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  • 1.
    Almroth, Per
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Hasselqvist, M.
    Demag Delaval Indust. Turbomach. AB, Finspång.
    Simonsson, Kjell
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära.
    Sjöström, Sören
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Viscoplastic-plastic modelling of IN7922004Ingår i: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 29, nr 4, s. 437-445Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    At high temperatures metallic materials behave in a viscous manner exemplified by strain rate dependence, stress relaxation and creep deformation. At low temperatures however, these effects are extremely small, and the behaviour is strain rate independent and shows no or very small relaxation effects. Finally there exists an intermediate region, in which the material behaviour is close to strain rate independent for high strain rates but at the same time shows time dependent inelastic effects, such as stress relaxation and creep. For IN792 this occurs at temperatures around 650 °C. The article describes the extension of a power-law viscoplastic model describing the behaviour of IN792 at 850 °C, also to describe the behaviour at 650 °C, by bounding the elastic-viscoplastic stress-space by a plastic yield surface. The model parameters have been estimated using data from creep test and tailored step relaxation tests, and the model fits well to both the step relaxation data aimed at resembling relevant component conditions and long term creep data. © 2003 Published by Elsevier B.V.

  • 2.
    Almroth, Per
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för konstruktions- och produktionsteknik, Hållfasthetslära.
    Hasselqvist, Magnus
    Sjöström, Karl Henning Sören
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för konstruktions- och produktionsteknik.
    Simonsson, Kjell
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för konstruktions- och produktionsteknik, Hållfasthetslära.
    Modeling of the high temperature behaviour of IN792 in gas turbine hot parts2002Ingår i: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 25, nr 3, s. 305-315Artikel i tidskrift (Övrigt vetenskapligt)
    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.

  • 3.
    Andersson, Håkan
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Hilding, Daniel
    DYNAmore Nordic AB, Brigadgatan 5, 587 58 Linköping, Sweden.
    Schill, Mikael
    DYNAmore Nordic AB, Brigadgatan 5, 587 58 Linköping, Sweden.
    Leidermark, Daniel
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    System level co-simulation of a control valve and hydraulic cylinder circuit in a hydraulic percussion unit2017Ingår i: Proceedings of 15:th Scandinavian International Conference on Fluid Power, June 7-9, 2017, Linköping, Sweden / [ed] Petter Krus, Liselott Ericson and Magnus Sethson, Linköping: Linköping University Electronic Press, 2017, Vol. 144, s. 225-235Konferensbidrag (Refereegranskat)
    Abstract [en]

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

  • 4.
    Azeez, Ahmed
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Eriksson, Robert
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Filosofiska fakulteten. Linköpings universitet, Tekniska fakulteten.
    Calmunger, Mattias
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten.
    Lindström, Stefan B
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Low Cycle Fatigue Modelling of Steam Turbine Rotor Steel2019Ingår i: Structural Integrity Procedia / [ed] Elsevier, Elsevier, 2019Konferensbidrag (Refereegranskat)
  • 5.
    Bergqvist, Göran
    et al.
    Private practice, Norrköping, Sweden.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Rydberg, Kristoffer
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Johansson, Fredrik
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Dérand, Tore
    Department of Dental Technology and Dental Materials Science, Faculty of Odontology, Malmö University, Malmö, Sweden.
    A finite element analysis of stress distribution in bone tissue surrounding uncoupled or splinted dental implants2008Ingår i: Clinical Implant Dentistry and Related Research, ISSN 1523-0899, E-ISSN 1708-8208, Vol. 10, nr 1, s. 40-46Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Background: Several studies on one-stage surgery in the treatment of the edentulous maxilla with implant-supported fixed prostheses have reported problems with removable provisional prostheses, which can load the implants in an uncontrollable manner during healing, and jeopardize healing. Immediate splinting of the implants with a fixed provisional prosthesis has been proposed to protect the bone-implant interface.

    Purpose: This study used the finite element method (FEM) to simulate stresses induced in bone tissue surrounding uncoupled and splinted implants in the maxilla because of bite force loading, and to determine whether the differences in these stress levels are related to differences in observed bone losses associated with the two healing methods.

    Materials and Methods: Stress levels in the maxilla were studied using the FEM program TRINITAS (Institute of Technology, Linköping University, Linköping, Sweden) in which all phases – preprocessing/modeling, equation solving, and postprocessing/evaluation – were simulated.

    Results: Stress levels in bone tissue surrounding splinted implants were markedly lower than stress levels surrounding uncoupled implants by a factor of nearly 9.

    Conclusion: From a mechanical viewpoint, FEM simulation supports the hypothesis that splinting reduces damage evolution in bone tissue, which agrees with clinical observations.

  • 6.
    Borg, Rikard
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för konstruktions- och produktionsteknik, Hållfasthetslära.
    Borg, Rikard
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för konstruktions- och produktionsteknik, Hållfasthetslära.
    Nilsson, Larsgunnar
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för konstruktions- och produktionsteknik, Hållfasthetslära.
    Nilsson, Larsgunnar
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för konstruktions- och produktionsteknik, Hållfasthetslära.
    Simonsson, Kjell
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för konstruktions- och produktionsteknik, Hållfasthetslära.
    Simonsson, Kjell
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för konstruktions- och produktionsteknik, Hållfasthetslära.
    Simulation of delamination in fiber composites with a discrete cohesive failure model2001Ingår i: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 61, nr 5, s. 667-677Övrigt (Övrig (populärvetenskap, debatt, mm))
    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.

  • 7.
    Borg, Rikard
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära.
    Nilsson, Larsgunnar
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära.
    Simonsson, Kjell
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära.
    Modeling of delamination using a discretized cohesive zone and damage formulation2002Ingår i: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 62, nr 10-11, s. 1299-1314Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Delamination initiation and growth are analyzed by using a discrete cohesive crack model. The delamination is constrained to grow along a tied interface. 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 this 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. A damage formulation is used to reduce the adhesive forces. Mode I, II and III loading or any combined loading is possible. An analytical solution is obtained for a single mode opening and the implications of this result on the governing equations is discussed. The delamination model is implemented in the finite element code LS-DYNA and simulation results are shown to be in agreement with experimental results. © 2002 Elsevier Science Ltd. All rights reserved.

  • 8.
    Borg, Rikard
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för konstruktions- och produktionsteknik, Hållfasthetslära.
    Nilsson, Larsgunnar
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för konstruktions- och produktionsteknik, Hållfasthetslära.
    Simonsson, Kjell
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för konstruktions- och produktionsteknik, Hållfasthetslära.
    Simulating DCB, ENF and MMB experiments using shell elements and a cohesive zone model2004Ingår i: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 64, nr 2, s. 269-278Artikel i tidskrift (Refereegranskat)
    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.

  • 9.
    Borg, Rikard
    et al.
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för konstruktions- och produktionsteknik, Hållfasthetslära.
    Nilsson, Larsgunnar
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för konstruktions- och produktionsteknik, Hållfasthetslära.
    Simonsson, Kjell
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för konstruktions- och produktionsteknik, Hållfasthetslära.
    Simulation of low velocity impact on fiber laminates using a cohesive zone based delamination model2004Ingår i: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, Vol. 64, nr 2, s. 279-288Artikel i tidskrift (Refereegranskat)
    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.

  • 10.
    Busse, Christian
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Gustafsson, David
    Siemens Ind Turbomachinery AB, Sweden.
    Rasmusson, Patrik
    Siemens Ind Turbomachinery AB, Sweden.
    Sjodin, Bjorn
    Siemens Ind Turbomachinery AB, Sweden.
    Moverare, Johan
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Leidermark, Daniel
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Three-Dimensional LEFM Prediction of Fatigue Crack Propagation in a Gas Turbine Disk Material at Component Near Conditions2016Ingår i: Journal of engineering for gas turbines and power, ISSN 0742-4795, E-ISSN 1528-8919, Vol. 138, nr 4, artikel-id 042506Artikel i tidskrift (Refereegranskat)
    Abstract [en]

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

  • 11.
    Ewest, Daniel
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten. Siemens Ind Turbomachinery AB,Finspång, Sweden.
    Almroth, P.
    Siemens Ind Turbomachinery AB, Finspång, Sweden.
    Leidermark, Daniel
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Sjodin, B.
    Siemens Ind Turbomachinery AB, Finspång, Sweden.
    Fatigue crack propagation in a ductile superalloy at room temperature and extensive cyclic plastic flow2015Ingår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 80, s. 40-49Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Fatigue crack propagation experiments under both force and displacement control have been performed on the wrought superalloy Haynes 230 at room temperature, using a single edge notched specimen. The force controlled tests are nominally elastic, and the displacement controlled tests have nominally large plastic hysteresis at the beginning of the tests, but saturates towards linear elastic conditions as the crack grows. As some tests are in the large scale yielding regime, a non-linear fracture mechanics approach is used to correlate crack growth rates versus the fracture parameter Delta J. It is shown that crack closure must be accounted for, to correctly model the crack growth seen in all the tests in a unified manner. For the force controlled small scale yielding tests the Newman crack closure model was used. The Newman equation is however not valid for large nominal cyclic plasticity, instead the crack closure in the displacement controlled tests is extracted from the test data. A good agreement between all tests is shown, when closure is accounted for and effective values of Delta J are used.

  • 12.
    Ewest, Daniel
    et al.
    Siemens Ind Turbomachinery AB, Sweden.
    Almroth, Per
    Siemens Ind Turbomachinery AB, Sweden.
    Sjodin, Bjorn
    Siemens Ind Turbomachinery AB, Sweden.
    Leidermark, Daniel
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    COMPARISON BETWEEN LINEAR AND NON-LINEAR FRACTURE MECHANICS ANALYSIS OF EXPERIMENTAL DATA FOR THE DUCTILE SUPERALLOY HAYNES 2302015Ingår i: PROCEEDINGS OF THE ASME TURBO EXPO: TURBINE TECHNICAL CONFERENCE AND EXPOSITION, 2015, VOL 7A, ASME Press, 2015, nr V07AT28A014Konferensbidrag (Refereegranskat)
    Abstract [en]

    Vith increasing use of renewable energy sources, an industrial us turbine is often a competitive solution to balance the power rid. However, life robustness approaches for gas turbine corn9nents operating under increasingly cyclic conditions, is a chalmging task. Ductile superalloys, as Haynes 230, are often used n stationary gas turbine hot parts such as combustors. The main cad for such components is due to non -homogeneous thermal xpansion within or between parts. As the material is ductile Jere is considerable redistribution of stresses and strains due to nelastic deformations during the crack initiation phase. There ore, the subsequent crack growth occurs through a material with :gnificant residual stresses and strains. In this work, fatigue ack propagation experiments, including the initiation phase, ave been performed on a single edge notched specimen under train controlled conditions. The test results are compared to -acture mechanics analyses using the linear AK and the non near AJ approaches, and an attempt to quantify the difference 2 terms of a life prediction is made. For the tested notched gemetry, material and strain ranges, the difference in the results using AKeff or ATeff are larger than the scatter seen when fitting the model to the experimental data. The largest differences can be found for short crack lengths, when the cyclic plastic work is the largest. The AJ approach clearly shows better agreement with the experimental results in this regime.

  • 13.
    Ewest, Daniel
    et al.
    Siemens Industrial Turbomachinery AB, Finspång, Sweden .
    Almroth, Per
    Siemens Industrial Turbomachinery AB, Finspång, Sweden .
    Sjödin, Björn
    Siemens Industrial Turbomachinery AB, Finspång, Sweden .
    Leidermark, Daniel
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Comparison between linear and non-linear fracture mechanics analysis of experimental data for the ductile superalloy Haynes 2302016Ingår i: Journal of engineering for gas turbines and power, ISSN 0742-4795, E-ISSN 1528-8919, Vol. 138, nr 6, s. 062101-1-062101-7Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    With increasing use of renewable energy sources, an industrial gas turbine is often a competitive solution to balance the power grid. However, life robustness approaches for gas turbine components operating under increasingly cyclic conditions are a challenging task. Ductile superalloys, as Haynes 230, are often used in stationary gas turbine hot parts such as combustors. The main load for such components is due to nonhomogeneous thermal expansion within or between parts. As the material is ductile, there is considerable redistribution of stresses and strains due to inelastic deformations during the crack initiation phase. Therefore, the subsequent crack growth occurs through a material with significant residual stresses and strains. In this work, fatigue crack propagation experiments, including the initiation phase, have been performed on a single edge notched specimen under strain controlled conditions. The test results are compared to fracture mechanics analyses using the linear ΔK and the nonlinear ΔJ approaches, and an attempt to quantify the difference in terms of a life prediction is made. For the tested notched geometry, material, and strain ranges, the difference in the results using ΔKeff or ΔJeff is larger than the scatter seen when fitting the model to the experimental data. The largest differences can be found for short crack lengths, when the cyclic plastic work is the largest. The ΔJ approach clearly shows better agreement with the experimental results in this regime.

  • 14.
    Ganghoffer, J. F.
    et al.
    Ecole des Mines, Nancy.
    Gautier, E.
    Ecole des Mines, Nancy.
    Denis, S.
    Ecole des Mines, Nancy.
    Simon, A.
    Ecole des Mines, Nancy.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Sjöström, Sören
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Micromechanical simulation of a martensitic transformation by Finite Elements1991Ingår i: Journal de Physique IV: Colloque, ISSN 1155-4339, E-ISSN 1764-7177, Vol. 1, s. C4-77-C4-82Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A micromechanical model describing the martensitic transformation on the grain scale has been developed, using Finite Elements. First results gained from the simulation illustrate how the morphological evolution within the grain is directly controlled by the internal stress state. The reversible and irreversible part of transformation "plasticity" strain and their evolution with the transformation can then be obtained from these calculations.

  • 15. Ganghoffer, Jean-Francois
    et al.
    Simonsson, Kjell
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära.
    A microstructural model of the martensitic transformation1998Ingår i: Mechanics of materials (Print), ISSN 0167-6636, E-ISSN 1872-7743, Vol. 27, s. 125-144Artikel i tidskrift (Refereegranskat)
  • 16.
    Ganghoffer, J.F.
    et al.
    Laboratoire de Science et Génie des Matériaux Métalliques, Ecole des Mines, Parc de Saurupt, F-54042 Nancy cedex, France.
    Denis, S.
    Laboratoire de Science et Génie des Matériaux Métalliques, Ecole des Mines, Parc de Saurupt, F-54042 Nancy cedex, France.
    Gautier, E.
    Laboratoire de Science et Génie des Matériaux Métalliques, Ecole des Mines, Parc de Saurupt, F-54042 Nancy cedex, France.
    Simon, A.
    Laboratoire de Science et Génie des Matériaux Métalliques, Ecole des Mines, Parc de Saurupt, F-54042 Nancy cedex, France.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Sjöström, Sören
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Mechanical and thermodynamical study of a macroscopically coherent phase transition: Case of the martensitic transformation1991Ingår i: Journal de Physique IV: Colloque, ISSN 1155-4339, E-ISSN 1764-7177, Vol. 1, s. C4-89-C4-94Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In the general framework of a macroscopically coherent phase transition, the mechanical and thermodynamical behaviour of a two-phase volume element under structural evolution will be investigated and discussed. The identification of internal entropy production will then allow to formulate a general evolution condition for such a system and the internal stress state will appear to influence strongly the transformation behaviour, via the interface. The case of a martensitic transformation is considered. From that rigourous mechanical approach, we obtain the thermodynamical balance equation used for martensitic transformation.

  • 17.
    Ganghoffer, J.F.
    et al.
    Laboratoire de Science et Génie des Matériaux Métalliques, Ecole des Mines, Parc de Saurupt, F-54042 Nancy cedex, France.
    Denis, S.
    Laboratoire de Science et Génie des Matériaux Métalliques, Ecole des Mines, Parc de Saurupt, F-54042 Nancy cedex, France.
    Gautier, E.
    Laboratoire de Science et Génie des Matériaux Métalliques, Ecole des Mines, Parc de Saurupt, F-54042 Nancy cedex, France.
    Simon, A.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Sjöström, Sören
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Mechanical and thermodynamical study of a macroscopically coherent phase transition.Case of the martensitic transformation1991Ingår i: Journal de Physique IV, ISSN 1155-4339, Vol. 1, s. C4-89-C4-94Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In the general framework of a macroscopically coherent phase transition, the mechanical and thermodynamical behaviour of a two-phase volume element under structural evolution will be investigated and discussed. The identification of internal entropy production will then allow to formulate a general evolution condition for such a system and the internal stress state will appear to influence strongly the transformation behaviour, via the interface. The case of a martensitic transformation is considered. From that rigourous mechanical approach, we obtain the thermodynamical balance equation used for martensitic transformation.

  • 18.
    Ganghoffer, J.F.
    et al.
    Laboratoire de Science et Génie des Matériaux Métalliques, Ecole des Mines, Parc de Saurupt, F-54042 Nancy cedex, France.
    Denis, S.
    Laboratoire de Science et Génie des Matériaux Métalliques, Ecole des Mines, Parc de Saurupt, F-54042 Nancy cedex, France.
    Gautier, E.
    Laboratoire de Science et Génie des Matériaux Métalliques, Ecole des Mines, Parc de Saurupt, F-54042 Nancy cedex, France.
    Simon, A.
    Laboratoire de Science et Génie des Matériaux Métalliques, Ecole des Mines, Parc de Saurupt, F-54042 Nancy cedex, France.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Sjöström, Sören
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Micromechanical simulation of a martensitic transformaation by Finite Elements1991Ingår i: Journal de Physique IV, ISSN 1155-4339, Vol. 1, s. C4-77-C4-82Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A micromechanical model describing the martensitic transformation on the grain scale has been developed, using Finite Elements. First results gained from the simulation illustrate how the morphological evolution within the grain is directly controlled by the internal stress state. The reversible and irreversible part of transformation "plasticity" strain and their evolution with the transformation can then be obtained from these calculations.

  • 19.
    Ganghoffer, J.F.
    et al.
    Laboratoire de Science et Génie des Matériaux Métalliques, Ecole des Mines, Parc de Saurupt, F-54042 Nancy cedex, France.
    Denis, S.
    Laboratoire de Science et Génie des Matériaux Métalliques, Ecole des Mines, Parc de Saurupt, F-54042 Nancy cedex, France.
    Gautier, E.
    Laboratoire de Science et Génie des Matériaux Métalliques, Ecole des Mines, Parc de Saurupt, F-54042 Nancy cedex, France.
    Simon, A.
    Laboratoire de Science et Génie des Matériaux Métalliques, Ecole des Mines, Parc de Saurupt, F-54042 Nancy cedex, France.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Sjöström, Sören
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Micromechanical simulation of martensitic transformation by Finite Elements1991Ingår i: Journal de Physique IV, ISSN 1155-4339, Vol. 1, s. C4-77-C4-82Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A micromechanical model describing the martensitic transformation on the grain scale has been developed, using Finite Elements. First results gained from the simulation illustrate how the morphological evolution within the grain is directly controlled by the internal stress state. The reversible and irreversible part of transformation "plasticity" strain and their evolution with the transformation can then be obtained from these calculations.

  • 20.
    Ganghoffer, J.F.
    et al.
    ICSI, 15, Rue Jean Starcky, BP 2478, 68057 Mulhouse Cedex, France.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    A micromechanical model of the martensitic transformation1998Ingår i: Mechanics of Materials, ISSN 0167-6636, Vol. 27, nr 3, s. 125-144Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A micromechanical model of the martensitic transformation at the grain scale has been established, considering the more specific case of ferrous alloys. The transformation proceeds through the formation of successive variants of the product phase within a unit cell representative of a grain; interactions between neighbouring grains are simulated by the choice of periodic boundary conditions. From a thermodynamical analysis, a selection rule for the order and orientation of the forming martensitic variants has been established, based on internal stresses anisotropy. These concepts have been implemented into a two-dimensional finite element simulation of the transformation, considering an elastoplastic behaviour of both parent and product phases. Morphological and crystallographical features of the transformation are considered: one variant consists of a thin layer of elements within the mesh that can form with four possible discrete orientations. Simulation results show the development of the plate pattern as a combination of the influence of both external load and internal stresses built during the progress of the transformation. These are related to global evolutions of transformation plasticity vs. transformation progress. Comparison with experiments show a similar form of the evolutions of the total strain; however, the model overestimates the strain levels. The possible reasons for this discrepancy are discussed.

  • 21.
    Ganghoffer, J.F.
    et al.
    Laboratoire de Science et Génie des Matériaux Métalliques, UA 159 du CNRS, Ecole des Mines, Parc de Saurupt, 54042 Nancy cedex, France.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Denis, S.
    Laboratoire de Science et Génie des Matériaux Métalliques, UA 159 du CNRS, Ecole des Mines, Parc de Saurupt, 54042 Nancy cedex, France.
    Gautier, E.
    Laboratoire de Science et Génie des Matériaux Métalliques, UA 159 du CNRS, Ecole des Mines, Parc de Saurupt, 54042 Nancy cedex, France.
    Sjöström, Sören
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Simon, A.
    Laboratoire de Science et Génie des Matériaux Métalliques, UA 159 du CNRS, Ecole des Mines, Parc de Saurupt, 54042 Nancy cedex, France.
    Martensitic transformation plasticity simulations by Finite Elements1994Ingår i: Journal de Physique IV, ISSN 1155-4339, Vol. 4, s. C3-215-C3-220Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The mechanical behaviour associated to the martensitic transformation has been modelled using a 2D FE description. The martensite variants are constituted of different elements of the mesh and four different variants are allowed to transform in the grain. The transformation progress is prescribed using a thermodynamical criterion based on the maximal work associated to the variant formation. Transformation plasticity deformation and plates orientation patterns are obtained for three stress levels. These results are discussed in regard to the model used and the physical parameters introduced in the model.

  • 22.
    Ganghoffer, J.F.
    et al.
    Ecole des Mines, Nancy.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Denis, S.
    Ecole des Mines, Nancy.
    Gautier, E.
    Ecole des Mines, Nancy.
    Sjöström, Sören
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Simon, A.
    Ecole des Mines, Nancy.
    Martensitic transformation plasticity simulations by finite elements1994Ingår i: Journal de Physique IV: Colloque, ISSN 1155-4339, E-ISSN 1764-7177, Vol. 4, s. C3-215-C3-220Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The mechanical behaviour associated to the martensitic transformation has been modelled using a 2D FE description. The martensite variants are constituted of different elements of the mesh and four different variants are allowed to transform in the grain. The transformation progress is prescribed using a thermodynamical criterion based on the maximal work associated to the variant formation. Transformation plasticity deformation and plates orientation patterns are obtained for three stress levels. These results are discussed in regard to the model used and the physical parameters introduced in the model.

  • 23.
    Gustafsson, David
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Lundström, Erik
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Modelling of high temperature fatigue crack growth in Inconel 718 under hold time conditions2013Ingår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 52, s. 124-130Artikel i tidskrift (Refereegranskat)
    Abstract [en]

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

  • 24.
    Gustafsson, David
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Moverare, Johan
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska högskolan.
    Johansson, Sten
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska högskolan.
    Hornqvist, Magnus
    Volvo Aero Corporation.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Sjöström, Sören
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Sharifimajd, Babak
    Siemens Industrial Turbomachinery AB.
    Fatigue crack growth behaviour of Inconel 718 with high temperature hold times2010Ingår i: Procedia Engineering, ISSN 1877-7058, E-ISSN 1877-7058, Vol. 2, nr 1, s. 1095-1104Artikel i tidskrift (Refereegranskat)
    Abstract [en]

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

  • 25.
    Gustafsson, David
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Moverare, Johan
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska högskolan.
    Johansson, Sten
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska högskolan.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Hornqvist, M
    Volvo Aero Corp.
    Mansson, T
    Volvo Aero Corp.
    Sjöström, Sören
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Influence of high temperature hold times on the fatigue crack propagation in Inconel 7182011Ingår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 33, nr 11, s. 1461-1469Artikel i tidskrift (Refereegranskat)
    Abstract [en]

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

  • 26.
    Gustafsson, David
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Moverare, Johan
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska högskolan.
    Simonsson, Kjell
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära.
    Johansson, Sten
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska högskolan.
    Hörnqvist, Magnus
    Volvo Aero Corporation, Trollhättan.
    Månsson, Tomas
    Volvo Aero Corporation, Trollhättan.
    Sjöström, Sören
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära.
    Fatigue Crack Growth behaviour of Inconel 718 - the Concept of a Damaged Zone Caused by High Temperature Hold Times2011Ingår i: Procedia Engineering, ISSN 1877-7058, E-ISSN 1877-7058, Vol. 10, s. 2821-2826Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Fatigue crack growth testing of Inconel 718 has been carried out at the temperatures 550 °C and 650 °C. The tests were conducted using a mix of hold times and pure cyclic loading, referred to as block tests. From the test results, the existence of an embrittled volume or damaged zone in the vicinity of the crack tip has been revealed. It has been found that the evolution of this damaged zone can be sufficiently well described using a power law function with an exponent n = 0.25.

  • 27.
    Gustafsson, David
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Moverare, Johan
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska högskolan.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Sjöström, Sören
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Modeling of the Constitutive Behavior of Inconel 718 at Intermediate Temperatures2011Ingår i: Journal of engineering for gas turbines and power, ISSN 0742-4795, E-ISSN 1528-8919, Vol. 133, s. 094501-1-094501-4Artikel i tidskrift (Refereegranskat)
    Abstract [en]

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

  • 28.
    Jansson, Mikael
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Nilsson, Larsgunnar
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    On constitutive modeling of aluminum alloys for tube hydroforming applications2005Ingår i: International Journal of Plasticity, ISSN 0749-6419, Vol. 21, nr 5, s. 1041-1058Artikel i tidskrift (Refereegranskat)
    Abstract [en]

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

  • 29.
    Jansson, Mikael
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Nilsson, Larsgunnar
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    On process parameter estimation for the tube hydroforming process2007Ingår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 190, nr 1-3, s. 1-11Artikel i tidskrift (Refereegranskat)
    Abstract [en]

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

  • 30.
    Jansson, Mikael
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Nilsson, Larsgunnar
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    On strain localisation in tube hydroforming of aluminium extrusions2008Ingår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 195, nr 1-3, s. 3-14Artikel i tidskrift (Refereegranskat)
    Abstract [en]

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

  • 31.
    Jansson, Mikael
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Nilsson, Larsgunnar
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    The use of biaxial test data in the validation of constitutive descriptions for tube hydroforming applications2007Ingår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 184, nr 1-3, s. 69-76Artikel i tidskrift (Refereegranskat)
    Abstract [en]

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

  • 32.
    Jansson, Mikael
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Nilsson, Larsgunnar
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Tube hydroforming of aluminium extrusions using a conical die and extensive feeding2008Ingår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 198, nr 1-3, s. 14-21Artikel i tidskrift (Refereegranskat)
    Abstract [en]

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

  • 33.
    Johansson, Sten
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska högskolan.
    Moverare, Johan
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska högskolan.
    Leidermark, Daniel
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Kanesund, Jan
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska högskolan.
    Investigation of localized damage in single crystals subjected to thermalmechanical fatigue (TMF)2010Ingår i: Procedia Engineering, ISSN 1877-7058, Vol. 2, nr 1, s. 657-666Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The deformation and damage mechanisms arising during thermalmechanical fatigue (TMF) of a CMSX-4 and high-Cr single crystal super alloy, SCA425 have been investigated and a completely new failure mechanism involving recrystallization and oxidation has been discovered. The primary deformation mechanism is slip along the {111} planes. The deformation is highly localised to a number of bands, where recrystallization eventually occur during the thermalmechanical fatigue process. When the final failure occurs along these recrystallized bands it is accompanied by the formation of voids due to the presence of grain boundaries. The damage process is further enhanced by oxidation, since recrystallization occurs more easily in the gamma depleted zone under the oxide scale. The macroscopic as well as the microscopic damage and fracture mechanisms are varying with alloy and heat treatment. The aim of this work is to further investigate, discuss the local damage mechanisms responsible for TMF damage. Of special interest is the localisation of damage into twins and extremely localized rafted deformation bands.

  • 34.
    Kapidzic, Zlatan
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska fakulteten. Saab AB, SE-58188 Linkoping, Sweden.
    Ansell, Hans
    Saab AB, SE-58188 Linkoping, Sweden.
    Schon, Joakim
    Swedish Def Research Agency, Sweden.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Fatigue bearing failure of CFRP composite in biaxially loaded bolted joints at elevated temperature2015Ingår i: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, Vol. 127, s. 298-307Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Hybrid composite-aluminium structures develop internal loads when exposed to elevated temperatures, due to the different thermal expansion properties of the constituent materials. In aircraft structures with long rows of bolted joints, the mechanical and the thermally induced bolt loads are oriented in different directions, creating a biaxial bearing load state. In this study, the bearing fatigue failure process and the influence of the biaxial load state on the failure are investigated. An experimental set-up was designed, where both the mechanical and the thermally induced bolt loads were applied by means of mechanical load actuators. Two-bolt, double-lap joints with quasi-isotropic carbon-epoxy composite specimens were subjected to uniaxial and biaxial cyclic loading at 90 degrees C. A microscopy study of the bearing plane revealed that the main fatigue driving mechanisms were matrix cracking and fibre-matrix debonding. Motivated by these findings, a fatigue prediction model based on the kinetic theory of fracture for polymer matrices was run in a finite element code and the results showed a satisfactory correlation to the experimental results. The biaxial loading resulted in a longer fatigue life than the uniaxial loading, for the same peak resultant force, which was explained by the smaller effective stress range in the biaxial case.

  • 35.
    Kapidzic, Zlatan
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling. Linköpings universitet, Tekniska fakulteten. Saab AB, SE-58188 Linkoping, Sweden.
    Ansell, Hans
    Saab AB, SE-58188 Linkoping, Sweden.
    Schon, Joakim
    Swedish Def Research Agency, Sweden.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Quasi-static bearing failure of CFRP composite in biaxially loaded bolted joints2015Ingår i: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, Vol. 125, s. 60-71Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Hybrid composite-aluminium bolted joints develop internal loads at elevated temperatures, due to the difference in thermal expansion properties of their constituent materials. In aircraft joints, the thermally induced bolt loads are commonly directed perpendicular to the mechanical loads, inducing a biaxial bearing load state. In this work, carbon-epoxy laminate specimens were tested in uniaxial and biaxial quasi-static bearing failure experiments in a specially designed test rig, at elevated temperature. A microscopy study of a failed specimen revealed that the failure process was mainly driven by fibre kinking, although extensive matrix cracking and delaminations were also found. The experiments were simulated by three-dimensional, explicit, finite element analyses, which included intralaminar damage and delamination. The experimental and simulated bearing failure loads differed by 1.7% in the uniaxial case and 2.1% in the biaxial case. It was suggested that the load-displacement response is influenced by the interaction of all damage mechanisms. Delamination modelling was, however, not essential for the prediction of the maximal bearing strength. The same effective bearing strengths were obtained for the biaxially loaded specimens as for the uniaxially loaded ones, but the damage accumulation process and the resulting damage distributions were different. (C) 2015 Elsevier Ltd. All rights reserved.

  • 36.
    Kapidzic, Zlatan
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska fakulteten. Saab AB, SE-58188 Linkoping, Sweden.
    Ansell, Hans
    Saab AB, SE-58188 Linkoping, Sweden.
    Schön, Joakim
    Swedish Def Research Agency, Sweden.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska fakulteten.
    Fatigue bearing failure of CFRP composite in bolted joints exposed to biaxial variable amplitude loading at elevated temperature2016Ingår i: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, Vol. 142, s. 71-77Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Hybrid structures than contain composite-aluminium interfaces tend to develop internal loads at elevated temperatures. In long bolted joints, the thermally induced bolt loads are superimposed onto the mechanically applied load and can induce a biaxial bearing load state. This paper presents an experimental and numerical study of the bearing fatigue failure of carbon-epoxy laminate specimens, exposed to uniaxial and biaxial variable amplitude loading at 90C. A specifically designed experimental rig was used, where both the mechanical and the thermally induced bolt loads were applied by means of mechanical load actuators. A fatigue model based on the kinetic theory of fracture for polymers, which was previously implemented for constant amplitude loading, is expanded to account for the variable amplitude load history. The results suggest that the biaxial loading gives a longer fatigue life than the uniaxial loading for the same maximum peak resultant force. This result can be utilized as a conservative dimensioning strategy by designing biaxially loaded joints in terms of maximum peak resultant bearing load using uniaxial fatigue data.

  • 37.
    Larsson, Rikard
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Björklund, Oscar
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Nilsson, Larsgunnar
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    A study of high strength steels undergoing non-linear strain paths—Experiments and modelling2011Ingår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 211, nr 1, s. 121-131Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper presents an evaluation of the constitutive behaviour, including plastic anisotropy and mixed isotropic-kinematic hardening of two high strength steels, Docol 600DP and Docol 1200M, during strain path changes. A series of tensile and shear tests was performed on both virgin and pre-strained materials. The initial anisotropy and work hardening parameters were obtained from tensile tests, shear tests and a bulge test of the virgin material, whereas the kinematic hardening parameters were identified by comparing numerical predictions to experimental results related to the pre-strained materials. Numerical predictions using the obtained parameters agree well with the experimental results, both in the case of proportional, and under non-proportional strain paths.

  • 38.
    Leidermark, Daniel
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Aspenberg, David
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Gustafsson, David
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Moverare, Johan
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska högskolan.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    The effect of random grain distributions on fatigue crack initiation in a notched coarse grained superalloy specimen2012Ingår i: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 51, nr 1, s. 273-280Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Coarse grained superalloys are of large interest in high temperature applications, and can be found in e.g.gas turbine components, where great care must be given with respect to high temperature fatigue. Due tothe large grain size, the material behaviour at e.g. sharp notches cannot be considered homogeneous. As aconsequence, the fatigue behaviour is likely to expose a large variation. In order to numerically investigatethis variation, a Monte Carlo analysis has been carried out by 100 FE-simulations of notched specimens,where placements and orientations of the grains were randomised. Furthermore, each grain wasmodelled as a unique single-crystal, displaying both anisotropic elastic and plastic behaviour and tension/compression asymmetry. The effect of randomness was investigated by the obtained dispersion infatigue crack initiation life. It was concluded that the fatigue life behaviour of coarse grained nickel-basesuperalloys may show a considerable variation, which cannot be captured by one single deterministicanalysis based on data for a homogenised material. Furthermore, the dispersion is of such a magnitudethat it needs to be taken into account in industrial applications where highly stressed coarse grainedmaterials are used.

  • 39.
    Leidermark, Daniel
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Moverare, Johan J.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska högskolan.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Sjöström, Sören
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Johansson, Sten
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska högskolan.
    Room temperature yield behaviour of a single-crystal nickel-base superalloy with tension/compression asymmetry2009Ingår i: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 47, nr 2, s. 366-372Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The constitutive behaviour at room temperature of a single-crystal nickel-base superalloy is presented in a new model. This model is based on crystal plasticity and takes Schmid- as well as non-Schmid stresses, elastic anisotropy and tension/compression asymmetry into account. By comparison with uniaxial tensile and compressive tests, the model is shown to reproduce the real behaviour well, including the tension/compression asymmetry. The model also shows that typically encountered deviations in orientations ofcastings have a non-negligible influence on stiffness and yield limit, which must be taken into account for industrial applications.

  • 40.
    Leidermark, Daniel
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Moverare, Johan
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska högskolan.
    Johansson, Sten
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska högskolan.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Sjöström, Sören
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Tension/Compression asymmetry of a single-crystal superalloy in virgin and degraded condition2010Ingår i: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 58, nr 15, s. 4986-4997Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The mechanical behaviour at room temperature of a single-crystal superalloy exposed to long term ageing at elevated temperature has been investigated, a topic important for the material’s resistance to thermal-mechanical fatigue. Specimens with several different crystallographic orientations were plastically deformed in either tension or compression before and after the long term furnace exposure. While the thermally activated degradation of the microstructure causes a reduction in yield limit of up to 25% for specimens initially deformed in the |001 and |011| directions, none or only moderate reduction was seen for specimens initially deformed along the |111| direction. This can be explained by the strong correlation between yield limit reduction and the amount of γ coarsening. By introducing an isotropic degradation function in a newly developed crystal plasticity model, the constitutive behaviour of both virgin and degraded materials has been described with good agreement with the experimental results.

  • 41.
    Leidermark, Daniel
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Moverare, Johan
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska högskolan.
    Segersäll, Mikael
    Linköpings universitet, Tekniska högskolan. Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Sjöström, Sören
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Johansson, Sten
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska högskolan.
    Evaluation of Fatigue Crack Initiation in a Notched Single-crystal Superalloy Component2011Ingår i: Procedia Engineering, ISSN 1877-7058, E-ISSN 1877-7058, Vol. 10, s. 619-624Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The fatigue crack initiation in a notched single-crystal nickel-base superalloy component at 500 °C was investigated and analysed. A critical plane approach in combination with a critical distance method has been adopted, in which the total shear strain ranges on the discrete slip planes are evaluated. Furthermore, a Coffin-Manson type of expression is used to predict the number of cycles to fatigue crack initiation. The experimental test specimens were studied by microscopy to determine on which crystallographic plane the fatigue initiation occurred. A good correlation between the experimental results and the simulated results were found.

  • 42.
    Leidermark, Daniel
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Moverare, Johan
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska högskolan. Siemens Industrial Turbomachinery AB, Finspång, Sweden.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Sjöström, Sören
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    A combined critical plane and critical distance approach for predicting fatigue crack initiation in notched single-crystal superalloy components2011Ingår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 33, nr 10, s. 1351-1359Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The fatigue crack initiation in notched single-crystal components of material MD2 is investigated and analysed. A critical plane approach in combination with a critical distance method has been adopted, in which the total shear strain ranges on the discrete crystallographic slip planes are evaluated. To determine the critical distance two approaches were evaluated, a mean value approach and a cycle dependent approach. Furthermore, a Coffin-Manson type of expression (derived from the results of a set of 12 smooth specimens) is used to predict the number of cycles to fatigue crack initiation. The numerical procedure is applied to a series of experiments, in which notched single-crystal components were exposed to uniaxial cyclic loading in the nominal [001] crystal direction at 500 degrees C with R(epsilon) = 0. A good correlation between the experimental results and the simulated results was found.

  • 43.
    Leidermark, Daniel
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Moverare, Johan
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska högskolan.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Sjöström, Sören
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Johansson, Sten
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska högskolan.
    Fatigue crack initiation in a notched single-crystal superalloy component2010Ingår i: Procedia Engineering, ISSN 1877-7058, E-ISSN 1877-7058, Vol. 2, nr 1, s. 1067-1075Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, the fatigue crack initiation in notched single-crystal test specimens of material MD2 is investigated and analysed. A critical plane approach is adopted, in which the total strain ranges on the discrete slip planes are evaluated. Furthermore, a Coffin-Manson type of expression is used to describe the number of cycles to fatigue crack initiation. This relation is determined from a set of smooth test specimens loaded uniaxially in the [001], [011] and directions at 500 °C with Rε=−1. The numerical procedure is then applied to a series of experiments, in which notched single-crystal test specimens were exposed to uniaxial cyclic loading in the [001] direction at 500 °C with Rε=0.

  • 44.
    Leidermark, Daniel
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Segersäll, Mikael
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska högskolan.
    Moverare, Johan
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska högskolan.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Modelling of TMF Crack Initiation in Smooth Single-Crystal Superalloy Specimens2014Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper the TMF crack initiation behaviour of the single-crystal nickel-base superalloyMD2 is investigated and modelled. TMF tests were performed in both IP and OP for varying mechanicalstrain ranges in the [001] crystallographic direction until TMF crack initiation was obtained. Acrystal plasticity-creep model was used in conjunction with a critical-plane approach, to evaluate thenumber of cycles to TMF crack initiation. The critical-plane model was evaluated and calibrated ata stable TMF cycle, where the effect of the stress relaxation had attenuated. This calibrated criticalplanemodel is able to describe the TMF crack initiation, taking tension/compression asymmetry aswell as stress relaxation anisotropy into account, with good correlation to the real fatigue behaviour.

  • 45.
    Lundström, Erik
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Evaluation and prediction of crack length in a Ni-based superalloy for sustained loading2014Manuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    Crack length evaluations for sustained loading have been conducted on Inconel 718 surface crack specimens for 550 and 650 ◦C. Hold times, e.g. slow ramp up of engine thrust, sustained load as continuous power output for stationary gas turbines or as cruise for aero engines, have been seen to result in material damage at the crack tip, causing the crack to grow by intergranular fracture and resulting in a strong increase of the crack growth rate. Here, sustained load tests as well as specially designed hold time tests are used to measure crack length and the size of the damaged zone (material damage) in front of the crack tip by comparing potential drop (PD) predictions with visible post-mortem beach marks on the fracture surface. Fracture surfaces were also investigated with scanning electron microscope (SEM), showing what the damaged zone most likely consists of. In addition, by applying a crack propagation model based on the damaged zone concept, crack length and damaged zone evaluations were conducted. The results show that the damaged zone must be taken into consideration, when evaluating post-mortem fracture surfaces if the test has included hold time loads, both when setting up post-mortem calibration curves and when evaluating crack propagation models.

  • 46.
    Lundström, Erik
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Gustafsson, David
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Månsson, T.
    GKN Aerospace Engine Systems, Trollhättan, Sweden.
    A load history dependent model for fatigue crack propagation in Inconel 718 under hold time conditions2014Ingår i: Engineering Fracture Mechanics, ISSN 0013-7944, E-ISSN 1873-7315, Vol. 118, s. 17-30Artikel i tidskrift (Refereegranskat)
    Abstract [en]

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

  • 47.
    Lundström, Erik
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Månsson, Tomas
    GKN Aerospace Engine Systems, Trollhättan, Sweden.
    Gustafsson, David
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Modelling of fatigue crack growth in Inconel 718 under hold time conditions - application to a flight spectrum2014Ingår i: Advanced Materials Research, ISSN 1662-8985, Vol. 891-892, s. 759-764Artikel i tidskrift (Refereegranskat)
    Abstract [en]

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

  • 48.
    Lönn, David
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Bergman, Greger
    Gestamp Hardtech AB, Luleå.
    Nilsson, Larsgunnar
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Experimental and finite element robustness studies of a bumper system subjected to an offset impact loading2011Ingår i: International Journal of Crashworthiness, ISSN 1358-8265, E-ISSN 1754-2111, Vol. 16, nr 2, s. 155-168Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A product of high quality is a product that performs well, not only in exactly the situations it was designed to handle but also in slightly different situations that arise in the usage of the product. As a specific example, the performance of a bumper system should not depend on small fluctuations in the manufacturing process or on small variations in the impact event. In this work, the robustness of an existing vehicle bumper system subjected to a crash load has been evaluated both experimentally and numerically. In the latter case, different widely used approaches to numerically assess the robustness have been utilised. A reliable numerical robustness study provides the designer with a valuable tool for improving a design, and an evaluation of these methods in this context is therefore of interest. It is concluded that for the example under study, both the Monte Carlo method and the metamodel-based Monte Carlo methods work well. Furthermore, for moderate dispersions levels, i.e. a small design space with no bifurcation in the deformation pattern, a linear response approximation is shown to have a sufficient accuracy to be used in the metamodel-based robustness analysis. The performed numerical robustness studies also point out that the performance of a nominal simulation, i.e. a simulation conducted with mean values for all variables, does not in general predict the mean performance of the finite element model. Finally, some possible design improvements for the bumper system under study are also identified

  • 49.
    Lönn, David
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Öman, Michael
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Nilsson, Larsgunnar
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Finite element based robustness study of a truck cab subjected to impact loading2009Ingår i: International Journal of Crashworthiness, ISSN 1358-8265, E-ISSN 1754-2111, Vol. 14, nr 2, s. 111-124Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Optimised designs have a tendency of being sensitive to variations. It is therefore of great importance to analyse this sensitivity to assure that a design is robust, i.e. sufficiently insensitive to variations. To analyse robustness, variations are introduced in model parameters and their influences on simulation responses are studied. This is usually achieved using the Monte Carlo method. Though, due to the large number of simulations needed, the Monte Carlo method is very costly for problems requiring a long computing time. Therefore, in this work a meta model-based Monte Carlo method is used to evaluate the robustness of a vehicle structure. That is, the Monte Carlo analysis is performed on a surface approximation of the true response, over the domain of interest. The methodology used is to first identify the variables that influence the response the most, referred to as a screening, using simple linear response surfaces. This is followed by a more detailed sensitivity analysis using only the identified variables and a quadratic response surface, thereby incorporating second order effects. A truck cab model exposed to a pendulum impact load is used as an evaluation of this method, and the important variables and their influence on the response are identified. The effect of including results from forming simulations is also evaluated using the truck cab model. Variations are introduced before forming simulations, thereby taking forming effects into account in the sensitivity analysis. The method was found to be a good tool to identify important dispersion variables and to give an approximate result of the total dispersion, all with a reasonable amount of simulations.

  • 50.
    Mikaelsson, Rickard
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Statsvetenskap. Linköpings universitet, Filosofiska fakulteten.
    Simonsson, Kjell
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Inspireras av andra: En inventering av metoder för kvalitetssäkring och utveckling av forskarutbildningen vid IEI2010Rapport (Övrigt vetenskapligt)
    Abstract [en]

    Sverige är en av världens ledande forskningsnationer, och för att behålla den positionen är det av vikt att landets lärosäten bedriver forskarutbildning av hög kvalitet. Vid Linköpings universitet faller ett stort ansvar på Institutionen för Ekonomisk och Industriell utveckling (IEI). Institutionen, som omfattar cirka 435 medarbetare (varav 153 är doktorander)1, är Linköpings universitets största, och forskarutbildning bedrivs där inom 24 olika forskningsmiljöer tillhörande såväl den filosofiska som den tekniska fakulteten. Dessa forskningsmiljöer har hittills varit relativt isolerade från varandra och endast ett begränsat kunskapsutbyte har förekommit dem emellan gällande hur forskarutbildningen kan kvalitetssäkras. Med syftet att förändra denna situation och främja ett ökat kunskapsutbyte mellan forskningsmiljöerna beslutade forskarutbildningsrådet vid IEI att under verksamhetsåret 09/10 genomföra en inventering av angreppssätt och metoder för kvalitetssäkring och utveckling av forskarutbildningen inom institutionen. Tanken bakom uppdraget var att fånga upp goda exempel på hur forskarutbildning bedrivs inom IEI, samt att sammanställa och förmedla dessa erfarenheter tillbaka till forskningsmiljöerna.

    Arbetet genomfördes av Rickard Mikaelsson, lektor i Statsvetenskap, och Kjell Simonsson, professor i Hållfasthetslära (hädanefter benämnda utredarna eller utredningsgruppen), och har avrapporterats i form av denna skrift samt via presentationer vid IEI under 09/10.

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