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  • 201.
    Spagnoli, A.
    et al.
    University of Parma, Italy.
    Terzano, M.
    University of Parma, Italy.
    Barber, J. R.
    University of Michigan, MI 48109 USA.
    Klarbring, Anders
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Non-linear programming in shakedown analysis with plasticity and friction2017Inngår i: Journal of the mechanics and physics of solids, ISSN 0022-5096, E-ISSN 1873-4782, Vol. 104, s. 71-83Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

    Fulltekst (pdf)
    fulltext
  • 202.
    Spinks, Geoffrey M.
    et al.
    Univ Wollongong, Australia.
    Bakarich, Shannon E.
    US Army, MD 20783 USA; Cornell Univ, NY 14850 USA.
    Aziz, Shazed
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Sensor- och aktuatorsystem. Linköpings universitet, Tekniska fakulteten.
    Salahuddin, Bidita
    Univ Wollongong, Australia.
    Xin, Hai
    Univ Wollongong, Australia.
    Using force-displacement relations to obtain actuation parameters from artificial muscles2019Inngår i: Sensors and Actuators A-Physical, ISSN 0924-4247, E-ISSN 1873-3069, Vol. 290, s. 90-96Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 203. Spånberg, Anders
    et al.
    Terio, Hikki
    Enberg, Anders
    Ask, Per
    Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik. Linköpings universitet, Tekniska högskolan.
    QUANTIFICATION OF URETHRAL FUNCTION BASED ON GRIFFITHS MODEL OF FLOW THROUGH ELASTIC TUBES1989Inngår i: Neurourology and Urodynamics, ISSN 0733-2467, E-ISSN 1520-6777, Vol. 8, nr 1, s. 29-52Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 204. Bestill onlineKjøp publikasjonen >>
    Storgärds, Erik
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    High Temperature Fatigue Crack Growth in a Ni-based Superalloy: Modelling Including the Interaction of Dwell Times2015Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

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

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

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

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

    Delarbeid
    1. High temperature fatigue crack growth behaviour of Inconel 718 under hold time and overload conditions
    Åpne denne publikasjonen i ny fane eller vindu >>High temperature fatigue crack growth behaviour of Inconel 718 under hold time and overload conditions
    2013 (engelsk)Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 48, s. 178-186Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

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

    sted, utgiver, år, opplag, sider
    Elsevier, 2013
    Emneord
    Nickel-base superalloys, fatigue crack propagation, Inconel 718, hold times, grain boundary embrittlement, crack propagation modelling, Finite Element modelling
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-85931 (URN)10.1016/j.ijfatigue.2012.10.018 (DOI)000315617500020 ()
    Tilgjengelig fra: 2013-03-13 Laget: 2012-12-03 Sist oppdatert: 2017-12-07bibliografisk kontrollert
    2. Modelling of high temperature fatigue crack growth in Inconel 718 under hold time conditions
    Åpne denne publikasjonen i ny fane eller vindu >>Modelling of high temperature fatigue crack growth in Inconel 718 under hold time conditions
    2013 (engelsk)Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 52, s. 124-130Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

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

    sted, utgiver, år, opplag, sider
    Elsevier, 2013
    Emneord
    Nickel-base superalloys, fatigue crack propagation, Inconel 718, hold times, grain boundary embrittlement, crack propagation modelling
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-85933 (URN)10.1016/j.ijfatigue.2013.03.004 (DOI)000318831300013 ()
    Tilgjengelig fra: 2012-12-03 Laget: 2012-12-03 Sist oppdatert: 2017-12-07bibliografisk kontrollert
    3. A load history dependent model for fatigue crack propagation in Inconel 718 under hold time conditions
    Åpne denne publikasjonen i ny fane eller vindu >>A load history dependent model for fatigue crack propagation in Inconel 718 under hold time conditions
    2014 (engelsk)Inngår i: Engineering Fracture Mechanics, ISSN 0013-7944, E-ISSN 1873-7315, Vol. 118, s. 17-30Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

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

    sted, utgiver, år, opplag, sider
    Elsevier, 2014
    Emneord
    Fatigue crack propagation, Inconel 718, Hold time effects, Crack growth modelling, Statistics
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-104809 (URN)10.1016/j.engfracmech.2014.02.005 (DOI)000334819600002 ()
    Tilgjengelig fra: 2014-02-27 Laget: 2014-02-27 Sist oppdatert: 2017-12-05bibliografisk kontrollert
    4. Modelling of fatigue crack growth in Inconel 718 under hold time conditions - application to a flight spectrum
    Åpne denne publikasjonen i ny fane eller vindu >>Modelling of fatigue crack growth in Inconel 718 under hold time conditions - application to a flight spectrum
    2014 (engelsk)Inngår i: Advanced Materials Research, ISSN 1662-8985, Vol. 891-892, s. 759-764Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

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

    sted, utgiver, år, opplag, sider
    Trans Tech Publications Inc., 2014
    Emneord
    Fatigue crack propagation, Inconel 718, Hold time effects, Crack growth modelling
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-104812 (URN)10.4028/www.scientific.net/AMR.891-892.759 (DOI)000337767700118 ()
    Tilgjengelig fra: 2014-02-27 Laget: 2014-02-27 Sist oppdatert: 2016-05-18bibliografisk kontrollert
    5. Crack Length Evaluation for Cyclic and Sustained Loading at High Temperature Using Potential Drop
    Åpne denne publikasjonen i ny fane eller vindu >>Crack Length Evaluation for Cyclic and Sustained Loading at High Temperature Using Potential Drop
    2015 (engelsk)Inngår i: Experimental mechanics, ISSN 0014-4851, E-ISSN 1741-2765, Vol. 55, nr 3, s. 559-568Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

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

    sted, utgiver, år, opplag, sider
    Society for Experimental Mechanics (SEM), 2015
    Emneord
    Fatigue crack propagation; Fatigue test evaluation; Sustained load; Dwell time effects; Crack length evaluation; Potential drop
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-117241 (URN)10.1007/s11340-014-9963-2 (DOI)000351444300007 ()
    Merknad

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

    Tilgjengelig fra: 2015-04-22 Laget: 2015-04-21 Sist oppdatert: 2017-12-04
    6. Three-dimensional crack growth modelling of a Ni-based superalloy at elevated temperature and sustained loading
    Åpne denne publikasjonen i ny fane eller vindu >>Three-dimensional crack growth modelling of a Ni-based superalloy at elevated temperature and sustained loading
    2016 (engelsk)Inngår i: Theoretical and applied fracture mechanics (Print), ISSN 0167-8442, E-ISSN 1872-7638Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

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

    Emneord
    Sustained load, Crack growth modelling, Crack tunnelling, Ni-based superalloy, High temperature
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-121004 (URN)10.1016/j.tafmec.2015.11.008 (DOI)000369204600002 ()
    Merknad

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

    Vid tiden för disputation förelåg publikationen som manuskript

    Tilgjengelig fra: 2015-09-02 Laget: 2015-09-02 Sist oppdatert: 2017-12-04bibliografisk kontrollert
    7. Modeling of Crack Growth With Dwell Time for Aero-engine Spectra Loadings in a Ni-Based Superalloy
    Åpne denne publikasjonen i ny fane eller vindu >>Modeling of Crack Growth With Dwell Time for Aero-engine Spectra Loadings in a Ni-Based Superalloy
    Vise andre…
    2016 (engelsk)Inngår i: Journal of engineering for gas turbines and power, ISSN 0742-4795, E-ISSN 1528-8919, Vol. 138, nr 1, s. 012501-012501Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

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

    sted, utgiver, år, opplag, sider
    ASME Press, 2016
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-121005 (URN)10.1115/1.4031155 (DOI)000371127900012 ()
    Merknad

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

    Tilgjengelig fra: 2015-09-02 Laget: 2015-09-02 Sist oppdatert: 2017-12-04bibliografisk kontrollert
    8. Scatter in Dwell Time Cracking for a Ni-Based Superalloy in Combination With Overloads
    Åpne denne publikasjonen i ny fane eller vindu >>Scatter in Dwell Time Cracking for a Ni-Based Superalloy in Combination With Overloads
    Vise andre…
    2016 (engelsk)Inngår i: Journal of engineering for gas turbines and power, ISSN 0742-4795, E-ISSN 1528-8919, Vol. 138, nr 1, s. 012502-012502Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

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

    sted, utgiver, år, opplag, sider
    ASME Press, 2016
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-121007 (URN)10.1115/1.4031157 (DOI)000371127900013 ()
    Merknad

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

    Tilgjengelig fra: 2015-09-02 Laget: 2015-09-02 Sist oppdatert: 2017-12-04bibliografisk kontrollert
    9. Thermomechanical Fatigue Crack Growth Modeling in a Ni-Based Superalloy Subjected to Sustained Load
    Åpne denne publikasjonen i ny fane eller vindu >>Thermomechanical Fatigue Crack Growth Modeling in a Ni-Based Superalloy Subjected to Sustained Load
    2016 (engelsk)Inngår i: Journal of engineering for gas turbines and power, ISSN 0742-4795, E-ISSN 1528-8919, Vol. 138, nr 1, s. 012503-012503Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

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

    sted, utgiver, år, opplag, sider
    ASME Press, 2016
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-121008 (URN)10.1115/1.4031158 (DOI)000371127900014 ()
    Merknad

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

    Tilgjengelig fra: 2015-09-02 Laget: 2015-09-02 Sist oppdatert: 2017-12-04bibliografisk kontrollert
    10. Impact of high cycle fatigue on dwell time crack growth in a Ni-based superalloy
    Åpne denne publikasjonen i ny fane eller vindu >>Impact of high cycle fatigue on dwell time crack growth in a Ni-based superalloy
    Vise andre…
    2015 (engelsk)Manuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

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

    Emneord
    Hold time effects, Dwell times, Sustained load, Crack growth modelling, Inconel 718, High temperature
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-121009 (URN)
    Tilgjengelig fra: 2015-09-02 Laget: 2015-09-02 Sist oppdatert: 2015-09-02bibliografisk kontrollert
    Fulltekst (pdf)
    fulltext
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  • 205.
    Storgärds, Erik
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Saarimäki, Jonas
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Sjöström, Sören
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Gustafsson, David
    Siemens Industrial Turbomachinery AB, Finspång, Sweden.
    Månsson, Tomas
    GKN Aerospace Engine Systems, Trollhättan, Sweden.
    Moverare, Johan
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten.
    Scatter in Dwell Time Cracking for a Ni-Based Superalloy in Combination With Overloads2016Inngår i: Journal of engineering for gas turbines and power, ISSN 0742-4795, E-ISSN 1528-8919, Vol. 138, nr 1, s. 012502-012502Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 206.
    Storgärds, Erik
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Saarimäki, Jonas
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Sjöström, Sören
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Månsson, Tomas
    GKN Aerospace Engine Systems, Trollhättan, Sweden.
    Moverare, Johan
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten.
    Impact of high cycle fatigue on dwell time crack growth in a Ni-based superalloy2015Manuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

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

  • 207.
    Storgärds, Erik
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Saarimäki, Jonas
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Sjöström, Sören
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Månsson, Tomas
    GDN Aerospace Engine Systems, Trollhättan.
    Moverare, Johan
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten.
    Influence of Superimposed Vibrational Load on Dwell Time Crack Growth in a Ni-Based Superalloy2016Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 87, s. 301-310Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

    Fulltekst (pdf)
    fulltext
  • 208.
    Storgärds, Erik
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Sjöström, Sören
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Three-dimensional crack growth modelling of a Ni-based superalloy at elevated temperature and sustained loading2016Inngår i: Theoretical and applied fracture mechanics (Print), ISSN 0167-8442, E-ISSN 1872-7638Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

    Fulltekst (pdf)
    fulltext
  • 209.
    Storgärds, Erik
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Sjöström, Sören
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Gustafsson, David
    Siemens Ind Turbomachinery AB, Sweden.
    Mansson, Tomas
    GKN Aerosp Engine Syst, Sweden.
    MODELLING OF CRACK GROWTH WITH DWELL TIME FOR AERO ENGINE SPECTRA LOADINGS IN A NI-BASED SUPERALLOY2015Inngår i: PROCEEDINGS OF THE ASME TURBO EXPO: TURBINE TECHNICAL CONFERENCE AND EXPOSITION, 2015, VOL 7A, ASME Press, 2015, nr V07AT28A003Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Testing and simulation of aero engine spectra with dwell Imes are reported in this paper. The modelling concept used built on LEFM and provides a history dependent evolution 2scription of dwell damage and its interaction with cyclic load. he simulations have been carried out for three spectra, 1) cyclic ?ads, 2) combined sustained load and cyclic loads and 3) slow ad ramps and cyclic loads, all for surface cracks at 550 C for nconel 718. All simulations show reasonable good agreement ith experimental results. Prediction of multiple tests of several atches is also provided to show statistical scatter

  • 210.
    Storgärds, Erik
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Sjöström, Sören
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Gustafsson, David
    Siemens Industrial Turbomachinery AB, Finspång, Sweden.
    Månsson, Tomas
    GKN Aerospace Engine Systems, Trollhättan, Sweden.
    Modeling of Crack Growth With Dwell Time for Aero-engine Spectra Loadings in a Ni-Based Superalloy2016Inngår i: Journal of engineering for gas turbines and power, ISSN 0742-4795, E-ISSN 1528-8919, Vol. 138, nr 1, s. 012501-012501Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 211.
    Storgärds, Erik
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Sjöström, Sören
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Moverare, Johan
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten.
    Thermomechanical Fatigue Crack Growth Modeling in a Ni-Based Superalloy Subjected to Sustained Load2016Inngår i: Journal of engineering for gas turbines and power, ISSN 0742-4795, E-ISSN 1528-8919, Vol. 138, nr 1, s. 012503-012503Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 212.
    Storgärds, Erik
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Sjöström, Sören
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Moverare, Johan
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten.
    THERMO-MECHANICAL FATIGUE CRACK GROWTH MODELLING IN A NI-BASED SUPERALLOY SUBJECTED TO SUSTAINED LOAD2015Inngår i: PROCEEDINGS OF THE ASME TURBO EXPO: TURBINE TECHNICAL CONFERENCE AND EXPOSITION, 2015, VOL 7A, ASME Press, 2015, nr V07AT28A006Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Thermo-mechanical fatigue (TMF) crack growth modelling as been conducted on Inconel 718 with dwell time at maximum;ad. A history dependent damage model taking dwell damage uto account, developed under isothermal conditions, has been xtended for TMF conditions. Parameter determination for the lodel is carried out on isothermal load controlled tests at 55050 C for surface cracks, which later have been used to extrapole parameters used for TMF crack growth. Further, validation the developed model is conducted on a notched specimen sub?cted to strain control at 50-550 C. Satisfying results are gained ithin reasonable scatter level compared for test and simulated umber of cycles to failure.

  • 213.
    Strömberg, Niclas
    et al.
    Jönköping University.
    Klarbring, Anders
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik. Linköpings universitet, Tekniska högskolan.
    Topology optimization of structures in unilateral contact2010Inngår i: Structural and multidisciplinary optimization (Print), ISSN 1615-147X, E-ISSN 1615-1488, Vol. 41, nr 1, s. 57-64Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Abstract In this paper a general framework for topologyoptimization of structures in unilateral contact isdeveloped. A linear elastic structure that is unilaterallyconstrained by rigid supports is considered. Thesupports are modeled by Signorini’s contact conditionswhich in turn are treated by the augmented Lagrangianapproach as well as by a smooth approximation. Thelatter approximation must not be confused with thewell-known penalty approach. The state of the system,which is defined by the equilibrium equation andthe two different contact formulations, is solved by aNewton method. The design parametrization is obtainedby using the SIMP-model. The minimization ofcompliance for a limited value of volume is considered.The optimization problems are solved by SLP. This isdone by using a nested approach where the state equationsare linearized and sensitivities are calculated bythe adjoint method. In order to avoid mesh-dependencythe sensitivities are filtered by Sigmund’s filter. Thefinal LP-problem is solved by an interior point methodthat is available inMatlab. The implementation is donefor a general design domain in 2D as well as in 3Dby using fully integrated isoparametric elements. Theimplementation seems to be very efficient and robust.

    Fulltekst (pdf)
    FULLTEXT01
  • 214.
    Stålhand, Jonas
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    McMeeking, Robert M.
    Department of Mechanical Engineering & Materials Department, University of California Santa Barbara, CA 93106, USA / School of Engineering, University of Aberdeen, Kings College, Aberdeen, AB24 3UE, UK.
    Holzapfel, Gerhard A.
    Institute of Biomechanics, Graz University of Technology, Stremayrgasse 16-II, 8010 Graz, Austria / Norwegian University of Science and Technology (NTNU), Faculty of Engineering Science and Technology, 7491 Trondheim, Norway.
    On the Thermodynamics of Smooth Muscle Contraction2016Inngår i: Journal of the mechanics and physics of solids, ISSN 0022-5096, E-ISSN 1873-4782, Vol. 94, s. 490-503Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Cell function is based on many dynamically complex networks of interacting biochemical reactions. Enzymes may increase the rate of only those reactions that are thermodynamically consistent. In this paper we specifically treat the contraction of smooth muscle cells from the continuum thermodynamics point of view by considering them as an open system where matter passes through the cell membrane. We systematically set up a well-known four-state kinetic model for the cross-bridge interaction of actin and myosin in smooth muscle, where the transition between each state is driven by forward and reverse reactions. Chemical, mechanical and energy balance laws are provided in local forms, while energy balance is also formulated in the more convenient temperature form. We derive the local (non-negative) production of entropy from which we deduce the reduced entropy inequality and the constitutive equations for the first Piola-Kirchhoff stress tensor, the heat flux, the ion and molecular flux and the entropy. One example for smooth muscle contraction is analyzed in more detail in order to provide orientation within the established general thermodynamic framework. In particular the stress evolution, heat generation, muscle shorting rate and a condition for muscle cooling is derived.

  • 215. Bestill onlineKjøp publikasjonen >>
    Suresh, Shyam
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Topology Optimization for Additive Manufacturing Involving High-Cycle Fatigue2020Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Additive Manufacturing (AM) is gaining popularity in aerospace and automotive industries. This is a versatile manufacturing process, where highly complex structures are fabricated and together with topology optimization, a powerful design tool, it shares the property of providing a very large freedom in geometrical form. The main focus of this work is to introduce new developments of Topology Optimization (TO) for metal AM.

    The thesis consists of two parts. The first part introduces background and theory, where TO and adjoint sensitivity analysis are described. Furthermore, methodology used to identify surface layer and high-cycle fatigue are introduced. In the second part, three papers are appended, where the first paper presents the treatment of surface layer effects, while the second and third papers provide high-cycle fatigue constraint formulations.

    In Paper I, a TO method is introduced to account for surface layer effects, where different material properties are assigned to bulk and surface regions. In metal AM, the fabricated components in as-built surface conditions significantly affect mechanical properties, particularly fatigue properties. Furthermore, the components are generally in-homogeneous and have different microstructures in bulk regions compared to surface regions. We implement two density filters to account for surface effects, where the width of the surface layer is controlled by the second filter radius. 2-D and 3-D numerical examples are treated, where the structural stiffness is maximized for a limited mass.

    For Papers II and III, a high-cycle fatigue constraint is implemented in TO. A continuous-time approach is used to predict fatigue-damage. The model uses a moving endurance surface and the development of damage occurs only if the stress state lies outside the endurance surface. The model is applicable not only for isotropic materials (Paper II) but also for transversely isotropic material properties (Paper III). It is capable of handling arbitrary load histories, including non-proportional loads. The anisotropic model is applicable for additive manufacturing processes, where transverse isotropic properties are manifested not only in constitutive elastic response but also in fatigue properties. Two optimization problems are solved: In the first problem the structural mass is minimized subject to a fatigue constraint while the second problem deals with stiffness maximization subjected to a fatigue constraint and mass constraint. Several numerical examples are tested with arbitrary load histories.

    Delarbeid
    1. Topology optimization using a continuous-time high-cycle fatigue model
    Åpne denne publikasjonen i ny fane eller vindu >>Topology optimization using a continuous-time high-cycle fatigue model
    Vise andre…
    2020 (engelsk)Inngår i: Structural and multidisciplinary optimization (Print), ISSN 1615-147X, E-ISSN 1615-1488, Vol. 61, nr 3, s. 1011-1025Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    We propose a topology optimization method that includes high-cycle fatigue as a constraint. The fatigue model is based on a continuous-time approach where the evolution of damage in each point of the design domain is governed by a system of ordinary differential equations, which employs the concept of a moving endurance surface being a function of the stress and back stress. Development of fatigue damage only occurs when the stress state lies outside the endurance surface. The fatigue damage is integrated for a general loading history that may include non-proportional loading. Thus, the model avoids the use of a cycle-counting algorithm. For the global high-cycle fatigue constraint, an aggregation function is implemented, which approximates the maximum damage. We employ gradient-based optimization, and the fatigue sensitivities are determined using adjoint sensitivity analysis. With the continuous-time fatigue model, the damage is load history dependent and thus the adjoint variables are obtained by solving a terminal value problem. The capabilities of the presented approach are tested on several numerical examples with both proportional and non-proportional loads. The optimization problems are to minimize mass subject to a high-cycle fatigue constraint and to maximize the structural stiffness subject to a high-cycle fatigue constraint and a limited mass.

    sted, utgiver, år, opplag, sider
    SPRINGER, 2020
    Emneord
    Continuous-time approach; Endurance surface; High-cycle fatigue; Topology optimization; Adjoint sensitivity analysis; Aggregation function
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-164857 (URN)10.1007/s00158-019-02400-w (DOI)000519378000009 ()
    Tilgjengelig fra: 2020-03-30 Laget: 2020-03-30 Sist oppdatert: 2020-05-05
    Fulltekst (pdf)
    fulltext
    Download (png)
    presentationsbild
  • 216.
    Suresh, Shyam
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Lindström, Stefan B
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Thore, Carl-Johan
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Torstenfelt, Bo
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Klarbring, Anders
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    An Evolution-Based High-Cycle Fatigue Constraint in Topology Optimization2018Konferansepaper (Fagfellevurdert)
    Abstract [en]

    We develop a topology optimization method including high-cycle fatigue as a constraint. The fatigue model is based on a continuous-time approach, which uses the concept of a moving endurance surface as a function of the stress history and back stress evolution. The development of damage only occurs when the stress state lies outside the endurance surface. Furthermore, an aggregation function, which approximates the maximum fatigue damage, is implemented. As the optimization workflow is sensitivity-based, the fatigue sensitivities are determined using an adjoint sensitivity analysis. The capabilities of the presented approach are tested on numerical models where the problem is to maximize the stiffness subject to high-cycle fatigue constraints.

  • 217.
    Suresh, Shyam
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Lindström, Stefan
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Thore, Carl-Johan
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Torstenfelt, Bo
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Klarbring, Anders
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Topology optimization using a continuous-time high-cycle fatigue model2020Inngår i: Structural and multidisciplinary optimization (Print), ISSN 1615-147X, E-ISSN 1615-1488, Vol. 61, nr 3, s. 1011-1025Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We propose a topology optimization method that includes high-cycle fatigue as a constraint. The fatigue model is based on a continuous-time approach where the evolution of damage in each point of the design domain is governed by a system of ordinary differential equations, which employs the concept of a moving endurance surface being a function of the stress and back stress. Development of fatigue damage only occurs when the stress state lies outside the endurance surface. The fatigue damage is integrated for a general loading history that may include non-proportional loading. Thus, the model avoids the use of a cycle-counting algorithm. For the global high-cycle fatigue constraint, an aggregation function is implemented, which approximates the maximum damage. We employ gradient-based optimization, and the fatigue sensitivities are determined using adjoint sensitivity analysis. With the continuous-time fatigue model, the damage is load history dependent and thus the adjoint variables are obtained by solving a terminal value problem. The capabilities of the presented approach are tested on several numerical examples with both proportional and non-proportional loads. The optimization problems are to minimize mass subject to a high-cycle fatigue constraint and to maximize the structural stiffness subject to a high-cycle fatigue constraint and a limited mass.

    Fulltekst (pdf)
    fulltext
  • 218.
    Söderberg, Johan
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik. Linköpings universitet, Tekniska högskolan.
    A finite element method for calculating load distributions in bolted joint assemblies2012Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    Bolted joints are often the most critical parts with respect to fatigue life of structures. Therefore, it is important to analyze these components and the forces they are subjected to.

    A one-dimensional nite element model of a bolted joint is created and implemented as a program module in the Saab software `DIM', together with a complete graphical user interface allowing the user to generate the structure freely, and to apply both mechanical and thermal loads.

    Available methods for calculating fastener exibility are reviewed. The ones derived by Grumman, Huth and Barrois are implemented in the module, and can thus be used when dening a geometry representing a bolted joint assembly. Investigations have shown that it cannot be said that either method is generally better than the other. Calculated properties of interest include the fastener forces, plate bearing and bypass loads, and - for simpler geometries without thermal loads - the load distribution between rows of fasteners.

    The program is fully functional and yields numerically accurate results for the most commonly used joints where fasteners connect two or three plates each. It has limited functionality on geometries with fasteners connecting four or more plates and for a certain loading combination also for three plates, due to the tilting of the fasteners not being accounted for in the model for these cases. Also, there is no explicit method available for nding an accurate value for the fastener exibility for these, less common, joint structures.

    Fulltekst (pdf)
    fem_bolted_joint_thesis
  • 219.
    Talus, Eva
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Optimal Use of Duplex Stainless Steel in Storage Tanks2013Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    The aim of this work is to get a better understanding of how optimal weight savings of the cylindrical shell plates in storage tanks can be reached using higher strength duplex material. The design criteria will be based on the requirements given by the American Petroleum Institute standards API 650 for welded storage tanks and API 12B for bolted storage tanks. The expected result is that use of duplex stainless steel instead of austenitic stainless steel can reduce the weight of the material needed to build a storage tank. A comparison between welded and bolted storage tanks will also be included in the work to find which joining method that is preferable. Additionally, an evaluation of the software TANKTM by Intergraph will be performed. Matlab® will be used in order to perform the evaluation to compare the results.

    The main difference between the standards API 650 and API 12B is that there are already given standard sizes of bolted storage tanks API 12B. Therefore, only storage tanks up to 1 625 m3 could be compared. When comparing storage tank sizes up to 1 625 m3 the result is that bolted storage tanks require a smaller mean thickness of the cylindrical shell than welded storage tanks and therefore less material and total weight of the shell. If the trend continues also for larger tank sizes, bolted storage tanks will be preferable to reduce the total weight of the storage tank.

    By use of duplex stainless steel instead of austenitic stainless steel in storage tanks, the minimum required thickness can be reduced because of the higher strength of duplex stainless steel. This leads to a smaller mean shell thickness and therefore a reduced weight compared to storage tanks made of austenitic stainless steel. For most dimensions of storage tanks, duplex stainless steel is cheaper than austenitic stainless steel, but for some smaller dimensions, grade 1.4307 (austenitic) is cheaper than LDX 2101® (duplex).

    Instability calculations have been performed for welded storage tanks, while no instability calculations have been performed for bolted storage tanks. With the wind speed 190 km/h (proposed by API 650), the welded storage tanks need to have wind girders to stiffen the cylindrical shell and in some cases also be anchored to the ground. Anchor is not required for large dimensions of storage tanks.

    The evaluation of TANKTM showed that most parameters agreed to the computed value of the same parameters in Matlab®. Why a few parameters not agrees is not fully known, therefore better explanations of the parameters used in the equations in API 650 would be preferable. To see the difference between Matlab® and TANKTM it would also be of interest to see how the calculations are performed in TANKTM, as only the results and inputs are printed at the moment.

    Fulltekst (pdf)
    fulltext
  • 220.
    Thellner, Mikael
    Linköpings universitet, Institutionen för konstruktions- och produktionsteknik. Linköpings universitet, Tekniska högskolan. Univ.,.
    Integrated structural optimization for mechanical optimal design2002Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    This thesis concerns integrated methods for structural optimization. Structural optimization is concerned with finding the best structural design while satisfying certain restrictions. We divide structural optimization into a number of subfield, e.g. shape, thickness and topology optimization. In this thesis we present different strategies to combine subfields of structural optimization to obtain integrated methods. The thesis consists of two papers.

    Paper I consists of a review of different methods to integrate topology and shape optimization that are presented in the literature. Integrated topology and shape optimization can be divided into to three steps. The first step is topology optimization where a concept of the structure to be is generated. This concept is transfered in the second step to an initial design for shape optimization. The last step is shape optimization where the final shape of the structure is determined.

    Paper II presents an implementation of simultaneous shape and thickness optimization in a general finite element software. The shape of the plane domain and the out­ of-plane thickness of the structure are simultaneous varied to obtain an optimal design. With this approach an essentially three dimensional optimization problem is solved by only performing a two dimensional analysis. The paper includes two applications of simultaneous shape and thickness optimization.

  • 221.
    Thomasson, Andreas
    et al.
    Linköpings universitet, Institutionen för systemteknik, Fordonssystem. Linköpings universitet, Tekniska fakulteten.
    Eriksson, Lars
    Linköpings universitet, Institutionen för systemteknik, Fordonssystem. Linköpings universitet, Tekniska fakulteten.
    Effects of Pulsating Flow on Mass Flow Balance and Surge Margin in Parallel Turbocharged Engines2015Inngår i: Proceedings of the 56th Conference on Simulation and Modelling (SIMS 56), October, 7-9, 2015, Linköping University, Sweden, Linköping: Linköping University Electronic Press, 2015, Vol. 119, s. 15-20Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The paper extends a mean value model of a parallel turbocharged internal combustion engine with a crank angle resolved cylinder model. The result is a 0D engine model that includes the pulsating flow from the intake and exhaust valves. The model captures variations in turbo speed and pressure, and therefore variations in the compressor operating point, during an engine cycle. The model is used to study the effect of the pulsating flow on mass flow balance and surge margin in parallel turbocharged engines, where two compressors are connected to a common intake manifold. This configuration is harder to control compared to single turbocharged systems, since the compressors interact and can work against each other, resulting in co-surge. Even with equal average compressor speed and flow, the engine pulsations introduce an oscillation in the turbo speeds and mass flow over the engine cycle. This simulation study use the developed model to investigates how the engine pulsations effect the in cycle variation in compressor operating point and the sensitivity to co-surge. It also shows how a short circuit pipe between the two exhaust manifolds could increase surge margin at the expense of less available turbine energy.

    Fulltekst (pdf)
    fulltext
  • 222.
    Thore, Carl-Johan
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Holmberg, Erik
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Klarbring, Anders
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Large-scale robust topology optimization under load-uncertainty2015Inngår i: Advances in Structural and Multidisciplinary Optimization - Proceedings of the 11th World Congress of Structural and Multidisciplinary Optimization(WCSMO-11) / [ed] Qing Li, Grant P Steven and Zhongpu (Leo) Zhang, 2015, s. 255-260Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Structures designed by topology optimization (TO) are frequently sensitive to loads different from the ones accounted for in the optimization. In extreme cases this means that loads differing ever so slightly from the ones it was designed to carry may cause a structure to collapse. It is therefore clear that handling uncertainty regarding the actual loadings is important. To address this issue in a systematic  manner is one of the main goals in the field of robust TO. In this work we present a deterministic robust formulation of TO for maximum stiffness design which accounts for uncertain variations around a set of nominal loads. The idea is to find a design which minimizes the maximum compliance obtained as the loads vary in infinite, so-called uncertainty sets. This naturally gives rise to a semi-infinite optimization problem, which we here reformulate into a non-linear, semi-definite program. With appropriate numerical algorithms this optimization problem can be solved at a cost similar to that of solving a standard multiple load-case TO problem with the number of loads equal to the number of spatial dimensions plus one, times the number of nominal loads. In contrast to most previously suggested methods, which can only be applied to small-scale problems, the presented method is – as illustrated by a numerical example – well-suited for large-scale TO problems.

  • 223.
    Tsirikoglou, Apostolia
    et al.
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Medie- och Informationsteknik. Linköpings universitet, Tekniska fakulteten.
    Kronander, Joel
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Medie- och Informationsteknik. Linköpings universitet, Tekniska fakulteten.
    Larsson, Per
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Medie- och Informationsteknik. Linköpings universitet, Tekniska fakulteten.
    Tongbuasirilai, Tanaboon
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Medie- och Informationsteknik. Linköpings universitet, Tekniska fakulteten.
    Gardner, Andrew
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Medie- och Informationsteknik. Linköpings universitet, Tekniska fakulteten.
    Unger, Jonas
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Medie- och Informationsteknik. Linköpings universitet, Tekniska fakulteten.
    Differential appearance editing for measured BRDFs2016Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    Data driven reflectance models using BRDF data measured from real materials, e.g. [Matusik et al. 2003], are becoming increasingly popular in product visualization, digital design and other applications driven by the need for predictable rendering and highly realistic results. Although recent analytic, parametric BRDFs provide good approximations for many materials, some effects are still not captured well [Löw et al. 2012]. Thus, it is hard to accurately model real materials using analytic models, even if the parameters are fitted to data. In practice, it is often desirable to apply small edits to the measured data for artistic purposes, or to model similar materials that are not available in measured form. A drawback of data driven models is that they are often difficult to edit and do not easily lend themselves well to artistic adjustments. Existing editing techniques for measured data [Schmidt et al. 2014], often use complex decompositions making them difficult to use in practice.

  • 224. Bestill onlineKjøp publikasjonen >>
    Unosson, Mattias
    Linköpings universitet, Institutionen för konstruktions- och produktionsteknik, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    On failure modelling in finite element analysis: material imperfections and element erosion2005Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    This dissertation concerns failure modelling with material imperfections and element erosion in finite element analyses. The aim has been to improve the element erosion technique, which is simple to use and implement and also computationally inexpensive. The first part of the dissertation serves as an introduction to the topic and as a summary of the methodologies presented in the following part. The second part consists of seven appended papers. In paper A the standard element erosion technique is used for projectile penetration. In papers B and C a methodology that accounts for size effects is developed and applied to crack initiation in armour steel and tungsten carbide. A methodology to better predict the stress state at crack tips with coarse meshes is presented and applied to armour steel in paper D. Papers E and F concern the development of selective mass scaling which allows for larger time steps in explicit methods. Finally, in paper G the previously presented methodologies are used in combination and validated against experimental results on tungsten carbide. The computations show good agreement with the experimental results on failure initiation for both materials, while the computational results on the propagation of cracks show better agreement for the armour steel than for the tungsten carbide.

    Delarbeid
    1. Projectile penetration and perforation of high performance concrete: Experimental results and macroscopic modelling
    Åpne denne publikasjonen i ny fane eller vindu >>Projectile penetration and perforation of high performance concrete: Experimental results and macroscopic modelling
    2006 (engelsk)Inngår i: International Journal of Impact Engineering, ISSN 0734-743X, E-ISSN 1879-3509, Vol. 32, nr 7, s. 1068-1085Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    Experiments and simulations of penetration and perforation of high performance concrete targets by steel projectiles have been carried out. A Doppler radar monitored the projectile pre-impact velocity history and a high-speed camera captured the projectile residual velocity. A continuum mechanical approach and the finite-element method were used for the simulations. The targets were modelled with the K&C concrete model. For perforation the computational results show acceptable agreement with the experimental results, but not for penetration. The article is concluded with suggestions on how to better model concrete material for the current application.

    sted, utgiver, år, opplag, sider
    Pergamon Press, 2006
    Emneord
    High performance concrete; Projectile; Penetration; Perforation; Experiments; Finite-element analysis
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-13412 (URN)10.1016/j.ijimpeng.2004.11.003 (DOI)
    Tilgjengelig fra: 2005-11-09 Laget: 2005-11-09 Sist oppdatert: 2017-12-13
    2. Failure modelling in finite element analyses: Random material imperfections
    Åpne denne publikasjonen i ny fane eller vindu >>Failure modelling in finite element analyses: Random material imperfections
    2005 (engelsk)Inngår i: Mechanics of Materials, ISSN 0167-6636, Vol. 37, nr 12, s. 1175-1179Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    A phenomenological failure model has been developed where the material is assumed to contain initial material imperfections that influence the material strength only through the largest imperfection. The imperfections are randomly distributed and characterized by material imperfection density functions. In a first approach one type of imperfection is assumed with an exponential imperfection density function. The model parameters are optimized, using results from a deterministic finite element analysis, to match a target function representing the probability of failure in a tensile test. The developed model manages to reproduce this data well.

    Emneord
    Explicit finite element analysis; Failure initiation; Element erosion; Random imperfections
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-13413 (URN)10.1016/j.mechmat.2005.05.001 (DOI)
    Tilgjengelig fra: 2005-11-09 Laget: 2005-11-09 Sist oppdatert: 2009-06-08
    3. Weakest link model with imperfection: Application to three point bend of a tungsten carbide
    Åpne denne publikasjonen i ny fane eller vindu >>Weakest link model with imperfection: Application to three point bend of a tungsten carbide
    2007 (engelsk)Inngår i: International Journal of Refractory Metals and Hard Materials, ISSN 0263-4368, Vol. 25, nr 1, s. 6-10Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    A general weakest link model adapted to finite element analyses recently proposed by the authors is in this paper applied and optimized against three point bending experiments on two geometrically identical specimens with different sizes. Influence of the choice of description of material imperfections in the model on the result is investigated together with two different types of failure criteria. Due to the choice of failure criteria only one finite element analysis has to be performed. The results show that the model can be fitted well to the experimental results.

    sted, utgiver, år, opplag, sider
    Elsevier, 2007
    Emneord
    Finite element method, Failure initiation, Size effect, Random imperfections
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-13414 (URN)10.1016/j.ijrmhm.2005.10.015 (DOI)000242508800002 ()
    Tilgjengelig fra: 2005-11-09 Laget: 2005-11-09 Sist oppdatert: 2012-08-24bibliografisk kontrollert
    4. Failure modelling in finite element analyses: Element erosion with crack-tip enhancement
    Åpne denne publikasjonen i ny fane eller vindu >>Failure modelling in finite element analyses: Element erosion with crack-tip enhancement
    2006 (engelsk)Inngår i: Finite elements in analysis and design (Print), ISSN 0168-874X, E-ISSN 1872-6925, Vol. 42, nr 4, s. 283-297Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    A method to better handle fracture using element erosion in finite element analyses is proposed. It is assumed that the crack-tip is blunt and that the solution in the vicinity of the crack-tip is separable when described in local polar co-ordinates. The numerical solution is enhanced by scaling strain rates at integration points to better match the state at the crack-tip. This material specific scaling function is empirically determined for modus I steady-state propagation and is applied to two problems. The results show that the method reduces mesh dependency such that the chosen fracture energy can be better matched for different element sizes.

    sted, utgiver, år, opplag, sider
    Elsevier, 2006
    Emneord
    Finite element analysis; Failure; Element erosion; Crack-tip enhancement; Steady-state propagation; Modus I
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-13415 (URN)10.1016/j.finel.2005.07.001 (DOI)
    Tilgjengelig fra: 2005-11-09 Laget: 2005-11-09 Sist oppdatert: 2017-12-13
    5. Selective mass scaling for thin walled structures modeled with tri-linear solid elements
    Åpne denne publikasjonen i ny fane eller vindu >>Selective mass scaling for thin walled structures modeled with tri-linear solid elements
    2004 (engelsk)Inngår i: Computational Mechanics, ISSN 1432-0924, Vol. 34, nr 2, s. 134-136Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    A method for selective mass scaling in explicit finite element analyses of thin walled structures, modeled with solid elements, is introduced. The method aims at increasing the critical time step without significantly altering the dynamical response of the system. The proposed method is based on the exclusion of certain rigid body motions from the applied mass scaling by filtering the local velocity field.

    Emneord
    Mass scaling, Finite element, Explicit time integration
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-13416 (URN)10.1007/s00466-004-0560-6 (DOI)
    Tilgjengelig fra: 2005-11-09 Laget: 2005-11-09 Sist oppdatert: 2009-05-28
    6. Selective mass scaling for explicit finite element analyses
    Åpne denne publikasjonen i ny fane eller vindu >>Selective mass scaling for explicit finite element analyses
    2005 (engelsk)Inngår i: International Journal for Numerical Methods in Engineering, ISSN 0029-5981, E-ISSN 1097-0207, Vol. 63, nr 10, s. 1436-1445Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    Due to their inherent lack of convergence problems explicit finite element techniques are widely used for analysing non-linear mechanical processes. In many such processes the energy content in the high frequency domain is small. By focusing an artificial mass scaling on this domain, the critical time step may be increased substantially without significantly affecting the low frequency behaviour. This is what we refer to as selective mass scaling. Two methods for selective mass scaling are introduced in this work. The proposed methods are based on non-diagonal mass matrices that scale down the eigenfrequencies of the system. The applicability of the methods is illustrated in two example models where the critical time step is increased by up to 30 times its original size.

    Emneord
    selective mass scaling, finite element, explicit time integration
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-13417 (URN)10.1002/nme.1293 (DOI)
    Tilgjengelig fra: 2005-11-09 Laget: 2005-11-09 Sist oppdatert: 2017-12-13bibliografisk kontrollert
    7. Imperfection density function and crack-tip enhancement: Validation against symmetrical bending of circular tungsten carbide plates
    Åpne denne publikasjonen i ny fane eller vindu >>Imperfection density function and crack-tip enhancement: Validation against symmetrical bending of circular tungsten carbide plates
    2007 (engelsk)Inngår i: Mechanics of materials (Print), ISSN 0167-6636, E-ISSN 1872-7743, Vol. 39, nr 8, s. 753-759Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    Experiments and finite element analyses of symmetrical bending of circular tungsten carbide plates have been carried out. In the numerical simulations, a material imperfection density that accounts for size effects on the failure strength was considered. In addition, a scaling of the solution near the crack-tips was performed, in order to improve the crack propagation prediction and to ensure a mesh independent fracture energy. The numerical results on failure initiation are shown to be in good agreement with the experiments. However, numerical noise in the solution makes it difficult to handle the crack propagation, which is a problem inherent to all brittle materials.

    sted, utgiver, år, opplag, sider
    Elsevier, 2007
    Emneord
    Explicit finite element analysis, Material imperfections, Element erosion, Tungsten carbide
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-13418 (URN)10.1016/j.mechmat.2006.12.005 (DOI)000246315700003 ()
    Tilgjengelig fra: 2005-11-09 Laget: 2005-11-09 Sist oppdatert: 2017-12-13
    Fulltekst (pdf)
    FULLTEXT01
  • 225.
    Venkatesan, Sreedhar
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära.
    Banglore Hanumantha Raju, Hariprasad
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära.
    Probabilistic Analysis of Brake Noise: A Hierarchical Multi-fidelity Statistical Approach2018Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    Computer Aided Engineering driven analysis is gaining grounds in automotive industry. Prediction of brake noise using CAE techniques has become populardue to its overall low cost as compared to physical testing. However, the presence of several uncertain parameters which affect brake noise and also the lack of basic understanding about brake noise, makes it difficult to make reliable decisions based on CAE analysis. Therefore, the confidence level in CAE techniques has to be increased to ensure reliability and robustness in the CAE solutions which support design work. One such way to achieve reliability in the CAE analysis isinvestigated in this thesis by incorporating the effects of different sources of uncertainty and variability in the analysis and estimating the probability of designfailure (probability of brake noise above a certain threshold). While incorporating the uncertainties in the CAE analysis ensures robustness, it is computationally intensive. This thesis work aims to gain an understanding about a brakenoise - creep groan, and to bring robustness into the CAE analysis along with reduction in computational time. A probabilistic analysis technique called hierarchical multi-fidelity statistical approachis explored in this thesis work, to estimate the probability of design failure or design robustness at a faster rate. It incorporates the stochasticity in the input parameters while running simulations. The method involves application of a hierarchy of approximations to the system response computed with variations in mesh resolution or variations in number of modes or changing solver time step,etc. And finally it uses the probability theory, to relate the information provided by approximate solutions to get the target failure estimation.Through this method, reliable data regarding the probability of design failure was approximated for every simulation and at a reduced computational time.Additionally, it provided information about critical parameters that influenced brake noise which was meritorious for design management. Estimation of probability of design failure by this method has been proved to be reliable in the case of brake noise according to the simulation results and the method can be considered robust.

    Fulltekst (pdf)
    Probabilistic Analysis of Brake Noise
  • 226.
    Vikström, Simon
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Thuresson, Robin
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Finite element analysis of winding sequence for cable drums2015Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    This project concerns large cable drums made of steel. Cable drums are cylindrical structures used to transport different kinds of cables or wires. The ones in focus in this work are used to transport very stiff and heavy cables to offshore sites in the oil industry. To reduce weight in structures is always of great interest, and for cable drums, that are designed according to standards, there is much that can be improved.

    The aim of this project is to predict the loads acting on a drum during the winding of cables. This was accomplished by performing explicit finite element simulations of the winding sequence. Modeling and meshing were done using LS-PrePost and ANSA, and the winding was simulated using LS-DYNA. LS-PrePost was also used to analyze the results, together with mETApost.

    A number of simplifications and delimitations have been made in order to make the simulation possible within the time frame of the project. Simplified models of both the cable and the drum have been used. Winding velocities in real life are really slow, so in order to reduce simulation times, the winding velocity had to be increased while still avoiding dynamic effects. From this, contact forces between the drum and the cable could be obtained. The contact forces were investigated with respect to different friction values between the cable and the drum, for the cable itself and also for different cable stiffnesses.

    The results obtained from the simulations provide contact force distributions for different parts of the drum. Much fewer rows and layers of cable were winched than in real life, and it is therefore hard to see any clear trends in the obtained forces. However, one important result of the contact forces, is that a previously used assumption, namely that the pretension of the cable only applies loads to a small fraction of the drum, was a bit too conservative. According to the simulations it actually gets distributed over the whole drum.

    It is hard to draw any conclusions from the obtained contact forces, due to the small size of the simulations. The conclusion one can draw from this report, is that it is fully possible to use finite element tools to simulate the winding sequence of cable drums and this report presents a methodology on how to achieve this. LS-DYNA handles the contact definitions in an adequate way and is, according to the authors, a strong candidate for future work in this area. 

    Fulltekst (pdf)
    fulltext
  • 227.
    von Rosen, Michael
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära.
    Modelling of bolt fracture2014Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    Computer simulations are widely used in the truck industry in order to provide assistance in the product development. Bolt joints are common in trucks. A bolt fracture usually has a great influence on how a truck structure will behave in a crash. Therefore, when simulating truck crashes it is important to be able to predict when bolt fracture occurs. A material model for 10.9 bolts has been calibrated and validated by using the finite element software LS-DYNA. The material model consists of a failure strain surface, which depends on the triaxiality, Lode parameter and the element size. In this thesis, the calibrated material model is referred to as the bolt model.

    A good agreement to predict the force at fracture in bolts between simulation model results and physical test results has been obtained. Still, further validation is needed to evaluate the bolt model completely.

    Fulltekst (pdf)
    Modelling of bolt fracture
  • 228.
    Wang, Fei
    Linköpings universitet, Institutionen för fysik, kemi och biologi, Teoretisk Fysik. Linköpings universitet, Tekniska fakulteten.
    Properties of multilayered and multicomponent nitride alloys from first principles2018Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    This thesis is a theoretical exploration of properties of multilayered and multicomponent nitride alloys, in particular their mixing thermodynamics and elastic behaviors. Systematic investigation of properties of a large class of materials, such as the multicomponent nitride solid solutions, is in line with the modern approach of high-throughput search of novel materials. In this thesis we benchmark and utilize simple but efficient methodological frameworks in predicting mixing thermodynamics, Young’s moduli distribution of multilayer alloys and the linear thermal expansion of quaternary nitride solid solutions.

    We demonstrate by accurate ab-initio calculations that Ti1−xAlxN solid solution is stabilized by interfacial effects if it is coherently sandwiched between TiN layers along (001). For TiN/AlN and ZrN/AlN multilayers we show higher thermodynamic stability with semicoherent interfaces than with isostructural coherent ones.

    Accurate 0 Kelvin elastic constants of cubic TixXyAl1xyN (X=Zr, Hf, Nb, V, Ta) solid solutions and their multilayers are derived and an analytic comparison of strengths and ductility are presented to reveal the potential of these materials in hard coating applications. The Young’s moduli variation of the bulk materials has provided a reliable descriptor to screen the Young’s moduli of coherent multilayers.

    The Debye model is used to reveal the high-temperature thermodynamics and spinodal decomposition of TixNbyAl1−x−yN. We show that though the effect of vibration is large on the mixing Gibbs free energy the local spinoal decomposition tendencies are not altered. A quasi-harmonic Debye model is benchmarked against results of molecular dynamics simulations in predicting the thermal expansion coefficients of TixXyAl1xyN (X=Zr, Hf, Nb, V, Ta).  

    Delarbeid
    1. Special quasirandom structure method in application for advanced properties of alloys: A study on Ti0.5Al0.5N and TiN/Ti0.5Al0.5N multilayer
    Åpne denne publikasjonen i ny fane eller vindu >>Special quasirandom structure method in application for advanced properties of alloys: A study on Ti0.5Al0.5N and TiN/Ti0.5Al0.5N multilayer
    2015 (engelsk)Inngår i: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 103, s. 194-199Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    The special quasirandom structure (SQS) approach is a successful technique for modelling of alloys, however it breaks inherently the point symmetry of the underlying crystal lattice. We demonstrate that monocrystalline and polycrystalline elastic moduli can scatter significantly depending on the chosen SQS model and even on the supercell orientation in space. Also, we demonstrate that local disturbances, such as vacancies or interfaces change the SQS configuration in a way, that significantly affects the values of the calculated physical properties. Moreover, the diversity of local environments in random alloys results in a large variation of the calculated local properties. We underline that improperly chosen, generated or handled SQS may result in erroneous theoretical findings. The challenges of the SQS method are discussed using bulk Ti0.5Al0.5N alloy and TiN/Ti0.5Al0.5N multilayer as model systems. We present methodological corrections for the mindful application of this approach in studies of advanced properties of alloys.

    sted, utgiver, år, opplag, sider
    Elsevier, 2015
    Emneord
    Modelling alloys; Special quasirandom structure approach; Elastic constants; Vacancy formation energy; Multilayers
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-118022 (URN)10.1016/j.commatsci.2015.03.030 (DOI)000353377100024 ()
    Merknad

    Funding Agencies|SSF project Designed Multicomponent coatings, MultiFilms; Erasmus Mundus Programme of the European Commission within the Doctoral Programme DocMASE; Grant of Ministry of Education and Science of the Russian Federation [14.Y26.31.0005]; Tomsk State University Academic D.I. Mendeleev Fund Program; Swedish Research Council (VR)

    Tilgjengelig fra: 2015-05-21 Laget: 2015-05-20 Sist oppdatert: 2018-02-09
    2. Coherency effects on the mixing thermodynamics of cubic Ti1-xAlxN/TiN(001) multilayers
    Åpne denne publikasjonen i ny fane eller vindu >>Coherency effects on the mixing thermodynamics of cubic Ti1-xAlxN/TiN(001) multilayers
    Vise andre…
    2016 (engelsk)Inngår i: PHYSICAL REVIEW B, ISSN 2469-9950, Vol. 93, nr 17, s. 174201-Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    In this work, we discuss the mixing thermodynamics of cubic (B1) Ti1-xAlxN/TiN(001) multilayers. We show that interfacial effects suppress the mixing enthalpy compared to bulk Ti1-xAlxN. The strongest stabilization occurs for compositions in which the mixing enthalpy of bulk Ti1-xAlxN has its maximum. The effect is split into a strain and an interfacial (or chemical) contribution, and we show that both contributions are significant. An analysis of the local atomic structure reveals that the Ti atoms located in the interfacial layers relax significantly different from those in the other atomic layers of the multilayer. Considering the electronic structure of the studied system, we demonstrate that the lower Ti-site projected density of states at epsilon(F) in the Ti1-xAlxN/TiN multilayers compared to the corresponding monolithic bulk explains a decreased tendency toward decomposition.

    sted, utgiver, år, opplag, sider
    AMER PHYSICAL SOC, 2016
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-129166 (URN)10.1103/PhysRevB.93.174201 (DOI)000375990200003 ()
    Merknad

    Funding Agencies|Swedish Foundation for Strategic Research (SSF) project SRL [10-0026]; Erasmus Mundus Joint European Doctoral Programme DocMASE; Multiscale computational-design of novel hard nanostructure coatings; Swedish Research Council (VR) [2015-04391, 621-2012-4401, 2014-4750]; Grant of Ministry of Education and Science of the Russian Federation [14.Y26.31.0005]; Tomsk State University Academic D. I. Mendeleev Fund Program [8.1.18.2015]; LiLi-NFM; Swedish Government Strategic Research Area Grant in Materials Science

    Tilgjengelig fra: 2016-06-13 Laget: 2016-06-13 Sist oppdatert: 2018-02-09
    3. Growth and thermal stability of TiN/ZrAlN: Effect of internal interfaces
    Åpne denne publikasjonen i ny fane eller vindu >>Growth and thermal stability of TiN/ZrAlN: Effect of internal interfaces
    Vise andre…
    2016 (engelsk)Inngår i: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 121, s. 396-406Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    Wear resistant hard films comprised of cubic transition metal nitride (c-TMN) and metastable c-AlN with coherent interfaces have a confined operating envelope governed by the limited thermal stability of metastable phases. However, equilibrium phases (c-TMN and wurtzite(w)-AlN) forming semicoherent interfaces during film growth offer higher thermal stability. We demonstrate this concept for a model multilayer system with TiN and ZrAlN layers where the latter is a nanocomposite of ZrN- and AlN-rich domains. The interfaces between the domains are tuned by changing the AlN crystal structure by varying the multilayer architecture and growth temperature. The interface energy minimization at higher growth temperature leads to formation of semicoherent interfaces between w-AlN and c-TMN during growth of 15 nm thin layers. Ab initio calculations predict higher thermodynamic stability of semicoherent interfaces between c-TMN and w-AlN than isostructural coherent interfaces between c-TMN and c-AlN. The combination of a stable interface structure and confinement of w-AlN to nm-sized domains by its low solubility in c-TMN in a multilayer, results in films with a stable hardness of 34 GPa even after annealing at 1150 degrees C. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

    sted, utgiver, år, opplag, sider
    Pergamon Press, 2016
    Emneord
    Thermal stability, TM-Al-N multilayer films, Nanostructured materials, Interface energy, Three-dimensional atom probe (3DAP), Transmission electron microscopy
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-132827 (URN)10.1016/j.actamat.2016.07.006 (DOI)000386984500038 ()
    Merknad

    Funding Agencies|Swedish Research Council (VR grant) [621-2012-4401]; Swedish Foundation for Strategic Research (SSF) through the program MultiFilms [RMA08-0069]; Swedish government strategic research area grant in material science AFM - SFO MatLiU [2009-00971]; EUs Erasmus Mundus graduate school in Material Science and Engineering (DocMASE); Swedish Governmental Agency for Innovation Systems [VINNMer 2011-03464, 2013-02355]; EU-funded project AME-Lab (European Regional Development Fund) [C/4-EFRE-13/2009/Br]; DFG; federal state government of Saarland [INST 256/298-1 FUGG]

    Tilgjengelig fra: 2016-12-06 Laget: 2016-11-30 Sist oppdatert: 2020-03-19
    4. Systematic ab initio investigation of the elastic modulus in quaternary transition metal nitride alloys and their coherent multilayers
    Åpne denne publikasjonen i ny fane eller vindu >>Systematic ab initio investigation of the elastic modulus in quaternary transition metal nitride alloys and their coherent multilayers
    Vise andre…
    2017 (engelsk)Inngår i: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 127, s. 124-132Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    We give a comprehensive overview of the elastic properties of cubic quaternary transition metal nitride alloys and coherent nitride multilayers for design of wear resistant hard coatings. The elastic stiffness constants of the alloys are calculated using the special quasirandom structure method. For multilayers with sharp interfaces we prove the applicability of a linear-elasticity approximation and show that it can be used with success instead of performing direct computationally demanding ab initio calculations. We explore the trends and the potential of multicomponent alloying in engineering the strength and ductility of both, quaternary alloys and their multilayers. We investigate X(i-x-y)TixAlyN alloys where Xis Zr, Hf, V, Nb or Ta, and present an analysis based on increasing x. We show that with increasing Ti content ductility can increase in each alloy. Elastic isotropy is observed only in (Zr,Hf,V)((i-x-y))TixAlyN alloys in the middle of the compositional triangle, otherwise a high Youngs modulus is observed along [001]. We predict that coherent TiN/X(1-x-y)TixAlyN and ZrN/X(i-x-3)TixAlyN alloy multilayers with the [111] interfacial direction show increasing ductility with increasing x, while the multilayers with the [001] orientation become more brittle. We show that the Youngs moduli variation in the parent bulk quaternary nitride alloy provide a reliable descriptor to screen the Youngs modulus of coherent multilayers in high-throughput calculations. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

    sted, utgiver, år, opplag, sider
    PERGAMON-ELSEVIER SCIENCE LTD, 2017
    Emneord
    Ab initio calculations; Elastic properties; Transition metal nitride alloys; Multicomponent; Multilayers
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-136865 (URN)10.1016/j.actamat.2017.01.017 (DOI)000397362600012 ()
    Merknad

    Funding Agencies|Swedish Foundation for Strategic Research (SSF) project SRL Grant [10-0026]; MERA.NET [2013-02355]; Erasmus Mundus Joint European Doctoral Programme DocMASE; Swedish Research Council (VR) [2015-04391]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009 00971]; Grant of Ministry of Education and Science of the Russian Federation [14.Y26.31.000]

    Tilgjengelig fra: 2017-04-30 Laget: 2017-04-30 Sist oppdatert: 2018-02-09
    Fulltekst (pdf)
    Properties of multilayered and multicomponent nitride alloys from first principles
    Download (pdf)
    omslag
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    presentationsbild
  • 229.
    Witt, Stephen
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling.
    The Influence of Under Sleeper Pads on Railway Track Dynamics2008Independent thesis Advanced level (degree of Magister), 20 poäng / 30 hpOppgave
    Abstract [en]

    In this work the influence of Under Sleeper Pads on the dynamic forces on a railway track is investigated. A special interest is devoted to the effect of using Under Sleeper Pads in a railway track with changing vertical stiffness. The contact force between wheel and rail and the ballast contact forces are examined. For the investigation a finite element model with the length of thirty sleepers is created and calculations are performed with the software LS-DYNA. Three different cases of varying vertical track stiffness are studied: the transition from an embankment to a bridge, a randomly varying track stiffness along the railway track and hanging sleepers.

    Fulltekst (pdf)
    FULLTEXT01
  • 230.
    Wranne, Bengt
    et al.
    Linköpings universitet, Institutionen för medicin och vård, Klinisk fysiologi. Linköpings universitet, Hälsouniversitetet. Östergötlands Läns Landsting, Hjärt- och Medicincentrum, Fysiologiska kliniken US.
    Ask, Per
    Linköpings universitet, Institutionen för medicinsk teknik, Fysiologisk mätteknik. Linköpings universitet, Tekniska högskolan.
    Loyd, Dan
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanisk värmeteori och strömningslära. Linköpings universitet, Tekniska högskolan.
    Quantification of heart valve regurgitation: a critical analysis from a theoretical and experimental point of view.1985Inngår i: Clinical Physiology, ISSN 0144-5979, E-ISSN 1365-2281, Vol. 5, nr 1, s. 81-88Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A theoretical analysis is presented regarding factors of importance for the determination of distance of intrusion of the regurgitant jet in heart valve regurgitation. The analysis is based on hydrodynamic theory. In the idealized model situation, for a circular hole, the intrusion of the regurgitant jet is linearly related to the product of the fluid mean velocity in the orifice and the diameter of the orifice. This was also shown to be true in an experimental fluid model. Thus, volume regurgitation cannot be quantified by the measurement of distance of intrusion of the regurgitant jet alone. On the other hand, an estimate of volume regurgitation can, in the idealized situation, be obtained if mean fluid velocity in the orifice, distance of intrusion of the jet and regurgitation time are known.

2345 201 - 230 of 230
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