liu.seSearch for publications in DiVA
Change search
Refine search result
12345 1 - 50 of 242
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • oxford
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 1.
    Ahlqvist, Max
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering. Epiroc Rock Drills AB, Sweden.
    Weddfelt, Kenneth
    Epiroc Rock Drills AB, Sweden.
    Norman, Viktor
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Leidermark, Daniel
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Probabilistic evaluation of the Step-Stress fatigue testing method considering cumulative damage2023In: Probabilistic Engineering Mechanics, ISSN 0266-8920, E-ISSN 1878-4275, Vol. 74, article id 103535Article in journal (Refereed)
    Abstract [en]

    A general testing and analysis framework for the Step-Stress fatigue testing method is identified, utilizing interval-censored data and maximum likelihood estimation in an effort to improve estimation of fatigue strength distribution parameters has been performed. The Step-Stress methods limitations are characterized, using a simple material model that considers cumulative damage to evaluate load history effects. In this way, the performance including cumulative damage was evaluated and quantified using a probabilistic approach with Monte-Carlo simulations, benchmarked against the Staircase method throughout the work. It was found that the Step-Stress method, even when cumulative damage occurs to a wide extent, outperforms the Staircase method, especially for small sample sizes. Furthermore, positive results reaches further than the increase performance in estimating fatigue strength distribution parameters, where improvements in secondary information, i.e. S-N data gained from failure specimens, are shown to be distributed more closely to the fatigue life region of interest.

  • 2.
    Ahn, Young Ju
    et al.
    Hongik Univ, South Korea.
    Klarbring, Anders
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Spagnoli, Andrea
    Univ Parma, Italy.
    Terzano, Michele
    Graz Univ Technol, Austria.
    Shakedown in frictional contact of discrete elastic systems: A review2022In: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 241, article id 111470Article, review/survey (Refereed)
    Abstract [en]

    When exposed to cyclic quasi-static loading, elastic bodies in contact may develop a favourable condition where slip ceases after a few cycles, an occurrence commonly known as frictional shakedown. If the amplitude of the cyclic load is greater than a so-called shakedown limit, shakedown cannot occur. In this review paper, the validity of shakedown theorems in the context of conforming contacts with a la Coulomb friction is first discussed. Then, an optimisation method for determining the shakedown limit of elastic discrete three-dimensional systems is reviewed. Finally, an incremental Gauss-Seidel algorithm, extended to three-dimensional systems, is here illustrated in details for the first time. The algorithm allows us to describe the transient response of normal-tangential coupled systems under a given cyclic loading scenario, and to determine their possible shakedown depending on the initial conditions. An example concerning a discrete conforming contact problem, where either coupling or uncoupling conditions can be imposed, is illustrated.

  • 3.
    Alimadadi, Majid
    et al.
    Department of Natural Sciences, Mid Sweden University, Sweden.
    Lindström, Stefan B
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Kulachenko, Artem
    Department of Solid Mechanics, Royal Institute of Technology (KTH), Stockholm, Sweden.
    Role of microstructures in the compression response of three-dimensional foam-formed wood fiber networks2018In: Soft Matter, ISSN 1744-683X, E-ISSN 1744-6848, Vol. 14, p. 8945-8955Article in journal (Refereed)
    Abstract [en]

    High-porosity, three-dimensional wood fiber networks made by foam forming present experimentally accessible instances of hierarchically structured, athermal fiber networks. We investigate the large deformation compression behavior of these networks using fiber-resolved finite element analyses to elucidate the role of microstructures in the mechanical response to compression. Three-dimensional network structures are acquired using micro-computed tomography and subsequent skeletonization into a Euclidean graph representation. By using a fitting procedure to the geometrical graph data, weare able to identify nine independent statistical parameters needed for the regeneration of artificial networks with the observed statistics. The compression response of these artificially generated networks and the physical network is then investigated using implicit finite element analysis. A direct comparison of the simulation results from the reconstructed and artificial network reveals remarkable differences already in the elastic region. These can neither be fully explained by density scaling, the size effect nor the boundary conditions. The only factor which provides the consistent explanation of the observed difference is the density and fiber orientation nonuniformities; these contribute to strain-localization so that the network becomes more compliant than expected for statistically uniform microstructures. We also demonstrate that the experimentally manifested strain-stiffening of such networks is due to development of new inter-fiber contacts during compression.

  • 4.
    Alm Grundström, Henrik
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Developments in Topology Optimization in the ADDMAN Project2018Report (Other academic)
    Abstract [en]

    This document gives an account of some of the work done so far on topology optimization (TO) in the ADDMAN project. As well as the mathematical formulations and implementations details, short discussions are presented on some of the nuances of the different formulations and how they should be used efficiently

    Download full text (pdf)
    fulltext
  • 5.
    Alm Grundström, Henrik
    Linköping University, Department of Management and Engineering, Solid Mechanics.
    Topology Optimization for Additive Manufacturing Considering Stress and Anisotropy2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Additive manufacturing (AM) is a particularly useful manufacturing method for components designed using topology optimization (TO) since it allows for a greater part complexity than any traditional manufacturing method. However, the AM process potentially leads to anisotropic material properties due to the layer-by-layer buildup of parts and the fast and directional cooling. For Ti6Al4V tensile specimens built using electron beam melting (EBM), it has been observed that flat built specimens show superior strength and elastic moduli compared to top built specimens. Designs with the loading direction parallel to the build layers are therefore expected to show greater reliability.

    In this thesis a procedure is developed to optimize the AM build orientation considering anisotropic elastic material properties. A transversely isotropic material model is used to represent the in-plane and out-of-plane characteristics of AM produced parts. Two additional design variables are added to the TO formulation in order to control the orientation of the material using a coordinate transformation. Sensitivity analysis for the material direction variables is conducted for compliance as well as maximum von-Mises stress using a -norm stress aggregation function.

    The procedures for the AM build orientation optimization and stress constraints are implemented in the finite element software TRINITAS and evaluated using a number of examples in 2D and 3D. It is found that the procedure works well for compliance as well as stress but that a combination of these may lead to convergence issues due to contradicting optimal material orientations. An evaluation of the -norm stress aggregation function showed that a single global stress measure in combination with a stress correction procedure works well for most problems given that the mesh is refined enough to resolve the stresses accurately.  

    Download full text (pdf)
    Topology Optimization for Additive Manufacturing Considering Stress and Anisotropy
  • 6.
    Alm Grundström, Henrik
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Trinitas Topology Optimization Tutorial Document2018Report (Other academic)
    Download full text (pdf)
    Trinitas Topology Optimization Tutorial Document
  • 7.
    Almroth, Per
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering. SIEMENS Energy AB, Sweden.
    Gustafsson, D.
    SIEMENS Energy AB, Sweden.
    Loureiro, Jordi
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Simonsson, Kjell
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Out-of-phase thermo-mechanical fatigue crack growth and the effect of the compressive minimum load level on crack closure at notches2020In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 141, article id 105906Article in journal (Refereed)
    Abstract [en]

    Fatigue crack growth rate in Room Temperature and Out-of-Phase Thermo-Mechanical Fatigue notched specimen experiments on the nickel-base alloy IN792 is studied. It is shown that it is possible to explain the observed higher crack growth rate in OP TMF compared to RT testing for the same external load, if plasticity induced crack closure is considered. Modeling utilizes node-release finite element simulations with a temperature dependent yield stress, resulting in different yield stress in tension and compression. It is shown that a simple extension of the analytical Newman crack closure equation can describe the opening level in the performed experiments.

  • 8. Order onlineBuy this publication >>
    Andersson, Håkan
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    A Co-Simulation Approach for Hydraulic Percussion Units2018Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    This Licentiate of Engineering thesis concerns modelling and simulation of hydraulic percussion units. These units are often found in equipment for breaking or drilling in rock and concrete, and are also often driven by oil hydraulics, in which complex fluid-structure couplings are essential for their operation.

    Current methodologies used today when developing hydraulic percussion units are based on decoupled analyses, which are not correctly capturing the important coupled mechanisms. Hence, an efficient method for coupled simulations is of high importance, since these mechanisms are critical for the function of these units. Therefore, a co-simulation approach between a 1D system simulation model representing the fluid system and a structural 3D FE-model is proposed.

    This approach is presented in detail, implemented for two well-known simulation tools and evaluated for a simple but relevant model. The Hopsan simulation tool was used for the fluid system and the FE-simulation software LS-DYNA was used for the structural mechanics simulation. The co-simulation interface was implemented using the Functional Mock-up Interface-standard.

    The approach was further developed to also incorporate multiple components for coupled simulations. This was considered necessary when models for the real application are to be developed. The use of two components for co-simulation was successfully evaluated for two models, one using the simple rigid body representation, and a second where linear elastic representations of the structural material were implemented.

    An experimental validation of the co-simulation approach applied to an existing hydraulic hammer was performed. Experiments on the hydraulic hammer were performed using an in-house test rig, and responses were registered at four different running conditions. The co-simulation model was developed using the same approach as before. The corresponding running conditions were simulated and the responses were successfully validated against the experiments. A parameter study was also performed involving two design parameters with the objective to evaluate the effects of a parameter change.

    This thesis consists of two parts, where Part I gives an introduction to the application, the simulation method and the implementation, while Part II consists of three papers from this project.

    List of papers
    1. A co-simulation method for system-level simulation of fluid-structure couplings in hydraulic percussion units
    Open this publication in new window or tab >>A co-simulation method for system-level simulation of fluid-structure couplings in hydraulic percussion units
    Show others...
    2017 (English)In: Engineering with Computers, ISSN 0177-0667, E-ISSN 1435-5663, Vol. 33, no 2, p. 317-333Article in journal (Refereed) Published
    Abstract [en]

    This paper addresses a co-simulation method for fluid power driven machinery equipment, i.e. oil hydraulic machinery. In these types of machinery, the fluid-structure interaction affects the end-product performance to a large extent, hence an efficient co-simulation method is of high importance. The proposed method is based on a 1D system model representing the fluid components of the hydraulic machinery, within which structural 3D Finite Element (FE) models can be incorporated for detailed simulation of specific sub-models or complete structural assemblies. This means that the fluid system simulation will get a more accurate structural response, and that the structural simulation will get more correct fluid loads at every time step, compared to decoupled analysis. Global system parameters such as fluid flow, performance and efficiency can be evaluated from the 1D system model simulation results. From the 3D FE-models, it is possible to evaluate displacements, stresses and strains to be used in stress analysis, fatigue evaluation, acoustic analysis, etc. The method has been implemented using two well-known simulation tools for fluid power system simulations and FE-simulations, respectively, where the interface between the tools is realised by use of the Functional Mock-up Interface standard. A simple but relevant model is used to validate the method.

    Place, publisher, year, edition, pages
    SPRINGER, 2017
    Keywords
    Co-simulation; Fluid-structure coupling; System simulation; Functional mock-up interface; Fluid power machinery; Transmission line modelling
    National Category
    Computer Systems
    Identifiers
    urn:nbn:se:liu:diva-136875 (URN)10.1007/s00366-016-0476-8 (DOI)000398468100012 ()
    Note

    Funding Agencies|Atlas Copco Construction Tools

    Available from: 2017-04-30 Created: 2017-04-30 Last updated: 2022-02-17
    2. System level co-simulation of a control valve and hydraulic cylinder circuit in a hydraulic percussion unit
    Open this publication in new window or tab >>System level co-simulation of a control valve and hydraulic cylinder circuit in a hydraulic percussion unit
    Show others...
    2017 (English)In: Proceedings of 15:th Scandinavian International Conference on Fluid Power, June 7-9, 2017, Linköping, Sweden / [ed] Petter Krus, Liselott Ericson and Magnus Sethson, Linköping: Linköping University Electronic Press, 2017, Vol. 144, p. 225-235Conference paper, Published paper (Refereed)
    Abstract [en]

    In this study a previously developed co-simulation method that is based on a 1D system model representing the fluid components of a hydraulic machinery, within which structural 3D Finite Element (FE) models can be incorporated for detailed simulation of specific sub-models or complete structural assemblies, is further developed. The fluid system model consists of ordinary differential equation sub-models that are computationally very inexpensive, but still represents the fluid dynamics very well. The co-simulation method has been shown to work very well for a simple model representing a hydraulic driven machinery. A more complex model was set up in this work, in which two cylinders in the hydraulic circuit were evaluated. Such type of models, including both the main piston and control valves, are necessary as they represent the real application to a further extent than the simple model, of only one cylinder. Two models have been developed and evaluated, from the simple rigid body representation of the structural mechanics model, to the more complex model using linear elastic representation. The 3D FE-model facilitates evaluation of displacements, stresses, and strains on a local level of the model. The results can be utilised for fatigue assessment, wear analysis and for predictions of noise radiation.

    Place, publisher, year, edition, pages
    Linköping: Linköping University Electronic Press, 2017
    Series
    Linköping Electronic Conference Proceedings, ISSN 1650-3686, E-ISSN 1650-3740 ; 144
    Keywords
    Co-simulation, Fluid-structure coupling, System simulation, Functional mockup interface, Fluid power machinery, Transmission line modelling
    National Category
    Applied Mechanics Vehicle Engineering Control Engineering
    Identifiers
    urn:nbn:se:liu:diva-151015 (URN)10.3384/ecp17144225 (DOI)9789176853696 (ISBN)
    Conference
    15th Scandinavian International Conference on Fluid Power, June 7-9, 2017, Linköping, Sweden
    Available from: 2018-09-11 Created: 2018-09-11 Last updated: 2022-02-17Bibliographically approved
    Download full text (pdf)
    A Co-Simulation Approach for Hydraulic Percussion Units
    Download (pdf)
    omslag
    Download (png)
    presentationsbild
  • 9. Order onlineBuy this publication >>
    Andersson, Håkan
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    A Co-Simulation Tool Applied to Hydraulic Percussion Units2022Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In this dissertation, a co-simulation tool is presented that is meant to comprise a more comprehensive environment for modelling and simulation of hydraulic percussion units, which are used in hydraulic hammers and rock drills. These units generates the large impact forces, which are needed to demolish concrete structures in the construction industry or to fragment rock when drilling blast holes in mine drifting. This type of machinery is driven by fluid power and is by that dependent of coupled fluid-structure mechanisms for their operation. This tool consists of a 1D fluid system model, a 3D structural mechanic model and an interface to establish the fluid-structure couplings, which has in this work been applied to a hydraulic hammer. This approach will enable virtual prototyping during product development with an ambition to reduce the need for testing of physical prototypes, but also to facilitate more detailed studies of internal mechanisms. 

    The tool has been implemented for two well-known simulation tools, and a co-simulation interface to enable communication between them has been devel-oped. The fluid system is simulated using the Hopsan simulation tool and the structural parts are simulated using the FE-simulation software LS-DYNA. The implementation of the co-simulation interface is based on the Functional Mock-up Interface standard in Hopsan and on the User Defined Feature module in LS-DYNA. The basic functions of the tool were first verified for a simple but relevant model comprising co-simulation of one component, and secondly co-simulation of two components were verified. These models were based on rigid body and linear elastic representation of the structural components. Further, it was experimentally validated using an existing hydraulic hammer product, where the responses from the experiments were compared to the corresponding simulated responses. To investigate the effects from a parameter change, the hammer was operated and simulated at four different running conditions. 

    Dynamic simulation of the sealing gap, which is a fundamental mechanism used for controlling the percussive motion, was implemented to further enhance the simulated responses of the percussion unit. This implementation is based on a parametrisation of the deformed FE-model, where the gap height and the eccentric position are estimated from the deformed geometry in the sealing gap region, and then the parameters are sent to the fluid simulation for a more accurate calculation of the leakage flow. 

    Wear in percussion units is an undesirable type of damage, which may cause significant reduction in performance or complete break-down, and today there are no methodology available to evaluate such damages on virtual prototypes. A method to study wear was developed using the co-simulation tool to simulate the fundamental behaviour of the percussion unit, and the wear routines in LS-DYNA were utilised for the calculation of wear.  

    List of papers
    1. A co-simulation method for system-level simulation of fluid-structure couplings in hydraulic percussion units
    Open this publication in new window or tab >>A co-simulation method for system-level simulation of fluid-structure couplings in hydraulic percussion units
    Show others...
    2017 (English)In: Engineering with Computers, ISSN 0177-0667, E-ISSN 1435-5663, Vol. 33, no 2, p. 317-333Article in journal (Refereed) Published
    Abstract [en]

    This paper addresses a co-simulation method for fluid power driven machinery equipment, i.e. oil hydraulic machinery. In these types of machinery, the fluid-structure interaction affects the end-product performance to a large extent, hence an efficient co-simulation method is of high importance. The proposed method is based on a 1D system model representing the fluid components of the hydraulic machinery, within which structural 3D Finite Element (FE) models can be incorporated for detailed simulation of specific sub-models or complete structural assemblies. This means that the fluid system simulation will get a more accurate structural response, and that the structural simulation will get more correct fluid loads at every time step, compared to decoupled analysis. Global system parameters such as fluid flow, performance and efficiency can be evaluated from the 1D system model simulation results. From the 3D FE-models, it is possible to evaluate displacements, stresses and strains to be used in stress analysis, fatigue evaluation, acoustic analysis, etc. The method has been implemented using two well-known simulation tools for fluid power system simulations and FE-simulations, respectively, where the interface between the tools is realised by use of the Functional Mock-up Interface standard. A simple but relevant model is used to validate the method.

    Place, publisher, year, edition, pages
    SPRINGER, 2017
    Keywords
    Co-simulation; Fluid-structure coupling; System simulation; Functional mock-up interface; Fluid power machinery; Transmission line modelling
    National Category
    Computer Systems
    Identifiers
    urn:nbn:se:liu:diva-136875 (URN)10.1007/s00366-016-0476-8 (DOI)000398468100012 ()
    Note

    Funding Agencies|Atlas Copco Construction Tools

    Available from: 2017-04-30 Created: 2017-04-30 Last updated: 2022-02-17
    2. System level co-simulation of a control valve and hydraulic cylinder circuit in a hydraulic percussion unit
    Open this publication in new window or tab >>System level co-simulation of a control valve and hydraulic cylinder circuit in a hydraulic percussion unit
    Show others...
    2017 (English)In: Proceedings of 15:th Scandinavian International Conference on Fluid Power, June 7-9, 2017, Linköping, Sweden / [ed] Petter Krus, Liselott Ericson and Magnus Sethson, Linköping: Linköping University Electronic Press, 2017, Vol. 144, p. 225-235Conference paper, Published paper (Refereed)
    Abstract [en]

    In this study a previously developed co-simulation method that is based on a 1D system model representing the fluid components of a hydraulic machinery, within which structural 3D Finite Element (FE) models can be incorporated for detailed simulation of specific sub-models or complete structural assemblies, is further developed. The fluid system model consists of ordinary differential equation sub-models that are computationally very inexpensive, but still represents the fluid dynamics very well. The co-simulation method has been shown to work very well for a simple model representing a hydraulic driven machinery. A more complex model was set up in this work, in which two cylinders in the hydraulic circuit were evaluated. Such type of models, including both the main piston and control valves, are necessary as they represent the real application to a further extent than the simple model, of only one cylinder. Two models have been developed and evaluated, from the simple rigid body representation of the structural mechanics model, to the more complex model using linear elastic representation. The 3D FE-model facilitates evaluation of displacements, stresses, and strains on a local level of the model. The results can be utilised for fatigue assessment, wear analysis and for predictions of noise radiation.

    Place, publisher, year, edition, pages
    Linköping: Linköping University Electronic Press, 2017
    Series
    Linköping Electronic Conference Proceedings, ISSN 1650-3686, E-ISSN 1650-3740 ; 144
    Keywords
    Co-simulation, Fluid-structure coupling, System simulation, Functional mockup interface, Fluid power machinery, Transmission line modelling
    National Category
    Applied Mechanics Vehicle Engineering Control Engineering
    Identifiers
    urn:nbn:se:liu:diva-151015 (URN)10.3384/ecp17144225 (DOI)9789176853696 (ISBN)
    Conference
    15th Scandinavian International Conference on Fluid Power, June 7-9, 2017, Linköping, Sweden
    Available from: 2018-09-11 Created: 2018-09-11 Last updated: 2022-02-17Bibliographically approved
    3. Validation of a co-simulation approach for hydraulic percussion units applied to a hydraulic hammer
    Open this publication in new window or tab >>Validation of a co-simulation approach for hydraulic percussion units applied to a hydraulic hammer
    Show others...
    2019 (English)In: Advances in Engineering Software, ISSN 0965-9978, E-ISSN 1873-5339, Vol. 131, p. 102-115Article in journal (Refereed) Published
    Abstract [en]

    In this study, a previously developed co-simulation approach has been adopted to simulate the responses of an existing hydraulic hammer product. This approach is based on a 1D system model representing the fluid components and a 3D finite element model representing the structural parts of the hydraulic hammer. The simulation model was validated against four experiments with different running conditions. The corresponding set-ups were analysed using the co-simulation method in order to evaluate the overall responses. A parameter study was also performed involving the working pressure and the restrictor diameter, with the objective to validate that a parameter change in the simulation model will affect the input and output power in the same direction as in the experiments. The experimental responses used in the validation were time history data of fluid pressure, component position and acceleration, and structural stresses. The experiments result in high frequency and high amplitude excitations of the hydraulic hammer and thus require a model with a high resolution of the model dynamics. The conclusion of the validation is that the simulation model is able to replicate the experimental responses with high accuracy including the high frequency dynamics. The favourable outcome of the validation makes the described co-simulation approach promising as an efficient tool for a wide range of other applications where short time duration mechanisms need to be studied.

    Place, publisher, year, edition, pages
    ELSEVIER SCI LTD, 2019
    Keywords
    Co-simulation; Fluid-structure coupling; System simulation; FEM; Experiments; Fluid power machinery
    National Category
    Production Engineering, Human Work Science and Ergonomics
    Identifiers
    urn:nbn:se:liu:diva-156375 (URN)10.1016/j.advengsoft.2018.12.001 (DOI)000462766100009 ()
    Note

    Funding Agencies|Epiroc Hydraulic Attachment Tools Division

    Available from: 2019-04-18 Created: 2019-04-18 Last updated: 2022-02-17
    4. Simulation of leakage flow through dynamic sealing gaps in hydraulic percussion units using a co-simulation approach
    Open this publication in new window or tab >>Simulation of leakage flow through dynamic sealing gaps in hydraulic percussion units using a co-simulation approach
    Show others...
    2021 (English)In: Simulation (San Diego, Calif.), ISSN 1569-190X, E-ISSN 1878-1462, Vol. 111, article id 102351Article in journal (Refereed) Published
    Abstract [en]

    In this study, a previously developed co-simulation method has been expanded to also simulate the dynamic behaviour of sealing gap regions in hydraulic percussion units. This approach is based on a 1D system model representing the fluid components and a 3D finite element model representing the structural parts of a hydraulic hammer. The sealing gap is a fundamental feature of a percussion unit, where the reciprocating motion of the piston is generated by the valve mechanism of the sealing gap. When the gap is closed it will prevent fluid flow between regions of different pressure levels. However, a small leakage flow through the gap will always occur which size depends on the clearance and the position of the piston. The method proposed here will take the structural motion and deformation into consideration when calculating the leakage flow. The deformed state of the structure is approximated by a cylindrical surface, in a least square manner, and communicated through the co-simulation interface to the fluid simulation module, and then used when calculating the leakage flow. This method aims at a more accurate simulation of the leakage flow that will not only yield a more realistic description of the mechanism on the local level, but also a more accurate estimation of global parameters such as overall performance and efficiency. The results indicate that the simulated leakage flow will decrease when dynamic gaps are used in comparison to static gaps, which is a consequence of the deformed structure that will generate smaller clearances. The leakage flow for the dynamic gaps will even be lower than for the static perfectly concentric case, mainly due to the reduction of clearances. The results also indicate that the dynamic eccentricity does not have a major influence on the leakage flow. The outcome from this study highlights the potentials of the described co-simulation approach for analysing the dynamics of the sealing gaps in a hydraulic percussion unit (i.e. gap heights, eccentricity ratios, etc.) including the evaluation of leakage flows and its impact on the overall performance. © 2021

    Place, publisher, year, edition, pages
    Elsevier B.V., 2021
    Keywords
    Co-simulation; FEM; Fluid power machinery; Fluid–structure coupling; Sealing gap; System simulation
    National Category
    Energy Engineering
    Identifiers
    urn:nbn:se:liu:diva-176028 (URN)10.1016/j.simpat.2021.102351 (DOI)000659279200002 ()2-s2.0-85106298046 (Scopus ID)
    Available from: 2021-06-01 Created: 2021-06-01 Last updated: 2023-05-13
    Download full text (pdf)
    A Co-Simulation Tool Applied to Hydraulic Percussion Units
    Download (png)
    presentationsbild
    Download (pdf)
    errata
  • 10.
    Andersson, Håkan
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering. Epiroc, Tools & Attachments Division, Dragonvägen 2, Kalmar, 391 27, Sweden.
    Holmberg, Joakim
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Simonsson, Kjell
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Hilding, D.
    Dynamore Nordic AB, Brigadgatan 5, Linköping, 587 58, Sweden.
    Schill, M.
    Dynamore Nordic AB, Brigadgatan 5, Linköping, 587 58, Sweden.
    Borrvall, T.
    Dynamore Nordic AB, Brigadgatan 5, Linköping, 587 58, Sweden.
    Sigfridsson, E.
    Epiroc, Tools & Attachments Division, Dragonvägen 2, Kalmar, 391 27, Sweden.
    Leidermark, Daniel
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Simulation of leakage flow through dynamic sealing gaps in hydraulic percussion units using a co-simulation approach2021In: Simulation (San Diego, Calif.), ISSN 1569-190X, E-ISSN 1878-1462, Vol. 111, article id 102351Article in journal (Refereed)
    Abstract [en]

    In this study, a previously developed co-simulation method has been expanded to also simulate the dynamic behaviour of sealing gap regions in hydraulic percussion units. This approach is based on a 1D system model representing the fluid components and a 3D finite element model representing the structural parts of a hydraulic hammer. The sealing gap is a fundamental feature of a percussion unit, where the reciprocating motion of the piston is generated by the valve mechanism of the sealing gap. When the gap is closed it will prevent fluid flow between regions of different pressure levels. However, a small leakage flow through the gap will always occur which size depends on the clearance and the position of the piston. The method proposed here will take the structural motion and deformation into consideration when calculating the leakage flow. The deformed state of the structure is approximated by a cylindrical surface, in a least square manner, and communicated through the co-simulation interface to the fluid simulation module, and then used when calculating the leakage flow. This method aims at a more accurate simulation of the leakage flow that will not only yield a more realistic description of the mechanism on the local level, but also a more accurate estimation of global parameters such as overall performance and efficiency. The results indicate that the simulated leakage flow will decrease when dynamic gaps are used in comparison to static gaps, which is a consequence of the deformed structure that will generate smaller clearances. The leakage flow for the dynamic gaps will even be lower than for the static perfectly concentric case, mainly due to the reduction of clearances. The results also indicate that the dynamic eccentricity does not have a major influence on the leakage flow. The outcome from this study highlights the potentials of the described co-simulation approach for analysing the dynamics of the sealing gaps in a hydraulic percussion unit (i.e. gap heights, eccentricity ratios, etc.) including the evaluation of leakage flows and its impact on the overall performance. © 2021

    Download full text (pdf)
    fulltext
  • 11.
    Andersson, Håkan
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering. Epiroc, Tools & Attachments Division, Kalmar, Sweden.
    Holmberg, Joakim
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Simonsson, Kjell
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Hilding, Daniel
    DYNAmore Nordic, Sweden.
    Schill, Mikael
    DYNAmore Nordic, Sweden.
    Leidermark, Daniel
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Simulation of wear in hydraulic percussion units using a co-simulation approach2023In: International Journal of Modelling and Simulation, ISSN 0228-6203, Vol. 43, no 3, p. 265-281Article in journal (Refereed)
    Abstract [en]

    In this study, a developed co-simulation method, which couples 1D-fluid and 3D-structural models, has been utilised to simulate wear in a hydraulic percussion unit. The effect of wear is generally detrimental on performance and lifetime for such units, but can also cause catastrophic failure and breakdown, requiring a total overhaul and replacement of core components. One experiment of standard straight impact was performed to investigate the tolerance against seizure. The percussion unit was operated at successively increasing operating pressures, and the level of wear was registered at each step, until seizure occurred. The co-simulation model was used to replicate the running conditions from the experiment to simulate the structural response to be used as input for the wear routine to calculate the wear depth. The wear pattern from the simulations corresponds well to the wear pattern from the experiment. Further, the effect of a misaligned impact on wear development was also studied, as this is a loading situation that typically occurs for hydraulic percussion units. The study demonstrates that the simulation method used has a potential for simulating wear and predicting seizure in hydraulic percussion units.

    Download full text (pdf)
    fulltext
  • 12.
    Andersson, Håkan
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering. Construct Tools PC AB, Sweden.
    Nordin, Peter
    Linköping University, Department of Management and Engineering, Fluid and Mechatronic Systems. Linköping University, Faculty of Science & Engineering.
    Borrvall, Thomas
    DYNAmore Nordic AB, Brigadgatan 5, S-58758 Linkoping, Sweden.
    Simonsson, Kjell
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Hilding, Daniel
    DYNAmore Nordic AB, Brigadgatan 5, S-58758 Linkoping, Sweden.
    Schill, Mikael
    DYNAmore Nordic AB, Brigadgatan 5, S-58758 Linkoping, Sweden.
    Krus, Petter
    Linköping University, Department of Management and Engineering, Fluid and Mechatronic Systems. Linköping University, Faculty of Science & Engineering.
    Leidermark, Daniel
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    A co-simulation method for system-level simulation of fluid-structure couplings in hydraulic percussion units2017In: Engineering with Computers, ISSN 0177-0667, E-ISSN 1435-5663, Vol. 33, no 2, p. 317-333Article in journal (Refereed)
    Abstract [en]

    This paper addresses a co-simulation method for fluid power driven machinery equipment, i.e. oil hydraulic machinery. In these types of machinery, the fluid-structure interaction affects the end-product performance to a large extent, hence an efficient co-simulation method is of high importance. The proposed method is based on a 1D system model representing the fluid components of the hydraulic machinery, within which structural 3D Finite Element (FE) models can be incorporated for detailed simulation of specific sub-models or complete structural assemblies. This means that the fluid system simulation will get a more accurate structural response, and that the structural simulation will get more correct fluid loads at every time step, compared to decoupled analysis. Global system parameters such as fluid flow, performance and efficiency can be evaluated from the 1D system model simulation results. From the 3D FE-models, it is possible to evaluate displacements, stresses and strains to be used in stress analysis, fatigue evaluation, acoustic analysis, etc. The method has been implemented using two well-known simulation tools for fluid power system simulations and FE-simulations, respectively, where the interface between the tools is realised by use of the Functional Mock-up Interface standard. A simple but relevant model is used to validate the method.

    Download full text (pdf)
    fulltext
  • 13.
    Andersson, Håkan
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering. Epiroc, Sweden.
    Simonsson, Kjell
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Hilding, D.
    Dynamore Nord AB, Brigadgatan 5, S-58758 Linkoping, Sweden.
    Schill, M.
    Dynamore Nord AB, Brigadgatan 5, S-58758 Linkoping, Sweden.
    Sigfridsson, E.
    Epiroc, Sweden.
    Leidermark, Daniel
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Validation of a co-simulation approach for hydraulic percussion units applied to a hydraulic hammer2019In: Advances in Engineering Software, ISSN 0965-9978, E-ISSN 1873-5339, Vol. 131, p. 102-115Article in journal (Refereed)
    Abstract [en]

    In this study, a previously developed co-simulation approach has been adopted to simulate the responses of an existing hydraulic hammer product. This approach is based on a 1D system model representing the fluid components and a 3D finite element model representing the structural parts of the hydraulic hammer. The simulation model was validated against four experiments with different running conditions. The corresponding set-ups were analysed using the co-simulation method in order to evaluate the overall responses. A parameter study was also performed involving the working pressure and the restrictor diameter, with the objective to validate that a parameter change in the simulation model will affect the input and output power in the same direction as in the experiments. The experimental responses used in the validation were time history data of fluid pressure, component position and acceleration, and structural stresses. The experiments result in high frequency and high amplitude excitations of the hydraulic hammer and thus require a model with a high resolution of the model dynamics. The conclusion of the validation is that the simulation model is able to replicate the experimental responses with high accuracy including the high frequency dynamics. The favourable outcome of the validation makes the described co-simulation approach promising as an efficient tool for a wide range of other applications where short time duration mechanisms need to be studied.

  • 14.
    Andersson, Håkan
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Simonsson, Kjell
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Hilding, Daniel
    DYNAmore Nordic AB, Brigadgatan 5, 587 58 Linköping, Sweden.
    Schill, Mikael
    DYNAmore Nordic AB, Brigadgatan 5, 587 58 Linköping, Sweden.
    Leidermark, Daniel
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    System level co-simulation of a control valve and hydraulic cylinder circuit in a hydraulic percussion unit2017In: Proceedings of 15:th Scandinavian International Conference on Fluid Power, June 7-9, 2017, Linköping, Sweden / [ed] Petter Krus, Liselott Ericson and Magnus Sethson, Linköping: Linköping University Electronic Press, 2017, Vol. 144, p. 225-235Conference paper (Refereed)
    Abstract [en]

    In this study a previously developed co-simulation method that is based on a 1D system model representing the fluid components of a hydraulic machinery, within which structural 3D Finite Element (FE) models can be incorporated for detailed simulation of specific sub-models or complete structural assemblies, is further developed. The fluid system model consists of ordinary differential equation sub-models that are computationally very inexpensive, but still represents the fluid dynamics very well. The co-simulation method has been shown to work very well for a simple model representing a hydraulic driven machinery. A more complex model was set up in this work, in which two cylinders in the hydraulic circuit were evaluated. Such type of models, including both the main piston and control valves, are necessary as they represent the real application to a further extent than the simple model, of only one cylinder. Two models have been developed and evaluated, from the simple rigid body representation of the structural mechanics model, to the more complex model using linear elastic representation. The 3D FE-model facilitates evaluation of displacements, stresses, and strains on a local level of the model. The results can be utilised for fatigue assessment, wear analysis and for predictions of noise radiation.

    Download full text (pdf)
    System level co-simulation of a control valve and hydraulic cylinder circuit in a hydraulic percussion unit
  • 15.
    Andric, J.
    et al.
    Chalmers, Sweden.
    Lindström, Stefan
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Sasic, S.
    Chalmers, Sweden.
    Nilsson, H.
    Chalmers, Sweden.
    Ballistic deflection of fibres in decelerating flow2016In: International Journal of Multiphase Flow, ISSN 0301-9322, E-ISSN 1879-3533, Vol. 85, p. 57-66Article in journal (Refereed)
    Abstract [en]

    We investigate the motion of inertial, rod-like fibres in the decelerating flow of a wedge-shaped channel with non-creeping fibre-flow interactions. We consider the trajectories of isolated fibres to identify the conditions for which these trajectories deflect from the streamlines of the flow as well as a rectilinear path. We carry out analytical and numerical studies under the assumption of an infinite fibre hydrodynamic resistance to transverse flow, and we expand the numerical study by taking into account a finite transverse hydrodynamic resistance. The analytical analysis identifies a longitudinal ballistic number Be and a transverse ballistic number B-t as two dimensionless parameters that govern the fibre dynamics. It is found that Be is the product of the Stokes number Ste(l) in the longitudinal direction of the fibre and the channel opening angle beta. As anticipated, a fibre moves along the streamlines in the viscosity-dominated regime (B-l amp;lt;amp;lt; 1, B-t amp;lt;amp;lt; 1), while it moves in a straight line without being rotated in the inertia-dominated regime (Bt amp;gt;amp;gt; 1). The focus of the present study is on the intermediate regime (B-l amp;gt;amp;gt; 1, B-t amp;lt; 1), in which we identify and analyse a fibre trajectory that significantly deviates from the streamlines of the flow. This behaviour is observed for both infinite and finite resistances to transverse flow, and it is referred to as ballistic deflection. We argue that ballistic deflection may increase the rate of collisions between suspended fibres, and thus potentially affects the rate of fibre aggregation in flowing suspensions. An order of magnitude estimate of the ballistic numbers identifies dry-forming of pulp mats, which includes an air-wood fibre flowing suspension, to operate in the regime of ballistic deflection. (C) 2016 Elsevier Ltd. All rights reserved.

  • 16.
    Andric, Jelena
    et al.
    Chalmers, Sweden.
    Lindström, Stefan B
    Linköping University, Department of Management and Engineering, Solid Mechanics.
    Sasic, Srdjan
    Chalmers, Sweden.
    Nilsson, Hakan
    Chalmers, Sweden.
    Numerical investigation of fiber flocculation in the air flow of an asymmetrical diffuser2014In: Proceedings of the 12th International Conference on Nanochannels, Microchannels and Minichannels (ICNMM), AMER SOC MECHANICAL ENGINEERS , 2014, no V001T12A013, p. V001T12A013-Conference paper (Refereed)
    Abstract [en]

    A particle-level rigid fiber model is used to study flocculation in an asymmetric planar diffuser with a turbulent Newtonian fluid flow, resembling one stage in dry-forming process of pulp mats. The fibers are modeled as chains of rigid cylindrical segments. The equations of motion incorporate hydrodynamic forces and torques from the interaction with the fluid, and the fiber inertia is taken into account. The flow is governed by the Reynolds-averaged Navier-Stokes equations with the standard k - omega turbulence model. A one-way coupling between the fibers and the flow is considered. A stochastic model is employed for the flow fluctuations to capture the fiber dispersion. The fibers are assumed to interact through short-range attractive forces, causing them to interlock as the fiber-fiber contacts occur during the flow. It is found that the formation of fiber flocs is driven by both the turbulence-induced dispersion and the gradient of the averaged flow field.

  • 17.
    Andric, Jelena S.
    et al.
    Chalmers University of Technology, Sweden.
    Lindström, Stefan B
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Sasic, Srdjan M.
    Chalmers University of Technology, Sweden.
    Nilsson, Håkan
    Chalmers University of Technology, Sweden.
    PARTICLE-LEVEL SIMULATIONS OF FLOCCULATION IN A FIBER SUSPENSION FLOWING THROUGH A DIFFUSER2017In: Thermal Science, ISSN 0354-9836, E-ISSN 2334-7163, Vol. 21, p. S573-S583Article in journal (Refereed)
    Abstract [en]

    We investigate flocculation in dilute suspensions of rigid, straight fibers in a decelerating flow field of a diffuser. We carry out numerical studies using a particle-level simulation technique that takes into account the fiber inertia and the non-creeping fiber-flow interactions. The fluid flow is governed by the Reynolds averaged Navier-Stokes equations with the standard k-omega eddy-viscosity turbulence model. A one-way coupling between the fibers and the flow is considered with a stochastic model for the fiber dispersion due to turbulence. The fibers interact through short-range attractive forces that cause them to aggregate into flocs when fiber-fiber collisions occur. We show that ballistic deflection of fibers greatly increases the flocculation in the diffilser. The inlet fiber kinematics and the fiber inertia are the main parameters that affect fiber flocculation in the predffuser region.

    Download full text (pdf)
    fulltext
  • 18.
    Arsiwala, Ali
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics.
    Shukla, Vatsal
    Linköping University, Department of Management and Engineering, Solid Mechanics.
    FE Modelling Of Two Femur Fixation Implants2021Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In the pool of women over the age of 50, the likeliness of an atypical fracture increase drastically, partly due to osteoporosis. With a pre-existing implant in the femur bone, inserted due to a prior atypical fracture, treating a later femoral neck fracture is complex and risky. Currently, a fractured femoral diaphysis is treated using an intermedullary nail which is fixed to the femur bone either through the femoral neck (Recon locking method)or through the lesser trochanter (Antegrade locking method). In a study conducted by Bögl et.al. JBJS102.17 (2020), pp. 1486-1494, it is found that the fixation of the intermedullary nail through the femoral neck reduces the risk of future femoral neck fractures. The study also states that more than 50% of the patients with atypical femoral fractures related to bisphosphonate treatment for osteoporosis (within the study sub population) were treated with the Antegrade locking implant. There does not exist much literature that reasons as to how one locking method is showing lesser risk of re-operation as compared to the other. The purpose of this study is to look into the effects these two implants have on the femur bone using the Finite Element Analysis (FEA). The study presented is aimed at comparing the results of the finite element analysis for the Recon implant model (Recon model) and Antegrade implant model (Antegrade model). The femur model without the implants (native bone model) is used to verify material behavior, while the other two are used for the comparison to study the stress-strain distribution, primarily in the neck region. This is a patient specific study, hence the femur bone model is generated using patient Computed Tomography (CT) scans. The bone model was assigned a heterogeneous isotropic material property derived from patient CT data. The finite element (FE) model of the bone was meshed using Hypermesh. The peak loading condition including the muscle forces were applied on the native bone model along with the Recon and the Antegrademodel. While the loading conditions during normal walking cycle were only applied to theRecon and the Antegrade model to compare the impacts of the two implant types. Both loading conditions were simulated by fixing the distal condyle region of the bone. The analysis results show that the Antegrade implant experiences much higher stresses and strains in the neck region as compared to Recon implant. Also, the presence of the intermedullary nail through the femur diaphysis helps to distribute the stresses and strains in the anterior distal diaphysis region of the bone. For the case of no implants, the model showed strains and stresses in the lateral distal region of femoral diaphysis.

    Download full text (pdf)
    fulltext
  • 19.
    Azeez, Ahmed
    Linköping University, Department of Management and Engineering, Solid Mechanics.
    Effect of dwell time on stress intensity factor of ferritic steel for steam turbine applications2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In the transition from conventional to green energy production resources, steam turbines are used to satisfy the lack of energy during peaks in the demand times and the limited access of renewable resources. This type of usage for steam turbines makes them operate on a flexible schedule, which leads to unpredictable issues related to shorter component life and faster crack propagation. Thus, the steam turbine components must be examined to determine their specific life period. This will help set proper maintenance intervals and prevent unexpected failures. For that, thermo-mechanical fatigue (TMF) testing is used, where a specimen made of the same material as the turbine component is subjected to both temperature and load variation. The specimen is pre-cracked to investigate the crack propagation behavior, which is the focus of this study.

    This thesis work concentrates on simulating the TMF cycle for the steam turbine casing component. The material is 9%-10%Cr ferritic steel. The aim is to understand the material behavior during crack propagation and to predict a useful testing parameter. The method provided in this work discusses two cases, both are out-of-phase (OP) TMF tests with strain control. The maximum and minimum temperatures for the cycle are 600 ˚C and 400 ˚C respectively, while the maximum and minimum strain levels are 0 and  respectively. The study will investigate different , which is the maximum compressive strain level. Case 1 has a dwell time at the maximum temperature only, while case 2 has dwell times at both maximum and minimum temperatures. The method utilizes the stress intensity factor (SIF) to characterize the crack tip conditions. Also, it uses Paris' law to estimate the duration of the tests. For simplification, only the elastic behavior of the material is considered.

    The results obtained show no effect of using different pre-crack lengths due to the strain control condition. Minor effects can be observed by using different dwell times, however very short dwell times must be avoided to produce reliable results. A recommended dwell time of 5 minutes could be used, since longer dwell times will make the test prohibitively time-consuming. The compressive strain levels used in the work shows large effects on the results. Using low compressive strain values will produce a very long time for the tests, while very high compressive strains produce large plasticity. Thus, high compressive strains must be avoided since the SIF describes cracks for only elastic or near elastic cases. Also, small compressive strain levels in case 2 should not be used since it will lead to results like case 1. This is due to the small creep effect at the minimum temperature. Finally, compressive strain levels of 0.6 %, 0.5 % and 0.4 % are recommended for case 1, while only 0.6 % compressive strain level is recommended for case 2.

    This thesis contributes to the fields of solid mechanics, fracture mechanics and the use of TMF testing, where a recommended set of testing parameters are provided.

    Download full text (pdf)
    fulltext
  • 20. Order onlineBuy this publication >>
    Azeez, Ahmed
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    High-Temperature Durability Prediction of Ferritic-Martensitic Steel2023Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Materials used for high-temperature steam turbine sections are generally subjected to harsh environments with temperatures up to 625 °C. The superior creep resistance of 9–12 % Cr ferritic-martensitic steels makes them desirable for those critical steam turbine components. Additionally, the demand for fast and frequent steam turbine start-ups, i.e. flexible operations, causes accelerated fatigue damage in critical locations, such as grooves and notches, at the high-temperature inner steam turbine casing. A durability assessment is necessary to understand the material behaviour under such high temperatures and repeated loading, and it is essential for life prediction. An accurate and less conservative fatigue life prediction approach is achieved by going past the crack initiation stage and allowing controlled growth of cracks within safe limits. Besides, beneficial load-temperature history effects, i.e. warm pre-stressing, must be utilised to enhance the fracture resistance to cracks. This dissertation presents the high-temperature durability assessment of FB2 steel, a 9-12 % Cr ferritic-martensitic steam turbine steel.

    Initially, isothermal low-cycle fatigue testing was performed on FB2 steel samples. A fatigue life model based on finite element strain range partitioning was utilised to predict fatigue life within the crack initiation phase. Two fatigue damage regimes were identified, i.e. plastic- and creep-dominated damage, and the transition between them depended on temperature and applied total strain. Cyclic deformation and stress relaxation behaviour were investigated to produce an elastic-plastic and creep material model that predicts the initial and mid-life cyclic behaviour of the FB2 steel.

    Furthermore, the thermomechanical fatigue crack growth behaviour of FB2 steel was studied. Crack closure behaviour was observed and accounted for numerically and experimentally, where crack growth rate curves collapsed into a single curve. Interestingly, the collapsed crack growth curves coincided with isothermal crack growth tests performed at the minimum temperature of the thermomechanical crack growth tests. In addition, hold times and changes in the minimum temperature of the thermomechanical fatigue cycle did not influence crack closure behaviour.

    Finally, warm pre-stressing effects were explored for FB2 steel. A numerical prediction model was produced to predict the increase in the apparent fracture toughness. Warm pre-stressing effects can benefit the turbine life by enhancing fracture resistance and allowing longer fatigue cracks to grow within safe limits.

    List of papers
    1. Low cycle fatigue life modelling using finite element strain range partitioning for a steam turbine rotor steel
    Open this publication in new window or tab >>Low cycle fatigue life modelling using finite element strain range partitioning for a steam turbine rotor steel
    2020 (English)In: Theoretical and applied fracture mechanics (Print), ISSN 0167-8442, E-ISSN 1872-7638, Vol. 107, article id 102510Article in journal (Refereed) Published
    Abstract [en]

    Materials made for modern steam power plants are required to withstand high temperatures and flexible operational schedule. Mainly to achieve high efficiency and longer components life. Nevertheless, materials under such conditions experience crack initiations and propagations. Thus, life prediction must be made using accurate fatigue models to allow flexible operation. In this study, fully reversed isothermal low cycle fatigue tests were performed on a turbine rotor steel called FB2. The tests were done under strain control with different total strain ranges and temperatures (20 °C to 625 °C). Some tests included dwell time to calibrate the short-time creep behaviour of the material. Different fatigue life models were evaluated based on total life approach. The stress-based fatigue life model was found unusable at 600 °C, while the strain-based models in terms of total strain or inelastic strain amplitudes displayed inconsistent behaviour at 500 °C. To construct better life prediction, the inelastic strain amplitudes were separated into plastic and creep components by modelling the deformation behaviour of the material, including creep. Based on strain range partitioning approach, the fatigue life depends on different damage mechanisms at different strain ranges at 500 °C. This allows for the formulation of life curves based on either plasticity-dominated damage or creep-dominated damage. At 600 °C, creep dominated while at 500 °C creep only dominates for higher strain ranges. The deformation mechanisms at different temperatures and total strain ranges were characterised by scanning electron microscopy and by quantifying the amount of low angle grain boundaries. The quantification of low angle grain boundaries was done by electron backscatter diffraction. Microscopy revealed that specimens subjected to 600 °C showed signs of creep damage in the form of voids close to the fracture surface. In addition, the amount of low angle grain boundaries seems to decrease with the increase in temperature even though the inelastic strain amplitude was increased. The study indicates that a significant amount of the inelastic strain comes from creep strain as opposed of being all plastic strain, which need to be taken into consideration when constructing a life prediction model.

    Place, publisher, year, edition, pages
    Elsevier, 2020
    Keywords
    Creep-fatigue interaction, Creep-resistant steel, EBSD, Low cycle fatigue, Steam turbine steel, Strain range partitioning
    National Category
    Applied Mechanics
    Identifiers
    urn:nbn:se:liu:diva-164610 (URN)10.1016/j.tafmec.2020.102510 (DOI)000528008200019 ()2-s2.0-85079627150 (Scopus ID)
    Note

    Funding agencies: European UnionEuropean Union (EU) [764545]

    Available from: 2020-03-26 Created: 2020-03-26 Last updated: 2023-09-29Bibliographically approved
    2. Out-of-phase thermomechanical fatigue crack propagation in a steam turbine steel — modelling of crack closure
    Open this publication in new window or tab >>Out-of-phase thermomechanical fatigue crack propagation in a steam turbine steel — modelling of crack closure
    Show others...
    2021 (English)In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 149, article id 106251Article in journal (Refereed) Published
    Abstract [en]

    Understanding of crack growth behaviour is necessary to predict accurate fatigue lives. Out-of-phase thermomechanical fatigue crack propagation tests were performed on FB2 steel used in high-temperature steam turbine sections. Testing results showed crack closure where the compressive part of the fatigue cycle affected crack growth rate. Crack closing stress was observed to be different, and had more influence on the growth rate, than crack opening stress. Crack growth rate was largely controlled by the minimum temperature of the cycle, which agreed with an isothermal crack propagation test. Finite element models with stationary sharp cracks captured the crack closure behaviour.

    Place, publisher, year, edition, pages
    Elsevier, 2021
    Keywords
    Thermomechanical fatigue, Fatigue crack growth, High temperature steel, Crack closure, Numerical modelling
    National Category
    Applied Mechanics
    Identifiers
    urn:nbn:se:liu:diva-174692 (URN)10.1016/j.ijfatigue.2021.106251 (DOI)000655657600001 ()
    Note

    Funding: European UnionEuropean Commission [764545]; Siemens AG

    Available from: 2021-03-30 Created: 2021-03-30 Last updated: 2023-09-29
    3. The effect of dwell times and minimum temperature on out-of-phase thermomechanical fatigue crack propagation in a steam turbine steel - Crack closure prediction
    Open this publication in new window or tab >>The effect of dwell times and minimum temperature on out-of-phase thermomechanical fatigue crack propagation in a steam turbine steel - Crack closure prediction
    Show others...
    2022 (English)In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 162, article id 106971Article in journal (Refereed) Published
    Abstract [en]

    Exploring crack growth behaviour is needed to establish accurate fatigue life predictions. Cracked specimens were tested under strain-controlled out-of-phase thermomechanical fatigue conditions. The tests included dwell times and three different minimum temperatures. Higher minimum temperature gave faster crack growth rates while the additions of dwell times showed no effects. Crack closure was observed in all the tests where the addition of dwell times and change in minimum temperature displayed little to no effect on crack closure stresses. Finite element models with a sharp stationary crack and material parameters switching provided acceptable predictions for the maximum, minimum, and crack closure stresses.

    Place, publisher, year, edition, pages
    Elsevier Science Ltd, 2022
    Keywords
    Thermomechanical fatigue; Fatigue crack growth; High temperature steel; Crack closure; Numerical modelling
    National Category
    Applied Mechanics
    Identifiers
    urn:nbn:se:liu:diva-187284 (URN)10.1016/j.ijfatigue.2022.106971 (DOI)000829870800006 ()
    Note

    Funding Agencies: SIEMENS AG

    Available from: 2022-08-17 Created: 2022-08-17 Last updated: 2023-09-29
    4. Stress intensity factor solution for single-edge cracked tension specimen considering grips bending effects
    Open this publication in new window or tab >>Stress intensity factor solution for single-edge cracked tension specimen considering grips bending effects
    2023 (English)In: Procedia Structural Integrity, ISSN 2452-3216, Vol. 47, p. 195-204Article in journal (Refereed) Published
    Abstract [en]

    Using the stress intensity factor to describe the stress field around a crack has become widely adopted due to its simplicity. The stress intensity factor depends on the applied nominal stress, the crack length, and a geometrical factor. Geometrical factors can be obtained from handbook solutions or, for complicated cases, through finite element simulations. Carefully defining the geometrical factor with realistic boundary conditions is vital to obtain accurate values for the stress intensity factor. For fatigue life predictions, even a small error in the stress intensity factor may get amplified as the total fatigue life is computed through integration over thousands of crack growth increments. A commonly used specimen geometry for fatigue crack growth testing is the single-edge cracked specimen. For such a specimen, the crack on one side of the geometry introduces bending, which, to some degree, is constrained by the grips that hold the specimen in the testing rig. The effect of bending on the geometrical factor, and consequently on the stress intensity factor, is generally overlooked due to the assumption that the test rig grips are infinitely stiff. Not considering the bending effects could lead to an inaccurate evaluation of the stress intensity factor, especially for long crack lengths. This work investigated the effect of bending on the stress intensity factor for a single-edge cracked specimen. Different grip dimensions were studied to understand the degree of bending and its impact on the stress intensity factor. The work resulted in recommendations for accurately evaluating the stress intensity factor for single-edge cracked specimens.

    Keywords
    Fracture mechanics, Stress intensity factor, Finite element, Single-edge cracked specimen
    National Category
    Applied Mechanics
    Identifiers
    urn:nbn:se:liu:diva-198204 (URN)10.1016/j.prostr.2023.07.012 (DOI)
    Available from: 2023-09-29 Created: 2023-09-29 Last updated: 2023-10-05
    5. Numerical prediction of warm pre-stressing effects for a steam turbine steel
    Open this publication in new window or tab >>Numerical prediction of warm pre-stressing effects for a steam turbine steel
    2023 (English)In: Theoretical and applied fracture mechanics (Print), ISSN 0167-8442, E-ISSN 1872-7638, Vol. 125, article id 103940Article in journal (Refereed) Published
    Abstract [en]

    In warm pre-stressing (WPS), the fracture resistance of cracked steel components is raised when subjected to certain temperature-load histories. WPS’s beneficial effects enhance safety margins and potentially prolong fatigue life. However, understanding and predicting the WPS effects is crucial for employing such benefits. This study utilised pre-cracked compact tension specimens made from steam turbine steel for WPS and baseline fracture toughness testing. Two typical WPS cycles were investigated (L-C-F and L-U-C-F), and an increase in fracture resistance was observed for both cycles. The WPS tests were simulated using finite element analysis to understand its effects and predict the increase in fracture resistance. A local approach was followed based on accumulative plastic strain magnitude ahead of the crack tip. Since cleavage fracture is triggered by active plasticity, the WPS fracture is assumed when accumulated plasticity exceeds the residual plastic zone formed at the crack tip due to the initial pre-load.

    Place, publisher, year, edition, pages
    Elsevier, 2023
    Keywords
    Finite element analysis; Fracture mechanics; Fracture toughness; High temperature steel; Warm pre-stressing
    National Category
    Applied Mechanics
    Identifiers
    urn:nbn:se:liu:diva-194734 (URN)10.1016/j.tafmec.2023.103940 (DOI)001012091400001 ()2-s2.0-85160508688 (Scopus ID)
    Available from: 2023-06-09 Created: 2023-06-09 Last updated: 2023-10-26Bibliographically approved
    Download full text (pdf)
    fulltext
    Download (png)
    presentationsbild
  • 21. Order onlineBuy this publication >>
    Azeez, Ahmed
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    High-Temperature Fatigue in a Steam Turbine Steel: Modelling of Cyclic Deformation and Crack Closure2021Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Existing conventional thermal power plants are retrofitted for flexible operations to assist the transition toward more renewable energies. The deployment of many renewable energy power plants is necessary to achieve a clean environment with less pollution. However, the intermittent nature of renewable energies, due to weather changes, and the lack of efficient large energy storage systems put renewables at a disadvantage. Flexible operations of power plants imply fast and frequent start-ups. Thus, retrofitted power production plants can be utilised as an energy backup to satisfy the immediate demand during peak energy times or when renewable energies are suddenly limited. 

    Large thermal power plants generally employ steam turbines with high inlet temperature and pressure steam conditions. Materials used for components at the high-temperature turbine sections are expected to withstand harsh environments. The use of 9-12 % Cr martensitic steels is desirable due to, among other things, their superior resistance to creep for temperatures up to 625 °C. Retrofitting for flexible operations put steam turbine components under high-temperature fatigue loading conditions different from how they were designed before. The flexible operations could lead to fatigue cracking at critical locations, such as grooves and notches at the inner steam turbine casing. Thus, fatigue behaviour understanding of steam turbine materials under such loading conditions is essential for components life prediction. Accurate and less conservative fatigue life prediction approach is necessary to extend the turbine components life, which reduces waste and provides economic benefits. This can be done by extending operations past crack initiation phase and allowing controlled propagation of cracks in the components. 

    Within the 9-12 % Cr steel class, the martensitic steam turbine steel called FB2 is studied under high-temperature fatigue. This includes investigating high-temperature fatigue life behaviour, cyclic deformation behaviour, stress relaxation behaviour, and crack propagation behaviour along with crack closure behaviour. This was achieved by experimentally testing samples made from FB2 steel under isothermal low cycle fatigue, isothermal fatigue crack propagation, and thermomechanical fatigue crack propagation. 

    List of papers
    1. Low cycle fatigue life modelling using finite element strain range partitioning for a steam turbine rotor steel
    Open this publication in new window or tab >>Low cycle fatigue life modelling using finite element strain range partitioning for a steam turbine rotor steel
    2020 (English)In: Theoretical and applied fracture mechanics (Print), ISSN 0167-8442, E-ISSN 1872-7638, Vol. 107, article id 102510Article in journal (Refereed) Published
    Abstract [en]

    Materials made for modern steam power plants are required to withstand high temperatures and flexible operational schedule. Mainly to achieve high efficiency and longer components life. Nevertheless, materials under such conditions experience crack initiations and propagations. Thus, life prediction must be made using accurate fatigue models to allow flexible operation. In this study, fully reversed isothermal low cycle fatigue tests were performed on a turbine rotor steel called FB2. The tests were done under strain control with different total strain ranges and temperatures (20 °C to 625 °C). Some tests included dwell time to calibrate the short-time creep behaviour of the material. Different fatigue life models were evaluated based on total life approach. The stress-based fatigue life model was found unusable at 600 °C, while the strain-based models in terms of total strain or inelastic strain amplitudes displayed inconsistent behaviour at 500 °C. To construct better life prediction, the inelastic strain amplitudes were separated into plastic and creep components by modelling the deformation behaviour of the material, including creep. Based on strain range partitioning approach, the fatigue life depends on different damage mechanisms at different strain ranges at 500 °C. This allows for the formulation of life curves based on either plasticity-dominated damage or creep-dominated damage. At 600 °C, creep dominated while at 500 °C creep only dominates for higher strain ranges. The deformation mechanisms at different temperatures and total strain ranges were characterised by scanning electron microscopy and by quantifying the amount of low angle grain boundaries. The quantification of low angle grain boundaries was done by electron backscatter diffraction. Microscopy revealed that specimens subjected to 600 °C showed signs of creep damage in the form of voids close to the fracture surface. In addition, the amount of low angle grain boundaries seems to decrease with the increase in temperature even though the inelastic strain amplitude was increased. The study indicates that a significant amount of the inelastic strain comes from creep strain as opposed of being all plastic strain, which need to be taken into consideration when constructing a life prediction model.

    Place, publisher, year, edition, pages
    Elsevier, 2020
    Keywords
    Creep-fatigue interaction, Creep-resistant steel, EBSD, Low cycle fatigue, Steam turbine steel, Strain range partitioning
    National Category
    Applied Mechanics
    Identifiers
    urn:nbn:se:liu:diva-164610 (URN)10.1016/j.tafmec.2020.102510 (DOI)000528008200019 ()2-s2.0-85079627150 (Scopus ID)
    Note

    Funding agencies: European UnionEuropean Union (EU) [764545]

    Available from: 2020-03-26 Created: 2020-03-26 Last updated: 2023-09-29Bibliographically approved
    2. Out-of-phase thermomechanical fatigue crack propagation in a steam turbine steel — modelling of crack closure
    Open this publication in new window or tab >>Out-of-phase thermomechanical fatigue crack propagation in a steam turbine steel — modelling of crack closure
    Show others...
    2021 (English)In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 149, article id 106251Article in journal (Refereed) Published
    Abstract [en]

    Understanding of crack growth behaviour is necessary to predict accurate fatigue lives. Out-of-phase thermomechanical fatigue crack propagation tests were performed on FB2 steel used in high-temperature steam turbine sections. Testing results showed crack closure where the compressive part of the fatigue cycle affected crack growth rate. Crack closing stress was observed to be different, and had more influence on the growth rate, than crack opening stress. Crack growth rate was largely controlled by the minimum temperature of the cycle, which agreed with an isothermal crack propagation test. Finite element models with stationary sharp cracks captured the crack closure behaviour.

    Place, publisher, year, edition, pages
    Elsevier, 2021
    Keywords
    Thermomechanical fatigue, Fatigue crack growth, High temperature steel, Crack closure, Numerical modelling
    National Category
    Applied Mechanics
    Identifiers
    urn:nbn:se:liu:diva-174692 (URN)10.1016/j.ijfatigue.2021.106251 (DOI)000655657600001 ()
    Note

    Funding: European UnionEuropean Commission [764545]; Siemens AG

    Available from: 2021-03-30 Created: 2021-03-30 Last updated: 2023-09-29
    Download full text (pdf)
    fulltext
    Download (png)
    presentationsbild
  • 22.
    Azeez, Ahmed
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Eriksson, Robert
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Arts and Sciences. Linköping University, Faculty of Science & Engineering.
    Calmunger, Mattias
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Characterisation of Deformation and Damage in a Steam Turbine Steel Subjected to Low Cycle Fatigue2019In: Structural Integrity Procedia / [ed] Elsevier, 2019, Vol. 23, p. 155-160Conference paper (Refereed)
    Abstract [en]

    The increased use of renewable energy pushes steam turbines toward a more frequent operation schedule. Consequently, components must endure more severe fatigue loads which, in turn, requires an understanding of the deformation and damage mechanisms under high-temperature cyclic loading. Based on this, low cycle fatigue tests were performed on a creep resistant steel, FB2, used in ultra-supercritical steam turbines. The fatigue tests were performed in strain control with 0.8-1.2 % strain range and at temperatures of 400 °C and 600 °C. The tests at 600 °C were run with and without dwell time. The deformation mechanisms at different temperatures and strain ranges were characterised by scanning electron microscopy and by quantifying the amount of low angle grain boundaries. The quantification of low angle grain boundaries was done by electron backscatter diffraction. Microscopy revealed that specimens subjected to 600 °C showed signs of creep damage, in the form of voids close to fracture surface, regardless of whether the specimen had been exposed to dwell time or been purely cycled. In addition, the amount of low angle grain boundaries was lower at 600 °C than at 400 °C. The study indicates that a significant amount of the inelastic strain comes from creep strain as opposed to being all plastic strain.

    Download full text (pdf)
    fulltext
  • 23.
    Azeez, Ahmed
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Eriksson, Robert
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Calmunger, Mattias
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Lindström, Stefan B
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Simonsson, Kjell
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Low Cycle Fatigue Modelling of Steam Turbine Rotor Steel2019In: 9th International Conference Materials Structure & Micromechanics of Fracture (MSMF9) / [ed] Jaroslav Pokluda, Pavel Šandera, Elsevier, 2019, Vol. 23, p. 149-154Conference paper (Refereed)
    Abstract [en]

    Materials in steam turbine rotors are subjected to cyclic loads at high temperature, causing cracks to initiate and grow. To allow for more flexible operation, accurate fatigue models for life prediction must not be overly conservative. In this study, fully reversed low cycle fatigue tests were performed on a turbine rotor steel called FB2. The tests were done isothermally, within temperature range of room temperature to 600 °C, under strain control with 0.8-1.2 % total strain range. Some tests included hold time to calibrate the short-time creep behaviour of the material. Different fatigue life models were constructed. The life curve in terms of stress amplitude was found unusable at 600 °C, while the life curve in terms of total strain or inelastic strain amplitudes displayed inconsistent behaviour at 500 °C. To construct better life model, the inelastic strain amplitudes were separated into plastic and creep components by modelling the deformation behaviour of the material, including creep. Based on strain range partitioning approach, the fatigue life depends on different damage mechanisms at different strain ranges. This allowed the formulation of life curves based on plasticity or creep domination, which showed creep domination at 600 °C, while at 500 °C, creep only dominates for higher strain range.

    Download full text (pdf)
    fulltext
  • 24.
    Azeez, Ahmed
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Eriksson, Robert
    Linköping University, Department of Management and Engineering, Solid Mechanics.
    Leidermark, Daniel
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Calmunger, Mattias
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Low cycle fatigue life modelling using finite element strain range partitioning for a steam turbine rotor steel2020In: Theoretical and applied fracture mechanics (Print), ISSN 0167-8442, E-ISSN 1872-7638, Vol. 107, article id 102510Article in journal (Refereed)
    Abstract [en]

    Materials made for modern steam power plants are required to withstand high temperatures and flexible operational schedule. Mainly to achieve high efficiency and longer components life. Nevertheless, materials under such conditions experience crack initiations and propagations. Thus, life prediction must be made using accurate fatigue models to allow flexible operation. In this study, fully reversed isothermal low cycle fatigue tests were performed on a turbine rotor steel called FB2. The tests were done under strain control with different total strain ranges and temperatures (20 °C to 625 °C). Some tests included dwell time to calibrate the short-time creep behaviour of the material. Different fatigue life models were evaluated based on total life approach. The stress-based fatigue life model was found unusable at 600 °C, while the strain-based models in terms of total strain or inelastic strain amplitudes displayed inconsistent behaviour at 500 °C. To construct better life prediction, the inelastic strain amplitudes were separated into plastic and creep components by modelling the deformation behaviour of the material, including creep. Based on strain range partitioning approach, the fatigue life depends on different damage mechanisms at different strain ranges at 500 °C. This allows for the formulation of life curves based on either plasticity-dominated damage or creep-dominated damage. At 600 °C, creep dominated while at 500 °C creep only dominates for higher strain ranges. The deformation mechanisms at different temperatures and total strain ranges were characterised by scanning electron microscopy and by quantifying the amount of low angle grain boundaries. The quantification of low angle grain boundaries was done by electron backscatter diffraction. Microscopy revealed that specimens subjected to 600 °C showed signs of creep damage in the form of voids close to the fracture surface. In addition, the amount of low angle grain boundaries seems to decrease with the increase in temperature even though the inelastic strain amplitude was increased. The study indicates that a significant amount of the inelastic strain comes from creep strain as opposed of being all plastic strain, which need to be taken into consideration when constructing a life prediction model.

    Download full text (pdf)
    fulltext
  • 25.
    Azeez, Ahmed
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Eriksson, Robert
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Norman, Viktor
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Leidermark, Daniel
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    The effect of dwell times and minimum temperature on out-of-phase thermomechanical fatigue crack propagation in a steam turbine steel - Crack closure prediction2022In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 162, article id 106971Article in journal (Refereed)
    Abstract [en]

    Exploring crack growth behaviour is needed to establish accurate fatigue life predictions. Cracked specimens were tested under strain-controlled out-of-phase thermomechanical fatigue conditions. The tests included dwell times and three different minimum temperatures. Higher minimum temperature gave faster crack growth rates while the additions of dwell times showed no effects. Crack closure was observed in all the tests where the addition of dwell times and change in minimum temperature displayed little to no effect on crack closure stresses. Finite element models with a sharp stationary crack and material parameters switching provided acceptable predictions for the maximum, minimum, and crack closure stresses.

    Download full text (pdf)
    fulltext
  • 26.
    Azeez, Ahmed
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Leidermark, Daniel
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Eriksson, Robert
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Stress intensity factor solution for single-edge cracked tension specimen considering grips bending effects2023In: Procedia Structural Integrity, ISSN 2452-3216, Vol. 47, p. 195-204Article in journal (Refereed)
    Abstract [en]

    Using the stress intensity factor to describe the stress field around a crack has become widely adopted due to its simplicity. The stress intensity factor depends on the applied nominal stress, the crack length, and a geometrical factor. Geometrical factors can be obtained from handbook solutions or, for complicated cases, through finite element simulations. Carefully defining the geometrical factor with realistic boundary conditions is vital to obtain accurate values for the stress intensity factor. For fatigue life predictions, even a small error in the stress intensity factor may get amplified as the total fatigue life is computed through integration over thousands of crack growth increments. A commonly used specimen geometry for fatigue crack growth testing is the single-edge cracked specimen. For such a specimen, the crack on one side of the geometry introduces bending, which, to some degree, is constrained by the grips that hold the specimen in the testing rig. The effect of bending on the geometrical factor, and consequently on the stress intensity factor, is generally overlooked due to the assumption that the test rig grips are infinitely stiff. Not considering the bending effects could lead to an inaccurate evaluation of the stress intensity factor, especially for long crack lengths. This work investigated the effect of bending on the stress intensity factor for a single-edge cracked specimen. Different grip dimensions were studied to understand the degree of bending and its impact on the stress intensity factor. The work resulted in recommendations for accurately evaluating the stress intensity factor for single-edge cracked specimens.

  • 27.
    Azeez, Ahmed
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Leidermark, Daniel
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Segersäll, Mikael
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Eriksson, Robert
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Numerical prediction of warm pre-stressing effects for a steam turbine steel2023In: Theoretical and applied fracture mechanics (Print), ISSN 0167-8442, E-ISSN 1872-7638, Vol. 125, article id 103940Article in journal (Refereed)
    Abstract [en]

    In warm pre-stressing (WPS), the fracture resistance of cracked steel components is raised when subjected to certain temperature-load histories. WPS’s beneficial effects enhance safety margins and potentially prolong fatigue life. However, understanding and predicting the WPS effects is crucial for employing such benefits. This study utilised pre-cracked compact tension specimens made from steam turbine steel for WPS and baseline fracture toughness testing. Two typical WPS cycles were investigated (L-C-F and L-U-C-F), and an increase in fracture resistance was observed for both cycles. The WPS tests were simulated using finite element analysis to understand its effects and predict the increase in fracture resistance. A local approach was followed based on accumulative plastic strain magnitude ahead of the crack tip. Since cleavage fracture is triggered by active plasticity, the WPS fracture is assumed when accumulated plasticity exceeds the residual plastic zone formed at the crack tip due to the initial pre-load.

    Download full text (pdf)
    fulltext
  • 28.
    Azeez, Ahmed
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Norman, Viktor
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Eriksson, Robert
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Leidermark, Daniel
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Out-of-phase thermomechanical fatigue crack propagation in a steam turbine steel — modelling of crack closure2021In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 149, article id 106251Article in journal (Refereed)
    Abstract [en]

    Understanding of crack growth behaviour is necessary to predict accurate fatigue lives. Out-of-phase thermomechanical fatigue crack propagation tests were performed on FB2 steel used in high-temperature steam turbine sections. Testing results showed crack closure where the compressive part of the fatigue cycle affected crack growth rate. Crack closing stress was observed to be different, and had more influence on the growth rate, than crack opening stress. Crack growth rate was largely controlled by the minimum temperature of the cycle, which agreed with an isothermal crack propagation test. Finite element models with stationary sharp cracks captured the crack closure behaviour.

    Download full text (pdf)
    fulltext
  • 29.
    Benselfelt, Tobias
    et al.
    Department of Fiber Technology, KTH, Stockholm, Sweden.
    Nordenström, Malin
    Department of Fiber Technology, KTH, Stockholm, Sweden.
    Lindström, Stefan B
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Wågberg, Lars
    Department of Fiber Technology, KTH, Stockholm, Sweden.
    Explaining the Exceptional Wet Integrity of Transparent Cellulose Nanofibril Films in the Presence of Multivalent Ions: Suitable Substrates for Biointerfaces2019In: Advanced Materials Interfaces, ISSN 2196-7350, Vol. 13, no 6, article id 1900333Article in journal (Refereed)
    Abstract [en]

    Cellulose nanofibrils (CNFs) assemble into water‐resilient materials in the presence of multivalent counter‐ions. The essential mechanisms behind these assemblies are ion–ion correlation and specific ion effects. A network model shows that the interfibril attraction indirectly influences the wet modulus by a fourth power relationship to the solidity of the network (Ew ∝ φ4). Ions that induce both ion–ion correlation and specific ion effects significantly reduce the swelling of the films, and due to the nonlinear relationship dramatically increase the wet modulus. Herein, this network model is used to explain the elastoplastic behavior of wet films of 2,2,6,6‐tetramethylpiperidine‐1‐oxyl radical (TEMPO)‐oxidized, carboxymethylated, and phosphorylated CNFs in the presence of different counter‐ions. The main findings are that the aspect ratio of the CNFs influences the ductility of the assemblies, that the bivalency of phosphorylate ligands probably limits the formation of interfibril complexes with divalent ions, and that a higher charge density increases the friction between fibrils by increasing the short‐range attraction from ion–ion correlation and specific ion effects. These findings can be used to rationally design CNF materials for a variety of applications where wet strength, ductility, and transparency are important, such as biomaterials or substrates for bioelectronics.

  • 30.
    Benselfelt, Tobias
    et al.
    KTH Royal Inst Technol, Sweden.
    Shakya, Jyoti
    KTH Royal Inst Technol, Sweden.
    Rothemund, Philipp
    Max Planck Inst Intelligent Syst, Germany.
    Lindström, Stefan
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Piper, Andrew
    KTH Royal Inst Technol, Sweden.
    Winkler, Thomas E.
    Tech Univ Carolo Wilhelmina Braunschweig, Germany; Tech Univ Carolo Wilhelmina Braunschweig, Germany.
    Hajian, Alireza
    KTH Royal Inst Technol, Sweden.
    Wagberg, Lars
    KTH Royal Inst Technol, Sweden.
    Keplinger, Christoph
    Max Planck Inst Intelligent Syst, Germany; Univ Colorado, CO 80309 USA; Univ Colorado, CO 80309 USA.
    Hamedi, Mahiar Max
    KTH Royal Inst Technol, Sweden.
    Electrochemically Controlled Hydrogels with Electrotunable Permeability and Uniaxial Actuation2023In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 35, no 45, article id 2303255Article in journal (Refereed)
    Abstract [en]

    The unique properties of hydrogels enable the design of life-like soft intelligent systems. However, stimuli-responsive hydrogels still suffer from limited actuation control. Direct electronic control of electronically conductive hydrogels can solve this challenge and allow direct integration with modern electronic systems. An electrochemically controlled nanowire composite hydrogel with high in-plane conductivity that stimulates a uniaxial electrochemical osmotic expansion is demonstrated. This materials system allows precisely controlled shape-morphing at only -1 V, where capacitive charging of the hydrogel bulk leads to a large uniaxial expansion of up to 300%, caused by the ingress of & AP;700 water molecules per electron-ion pair. The material retains its state when turned off, which is ideal for electrotunable membranes as the inherent coupling between the expansion and mesoporosity enables electronic control of permeability for adaptive separation, fractionation, and distribution. Used as electrochemical osmotic hydrogel actuators, they achieve an electroactive pressure of up to 0.7 MPa (1.4 MPa vs dry) and a work density of & AP;150 kJ m-3 (2 MJ m-3 vs dry). This new materials system paves the way to integrate actuation, sensing, and controlled permeation into advanced soft intelligent systems. The unique properties of hydrogels enable the design of life-like soft intelligent systems. This work demonstrates how the swelling of hydrogels from cellulose nanofibrils and carbon nanotubes can be electrochemically controlled to achieve electrochemical osmotic actuation. This new materials system paves the way for integrated actuation, sensing, and controlled permeation in electrotunable separation membranes or soft actuators.image

    Download full text (pdf)
    fulltext
  • 31.
    Berglund, Martina
    et al.
    Linköping University, Department of Management and Engineering, Logistics & Quality Management. Linköping University, Faculty of Science & Engineering.
    Andersson, Torbjörn
    Linköping University, Department of Management and Engineering, Machine Design. Linköping University, Faculty of Science & Engineering.
    Hedbrant, Johan
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, Faculty of Science & Engineering.
    Pavlasevic, Vanja
    Linköping University, Department of Management and Engineering, Machine Design. Linköping University, Faculty of Science & Engineering.
    Stålhand, Jonas
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Understanding the user beyond ‘common sense’ – teaching Product Ergonomics to design engineering students2015In: Proceedings 19th Triennial Congress of the IEA, International Ergonomics Association , 2015Conference paper (Refereed)
    Abstract [en]

    Multidisciplinary frameworks are needed to develop products that fit the human. Ergonomics is a multifaceted field that encompasses physical, cognitive and organizational aspects, and it is therefore a suitable subject to be taught to design engineering students.

    The objective of this paper was to describe and reflect upon how a systems perspective on Ergonomics is developed and conveyed in a course in Product Ergonomics to engineering students at the Design and Product Development (DPD) programme at Linköping University, Sweden. The paper is based on the authors’ experiences from teaching the course in Product Ergonomicsas well ason 52 students’ written reflections about their view on Ergonomics before and after taking the course.

    Means and ideas for teaching Ergonomics with a systems perspective included organizing a theoretical introduction into weekly themes and thereafter integrating and applying these themes in a product concept project under supervision of a multidisciplinary teacher team.

    The paper also reflects on how the systems perspective of Ergonomics is planned for and realized in the intended, implemented and attained curriculum.

  • 32.
    Berglund, Martina
    et al.
    Linköping University, Department of Management and Engineering, Logistics & Quality Management. Linköping University, Faculty of Science & Engineering.
    Pavlasevic, Vanja
    Linköping University, Department of Management and Engineering, Machine Design. Linköping University, Faculty of Science & Engineering.
    Andersson, Torbjörn
    Linköping University, Department of Management and Engineering, Machine Design. Linköping University, Faculty of Science & Engineering.
    Hedbrant, Johan
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, Faculty of Science & Engineering.
    Stålhand, Jonas
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Theme-based assessment of education in design and product development2014In: Proceedings of the 10th International CDIO Conference, Universitat Politècnica de Catalunya, 2014Conference paper (Other academic)
    Abstract [en]

    One fundamental challenge in choosing an examination form to assess student achievements is to find an examination which, both encourages students to continuously elaborate the course content and constitutes a learning process itself. The objective of this paper is to share and reflect on the development and implementation of a new theme-based examination in a six credit course in Product Ergonomics given in the engineering programme Design and Product Development at Linköping University, Sweden. The course runs during four months and has two parts: one theoretical and one applied. The former focuses on theoretical ergonomic topics, models and methods while the latter is a project aiming at consolidating the students’ understanding of the theory by implementing the knowledge in a product development case. To encourage the students to adapt a deep learning approach, the traditional written mid-term exam for the theoretical part was abandoned and another concept developed. In the new concept, the theoretical part was split onto six weekly themes. Each theme was introduced at the beginning of the week by high-lighting main theories and models followed by a group-work assignment to be elaborated on by the students during the week. The theme was examined at the end of the week through a short written exam and a seminar to discuss and reflect upon the theme. From a student perspective, the positive outcome of the theme-based examination was peer learning and a more active learning style. The students appreciated the theme-based structure of the course. Occasionally, some students commented that weekly examinations could be perceived as stressful. The teachers perceived the students to be more acquainted with ergonomics theory and methods which increased the quality of the course project. The reported theme-based assessment is one example of implementing among others the CDIO syllabus parts 2.2 and 3.1and CDIO standards 8 and 11.

  • 33.
    Blomgren, Gustav
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics.
    Carlsson, Ebba
    Linköping University, Department of Management and Engineering, Solid Mechanics.
    Structural responses due to underwater detonations: Validation of explosion modelling methods using LS-DYNA2023Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Modelling the full event of an underwater explosion (UNDEX) is complex and requires advanced modelling methods in order to achieve accurate responses. The process of an UNDEX includes a series of events that has to be considered. When a detonation is initiated, a shock-wave propagates and the rest products from the explosive material creates a gaseous bubble with high pressure which pulsates and impacts the surroundings. Reflections of the initial shock-wave can also appear if it hits the sea floor, water surface or other obstacles.

    There are different approaches how to numerically model the impact of an UNDEX on a structure, some with analytical approaches without a water domain and others where a water domain has to be modelled. This master’s thesis focuses on two modelling methods that are available in the finite element software LS-DYNA. The simpler method is called Sub-Sea Analysis (SSA) and does not require a water domain, thus it can be beneficial to use in an early design stage, or when only approximated responses are desired. To increase the accuracy, a more complex method called S-ALE can be used. By implementing this method, the full process of an UNDEX can be studied since both the fluid domain and explosive material are meshed. These methods are studied separately together with a combination of them.

    Another important aspect to be considered is that oscillations of a structure submerged in water differs from the behavior it has in air. Depending on the numerical method used, the impact of the water can be included. Natural frequencies of structures submerged in water are studied, how it changes and how the methods takes this into account.

    To verify the numerical models, experiments were executed with a cylindrical test object where the distance and weight of charge were altered through out the test series. It was found that multiple aspects affects the results from the experiments, that are not captured in the numerical models. These aspects have for instance to do with reflections, how accurate the test object is modelled and the damping effects of the water.

    It is concluded that the numerical models are sensitive when small charges and fragile structures are studied. High frequency oscillations were not triggered in the experiment but found for both methods. It should be further investigated if the methods are more accurate for larger charges and stronger structures. Experiments with larger water domain would also be beneficial to reduce effects from reflections, as well as a more accurate model of the cylinder in the simulations.

    Download full text (pdf)
    fulltext
  • 34. Order onlineBuy this publication >>
    Busse, Christian
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Aspects of Crack Growth in Single-Crystal Nickel-Base Superalloys2017Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    This Licentiate of Engineering thesis is a product of the results generated in the research project KME-702, which comprises modelling, microstructure investigations and material testing of cast nickel-base superalloys.

    The main objective of this work is to model the fatigue crack propagation behaviour in single-crystal nickel-base superalloys. To achieve this, the influence of the crystal orientations on the cracking behaviour is assessed. The results show that the crystal orientation is strongly affecting the material response and must be accounted for. Furthermore, a linear elastic crack driving force parameter suitable for describing crystallographic cracking has been developed. This parameter is based on resolved anisotropic stress intensity factors and is able to predict the correct crystallographic cracking plane after a transition from a Mode I crack. Finally, a method to account for inelastic deformations in a linear elastic fracture mechanics context was investigated. A residual stress field is extracted from an uncracked finite-element model with a perfectly plastic material model and superimposed on the stress field from the cracked model with a linear elastic material model to account for the inelastic deformations during the determination of the crack driving force. The modelling work is validated by material testing on two different specimen geometries at different temperatures.

    This Licentiate of Engineering thesis consists of two parts, where Part I gives an introduction and background to the research area, while Part II consists of three papers.

    List of papers
    1. A FINITE ELEMENT STUDY OF THE EFFECT OF CRYSTAL ORIENTATION AND MISALIGNMENT ON THE CRACK DRIVING FORCE IN A SINGLE-CRYSTAL SUPERALLOY
    Open this publication in new window or tab >>A FINITE ELEMENT STUDY OF THE EFFECT OF CRYSTAL ORIENTATION AND MISALIGNMENT ON THE CRACK DRIVING FORCE IN A SINGLE-CRYSTAL SUPERALLOY
    Show others...
    2016 (English)In: PROCEEDINGS OF THE ASME TURBO EXPO: TURBINE TECHNICAL CONFERENCE AND EXPOSITION, 2016, VOL 7A, AMER SOC MECHANICAL ENGINEERS , 2016, no UNSP V07AT28A002Conference paper, Published paper (Refereed)
    Abstract [en]

    The elastic and plastic anisotropy of the single-crystal materials bring many difficulties in terms of modeling, evaluation and prediction of fatigue crack growth. In this paper a single-crystal material model has been adopted to a finite element-environment, which is paired with a crack growth tool. All simulations are performed in a three-dimensional context. This methodology makes it possible to analyze complex finite element-models, which are more application-near than traditional two-dimensional models. The influence of the crystal orientation, as well as the influence of misalignments of the crystal orientation due to the casting process are investigated. It is shown that both the crystal orientation and the misalignment from the ideal crystal orientation are important for the crack driving force. The realistic maximum limit of 10 degrees misalignment is considered. It can be seen that crack growth behavior is highly influenced by the misalignment. This knowledge is of great interest for the industry in order to evaluate the crack growth in single-crystal components more accurately.

    Place, publisher, year, edition, pages
    AMER SOC MECHANICAL ENGINEERS, 2016
    National Category
    Applied Mechanics
    Identifiers
    urn:nbn:se:liu:diva-132570 (URN)10.1115/GT2016-56305 (DOI)000385461600011 ()978-0-7918-4983-5 (ISBN)
    Conference
    ASME Turbo Expo: Turbine Technical Conference and Exposition
    Available from: 2016-11-14 Created: 2016-11-14 Last updated: 2019-11-19
    2. Three-Dimensional LEFM Prediction of Fatigue Crack Propagation in a Gas Turbine Disk Material at Component Near Conditions
    Open this publication in new window or tab >>Three-Dimensional LEFM Prediction of Fatigue Crack Propagation in a Gas Turbine Disk Material at Component Near Conditions
    Show others...
    2016 (English)In: Journal of engineering for gas turbines and power, ISSN 0742-4795, E-ISSN 1528-8919, Vol. 138, no 4, article id 042506Article in journal (Refereed) Published
    Abstract [en]

    In this paper, the possibility to use linear elastic fracture mechanics (LEFM), with and without a superimposed residual stress field, to predict fatigue crack propagation in the gas turbine disk material Inconel 718 has been studied. A temperature of 400 degrees C and applied strain ranges corresponding to component near conditions have been considered. A three-dimensional crack propagation software was used for determining the stress intensity factors (SIFs) along the crack path. In the first approach, a linear elastic material behavior was used when analyzing the material response. The second approach extracts the residual stresses from an uncracked model with perfectly plastic material behavior after one loading cycle. As a benchmark, the investigated methods are compared to experimental tests, where the cyclic lifetimes were calculated by an integration of Paris law. When comparing the results, it can be concluded that the investigated approaches give good results, at least for longer cracks, even though plastic flow was taking place in the specimen. The pure linear elastic simulation overestimates the crack growth for all crack lengths and gives conservative results over all considered crack lengths. Noteworthy with this work is that the 3D-crack propagation could be predicted with the two considered methods in an LEFM context, although plastic flow was present in the specimens during the experiments.

    Place, publisher, year, edition, pages
    ASME, 2016
    National Category
    Mechanical Engineering
    Identifiers
    urn:nbn:se:liu:diva-126240 (URN)10.1115/1.4031526 (DOI)000371125800020 ()
    Note

    Funding Agencies|Siemens Industrial Turbomachinery AB through Research Consortium of Materials Technology for Thermal Energy Processes [KME-702]; Swedish Energy Agency

    Available from: 2016-03-21 Created: 2016-03-21 Last updated: 2019-11-19
    Download full text (pdf)
    Aspects of Crack Growth in Single-Crystal Nickel-Base Superalloys
    Download (pdf)
    omslag
    Download (png)
    presentationsbild
  • 35.
    Busse, Christian
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Modelling of Crack Growth in Single-Crystal Nickel-Base Superalloys2019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This dissertation was produced at the Division of Solid Mechanics at Linköping University and is part of a research project, which comprises modelling, microstructure investigations and material testing of cast nickel-base superalloys. The main objective of this work was to deepen the understanding of the fracture behaviour of single-crystal nickel-base superalloys and to develop a model to predict the fatigue crack growth behaviour. Frequently, crack growth in these materials has been observed to follow one of two distinct cracking modes; Mode I like cracking perpendicular to the loading direction or crystallographic crack growth on the octahedral {111}-planes, where the latter is associated with an increased fatigue crack growth rate. Thus, it is of major importance to account for this behaviour in component life prediction. Consequently, a model for the prediction of the transition of cracking modes and the correct active crystallographic plane, i.e. the crack path, and the crystallographic crack growth rate has been developed. This model is based on the evaluation of appropriate crack driving forces using three-dimensional finite-element simulations. A special focus was given towards the influence of the crystallographic orientation on the fracture behaviour. Further, a model to incorporate residual stresses in the crack growth modelling is presented. All modelling work is calibrated and validated by experiments on different specimen geometries with different crystallographic orientations. This dissertation consists of two parts, where Part I gives an introduction and background to the field of research, while Part II consists of six appended papers.

    List of papers
    1. A FINITE ELEMENT STUDY OF THE EFFECT OF CRYSTAL ORIENTATION AND MISALIGNMENT ON THE CRACK DRIVING FORCE IN A SINGLE-CRYSTAL SUPERALLOY
    Open this publication in new window or tab >>A FINITE ELEMENT STUDY OF THE EFFECT OF CRYSTAL ORIENTATION AND MISALIGNMENT ON THE CRACK DRIVING FORCE IN A SINGLE-CRYSTAL SUPERALLOY
    Show others...
    2016 (English)In: PROCEEDINGS OF THE ASME TURBO EXPO: TURBINE TECHNICAL CONFERENCE AND EXPOSITION, 2016, VOL 7A, AMER SOC MECHANICAL ENGINEERS , 2016, no UNSP V07AT28A002Conference paper, Published paper (Refereed)
    Abstract [en]

    The elastic and plastic anisotropy of the single-crystal materials bring many difficulties in terms of modeling, evaluation and prediction of fatigue crack growth. In this paper a single-crystal material model has been adopted to a finite element-environment, which is paired with a crack growth tool. All simulations are performed in a three-dimensional context. This methodology makes it possible to analyze complex finite element-models, which are more application-near than traditional two-dimensional models. The influence of the crystal orientation, as well as the influence of misalignments of the crystal orientation due to the casting process are investigated. It is shown that both the crystal orientation and the misalignment from the ideal crystal orientation are important for the crack driving force. The realistic maximum limit of 10 degrees misalignment is considered. It can be seen that crack growth behavior is highly influenced by the misalignment. This knowledge is of great interest for the industry in order to evaluate the crack growth in single-crystal components more accurately.

    Place, publisher, year, edition, pages
    AMER SOC MECHANICAL ENGINEERS, 2016
    National Category
    Applied Mechanics
    Identifiers
    urn:nbn:se:liu:diva-132570 (URN)10.1115/GT2016-56305 (DOI)000385461600011 ()978-0-7918-4983-5 (ISBN)
    Conference
    ASME Turbo Expo: Turbine Technical Conference and Exposition
    Available from: 2016-11-14 Created: 2016-11-14 Last updated: 2019-11-19
    2. Prediction of crystallographic cracking planes in single-crystal nickel-base superalloys
    Open this publication in new window or tab >>Prediction of crystallographic cracking planes in single-crystal nickel-base superalloys
    Show others...
    2018 (English)In: Engineering Fracture Mechanics, ISSN 0013-7944, E-ISSN 1873-7315, Vol. 196, p. 206-223Article in journal (Refereed) Published
    Abstract [en]

    The inherent anisotropy of single-crystal nickel-base superalloys brings many difficulties in terms of modelling, evaluation and prediction of fatigue crack growth. Two models to predict on which crystallographic plane cracking will occur is presented. The models are based on anisotropic stress intensity factors resolved on crystallographic slip planes calculated in a three-dimensional finite-element context. The developed models have been compared to experiments on two different test specimen geometries. The results show that a correct prediction of the crystallographic cracking plane can be achieved. This knowledge is of great interest for the industry and academia to better understand and predict crack growth in single-crystal materials.

    Place, publisher, year, edition, pages
    Elsevier, 2018
    Keywords
    Single-crystal nickel-base superalloys; Anisotropy; Fracture mechanics; Stress intensity factor; Crystallographic cracking
    National Category
    Applied Mechanics
    Identifiers
    urn:nbn:se:liu:diva-148380 (URN)10.1016/j.engfracmech.2018.04.047 (DOI)000432704300014 ()
    Note

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

    Available from: 2018-06-15 Created: 2018-06-15 Last updated: 2019-11-19
    3. Evaluation of the crystallographic fatigue crack growth rate in a single-crystal nickel-base superalloy
    Open this publication in new window or tab >>Evaluation of the crystallographic fatigue crack growth rate in a single-crystal nickel-base superalloy
    Show others...
    2019 (English)In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 127, p. 259-267Article in journal (Refereed) Published
    Abstract [en]

    Cracks in single-crystal nickel-base superalloys have been observed to switch cracking mode from Mode I to crystallographic cracking. The crack propagation rate is usually higher on the crystallographic planes compared to Mode I, which is important to account for in crack growth life predictions. In this paper, a method to evaluate the crystallographic fatigue crack growth rate, based on a previously developed crystallographic crack driving force parameter, is presented. The crystallographic crack growth rate was determined by evaluating heat tints on the fracture surfaces of the test specimens from the experiments. Complicated crack geometries including multiple crystallographic crack fronts were modelled in a three dimensional finite element context, The data points of the crystallographic fatigue crack growth rate collapse on a narrow scatter band for the crystallographic cracks indicating a correlation with the previously developed crystallographic crack driving force.

    Place, publisher, year, edition, pages
    ELSEVIER SCI LTD, 2019
    Keywords
    Single-crystal nickel-base superalloys; Finite element analysis; Fracture mechanics; Stress intensity factor; Crystallographic cracking; Fatigue crack growth rate
    National Category
    Applied Mechanics
    Identifiers
    urn:nbn:se:liu:diva-160388 (URN)10.1016/j.ijfatigue.2019.05.023 (DOI)000482492600024 ()
    Note

    Funding Agencies|Linkoping University; Siemens Industrial Turbomachinery AB

    Available from: 2019-09-23 Created: 2019-09-23 Last updated: 2021-05-24
    4. Three-Dimensional LEFM Prediction of Fatigue Crack Propagation in a Gas Turbine Disk Material at Component Near Conditions
    Open this publication in new window or tab >>Three-Dimensional LEFM Prediction of Fatigue Crack Propagation in a Gas Turbine Disk Material at Component Near Conditions
    Show others...
    2016 (English)In: Journal of engineering for gas turbines and power, ISSN 0742-4795, E-ISSN 1528-8919, Vol. 138, no 4, article id 042506Article in journal (Refereed) Published
    Abstract [en]

    In this paper, the possibility to use linear elastic fracture mechanics (LEFM), with and without a superimposed residual stress field, to predict fatigue crack propagation in the gas turbine disk material Inconel 718 has been studied. A temperature of 400 degrees C and applied strain ranges corresponding to component near conditions have been considered. A three-dimensional crack propagation software was used for determining the stress intensity factors (SIFs) along the crack path. In the first approach, a linear elastic material behavior was used when analyzing the material response. The second approach extracts the residual stresses from an uncracked model with perfectly plastic material behavior after one loading cycle. As a benchmark, the investigated methods are compared to experimental tests, where the cyclic lifetimes were calculated by an integration of Paris law. When comparing the results, it can be concluded that the investigated approaches give good results, at least for longer cracks, even though plastic flow was taking place in the specimen. The pure linear elastic simulation overestimates the crack growth for all crack lengths and gives conservative results over all considered crack lengths. Noteworthy with this work is that the 3D-crack propagation could be predicted with the two considered methods in an LEFM context, although plastic flow was present in the specimens during the experiments.

    Place, publisher, year, edition, pages
    ASME, 2016
    National Category
    Mechanical Engineering
    Identifiers
    urn:nbn:se:liu:diva-126240 (URN)10.1115/1.4031526 (DOI)000371125800020 ()
    Note

    Funding Agencies|Siemens Industrial Turbomachinery AB through Research Consortium of Materials Technology for Thermal Energy Processes [KME-702]; Swedish Energy Agency

    Available from: 2016-03-21 Created: 2016-03-21 Last updated: 2019-11-19
    Download full text (pdf)
    Modelling of Crack Growth in Single-Crystal Nickel-Base Superalloys
    Download (jpg)
    presentationsbild
  • 36.
    Busse, Christian
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Gustafsson, D.
    Siemens Ind Turbomachinery AB, Sweden.
    Palmert, Frans
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Sjodin, B.
    Siemens Ind Turbomachinery AB, Sweden.
    Almroth, P.
    Siemens Ind Turbomachinery AB, Sweden.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Simonsson, Kjell
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Leidermark, Daniel
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Criteria evaluation for the transition of cracking modes in a single-crystal nickel-base superalloy2020In: Theoretical and applied fracture mechanics (Print), ISSN 0167-8442, E-ISSN 1872-7638, Vol. 106, article id 102453Article in journal (Refereed)
    Abstract [en]

    Single-crystal nickel-base superalloys frequently experience two distinct fatigue crack growth modes. It has been observed that, under certain conditions, cracks transition from a path perpendicular to the loading direction to a crystallographic slip plane. As crystallographic cracking is associated with an increased fatigue crack growth rate, it is important to be able to predict when this transition occurs. In this work three different criteria for crystallographic cracking based on resolved anisotropic stress intensity factors are evaluated in a three-dimensional finite element context. The criteria were calibrated and evaluated using isothermal fatigue experiments on two different specimen geometries. It is suggested by the results, that a threshold value of a resolved shear stress intensity factor can act as a conservative criterion indicating cracking mode transition. Further, a trend hinting towards a loading frequency dependency could be observed.

    Download full text (pdf)
    fulltext
  • 37.
    Busse, Christian
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Gustafsson, David
    Siemens Ind Turbomachinery AB, Sweden.
    Rasmusson, Patrik
    Siemens Ind Turbomachinery AB, Sweden.
    Sjodin, Bjorn
    Siemens Ind Turbomachinery AB, Sweden.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Simonsson, Kjell
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Leidermark, Daniel
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Three-Dimensional LEFM Prediction of Fatigue Crack Propagation in a Gas Turbine Disk Material at Component Near Conditions2016In: Journal of engineering for gas turbines and power, ISSN 0742-4795, E-ISSN 1528-8919, Vol. 138, no 4, article id 042506Article in journal (Refereed)
    Abstract [en]

    In this paper, the possibility to use linear elastic fracture mechanics (LEFM), with and without a superimposed residual stress field, to predict fatigue crack propagation in the gas turbine disk material Inconel 718 has been studied. A temperature of 400 degrees C and applied strain ranges corresponding to component near conditions have been considered. A three-dimensional crack propagation software was used for determining the stress intensity factors (SIFs) along the crack path. In the first approach, a linear elastic material behavior was used when analyzing the material response. The second approach extracts the residual stresses from an uncracked model with perfectly plastic material behavior after one loading cycle. As a benchmark, the investigated methods are compared to experimental tests, where the cyclic lifetimes were calculated by an integration of Paris law. When comparing the results, it can be concluded that the investigated approaches give good results, at least for longer cracks, even though plastic flow was taking place in the specimen. The pure linear elastic simulation overestimates the crack growth for all crack lengths and gives conservative results over all considered crack lengths. Noteworthy with this work is that the 3D-crack propagation could be predicted with the two considered methods in an LEFM context, although plastic flow was present in the specimens during the experiments.

  • 38.
    Busse, Christian
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Loureiro Homs, Jordi
    Siemens Ind Turbomachinery AB, Sweden.
    Gustafsson, David
    Siemens Ind Turbomachinery AB, Sweden.
    Palmert, Frans
    Siemens Ind Turbomachinery AB, Sweden.
    Sjodin, Bjorn
    Siemens Ind Turbomachinery AB, Sweden.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Simonsson, Kjell
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Leidermark, Daniel
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    A FINITE ELEMENT STUDY OF THE EFFECT OF CRYSTAL ORIENTATION AND MISALIGNMENT ON THE CRACK DRIVING FORCE IN A SINGLE-CRYSTAL SUPERALLOY2016In: PROCEEDINGS OF THE ASME TURBO EXPO: TURBINE TECHNICAL CONFERENCE AND EXPOSITION, 2016, VOL 7A, AMER SOC MECHANICAL ENGINEERS , 2016, no UNSP V07AT28A002Conference paper (Refereed)
    Abstract [en]

    The elastic and plastic anisotropy of the single-crystal materials bring many difficulties in terms of modeling, evaluation and prediction of fatigue crack growth. In this paper a single-crystal material model has been adopted to a finite element-environment, which is paired with a crack growth tool. All simulations are performed in a three-dimensional context. This methodology makes it possible to analyze complex finite element-models, which are more application-near than traditional two-dimensional models. The influence of the crystal orientation, as well as the influence of misalignments of the crystal orientation due to the casting process are investigated. It is shown that both the crystal orientation and the misalignment from the ideal crystal orientation are important for the crack driving force. The realistic maximum limit of 10 degrees misalignment is considered. It can be seen that crack growth behavior is highly influenced by the misalignment. This knowledge is of great interest for the industry in order to evaluate the crack growth in single-crystal components more accurately.

  • 39.
    Busse, Christian
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Palmert, Frans
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Sjodin, B.
    Siemens Ind Turbomachinery AB, Sweden.
    Almroth, P.
    Siemens Ind Turbomachinery AB, Sweden.
    Gustafsson, D.
    Siemens Ind Turbomachinery AB, Sweden.
    Simonsson, Kjell
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Leidermark, Daniel
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Evaluation of the crystallographic fatigue crack growth rate in a single-crystal nickel-base superalloy2019In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 127, p. 259-267Article in journal (Refereed)
    Abstract [en]

    Cracks in single-crystal nickel-base superalloys have been observed to switch cracking mode from Mode I to crystallographic cracking. The crack propagation rate is usually higher on the crystallographic planes compared to Mode I, which is important to account for in crack growth life predictions. In this paper, a method to evaluate the crystallographic fatigue crack growth rate, based on a previously developed crystallographic crack driving force parameter, is presented. The crystallographic crack growth rate was determined by evaluating heat tints on the fracture surfaces of the test specimens from the experiments. Complicated crack geometries including multiple crystallographic crack fronts were modelled in a three dimensional finite element context, The data points of the crystallographic fatigue crack growth rate collapse on a narrow scatter band for the crystallographic cracks indicating a correlation with the previously developed crystallographic crack driving force.

    Download full text (pdf)
    fulltext
  • 40.
    Busse, Christian
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Palmert, Frans
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Sjodin, B.
    Siemens Ind Turbomachinery AB, Sweden.
    Almroth, P.
    Siemens Ind Turbomachinery AB, Sweden.
    Gustafsson, D.
    Siemens Ind Turbomachinery AB, Sweden.
    Simonsson, Kjell
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Leidermark, Daniel
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Prediction of crystallographic cracking planes in single-crystal nickel-base superalloys2018In: Engineering Fracture Mechanics, ISSN 0013-7944, E-ISSN 1873-7315, Vol. 196, p. 206-223Article in journal (Refereed)
    Abstract [en]

    The inherent anisotropy of single-crystal nickel-base superalloys brings many difficulties in terms of modelling, evaluation and prediction of fatigue crack growth. Two models to predict on which crystallographic plane cracking will occur is presented. The models are based on anisotropic stress intensity factors resolved on crystallographic slip planes calculated in a three-dimensional finite-element context. The developed models have been compared to experiments on two different test specimen geometries. The results show that a correct prediction of the crystallographic cracking plane can be achieved. This knowledge is of great interest for the industry and academia to better understand and predict crack growth in single-crystal materials.

    Download full text (pdf)
    fulltext
  • 41.
    Busse, Christian
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Palmert, Frans
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering. Siemens Ind Turbomachinery AB, Sweden.
    Wawrzynek, Paul
    Fracture Anal Consultants Inc, NY USA.
    Sjodin, Bjorn
    Siemens Ind Turbomachinery AB, Sweden.
    Gustafsson, David
    Siemens Ind Turbomachinery AB, Sweden.
    Leidermark, Daniel
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Crystallographic crack propagation rate in single-crystal nickel-base superalloys2018In: 12TH INTERNATIONAL FATIGUE CONGRESS (FATIGUE 2018), E D P SCIENCES , 2018, Vol. 165, article id 13012Conference paper (Refereed)
    Abstract [en]

    Single-crystal nickel-base superalloys are often used in the hot sections of gas turbines due to their good mechanical properties at high temperatures such as enhanced creep resistance. However, the anisotropic material properties of these materials bring many difficulties in terms of modelling and crack growth prediction. Cracks tend to switch cracking mode from Mode I cracking to crystallographic cracking. Crystallographic crack growth is often associated with a decrease in crack propagation life compared to Mode I cracking and this must be taken into account for reliable component lifing. In this paper a method to evaluate the crystallographic crack propagation rate related to a crystallographic crack driving force parameter is presented. The crystallographic crack growth rate is determined by an evaluation of heat tints on the fracture surface of a specimen subjected to fatigue loading. The complicated crack geometry including two crystallographic crack fronts is modelled in a three dimensional finite element context. The crack driving force parameter is determined by calculating anisotropic stress intensity factors along the two crystallographic crack fronts by finite-element simulations and post-processing the data in a fracture mechanics tool that resolves the stress intensity factors on the crystallographic slip planes in the slip directions. The evaluated crack propagation rate shows a good correlation for both considered crystallographic cracks fronts.

  • 42.
    Bysani, Sucheth Krishna Kumar
    Linköping University, Department of Management and Engineering, Solid Mechanics.
    Study of Diamond Folds in Mass-Impregnated(MI) Cables2021Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    High Voltage (HV) cables are designed to transmit electrical power from the source to the placewhere it is consumed. The global trend towards renewable energy sources e.g. wind farms, hy-droelectric and solar panels have led to an increase in the use of HV cables, as these sources aresituated in remote locations far from the areas where they are consumed. Therefore. there is aneed for developing efficient power transmission cables.Mass-impregnated (MI) cable is a type of HV cable which contains an electrical insulation layerof oil or mass impregnated cellulose paper. Due to its excellent dielectric properties, MI cableshas been established as a solution for high voltage electrical transmission system, which has beenused for several decades.The main area of interest in this thesis is the paper insulation in the MI cable. It is importantto ensure that the paper insulation structure is robust enough to avoid any formation of damageand/or defects due to excessive deformations during cable production, handling and installation,which might affect the overall electrical performance of the cable. During handling, the drylapped cable needs to be bent and unbent several times and there is a risk that the insulationwill develop voids due to structural defects, thereby reducing the dielectric capacity of the cable.An example of typical structural defects in MI cables is, so-called, diamond folds, i.e. a collec-tive buckling of several paper strips due to axial compressive load resembling a diamond shapedpattern.The goal of this thesis work is to contribute to the knowledge of the mechanism of diamond foldsin MI cable; the onset of diamond fold and post-buckling responses. The contributions from thecable design or production parameters are also studied. The analyses will be conducted usingnumerical simulation techniques and will be compared to results from characterization tests al-ready conducted in mechanics lab at NKT Technology consulting.The results of this thesis has given an insight about the effect of insulation design parameterssuch as registration, butt-gaps, coefficient of friction and number of layers, on the diamond foldbuckling behavior in an MI cable insulation. It is recommended that these parameters have tobe carefully controlled so as to avoid formation of diamond fold buckling in the insulation.

    Download full text (pdf)
    fulltext
  • 43.
    Calmunger, Mattias
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Chai, Guocai
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering. Sandvik Materials Technology, Sandviken, Sweden.
    Eriksson, Robert
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Moverare, Johan J.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Characterization of austenitic stainless steels deformed at elevated temperature2017In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 48A, no 10, p. 4525-4538Article in journal (Refereed)
    Abstract [en]

    Highly alloyed austenitic stainless steels are promising candidates to replace more expansive nickel-based alloys within the energy-producing industry. The present study investigates the deformation mechanisms by microstructural characterisation, mechanical properties and stress-strain response of three commercial austenitic stainless steels and two commercial nickel-based alloys using uniaxial tensile tests at elevated temperatures from 400 C up to 700 C. The materials showed different influence of temperature on ductility, where the ductility at elevated temperatures increased with increasing nickel and solid solution hardening element content. The investigated materials showed planar dislocation driven deformation at elevated temperature. Scanning electron microscopy showed that deformation twins were an active deformation mechanism in austenitic stainless steels during tensile deformation at elevated temperatures up to 700 C.

    Download full text (pdf)
    fulltext
  • 44.
    Calmunger, Mattias
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Eriksson, Robert
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Chai, Guocai
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Influence of Cyclic Oxidation in Moist Air on Surface Oxidation-Affected Zones2017Conference paper (Refereed)
  • 45.
    Calmunger, Mattias
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Eriksson, Robert
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Arts and Sciences. Linköping University, Faculty of Science & Engineering.
    Lindström, Thomas
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Leidermark, Daniel
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Effect of Additive Manufacturing on Fatigue Crack Propagation of a Gas Turbine Superalloy2019In: Procedia Structural Integrity, Elsevier, 2019, Vol. 23, p. 215-220Conference paper (Refereed)
  • 46.
    Czarnowski, Jan
    Linköping University, Department of Management and Engineering, Solid Mechanics.
    Strength testing based automatic scaling of muscle-tendon parameters for musculoskeletal models: An automated method of scaling subject specific muscle-tendon parameters of thigh muscles2022Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    A method of estimating subject specific muscle parameters of musculoskeletal models of elite athletes (skiers) was sought. Subject specific models are necessary due to large differences in general anatomy and physical performance of elite athletes relative the general population. Sought muscle parameters concern the force generating capabilities of muscles. The estimation was limited to only include the quadriceps-femoris and hamstring muscle groups due to these muscle having the highest influence on the performance of a skier. A modified interpretation of the method proposed by Heinen et al. [19] was implemented. The method includes experimental strength tests of knee extension and flexion muscles of a test subject, a musculoskeletal model of the experiments coupled with a mathematical optimisation minimisation formulation. The aim of the optimisation was to match the strength of a model to the experimentally obtained strength curve by minimising  error between the model and experimental results. The optimisation minimises the error between the model and the experimental data by varying the operating range and strength of the involved muscles. The musculo-tendon parameters are estimated through transformation equations, explicitly related to the design variables. Three healty and active males were involved in this study. An overall increase of the accuracy of the optimised model relative an unscaled reference model was observed, with the reduction of the objective function in a range of 80.2-92\% and a mean absolute error varying between 6.8 to 16.5 Nm. In the case of quadriceps-femoris muscles, the optimised model struggles with incorrect prediction of the peak torque and peak torque angle due to limitations of the muscle model and the distribution of the moment arm. The model predicts both peak torque and peak torque angle with high accuracy in the case of hamstring muscles. In addition, the model struggles with low precision for both knee extension and flexion for all of the involved test subjects. Although great improvement in the accuracy was observed, the model prediction was deemed to have low clinical significance, due too low accuracy and precision. The clinical significance could be improved, for example by a more detailed musculoskeletal model or by modifying the behaviour of the muscle model. Future work should focus on addressing the current issues presented in this study and a further development, as the method still is relatively new and untested. Parallelly, the researches should try to test the method in clinical studies, in order to evaluate the influence on the results by the implementation of this method of parameter estimation.

    Download full text (pdf)
    fulltext
  • 47.
    Daghighi, Abtin
    et al.
    Linköping University, Department of Clinical and Experimental Medicine, Division of Surgery, Orthopedics and Oncology. Linköping University, Faculty of Medicine and Health Sciences.
    Tropp, Hans
    Linköping University, Department of Clinical and Experimental Medicine, Division of Surgery, Orthopedics and Oncology. Linköping University, Faculty of Medicine and Health Sciences. Region Östergötland, Center for Surgery, Orthopaedics and Cancer Treatment, Department of Spinal Surgery.
    Dahlström, Nils
    Linköping University, Department of Medical and Health Sciences, Division of Radiological Sciences. Linköping University, Faculty of Medicine and Health Sciences. Region Östergötland, Center for Diagnostics, Department of Radiology in Linköping. Linköping University, Center for Medical Image Science and Visualization (CMIV).
    Klarbring, Anders
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    F.E.M. Stress-Investigation of Scolios Apex2018In: Open Biomedical Engineering Journal, E-ISSN 1874-1207, Vol. 12, p. 51-71Article in journal (Refereed)
    Abstract [en]

    In scoliosis, kypholordos and wedge properties of the vertebrae should be involved in determining how stress is distributed in the vertebral column. The impact is logically expected to be maximal at the apex.

    Download full text (pdf)
    fulltext
  • 48.
    Deng, Dunyong
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Eriksson, Robert
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    On the Dwell-Fatigue Crack Propagation Behavior of a High-Strength Ni-Base Superalloy Manufactured by Selective Laser Melting2020In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 51, p. 962-972Article in journal (Refereed)
    Abstract [en]

    This study focuses on the dwell-fatigue crack propagation behavior of IN718 manufactured via selective laser melting (SLM). The dwell-fatigue test condition is 823 K (550 with a long 2160-s dwell-holding period. Effects of heat treatment and loading direction on dwell-fatigue crack propagation rates are studied. A grain boundary delta precipitate seems to be slightly beneficial to the dwell-fatigue cracking resistance of SLM IN718. A comparison has been made between SLM IN718 and forged counterparts at different temperatures, indicating that a creep damage mechanism is likely dominant for SLM IN718 under the present test condition. A general discussion of the inferior creep resistance of SLM IN718 is also included. The anisotropic dwell-fatigue cracking resistance has also been studied and rationalized with the effective stress intensity factor calculated from finite element modeling.

    Download full text (pdf)
    fulltext
  • 49.
    Domeij Bäckryd, Rebecka
    et al.
    Linköping University, Faculty of Science & Engineering. Linköping University, Department of Management and Engineering, Solid Mechanics.
    Ryberg, Ann-Britt
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering. Combitech AB, Trollhättan, Sweden.
    Nilsson, Larsgunnar
    Linköping University, Faculty of Science & Engineering. Linköping University, Department of Management and Engineering, Solid Mechanics.
    Multidisciplinary design optimisation methods for automotive structures2017In: International Journal of Automotive and Mechanical Engineering, ISSN 2229-8649, Vol. 14, no 1, p. 4050-4067Article in journal (Refereed)
    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.

    Download full text (pdf)
    Multidisciplinary design optimisation methods for automotive structures
  • 50.
    Dümig, Patrick
    Linköping University, Department of Management and Engineering, Solid Mechanics.
    Transformation of In-Flight Measured Loads to a Fatigue Test Spectrum2022Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Fatigue is a well-recognized issue in lightweight and high-performance aircraft structures. As fatigue failures have led to serious accidents and caused significant economic impact in the past, design against fatigue is crucial. Fatigue testing of full-scale aircraft as well as components is an important tool for the advance identification of potential fatigue issues in both new and operational aircraft. Furthermore, coupon testing is used extensively to obtain allowables for materials and structural details to be used in the design process.

    To obtain accurate results from fatigue testing, not only the test object but also the used load spectrum must accurately represent reality. If the aircraft is operational, an accurate load spectrum can be obtained by measuring the loads in-flight during a sufficiently long period of normal operation of the aircraft. However, the in-flight measured loads data contains an extraordinarily large number of cycles, resulting in long and uneconomical test durations.

    This thesis aims to propose a method for the selection of an optimal filtering level for fatigue test spectra developed from in-flight measured loads. The thesis also discusses and recommends methods for in-flight measurement of loads, cycle counting as well as damage evaluation using a crack-growth approach. Furthermore, ways to validate the proposed method and its practical application are discussed.

    An example filtering study is conducted using four different specimens chosen to represent typical structural details of aircraft. The study uses real in-flight measured loads of a light aircraft and also discusses temperature compensation of the loads data. The effect of filtering on fatigue damage is evaluated using crack-growth simulations conducted at a range of filtering and stress levels. 

    The results show that a remarkable reduction of testing time is possible and as many as 99 % of all cycles in the studied flight load history can be discarded without significantly reducing fatigue damage. The allowable filtering level is shown to differ between the specimens and the different stages of fatigue crack growth. In addition, the applied stress level is found to have a consistent effect on the allowable filtering level.

    Download full text (pdf)
    Transformation of In-Flight Measured Loads to a Fatigue Test Spectrum
12345 1 - 50 of 242
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • oxford
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf