Finite Element model design example. The fifth paper studies the variations in mechanical properties between several different batches of the same steel grade. A material model is fitted to each batch of material, whereby dispersions seen in test specimens are transferred to material model parameter variations. The correlations between both test and material model parameters are studied.

    List of papers
    1. Finite element based robustness study of a truck cab subjected to impact loading
    Open this publication in new window or tab >>Finite element based robustness study of a truck cab subjected to impact loading
    2009 (English)In: International Journal of Crashworthiness, ISSN 1358-8265, E-ISSN 1754-2111, Vol. 14, no 2, p. 111-124Article in journal (Refereed) Published
    Abstract [en]

    Optimised designs have a tendency of being sensitive to variations. It is therefore of great importance to analyse this sensitivity to assure that a design is robust, i.e. sufficiently insensitive to variations. To analyse robustness, variations are introduced in model parameters and their influences on simulation responses are studied. This is usually achieved using the Monte Carlo method. Though, due to the large number of simulations needed, the Monte Carlo method is very costly for problems requiring a long computing time. Therefore, in this work a meta model-based Monte Carlo method is used to evaluate the robustness of a vehicle structure. That is, the Monte Carlo analysis is performed on a surface approximation of the true response, over the domain of interest. The methodology used is to first identify the variables that influence the response the most, referred to as a screening, using simple linear response surfaces. This is followed by a more detailed sensitivity analysis using only the identified variables and a quadratic response surface, thereby incorporating second order effects. A truck cab model exposed to a pendulum impact load is used as an evaluation of this method, and the important variables and their influence on the response are identified. The effect of including results from forming simulations is also evaluated using the truck cab model. Variations are introduced before forming simulations, thereby taking forming effects into account in the sensitivity analysis. The method was found to be a good tool to identify important dispersion variables and to give an approximate result of the total dispersion, all with a reasonable amount of simulations.

    Place, publisher, year, edition, pages
    Taylor & Francis, 2009
    Keywords
    Monte Carlo, meta model, robust design, response surface method, sensitivity analysis, robustness
    National Category
    Applied Mechanics
    Identifiers
    urn:nbn:se:liu:diva-15474 (URN)10.1080/13588260802412992 (DOI)
    Projects
    ROBDES
    Note
    On the day of the defence date the status of this article was: Accepted.Available from: 2008-11-11 Created: 2008-11-11 Last updated: 2017-12-14Bibliographically approved
    2. An approach to robust optimization of impact problems using random samples and meta-modelling
    Open this publication in new window or tab >>An approach to robust optimization of impact problems using random samples and meta-modelling
    2010 (English)In: International Journal of Impact Engineering, ISSN 0734-743X, E-ISSN 1879-3509, Vol. 37, no 6, p. 723-734Article in journal (Refereed) Published
    Abstract [en]

    Conventionally optimized structures may show a tendency to be sensitive to variations, for instance in geometry and loading conditions. To avoid this, research has been carried out in the field of robust optimization where variations are taken into account in the optimization process. The overall objective is to create solutions that are optimal both in the sense of mean performance and minimum variability. This work presents an alternative approach to robust optimization, where the robustness of each design is assessed through multiple sampling of the stochastic variables at each design point. Meta-models for the robust optimization are created for both the mean value and the standard deviation of the response. Furthermore, the method is demonstrated on an analytical example and an example of an aluminium extrusion with quadratic cross-section subjected to axial crushing. It works well for the chosen examples and it is concluded that the method is especially well suited for problems with a large number of random variables, since the computational cost is essentially independent of the number of random variables. In addition, the presented approach makes it possible to take into consideration variations that cannot be described with a variable. This is demonstrated in this work by random geometrical perturbations described with the use of Gaussian random fields.

    Keywords
    Robust optimisation, geometric imperfections, meta model, robustness
    National Category
    Applied Mechanics
    Identifiers
    urn:nbn:se:liu:diva-15478 (URN)10.1016/j.ijimpeng.2009.07.002 (DOI)
    Projects
    ROBDES
    Note
    Tidigare titel: Robust optimisation methodology using random samples and meta modelling Available from: 2008-11-11 Created: 2008-11-11 Last updated: 2017-12-14Bibliographically approved
    3. Experimental and finite element robustness studies of a bumper system subjected to an offset impact loading
    Open this publication in new window or tab >>Experimental and finite element robustness studies of a bumper system subjected to an offset impact loading
    2011 (English)In: International Journal of Crashworthiness, ISSN 1358-8265, E-ISSN 1754-2111, Vol. 16, no 2, p. 155-168Article in journal (Refereed) Published
    Abstract [en]

    A product of high quality is a product that performs well, not only in exactly the situations it was designed to handle but also in slightly different situations that arise in the usage of the product. As a specific example, the performance of a bumper system should not depend on small fluctuations in the manufacturing process or on small variations in the impact event. In this work, the robustness of an existing vehicle bumper system subjected to a crash load has been evaluated both experimentally and numerically. In the latter case, different widely used approaches to numerically assess the robustness have been utilised. A reliable numerical robustness study provides the designer with a valuable tool for improving a design, and an evaluation of these methods in this context is therefore of interest. It is concluded that for the example under study, both the Monte Carlo method and the metamodel-based Monte Carlo methods work well. Furthermore, for moderate dispersions levels, i.e. a small design space with no bifurcation in the deformation pattern, a linear response approximation is shown to have a sufficient accuracy to be used in the metamodel-based robustness analysis. The performed numerical robustness studies also point out that the performance of a nominal simulation, i.e. a simulation conducted with mean values for all variables, does not in general predict the mean performance of the finite element model. Finally, some possible design improvements for the bumper system under study are also identified

    Place, publisher, year, edition, pages
    Abingdon, Oxford, UK: Taylor & Francis Group, 2011
    Keywords
    experimental robustness, numerical robustness, Monte Carlo, metamodel, sensitivity analysis
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-70195 (URN)10.1080/13588265.2010.539339 (DOI)
    Available from: 2011-08-24 Created: 2011-08-24 Last updated: 2017-12-08
    4. Robust optimisation of front members in a full frontal car impact
    Open this publication in new window or tab >>Robust optimisation of front members in a full frontal car impact
    (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    In the search of a lightweight design of automobiles, it is necessary to assure that a robust crashworthiness performance is achieved. Structures that are optimised to handle a finite number of load cases may perform poorly when subjected to various dispersions. Thus, uncertainties must be accounted for in the optimisation process. This paper presents an approach to optimisation where all design evaluations include an evaluation of the robustness. Metamodel approximations are applied both to the design space and the robustness evaluations, using Artifical Neural Networks and polynomials, respectively. The features of the robust optimisation approach are displayed in an analytical example, and further demonstrated in a large scale design example of front side members of a car. Different optimisation formulations are applied and it is shown that the proposed approach works well. It is also concluded that a robust optimisation puts higher demands on the FE model performance than normally.

    Keywords
    Robust optimisation; dual response surface; metamodel; genetic algorithm
    National Category
    Materials Engineering
    Identifiers
    urn:nbn:se:liu:diva-70192 (URN)
    Available from: 2011-08-24 Created: 2011-08-24 Last updated: 2011-09-07Bibliographically approved
    5. An evaluation of the statistics of steel material model parameters
    Open this publication in new window or tab >>An evaluation of the statistics of steel material model parameters
    2012 (English)In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 212, no 6, p. 1288-1297Article in journal (Refereed) Published
    Abstract [en]

    In robustness studies, variations of material properties are often represented by simple assumptions, such as scaling of stress-strain relations, often due to lack of knowledge or deeper understanding of the material physics and the material model applied. By performing material characterisation tests on several batches of a DP600 steel and fitting a phenomenological material model to each batch, this paper studies the dispersion of material model parameters, as well as correlations between both experimental and model parameters. It is concluded that some of the charcterisation tests may be omitted in the future, due to correlations found between parameters. The results may also be applied in a robustness study by inversely using the retrieved statistics to generate reasonable new sets of material model parameters. The methodology presented may be adopted for any other type of material characterisation process.

    Place, publisher, year, edition, pages
    Elsevier, 2012
    Keywords
    Robustness studies, material model parameter variations, dual phase steel
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-70193 (URN)10.1016/j.jmatprotec.2012.01.016 (DOI)000303176900008 ()
    Note
    funding agencies|SFS ProViking project Super Light Steel Structures||Available from: 2011-08-24 Created: 2011-08-24 Last updated: 2017-12-08Bibliographically approved
  • 5.
    Aspenberg, David
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Jergeus, Johan
    Volvo Cars Safety Centre, Göteborg.
    Nilsson, Larsgunnar
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Robust optimisation of front members in a full frontal car impactManuscript (preprint) (Other academic)
    Abstract [en]

    In the search of a lightweight design of automobiles, it is necessary to assure that a robust crashworthiness performance is achieved. Structures that are optimised to handle a finite number of load cases may perform poorly when subjected to various dispersions. Thus, uncertainties must be accounted for in the optimisation process. This paper presents an approach to optimisation where all design evaluations include an evaluation of the robustness. Metamodel approximations are applied both to the design space and the robustness evaluations, using Artifical Neural Networks and polynomials, respectively. The features of the robust optimisation approach are displayed in an analytical example, and further demonstrated in a large scale design example of front side members of a car. Different optimisation formulations are applied and it is shown that the proposed approach works well. It is also concluded that a robust optimisation puts higher demands on the FE model performance than normally.

  • 6.
    Aspenberg, David
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology. Linkoping Univ, Div Solid Mech, SE-58183 Linkoping, Sweden .
    Jergeus, Johan
    Volvo Cars Safety Centre, Sweden .
    Nilsson, Larsgunnar
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Robust optimization of front members in a full frontal car impact2013In: Engineering optimization (Print), ISSN 0305-215X, E-ISSN 1029-0273, Vol. 45, no 3, p. 245-264Article in journal (Refereed)
    Abstract [en]

    In the search for lightweight automobile designs, it is necessary to assure that robust crashworthiness performance is achieved. Structures that are optimized to handle a finite number of load cases may perform poorly when subjected to various dispersions. Thus, uncertainties must be accounted for in the optimization process. This article presents an approach to optimization where all design evaluations include an evaluation of the robustness. Metamodel approximations are applied both to the design space and the robustness evaluations, using artifical neural networks and polynomials, respectively. The features of the robust optimization approach are displayed in an analytical example, and further demonstrated in a large-scale design example of front side members of a car. Different optimization formulations are applied and it is shown that the proposed approach works well. It is also concluded that a robust optimization puts higher demands on the finite element model performance than normally.

  • 7.
    Aspenberg, David
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Larsson, Rikard
    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.
    An evaluation of the statistics of steel material model parameters2012In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 212, no 6, p. 1288-1297Article in journal (Refereed)
    Abstract [en]

    In robustness studies, variations of material properties are often represented by simple assumptions, such as scaling of stress-strain relations, often due to lack of knowledge or deeper understanding of the material physics and the material model applied. By performing material characterisation tests on several batches of a DP600 steel and fitting a phenomenological material model to each batch, this paper studies the dispersion of material model parameters, as well as correlations between both experimental and model parameters. It is concluded that some of the charcterisation tests may be omitted in the future, due to correlations found between parameters. The results may also be applied in a robustness study by inversely using the retrieved statistics to generate reasonable new sets of material model parameters. The methodology presented may be adopted for any other type of material characterisation process.

  • 8.
    Bergqvist, Göran
    et al.
    Private practice, Norrköping, Sweden.
    Simonsson, Kjell
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Rydberg, Kristoffer
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Johansson, Fredrik
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Dérand, Tore
    Department of Dental Technology and Dental Materials Science, Faculty of Odontology, Malmö University, Malmö, Sweden.
    A finite element analysis of stress distribution in bone tissue surrounding uncoupled or splinted dental implants2008In: Clinical Implant Dentistry and Related Research, ISSN 1523-0899, E-ISSN 1708-8208, Vol. 10, no 1, p. 40-46Article in journal (Refereed)
    Abstract [en]

    Background: Several studies on one-stage surgery in the treatment of the edentulous maxilla with implant-supported fixed prostheses have reported problems with removable provisional prostheses, which can load the implants in an uncontrollable manner during healing, and jeopardize healing. Immediate splinting of the implants with a fixed provisional prosthesis has been proposed to protect the bone-implant interface.

    Purpose: This study used the finite element method (FEM) to simulate stresses induced in bone tissue surrounding uncoupled and splinted implants in the maxilla because of bite force loading, and to determine whether the differences in these stress levels are related to differences in observed bone losses associated with the two healing methods.

    Materials and Methods: Stress levels in the maxilla were studied using the FEM program TRINITAS (Institute of Technology, Linköping University, Linköping, Sweden) in which all phases – preprocessing/modeling, equation solving, and postprocessing/evaluation – were simulated.

    Results: Stress levels in bone tissue surrounding splinted implants were markedly lower than stress levels surrounding uncoupled implants by a factor of nearly 9.

    Conclusion: From a mechanical viewpoint, FEM simulation supports the hypothesis that splinting reduces damage evolution in bone tissue, which agrees with clinical observations.

  • 9.
    Björklund, Oscar
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Ductile Failure in High Strength Steel Sheets2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Developments in computer-aided engineering and the rapid growth of computational power have made simulation-driven process and product development efficient and useful since it enables detailed evaluation of product designs and their manufacturing processes. In the context of a sheet metal component, it is vital to predict possible failure both during its forming process and its subsequent usage. Accurate numerical models are needed in order to obtain trustworthy simulation results. Furthermore, the increasing demands imposed on improved weight-to-performance ratio for many products endorse the use of high-strength steels. These steels often show anisotropic behaviour and more complex hardening and fracturing compared to conventional steels. Consequently, demand for research on material and failure models suitable for these steels has increased.

    In this work, the mechanical and fracture behaviour of two high-strength steels, Docol 600DP and Docol 1200M, have been studied under various deformation processes. Experimental results have been used both for material characterisation and for calibration of fracture criteria. One major requirement as concerns the fracture criteria studied is that they should be simple to apply in industrial applications, i.e. it should be possible to easily calibrate the fracture criteria in simple mechanical experiments and they should be efficient and accurate. Consequently, un-coupled phenomenological damage models have been the main focus throughout this work.

    Detailed finite element models including accurate constitutive laws have be used to predict and capture material instabilities. Most of the fracture criteria studied are modifications of the plastic work to fracture. Ductile tensile and ductile shear types of fracture are of particular interest in sheet metal applications. For these fractures the modification of the plastic work relates to void coalescence and void collapse, respectively. Anisotropy in fracture behaviour can be captured by the introduction of a material directional function.

    The dissertation consists of two parts. The first part contains theory and background. The second consists of five papers.

    List of papers
    1. A study of high strength steels undergoing non-linear strain paths—Experiments and modelling
    Open this publication in new window or tab >>A study of high strength steels undergoing non-linear strain paths—Experiments and modelling
    2011 (English)In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 211, no 1, p. 121-131Article in journal (Refereed) Published
    Abstract [en]

    This paper presents an evaluation of the constitutive behaviour, including plastic anisotropy and mixed isotropic-kinematic hardening of two high strength steels, Docol 600DP and Docol 1200M, during strain path changes. A series of tensile and shear tests was performed on both virgin and pre-strained materials. The initial anisotropy and work hardening parameters were obtained from tensile tests, shear tests and a bulge test of the virgin material, whereas the kinematic hardening parameters were identified by comparing numerical predictions to experimental results related to the pre-strained materials. Numerical predictions using the obtained parameters agree well with the experimental results, both in the case of proportional, and under non-proportional strain paths.

    Place, publisher, year, edition, pages
    Elsevier, 2011
    Keywords
    Non-linear strain paths, Plastic anisotropy, Mixed isotropic-kinematic hardening, Shear test
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-60772 (URN)10.1016/j.jmatprotec.2010.09.004 (DOI)
    Available from: 2010-12-01 Created: 2010-10-26 Last updated: 2017-12-12
    2. Failure of high strength steel sheets: Experiments and modelling
    Open this publication in new window or tab >>Failure of high strength steel sheets: Experiments and modelling
    2013 (English)In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 213, no 7, p. 1103-1117Article in journal (Refereed) Published
    Abstract [en]

    Failure in sheet metal structures of ductile material is usually caused by one of, or a combination of, ductile fracture, shear fracture or localised instability. In this paper the failure of the high strength steel Docol 600DP and the ultra high strength steel Docol 1200M is explored. The constitutive model used in this study includes plastic anisotropy and mixed isotropic-kinematic hardening. For modelling of the ductile and shear fracture the models presented by Cockroft–Latham and Bressan–Williams have been used. The instability phenomenon is described by the constitutive law and the finite element (FE) models. For calibration of the failure models and validation of the results, an extensive experimental series has been conducted including shear tests, plane strain tests and Nakajima tests. The geometries of the Nakajima tests have been chosen so that the first quadrant of the forming limit diagram (FLD) were covered. The results are presented both in an FLD and using prediction of force–displacement response of the Nakajima test employing element erosion during the FE simulations. The classical approach for failure prediction is to compare the principal plastic strains obtained from FE simulations with experimental determined forming limit curves (FLCs). It is well known that the experimental FLC requires proportional strains to be useful. In this work failure criteria, both of the instability and fracture, are proposed which can be used also for non-proportional strain paths.

    Keywords
    Sheet metal failure, high strength steels, forming limits, ductile fracture, shear fracture
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-77758 (URN)10.1016/j.jmatprotec.2013.01.027 (DOI)000318325100011 ()
    Available from: 2012-05-28 Created: 2012-05-28 Last updated: 2017-12-07Bibliographically approved
    3. Failure characteristics of a dual-phase steel sheet
    Open this publication in new window or tab >>Failure characteristics of a dual-phase steel sheet
    2014 (English)In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 214, p. 1190-1204Article in journal (Refereed) Published
    Abstract [en]

    Failure in ductile sheet metal structures is usually caused by one, or a combination of, ductile tensile fractures, ductile shear fractures or localised instability. In this paper the failure characteristics of the high strength steel Docol 600DP are explored. The study includes both experimental and numerical sections. In the experimental sections, the fracture surface of the sheet subjected to Nakajima tests is studied under the microscope with the aim of finding which failure mechanism causes the fracture. In the numerical sections, finite element (FE) simulations have been conducted using solid elements. From these simulations, local stresses and strains have been extracted and analysed with the aim of identifying the fracture dependency of the stress triaxiality and Lode parameter.

    Place, publisher, year, edition, pages
    Elsevier, 2014
    Keywords
    Sheet metal failure; Forming limit; Instability; Ductile tensile fracture; Ductile shear fracture
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-105209 (URN)10.1016/j.jmatprotec.2014.01.004 (DOI)000334006600003 ()
    Available from: 2014-03-13 Created: 2014-03-13 Last updated: 2017-12-05Bibliographically approved
    4. Prediction of fracture in a dual-phase steel subjected to non-linear straining
    Open this publication in new window or tab >>Prediction of fracture in a dual-phase steel subjected to non-linear straining
    2014 (English)In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 214, no 11, p. 2748-2758Article in journal (Refereed) Published
    Abstract [en]

    In this work, selected fracture criteria are applied to predict the fracture of dualphase steel subjected to non-linear strain paths. Furthermore, the effects of manufacturing history are studied. Four fracture criteria were calibrated in three tests using standard specimens. The fracture criteria were first validated in the circular Nakajima test. A second validation test case was included in order to validate fracture prediction for non-linear strain paths. In this test a sheet metal component was manufactured and subsequently stretched until it fractured. All fracture criteria included in this study predict fracture during the Nakajima test with reasonable accuracy. In the second validation test however, the different fracture criteria show considerable diversity in accumulated damage during manufacturing which caused substantial scatter of the fracture prediction in the subsequent stretching. This shows that manufacturing history influences the prediction of fracture.

    Place, publisher, year, edition, pages
    Elsevier, 2014
    Keywords
    Sheet metal failure, high strength steels, forming limits, non-linear strain paths, forming history
    National Category
    Mechanical Engineering
    Identifiers
    urn:nbn:se:liu:diva-105211 (URN)10.1016/j.jmatprotec.2014.05.028 (DOI)000340300400059 ()
    Note

    Funders: SSF ProViking project entitled "SuperLight Steel Structures"

    Available from: 2014-03-13 Created: 2014-03-13 Last updated: 2017-12-05
    5. Anisotropic fracture criteria for a dual-phase steel
    Open this publication in new window or tab >>Anisotropic fracture criteria for a dual-phase steel
    2014 (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    The main objective of this work is to examine the use of anisotropic fracture criteria in order to predict fracture in dual-phase steel. The introduction of a material directional function into the fracture criterion was used in order to account for anisotropy observed in experiments. Selected fracture criteria were fist calibrated by ordinary tensile and in-plane shear tests using specimens cut in three material directions. In order to validate the performance, two types of validation tests were conducted. First, plane strain (notched tensile) tests were carried out in three material directions. Second, Nakajima tests with a waist of 130 mm were conducted, also in three material directions. The fit to the calibration tests was improved with all material directional functions compared to the isotropic criterion. Overall best performance was achieved when a material direction function based on the structural tensors was introduced.

    Keywords
    Sheet metal failure, anisotropy, ductile tensile fracture, ductile shear fracture
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-105212 (URN)
    Available from: 2014-03-13 Created: 2014-03-13 Last updated: 2014-03-13Bibliographically approved
  • 10.
    Björklund, Oscar
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Modelling of Failure in High Strength Steel Sheets2012Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    In this theses the high strength steel Docol 600DP and the ultra high strength steel Docol 1200M are studied. Constitutive laws and failure models are calibrated and veried by the use of experiments and numerical simulations. For the constitutive equations, an eight parameter high exponent yield surface has been adopted, representing the anisotropic behaviour, and a mixed isotropic-kinematic hardening has been used to capture non-linear strain paths.

    For ductile sheet metals three dierent failure phenomena have been observed: (i) ductile fracture, (ii) shear fracture, and (iii) instability with localised necking. The models for describing the dierent failure types have been chosen with an attempt to use just a few tests in addition to these used for the constitutive model. In this work the ductile and shear fracture have been prescribed by models presented by Cockroft-Latham and Bressan-Williams, respectively. The instability phenomenon is described by the constitutive law and the nite element models. The results obtained are in general in good agreement with test results.

    The thesis is divided into two main parts. The background, theoretical framework, mechanical experiments and nite element models are presented in the rst part. In the second part, two papers are appended.

    List of papers
    1. A study of high strength steels undergoing non-linear strain paths—Experiments and modelling
    Open this publication in new window or tab >>A study of high strength steels undergoing non-linear strain paths—Experiments and modelling
    2011 (English)In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 211, no 1, p. 121-131Article in journal (Refereed) Published
    Abstract [en]

    This paper presents an evaluation of the constitutive behaviour, including plastic anisotropy and mixed isotropic-kinematic hardening of two high strength steels, Docol 600DP and Docol 1200M, during strain path changes. A series of tensile and shear tests was performed on both virgin and pre-strained materials. The initial anisotropy and work hardening parameters were obtained from tensile tests, shear tests and a bulge test of the virgin material, whereas the kinematic hardening parameters were identified by comparing numerical predictions to experimental results related to the pre-strained materials. Numerical predictions using the obtained parameters agree well with the experimental results, both in the case of proportional, and under non-proportional strain paths.

    Place, publisher, year, edition, pages
    Elsevier, 2011
    Keywords
    Non-linear strain paths, Plastic anisotropy, Mixed isotropic-kinematic hardening, Shear test
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-60772 (URN)10.1016/j.jmatprotec.2010.09.004 (DOI)
    Available from: 2010-12-01 Created: 2010-10-26 Last updated: 2017-12-12
    2. Failure of high strength steel sheets: Experiments and modelling
    Open this publication in new window or tab >>Failure of high strength steel sheets: Experiments and modelling
    2013 (English)In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 213, no 7, p. 1103-1117Article in journal (Refereed) Published
    Abstract [en]

    Failure in sheet metal structures of ductile material is usually caused by one of, or a combination of, ductile fracture, shear fracture or localised instability. In this paper the failure of the high strength steel Docol 600DP and the ultra high strength steel Docol 1200M is explored. The constitutive model used in this study includes plastic anisotropy and mixed isotropic-kinematic hardening. For modelling of the ductile and shear fracture the models presented by Cockroft–Latham and Bressan–Williams have been used. The instability phenomenon is described by the constitutive law and the finite element (FE) models. For calibration of the failure models and validation of the results, an extensive experimental series has been conducted including shear tests, plane strain tests and Nakajima tests. The geometries of the Nakajima tests have been chosen so that the first quadrant of the forming limit diagram (FLD) were covered. The results are presented both in an FLD and using prediction of force–displacement response of the Nakajima test employing element erosion during the FE simulations. The classical approach for failure prediction is to compare the principal plastic strains obtained from FE simulations with experimental determined forming limit curves (FLCs). It is well known that the experimental FLC requires proportional strains to be useful. In this work failure criteria, both of the instability and fracture, are proposed which can be used also for non-proportional strain paths.

    Keywords
    Sheet metal failure, high strength steels, forming limits, ductile fracture, shear fracture
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-77758 (URN)10.1016/j.jmatprotec.2013.01.027 (DOI)000318325100011 ()
    Available from: 2012-05-28 Created: 2012-05-28 Last updated: 2017-12-07Bibliographically approved
  • 11.
    Björklund, Oscar
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Govik, Alexander
    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.
    Prediction of fracture in a dual-phase steel subjected to non-linear straining2014In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 214, no 11, p. 2748-2758Article in journal (Refereed)
    Abstract [en]

    In this work, selected fracture criteria are applied to predict the fracture of dualphase steel subjected to non-linear strain paths. Furthermore, the effects of manufacturing history are studied. Four fracture criteria were calibrated in three tests using standard specimens. The fracture criteria were first validated in the circular Nakajima test. A second validation test case was included in order to validate fracture prediction for non-linear strain paths. In this test a sheet metal component was manufactured and subsequently stretched until it fractured. All fracture criteria included in this study predict fracture during the Nakajima test with reasonable accuracy. In the second validation test however, the different fracture criteria show considerable diversity in accumulated damage during manufacturing which caused substantial scatter of the fracture prediction in the subsequent stretching. This shows that manufacturing history influences the prediction of fracture.

  • 12.
    Björklund, Oscar
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Larsson, Rikard
    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.
    Failure of high strength steel sheets: Experiments and modelling2013In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 213, no 7, p. 1103-1117Article in journal (Refereed)
    Abstract [en]

    Failure in sheet metal structures of ductile material is usually caused by one of, or a combination of, ductile fracture, shear fracture or localised instability. In this paper the failure of the high strength steel Docol 600DP and the ultra high strength steel Docol 1200M is explored. The constitutive model used in this study includes plastic anisotropy and mixed isotropic-kinematic hardening. For modelling of the ductile and shear fracture the models presented by Cockroft–Latham and Bressan–Williams have been used. The instability phenomenon is described by the constitutive law and the finite element (FE) models. For calibration of the failure models and validation of the results, an extensive experimental series has been conducted including shear tests, plane strain tests and Nakajima tests. The geometries of the Nakajima tests have been chosen so that the first quadrant of the forming limit diagram (FLD) were covered. The results are presented both in an FLD and using prediction of force–displacement response of the Nakajima test employing element erosion during the FE simulations. The classical approach for failure prediction is to compare the principal plastic strains obtained from FE simulations with experimental determined forming limit curves (FLCs). It is well known that the experimental FLC requires proportional strains to be useful. In this work failure criteria, both of the instability and fracture, are proposed which can be used also for non-proportional strain paths.

  • 13.
    Björklund, Oscar
    et al.
    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.
    Anisotropic fracture criteria for a dual-phase steel2014Manuscript (preprint) (Other academic)
    Abstract [en]

    The main objective of this work is to examine the use of anisotropic fracture criteria in order to predict fracture in dual-phase steel. The introduction of a material directional function into the fracture criterion was used in order to account for anisotropy observed in experiments. Selected fracture criteria were fist calibrated by ordinary tensile and in-plane shear tests using specimens cut in three material directions. In order to validate the performance, two types of validation tests were conducted. First, plane strain (notched tensile) tests were carried out in three material directions. Second, Nakajima tests with a waist of 130 mm were conducted, also in three material directions. The fit to the calibration tests was improved with all material directional functions compared to the isotropic criterion. Overall best performance was achieved when a material direction function based on the structural tensors was introduced.

  • 14.
    Björklund, Oscar
    et al.
    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.
    Failure characteristics of a dual-phase steel sheet2014In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 214, p. 1190-1204Article in journal (Refereed)
    Abstract [en]

    Failure in ductile sheet metal structures is usually caused by one, or a combination of, ductile tensile fractures, ductile shear fractures or localised instability. In this paper the failure characteristics of the high strength steel Docol 600DP are explored. The study includes both experimental and numerical sections. In the experimental sections, the fracture surface of the sheet subjected to Nakajima tests is studied under the microscope with the aim of finding which failure mechanism causes the fracture. In the numerical sections, finite element (FE) simulations have been conducted using solid elements. From these simulations, local stresses and strains have been extracted and analysed with the aim of identifying the fracture dependency of the stress triaxiality and Lode parameter.

  • 15.
    Borg, Rikard
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Solid Mechanics .
    Nilsson, Larsgunnar
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Solid Mechanics .
    Simonsson, Kjell
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Solid Mechanics .
    Modeling of delamination using a discretized cohesive zone and damage formulation2002In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 62, no 10-11, p. 1299-1314Article in journal (Refereed)
    Abstract [en]

    Delamination initiation and growth are analyzed by using a discrete cohesive crack model. The delamination is constrained to grow along a tied interface. The model is derived by postulating the existence of a maximum load surface which limits the adhesive forces in the process zone of the crack. The size of this maximum load surface is made dependent on the amount of dissipated crack opening work, such that the maximum load surface shrinks to zero as a predefined amount of work is consumed. A damage formulation is used to reduce the adhesive forces. Mode I, II and III loading or any combined loading is possible. An analytical solution is obtained for a single mode opening and the implications of this result on the governing equations is discussed. The delamination model is implemented in the finite element code LS-DYNA and simulation results are shown to be in agreement with experimental results. © 2002 Elsevier Science Ltd. All rights reserved.

  • 16.
    Brodin, Håkan
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology. Siemens Industrial Turbomachinery AB, Finspång, Sweden.
    Eriksson, Robert
    Siemens Industrial Turbomachinery AB, Finspång, Sweden.
    Johansson, Sten
    Siemens Industrial Turbomachinery AB, Finspång, Sweden.
    Sjöström, Sören
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology. Siemens Industrial Turbomachinery AB, Finspång, Sweden.
    Fracture Mechanical Modelling of a Plasma Sprayed TBC System2009In: Advanced Ceramic Coatings and Interfaces IV / [ed] Dongming Zhu and Hua-Tay Lin, Westerville, OH, United States: American Ceramic Society Inc. , 2009, Vol. 30, no 3, p. 113-124Conference paper (Refereed)
    Abstract [en]

    A thermal barrier coating (TBC) system subjected to thermal cycling will develop a microcrack partem near the interface between the metallic bond coat and the ceramic top coat. These small cracks link up and form internal TBC delaminations during repeated heating / cooling. After a longer time period, the internal delamination cracks will form a larger spallation damage, where the TBC is detached from the underlying material. Since cracks are initiated in multiple sites of the thermal barrier coating, the damage is initially considered to be governed by local stress conditions. The purpose of the present work is to compare experimental data with predictions of a physically based fatigue life model. The present study has been performed on plasma-sprayed TBCs where the interface geometry has been varied. In the present work, calculation of fatigue life is done for a number of cases under thermal fatigue loading. Different interface geometries are compared in order to understand the influence of variations in the TC/BC interface roughness on oxidation behaviour and thermal fatigue life. Thermal fatigue tests indicate that an increased surface roughness is beneficial from a fatigue life point of view.

  • 17.
    Brodin, Håkan
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Engineering Materials.
    Eriksson, Robert
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Engineering Materials.
    Li, Xin-Hai
    Siemens Industrial Turbomachinery AB, Finspång.
    Östergren, Lars
    Volvo Aero Corporation, Trollhättan.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Sjöström, Sören
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Solid Mechanics.
    Finite Element Modelling and Damage Evaluation of Air Plasma Sprayed Thermal Barrier Coatings2012Conference paper (Refereed)
  • 18.
    Brodin, Håkan
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials . Linköping University, The Institute of Technology.
    Li, Xin-Hai
    Siemens Industrial Turbomchinery AB.
    Sjöström, Sören
    Linköping University, Department of Management and Engineering, Solid Mechanics . Linköping University, The Institute of Technology.
    Influence on thermal barrier coating delamination behaviour of edge geometry2006Conference paper (Refereed)
  • 19.
    Brodin, Håkan
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Sjöström, Sören
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Damage development in two thermal barrier coating systems2009In: ICF12,2009, 2009Conference paper (Other academic)
    Abstract [en]

          

  • 20.
    Burrow, Michael
    et al.
    Center for Railway research and Education University of Birmingham, UK.
    Texeira, Paulo
    CENIT Technical University of Catalonia, Barcelona, Spain.
    Berggren, Eric
    Banverket, Borlänge.
    Dahlberg, Tore
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Solid Mechanics.
    Track stiffness considerations for high speed railway lines2009In: Railway Transportations: Policies, Technology and Perspectives / [ed] Nicholas P. Scott, Hauppauge, NY: Nova Science Publishers , 2009, p. 425-Chapter in book (Other academic)
    Abstract [en]

         This book provides the latest scientific research regarding the importance of infrastructure charges in establishing competitive conditions in the railway market. The current charging regimes applied throughout the EU member states are analyzed as well as the planning and scheduling that determine how and when the company's resources will be used in the case of railway organizations. Railway noise emission and its reduction are considered among the most important topics in the future development of transportation systems. This book gives an overview on the noise emitted by wheels and rails from the basic emission mechanisms up to noise attenuation by means of passive/active control. The importance of the vertical track stiffness as a means to guide railway track bed design for high speed railway lines are discussed as well. A rational approach to substructure design is described, which it is hoped will further an understanding of the process of appropriate track design and enable the adaptation of existing design procedures to provide a realistic design for the conditions at hand.

  • 21.
    Busse, Christian
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Accounting for non-linear effects in fatigue crack propagation simulations using FRANC3D2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In this thesis methods to account for non-linear effects in fatigue crack propagation simulations using FRANC3D are evaluated. FRANC3D is a crack growth software that supports automated crack growth in the FE mesh using the power of an external FE code.

    Introductorily, a theoretical base in fracture mechanics, especially regarding crack propagation models is established. Furthermore, the functionality of FRANC3D is shown for several different applications.

    As a benchmark for the investigated methods the associated results are compared to data from laboratory tests. The conditions in the test are closely modeled, but with relevant simplifications. The cyclic life-times are calculated using Paris’ law incorporating the stress intensity factors computed by FRANC3D and with material parameters derived from a different set of experiments than those simulated. When comparing the calculated cyclic life-time with the test data it can be seen that the pure linear elastic simulation, for this particular test set-up, gives nearly as good results as the investigated approaches that account for non-linear effects. 

  • 22.
    Dahlberg , Tore
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Solid Mechanics .
    Modelling of the dynamic behaviour of in situ concrete railway sleepers2008In: Proceedings of the Institution of Mechanical Engineers. P. F, Journal of rail and rapid transit, ISSN 0954-4097 , Vol. 222, no 4, p. 433-440Article in journal (Refereed)
    Abstract [en]

    An analytical Solution to the problem of a vibrating beam on an elastic foundation is presented. An application example of a concrete railway sleeper embedded in an elastic medium (the ballast) is provided. The sleeper is also elastically connected to the rails. The Rayleigh-Timoshenko (R-T) beam theory for a beam on an elastic foundation is used and eigenfrequencies are calculated. The beam (sleeper) is divided into three sections that have piecewise constant properties. The central portion of the beam is slightly thinner than the outer parts, and each one of the three parts may or may not be supported by the elastic foundation. The elastic connections to the rails are situated at the two joinings of the three sleeper sections.

    Conclusions drawn are that the Euler-Bernoulli beam theory can be used to calculate two, or maximum three, eigenfrequencies of the sleeper. For higher frequencies, the R-T beam theory should be used. The foundation stiffness influences the lowest bending-mode eigenfrequency the most; higher eigenfrequencies are practically unaffected by the foundation stiffness. The influence of railpad (and rail) stiffness on the sleeper eigenfrequencies is negligible.

  • 23.
    Dahlberg, Tore
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Solid Mechanics .
    Catenary, pantograph, and their interaction2006In: Vehicle System Dynamics, ISSN 0042-3114, E-ISSN 1744-5159, Vol. 44, no 8, p. 591-593Other (Other academic)
    Abstract [en]

    [No abstract available]

  • 24.
    Dahlberg, Tore
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Solid Mechanics .
    Catenary, pantograph, and their interaction2006In: Vehicle System Dynamics, ISSN 0042-3114, E-ISSN 1744-5159, Vol. 44, no 8, p. 591-593Article in journal (Other academic)
    Abstract [en]

      

  • 25.
    Dahlberg, Tore
    Linköping University, Department of Management and Engineering, Solid Mechanics . Linköping University, The Institute of Technology.
    On the Use of Under-Sleeper Pads in Tracks with Varying Track Stiffness2009In: Proc 9th International Heavy Haul Conference, June 2009, Shanghai, P R China: Heavy Haul and Innovation Development, Beijing, China: China Railway Publishing House , 2009, p. 293-299Conference paper (Refereed)
    Abstract [en]

    The track stiffness experienced by a train will vary along the track. Sometimes the stiffness variation may be very large within a short distance. One example is when an unsupported sleeper is hanging in the rail. Track stiffness is then, locally at that sleeper, very low. At insulation joints the bending stiffness of the rail has a discontinuity. A third example of an abrupt change of track stiffness is the transition from an embankment to a bridge.

    The variations of track stiffness will induce variations in the wheel/rail contact force. This will intensify track degradation such as increased wear, fatigue, track settlement due to permanent deformation of the ballast and the substructure, and so on. In the work reported here the possibility to smooth out track stiffness variations by use of under-sleeper pads is discussed. It is demonstrated that the wheel/rail contact force variations can be made small by modifying the stiffness variations along the track.

  • 26.
    Dahlberg, Tore
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Solid Mechanics .
    Railway Track Stiffness Variations - A Literature Review2007Report (Other academic)
  • 27.
    Dahlberg, Tore
    Linköping University, Department of Management and Engineering, Solid Mechanics . Linköping University, The Institute of Technology.
    Railway track stiffness variations - consequences and countermeasures2009In: Proc of the 2nd International Conference on Recent Advances in Railway Engineering, Teheran: Iran University of Science and Technology , 2009, p. 38-46Conference paper (Other academic)
    Abstract [en]

    The track stiffness experienced by a train will vary along the track. Sometimes the stiffness variation may be very large within a short distance. One example is when an unsupported sleeper is hanging in the rail. Track stiffness is then, locally at that sleeper, very low. At insulated joints the bending stiffness of the rail has a discontinuity implying a discontinuity also of the track stiffness. A third example of an abrupt change of track stiffness is the transition from an embankment to a bridge. At switches both mass and stiffness change rapidly.

     

    The variations of track stiffness will induce variations in the wheel/rail contact force. This will intensify track degradation such as increased wear, fatigue, track settlement due to permanent deformation of the ballast and the substructure, and so on. As soon as the track geometry starts to deteriorate, the variations of the wheel/rail interaction forces will increase, and the track deterioration rate increases. In the work reported here the possibility to smooth out track stiffness variations is discussed. It is demonstrated that by modifying the stiffness variations along the track, for example by use of grouting or under-sleeper pads, the variations of the wheel/rail contact force may be considerably reduced.

  • 28.
    Dahlberg, Tore
    Linköping University, Department of Management and Engineering, Solid Mechanics . Linköping University, The Institute of Technology.
    Railway Track Stiffness Variations - Consequences and Countermeasures2010In: INTERNATIONAL JOURNAL OF CIVIL ENGINEERING, ISSN 1735-0522, Vol. 8, no 1, p. 1-12Article in journal (Refereed)
    Abstract [en]

    The track stiffness experienced by a train will vary along the track. Sometimes the stiffness variation may be very large within a short distance. One example is when an unsupported sleeper is hanging in the rail. Track stiffness is then, locally at that sleeper, very low At insulated joints the bending stiffness of the rail has a discontinuity implying a discontinuity also of the track stiffness. A third example of an abrupt change of track stiffness is the transition from an embankment to a bridge. At switches both mass and stiffness change rapidly The variations of track stiffness will induce variations in the wheel/rail contact force. This will intensify track degradation such as increased wear fatigue, track settlement due to permanent deformation of the ballast and the substructure, and so on. As soon as the track geometry starts to deteriorate, the variations of the wheel/rail interaction forces will increase, and the track deterioration rate increases. In the work reported here the possibility to smooth out track stiffness variations is discussed. It is demonstrated that by modifying the stiffness variations along the track, for example by use of grouting or under-sleeper pads, the variations of the wheel/rail contact force may be considerably reduced.

  • 29.
    Dahlberg, Tore
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Solid Mechanics .
    Some railroad settlement models - A critical review2001In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 215, no 4, p. 289-300Conference paper (Other academic)
    Abstract [en]

    Mathematical models to simulate railroad track settlements are reviewed and commented upon. There do not seem to be any generally accepted damage and settlement equations describing the long-term behaviour of the track. This also seems to be the case for the ballast material. Most descriptions of the settlement found in the literature are empirical, only different suggestions to describe the track settlement from a phenomenological point of view are available. The track settlement is mostly considered to be a function of number of loading cycles and/or a function of the magnitude of the loading. The settlement should also be a function of the properties of the ballast and subground materials, but very little has been found on this in the literature. By use of the finite element program LS-DYNA, a computer model (very simple) has been created to simulate the long-term behaviour of the track. The model consists of a rail, rigid sleepers, non-linear ballast springs (stiffnesses) and ballast damping. In a solid element beneath each ballast spring, track settlement can be accumulated. Settlement will occur if the stresses in that element exceed a yield limit of the element material. Also 'hanging sleepers' may be modelled and obtained as a result of the track settlement.

  • 30.
    Dahlberg, Tore
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Solid Mechanics .
    Summary of work performed by Linköping university in the SUPERTRACK project2005Report (Other academic)
  • 31.
    Dahlberg, Tore
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Solid Mechanics.
    Track Issues2006In: Handbook of Railway Vehicle Dynamics / [ed] Simon Iwnicki, New York: Taylor & Francis Group , 2006, p. 143-179Chapter in book (Other academic)
    Abstract [en]

       Understanding the dynamics of railway vehicles, and indeed of the entire vehicle–track system, is critical to ensuring safe and economical operation of modern railways. As the challenges of higher speed and higher loads with very high levels of safety require ever more innovative engineering solutions, better understanding of the technical issues and use of new computer based tools is required. Encompassing the field from historical development to state-of-the-art modeling and simulation methods, Simon Iwnicki’s Handbook of Railway Vehicle Dynamicssets a new standard of authority and practicality in the study of railway vehicle dynamics.

    Drawing on the experiences and research of leading international experts, this critical reference surveys the main areas of railway vehicle dynamics. Through mathematical analysis and practical examples, it builds a deep and functional understanding of the wheel–rail interface, suspension and suspension component design, simulation and testing of electrical and mechanical systems, interaction with surrounding infrastructure, and noise and vibration. In-depth discussions deconstruct the components of both vehicle and track systems, explain their contribution to dynamic behavior, and evaluate the advantages and disadvantages of various practical solutions. The book also considers the unique issues of railway tribology, gauging, and derailment.

    Coverage of computer models, test procedures, roller rigs, and scale testing completes this essential handbook. Whether for the newcomer or the seasoned professional, the Handbook of Railway Vehicle Dynamics is an indispensable tool for modern railway vehicle design.

  • 32.
    Dahlberg, Tore
    Linköping University, Department of Management and Engineering, Solid Mechanics . Linköping University, The Institute of Technology.
    Vågutbredning i kontaktledningar (Wave propagations in contact wires, in Swedish).2009Report (Other academic)
    Abstract [sv]

    Teoretisk analys av vågutbredning i kontaktledning modellerad som en spänd sträng med böjstyvhet (eller axialbelastad balk) belastad med rörlig kraft.

  • 33.
    Dahlberg, Tore
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Solid Mechanics .
    Larsson, Rikard
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Solid Mechanics .
    Influence of railway track stiffness variations on wheel/rail contact force2006In: Tracks for high-speed railways,2006, Porto: Faculty of Eng, Univ of Porto , 2006, p. 67-Conference paper (Refereed)
  • 34.
    Dahlberg, Tore
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Solid Mechanics .
    Lundqvist, Andreas
    SAAB.
    Verification of track model versus Spanish measurements2005Report (Other academic)
    Abstract [en]

      

  • 35.
    Domeij Bäckryd, Rebecka
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Multidisciplinary Design Optimization of Automotive Structures2013Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Multidisciplinary design optimization (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 for reasons of efficiency. When performing MDO, a large number of designs need to be rated. Detailed simulation models used to assess automotive design proposals are often computationally expensive to evaluate. A useful MDO process must distribute work to the groups involved and be computationally efficient.

    In this thesis, MDO methods are assessed in relation to the characteristics of automotive structural applications. Single-level optimization methods have a single optimizer, while multi-level optimization methods have a distributed optimization process. Collaborative optimization and analytical target cascading are possible choices of multi-level optimization methods for automotive structures. They distribute the design process, but are complex. One approach to handle the computationally demanding simulation models involves metamodel-based design optimization (MBDO), where metamodels are used as approximations of the detailed models during optimization studies. Metamodels can be created by individual groups prior to the optimization process, and therefore also offer a way of distributing work. A single-level optimization method in combination with metamodels is concluded to be the most straightforward way of implementing MDO into the development of automotive structures.

    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
  • 36.
    Ekman, Patrik
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics.
    Larsson, Niklas
    Linköping University, Department of Management and Engineering, Solid Mechanics.
    Konstruktion av formkropp pa JAS 39 E/F Gripen2013Independent thesis Basic level (university diploma), 10,5 credits / 16 HE creditsStudent thesis
    Abstract [en]

    The aim of this work is to develop new conceptual designs for the fairings that are situated between the fin and the rear fuselage on the new version of the JAS 39 Gripen aircraft, called the Gripen E/F. The designs presented should show a profit in the form of lower weight. To achieve weight loss, the possibilities of using other construction materials other than those which are available at Saab today were studied. Therefore, a material survey was carried out in which the market for modern construction materials was studied to get an idea of today’s level of technology. Furthermore, a procedure was performed to produce new designs, which in turn can be used to create new concepts. The new concepts are then evaluated by means of systematic concept development. This resulted in a total of four concepts for the left side fairing and two for the right. These were then evaluated carefully, and finally, an estimation of the weight was made for the different concepts to see how it related to the original concept. In analysis of the four concepts, it was found that the temperature differences in the structure constitute a much larger problem factor than the materials coefficient of thermal expansion. This resulted in the exclusion of one of the concepts. The right side was treated somewhat more briefly as it quickly became clear that the only thing that prevented from making the right side fairing according to the methods already used today for the Gripen C/D was cost, which was considered to be outside the scope of this report. Finally the three concepts for the left side fairing were compiled and it became clear that there were significant benefits to be made, in terms of reduced weight, if one were to investigate the possibility of approving new construction materials for use at Saab.

  • 37.
    Eriksson, Erik
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Jonsson, Ida
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Skog, Christian
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Öhrn, Robin
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Dimensionering av momentskärmstativ2013Report (Other academic)
    Abstract [sv]

    På uppdrag av Saab ska fyra studenter vid Linköpings tekniska högskola designa och dimensionera ett momentskärmstativ till nya JAS39 Gripen E. På stativet fästs en skärmbehållare med en skärm, som används vid testflygning. Stativet sitter längst bak på planet, bakom sidorodret och ovanför stjärtkonen. Skärmen är en säkerhetsfunktion och kan skjutas ut och ge flygplanet ett stabiliserande tippmoment vid okontrollerade spinnfall som kan uppkomma vid högalfaflygning. Stativet ska klara av från uppdragsgivare givna lastfall och deformationskrav samtidigt som fokus skall ligga på viktreducering.

    Projektet började med konceptgenerering för att få fram ett grundkoncept att arbeta vidare med. Materialundersökningar genomfördes med hjälp av materialdatabasen CES EduPack 2012 för att hitta ett material med bättre egenskaper än det som använts i tidigare stativ. Utifrån materialet undersöktes även fogar, tillåtna initialsprickor samt knäckningsrisk. Olika tvärsnitt undersöktes och för att ta reda på deformationer och spänningar genomfördes FEM-analyser i Ansys Workbench 14.0. Utifrån analysresultaten förändrades stativets design tills det klarade kraven.

    Arbetet resulterade i ett fackverksstativ huvudsakligen uppbyggt av ihåliga kvadratiska balkar med yttermåtten 70 mm och innermåtten 63,8 mm. Maximala deformationen blir 53,1 mm, maximala spänningen 883 MPa och materialet som användes var titanlegeringen Ti-6Al-4V. Stativets balkar sammanfogas med lasersvets och det finns ingen risk för knäckning. Den tillåtna längden på en eventuell initialspricka är 0,7 mm för ytspricka och 0,9 mm för inre genomgående spricka. Det designade stativets slutvikt uppmättes till 60,5 kg.

  • 38.
    Eriksson, Robert
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Sjöström, Sören
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Solid Mechanics.
    Brodin, Håkan
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Engineering Materials.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Östergren, Lars
    GKN Aerospace Engine Systems, Trollhättan.
    Li, Xin-Hai
    Siemens Industrial Turbomachinery AB, Finspång.
    Influence of Interface Roughness on the Fatigue Life of Thermal Barrier Coatings2013Conference paper (Refereed)
  • 39.
    Eriksson, Robert
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Sjöström, Sören
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Brodin, Håkan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Östergren, Lars
    GKN Aerospace Engine Systems, Trollhättan, Sweden.
    Li, Xin-Hai
    Siemens Industrial Turbomachinery AB, Finspång, Sweden.
    TBC bond coat-top coat interface roughness: influence on fatigue life and modelling aspects2013In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 236, p. 230-238Article in journal (Refereed)
    Abstract [en]

    Thermal barrier coatings (TBCs), when used in gas turbines, may fail through thermal fatigue, causing the ceramic top coat to spall off the metallic bond coat. The life prediction of TBCs often involves finite element modelling of the stress field close to the bond coat/top coat interface and thus relies on accurate modelling of the interface. The present research studies the influence of bond coat/top coat interface roughness on the thermal fatigue life of plasma sprayed TBCs. By using different spraying parameters, specimens with varying interface roughness were obtained. During thermal cycling it was found that higher interface roughness promoted longer thermal fatigue life. The interfaces were characterised by roughness parameters, such as Ra, Rq and Rq, as well as by autocorrelation, material ratio curves, probability plots and slope distribution. The variation of spray parameters was found to affect amplitude parameters, such as Ra, but not spacing parameters, such as RSm. Three different interface geometries were tried for finite element crack growth simulation: cosine, ellipse and triangular shape. The cosine model was found to be an appropriate interface model and a procedure for obtaining the necessary parameters, amplitude and wavelength, was suggested. The positive effect of high roughness on life was suggested to be due to a shift from predominantly interface failure, for low roughness, to predominantly top coat failure, for high roughness.

  • 40.
    Forsberg, Jimmy
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Nilsson, Lars
    Linköping University, Department of Management and Engineering, Energy Systems. Linköping University, The Institute of Technology.
    Topology optimization in crashworthiness design2007In: Structural and multidisciplinary optimization (Print), ISSN 1615-147X, E-ISSN 1615-1488, Vol. 33, no 1, p. 1-12Article in journal (Refereed)
    Abstract [en]

    Topology optimization has developed rapidly, primarily with application on linear elastic structures subjected to static loadcases. In its basic form, an approximated optimization problem is formulated using analytical or semi-analytical methods to perform the sensitivity analysis. When an explicit finite element method is used to solve contact–impact problems, the sensitivities cannot easily be found. Hence, the engineer is forced to use numerical derivatives or other approaches. Since each finite element simulation of an impact problem may take days of computing time, the sensitivity-based methods are not a useful approach. Therefore, two alternative formulations for topology optimization are investigated in this work. The fundamental approach is to remove elements or, alternatively, change the element thicknesses based on the internal energy density distribution in the model. There is no automatic shift between the two methods within the existing algorithm. Within this formulation, it is possible to treat nonlinear effects, e.g., contact–impact and plasticity. Since no sensitivities are used, the updated design might be a step in the wrong direction for some finite elements. The load paths within the model will change if elements are removed or the element thicknesses are altered. Therefore, care should be taken with this procedure so that small steps are used, i.e., the change of the model should not be too large between two successive iterations and, therefore, the design parameters should not be altered too much. It is shown in this paper that the proposed method for topology optimization of a nonlinear problem gives similar result as a standard topology optimization procedures for the linear elastic case. Furthermore, the proposed procedures allow for topology optimization of nonlinear problems. The major restriction of the method is that responses in the optimization formulation must be coupled to the thickness updating procedure, e.g., constraint on a nodal displacement, acceleration level that is allowed.

  • 41.
    Forsberg, Jimmy
    et al.
    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.
    Evaluation of response surface methodologies used in crashworthiness optimization2006In: International Journal of Impact Engineering, ISSN 0734-743X, E-ISSN 1879-3509, Vol. 32, no 5, p. 759-777Article in journal (Refereed)
    Abstract [en]

    Optimization of car structures is of great interest to the automotive industry. This work is concerned with structural optimization of a car body with the intent to increase the crashworthiness properties of the vehicle or decrease weight with the crashworthiness properties unaffected. In this work two different methodologies of constructing an intermediate approximation to the optimization problem are investigated, i.e. classical response surface methodology and Kriging. The major difference between the two methodologies is how the residuals between the true function value and the polynomial surface approximation value at a design point are treated.

    Several different optimization problems have been investigated, both analytical problems as well as finite element impact problems.

    The major conclusion is that even if the same kind of updating scheme is used both for Kriging and linear classic response surface methodology, Kriging improves the sequential behaviour of the optimization algorithm in the beginning of the optimization process. Problems may occur if a constraint is violated after several iterations and then classic response surface methodology seems to more easily be able to find a design point which satisfies the constraint.

  • 42.
    Forsberg, Jimmy
    et al.
    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.
    On polynomial response surfaces and Kriging for use in structural optimization of crashworthiness2005In: Structural and multidisciplinary optimization (Print), ISSN 1615-147X, E-ISSN 1615-1488, Vol. 29, no 3, p. 232-243Article in journal (Refereed)
    Abstract [en]

    The accuracy of different approximating response surfaces is investigated. In the classical response surface methodology (CRSM) the true response function is usually replaced with a low-order polynomial. In Kriging the true response function is replaced with a low-order polynomial and an error correcting function. In this paper the error part of the approximating response surface is obtained from “simple point Kriging” theory. The combined polynomial and error correcting function will be addressed as a Kriging surface approximation.

    To be able to use Kriging the spatial correlation or covariance must be known. In this paper the error is assumed to have a normal distribution and the covariance to depend only on one parameter. The maximum-likelihood method is used to find the latter parameter. A weighted least-square procedure is used to determine the trend before simple point Kriging is used for the error function. In CRSM the surface approximation is determined through an ordinary least-square fit. In both cases the D-optimality criterion has been used to distribute the design points.

    From this investigation we have found that a low-ordered polynomial assumption should be made with the Kriging approach. We have also concluded that Kriging better than CRSM resolves abrupt changes in the response, e.g. due to buckling, contact or plastic deformation.

  • 43.
    Forsberg, Jimmy
    et al.
    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.
    The optimisation process of an energy absorbing frontal underrun protection device2008In: International Journal of Vehicle Design, ISSN 0143-3369, E-ISSN 1741-5314, Vol. 46, no 3, p. 271-293Article in journal (Refereed)
    Abstract [en]

    This paper describes the methodology used during the development of an energy absorbing Frontal Underrun Protection device (eaFUP). The aim of this study is to show how different optimisation methods can be used at different stages during the design process. It also shows one approach to derive an optimal design taking several different design alternatives into account, each of which consists of several different materials. The outcome of the optimisation process is three different designs of the eaFUP.

  • 44.
    Fredriksson, B
    et al.
    Saab-Scania AB, Aircraft Division.
    Torstenfelt, Bo
    Linköping University, Department of Management and Engineering, Solid Mechanics . Linköping University, The Institute of Technology.
    Endahl, Nils
    Linköping University, Department of Management and Engineering, Solid Mechanics . Linköping University, The Institute of Technology.
    Numerical Solutions to Contact, Friction and Crack problems with Applications1984In: Engineering computations, ISSN 0264-4401, E-ISSN 1758-7077, Vol. 1, no 2, p. 133-143Article in journal (Refereed)
    Abstract [en]

    The importance of contact and friction problems in different application areas is discussed. Methods and algorithms for numerical solutions using the finite element method are presented. Both elastic and elastic plastic materials are included as well as combination of contact and crack problems. The methods are applied to practical applications such as bolted joints, lugs and roller bearings.

  • 45.
    Fredriksson, Billy
    et al.
    Saab-Scania AB, Aircraft Division.
    Torstenfelt, Bo
    Linköping University, Department of Management and Engineering, Solid Mechanics . Linköping University, The Institute of Technology.
    Pressure Distribution in Crowned Roller Contacts1984In: Engineering Analysis, ISSN 0955-7997, Vol. 1, no 1, p. 32-39Article in journal (Refereed)
    Abstract [en]

    The fatigue life of a roller bearing is heavily influenced by the crowning profile of the rollers. The pressure distribution for different types of crowning has been studied. For solving this three-dimensional contact problem a numerical procedure for analysis of general elasto-static contact problems has been used. The method is based on an incremental and iterative algorithm applied to a set of linear equations established with finite element technique. The contact surfaces are assumed to be perfectly smooth, dry and frictionless. The pressure distribution between the bodies has been compared with results obtained from other methods. The influence on the pressure distribution by the free boundary at the end of the finite cylinders has also been investigated. It is also shown that it is possible to use the same finite element model to study different types of crowning, thus making it efficient to perform paramater surveys. A method of obtaining required or ‘optimal’ pressure distribution is suggested.

  • 46.
    Ganghoffer, J. F.
    et al.
    Ecole des Mines, Nancy.
    Gautier, E.
    Ecole des Mines, Nancy.
    Denis, S.
    Ecole des Mines, Nancy.
    Simon, A.
    Ecole des Mines, Nancy.
    Simonsson, Kjell
    Linköping University, Department of Management and Engineering, Solid Mechanics . Linköping University, The Institute of Technology.
    Sjöström, Sören
    Linköping University, Department of Management and Engineering, Solid Mechanics . Linköping University, The Institute of Technology.
    Micromechanical simulation of a martensitic transformation by Finite Elements1991In: Journal de Physique IV: Colloque, ISSN 1155-4339, E-ISSN 1764-7177, Vol. 1, p. C4-77-C4-82Article in journal (Refereed)
    Abstract [en]

    A micromechanical model describing the martensitic transformation on the grain scale has been developed, using Finite Elements. First results gained from the simulation illustrate how the morphological evolution within the grain is directly controlled by the internal stress state. The reversible and irreversible part of transformation "plasticity" strain and their evolution with the transformation can then be obtained from these calculations.

  • 47. Ganghoffer, Jean-Francois
    et al.
    Simonsson, Kjell
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Solid Mechanics .
    A microstructural model of the martensitic transformation1998In: Mechanics of materials (Print), ISSN 0167-6636, E-ISSN 1872-7743, Vol. 27, p. 125-144Article in journal (Refereed)
  • 48.
    Ganghoffer, J.F.
    et al.
    Ecole des Mines, Nancy.
    Denis, S.
    Ecole des Mines, Nancy.
    Gautier, E.
    Ecole des Mines, Nancy.
    Simon, A.
    Ecole des Mines, Nancy.
    Simonsson, Kjell
    Linköping University, Department of Management and Engineering, Solid Mechanics . Linköping University, The Institute of Technology.
    Sjöström, S.
    Linköping University, Department of Management and Engineering, Solid Mechanics . Linköping University, The Institute of Technology.
    Micromechanical simulation of a martensitic transformation by Finite Elements1991In: ICRS3, Tokushima, Japan, 1991Conference paper (Refereed)
  • 49.
    Ganghoffer, J.F.
    et al.
    Laboratoire de Science et Génie des Matériaux Métalliques, Ecole des Mines, Parc de Saurupt, F-54042 Nancy cedex, France.
    Denis, S.
    Laboratoire de Science et Génie des Matériaux Métalliques, Ecole des Mines, Parc de Saurupt, F-54042 Nancy cedex, France.
    Gautier, E.
    Laboratoire de Science et Génie des Matériaux Métalliques, Ecole des Mines, Parc de Saurupt, F-54042 Nancy cedex, France.
    Simon, A.
    Laboratoire de Science et Génie des Matériaux Métalliques, Ecole des Mines, Parc de Saurupt, F-54042 Nancy cedex, France.
    Simonsson, Kjell
    Linköping University, Department of Management and Engineering, Solid Mechanics . Linköping University, The Institute of Technology.
    Sjöström, Sören
    Linköping University, Department of Management and Engineering, Solid Mechanics . Linköping University, The Institute of Technology.
    Mechanical and thermodynamical study of a macroscopically coherent phase transition: Case of the martensitic transformation1991In: Journal de Physique IV: Colloque, ISSN 1155-4339, E-ISSN 1764-7177, Vol. 1, p. C4-89-C4-94Article in journal (Refereed)
    Abstract [en]

    In the general framework of a macroscopically coherent phase transition, the mechanical and thermodynamical behaviour of a two-phase volume element under structural evolution will be investigated and discussed. The identification of internal entropy production will then allow to formulate a general evolution condition for such a system and the internal stress state will appear to influence strongly the transformation behaviour, via the interface. The case of a martensitic transformation is considered. From that rigourous mechanical approach, we obtain the thermodynamical balance equation used for martensitic transformation.

  • 50.
    Ganghoffer, J.F.
    et al.
    Ecole des Mines, Nancy.
    Simonsson, Kjell
    Linköping University, Department of Management and Engineering, Solid Mechanics . Linköping University, The Institute of Technology.
    Denis, S.
    Ecole des Mines, Nancy.
    Gautier, E.
    Ecole des Mines, Nancy.
    Sjöström, Sören
    Linköping University, Department of Management and Engineering, Solid Mechanics . Linköping University, The Institute of Technology.
    Simon, A.
    Ecole des Mines, Nancy.
    Martensitic transformation plasticity simulations by finite elements1994In: Journal de Physique IV: Colloque, ISSN 1155-4339, E-ISSN 1764-7177, Vol. 4, p. C3-215-C3-220Article in journal (Refereed)
    Abstract [en]

    The mechanical behaviour associated to the martensitic transformation has been modelled using a 2D FE description. The martensite variants are constituted of different elements of the mesh and four different variants are allowed to transform in the grain. The transformation progress is prescribed using a thermodynamical criterion based on the maximal work associated to the variant formation. Transformation plasticity deformation and plates orientation patterns are obtained for three stress levels. These results are discussed in regard to the model used and the physical parameters introduced in the model.

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