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  • 51.
    Gunnarsson, Pontus
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Methods to Predict Structural Response due to Random Sound Pressure Fields2015Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    To predict structural responses due to random sound pressure fields are of great interest within many fields of aircraft development, particularly within acoustic fatigue problems and definition of vibration requirements.  Today there exist some methods to quantify sound pressure fields affecting the air-fighters. Some of them are considered to be expensive, time consuming or with high computational cost. Examples of this would be to measure a real flight, produce data from wind tunnels, use Computational Fluid Dynamics (CFD) or obtain data from an engineering database. Once the sound pressure levels are known they can be applied as loads to structural models and this is the area studied in this work. To study these problems a new working tool is made using MATLAB. The tool’s main purpose is to give an opportunity to study structural responses caused by random sound pressure fields with different correlation methods.  Because of the complexity of both the sound pressure and different structures of the aircraft a few limitations are considered. The plate is used since this makes is easy to produce different mode shape functions. The mode shape function is an important part in this work as it can be used to create all possible frequency response functions in a structure. Then, to determine a structure response, different methods to produce pressure fields are used. The methods are called correlation-models and five different models are considered: uncorrelated, fully correlated and moving correlated load (MCL) and two empirical models due to the similarity to real sound pressure fields called Turbulent Boundary Layer (TBL) and a diffuse excitation model. To prove the accuracy of the created working tool, an independent FE-solver is used called Abaqus. Abaqus  is  used  to  validate  the  mode  shape-  and  the  frequency  response-fucntions.  Another advantage  with  Abaqus  is  that  the  solver  already  includes  three  of  the  correlation  models  which therefore simplify the verification of the new tool. Finally,  a  simulation  study  is  carried  out  in  order  to  validate  the  MATLAB  functions  and  test  the sensitivity  to  different  correlation  models.  In  order  to  do  this,  the  sound  pressure  field  is  to  be reasonable  approximated  and  therefore  data  from  the  database  ESDU  (acronym  of  Engineering Sciences Data Unit) is used that predicts sound pressure fields for different flight envelopes. In the simulation study all correlation models are compared to TBL due to its sound pressure and here it can be seen that fully correlated loads fails to predict response due to certain modes. On the other hand, the MCL model increases this accuracy for low Mach numbers and even more for high Mach numbers  due  to  its  velocity  dependence.  The  diffuse  model,  which  is  supposed  to  imitate  a  real pressure chamber load, is often believed to be conservative but in this study it can be seen that this is not always the case.

    Fulltekst (pdf)
    Methods to Predict Structural Response due to Random Sound Pressure Fields
  • 52. Bestill onlineKjøp publikasjonen >>
    Gustafsson, David
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Constitutive and fatigue crack propagation behaviour of Inconel 7182010Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    In this licentiate thesis the work done in the TURBO POWER project Influence of high temperature hold times on the fatigue life of nickel-based superalloys will be presented. The overall objective of this project is to develop and evaluate tools for designing against fatigue in gas turbine applications, with special focus on the nickel-based superalloy Inconel 718. Firstly, the constitutive behaviour of the material has been been studied, where focus has been placed on trying to describe the mean stress relaxation and initial softening of the material under intermediate temperatures. Secondly, the fatigue crack propagation behaviour under high temperature hold times has been studied. Focus has here been placed on investigating the main fatigue crack propagation phenomena with the aim of setting up a basis for fatigue crack propagation modelling.

    This thesis is divided into two parts. The first part describes the general framework, including basic constitutive and fatigue crack propagation behaviour as well as a theoretical background for the constitutive modelling of mean stress relaxation. This framework is then used in the second part, which consists of the four included papers.

    Delarbeid
    1. Fatigue crack growth behaviour of Inconel 718 with high temperature hold times
    Åpne denne publikasjonen i ny fane eller vindu >>Fatigue crack growth behaviour of Inconel 718 with high temperature hold times
    Vise andre…
    2010 (engelsk)Inngår i: Procedia Engineering, ISSN 1877-7058, E-ISSN 1877-7058, Vol. 2, nr 1, s. 1095-1104Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    In this work, fatigue crack growth measurements have been made on center-cracked tension specimens of Inconel 718, where the focus has been to observe the effect of high temperature hold times on the fatigue crack growth behaviour of the material. The material testing has been done at three different temperatures, namely 450 degrees C, 550 degrees C and 650 degrees C. All testing were done in an isothermal LCF context with a standard test method for measuring the fatigue crack growth rates.

    sted, utgiver, år, opplag, sider
    ELSEVIER SCIENCE BV, 2010
    Emneord
    nickel-base superalloys; fatigue crack propagation; Inconel 718
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-58352 (URN)10.1016/j.proeng.2010.03.118 (DOI)000278762900116 ()
    Tilgjengelig fra: 2010-08-13 Laget: 2010-08-11 Sist oppdatert: 2017-12-12bibliografisk kontrollert
    2. Modeling of the Constitutive Behavior of Inconel 718 at Intermediate Temperatures
    Åpne denne publikasjonen i ny fane eller vindu >>Modeling of the Constitutive Behavior of Inconel 718 at Intermediate Temperatures
    2011 (engelsk)Inngår i: Journal of engineering for gas turbines and power, ISSN 0742-4795, E-ISSN 1528-8919, Vol. 133, s. 094501-1-094501-4Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    Turbine disks are of large importance to turbine designers as theyare exposed to hot environment and subjected to high loads. Inorder to analyze such components with respect to fatigue crackinitiation, the work generally starts with a rigorous analysis of thefirst few cycles, during which an important stress redistributionwill always take place in an inelastic structure. In this work, thenonlinear kinematic hardening law by Ohno and Wang (1998,“Constitutive Modeling of Cyclic Plasticity With Emphasis onRatchetting,” Int. J. Mech. Sci., 40, pp. 251–261) has been used incombination with an isotropic softening law for describing theinitial stress-strain distribution for strain controlled uniaxial testsof the material Inconel 718. Focus has been placed on finding asimple model with few material parameters and to describe theinitial softening and the comparatively small mean stress relaxationobserved during the material testing. The simulation resultsobtained by using the model fit the experimental resultswell.

    sted, utgiver, år, opplag, sider
    ASME, 2011
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-68035 (URN)10.1115/1.4002913 (DOI)000290494800020 ()
    Tilgjengelig fra: 2011-05-06 Laget: 2011-05-06 Sist oppdatert: 2017-12-11
    3. Influence of high temperature hold times on the fatigue crack propagation in Inconel 718
    Åpne denne publikasjonen i ny fane eller vindu >>Influence of high temperature hold times on the fatigue crack propagation in Inconel 718
    Vise andre…
    2011 (engelsk)Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 33, nr 11, s. 1461-1469Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    High temperature fatigue crack growth in Inconel 718 has been studied at the temperatures 450 degrees C, 500 degrees C, 550 degrees C and 650 degrees C. The tests were conducted both without hold times and with hold times of different lengths and with a mix of both. Focus has been on quantifying the effect the hold time has upon the crack growth rate and how much it damages the material. Furthermore, it has been investigated how this damage influences the actual cracking behavior, i.e. where in the loading cycle the damage contributes most to the crack growth. This damage is related to the concept of a damaged zone in front of the crack tip. The size of the damaged zone has been derived from the tests and a microscopy study to confirm the findings has also been carried out. It is found that the concept of a damaged zone can be a successful explanatory model for the observed crack growth behavior under high temperature hold time.

    sted, utgiver, år, opplag, sider
    Elsevier, 2011
    Emneord
    Nickel-base superalloys, Fatigue crack propagation, Inconel 718, Hold times, Grain boundary embrittlement
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-70317 (URN)10.1016/j.ijfatigue.2011.05.011 (DOI)000293991000006 ()
    Merknad
    Funding Agencies|Swedish Energy Agency||Siemens Industrial Turbomachinery AB||Volvo Aero Corporation||Royal Institute of Technology||Tilgjengelig fra: 2011-09-02 Laget: 2011-09-02 Sist oppdatert: 2017-12-08
    4. Hold-time effect on the thermo-mechanical fatigue crack growth behaviour of Inconel 718
    Åpne denne publikasjonen i ny fane eller vindu >>Hold-time effect on the thermo-mechanical fatigue crack growth behaviour of Inconel 718
    2011 (engelsk)Inngår i: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 528, nr 29-30, s. 8660-8670Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    In-phase TMF crack growth testing with different lengths of the hold time at the maximum temperature of 550 °C has been conducted on Inconel 718 specimens. Focus has been on establishing a method for TMF crack growth testing and investigating the effect of high temperature hold times on the TMF crack growth of the material. The tests are compared to isothermal crack propagation tests and show good correlation. It is concluded that the controlling effect of the crack growth is an embrittlement of the material. This embrittlement is related to the concept of a damaged zone active in front of the crack tip. The size of this damaged zone will control the crack propagation rate and therefore it does not matter if the load is cycled under isothermal or TMF conditions.

    sted, utgiver, år, opplag, sider
    Elsevier, 2011
    Emneord
    TMF, crack growth
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-71304 (URN)10.1016/j.msea.2011.08.027 (DOI)000296676800046 ()
    Merknad
    Funding agencies|Swedish Energy Agency||Siemens Industrial Turbomachinery AB||Volvo Aero Corporation||Royal Institute of Technology||Tilgjengelig fra: 2011-10-11 Laget: 2011-10-11 Sist oppdatert: 2017-12-08
    Fulltekst (pdf)
    Constitutive and fatigue crack propagation behaviour of Inconel 718
    Download (pdf)
    omslag
  • 53.
    Gustafsson, David
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära.
    Constitutive modelling of the nickel base superalloy IN718; a preparatory study2008Independent thesis Advanced level (degree of Master (One Year)), 20 poäng / 30 hpOppgave
    Abstract [en]

    One of the limiting factors in gas turbine design is the allowable metal temperatures and loads in critical components. Specially designed superalloys are used when the conditions are most severe. One of these superalloys is Inconel 718. To be able to design components for higher temperature and higher loads, an accurate understanding and computational model of the material is needed. In this thesis the deformation mechanisms of Inconel 718 have been investigated and a theoretical basis for modelling in a large deformation context has been established. Finally a viscoplastic nonlinear kinematic hardening material model with an Armstrong-Frederick backstress evolution law has been implemented as a first step in describing the constitutive behaviour of the material Inconel 718.

    Fulltekst (pdf)
    fulltext
  • 54.
    Gustafsson, David
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Moverare, Johan
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska högskolan.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Sjöström, Sören
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Modeling of the Constitutive Behavior of Inconel 718 at Intermediate Temperatures2011Inngår i: Journal of engineering for gas turbines and power, ISSN 0742-4795, E-ISSN 1528-8919, Vol. 133, s. 094501-1-094501-4Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Turbine disks are of large importance to turbine designers as theyare exposed to hot environment and subjected to high loads. Inorder to analyze such components with respect to fatigue crackinitiation, the work generally starts with a rigorous analysis of thefirst few cycles, during which an important stress redistributionwill always take place in an inelastic structure. In this work, thenonlinear kinematic hardening law by Ohno and Wang (1998,“Constitutive Modeling of Cyclic Plasticity With Emphasis onRatchetting,” Int. J. Mech. Sci., 40, pp. 251–261) has been used incombination with an isotropic softening law for describing theinitial stress-strain distribution for strain controlled uniaxial testsof the material Inconel 718. Focus has been placed on finding asimple model with few material parameters and to describe theinitial softening and the comparatively small mean stress relaxationobserved during the material testing. The simulation resultsobtained by using the model fit the experimental resultswell.

  • 55.
    Gustner Börstell, Simon
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Fluida och mekatroniska system.
    Olsson, Tobias
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Fluida och mekatroniska system.
    Optimerad installation av hydraulslang i simuleringsmiljö: Industrial Path Solution - Cable Simulation2017Independent thesis Basic level (degree of Bachelor), 10,5 poäng / 16 hpOppgave
    Abstract [sv]

    Examensarbetet som presenteras i rapporten görs på uppdrag av Specma Group AB i Göteborg. Syftet är att analysera och utvärdera den nuvarande slangdragningen på Rolls Royce vattenjet aggregat S71-4. Efter analysen ska det undersökas om det är möjligt att optimera slangdragningen. I så fall ska ett konceptförslag presenteras som fördelaktigt innefattar en förklaring till varför den teoretiska livslängden ökar för slangarna i systemet.

    Arbetet utfördes genom förstudier om bakomliggande hydraulikteori och kvalitativa intervjuer av personer med stor erfarenhet av hydraulik. Det utfördes också tester i Specmas testcenter där slangarnas materialkarakteristik togs fram, vilket användes för att möjliggöra simuleringar. Programvaror som används är Creo Parametric vid modellering av modellen samt Industrial Path Solution – Cable Simulator (IPS CS) vid simulering och analyser. Det gjordes också en utbildning på Fraunhofer – Chalmer Centre för att fördjupa kunskaperna om IPS CS.

    Under arbetets gång har det genomförts analyser och utvärderingar av slangdragningen med uppmätta verkliga parametrar. Resultatet har sedan presenterats för Rolls Royce. Det visualiserades genom filmer hur valda parametrar påverkar slangarna, vilket också sammanställdes i diagram med exakta värden. Det presenterade materialet resulterade i att två förbättringsförslag kunde göras där fokuspunkterna specificerades av Rolls Royce.

    De två optimeringsförslagen som arbetet har resulterat i har utgått från två olika huvudfokus. Det första förslaget fokuserade på att optimera slangarnas längder medan det andra förslaget i att reducera läckagepunkterna i systemet. Optimeringsförslagen presenterades för Rolls Royce, vilket ledde till att de valde att implementera ett av dem i framtida produktion av S71-4.

    Fulltekst (pdf)
    fulltext
  • 56.
    Göransson, Andréas
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Fatigue life analysis of weld ends: Comparison between testing and FEM-calculations2014Independent thesis Advanced level (degree of Master (Two Years)), 300 hpOppgave
    Abstract [en]

    The thesis examines the fatigue life of weld ends, where very little usable research previously has been conducted, and often the weld ends are the critical parts of the weld. It is essential knowing the fatigue life of welds to be able to use them most efficiently.The report is divided into two parts; in the first the different calculation methods used today at Toyota Material Handling are examined and compared. Based on the results from the analysis and what is used mostly today, the effective notch approach is the method used in part two.To validate the calculation methods and models used, fatigue testing of the welded test specimens was conducted together with a stress test. New modelling methods of the weld ends that coincide with the test results were made in the finite element software Abaqus. A new way of modelling the weld ends for the effective notch method is also proposed. By using a notch radius of 0.2 mm and rounded weld ends the calculated fatigue life better matches the life of the real weld ends.

    Fulltekst (pdf)
    fulltext
  • 57.
    Hellberg, Viktor
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära.
    Fredrikson, Rikard
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära.
    Topologioptimering av kölskydd för segelbåtar2014Independent thesis Basic level (degree of Bachelor), 10,5 poäng / 16 hpOppgave
    Abstract [sv]

    I detta arbete har utformningen av ett kölskydd av metall för segelbåtar tagits fram. Kölskyddet som framtagits monteras längst ner på kölen. Syftet är att minska krafterna som verkar på båten vid en grundstötning genom att ta upp en del av rörelseenergin genom plastisk deformation.

    Vid utformningen av kölskyddets struktur har en metod för topologioptimering använts där målet varit att få så hög töjningsenergi (IED) i strukturen som möjligt. En heuristisk lösningsmetod där ineffektiva element tas bort ur strukturen har använts.

    Lämpliga material har undersökts och utvärderats utifrån mekaniska egenskaper samt motståndskraft mot korrosion i havsmiljö.

    Arbetet har resulterat i ett designförslag på en struktur av aluminium 5086 som enligt beräkningar kan absorbera 5 kJ energi. Detta motsvarar, för en båt som väger fyra ton, en minskning av energin som överförs till kölen på ca 10 %.

    Fulltekst (pdf)
    fulltext
  • 58.
    Hellberg, Viktor
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanisk värmeteori och strömningslära.
    Fredriksson, Rikard
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanisk värmeteori och strömningslära.
    Calculation of Fluid Dynamic Loads on a Projectile During Firing: Development of a CFD-modelling Approach2016Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    The transition from inner to outer ballistics is a crucial part of the launch of a projectile from a recoilless rifle. Since a launch of the rifle is a rapid process and due to the extreme conditions in terms of accelerations and temperature, physical measurements are hard to achieve.

    To gain knowledge about the fluid dynamic loads that act on the projectile during a launch CFD can be a useful technique. In this work a CFD model of the launch process has been developed. Different methods to implement the most important parts of the launch process have been evaluated and compared. An unsteady RANS-model have been utilised in combination with a dynamic mesh to handle the motion of the projectile.

    In this work, a spin-stable type of projectile has been analysed. To force the projectile to spin, helical grooves are used inside the launch tube. If the projectile does not fill out and seal the grooves completely, propellant gas can leak through these grooves. In the model it has been evaluated if the leak flow has an impact on the flow field around the projectile and its stability. To simplify the model the grooves were approximated as a gap with constant thickness between the tube and the projectile.

    Two different methods to implement the propellant burning have been tested. In the first case a pressure curve known from measurements are implemented. In the second, the mass flow from the combustion is modelled.

    This work shows that it is possible to predict the behaviour of the flow during a launch with a CFD model. The leak flow was found to have a significant impact on the flow field in front of the projectile. However, it has also been found that the leakage only have a limited effect on the fluid dynamic forces that works on the projectile during the transition phase.

    From this work it has been concluded that CFD can be a useful complement to physical tests and it gives a deeper understanding about the flow when the projectile leaves the launch tube. It has also been concluded that the launch process is an extensive topic and contains many different disciplines; therefore more work is needed to refine the model. 

    Fulltekst (pdf)
    fulltext
  • 59.
    Hilding, Daniel
    et al.
    DYNAmore Nordic AB, Linköping.
    Klarbring, Anders
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik. Linköpings universitet, Tekniska högskolan.
    Optimization of structures in frictional contact2012Inngår i: Computer Methods in Applied Mechanics and Engineering, ISSN 0045-7825, E-ISSN 1879-2138, Vol. 205-208, nr S1, s. 83-90Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper describes a new approach to optimization of linear elastic structures in frictional contact. It uses a novel method to determine an, in a specified sense, likely equilibrium state of the structure, using only the static equilibrium conditions. That is, no complex dynamic/quasi-static analyses have to be performed. The approach has the advantage that it is not necessary to know the complete load history, which is most often unknown for practical problems. To illustrate the theory, numerical results are given for the optimal design problem of sizing a truss to attain a more uniform normal contact force distribution.

    Fulltekst (pdf)
    fulltext
  • 60. Bestill onlineKjøp publikasjonen >>
    Hochwallner, Martin
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Industriell Produktion. Linköpings universitet, Tekniska fakulteten.
    On Motion Control of Linear Incremental Hydraulic Actuators2017Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Linear Incremental Hydraulic Actuators combine one or more short-stroke cylinders, and two or more engaging/disengaging mechanisms into one actuator with long, medium, or even unlimited stroke length. The motion of each single short-stroke actuator concatenated by the engaging/disengaging mechanisms forms the motion of the linear incremental hydraulic actuator.

    The patterns of how these motions are concatenated form the gaits of a specific linear incremental hydraulic actuator. Linear incremental hydraulic actuators may have more than one gait. In an application, the gaits may be combined to achieve optimal performance at various operating points.

    The distinguishing characteristic of linear incremental hydraulic actuators is the incremental motion. The term incremental actuator is seen as analogous to the incremental versus absolute position sensor. Incremental actuators realize naturally relative positioning. Incremental motion means also that the behavior does not depend on an absolute position but only on the relative position within a cycle or step.

    Incremental actuators may realize discrete incremental or continuous incremental motion. Discrete incremental actuators can only approach discrete positions, whereby stepper drives are one prominent example. In contrast, continuous incremental actuators may approach any position. Linear electric motors are one example of continuous incremental actuators. The actuator has no inherent limitation in stroke length, as every step or cycle adds only to the state at the beginning of the step or cycle and does not depend on the absolute position. This led to the alternative working title Hydraulic Infinite Linear Actuator.

    Linear incremental hydraulic actuator provides long stroke, high force, and linear motion and has the potential to

    • decrease the necessary resource usage,
    • minimize environmental impact, e.g. from potential oil spillage,
    • extend the range of feasible products: longer, stiffer, better, etc.

    This thesis presents an analysis of the characteristics and properties of linear incremental hydraulic actuators as well as the gaits and possible realizations of some gaits. The gait for continuous, smooth motion with two cylinders is comprehensively studied and a control concept for the tracking problem is proposed. The control concept encapsulates the complexity of the linear incremental hydraulic actuator so that an application does not have to deal with it. One other gait, the ballistic gait, which realizes fast, energy-efficient motion, enabling energy recuperation is studied.

    Fulltekst (pdf)
    On Motion Control of Linear Incremental Hydraulic Actuators
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    presentationsbild
  • 61. Bestill onlineKjøp publikasjonen >>
    Holmberg, Erik
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Topology optimization considering stress, fatigue and load uncertainties2016Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    This dissertation concerns structural topology optimization in conceptual design stages. The objective of the project has been to identify and solve problems that prevent structural topology optimization from being used in a broader sense in the avionic industry; therefore the main focus has been on stress and fatigue constraints and robustness with respect to load uncertainties.

    The thesis consists of two parts. The first part gives an introduction to topology optimization, describes the new contributions developed within this project and motivates why these are important. The second part includes five papers.

    The first paper deals with stress constraints and a clustered approach is presented where stress constraints are applied to stress clusters, instead of being defined for each point of the structure. Different approaches for how to create and update the clusters, such that sufficiently accurate representations of the local stresses are obtained at a reasonable computational cost, are developed and evaluated.

    High-cycle fatigue constraints are developed in the second paper, where loads described by a variable-amplitude load spectrum and material data from fatigue tests are used to determine a limit stress, for which below fatigue failure is not expected. A clustered approach is then used to constrain the tensile principal stresses below this limit.

    The third paper introduces load uncertainties and stiffness optimization considering the worst possible loading is then formulated as a semi-definite programming problem, which is solved very efficiently. The load is due to acceleration of point masses attached to the structure and the mass of the structure itself, and the uncertainty concerns the direction of the acceleration. The fourth paper introduces an extension to the formulated semi-definite programming problem such that both fixed and uncertain loads can be optimized for simultaneously.

    Game theory is used in the fifth paper to formulate a general framework, allowing essentially any differentiable objective and constraint functions, for topology optimization under load uncertainty. Two players, one controlling the structure and one the loads, are in conflict such that a solution to the game, a Nash equilibrium, is a design optimized for the worst possible load.

    Delarbeid
    1. Stress constrained topology optimization
    Åpne denne publikasjonen i ny fane eller vindu >>Stress constrained topology optimization
    2013 (engelsk)Inngår i: Structural and multidisciplinary optimization (Print), ISSN 1615-147X, E-ISSN 1615-1488, Vol. 48, nr 1, s. 33-47Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    This paper develops and evaluates a method for handling stress constraints in topology optimization. The stress constraints are used together with an objective function that minimizes mass or maximizes stiffness, and in addition, the traditional stiffness based formulation is discussed for comparison. We use a clustering technique, where stresses for several stress evaluation points are clustered into groups using a modified P-norm to decrease the number of stress constraints and thus the computational cost. We give a detailed description of the formulations and the sensitivity analysis. This is done in a general manner, so that different element types and 2D as well as 3D structures can be treated. However, we restrict the numerical examples to 2D structures with bilinear quadrilateral elements. The three formulations and different approaches to stress constraints are compared using two well known test examples in topology optimization: the L-shaped beam and the MBB-beam. In contrast to some other papers on stress constrained topology optimization, we find that our formulation gives topologies that are significantly different from traditionally optimized designs, in that it actually manage to avoid stress concentrations. It can therefore be used to generate conceptual designs for industrial applications.

    Emneord
    Topology optimization, Stress constraints, Clusters, SIMP, MMA
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-88092 (URN)10.1007/s00158-012-0880-7 (DOI)000320865900003 ()
    Tilgjengelig fra: 2013-01-30 Laget: 2013-01-30 Sist oppdatert: 2017-12-06bibliografisk kontrollert
    2. Fatigue constrained topology optimization
    Åpne denne publikasjonen i ny fane eller vindu >>Fatigue constrained topology optimization
    2014 (engelsk)Inngår i: Structural and multidisciplinary optimization (Print), ISSN 1615-147X, E-ISSN 1615-1488, Vol. 50, nr 2, s. 207-219Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    We present a contribution to a relatively unexplored application of topology optimization: structural topology optimization with fatigue constraints. A probability based high-cycle fatigue analysis is combined with principal stress calculations in order to find the topology with minimal mass that can withstand prescribed loading conditions for a specific life time. This allows us to generate optimal conceptual designs of structural components where fatigue life is the dimensioning factor.

    We describe the fatigue analysis and present ideas that makes it possible to separate the fatigue analysis from the topology optimization. The number of constraints is kept low as they are applied to stress clusters, which are created such that they give adequate representations of the local stresses. Optimized designs constrained by fatigue and static stresses are shown and a comparison is also made between stress constraints based on the von Mises criterion and the highest tensile principal stresses.

    sted, utgiver, år, opplag, sider
    Springer-Verlag New York, 2014
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-88093 (URN)10.1007/s00158-014-1054-6 (DOI)000339944100003 ()
    Tilgjengelig fra: 2013-01-30 Laget: 2013-01-30 Sist oppdatert: 2017-12-06bibliografisk kontrollert
    3. Worst-case topology optimization of self-weight loaded structures using semi-definite programming
    Åpne denne publikasjonen i ny fane eller vindu >>Worst-case topology optimization of self-weight loaded structures using semi-definite programming
    2015 (engelsk)Inngår i: Structural and multidisciplinary optimization (Print), ISSN 1615-147X, E-ISSN 1615-1488, Vol. 52, nr 5, s. 915-928Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    The paper concerns worst-case compliance optimization by finding the structural topology with minimum compliance for the loading due to the worst possible acceleration of the structure and attached non-structural masses. A main novelty of the paper is that it is shown how this min-max problem can be formulated as a non-linear semi-definite programming (SDP) problem involving a small-size constraint matrix and how this problem is solved numerically. Our SDP formulation is an extension of an eigenvalue problem seen previously in the literature; however, multiple eigenvalues naturally arise which makes the eigenvalue problem non-smooth, whereas the SDP problem presented in this paper provides a computationally tractable problem. Optimized designs, where the uncertain loading is due to acceleration of applied masses and the weight of the structure itself, are shown in two and three dimensions and we show that these designs satisfy optimality conditions that are also presented.

    Emneord
    Topology optimization; Semi-definite programming; Worst-case compliance; Self-weight; Robust optimization
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-123002 (URN)10.1007/s00158-015-1285-1 (DOI)000366590800006 ()
    Tilgjengelig fra: 2015-12-01 Laget: 2015-12-01 Sist oppdatert: 2017-12-01bibliografisk kontrollert
    4. Large-scale robust topology optimization under load-uncertainty
    Åpne denne publikasjonen i ny fane eller vindu >>Large-scale robust topology optimization under load-uncertainty
    2015 (engelsk)Inngår 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, Publicerat paper (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.

    Emneord
    Robust optimization, Topology optimization, Large-scale optimization, Non-linear semi-definite programming
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-123004 (URN)978-0-646-94394-7 (ISBN)
    Konferanse
    11th World Congress on Structural and Multidisciplinary Optimization (WCSMO-11), Sydney Australia, 7–12 June
    Tilgjengelig fra: 2015-12-01 Laget: 2015-12-01 Sist oppdatert: 2017-05-15bibliografisk kontrollert
    5. Game theory approach to robust topology optimization with uncertain loading
    Åpne denne publikasjonen i ny fane eller vindu >>Game theory approach to robust topology optimization with uncertain loading
    2017 (engelsk)Inngår i: Structural and multidisciplinary optimization (Print), ISSN 1615-147X, E-ISSN 1615-1488, Vol. 55, nr 4, s. 1383-1397Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    The paper concerns robustness with respect to uncertain loading in topology optimization problems with essentially arbitrary objective functions and constraints. Using a game theoretic framework we formulate problems, or games, defining Nash equilibria. In each game a set of topology design variables aim to find an optimal topology, while a set of load variables aim to find the worst possible load. Several numerical examples with uncertain loading are solved in 2D and 3D. The games are formulated using global stress, mass and compliance as objective functions or constraints.

    sted, utgiver, år, opplag, sider
    Springer, 2017
    Emneord
    Topology optimization, Robust optimization, Game theory, Nash equilibrium, Stress constraints
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-123006 (URN)10.1007/s00158-016-1548-5 (DOI)000398951100015 ()
    Merknad

    Funding agencies: NFFP [2013-01221]; Swedish Armed Forces; Swedish Defence Materiel Administration; Swedish Governmental Agency for Innovation Systems; Swedish Foundation for Strategic Research [AM13-0029]

    Tilgjengelig fra: 2015-12-01 Laget: 2015-12-01 Sist oppdatert: 2017-05-18bibliografisk kontrollert
    Fulltekst (pdf)
    fulltext
    Download (pdf)
    omslag
    Download (jpg)
    presentationsbild
  • 62.
    Holmberg, Erik
    et al.
    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.
    Klarbring, Anders
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Game theory approach to robust topology optimization with uncertain loading2017Inngår i: Structural and multidisciplinary optimization (Print), ISSN 1615-147X, E-ISSN 1615-1488, Vol. 55, nr 4, s. 1383-1397Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The paper concerns robustness with respect to uncertain loading in topology optimization problems with essentially arbitrary objective functions and constraints. Using a game theoretic framework we formulate problems, or games, defining Nash equilibria. In each game a set of topology design variables aim to find an optimal topology, while a set of load variables aim to find the worst possible load. Several numerical examples with uncertain loading are solved in 2D and 3D. The games are formulated using global stress, mass and compliance as objective functions or constraints.

  • 63.
    Holmberg, Erik
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten. Saab AB, SE 581 88, Linköping, Sweden .
    Thore, Carl-Johan
    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.
    Worst-case topology optimization of self-weight loaded structures using semi-definite programming2015Inngår i: Structural and multidisciplinary optimization (Print), ISSN 1615-147X, E-ISSN 1615-1488, Vol. 52, nr 5, s. 915-928Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The paper concerns worst-case compliance optimization by finding the structural topology with minimum compliance for the loading due to the worst possible acceleration of the structure and attached non-structural masses. A main novelty of the paper is that it is shown how this min-max problem can be formulated as a non-linear semi-definite programming (SDP) problem involving a small-size constraint matrix and how this problem is solved numerically. Our SDP formulation is an extension of an eigenvalue problem seen previously in the literature; however, multiple eigenvalues naturally arise which makes the eigenvalue problem non-smooth, whereas the SDP problem presented in this paper provides a computationally tractable problem. Optimized designs, where the uncertain loading is due to acceleration of applied masses and the weight of the structure itself, are shown in two and three dimensions and we show that these designs satisfy optimality conditions that are also presented.

    Fulltekst (pdf)
    fulltext
  • 64.
    Holmberg, Joakim
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Classification of Paralympic Athletes using Musculoskeletal Simulations2016Konferansepaper (Annet vitenskapelig)
  • 65.
    Holmberg, Joakim
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik. Linköpings universitet, Tekniska högskolan.
    Cross-country Skiing Biomechanics using the AnyBody Modeling System2007Konferansepaper (Annet vitenskapelig)
  • 66.
    Holmberg, Joakim
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Skiers’ summer training – to bike or not to bike?2015Konferansepaper (Annet vitenskapelig)
    Fulltekst (pdf)
    fulltext
  • 67.
    Holmberg, Joakim
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik. Linköpings universitet, Tekniska högskolan.
    Lund Ohlsson, Marie
    Department of Engineering and Sustainable Development, Mid Sweden University, Sweden .
    Danvind, Jonas
    Department of Engineering and Sustainable Development, Mid Sweden University, Sweden .
    Letter: Musculoskeletal simulations: a complementary tool for classification of athletes with physical impairments2012Inngår i: Prosthetics and orthotics international, ISSN 0309-3646, E-ISSN 1746-1553, Vol. 36, nr 3, s. 396-397Artikkel i tidsskrift (Annet vitenskapelig)
    Abstract [en]

    n/a

    Fulltekst (pdf)
    fulltext
  • 68.
    Holmberg, Joakim
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik. Linköpings universitet, Tekniska högskolan.
    Wagenius, P.
    Mid Sweden University.
    A biomechanical model of a double‐poling skier2003Inngår i: In International Society of Biomechanics XIXth Congress on The human body in motion, CD Rom Abstracts and Proceedings, Milburn, P. (Ed.), University of Otago, Dunedin, New Zealand, 6‐11 July, 2003Konferansepaper (Annet vitenskapelig)
  • 69.
    Holmberg, L. Joakim
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik. Linköpings universitet, Tekniska högskolan.
    A simulation study on the necessity of muscle contraction dynamics in cross-country skiingManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    Competitive cross-country skiing is considered to be a fast and powerful dynamic movement. It is unknown what level of complexity that is needed in a musculoskeletal model of a skiing movement, e.g. double-poling. Therefore, a simulation study is carried out to explore the influence of muscle model choice. The theoretical framework of two types of muscle models and their respective implementations are given. These models are a Hill-type model with contraction dynamics and a constant force model, respectively. Results show that it is necessary to incorporate muscle contraction dynamics to estimate individual muscle behaviour in double-poling. Moreover, it may be bad practice to model different body parts with different muscle models; the musculoskeletal system is not a collection of discrete uncoupled body parts and kinetic effects will propagate through the system.

  • 70.
    Holmberg, L. Joakim
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik. Linköpings universitet, Tekniska högskolan.
    Biomekanisk simulering av längdskidåkning2012Inngår i: Svensk idrottsmedicin, ISSN 1103-7652, Vol. 31, nr 3, s. 11-13Artikkel i tidsskrift (Annet (populærvitenskap, debatt, mm))
    Fulltekst (pdf)
    fulltext
  • 71.
    Holmberg, L. Joakim
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik. Linköpings universitet, Tekniska högskolan.
    Musculoskeletal Biomechanics for Paralympic Classification2013Konferansepaper (Annet vitenskapelig)
  • 72. Bestill onlineKjøp publikasjonen >>
    Holmberg, L. Joakim
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik. Linköpings universitet, Tekniska högskolan.
    Musculoskeletal Biomechanics in Cross-country Skiing2012Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Why copy the best athletes? When you finally learn their technique, they may have already moved on. Using muscluloskeletal biomechanics you might be able to add the "know-why" so that you can lead, instead of being left in the swells.

    This dissertation presents the theoretical framework of musculoskeletal modeling using inverse dynamics with static optimization. It explores some of the possibilities and limitations of musculoskeletal biomechanics in cross-country skiing, especially double-poling. The basic path of the implementation is shown and discussed, e.g. the issue of muscle model choice. From that discussion it is concluded that muscle contraction dynamics is needed to estimate individual muscle function in double-poling. Several computer simulation models, using The Anybody Modeling System™, have been created to study different cross-country skiing applications. One of the applied studies showed that the musculoskeletal system is not a collection of discrete uncoupled parts because kinematic differences in the lower leg region caused kinetic differences in the other end of the body. An implication of the results is that the kinematics and kinetics of the whole body probably are important when studying skill and performance in sports. Another one of the applied studies showed how leg utilisation may affect skiing efficiency and performance in double-poling ergometry. Skiing efficiency was defined as skiing work divided by metabolic muscle work, performance was defined as forward impulse. A higher utilization of the lower-body increased the performance, but decreased the skiing efficiency. The results display the potential of musculoskeletal biomechanics for skiing efficiency estimations. The subject of muscle decomposition is also studied. It is shown both analytically and with numerical simulations that muscle force estimates may be affected by muscle decomposition depending on the muscle recruitment criteria. Moreover, it is shown that proper choices of force normalization factors may overcome this issue. Such factors are presented for two types of muscle recruitment criteria.

    To sum up, there are still much to do regarding both the theoretical aspects as well as the practical implementations before predictions on one individual skier can be made with any certainty. But hopefully, this disseration somewhat furthers the fundamental mechanistic understanding of cross-country skiing, and shows that musculoskeletal biomechanics will be a useful complement to existing experimental methods in sports biomechanics.

    Delarbeid
    1. A musculoskeletal full‐body simulation of cross‐country skiing
    Åpne denne publikasjonen i ny fane eller vindu >>A musculoskeletal full‐body simulation of cross‐country skiing
    2008 (engelsk)Inngår i: Proc. IMechE Vol. 222 Part P: J. Sports Engineering and Technology, ISSN 1754-3371, Vol. 222, nr 1, s. 11-22Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    This paper presents a measurement-driven, musculoskeletal, full-body simulation model for biomechanical analysis of the double-poling (DP) technique in cross-country skiing. DP is a fast and powerful full-body movement; therefore, it is interesting to examine whether inverse dynamics using static optimization is working for a musculoskeletal full-body model with high accelerations, a large range of motion, and realistic loads. An experiment was carried out to measure motion and pole force of a skier on a double-poling ergometer. Using the measurement data, a simulation model was implemented in the AnyBody Modeling System (AnyBody Technology A/S, Denmark). Experimental results of motion and pole force from the DP ergometer, and also simulation results of relative muscle force profiles, are presented. These results agree with results found in literature when the kinematics and external kinetics are similar. Consequently, it should be possible to use computer simulations of this type for cross-country skiing simulations. With a simulation model, it is possible to perform optimization studies and to ask and answer ‘what if’ questions. Solutions to such problems are not easy to obtain by traditional testing alone.

    Emneord
    biomechanics, double poling, ergometer, inverse dynamics
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-12912 (URN)10.1243/17543371JSET10 (DOI)
    Tilgjengelig fra: 2008-01-28 Laget: 2008-01-28 Sist oppdatert: 2015-01-14
    2. Performance optimization by musculoskeletal simulation
    Åpne denne publikasjonen i ny fane eller vindu >>Performance optimization by musculoskeletal simulation
    Vise andre…
    2012 (engelsk)Inngår i: Movement & Sport Sciences – Science & Motricité, ISSN 2118-5735, Vol. 75, s. 73-83Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

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

    Abstract [fr]

    Cet article s’appuie sur deux exemples, ski de fond et badminton, pour illustrer l’utilisation de la simulation musculo-squelettique comme un outil pour comprendre et finalement optimiser les performances sportives. Les r ́sultats montrent que l’analyse donne un aper ̧u des performances qui ne peuvent pas ˆtre obtenues par d’autres moyens, et il est pr ́conis ́ que cette id ́e peut finalement conduire ` un meilleur entraˆaınement. L’importance du (( savoir-pourquoi )) en plus du (( savoir-faire )) est soulign ́, et il est suppos ́ que cela pourrait permettre aux athl`tes d’apprendre plus rapidement des techniques difficiles.

    sted, utgiver, år, opplag, sider
    Les Ulis, France: EDP Sciences, 2012
    Emneord
    Simulation, musculoskeletal model, sport, optimization
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-71022 (URN)10.1051/sm/2011122 (DOI)
    Prosjekter
    Beräkningsbaserad biomekanik inom längdskidåkning - möjligheter och begränsningar
    Merknad
    This study has received support from the following sources: The Danish Advanced Technology Foundation, The Swedish National Centre for Research in Sports (Grant No. 168/09) and Active Sportswear A/S. The authors wish to thank the Swedish Winter Sports Research Centre for providing laboratory resources.Tilgjengelig fra: 2011-09-27 Laget: 2011-09-27 Sist oppdatert: 2015-01-14
    3. Skiing efficiency versus performance in double-poling ergometry
    Åpne denne publikasjonen i ny fane eller vindu >>Skiing efficiency versus performance in double-poling ergometry
    2013 (engelsk)Inngår i: Computer Methods in Biomechanics and Biomedical Engineering, ISSN 1025-5842, E-ISSN 1476-8259, Vol. 16, nr 9, s. 987-992Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    This study is on how leg utilisation may affect skiing efficiency and performance in double-poling ergometry. Three experiments were conducted, each with a different style of the double-poling technique: traditional with small knee range-of-motion and fixed heels (TRAD); modern with large knee range-of-motion and fixed heels (MOD1) and modern with large knee range-of-motion and free heels (MOD2). For each style, motion data were extracted with automatic marker recognition of reflective markers and applied to a 3D full-body musculoskeletal simulation model. Skiing efficiency (skiing work divided by metabolic muscle work) and performance (forward impulse) were computed from the simulation output. Skiing efficiency was 4.5%, 4.1% and 4.1% for TRAD, MOD1 and MOD2, respectively. Performance was 111, 143 and 149Ns for TRAD, MOD1 and MOD2, respectively. Thus, higher lower body utilisation increased the performance but decreased the skiing efficiency. These results demonstrate the potential of musculoskeletal simulations for skiing efficiency estimations.

    sted, utgiver, år, opplag, sider
    Taylor & Francis, 2013
    Emneord
    AnyBody Modeling System; AviMes AD; biomechanics; cross-country skiing; impulse; musculoskeletal simulation
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-71027 (URN)10.1080/10255842.2011.648376 (DOI)000324612300008 ()
    Prosjekter
    Beräkningsbaserad biomekanik inom längdskidåkning - möjligheter och begränsningar
    Merknad

    This study was sponsored in part by the Swedish National Centre for Research in Sports (Grant No. 168/09). The Swedish Winter Sports Research Centre provided laboratory resources.

    Tilgjengelig fra: 2011-09-27 Laget: 2011-09-27 Sist oppdatert: 2017-12-08bibliografisk kontrollert
    4. Muscle decomposition and recruitment criteria influence muscle force estimates
    Åpne denne publikasjonen i ny fane eller vindu >>Muscle decomposition and recruitment criteria influence muscle force estimates
    2012 (engelsk)Inngår i: Multibody system dynamics, ISSN 1384-5640, E-ISSN 1573-272X, Vol. 28, nr 3, s. 283-289Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    It has recently been pointed out that muscle decomposition influence muscle force estimates in musculoskeletal simulations. We show analytically and with numerical simulations that this influence depends on the recruitment criteria. Moreover, we also show that the proper choices of force normalization factors may overcome the issue. Such factors for the minmax and the polynomial criteria are presented.

    sted, utgiver, år, opplag, sider
    Springer, 2012
    Emneord
    force normalization factor, minmax optimization criteria, musculoskeletal simulation, polynomial optimization criteria
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-71021 (URN)10.1007/s11044-011-9277-4 (DOI)000306734500005 ()
    Prosjekter
    Beräkningsbaserad biomekanik inom längdskidåkning - möjligheter och begränsningar
    Merknad

    This study was sponsored in part by the Swedish National Centre for Research in Sports (Grant No. 168/09). The authors wish to thank the Swedish Winter Sports Research Centre for providing laboratory resources.

    Tilgjengelig fra: 2011-09-27 Laget: 2011-09-27 Sist oppdatert: 2017-12-08bibliografisk kontrollert
    5. A simulation study on the necessity of muscle contraction dynamics in cross-country skiing
    Åpne denne publikasjonen i ny fane eller vindu >>A simulation study on the necessity of muscle contraction dynamics in cross-country skiing
    (engelsk)Manuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    Competitive cross-country skiing is considered to be a fast and powerful dynamic movement. It is unknown what level of complexity that is needed in a musculoskeletal model of a skiing movement, e.g. double-poling. Therefore, a simulation study is carried out to explore the influence of muscle model choice. The theoretical framework of two types of muscle models and their respective implementations are given. These models are a Hill-type model with contraction dynamics and a constant force model, respectively. Results show that it is necessary to incorporate muscle contraction dynamics to estimate individual muscle behaviour in double-poling. Moreover, it may be bad practice to model different body parts with different muscle models; the musculoskeletal system is not a collection of discrete uncoupled body parts and kinetic effects will propagate through the system.

    Emneord
    Double-poling, fast movements, Hill-type muscle, musculoskeletal model
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-75335 (URN)
    Prosjekter
    Beräkningsbaserad biomekanik inom längdskidåkningen - möjligheter och begränsningar
    Tilgjengelig fra: 2012-02-26 Laget: 2012-02-26 Sist oppdatert: 2015-01-14bibliografisk kontrollert
    Fulltekst (pdf)
    Musculoskeletal Biomechanics in Cross-country Skiing
    Download (pdf)
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  • 73.
    Holmberg, L. Joakim
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik. Linköpings universitet, Tekniska högskolan.
    Holmberg, Hans-Christer
    Mittuniversitetet.
    The role of triceps in double-poling biomechanics, an introductory study2007Inngår i: 4th International Congress on Science and Skiing: Book of Abstracts / [ed] E. Müller, S. Lindinger, T. Stöggl & V. Fastenbauer, Salzburg, 2007, s. 184-Konferansepaper (Annet vitenskapelig)
  • 74.
    Holmberg, L. Joakim
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik. Linköpings universitet, Tekniska högskolan.
    Klarbring, Anders
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik. Linköpings universitet, Tekniska högskolan.
    Muscle decomposition and recruitment criteria influence muscle force estimates2012Inngår i: Multibody system dynamics, ISSN 1384-5640, E-ISSN 1573-272X, Vol. 28, nr 3, s. 283-289Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    It has recently been pointed out that muscle decomposition influence muscle force estimates in musculoskeletal simulations. We show analytically and with numerical simulations that this influence depends on the recruitment criteria. Moreover, we also show that the proper choices of force normalization factors may overcome the issue. Such factors for the minmax and the polynomial criteria are presented.

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  • 75.
    Holmberg, L. Joakim
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik. Linköpings universitet, Tekniska högskolan.
    Lund, A. M.
    Mid Sweden University.
    A musculoskeletal full‐body simulation of cross‐country skiing2008Inngår i: Proc. IMechE Vol. 222 Part P: J. Sports Engineering and Technology, ISSN 1754-3371, Vol. 222, nr 1, s. 11-22Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper presents a measurement-driven, musculoskeletal, full-body simulation model for biomechanical analysis of the double-poling (DP) technique in cross-country skiing. DP is a fast and powerful full-body movement; therefore, it is interesting to examine whether inverse dynamics using static optimization is working for a musculoskeletal full-body model with high accelerations, a large range of motion, and realistic loads. An experiment was carried out to measure motion and pole force of a skier on a double-poling ergometer. Using the measurement data, a simulation model was implemented in the AnyBody Modeling System (AnyBody Technology A/S, Denmark). Experimental results of motion and pole force from the DP ergometer, and also simulation results of relative muscle force profiles, are presented. These results agree with results found in literature when the kinematics and external kinetics are similar. Consequently, it should be possible to use computer simulations of this type for cross-country skiing simulations. With a simulation model, it is possible to perform optimization studies and to ask and answer ‘what if’ questions. Solutions to such problems are not easy to obtain by traditional testing alone.

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    fulltext
  • 76.
    Holmberg, L. Joakim
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik.
    Lund Ohlsson, Marie
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik.
    Danvind, Jonas
    Mittuniversitetet.
    Can Simulations Assist in Classification Development?2013Inngår i: Equipment and Technology in Paralympic Sports, International Paralympic Committee , 2013Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    There is a critical need for research that describes the extent to which impairments of varying type, severity and distribution impact performance in Paralympic sports. It is important with evidence-based judgment on how the impairments aect performance. In the following, we present a complementary evidence-based tool for classication.

    Let us start with an example. We recently presented a study (Holmberg et al., 2012)1 that utilized two full-body musculoskeletal simulation models of cross-country skiing (double-poling). The models were identical except that one carried no muscles in the right lower leg and foot; thus mimicking a lower leg prosthesis. It was hypothesized that a lower leg prosthesis would inuence muscular work throughout the whole body. Results showed that to generate the same motion and external work, an able-bodied skier only had to produce about 80% metabolic muscle work compared to a disabled skier (with a non-active right lower leg prosthesis).

    In reality there is always psychological factors present and it is probably not possible to nd two human beings (one fully functional and one impaired) with the same tness, size, strength and technique. Thus, it is hard to nd the unbiased eect of an impairment on performance in a speci c sport. The example above shows the strength of using simulations because a  musculoskeletal model yields quantitative data on the unbiased eect of dierent functional impairments.

    In cross-country skiing, athletes with functional impairments are, in 'competition format' classification, assigned to dierent categories with weight factors. Athletes perform their race and the result list is presented as race time multiplied by weight factor. In the future, musculoskeletal simulations may assist in answering how a specic functional impairment aects performance and thereby improve the fairness in assigning weight factors for classication.

    Download (pdf)
    Presentation: Can Simulations Assist in Classification Development?
  • 77.
    Holmberg, L. Joakim
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik. Linköpings universitet, Tekniska högskolan.
    Lund Ohlsson, Marie
    Department of Engineering and Sustainable Development, Mid Sweden University, Östersund, Sweden.
    Supej, Matej
    Faculty of Sport, University of Ljubljana, Ljubljana, Slovenia.
    Holmberg, Hans-Christer
    Swedish Winter Sports Research Centre, Department of Health Sciences, Mid Sweden University, Östersund.
    Skiing efficiency versus performance in double-poling ergometry2013Inngår i: Computer Methods in Biomechanics and Biomedical Engineering, ISSN 1025-5842, E-ISSN 1476-8259, Vol. 16, nr 9, s. 987-992Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This study is on how leg utilisation may affect skiing efficiency and performance in double-poling ergometry. Three experiments were conducted, each with a different style of the double-poling technique: traditional with small knee range-of-motion and fixed heels (TRAD); modern with large knee range-of-motion and fixed heels (MOD1) and modern with large knee range-of-motion and free heels (MOD2). For each style, motion data were extracted with automatic marker recognition of reflective markers and applied to a 3D full-body musculoskeletal simulation model. Skiing efficiency (skiing work divided by metabolic muscle work) and performance (forward impulse) were computed from the simulation output. Skiing efficiency was 4.5%, 4.1% and 4.1% for TRAD, MOD1 and MOD2, respectively. Performance was 111, 143 and 149Ns for TRAD, MOD1 and MOD2, respectively. Thus, higher lower body utilisation increased the performance but decreased the skiing efficiency. These results demonstrate the potential of musculoskeletal simulations for skiing efficiency estimations.

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    fulltext
  • 78.
    Hugo, Anton
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Fluida och mekatroniska system. Linköpings universitet, Tekniska högskolan.
    Pettersson, Karl
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Fluida och mekatroniska system. Linköpings universitet, Tekniska högskolan.
    Heybroek, Kim
    Volvo Construction Equipment AB, Eskilstuna, Sweden.
    Krus, Petter
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Fluida och mekatroniska system. Linköpings universitet, Tekniska högskolan.
    Modelling and Control of a Complementary Energy Recuperation System for Mobile Working Machines2013Inngår i: / [ed] Petter Krus, Magnus Sethson, Liselott Ericson, Linköping: Linköping University Electronic Press, 2013, s. 21-30Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The concept of hybrid technologies for mobile working machines has gained increased attention in recent years. This paper deals with a parallel hybrid system for energy recuperation based on a two-machine hydraulic transformer. The system can be connected hydraulically to an existing hydraulic circuit as a complementary add-on system. The linear analysis of the system visualises the control difficulties coming from a low inertia, slow control dynamics of the machines and the non-linear stick-slip friction during low speeds. A control strategy based on linear control methods is proposed and evaluated in a hardware test bench. It is shown that an acceptable performance can be achieved even with fairly simple models. Additionally, a start-up procedure is proposed to start the transformer from zero speed

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  • 79.
    Hällqvist, Robert
    et al.
    Systems Simulation and Concept Design, Saab Aeronautics, Linköping, Sweden.
    Schminder, Jörg
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanisk värmeteori och strömningslära. Linköpings universitet, Tekniska fakulteten.
    Eek, Magnus
    Systems Simulation and Concept Design, Saab Aeronautics, Linköping, Sweden.
    Braun, Robert
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Fluida och mekatroniska system. Linköpings universitet, Tekniska fakulteten.
    Gårdhagen, Roland
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanisk värmeteori och strömningslära. Linköpings universitet, Tekniska fakulteten.
    Krus, Petter
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Fluida och mekatroniska system. Linköpings universitet, Tekniska fakulteten.
    A Novel FMI and TLM-based Desktop Simulator for Detailed Studies of Thermal Pilot Comfort2018Inngår i: ICAS congress proceeding, International Council of the Aeronautical Sciences , 2018, artikkel-id ICAS2018_0203Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    Modelling and Simulation is key in aircraft system development. This paper presents a novel, multi-purpose, desktop simulator that can be used for detailed studies of the overall performance of coupled sub-systems, preliminary control design, and multidisciplinary optimization. Here, interoperability between industrially relevant tools for model development and simulation is established via the Functional Mockup Interface (FMI) and System Structure and Parametrization (SSP) standards. Robust and distributed simulation is enabled via the Transmission Line element Method (TLM). The advantages of the presented simulator are demonstrated via an industrially relevant use-case where simulations of pilot thermal comfort are coupled to Environmental Control System (ECS) steadystate and transient performance.

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    fulltext
  • 80.
    Imtiaz, Nasir
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanisk värmeteori och strömningslära.
    CFD simulation of dip-lubricated single-stage gearboxes through coupling of multiphase flow and multiple body dynamics: an initial investigation2018Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    Transmissions are an essential part of a vehicle powertrain. An optimally designed powertrain can result in energy savings, reduced environmental impact and increased comfort and reliability. Along with other components of the powertrain, efficiency is also a major concern in the design of transmissions. The churning power losses associated with the motion of gears through the oil represent a significant portion of the total power losses in a transmission and therefore need to be estimated. A lack of reliable empirical models for the prediction of these losses has led to the emergence of CFD (Computational Fluid Dynamics) as a means to (i) predict these losses and (ii) promote a deeper understanding of the physical phenomena responsible for theselosses in order to improve existing models.

    The commercial CFD solver STAR-CCM+ is used to investigate the oil distribution and the churning power losses inside two gearbox configurations namely an FZG (Technical Institute for the Study of Gears and Drive Mechanisms) gearbox and a planetary gearbox. A comparison of two motion handling techniques in STARCCM+ namely MRF (Moving Reference Frame) and RBM (Rigid Body Motion) models is made in terms of the accuracy of results and the computational requirements using the FZG gearbox. A sensitivity analysis on how the size of gap between the meshing gear teeth affects the flow and the computational requirements is also done using the FZG gearbox. Different modelling alternatives are investigated for the planetary gearbox and the best choices have been determined. The numerical simulations are solved in an unsteady framework where the VOF (Volume Of Fluid) multiphase model is used to track the interface between the immiscible phases. The overset meshing technique has been used to reconfigure the mesh at each time step.

    The results from the CFD simulations are presented and discussed in terms of the modelling choices made and their effect on the accuracy of the results. The MRF method is a cheaper alternative compared to the RBM model however, the former model does not accurately simulate the transient start-up and instead provides just a regime solution of the unsteady problem. As expected, the accuracy of the results suffers from having a large gap between the meshing gear teeth. The use of compressible ideal gas model for the air phase with a pressure boundary condition gives the optimum performance for the planetary gearbox. The outcomes can be used toeffectively study transmission flows using CFD and thereby improve the design of future transmissions for improved efficiency.

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  • 81.
    Jansson, Marcus
    et al.
    Atlas Copco Rock Drills AB, Örebro, Sweden.
    Andersson, Magnus
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanisk värmeteori och strömningslära. Linköpings universitet, Tekniska fakulteten.
    Pettersson, Maria
    Atlas Copco Rock Drills AB, Örebro, Sweden.
    Karlsson, Matts
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanisk värmeteori och strömningslära. Linköpings universitet, Tekniska fakulteten.
    Water Hammer Induced Cavitation - A Numerical and Experimental Study2017Inngår i: Fluid Power in the Digital Age, 2017Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    Cavitation erosion is one of the main concerns in hydraulic rock drills and can reduce both performance as well as life span. Current simulation tools can detect a potential risk of cavitation, however, the equations do not include cavitation physics and therefore cannot estimate the severity nor erosion locations. In order to evaluate the cavitation damage, long term tests are performed which are both costly and time consuming. With better computational capacity and more accurate numerical flow models, the possibilities to simulate the course of cavitation have increased. So far, most numerical studies on cavitation focus on steady-state problems while studies on hydraulic transients and water hammer effects have received less attention. This paper is a step towards simulation of water hammer induced cavitation and cavitation erosion in pipe flow using Computational Fluid Dynamics (CFD). In order to validate the results, experimental measurements are performed with a test equipment that creates hydraulic transients in a pipe and records these using piezoelectric pressure sensors. The results from CFD are compared to both the experimental data and to numerical results from a software called Hopsan, a one-dimensional multi-domain system simulation tool that uses wave characteristics to calculate pressures and flows. For smaller transients where no cavitation occur, all results show good agreement. For larger transients with cavitation, the results from Hopsan do not longer agree with the measurements, while the CFD model still performs well and is able to predict both formation and collapse of cavitation.

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  • 82. Bestill onlineKjøp publikasjonen >>
    Jansson, Mikael
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Hydro-mechanical forming of aluminium tubes: on constitutive modelling and process design2006Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Tube hydroforming is a forming method which has several advantages. By using pressure in combination with material feeding it is possible to manufacture products with high structural integration and tight dimensional tolerances. The forming method is especially suited for aluminium alloys which have a relatively low ductility. Finite Element simulations are used extensively in the sheet metal stamping industry, where the methodology has contributed to a better understanding of the process and the new prediction capability has significantly reduced costly die tryouts. Similarly, the tube hydroforming industry can benefit from Finite Element simulations, and this simulation methodology is the topic of this dissertation.

    Deep drawing and tube hydroforming have a basic difference, namely that the latter process essentially is a force controlled process. This fact, in combination with the anisotropic behaviour of aluminium tubes, enforces a need for accurate constitutive descriptions. Furthermore, the material testing needs to account for the specifics of tube hydroforming. The importance of proper material modelling is in this work shown for hydrobulging and hydroforming in a die with extensive feeding.

    The process parameters in hydroforming are the inner pressure and the material feeding, where a correct combination of these parameters is crucial for the success of the process. It is here shown, that Finite Element simulations together with an optimisation routine are powerful tools for estimating the process parameters in an automated procedure.

    Finally, the reliability and quality of the simulation results depend on how failure is evaluated, which in the case of hydroforming mainly oncerns wrinkling and strain localisation. Since tube hydroforming often is preceded by bending operations this fact also demands the criteria to be strain path independent. In this work, it is shown that the prediction of strain localisation depends on the ability to predict diffuse necking, which in turn is strongly related to the chosen constitutive model.

    Delarbeid
    1. On constitutive modeling of aluminum alloys for tube hydroforming applications
    Åpne denne publikasjonen i ny fane eller vindu >>On constitutive modeling of aluminum alloys for tube hydroforming applications
    2005 (engelsk)Inngår i: International Journal of Plasticity, ISSN 0749-6419, Vol. 21, nr 5, s. 1041-1058Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    The increased interest in lightweight materials for automotive structures has also lead to a search for efficient forming methods that suit these materials. One attractive concept is to use hydroforming of aluminum tubes. The advantages of this forming method includes better tolerances, decreased number of parts and an increased range of forming options. By using FE simulations, the process can be optimized to reduce the risk for failure, i.e. bursting or wrinkling. However, extruded aluminum is highly anisotropic and it is crucial that the material model used for simulations is able to accurately describe this behavior. Also, tube hydroforming occurs predominantly in a biaxial stress state which should be considered in the material testing, where uniaxial tests are used extensively in the industry today. The present study accentuates the need for improved constitutive models. It is shown that a material model, which accurately describes the anisotropic behavior of aluminum tubes, can be obtained from simple and robust experiments.

    Emneord
    Aluminum alloys; Hydroforming; Anisotropic material; Biaxial loading
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-14246 (URN)10.1016/j.ijplas.2004.06.005 (DOI)
    Tilgjengelig fra: 2007-01-25 Laget: 2007-01-25
    2. The use of biaxial test data in the validation of constitutive descriptions for tube hydroforming applications
    Åpne denne publikasjonen i ny fane eller vindu >>The use of biaxial test data in the validation of constitutive descriptions for tube hydroforming applications
    2007 (engelsk)Inngår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 184, nr 1-3, s. 69-76Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    When considering finite element simulations of aluminium tube hydroforming, the user is facing several challenges. Firstly, extruded aluminium is anisotropic in yield stress and plastic flow. Secondly, the hydroforming process introduces new issues concerning friction and process control. This imposes a demand for accurate constitutive models as well as for hydroforming process related testing methods. The present study focuses on how biaxial tests can be used to calibrate and validate a constitutive model. It is also shown that by using inverse modelling, additional information can be obtained through these types of tests, such as, e.g. the frictional behaviour for different lubrication conditions.

    Emneord
    Aluminum alloys, Hydroforming, Anisotropic material, Friction
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-14247 (URN)10.1016/j.jmatprotec.2006.09.039 (DOI)
    Tilgjengelig fra: 2007-01-25 Laget: 2007-01-25 Sist oppdatert: 2017-12-13
    3. Tube hydroforming of aluminium extrusions using a conical die and extensive feeding
    Åpne denne publikasjonen i ny fane eller vindu >>Tube hydroforming of aluminium extrusions using a conical die and extensive feeding
    2008 (engelsk)Inngår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 198, nr 1-3, s. 14-21Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    Tube hydroforming is gaining increasing interest from the metal forming industry. Complicated parts with a high level of structural component integration, e.g. engine cradles, subframes and exhaust systems, can be manufactured at a low cost with excellent repeatability. By using finite element (FE) simulations, there is a possibility to reduce the cost of expensive prototypes and reduce the trial and error design process to a minimum. However, when simulating a hydroforming process, the knowledge and computational methods used in conventional metal forming simulations are not always applicable. This concerns, e.g. the material modelling and validation. In this work, the influence of constitutive modelling on the results from a hydroforming process with extensive feeding is studied. In addition, interrupted tests have been used in order to validate the prediction of radial deformation and wall thickness throughout the complete process.

    Emneord
    Aluminium alloys; Hydroforming; Anisotropic material
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-14248 (URN)10.1016/j.jmatprotec.2007.09.043 (DOI)
    Tilgjengelig fra: 2007-01-25 Laget: 2007-01-25 Sist oppdatert: 2017-12-13
    4. On process parameter estimation for the tube hydroforming process
    Åpne denne publikasjonen i ny fane eller vindu >>On process parameter estimation for the tube hydroforming process
    2007 (engelsk)Inngår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 190, nr 1-3, s. 1-11Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    Tube hydroforming is a forming process where an inner pressure combined with axial feeding deforms the tube to the shape of a die cavity. One of the main concerns when designing such a process is to avoid burst pressure, i.e. the process state where the hardening of the material is unable to resist the increase in inner pressure and wall thickness reduction. The success of a hydroforming process strongly depends on the choice of process parameters, i.e. the combination of material feeding and inner pressure. Especially in hydroforming processes, where the free forming phase is substantial, the process is proved to be very sensitive to the inner pressure. By transforming the problem into a deformation controlled rather than a force controlled process, the results from the process parameter estimation become more reliable but on the other hand less intuitive. In this context, three distinct parameter estimation procedures are suggested. Firstly, a self feeding based procedure is proposed with the intention of being a fast method to be used as a first estimate of suitable process parameters. Secondly, an iterative optimization problem set up is presented. Thirdly, and finally, an adaptive simulation procedure based on process response approximations is proposed, which only requires a limited number of simulation runs.

    Emneord
    Aluminium alloys, Hydroforming, Adaptive process, Optimization
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-14249 (URN)10.1016/j.jmatprotec.2007.02.050 (DOI)
    Tilgjengelig fra: 2007-01-25 Laget: 2007-01-25 Sist oppdatert: 2017-12-13
    5. On strain localisation in tube hydroforming of aluminium extrusions
    Åpne denne publikasjonen i ny fane eller vindu >>On strain localisation in tube hydroforming of aluminium extrusions
    2008 (engelsk)Inngår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 195, nr 1-3, s. 3-14Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    One important issue when simulating tube hydroforming is to predict bursting, i.e. when the increase in cavity pressure cannot be compensated by hardening of the tube material. Traditionally, this is made by a forming limit diagram (FLD), where the limit strains determine whether a material point is experiencing necking or failure. However, the experimental FLD depends on the strain path, and the methods which are used to determine the FLD are adapted to conventional deep drawing which, depending on the process characteristics, could make it unsuitable for tube hydroforming applications. In this work, analytical and numerical forming limit predictions are studied from a hydroforming point of view. These predictions are then applied to free bulge cases, and a case with extensive feeding in a die where the results from the latter case is compared to experiments. Further, the influence from extrusion welds and a circumferential thickness distribution on the forming limit is also evaluated.

    Emneord
    Aluminium alloys, Hydroforming, Forming limit, Extrusion weld
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-14250 (URN)10.1016/j.jmatprotec.2007.05.040 (DOI)
    Tilgjengelig fra: 2007-01-25 Laget: 2007-01-25 Sist oppdatert: 2017-12-13
    Fulltekst (pdf)
    FULLTEXT01
  • 83.
    Joakim, Torstensson
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära.
    Topology Optimization as a Conceptual Tool for Designing New Airframes2016Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    During the two last decades, topology optimization has grown to be an accepted and used method to produce conceptual designs. Topology optimization is traditionally carried out on a component level, but in this project, the possibility to apply it to airframe design on a full scale aeroplane model is evaluated.

    The project features a conceptual flying-wing design on which the study is to be carried out. Inertia Relief is used to constrain the aeroplane instead of traditional single point constraints with rigid body motion being suppressed by the application of accelerations instead of traditional forces and moments. The inertia relief method utilized the inertia of the aeroplane to achieve a state of quasi-equilibrium such that static finite element analysis can be carried out. Two load cases are used: a steep pitch-up manoeuvre and a landing scenario. Aerodynamic forces are calculated for the pitch-up load case via an in-house solver, with the pressure being mapped to the finite element mesh via a Matlab-script to account for different mesh sizes. Increased gravitational loads are used in the landing load case to simulate the dynamic loading caused in a real landing scenario, which is unable to be accounted for directly in the topology optimization.

    It can be concluded that the optimization is unable to account for one of the major design limitations: buckling of the outer skin. Approaches to account for the buckling of the outer skin are introduced and analysed, with a focus on local compression constraints throughout the wing. The compression constraints produce some promising results but are not without major drawbacks and complications.

    In general, a one-step topology optimization to produce a mature conceptual airframe design is not possible with optimization algorithms today. It may be possible to adopt a multiple-step optimization approach utilizing topology optimization with following size and shape optimization to achieve a design, which could be expanded on in a future project.

    Fulltekst (pdf)
    fulltext
  • 84.
    Johansson, Nils
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära.
    Estimation of fatigue life by using a cyclic plasticity model and multiaxial notch correction2019Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    Mechanical components often possess notches. These notches give rise to stress concentrations, which in turn increases the likelihood that the material will undergo yielding. The finite element method (FEM) can be used to calculate transient stress and strain to be used in fatigue analyses. However, since yielding occurs, an elastic-plastic finite element analysis (FEA) must be performed. If the loading sequence to be analysed with respect to fatigue is long, the elastic-plastic FEA is often not a viable option because of its high computational requirements.

    In this thesis, a method that estimates the elastic-plastic stress and strain response as a result of input elastic stress and strain using plasticity modelling with the incremental Neuber rule has been derived and implemented. A numerical methodology to increase the accuracy when using the Neuber rule with cyclic loading has been proposed and validated for proportional loading. The results show fair albeit not ideal accuracy when compared to elastic-plastic finite element analysis. Different types of loading have been tested, including proportional and non-proportional as well as complex loadings with several load reversions.

    Based on the computed elastic-plastic stresses and strains, fatigue life is predicted by the critical plane method. Such a method has been reviewed, implemented and tested in this thesis. A comparison has been made between using a new damage parameter by Ince and an established damage parameter by Fatemi and Socie (FS). The implemented algorithm and damage parameters were evaluated by comparing the results of the program using either damage parameter to fatigue experiments of several different load cases, including non-proportional loading. The results are fairly accurate for both damage parameters, but the one by Ince tend to be slightly more accurate, if no fitted constant to use in the FS damage parameter can be obtained.

    Fulltekst (pdf)
    fulltext
  • 85.
    Jones, J.
    et al.
    Swansea Univ, Wales.
    Whittaker, M.
    Swansea Univ, Wales.
    Lancaster, R.
    Swansea Univ, Wales.
    Hyde, C.
    Univ Nottingham, England.
    Rouse, J.
    Univ Nottingham, England.
    Engel, B.
    Univ Nottingham, England.
    Pattison, S.
    Rolls Royce Plc, England.
    Stekovic, Svjetlana
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten.
    Jackson, C.
    Univ Birmingham, England.
    Li, H. Y.
    Univ Birmingham, England.
    The effect of phase angle on crack growth mechanisms under thermo-mechanical fatigue loading2020Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 135, artikkel-id 105539Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The current paper describes TMF crack growth behaviour in an advanced nickel-based superalloy. Changes in behaviour are examined which occur as a function of the phase angle between applied stress and temperature. The fractography of the failed specimens reveals changes from transgranular to intergranular growth between high and low phase angle tests as a result of the onset of high temperature damage mechanisms. More targeted testing has also been undertaken to isolate the contributions of these mechanisms, with specific transitions in behaviour becoming clear in 90 degrees diamond cycles, where dynamic crack growth and oxidation strongly interact.

  • 86.
    Jonsson, Ida
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Öhrn, Robin
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Dimensionering av momentskärmstativ: Analys med finita elementmetoden2013Independent thesis Basic level (degree of Bachelor), 10,5 poäng / 16 hpOppgave
    Abstract [sv]

    På uppdrag av Saab har en grupp studenter på Linköpings tekniska högskola utvecklat ett skärmstativ för nya generationens JAS 39 Gripen E. Vid testflygning är stativet placerat vid planets stjärtkon och på stativet ska en skärm fästas. Skärmens funktion är att stabilisera flygplanet genom att ge det ett tippmoment vid okontrollerade spinnfall.

    Detta kandidatarbete hade till uppgift att designa och dimensionera ett stativ efter givna lastfall, begränsad volym, deformationskrav och givna infästningspunkter, samtidigt som fokus skulle ligga på viktreducering. För att möjliggöra detta togs en CAD-modell fram i Creo Parametric 2.0, som sedan exporterades till Ansys Workbench 14.0 där det utfördes beräkningar enligt finita elementmetoden. Under projektets gång testades olika material, tvärsnitt och konstruktioner, vilka utvärderades för att få fram en så lätt och hållbar konstruktion som möjligt.  

    Resultatet blev ett stativ med fackverksstruktur, som är gjord av fyrkantiga balkar med yttermått 70 mm och innermått 63,8 mm. Den maximala spänningen blev 883 MPa och maximal deformation var 53,1  mm. Stativets totalvikt blev 60,5 kg. 

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  • 87.
    Jung, Daniel
    Linköpings universitet, Institutionen för systemteknik, Fordonssystem. Linköpings universitet, Tekniska fakulteten.
    A generalized fault isolability matrix for improved fault diagnosability analysis2016Inngår i: 2016 3RD CONFERENCE ON CONTROL AND FAULT-TOLERANT SYSTEMS (SYSTOL), IEEE , 2016, s. 519-524Konferansepaper (Fagfellevurdert)
    Abstract [en]

    A generalized fault isolability matrix is proposed for quantitative analysis of fault isolability properties. The original fault isolability matrix gives information about which faults that are isolable from each other. However, other relavant isolability properties are not visible which can be important, for example, information regarding alternative fault hypotheses and multiple-fault isolability. The result of the analysis can be presented in the same compact form as the existing fault isolability matrix which makes it simple to visualize. As a case study, a model of an internal combustion engine is analyzed and two different solutions to the test selection problem are compared.

  • 88.
    Jung, Daniel
    et al.
    Linköpings universitet, Institutionen för systemteknik, Fordonssystem. Linköpings universitet, Tekniska fakulteten.
    Yew Ng, Kok
    Monash University, Malaysia.
    Frisk, Erik
    Linköpings universitet, Institutionen för systemteknik, Fordonssystem. Linköpings universitet, Tekniska fakulteten.
    Krysander, Mattias
    Linköpings universitet, Institutionen för systemteknik, Datorteknik. Linköpings universitet, Tekniska fakulteten.
    A combined diagnosis system design using model-based and data-driven methods2016Inngår i: 2016 3RD CONFERENCE ON CONTROL AND FAULT-TOLERANT SYSTEMS (SYSTOL), IEEE , 2016, s. 177-182Konferansepaper (Fagfellevurdert)
    Abstract [en]

    A hybrid diagnosis system design is proposed that combines model-based and data-driven diagnosis methods for fault isolation. A set of residuals are used to detect if there is a fault in the system and a consistency-based fault isolation algorithm is used to compute all diagnosis candidates that can explain the triggered residuals. To improve fault isolation, diagnosis candidates are ranked by evaluating the residuals using a set of one-class support vector machines trained using data from different faults. The proposed diagnosis system design is evaluated using simulations of a model describing the air-flow in an internal combustion engine.

  • 89. Bestill onlineKjøp publikasjonen >>
    Kahlin, Magnus
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling. Linköpings universitet, Tekniska fakulteten.
    Fatigue Performance of Additive Manufactured Ti6Al4V in Aerospace Applications2017Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Additive Manufacturing (AM) for metals includes is a group of production methodst hat use a layer-by-layer approach to directly manufacture final parts. In recent years, the production rate and material quality of additive manufactured materials have improved rapidly which has gained increased interest from the industry to use AM not only for prototyping, but for serial production. AM offers a greater design freedom, compared to conventional production methods, which allows for parts with new innovative design. This is very attractive to the aerospace industry, in which parts could be designed to have reduced weight and improved performance contributing to reduced fuel consumption, increased payload and extended flight range. There are, however, challenges yet to solve before the potential of AM could be fully utilized in aerospace applications. One of the major challenges is how to deal with the poor fatigue behaviour of AM material with rough as-built surface.

    The aim of this thesis is to increase the knowledge of how AM can be used for high performance industrial parts by investigating the fatigue behaviour of the titanium alloy Ti6Al4V produced with different AM processes. Foremost, the intention is to improve the understanding of how rough as-built AM surfaces in combination with AM built geometrical notches affects the fatigue properties.This was done by performing constant amplitude fatigue testing to compare different combinations of AM material produced by Electron Beam Melting(EBM) and Laser Sintering (LS) with machined or rough as-built surfaces with or without geometrical notches and Hot Isostatic Pressing (HIP) treatment. Furthermore, the material response can be different between constant amplitude and variable amplitude fatigue loading due to effects of overloads and local plastic deformations. The results from constant amplitude testing were used to predict the fatigue life for variable amplitude loading by cumulative damage approach and these predictions were then verified by experimental variable amplitude testing.

    The constant amplitude fatigue strength of material with rough as-built surfaces was found to be 65-75 % lower, compared to conventional wrought bar, in which HIP treatments had neglectable influence on the fatigue strength. Furthermore, the fatigue life predictions with cumulative damage calculations showed good agreement with the experimental results which indicates that a cumulative damage approach can be used, at least for a tensile dominated load sequences, to predict the fatigue behaviour of additive manufactured Ti6Al4V.

    Delarbeid
    1. Fatigue Behaviour of Notched Additive Manufactured Ti6Al4V with As-built Surfaces
    Åpne denne publikasjonen i ny fane eller vindu >>Fatigue Behaviour of Notched Additive Manufactured Ti6Al4V with As-built Surfaces
    2017 (engelsk)Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, nr 101, s. 51-60Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    Additive manufacturing (AM) allows the manufacturer to produce parts with complex geometries that are difficult to produce with conventional production methods. Generally, AM is considered to have great potential for the aerospace industry by contributing to reduced weight and lower costs. There are a number of challenges to be solved before AM can be fully utilized in the aerospace industry, and the understanding of fatigue behaviour is one of the major challenges. Although the fatigue properties of flat additive manufactured specimens with rough as-built surfaces already have been widely studied, in practice, few aerospace components have a simple flat geometry with no corners or radii that would act as stress concentrations. Therefore, the combined effect on fatigue life of a rough as-built surface and a geometrical notch needs to be established. In this study, the fatigue properties of both laser sintered and electron beam melted Ti6Al4V have been investigated and a combined effect of a rough as-built surface and a geometrical notch has been determined. In addition, hot isostatic pressing was found to have no impact on fatigue life for rough as-built surfaces. These findings can be directly applied to predict fatigue behaviour of an AM industrial component.

    sted, utgiver, år, opplag, sider
    Elsevier, 2017
    Emneord
    Additive manufacturing, Fatigue, Ti6Al4V, Stress concentration, Fatigue notch factor
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-137163 (URN)10.1016/j.ijfatigue.2017.04.009 (DOI)000403635300007 ()
    Merknad

    Funding agences: Saab AB; Swedish Foundation for Strategic Research; European commission, through the Clean Sky 2 programme

    Tilgjengelig fra: 2017-05-08 Laget: 2017-05-08 Sist oppdatert: 2019-11-12bibliografisk kontrollert
    2. Fatigue behaviour of additive manufactured Ti6Al4V, with as-built surfaces, exposed to variable amplitude loading
    Åpne denne publikasjonen i ny fane eller vindu >>Fatigue behaviour of additive manufactured Ti6Al4V, with as-built surfaces, exposed to variable amplitude loading
    2017 (engelsk)Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 103, s. 353-362Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    Additive Manufacturing (AM) allows for great design freedom compared to conventional manufacturing. This is very attractive for the aerospace industry in which AM could contribute to lightweight designs and thereby reduce fuel consumption, increase payload and extend flight range. The fatigue behaviour for rough as-built AM surfaces has previously been characterized with constant amplitude testing but in aerospace applications, most parts are exposed to variable amplitude loading. The fatigue behaviour for variable amplitude is not always consistent with the behaviour for constant amplitude due to effects of overloads and local plastic deformations. Therefore, variable amplitude loading behaviour of laser sintered and electron beam melted Ti6Al4V, with rough as-built surfaces have been investigated in this study using the Short-FALSTAFF (Fighter Aircraft Loading STAndard For Fatigue) load sequence. The predicted and the experimental fatigue life was overall consistent even though most experimental results exceeded the predicted life, especially for the laser sintered material. These findings show that conventional cumulative damage fatigue life predictions give reliable predictions for AM materials with rough as-built surfaces for the type of tension dominated load sequence used. (C) 2017 Elsevier Ltd. All rights reserved.

    sted, utgiver, år, opplag, sider
    ELSEVIER SCI LTD, 2017
    Emneord
    Additive manufacturing; Ti6Al4V; Fatigue; Variable amplitude loading; Stress concentration
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-140783 (URN)10.1016/j.ijfatigue.2017.06.023 (DOI)000407982800034 ()
    Merknad

    Funding Agencies|Saab AB; Swedish Foundation for Strategic Research; European Commission, through the Clean Sky 2 programme

    Tilgjengelig fra: 2017-09-13 Laget: 2017-09-13 Sist oppdatert: 2019-11-12
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  • 90.
    Kahlin, Magnus
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Saab AB, Aeronaut, SE-58188 Linkoping, Sweden.
    Ansell, Hans
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten. Saab AB, Aeronaut, SE-58188 Linkoping, Sweden.
    Moverare, Johan
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten.
    Fatigue behaviour of additive manufactured Ti6Al4V, with as-built surfaces, exposed to variable amplitude loading2017Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 103, s. 353-362Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Additive Manufacturing (AM) allows for great design freedom compared to conventional manufacturing. This is very attractive for the aerospace industry in which AM could contribute to lightweight designs and thereby reduce fuel consumption, increase payload and extend flight range. The fatigue behaviour for rough as-built AM surfaces has previously been characterized with constant amplitude testing but in aerospace applications, most parts are exposed to variable amplitude loading. The fatigue behaviour for variable amplitude is not always consistent with the behaviour for constant amplitude due to effects of overloads and local plastic deformations. Therefore, variable amplitude loading behaviour of laser sintered and electron beam melted Ti6Al4V, with rough as-built surfaces have been investigated in this study using the Short-FALSTAFF (Fighter Aircraft Loading STAndard For Fatigue) load sequence. The predicted and the experimental fatigue life was overall consistent even though most experimental results exceeded the predicted life, especially for the laser sintered material. These findings show that conventional cumulative damage fatigue life predictions give reliable predictions for AM materials with rough as-built surfaces for the type of tension dominated load sequence used. (C) 2017 Elsevier Ltd. All rights reserved.

    Fulltekst (pdf)
    fulltext
  • 91.
    Kanesund, Jan
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten.
    Brodin, Håkan
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten. Siemens Ind Turbomachinery AB, Sweden.
    Johansson, Sten
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten.
    Hot corrosion influence on deformation and damage mechanisms in turbine blades made of IN-792 during service2019Inngår i: Engineering Failure Analysis, ISSN 1350-6307, E-ISSN 1873-1961, Vol. 96, s. 118-129Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The deformation and damage mechanisms of a gamma-prime hardened superalloy is investigated in the current paper. Two turbine blades made of precision cast polycrystalline superalloy IN-792 have been examined after service exposure under engine conditions typical for industrial gas turbines. This study is compared to a previous study with focus on deformation and damage mechanisms in IN-792 during thermal mechanical fatigue testing performed under laboratory conditions. The failure of the two turbine blades is explained as a combination of two damage mechanisms, mechanical and chemical damage. In the current investigation, type I hot corrosion and creep are the two dominant damage mechanisms. The type I hot corrosion is confirmed by the presence of Ti-sulfides and sulfur in free form at the grain boundaries, which has caused embrittlement and loss of resistance to crack growth. In turn, this has shortened the turbine blade life dramatically and intercrystalline failure is the dominant damage mechanism. Almost all cracks have propagated intercrystalline in the two turbine blades. In the previous study, mechanical damage mechanism is the dominant mechanism and for the highest temperature also oxidation give is contribution. In the previous study, almost all cracks propagated transcrystalline. When exposed to laboratory conditions, the areas around cracks are more plastically deformed compared to the area around the cracks in the turbine blades. In the two studies, dynamic recrystallization has occurred at the grain boundaries.

  • 92.
    Karjalainen, Marcus
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Fluida och mekatroniska system.
    Klarholm, David
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Fluida och mekatroniska system.
    Termomekanisk utmattning av Sanicro 25: Materialmodellering med finita elementmetoden2014Independent thesis Basic level (degree of Bachelor), 10,5 poäng / 16 hpOppgave
    Abstract [en]

    The report aims to describe the austenitic stainless steel Sanicro 25 from a thermomechanical point of view. The thermal and mechanical properties of the material make it suitable for use in coal – and thermal power plants. By the use of Sanicro 25 it would be possible to bring the efficiency of these plants up while bringing the carbon emissions down.A material model is created from material testing and validated through simulation in the finite element software Abaqus. The model that has been derived describes the material behavior during loading and stress relaxation for the first cycle in a thermomechanical fatigue test well. The unloading part of the cycle however cannot be described correctly by the use of this model.

    Fulltekst (pdf)
    Termomekanisk utmattning av Sanicro 25
  • 93.
    Karlsson, Henrik
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära.
    Gustavsson, Joakim
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära.
    Stabilitetsanalys av ledstaplartruck med avseende på tippning: En FEM-baserad metod för heltrucksmodeller2018Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    The purpose has been to analyze a modelling process based on the finite element method (FEM), for a powered stacker truck of the model SPE 140 TX HILO. It was analyzed how such a model should be designed in order to perform stability analyses. This was done by analyzing which of the trucks components that were relevant from a stability perspective. These components were analyzed in order to figure out which modelling approach that was best suited to model the components in a FEM-software. The result of these analyses is a modelling methodology describing which approach that should be used during the entire modelling process of a FEM-model consisting of an entire truck.

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  • 94.
    Karlsson, Matts
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanisk värmeteori och strömningslära. Linköpings universitet, Tekniska högskolan. Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV.
    Andersson, Magnus
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanisk värmeteori och strömningslära. Linköpings universitet, Tekniska högskolan.
    Lantz, Jonas
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Medie- och Informationsteknik. Linköpings universitet, Tekniska högskolan.
    Quantitative Assessment of Wall Shear Stress in an Aortic Coarctation - Impact of Virtual Interventions2014Inngår i: Abstract: L7.00007 : Quantitative Assessment of Wall Shear Stress in an Aortic Coarctation - Impact of Virtual Interventions, Maryland, 2014, Vol. 59Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Turbulent and wall impinging blood flow causes abnormal shear forces onto the lumen and may play an important role in the pathogenesis of numerous cardiovascular diseases. In the present study, wall shear stress (WSS) and related flow parameters were studied in a pre-treated aortic coarctation (CoA) as well as after several virtual interventions using computational fluid dynamics (CFD). Patient-specific geometry and flow conditions were derived from magnetic resonance imaging (MRI) data. Finite element analysis was performed to acquire six different dilated CoAs. The unsteady pulsatile flow was resolved by large eddy simulation (LES) including non-Newtonian blood rheology. Pre-intervention, the presence of jet flow wall impingement caused an elevated WSS zone, with a distal region of low and oscillatory WSS. After intervention, cases with a more favorable centralized jet showed reduced high WSS values at the opposed wall. Despite significant turbulence reduction post-treatment, enhanced regions of low and oscillatory WSS were observed for all cases. This numerical method has demonstrated the morphological impact on WSS distribution in an CoA. With the predictability and validation capabilities of a combined CFD/MRI approach, a step towards patient-specific intervention planning is taken.  

  • 95.
    Karlsson, Matts
    et al.
    Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanisk värmeteori och strömningslära. Linköpings universitet, Tekniska högskolan.
    Lantz, Jonas
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanisk värmeteori och strömningslära. Linköpings universitet, Tekniska högskolan.
    Gårdhagen, Roland
    Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanisk värmeteori och strömningslära. Linköpings universitet, Tekniska högskolan.
    Renner, Johan
    Linköpings universitet, Centrum för medicinsk bildvetenskap och visualisering, CMIV. Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanisk värmeteori och strömningslära. Linköpings universitet, Tekniska högskolan.
    Biofluid Mechanics -LES and FSI2011Inngår i: / [ed] B. Skallerud and H.I. Andersson, tapir academic press , 2011, s. 23-28Konferansepaper (Annet vitenskapelig)
  • 96.
    Khayyeri, Hanifeh
    et al.
    Lund University, Sweden.
    Gustafsson, Anna
    Lund University, Sweden.
    Heuijerjans, Ashley
    Eindhoven University of Technology, Netherlands.
    Matikainen, Marko K.
    Lappeenranta University of Technology, Finland.
    Julkunen, Petro
    Kuopio University Hospital, Finland; University of Eastern Finland, Finland.
    Eliasson, Pernilla
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Avdelningen för kliniska vetenskaper. Linköpings universitet, Medicinska fakulteten.
    Aspenberg, Per
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Avdelningen för kliniska vetenskaper. Linköpings universitet, Medicinska fakulteten. Region Östergötland, Centrum för kirurgi, ortopedi och cancervård, Ortopedkliniken i Linköping.
    Isaksson, Hanna
    Lund University, Sweden.
    A Fibre-Reinforced Poroviscoelastic Model Accurately Describes the Biomechanical Behaviour of the Rat Achilles Tendon2015Inngår i: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 10, nr 6, artikkel-id e0126869Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Background Computational models of Achilles tendons can help understanding how healthy tendons are affected by repetitive loading and how the different tissue constituents contribute to the tendons biomechanical response. However, available models of Achilles tendon are limited in their description of the hierarchical multi-structural composition of the tissue. This study hypothesised that a poroviscoelastic fibre-reinforced model, previously successful in capturing cartilage biomechanical behaviour, can depict the biomechanical behaviour of the rat Achilles tendon found experimentally. Materials and Methods We developed a new material model of the Achilles tendon, which considers the tendons main constituents namely: water, proteoglycan matrix and collagen fibres. A hyperelastic formulation of the proteoglycan matrix enabled computations of large deformations of the tendon, and collagen fibres were modelled as viscoelastic. Specimen-specific finite element models were created of 9 rat Achilles tendons from an animal experiment and simulations were carried out following a repetitive tensile loading protocol. The material model parameters were calibrated against data from the rats by minimising the root mean squared error (RMS) between experimental force data and model output. Results and Conclusions All specimen models were successfully fitted to experimental data with high accuracy (RMS 0.42-1.02). Additional simulations predicted more compliant and soft tendon behaviour at reduced strain-rates compared to higher strain-rates that produce a stiff and brittle tendon response. Stress-relaxation simulations exhibited strain-dependent stress-relaxation behaviour where larger strains produced slower relaxation rates compared to smaller strain levels. Our simulations showed that the collagen fibres in the Achilles tendon are the main load-bearing component during tensile loading, where the orientation of the collagen fibres plays an important role for the tendons viscoelastic response. In conclusion, this model can capture the repetitive loading and unloading behaviour of intact and healthy Achilles tendons, which is a critical first step towards understanding tendon homeostasis and function as this biomechanical response changes in diseased tendons.

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  • 97.
    Kihlander, Jesper
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Finite Element simulation of vibrating plastic components2013Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    For automotive plastic parts there is a clear demand on an increased quality of the FE models. This demand is related to the increased use of simulations, both due to a reduced number of prototypes and an increased number of load cases. There have been studies showing a change of dynamic properties in injection molded components. The conclusion from these studies are that the change depends on residual stresses built in during the injection process. This study use simple models to try to get a working method and from the results find out the basic relations between residual stresses and dynamic properties. A method was developed and the results showed that the residuals had a major impact on the dynamic properties. Continuation on this work would be to use more complex models, to try to mimic results from reference studies and tests.

    Fulltekst (pdf)
    Finite Element simulation of vibrating plastic components
  • 98.
    Klarbring, Anders
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Barber, J. R.
    University of Michigan, MI 48109 USA.
    Spagnoli, A.
    University of Parma, Italy.
    Terzano, M.
    University of Parma, Italy.
    Shakedown of discrete systems involving plasticity and friction2017Inngår i: European journal of mechanics. A, Solids, ISSN 0997-7538, E-ISSN 1873-7285, Vol. 64, s. 160-164Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In associated plasticity, systems subjected to cyclic loading are sometimes predicted to shake down, meaning that, after some dissipative cycles, the response goes back to a purely elastic state, where no plastic flow occurs. Frictional systems show a similar behaviour, in the sense that frictional slips due to the external loads may cease after some cycles. It has been proved that, for complete contacts with elastic behaviour and Coulomb friction, Melans theorem gives a sufficient condition for the system to shake down, if and only if there is no normal-tangential coupling at the interfaces. In this paper, the case of discrete systems combining elastic-plastic behaviour and Coulomb friction is considered. In particular, it is proved that Melans theorem still holds for contact-wise uncoupled systems, i.e., the existence of a residual state, comprised of frictional slips and plastic strains, is a sufficient condition for the system to shake down. (C) 2017 Elsevier Masson SAS. All rights reserved.

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    fulltext
  • 99.
    Klarbring, Anders
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik. Linköpings universitet, Tekniska högskolan.
    Strömberg, Niclas
    Department of Mechanical Engineering, Jönköping University.
    A note on the min-max formulation of stiffness optimization including non-zero prescribed displacements2012Inngår i: Structural and multidisciplinary optimization (Print), ISSN 1615-147X, E-ISSN 1615-1488, Vol. 45, nr 1, s. 147-149Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The present theoretical note shows how a natural objective function in stiffness optimization, including both prescribed forces and non-zero prescribed displacements, is the equilibrium potential energy. It also shows how the resulting problem has a saddle point character that may be utilized when calculating sensitivities.

  • 100.
    Klarbring, Anders
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik. Linköpings universitet, Tekniska högskolan.
    Strömberg, Niclas
    Department of Mechanical Engineering, Jönköping University, Sweden.
    Topology optimization of hyperelastic bodies including non-zero prescribed displacements2013Inngår i: Structural and multidisciplinary optimization (Print), ISSN 1615-147X, E-ISSN 1615-1488, Vol. 47, nr 1, s. 37-48Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Stiffness topology optimization is usually based on a state problem of linear elasticity, and there seems to be little discussion on what is the limit for such a small rotation-displacement assumption. We show that even for gross rotations that are in all practical aspects small (<3 deg), topology optimization based on a large deformation theory might generate different design concepts compared to what is obtained when small displacement linear elasticity is used. Furthermore, in large rotations, the choice of stiffness objective (potential energy or compliance), can be crucial for the optimal design concept. The paper considers topology optimization of hyperelastic bodies subjected simultaneously to external forces and prescribed non-zero displacements. In that respect it generalizes a recent contribution of ours to large deformations, but we note that the objectives of potential energy and compliance are no longer equivalent in the non-linear case. We use seven different hyperelastic strain energy functions and find that the numerical performance of the Kirchhoff–St.Venant model is in general significantly worse than the performance of the other six models, which are all modifications of this classical law that are equivalent in the limit of infinitesimal strains, but do not contain the well-known collapse in compression. Numerical results are presented for two different problem settings.

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