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  • 201.
    Storgärds, Erik
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Simonsson, Kjell
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Sjöström, Sören
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Gustafsson, David
    Siemens Industrial Turbomachinery AB, Finspång, Sweden.
    Månsson, Tomas
    GKN Aerospace Engine Systems, Trollhättan, Sweden.
    Modeling of Crack Growth With Dwell Time for Aero-engine Spectra Loadings in a Ni-Based Superalloy2016In: Journal of engineering for gas turbines and power, ISSN 0742-4795, E-ISSN 1528-8919, Vol. 138, no 1, p. 012501-012501Article in journal (Refereed)
    Abstract [en]

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

  • 202.
    Storgärds, Erik
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Simonsson, Kjell
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Sjöström, Sören
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Thermomechanical Fatigue Crack Growth Modeling in a Ni-Based Superalloy Subjected to Sustained Load2016In: Journal of engineering for gas turbines and power, ISSN 0742-4795, E-ISSN 1528-8919, Vol. 138, no 1, p. 012503-012503Article in journal (Refereed)
    Abstract [en]

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

  • 203.
    Storgärds, Erik
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Simonsson, Kjell
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Sjöström, Sören
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    THERMO-MECHANICAL FATIGUE CRACK GROWTH MODELLING IN A NI-BASED SUPERALLOY SUBJECTED TO SUSTAINED LOAD2015In: PROCEEDINGS OF THE ASME TURBO EXPO: TURBINE TECHNICAL CONFERENCE AND EXPOSITION, 2015, VOL 7A, ASME Press, 2015, no V07AT28A006Conference paper (Refereed)
    Abstract [en]

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

  • 204.
    Strömberg, Niclas
    et al.
    Jönköping University.
    Klarbring, Anders
    Linköping University, Department of Management and Engineering, Mechanics . Linköping University, The Institute of Technology.
    Topology optimization of structures in unilateral contact2010In: Structural and multidisciplinary optimization (Print), ISSN 1615-147X, E-ISSN 1615-1488, Vol. 41, no 1, p. 57-64Article in journal (Refereed)
    Abstract [en]

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

  • 205.
    Stålhand, Jonas
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    McMeeking, Robert M.
    Department of Mechanical Engineering & Materials Department, University of California Santa Barbara, CA 93106, USA / School of Engineering, University of Aberdeen, Kings College, Aberdeen, AB24 3UE, UK.
    Holzapfel, Gerhard A.
    Institute of Biomechanics, Graz University of Technology, Stremayrgasse 16-II, 8010 Graz, Austria / Norwegian University of Science and Technology (NTNU), Faculty of Engineering Science and Technology, 7491 Trondheim, Norway.
    On the Thermodynamics of Smooth Muscle Contraction2016In: Journal of the mechanics and physics of solids, ISSN 0022-5096, E-ISSN 1873-4782, Vol. 94, p. 490-503Article in journal (Refereed)
    Abstract [en]

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

  • 206.
    Suresh, Shyam
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Lindström, Stefan B
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Thore, Carl-Johan
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Torstenfelt, Bo
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Klarbring, Anders
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    An Evolution-Based High-Cycle Fatigue Constraint in Topology Optimization2018Conference paper (Refereed)
    Abstract [en]

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

  • 207.
    Söderberg, Johan
    Linköping University, Department of Management and Engineering, Mechanics. Linköping University, The Institute of Technology.
    A finite element method for calculating load distributions in bolted joint assemblies2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

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

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

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

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

  • 208.
    Talus, Eva
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Optimal Use of Duplex Stainless Steel in Storage Tanks2013Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

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

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

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

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

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

  • 209.
    Thellner, Mikael
    Linköping University, Department of Mechanical Engineering. Linköping University, The Institute of Technology. Univ.,.
    Integrated structural optimization for mechanical optimal design2002Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

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

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

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

  • 210.
    Thomasson, Andreas
    et al.
    Linköping University, Department of Electrical Engineering, Vehicular Systems. Linköping University, Faculty of Science & Engineering.
    Eriksson, Lars
    Linköping University, Department of Electrical Engineering, Vehicular Systems. Linköping University, Faculty of Science & Engineering.
    Effects of Pulsating Flow on Mass Flow Balance and Surge Margin in Parallel Turbocharged Engines2015In: Proceedings of the 56th Conference on Simulation and Modelling (SIMS 56), October, 7-9, 2015, Linköping University, Sweden, Linköping: Linköping University Electronic Press, 2015, Vol. 119, p. 15-20Conference paper (Refereed)
    Abstract [en]

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

  • 211.
    Thore, Carl-Johan
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Holmberg, Erik
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Klarbring, Anders
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Large-scale robust topology optimization under load-uncertainty2015In: 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, p. 255-260Conference paper (Refereed)
    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.

  • 212.
    Unosson, Mattias
    Linköping University, Department of Mechanical Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    On failure modelling in finite element analysis: material imperfections and element erosion2005Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

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

    List of papers
    1. Projectile penetration and perforation of high performance concrete: Experimental results and macroscopic modelling
    Open this publication in new window or tab >>Projectile penetration and perforation of high performance concrete: Experimental results and macroscopic modelling
    2006 (English)In: International Journal of Impact Engineering, ISSN 0734-743X, E-ISSN 1879-3509, Vol. 32, no 7, p. 1068-1085Article in journal (Refereed) Published
    Abstract [en]

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

    Place, publisher, year, edition, pages
    Pergamon Press, 2006
    Keywords
    High performance concrete; Projectile; Penetration; Perforation; Experiments; Finite-element analysis
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-13412 (URN)10.1016/j.ijimpeng.2004.11.003 (DOI)
    Available from: 2005-11-09 Created: 2005-11-09 Last updated: 2017-12-13
    2. Failure modelling in finite element analyses: Random material imperfections
    Open this publication in new window or tab >>Failure modelling in finite element analyses: Random material imperfections
    2005 (English)In: Mechanics of Materials, ISSN 0167-6636, Vol. 37, no 12, p. 1175-1179Article in journal (Refereed) Published
    Abstract [en]

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

    Keywords
    Explicit finite element analysis; Failure initiation; Element erosion; Random imperfections
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-13413 (URN)10.1016/j.mechmat.2005.05.001 (DOI)
    Available from: 2005-11-09 Created: 2005-11-09 Last updated: 2009-06-08
    3. Weakest link model with imperfection: Application to three point bend of a tungsten carbide
    Open this publication in new window or tab >>Weakest link model with imperfection: Application to three point bend of a tungsten carbide
    2007 (English)In: International Journal of Refractory Metals and Hard Materials, ISSN 0263-4368, Vol. 25, no 1, p. 6-10Article in journal (Refereed) Published
    Abstract [en]

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

    Place, publisher, year, edition, pages
    Elsevier, 2007
    Keywords
    Finite element method, Failure initiation, Size effect, Random imperfections
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-13414 (URN)10.1016/j.ijrmhm.2005.10.015 (DOI)000242508800002 ()
    Available from: 2005-11-09 Created: 2005-11-09 Last updated: 2012-08-24Bibliographically approved
    4. Failure modelling in finite element analyses: Element erosion with crack-tip enhancement
    Open this publication in new window or tab >>Failure modelling in finite element analyses: Element erosion with crack-tip enhancement
    2006 (English)In: Finite elements in analysis and design (Print), ISSN 0168-874X, E-ISSN 1872-6925, Vol. 42, no 4, p. 283-297Article in journal (Refereed) Published
    Abstract [en]

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

    Place, publisher, year, edition, pages
    Elsevier, 2006
    Keywords
    Finite element analysis; Failure; Element erosion; Crack-tip enhancement; Steady-state propagation; Modus I
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-13415 (URN)10.1016/j.finel.2005.07.001 (DOI)
    Available from: 2005-11-09 Created: 2005-11-09 Last updated: 2017-12-13
    5. Selective mass scaling for thin walled structures modeled with tri-linear solid elements
    Open this publication in new window or tab >>Selective mass scaling for thin walled structures modeled with tri-linear solid elements
    2004 (English)In: Computational Mechanics, ISSN 1432-0924, Vol. 34, no 2, p. 134-136Article in journal (Refereed) Published
    Abstract [en]

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

    Keywords
    Mass scaling, Finite element, Explicit time integration
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-13416 (URN)10.1007/s00466-004-0560-6 (DOI)
    Available from: 2005-11-09 Created: 2005-11-09 Last updated: 2009-05-28
    6. Selective mass scaling for explicit finite element analyses
    Open this publication in new window or tab >>Selective mass scaling for explicit finite element analyses
    2005 (English)In: International Journal for Numerical Methods in Engineering, ISSN 0029-5981, E-ISSN 1097-0207, Vol. 63, no 10, p. 1436-1445Article in journal (Refereed) Published
    Abstract [en]

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

    Keywords
    selective mass scaling, finite element, explicit time integration
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-13417 (URN)10.1002/nme.1293 (DOI)
    Available from: 2005-11-09 Created: 2005-11-09 Last updated: 2017-12-13Bibliographically approved
    7. Imperfection density function and crack-tip enhancement: Validation against symmetrical bending of circular tungsten carbide plates
    Open this publication in new window or tab >>Imperfection density function and crack-tip enhancement: Validation against symmetrical bending of circular tungsten carbide plates
    2007 (English)In: Mechanics of materials (Print), ISSN 0167-6636, E-ISSN 1872-7743, Vol. 39, no 8, p. 753-759Article in journal (Refereed) Published
    Abstract [en]

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

    Place, publisher, year, edition, pages
    Elsevier, 2007
    Keywords
    Explicit finite element analysis, Material imperfections, Element erosion, Tungsten carbide
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-13418 (URN)10.1016/j.mechmat.2006.12.005 (DOI)000246315700003 ()
    Available from: 2005-11-09 Created: 2005-11-09 Last updated: 2017-12-13
  • 213.
    Venkatesan, Sreedhar
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics.
    Banglore Hanumantha Raju, Hariprasad
    Linköping University, Department of Management and Engineering, Solid Mechanics.
    Probabilistic Analysis of Brake Noise: A Hierarchical Multi-fidelity Statistical Approach2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

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

  • 214.
    Vikström, Simon
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Thuresson, Robin
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, Faculty of Science & Engineering.
    Finite element analysis of winding sequence for cable drums2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

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

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

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

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

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

  • 215.
    von Rosen, Michael
    Linköping University, Department of Management and Engineering, Solid Mechanics.
    Modelling of bolt fracture2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

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

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

  • 216.
    Wang, Fei
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics. Linköping University, Faculty of Science & Engineering.
    Properties of multilayered and multicomponent nitride alloys from first principles2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

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

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

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

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

    List of papers
    1. Special quasirandom structure method in application for advanced properties of alloys: A study on Ti0.5Al0.5N and TiN/Ti0.5Al0.5N multilayer
    Open this publication in new window or tab >>Special quasirandom structure method in application for advanced properties of alloys: A study on Ti0.5Al0.5N and TiN/Ti0.5Al0.5N multilayer
    2015 (English)In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 103, p. 194-199Article in journal (Refereed) Published
    Abstract [en]

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

    Place, publisher, year, edition, pages
    Elsevier, 2015
    Keywords
    Modelling alloys; Special quasirandom structure approach; Elastic constants; Vacancy formation energy; Multilayers
    National Category
    Physical Sciences
    Identifiers
    urn:nbn:se:liu:diva-118022 (URN)10.1016/j.commatsci.2015.03.030 (DOI)000353377100024 ()
    Note

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

    Available from: 2015-05-21 Created: 2015-05-20 Last updated: 2018-02-09
    2. Coherency effects on the mixing thermodynamics of cubic Ti1-xAlxN/TiN(001) multilayers
    Open this publication in new window or tab >>Coherency effects on the mixing thermodynamics of cubic Ti1-xAlxN/TiN(001) multilayers
    Show others...
    2016 (English)In: PHYSICAL REVIEW B, ISSN 2469-9950, Vol. 93, no 17, p. 174201-Article in journal (Refereed) Published
    Abstract [en]

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

    Place, publisher, year, edition, pages
    AMER PHYSICAL SOC, 2016
    National Category
    Condensed Matter Physics
    Identifiers
    urn:nbn:se:liu:diva-129166 (URN)10.1103/PhysRevB.93.174201 (DOI)000375990200003 ()
    Note

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

    Available from: 2016-06-13 Created: 2016-06-13 Last updated: 2018-02-09
    3. Growth and thermal stability of TiN/ZrAlN: Effect of internal interfaces
    Open this publication in new window or tab >>Growth and thermal stability of TiN/ZrAlN: Effect of internal interfaces
    Show others...
    2016 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 121, p. 396-406Article in journal (Refereed) Published
    Abstract [en]

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

    Place, publisher, year, edition, pages
    Pergamon Press, 2016
    Keywords
    Thermal stability, TM-Al-N multilayer films, Nanostructured materials, Interface energy, Three-dimensional atom probe (3DAP), Transmission electron microscopy
    National Category
    Condensed Matter Physics
    Identifiers
    urn:nbn:se:liu:diva-132827 (URN)10.1016/j.actamat.2016.07.006 (DOI)000386984500038 ()
    Note

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

    Available from: 2016-12-06 Created: 2016-11-30 Last updated: 2018-02-09
    4. Systematic ab initio investigation of the elastic modulus in quaternary transition metal nitride alloys and their coherent multilayers
    Open this publication in new window or tab >>Systematic ab initio investigation of the elastic modulus in quaternary transition metal nitride alloys and their coherent multilayers
    Show others...
    2017 (English)In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 127, p. 124-132Article in journal (Refereed) Published
    Abstract [en]

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

    Place, publisher, year, edition, pages
    PERGAMON-ELSEVIER SCIENCE LTD, 2017
    Keywords
    Ab initio calculations; Elastic properties; Transition metal nitride alloys; Multicomponent; Multilayers
    National Category
    Other Materials Engineering
    Identifiers
    urn:nbn:se:liu:diva-136865 (URN)10.1016/j.actamat.2017.01.017 (DOI)000397362600012 ()
    Note

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

    Available from: 2017-04-30 Created: 2017-04-30 Last updated: 2018-02-09
  • 217.
    Witt, Stephen
    Linköping University, Department of Management and Engineering.
    The Influence of Under Sleeper Pads on Railway Track Dynamics2008Independent thesis Advanced level (degree of Magister), 20 points / 30 hpStudent thesis
    Abstract [en]

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

  • 218.
    Wranne, Bengt
    et al.
    Linköping University, Department of Medicine and Care, Clinical Physiology. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Heart and Medicine Center, Department of Clinical Physiology in Linköping.
    Ask, Per
    Linköping University, Department of Biomedical Engineering, Physiological Measurements. Linköping University, The Institute of Technology.
    Loyd, Dan
    Linköping University, Department of Management and Engineering, Applied Thermodynamics and Fluid Mechanics. Linköping University, The Institute of Technology.
    Quantification of heart valve regurgitation: a critical analysis from a theoretical and experimental point of view.1985In: Clinical Physiology, ISSN 0144-5979, E-ISSN 1365-2281, Vol. 5, no 1, p. 81-88Article in journal (Refereed)
    Abstract [en]

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

2345 201 - 218 of 218
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