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  • 1.
    Almroth, Per
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Solid Mechanics.
    Hasselqvist, Magnus
    Sjöström, Karl Henning Sören
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering.
    Simonsson, Kjell
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Solid Mechanics.
    Modeling of the high temperature behaviour of IN792 in gas turbine hot parts2002In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 25, no 3, p. 305-315Article in journal (Other academic)
    Abstract [en]

    The material parameters for two isothermal viscoplastic models with deliberately limited sets of material parameters have been estimated. The models are to describe the behaviour of the nickel based superalloy IN792 in a gas turbine hot part application. The models are based on a power law flow equation and the state variable used is backstress. The model calibration is done by least-squares optimization using non-standard constitutive tests that are aimed at describing relevant component conditions. The constitutive tests give information about the kinematic hardening effects for the backstress evolution equations, while secondary creep data provides stress versus inelastic strain rate information for the flow equation. All tests are uniaxial and isothermal. With the estimated parameter sets the models give relatively good fits to the data. The results suggest that the models can be used to describe the high temperature behaviour of IN792. ⌐ 2002 Elsevier Science B.V. All rights reserved.

  • 2.
    Andersson, Johan
    et al.
    Linköping University, Department of Mechanical Engineering, Machine Design. Linköping University, The Institute of Technology.
    Redhe, Marcus
    Linköping University, Department of Mechanical Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Response surface methods and pareto optimization in crashworthiness design2003In: Proceedings of Design Engineering Technical Conferences and Computers and Information in Engineering Conference/Design Automation Conference: Volume 2: 29th Design Automation Conference, Parts A and B, Chicago, USA: ASME , 2003, p. 473-479Conference paper (Refereed)
    Abstract [en]

    This paper presents a method where a multi objective optimization techniqueis used together with response surface methods in order to support crashworthiness design. As in most engineering design problems thereare several conflicting objectives that have to be considered when formulating a design problem as an optimization problem. Here this is exemplified by the desire to minimize the intrusion into the passenger compartment area and simultaneously obtain low maximum acceleration during vehicle impact. These two objectives are naturally conflicting, since low maximum acceleration implies large intrusion. The contribution of thispaper is to show a successful application of a set of existing methods to solve a real world engineering problem.The paper also presents methods of illustrating the results obtained from the multi-objective optimization.

  • 3.
    Borg, Rikard
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Solid Mechanics.
    Borg, Rikard
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Solid Mechanics.
    Nilsson, Larsgunnar
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Solid Mechanics.
    Nilsson, Larsgunnar
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Solid Mechanics.
    Simonsson, Kjell
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Solid Mechanics.
    Simonsson, Kjell
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Solid Mechanics.
    Simulation of delamination in fiber composites with a discrete cohesive failure model2001In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 61, no 5, p. 667-677Other (Other (popular science, discussion, etc.))
    Abstract [en]

    Delamination initiation and growth are analyzed by using a discrete cohesive crack model. The model is derived by postulating the existence of a maximum load surface which limits the adhesive forces in the process zone of the crack. The size of the maximum load surface is made dependent on the amount of dissipated crack opening work such that the maximum load surface shrinks to zero as a predefined amount of work is consumed. Mode I, II, III loading or any combined loading is possible. The delamination model is implemented in the explicit finite-element code LS-DYNA and simulation results are found to be in agreement with experimental results. ⌐ 2001 Elsevier Science Ltd. All rights reserved.

  • 4.
    Borg, Rikard
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Solid Mechanics.
    Nilsson, Larsgunnar
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Solid Mechanics.
    Simonsson, Kjell
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Solid Mechanics.
    Simulating DCB, ENF and MMB experiments using shell elements and a cohesive zone model2004In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 64, no 2, p. 269-278Article in journal (Refereed)
    Abstract [en]

    A delamination model for shell elements is presented. It consists of an adhesive penalty contact formulation for initially tying shells together and a cohesive zone model for degrading the adhesive forces. An adhesive contact used between shell elements has to account for the thickness offset, such that the rotational degrees of freedom in the shell elements are included in the algorithm. This is considered in the present contact model and the complete delamination model is implemented in the explicit Finite Element code LS-DYNA. By preventing delamination growth the delamination model can be turned into a tied contact. As such it is used in two FE-models, where plates are bonded together and subjected to various loads. The adhesive penalty contact performs well. The complete delamination is validated by simulating the Double Cantilever Beam, End-Notch Flexural and Mixed Mode Bending setups, and the results are shown to be in agreement with experimental data.

  • 5.
    Borg, Rikard
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Solid Mechanics.
    Nilsson, Larsgunnar
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Solid Mechanics.
    Simonsson, Kjell
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Solid Mechanics.
    Simulation of low velocity impact on fiber laminates using a cohesive zone based delamination model2004In: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 64, no 2, p. 279-288Article in journal (Refereed)
    Abstract [en]

    An existing delamination model is further developed for use in transverse impact simulations. An algorithm is developed making it possible to determine the propagation direction of the delamination front. Using this it is possible to determine relative orientation of the delamination front with respect to the fibers above and below the interface. In a qualitative evaluation it is shown that the present delamination model can be used for modeling delamination initiation and growth in transverse impact simulations.

  • 6. Brandt, Jan
    et al.
    Nilsson, Larsgunnar
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Solid Mechanics.
    A consutitutive model for compaction of granular media, with account for deformation induced anisotropy2000In: Mechanics of materials (Print), ISSN 0167-6636, E-ISSN 1872-7743, Vol. 4, p. 391-418Article in journal (Refereed)
  • 7.
    Brodin, Håkan
    et al.
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Jinnestrand, Magnus
    Linköping University, Department of Mechanical Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Sjöström, Sören
    Linköping University, Department of Mechanical Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Modelling and experimental verification of delamination crack growth in an air-plasma-sprayed thermal barrier coating2004In: 15th European Conference of Fracture (ECF15), Stockholm, Sweden, 2004, 2004Conference paper (Refereed)
  • 8.
    Dahlberg, Tore
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Solid Mechanics.
    Dynamic train/track interaction model2004Report (Other academic)
  • 9.
    Dahlberg, Tore
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Solid Mechanics.
    Kontinuerligt understödd räl2004Patent (Other (popular science, discussion, etc.))
  • 10.
    Dahlberg, Tore
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Solid Mechanics.
    Modelling of railroad track settlements2001In: TransportForum,2001, 2001Conference paper (Other academic)
    Abstract [en]

          

  • 11.
    Dahlberg, Tore
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Solid Mechanics.
    Moving force on an axially loaded beam - With applications to a railway overhead contact wire2006In: Vehicle System Dynamics, ISSN 0042-3114, E-ISSN 1744-5159, Vol. 44, no 8, p. 631-644Article in journal (Refereed)
    Abstract [en]

    Using modal analysis, the deflection of a beam subjected to an axial tensile force N and a moving vertical force P , has been determined. This solution was exploited in a study of deflection and wave propagation in the contact wire of a railway overhead catenary system. For moderate values of speed c of the moving force P ( i.e ., c less than half the lowest critical speed c crit ) travelling waves reflect at the boundaries of the contact wire so that the waves meet and catch up with the moving force several times. In practice, when a pantograph (here modelled by the force P ) touches the contact wire some distance from the end of the wire, waves are sent out both in the forward and backward direction, giving even more reflections and wave interactions with the contact force. These waves will add or subtract to the wire deflection at the point of force application. The stress in the wire due to bending is estimated and it appears to be moderate for the speeds investigated here ( i.e ., for c < 0.5ccrit). Close to the critical speed, however, bending stresses will be significant.

  • 12.
    Dahlberg, Tore
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Solid Mechanics.
    Procedure to calculate deflections of curved beams2004In: International journal of engineering education, ISSN 0949-149X, Vol. 20, p. 503-513Article in journal (Refereed)
  • 13.
    Dahlberg, Tore
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Solid Mechanics.
    Rewiew of research on railroad ballast as track substructure2000In: TransportForum,1999, 2000Conference paper (Other academic)
  • 14.
    Dahlberg, Tore
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Solid Mechanics.
    The Effect of Modal Coupling in Random Vibration Analysis1999In: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568, p. 157-176Article in journal (Other academic)
  • 15.
    Dahlberg, Tore
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Solid Mechanics.
    Lundqvist, Andreas
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Solid Mechanics.
    Dynamic forces in railway track due to unsupported sleeper2004In: Nordic Vibration Research 2004,2004, Stockholm: SVIB , 2004, p. 14:1-14:11Conference paper (Other academic)
  • 16.
    Dahlberg, Tore
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Solid Mechanics.
    Lundqvist, Andreas
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Solid Mechanics.
    Dynamic forces in railway track due to unsupported sleepers2004In: Twelfth Nordic Seminar in Railway Mechanics,2004, 2004Conference paper (Other academic)
  • 17.
    Dahlberg, Tore
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Solid Mechanics.
    Lundqvist, Andreas
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Solid Mechanics.
    Dynamic train/track interaction including model for track settlement evolvement2004Report (Other academic)
  • 18.
    Fjällström, Per-Olof
    et al.
    Linköping University, Department of Computer and Information Science, ACTLAB - Laboratory for Complexity of Algorithms. Linköping University, The Institute of Technology.
    Petersson, Jan
    Linköping University, Department of Science and Technology, Visual Information Technology and Applications (VITA). Linköping University, The Institute of Technology.
    Nilsson, Larsgunnar
    Linköping University, Department of Mechanical Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Zhong, Zhi-Hua
    Evaluation of Range Searching Methods for Contact Searching in Mechanical Engineering1998In: International Journal of Computational Geometry & Applications, ISSN 0218-1959, Vol. 8, no 1, p. 67-83Article in journal (Refereed)
    Abstract [en]

    Contact searching is an important and time-consuming part of computer simulation of certain deformation processes. Contact searching can be facilitated by orthogonal range searching. We have experimentally evaluated four methods for orthogonal range searching: the projection method, the cell method, the k-d tree method, and the range tree method.

     

    The results of our experiments indicate that two of these methods, the cell and k-d tree methods, have practical significance. The cell method is in most cases faster than the k-d tree method.

  • 19.
    Forsberg, Jimmy
    Linköping University, Department of Mechanical Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Structural optimization in vehicle crashworthiness design2005Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis concerns the optimization of structures subjected to impact loading. Major applications can be found in the crashworthiness design of vehicles. There is an industrial interest in using optimization methods in the crashworthiness design process. However, strongly nonlinear responses, including high frequency components, make the Finite Element (FE) simulations computationally demanding. This fact restricts the number of possible optimization methods that can be applied.

    In this work two optimization methods have been investigated: Response Surface Methodology (RSM) and Kriging. In both these methods the number of functional evaluations, i.e. here FE simulations, depends at least linearly on the number of design parameters. Thus, the number of design parameters is limited due to the computational effort. One objective of this work has been to reduce the total computational cost of the optimization process, or alternatively the possibility to use more design parameters at the same computational cost. When using RSM and Kriging, the number of functional evaluations in each iteration can be reduced, and/or the convergence of the optimization process can be improved. In many applications, RSM has been used with linear approximating response surfaces for robustness and efficiency reasons. Linear RSM may suffer from iterative oscillations, since the optimal design is often found on the boundary of the feasible design region. This oscillatory behaviour can be reduced if Kriging is used for the approximating response surfaces. However, it has been found that Kriging may have problems in fulfilling the constraints. In the initial design process of a structure very many alternative designs exist. At these early stages topology optimization is a mean of finding a structure that is optimal for the objective at hand. In this work a topology optimization approach is proposed for the design of crashworthiness structures. The resulting structure must still be subjected to an interpretation by engineers and also be improved by further optimization.

    List of papers
    1. Using the response surface methodology and the D-optimality criterion in crashworthiness related problems
    Open this publication in new window or tab >>Using the response surface methodology and the D-optimality criterion in crashworthiness related problems
    2002 (English)In: Structural and multidisciplinary optimization (Print), ISSN 1615-147X, E-ISSN 1615-1488, Vol. 24, no 3, p. 185-194Article in journal (Refereed) Published
    Abstract [en]

    The aim of this paper is to determine the efficient number of experimental points when using the response surface methodology in crashworthiness problems.

    The D-optimality criterion is used as experimental design method. Two application models have been studied, one square tube and one front rail from Saab Automobile AB. Both models were fully parameterized in the preprocessor LS-INGRID but only two design variables were used. The optimization package LS-OPT was used to determine the design of experiments using the D-optimality criterion. Both models were subjected to an impact into a rigid wall and the simulations were carried out using LS-DYNA. A general recommendation is to to use 1.5 times the minimum number of experimental points. A more specialized recommendation is for linear surfaces 1.5, elliptic surfaces 2.2 and for quadratic surfaces 1.6 times the minimum number of experimental points.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-35584 (URN)10.1007/s00158-002-0228-9 (DOI)27810 (Local ID)27810 (Archive number)27810 (OAI)
    Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2017-12-13
    2. On polynomial response surfaces and Kriging for use in structural optimization of crashworthiness
    Open this publication in new window or tab >>On polynomial response surfaces and Kriging for use in structural optimization of crashworthiness
    2005 (English)In: Structural and multidisciplinary optimization (Print), ISSN 1615-147X, E-ISSN 1615-1488, Vol. 29, no 3, p. 232-243Article in journal (Refereed) Published
    Abstract [en]

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

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

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

    Keywords
    Crashworthiness, FEM, Kriging RSM
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-45499 (URN)10.1007/s00158-004-0487-8 (DOI)
    Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-13
    3. Evaluation of response surface methodologies used in crashworthiness optimization
    Open this publication in new window or tab >>Evaluation of response surface methodologies used in crashworthiness optimization
    2006 (English)In: International Journal of Impact Engineering, ISSN 0734-743X, E-ISSN 1879-3509, Vol. 32, no 5, p. 759-777Article in journal (Refereed) Published
    Abstract [en]

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

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

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

    Keywords
    RSM, kriging, I-S-DYNA, crashworthiness optimization
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-46051 (URN)10.1016/j.ijimpeng.2005.01.007 (DOI)
    Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-13
    4. The optimisation process of an energy absorbing frontal underrun protection device
    Open this publication in new window or tab >>The optimisation process of an energy absorbing frontal underrun protection device
    2008 (English)In: International Journal of Vehicle Design, ISSN 0143-3369, E-ISSN 1741-5314, Vol. 46, no 3, p. 271-293Article in journal (Refereed) Published
    Abstract [en]

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

    Keywords
    Design process, FEM, Finite element method, Frontal underrun protection, FUP, Optimisation, Response surface methodology, RSM
    National Category
    Natural Sciences
    Identifiers
    urn:nbn:se:liu:diva-46033 (URN)10.1504/IJVD.2008.019087 (DOI)
    Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-13
    5. Topology optimization in crashworthiness design
    Open this publication in new window or tab >>Topology optimization in crashworthiness design
    2007 (English)In: Structural and multidisciplinary optimization (Print), ISSN 1615-147X, E-ISSN 1615-1488, Vol. 33, no 1, p. 1-12Article in journal (Refereed) Published
    Abstract [en]

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

    Keywords
    Contact-impacts, Explicit finite element analysis, Nonlinear problems, Topology optimization
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-50018 (URN)10.1007/s00158-006-0040-z (DOI)
    Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-12
  • 20.
    Fredricson, Harald
    Linköping University, Department of Mechanical Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Optimization methods for vehicle body structures2002Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis is concerned with the use of optimization methods in the vehicle industry. Numerical optimization has been used with limited extend in the vehicle industry. However, great potential of using optimization methods has been identified during the development process of vehicle body structures. One driving force in this direction is the increased focus on building lighter and cheaper vehicles with better crashworthiness. There is also an interest, from an academic point of view in the area of optimization research, to establish the use of optimization methods in the industry.

    This thesis presents a method that introduces optimization as a tool to be used during the design procedure of vehicle body structures. The three included papers introduces a way of including optimization methods during the development of vehicle body structures.

  • 21.
    Hasselqvist, Magnus
    Linköping University, Department of Mechanical Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Aspects of creep-fatigue in gas turbine hot parts2001Doctoral thesis, monograph (Other academic)
    Abstract [en]

    The goal is reliable creep-fatigue lifing methodology for industrial gas turbines.

    A literature study on high temperature materials used in gas turbines reveals that:

    • Most testing/modelling work has focused on characterisation and modelling of material response in isothermal standard tests, i.e. creep, tensile and LCF tests. This is not applicable to creep-fatigue lifing of industrial gas turbines. The difference between test and component conditions implies that models calibrated with standard data would be used far outside their domain of confidence.

    • A limited amount of testing/modelling work has included TMF testing. TMF test conditions are reasonably close to component conditions in aero turbines but the results are still not applicable for industrial gas turbines which, unlike TMF tests and aero gas turbines, are run at full load and therefore at maximum temperature, for extended times, typically in the order of 40000h.

    • A small amount of tests on aged material can be found in literature. It provides valuable but

    insufficient insight into the effects of long temperature exposure.

    The conclusion is that methodology improvement requires more appropriate testing. Testing/modelling work based on this has been done. Results so far:

    • Constitutive and life models have been developed for the carbide precipitating material Haynes 230. We have been limited to 'what can be done' in existing test rigs but the resulting methodology constitutes a definite step forward.

    • Constitutive models for the gamma prime strengthened material IN792 have been evaluated and calibrated using creep and 'step relaxation' data. This is a step forward compared to use of standard data but we have yet to perform tests on aged material and anisothermal verification tests to finalise the modelling.

    • We are developing a prototype for a new class of TMF rigs. Heating, cooling and insulation is used to reproduce local conditions at critical points in components under controlled laboratory conditions. The rigs will be designed for long term testing at a reasonable cost. The drawback is that the test conditions, e.g. strain ranges, must be calculated by FE simulation rather than measured.

    • Tests on virgin and aged specimen are ongoing to characterise the embrittling effect of long term exposure as a basis for a rational ranking of materials, i.e. on the basis of tests on appropriately aged rather than virgin material.

    Most of the results of the testing/modelling work should be of generic value for the material classes

    represented by Haynes 230 and IN792.

  • 22.
    Jansson, Tomas
    Linköping University, Department of Mechanical Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Optimization of sheet metal forming processes2005Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The potential of using simulation and optimization techniques in the design of sheet metal forming processes has been investigated. Optimization has been used in a variety of sheet metal forming applications. This usage has given ideas and guidelines on how to formulate an optimization problems, how to ensure its rapid convergence and how to reach a feasible process design. Furthermore one method to include the uncertainty and variation in the governing parameters has been evaluated.

    For each forming process many formability problems exist which usually are associated with fracture, wrinkling and springback. The aim of a good process design is to avoid these problems. By the use of simulation based design the physical trial- and error iterations can to a large extent be replaced by virtual iterations. When optimization techniques are used in the design process the number of iterations can be very large. In this work effort has been made to develop an optimization method, Space Mapping (SM), which is less computing intensive. It has been shown that SM can drastically reduce the required computing time and that its optimal solution is close to the optimal solution obtained by the more computing intensive Response Surface Methodology (RSM). The drawback of SM is that the method is less robust compared to RSM, and that it requires a better initial design for convergence.

    Each industrial sheet metal forming process exhibits a certain degree of stochastic behavior due to uncertainties and variations in material properties, geometry and other process parameters. The forming process must be designed such that it is insensitive to these uncertainties and variations, i.e. the process must be robust. One possibility to consider uncer tainties and variations in a simulation and optimization based design process is to use the Monte Carlo method, in particular in combination with response surfaces as metamodels. It has been shown in this work that a linear response surface can successfully be used to identify the important design variables and to give an estimate of the probabilistic response. It has also been found that quadratic surfaces are required for a more accurate evaluation of the response.

    List of papers
    1. Using surrogate models and response surfaces in structural optimization: with application to crashworthiness design and sheet metal forming
    Open this publication in new window or tab >>Using surrogate models and response surfaces in structural optimization: with application to crashworthiness design and sheet metal forming
    2003 (English)In: Structural and multidisciplinary optimization (Print), ISSN 1615-147X, E-ISSN 1615-1488, Vol. 25, no 2, p. 129-140Article in journal (Refereed) Published
    Abstract [en]

    The aim of this paper is to determine if the Space Mapping technique using surrogate models together with response surfaces is useful in the optimization of crashworthiness and sheet metal forming. In addition, the efficiency of optimization using Space Mapping will be compared to traditional structural optimization using the Response Surface Methodology (RSM). Five examples are used to study the algorithm: one optimization of an analytic function and four structural optimization problems. All examples are constrained optimization problems. In all examples, the algorithm converged to an improved design with all constraints fulfilled, even when a conventional RSM optimization failed to converge. For the crashworthiness design problems, the total computing time for convergence was reduced by 53% using Space Mapping compared to conventional RSM. For the sheet metal forming problems the total computing time was reduced by 63%. The conclusions are that optimization using Space Mapping and surrogate models can be used for optimization in crashworthiness design and sheet metal forming applications with a significant reduction in computing time.

    Keywords
    Crashworthiness, Finite element, Optimization, Response surface, Sheet metal forming, Space mapping
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-46579 (URN)10.1007/s00158-002-0279-y (DOI)
    Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-13
    2. Optimization of draw-in for an automotive sheet metal part: an evaluation using surrogate models and response surfaces
    Open this publication in new window or tab >>Optimization of draw-in for an automotive sheet metal part: an evaluation using surrogate models and response surfaces
    2005 (English)In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 159, no 3, p. 426-434Article in journal (Refereed) Published
    Abstract [en]

    In the present paper, an optimization of the draw-in of an automotive sheet metal part has been carried out using response surface methodology (RSM) and space mapping technique. The optimization adjusts the draw bead restraining force in the model such that the draw-in in the FE-model corresponds to the draw-in in the physical process. The conclusion of this study is that space mapping is a very effective and accurate method to use when calibrating the draw-in of a sheet metal process. In order to establish draw bead geometry from the draw bead restraining force a 2D-model was utilized. The draw bead geometry found showed good agreement with the physical draw bead geometry.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-31418 (URN)10.1016/j.jmatprotec.2004.06.011 (DOI)17196 (Local ID)17196 (Archive number)17196 (OAI)
    Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2017-12-13
    3. Minimizing the risk of failure in a sheet metal forming process: optimization using space mapping with one-step and incremental solvers
    Open this publication in new window or tab >>Minimizing the risk of failure in a sheet metal forming process: optimization using space mapping with one-step and incremental solvers
    2006 (English)In: Structural and multidisciplinary optimization (Print), ISSN 1615-147X, E-ISSN 1615-1488, Vol. 31, no 4, p. 320-332Article in journal (Refereed) Published
    Abstract [en]

    In the present paper, an optimization technique has been used to minimize the risk of failure in a sheet metal forming process. Two different types of finite element solvers, one using total plasticity and the other using incremental plasticity, have been used. A comparison between response surface methodology and space mapping (SM) with the one-step solver as surrogate model has been done. The conclusion of this study is that the use of the total plasticity theory drastically reduces the required computing time. Furthermore, the solution from the SM optimization algorithm is close to the solution obtained by the incremental plasticity solver.

    Keywords
    Incremental solver, One-step solver, Response surface methodology, Sheet metal forming, Space mapping
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-50249 (URN)10.1007/s00158-005-0604-3 (DOI)
    Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-12
    4. Optimizing sheet metal forming processes: using a design hierarchy and response surface methodology
    Open this publication in new window or tab >>Optimizing sheet metal forming processes: using a design hierarchy and response surface methodology
    2006 (English)In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 178, no 1-3, p. 218-233Article in journal (Refereed) Published
    Abstract [en]

    In the present paper optimization has been used to evaluate alternative sheet metal forming processes. Six process set-ups were first defined in a hierarchy of designs and optimization was then used to evaluate each forming process of these designs. The challenge in designing the forming process was to avoid failure in the material and at the same time reach an acceptable through thickness strain. The conclusions of this study is that there may exist a different process that can give an improved product for the desired geometry. This process might be impossible for the optimization algorithm to reach due to either a poor starting point or a not so wise process set-up.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-41602 (URN)10.1016/j.jmatprotec.2005.03.040 (DOI)58201 (Local ID)58201 (Archive number)58201 (OAI)
    Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2017-12-13
    5. Reliability analysis of a sheet metal forming process using Monte Carlo analysis and metamodels
    Open this publication in new window or tab >>Reliability analysis of a sheet metal forming process using Monte Carlo analysis and metamodels
    2008 (English)In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 202, no 1-3, p. 255-268Article in journal (Refereed) Published
    Abstract [en]

    The aim of the present paper is to evaluate the use of linear and quadratic approximating response surfaces as metamodels in a reliability assessment of a sheet metal forming process using the Monte Carlo simulation technique. Monte Carlo simulation was used to determine the probability for springback and thickness variation in a sheet metal part. The conclusions of this study is that Monte Carlo analysis can be used to identify the most important variables and to estimate the range of the studied responses. Linear metamodels can be used to identify the important variables and to give an estimate of the probabilistic response. But quadratic surfaces are required for a more accurate analysis.

    Keywords
    Monte carlo analysis, Reliability, Sheet metal forming, Springback, Thickness variation
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-45955 (URN)10.1016/j.jmatprotec.2007.09.005 (DOI)
    Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-13
  • 23.
    Jansson, Tomas
    Linköping University, Department of Mechanical Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Optimization of sheet metal forming processes2002Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The aim of the present work is to find a stable and effective optimization algorithm that can be used to determine the location and size of drawbeads in sheet metal forming processes. The result from the optimization will be the restraining force that each drawbead applies to the blank. In addition, optimization has been used to determine the physical dimensions of the drawbead.

    The study in Paper I is limited to two structures in crashworthiness design, each with two design variables and three responses. The conclusion is that 1.5 times the minimum number of function evaluation should be used to fit the surface approximations. The conclusion of this study gives an indication on how many evaluations that are needed in order to efficiently construct the response surface approximations.

    Paper II shows that the optimization algorithm using Space Mapping is well suited for optimization problems in crashworthiness design and in the design of sheet metal forming processes. All optimization applications converged to the correct optimum and the computing time was decreased with a maximum of 63% relative to the traditional RSM optimization.

    The Space Mapping algorithm presented in Paper III converged to an optimum value that is lower than the optimum value from the traditional RSM, when the approximated surfaces from the first RSM iteration were used as the coarse model. The Space Mapping algorithm, however, reached a higher value compared to RSM, when surfaces from the third RSM iteration was used as the coarse model. Hence, the Space Mapping algorithm converged to a better objective value compared to RSM with less evaluations.

    This thesis has shown that it is possible to apply optimization on the design of sheet metal forming processes. For the problem used in the last paper both the traditional Response Surface Methodology and the Space Mapping technique were successful in avoiding failure due to necking and to decrease the risk of wrinkles. The Response Surface Methodology is robust enough to be used in the industrial tool design process. The Space Mapping technique using linear response surfaces as coarse model needs further research before it can be used efficiently in industry.

  • 24.
    Jansson, Tomas
    et al.
    Linköping University, Department of Mechanical Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Andersson, A.
    Volvo Car Corporation, Body Components, Olofström, Sweden and the Division of Production and Materials Engineering, Lund University, Sweden.
    Nilsson, Larsgunnar
    Linköping University, Department of Mechanical Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Optimization of draw-in for an automotive sheet metal part: an evaluation using surrogate models and response surfaces2005In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 159, no 3, p. 426-434Article in journal (Refereed)
    Abstract [en]

    In the present paper, an optimization of the draw-in of an automotive sheet metal part has been carried out using response surface methodology (RSM) and space mapping technique. The optimization adjusts the draw bead restraining force in the model such that the draw-in in the FE-model corresponds to the draw-in in the physical process. The conclusion of this study is that space mapping is a very effective and accurate method to use when calibrating the draw-in of a sheet metal process. In order to establish draw bead geometry from the draw bead restraining force a 2D-model was utilized. The draw bead geometry found showed good agreement with the physical draw bead geometry.

  • 25.
    Jansson, Tomas
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Nilsson, Lars
    Linköping University, Department of Management and Engineering, Energy Systems. Linköping University, The Institute of Technology.
    Moshfegh, Ramin
    Linköping University, Department of Mechanical Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Reliability analysis of a sheet metal forming process using Monte Carlo analysis and metamodels2008In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 202, no 1-3, p. 255-268Article in journal (Refereed)
    Abstract [en]

    The aim of the present paper is to evaluate the use of linear and quadratic approximating response surfaces as metamodels in a reliability assessment of a sheet metal forming process using the Monte Carlo simulation technique. Monte Carlo simulation was used to determine the probability for springback and thickness variation in a sheet metal part. The conclusions of this study is that Monte Carlo analysis can be used to identify the most important variables and to estimate the range of the studied responses. Linear metamodels can be used to identify the important variables and to give an estimate of the probabilistic response. But quadratic surfaces are required for a more accurate analysis.

  • 26.
    Jansson, Tomas
    et al.
    Linköping University, Department of Mechanical Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Nilsson, Larsgunnar
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Optimizing sheet metal forming processes: using a design hierarchy and response surface methodology2006In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 178, no 1-3, p. 218-233Article in journal (Refereed)
    Abstract [en]

    In the present paper optimization has been used to evaluate alternative sheet metal forming processes. Six process set-ups were first defined in a hierarchy of designs and optimization was then used to evaluate each forming process of these designs. The challenge in designing the forming process was to avoid failure in the material and at the same time reach an acceptable through thickness strain. The conclusions of this study is that there may exist a different process that can give an improved product for the desired geometry. This process might be impossible for the optimization algorithm to reach due to either a poor starting point or a not so wise process set-up.

  • 27.
    Jinnestrand, Magnus
    Linköping University, Department of Mechanical Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Delamination in APS applied thermal barrier coatings: life modelling2004Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Thermal barrier coatings, TBCs, are used in gas turbines as a thermal shield resulting in lower temperature in coated components. The decrease of temperature allows higher gas temperatures in the turbine, which increase the efficiency. The bimaterial construction with an outer ceramic layer applied onto a metallic material give rice to problems during thermal cycling. Thermal induced stresses will gradually break down the coating. The ceramic layer will delaminate from the substrate, resulting in spallation, and the component will break down due to overheating.

    The delamination process is investigated in this thesis by finite element simulations. The growth of an internal alumina layer in the top/bond coat interface is investigated by 3D finite element simulations which show that the local stress state change in such way that the alumina growth help nucleation and growth of small delamination cracks. Finite element simulations, in which t he energy release rate and stress intensity factors are calculated, investigate the growth of small delamination cracks in or close to the top/bond coat interface. Experiments show that these cracks grow parallel to or in the sinusoidal top/bond coat interface and the results of the simulations show that the mode mixity changes as the delamination cracks grow.

    A new delamination life model is proposed which is based on results of the fracture mechanical simulations and experimental observations. The model predicts the growth of small cracks in the TBC before they form a large delamination crack. The model is based on a modified Paris law where a mode mixity dependence on the crack growth rate is included, meaning lower crack growth rate in mode 2 load compared with mode 1. Parameters of the model are obtained by optimisation of the model against experimental data, describing the delamination damage evolution in the TBC. The data are obtained from interrupted thermal cycling tests and the prediction of the model corresponds well with these data.

    List of papers
    1. Investigation by 3D FE simulations of delamination crack initiation in TBC caused by alumina growth
    Open this publication in new window or tab >>Investigation by 3D FE simulations of delamination crack initiation in TBC caused by alumina growth
    2001 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 135, no 2-3, p. 188-195Article in journal (Refereed) Published
    Abstract [en]

    In gas turbines, thermal barrier coatings (TBCs) applied by air plasma spraying are widely used to reduce the temperature in hot components. The TBC allows higher gas temperature and/or reduces the need for internal cooling in the hot components, thus increasing the efficiency of the gas turbine. Spallation is a common failure mechanism of TBC and occurs after a critical number of thermal cycles, when the alumina layer has grown to a critical thickness. The influence of the growing alumina layer and the top/bond-coat interface roughness in the TBC has been investigated. The primary goal was to identify failure mechanisms that can be incorporated into a life model of the TBC, and to increase the understanding of the delamination process in the TBC. A new formulation of alumina growth is proposed, in which the swelling strains caused by the volumetric increase during alumina growth depends on the stress state. The alumina growth model is used in 3D FE thermal cycling simulations of a TBC in which the thermal cycle time is long enough to characterize a typical cycle of a gas turbine. From the simulations, the growing alumina layer is observed to be one failure mechanism of the TBC. Without an alumina layer in the model, high delamination stress is observed at room temperature, above ridges of the top/bond-coat interface in the top coat. When the alumina is growing, the point of maximum delamination stress is moved towards the valleys. When the thickness of the alumina layer has grown to approximately 8–10 μm, positive delamination stress is found above the valleys in the top coat. The movement of the positive delamination stress region can explain why a delamination crack develops, which will cause spallation of the TBC during shutdown to room temperature.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-47480 (URN)10.1016/S0257-8972(00)01084-7 (DOI)
    Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-13
    2. Crack initiation and propagation in air plasma sprayed thermal barrier coatings, testing and mathematical modelling of low cycle fatigue behaviour
    Open this publication in new window or tab >>Crack initiation and propagation in air plasma sprayed thermal barrier coatings, testing and mathematical modelling of low cycle fatigue behaviour
    2004 (English)In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 379, no 1-2, p. 45-57Article in journal (Refereed) Published
    Abstract [en]

    In the present paper failure mechanisms in air plasma sprayed thermal barrier coatings for land-based gas turbines have been studied. This has been done by finite element simulations and fractographic investigations of low cycle fatigue (LCF) tested material, here chosen as an 350 μm thick partially stabilised zirconia top coat (TC) together with a 150 μm thick Ni-Co-Cr-Al-Y bond coat (BC) on a nickel base substrate (Haynes 230). Both LCF testing, modelling results and fractographic investigations point in the same direction. An increased thickness of the thermally grown oxide (TGO) does decrease the LCF life of a coated structural alloy. Several points of crack initiation were found, in the TGO at the TC/BC interface, at the oxide network within the BC and at oxide inclusions between BC and substrate. During LCF tests the initiated cracks will grow radially into the substrate material. The behaviour is explained by increased TC/BC delamination stresses and changed oxidation behaviour with increased oxidation times.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-22790 (URN)10.1016/j.msea.2003.12.063 (DOI)2123 (Local ID)2123 (Archive number)2123 (OAI)
    Available from: 2009-10-07 Created: 2009-10-07 Last updated: 2017-12-13
    3. Fracture mechanics analysis of an APS applied TBC
    Open this publication in new window or tab >>Fracture mechanics analysis of an APS applied TBC
    (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    An air plasma sprayed thermal barrier coating is investigated by fracture-mechanical analysis. The virtual crack extension method is used to calculatethe energy release rate, G, and the displacements of the crack surfaces are used to split the energy release rate into mode 1 and 2 stress intensity factors, K1 and K2 . The results of the investigation are evolutions of G, K1 and K2 as functions of delamination crack length for small delamination cracks.

    An approximation of a hot spot is investigated by applying an out-of-phase load at room temperature. The results show that the out-of-phase load results in a more open crack compared with only a thermal load on the TBC system. This can explain why the out-of-phase load is dangerous.

    The results show that it might be possible to base a delamination life model on fracture-mechanical data of an interface crack in the top/bond coat interface. If so, it is important that the mode mixity effects on crack growth rate is included in the life model.

    Keywords
    Thermal barrier coating, Virtual crack extension, Interface crack, Crack initiation, Life modelling
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-87826 (URN)
    Available from: 2013-01-23 Created: 2013-01-23 Last updated: 2013-01-23
    4. Fatigue life prediction of a plasma sprayed thermal barrier coating system
    Open this publication in new window or tab >>Fatigue life prediction of a plasma sprayed thermal barrier coating system
    (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    Thermal barrier coatings are commonly used in gas turbines for power generation. One major issue in TBC design is how to determine fatigue life in these material systems. The present paper aims at presenting a model for determination of TBC life based on the behavior of an air plasma sprayed coating system. This is done by analysis of fracture behavior and evaluation of data from thermal fatigue tests. The knowledge regarding fracture behavior in thermal fatigue tests is used as an input to the modelling work. For formulation of the fatigue life model, a Paris law approach has been used. FE calculations are used to obtain energy release rate and stress intensity factors, KI and KII, for a propagating delamination crack in the top/ bond coat interface. As a measure of failure, a delamination damage measure is used. A method for determination of delamination crack growth data is presented.

    Keywords
    Thermal barrier coating, delamination, fatigue, fracture mechanics, modelling, crack growth
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-24277 (URN)3886 (Local ID)3886 (Archive number)3886 (OAI)
    Available from: 2009-10-07 Created: 2009-10-07 Last updated: 2013-01-31
  • 28.
    Jinnestrand, Magnus
    et al.
    Linköping University, Department of Mechanical Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Brodin, Håkan
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Crack initiation and propagation in air plasma sprayed thermal barrier coatings, testing and mathematical modelling of low cycle fatigue behaviour2004In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 379, no 1-2, p. 45-57Article in journal (Refereed)
    Abstract [en]

    In the present paper failure mechanisms in air plasma sprayed thermal barrier coatings for land-based gas turbines have been studied. This has been done by finite element simulations and fractographic investigations of low cycle fatigue (LCF) tested material, here chosen as an 350 μm thick partially stabilised zirconia top coat (TC) together with a 150 μm thick Ni-Co-Cr-Al-Y bond coat (BC) on a nickel base substrate (Haynes 230). Both LCF testing, modelling results and fractographic investigations point in the same direction. An increased thickness of the thermally grown oxide (TGO) does decrease the LCF life of a coated structural alloy. Several points of crack initiation were found, in the TGO at the TC/BC interface, at the oxide network within the BC and at oxide inclusions between BC and substrate. During LCF tests the initiated cracks will grow radially into the substrate material. The behaviour is explained by increased TC/BC delamination stresses and changed oxidation behaviour with increased oxidation times.

  • 29.
    Jinnestrand, Magnus
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Solid Mechanics.
    Sjöström, Karl Henning Sören
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering.
    Stress state in thermal barrier coatings from 3D finite element simulations2001In: Int. Congress on theoretical and Applied Mechanics,2001, 2001Conference paper (Other academic)
    Abstract [en]

       

  • 30.
    Krishnasamy, Ezhilmathi
    Linköping University, Department of Mechanical Engineering, Solid Mechanics.
    Hybrid CPU-GPU Parallel Simulations of 3D Front Propagation2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This master thesis studies GPU-enabled parallel implementations of the 3D Parallel Marching Method (PMM). 3D PMM is aimed at solving the non-linear static Jacobi-Hamilton equations, which has real world applications such as in the study of geological foldings, where each layer of the Earth’s crust is considered as a front propagating over time. Using the parallel computer architectures, fast simulationscan be achieved, leading to less time consumption, quicker understanding of the inner Earth and enables early exploration of oil and gas reserves. Currently 3D PMM is implemented in shared memory architecture using OpenMP Application Programming Interface (API) and the MINT programming model, which translates C code into Compute Unified Device Architecture (CUDA) code for a single Graphical Process Unit (GPU). Parallel architectures have seen rapid growth in recent years, especially GPUs, allowing us to do faster simulations. In this thesis work, a new parallel implementation for 3D PMM has been done to exploit multicore CPU architectures as well as single and multiple GPUs. In a multiple GPU implementation, 3D data isdecomposed into 1D data for each GPU. CUDA streams are used to overlap the computation and communication within the single GPU. Part of the decomposed 3D volume data is kept in the respective GPU to avoid complete data transfer between the GPUs over a number of iterations. In total, there are two kinds of datatransfers that are involved while doing computation in the multiple GPUs: boundary value data transfer and decomposed 3D volume data transfer. The decomposed 3D volume data transfer is optimized between the multiple GPUs by using the peer to peer memory transfer in CUDA. The speedup is shown and compared between shared memory CPUs (E5-2660, 16cores), single GPU (GTX-590, C2050 and K20m) and multiple GPUs. Hand coded CUDA has shown slightly better performance than the Mint translated CUDA, and the multiple GPU implementation showed promising speedup compared to shared memory multicore CPUs and single GPU implementations.

  • 31. lI, M. X.D.
    et al.
    Moshfegh, Ramin
    Hållfasthetslära Tekniska fakultetet.
    Nilsson, Larsgunnar
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Solid Mechanics.
    Two-mesh refinement indicators and adaptivity in non-linear explicit finite element analysis of shells using LS-DYNA2000In: International Journal for Numerical Methods in Engineering, ISSN 0029-5981, E-ISSN 1097-0207, International Journal for Numerical Methods in Biomedical Engineering, ISSN 2040-7939, Vol. 16, no 11, p. 785-800Article in journal (Refereed)
    Abstract [en]

    Two-mesh refinement indicators based on the gradients of effective stresses and effective plastic strains, respectively, are proposed for adaptive finite element analysis of the large deformation, materially non-linear dynamic response of shells. The refinement strategy consists of equi-distributing the variation of stresses or plastic strains over the elements of the mesh. A program module for implementing these refinement indicators has been developed and coupled with the general non-linear finite element explicit code LS-DYNA. Numerical examples including both material and geometric non-linearities are presented. It is shown that these indicators can effectively identify those finite elements, which have high gradients of stresses and strains so that the mesh is refined in the region's undergoing the most severe deformations.

  • 32.
    Lundh, Karin
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Solid Mechanics.
    Influence of stiffness of the track bed on dynamics of the railway track2004Report (Other academic)
  • 33.
    Lundqvist, Andreas
    Linköping University, Department of Mechanical Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Dynamic train/track interaction: hanging sleepers, track stiffness variations and track settlement2005Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Trains have been operating on ballasted tracks for over 150 years. During this time demands from the railway organisations and from the industry to increase axle loads and train speeds on the existing railway lines have increased. The reasons for this are both economial and environmental.

    Both higher axle loads and train speeds will increase the deterioration rate of the track and cause permanent settlements in the ballast and the underlaying soil. When the track quality decreases beyond certain limits maintenance for relevelling and realignment of the track is necessary, and this is expensive.

    The aim of the work presented in this thesis, and of the work performed within the EU project SUstained PErformance of Railway TRACK (SUPERTRACK), is to investigate the dynamic train/track interaction and its effect on track degradation. Less degradation will reduce the maintenance costs regarding track settlement.

    The work presented in this thesis focuses on different factors affecting the differential track settlement. By using the finite element method, the dynamic behaviour of a railway track subjected to a moving load has been studied. Dynamic effects of unsupported sleepers and their effect on track settlement have been investigated. Also track stiffness irregularities along the track have been studied, and an optimazation of the track stiffness at a transition zone has been performed.

    List of papers
    1. Dynamic train/track interaction including model for track settlement evolvement
    Open this publication in new window or tab >>Dynamic train/track interaction including model for track settlement evolvement
    2004 (English)In: Vehicle System Dynamics, ISSN 0042-3114, E-ISSN 1744-5159, Vol. 41 (Supplement), p. 667-676Article in journal (Other academic) Published
    Abstract [en]

    A ballasted railway track exposed to train traffic will degenerate. Track alignment and track level will deteriorate. Settlements of the track (loss of track level and alignment) require maintenance; the track is lifted and aligned, and new ballast material is injected under the sleepers. This paper presents a computer model by which the dynamic train/track interaction can be simulated and the permanent deformation of the track (i.e. track settlements) can be calculated. The voided sleepers ("hanging" sleepers) phenomenon will also be discussed.

    Keywords
    track settlement, train/track interaction, railway ballast, numerical model
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-100390 (URN)
    Available from: 2013-11-05 Created: 2013-11-05 Last updated: 2017-12-06
    2. Load impact on railway track due to unsupported sleepers
    Open this publication in new window or tab >>Load impact on railway track due to unsupported sleepers
    2005 (English)In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 219, no 2, p. 67-77Article in journal (Refereed) Published
    Abstract [en]

    Ballasted railway tracks will settle as a result of permanent deformations in the ballast and in the underlying material layers. The settlement is caused by the repeated traffic loading and the severity of the settlement depends on the quality and the behaviour of the ballast, the sub-ballast, and the subgrade.

    As the behaviour of the material is not exactly the same under all sleepers, and since the loading of the track is irregular, the amount of settlement will differ from one sleeper to another. A result of this is that the sleepers are not always fully supported, and some sleepers may even become completely unsupported (voided). A gap appears between the sleeper and the ballast bed. As soon as the track geometry starts to deteriorate, the variations of the train/track interaction force increase, and this speeds up the track deterioration rate.

    This paper presents a computer model by which the dynamic train/track interaction can be simulated. The influence of one or several voided sleepers on the train/track interaction force and on the track dynamics is investigated. Track settlement due to hanging sleeper(s) is discussed.

    Keywords
    unsupported sleeper, train/track interaction, railway model, track settlement
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-46081 (URN)10.1243/095440905X8790 (DOI)000231159600002 ()
    Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-13
    3. Railway track stiffness variation - consequences and countermeasures
    Open this publication in new window or tab >>Railway track stiffness variation - consequences and countermeasures
    2005 (English)In: 19th IAVSD Symposium of Dynamics of Vehicles on Roads and Tracks, 2005, Milano: Dept Mech Eng, Politecnico di Milano , 2005Conference paper, Published paper (Other academic)
    Abstract [en]

    The track stiffness experienced by a train will vary along the track. Sometimes the stiffness variation can be very large whitin short distances. These changes in track stiffness will cause variations in the train/track interaction forces, and force variations will normaly imply settlements of the track as a result of permanent deformation in the ballast and in the underlying structure.

    Since the behaviour of the ballast and subground material is not exactly the same under all sleepers. and since the loading of the track is irregular. the amount of settlement will differ from one sleeper to another. As soon as the track geometry starts to deteriorate, the variations of the train/track interaction force increase, and this speeds up the track deterioration rate.

    This paper discusses how the transition zone between two track stiffnesses should be designed to reduce the track settlement. The transition from one track stiffness to another is optimized to obtain a wheel/rail contact force with as small variations as possible. A smooth wheel/rail contact force at the transition area will minimize the track settlement.

    Place, publisher, year, edition, pages
    Milano: Dept Mech Eng, Politecnico di Milano, 2005
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-41855 (URN)59253 (Local ID)59253 (Archive number)59253 (OAI)
    Conference
    19th IAVSD Symposium of Dynamics of Vehicles on Roads and Tracks, Milano, August 29-Seprember 2, 2005
    Note

    Poster

    Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2013-11-05
  • 34.
    Lundqvist, Andreas
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Solid Mechanics.
    Dahlberg, Tore
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Solid Mechanics.
    Dynamic train/track interaction including model for track settlement evolvement2004In: 18th IAVSD Symposium on Dynamics of Vehicles on Roads and on Tracks,2003, London, UK: Taylor & Francis Group , 2004, p. 667-Conference paper (Refereed)
  • 35.
    Lundqvist, Andreas
    et al.
    Linköping University, Department of Mechanical Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Dahlberg, Tore
    Linköping University, Department of Mechanical Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Dynamic train/track interaction including model for track settlement evolvement2004In: Vehicle System Dynamics, ISSN 0042-3114, E-ISSN 1744-5159, Vol. 41 (Supplement), p. 667-676Article in journal (Other academic)
    Abstract [en]

    A ballasted railway track exposed to train traffic will degenerate. Track alignment and track level will deteriorate. Settlements of the track (loss of track level and alignment) require maintenance; the track is lifted and aligned, and new ballast material is injected under the sleepers. This paper presents a computer model by which the dynamic train/track interaction can be simulated and the permanent deformation of the track (i.e. track settlements) can be calculated. The voided sleepers ("hanging" sleepers) phenomenon will also be discussed.

  • 36.
    Lundqvist, Andreas
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Solid Mechanics.
    Dahlberg, Tore
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Solid Mechanics.
    Dynamic train/track interaction model: verification, modelling of track settlement, hanging sleeper (s), and varying track stiffness2004Report (Other academic)
  • 37.
    Lundqvist, Andreas
    et al.
    Linköping University, Department of Mechanical Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Dahlberg, Tore
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Railway track stiffness variation - consequences and countermeasures2005In: 19th IAVSD Symposium of Dynamics of Vehicles on Roads and Tracks, 2005, Milano: Dept Mech Eng, Politecnico di Milano , 2005Conference paper (Other academic)
    Abstract [en]

    The track stiffness experienced by a train will vary along the track. Sometimes the stiffness variation can be very large whitin short distances. These changes in track stiffness will cause variations in the train/track interaction forces, and force variations will normaly imply settlements of the track as a result of permanent deformation in the ballast and in the underlying structure.

    Since the behaviour of the ballast and subground material is not exactly the same under all sleepers. and since the loading of the track is irregular. the amount of settlement will differ from one sleeper to another. As soon as the track geometry starts to deteriorate, the variations of the train/track interaction force increase, and this speeds up the track deterioration rate.

    This paper discusses how the transition zone between two track stiffnesses should be designed to reduce the track settlement. The transition from one track stiffness to another is optimized to obtain a wheel/rail contact force with as small variations as possible. A smooth wheel/rail contact force at the transition area will minimize the track settlement.

  • 38.
    Mackerle, Jaroslav
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Solid Mechanics.
    Coatings and surface modification technologies: A finite element bibliography (1995-2005)2005In: Modelling and Simulation in Materials Science and Engineering, ISSN 0965-0393, E-ISSN 1361-651X, Vol. 13, no 6, p. 935-979Article in journal (Refereed)
    Abstract [en]

    This paper gives a bibliographical review of the finite element methods applied to the analysis and simulation of coatings, their mechanical and material properties from the theoretical and application points of view. The surface modification technologies in the context of coatings are also included. The added bibliography at the end of this paper contains 1032 references to papers and conference proceedings on the subject that were published in 1995-2005. The following topics are included: coating property simulations, surface modification process simulations and practical coating applications. © 2005 IOP Publishing Ltd.

  • 39.
    Mackerle, Jaroslav
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Solid Mechanics.
    Creep and Creep Fracture/Damage Finite Element Modelling of Engineering materials and Structures2000In: International Journal of Pressure Vessels and Piping, ISSN 0308-0161, E-ISSN 1879-3541, Vol. 77, no 1, p. 53-77Article in journal (Other academic)
  • 40.
    Mackerle, Jaroslav
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Solid Mechanics.
    Creep and Creep Fracture/Damage Finite Element Modelling of Engineering Materials and Structures: An Addendum2004In: International Journal of Pressure Vessels and Piping, ISSN 0308-0161, E-ISSN 1879-3541, Vol. 81, p. 381-392Article in journal (Refereed)
  • 41.
    Mackerle, Jaroslav
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Solid Mechanics.
    FEM and BEM in the context of information retrieval2000In: Conference Numerical Methods in Continuum Mechanics,2000, 2000Conference paper (Other academic)
    Abstract [en]

       

  • 42.
    Mackerle, Jaroslav
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Solid Mechanics.
    Finite element analyses and simulations in biomedicine2001In: Engineering computations, ISSN 0264-4401, E-ISSN 1758-7077, p. 813-856Article in journal (Refereed)
  • 43.
    Mackerle, Jaroslav
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Solid Mechanics.
    Finite Element Analyses and Simulations of Manufacturing Processes of Composites and Their Mechanical Properties: A Bibliography (1985-2003)2004In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 31, p. 187-219Article in journal (Refereed)
  • 44.
    Mackerle, Jaroslav
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Solid Mechanics.
    Finite Element Analyses and Simulations of Sheet Metal Forming Process (A Bibliography 1995-2003)2004In: Engineering computations, ISSN 0264-4401, E-ISSN 1758-7077, Vol. 21, p. 891-940Article in journal (Refereed)
  • 45.
    Mackerle, Jaroslav
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Solid Mechanics.
    Finite Element Analyses in Wood Research: A Bibliography in Wood Science and Technology(ISSN 0043-7719), pp 579-6002005Other (Other academic)
  • 46.
    Mackerle, Jaroslav
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Solid Mechanics.
    Finite Element and Boundary Element Modelling of Surface Engineering Systems2000In: Finite elements in analysis and design (Print), ISSN 0168-874X, E-ISSN 1872-6925, Vol. 34, no 2, p. 113-124Article in journal (Other academic)
    Abstract [en]

        

  • 47.
    Mackerle, Jaroslav
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Solid Mechanics.
    Finite Element Crash Simulationas and Impact-Induced Injuries2000Other (Other (popular science, discussion, etc.))
  • 48.
    Mackerle, Jaroslav
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Solid Mechanics.
    Finite Element Linear and Nonlinear, Static and Dynamic Analys of Structural Elements- An Addendum2001In: Engineering computations, ISSN 0264-4401, E-ISSN 1758-7077, p. 274-360Article in journal (Refereed)
  • 49.
    Mackerle, Jaroslav
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Solid Mechanics.
    Finite Element Modelling and Simulation of Indentation Testing (1990-2002)2004In: Engineering computations, ISSN 0264-4401, E-ISSN 1758-7077, Vol. 21, p. 23-52Article in journal (Refereed)
  • 50.
    Mackerle, Jaroslav
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Solid Mechanics.
    Finite Element Modelling and Simulations in Cardiovascular Mechanics and Cardiology: A Bibliography2005In: Computer Methods in Biomechanics and Biomedical Engineering, ISSN 1025-5842, E-ISSN 1476-8259, p. 59-81Article in journal (Refereed)
12 1 - 50 of 80
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