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  • 51.
    Eriksson, Robert
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Brodin, Håkan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Östergren, Lars
    Volvo Aero Corporation, SE-46181 Trollhättan, Sweden.
    Li, Xin-Hai
    Siemens Industrial Turbomachinery AB, SE-61283 Finspång, Sweden.
    Influence of isothermal and cyclic heat treatments on the adhesion of plasma sprayed thermal barrier coatings2011In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 205, no 23-24, p. 5422-5429Article in journal (Refereed)
    Abstract [en]

    The adhesion of thermal barrier coatings (TBC) has been studied using the standard method described in ASTM C633, which makes use of a tensile test machine to measure the adhesion. The studied specimens consist of air plasma sprayed (APS) TBC deposited on disc-shaped substrate coupons of Ni-base alloy Hastelloy X. The bond coat (BC) is of a NiCoCrAlY type and the top coat (TC) consists of yttria–stabilised–zirconia. Before the adhesion test, the specimens were subjected to three different heat treatments: 1) isothermal oxidation at 1100 °C up to 290 h, 2) thermal cycling fatigue (TCF) at 1100 °C up to 300 cycles and 3) thermal shock at ~ 1140 °C BC/TC interface temperature up to 1150 cycles. The adhesion of the specimens is reported and accompanied by a microstructural study of the BC and the thermally grown oxides (TGO), as well as a discussion on the influence of BC/TC interfacial damage on adhesion properties of TBC. The adhesion was found to vary with heat treatment, as well as with heat treatment length.

  • 52.
    Eriksson, Robert
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Engineering Materials.
    Brodin, Håkan
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Engineering Materials.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Östergren, Lars
    Volvo Aero Corporation, Trollhättan.
    Li, Xin-Hai
    Siemens Industrial Turbomachinery AB, Finspång.
    The Influence of Substate Material on the Thermal Cycling Fatigue Life of Thermal Barrier Coating Systems2012In: ECF19 Proceedings, 2012Conference paper (Refereed)
  • 53.
    Eriksson, Robert
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Brodin, Håkan
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Engineering Materials.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Östergren, Lars
    GKN Aerospace Engine Systems, Trollhättan.
    Li, Xin-Hai
    Siemens Industrial Turbomachinery AB, Finspång.
    Thermal Cycling Fatigue of Thermal Barrier Coatings- Rig and Experiment Design2014Conference paper (Refereed)
    Abstract [en]

    Ceramic thermal barrier coatings are used for thermal insulation in gas turbines to protect metallic components from high-temperature degradation. The ceramic coating may, due to its different coefficient of thermal expansion, crack and spall off the metallic component, thus rendering the component unprotected against high-temperature. Thermal cycling rigs of various designs are used to evaluate the durability of thermal barrier coatings. The present paper reports the result from a round robin test including three thermal cycling rigs at different locations. To better understand the influence of rig design on the thermal cyclic lives of thermal barrier coatings, some test parameters, such as the material of the specimen table and the cooling rate, were varied in one of the rigs. Furthermore, two different specimen geometries, rectangular and disc-shaped, were tested. The specimen table material was found to greatly influence the cooling rate of the specimens, more so than variations in the cooling airflow. The rectangular specimens were found to be more sensitive to test setup than the disc-shaped specimens; under certain conditions, the rectangular specimens could be made to fracture from the long side, rather than the short side of the specimen edge, which shortened the thermal cyclic life of the coatings.

  • 54.
    Eriksson, Robert
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Brodin, Håkan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Broitman, Esteban
    Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
    Östergren, Lars
    GKN Aerospace Engine Systems, Trollhättan, Sweden.
    Li, Xin-Hai
    Siemens Industrial Turbomachinery AB, Finspång, Sweden.
    Influence of substrate material on the life of atmospheric plasmas prayed thermal barrier coatings2013In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 232, no 15, p. 795-803Article in journal (Refereed)
    Abstract [en]

    Thermal barrier coatings (TBCs) are used in gas turbines to prolong the life of the underlying substrates and to increase the efficiency of the turbines by enabling higher combustion temperatures. TBCs may fail during service due to thermal fatigue or through the formation of non-protective thermally grown oxides (TGOs). This study compares two atmospheric plasma sprayed (APS) TBC systems comprising of two identical TBCs deposited on two different substrates (Haynes 230 and Hastelloy X). The thermal fatigue life was found to differ between the two TBC systems. The interdiffusion of substrate elements into the coating was more pronounced in the TBC system with shorter life, however, very few of the substrate elements (only Mn and to some extent Fe) formed oxides in the bond coat/top coat interface. Fractography revealed no differences in the fracture behaviour of the TBCs; the fracture occurred, in both cases, to about 60% in the top coat close to the interface and the remainder in the interface. Nanoindentation revealed only small differences in mechanical properties between the TBC systems and a finite element crack growth analysis showed that such small differences did not cause any significant change in the crack driving force. The oxidation kinetics was found to be similar for both TBC systems for the formation of Al2O3 but differed for the kinetics of non-Al2O3 TGOs where the TBC system with shortest life had a faster formation of non-Al2O3 TGOs caused by a faster Al depletion. The difference in non-Al2O3 TGO growth kinetics was considered to be the main reason for the difference in life.

  • 55.
    Eriksson, Robert
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology. Siemens AG, Berlin, Germany.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Li, Xin-Hai
    Siemens Industrial Turbomachinery AB, Finspång, Sweden.
    Influence of Cu and Zn Residues from Wire Electro-Discharge machining on TBS Durability2014In: Proceedings of the 2014 Energy Materials Conference  (CD-ROM), Wiley-TMS , 2014, p. 387-392Conference paper (Refereed)
    Abstract [en]

    Thermal barrier coatings (TBC) are deposited on superalloys in gas turbines to prolong component life. Electro-discharge machining (EDM) provides a convenient way of machining superalloys prior to coating deposition. Wire-EDM may leave residues from the wire material on the cut surface. A study was performed to investigate if brass residues from the EDM wire affected TBC oxidation behavior and spallation life. Isothermal oxidation at 1050 ℃ and thermal cycling at 1100 ℃ were performed on plasma sprayed TBCs on two different EDM cut substrates. No decrease in TBC life was detected due to the brass residues on the cut surfaces.

  • 56.
    Eriksson, Robert
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Sjöström, Sören
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Solid Mechanics.
    Brodin, Håkan
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Engineering Materials.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Östergren, Lars
    GKN Aerospace Engine Systems, Trollhättan.
    Li, Xin-Hai
    Siemens Industrial Turbomachinery AB, Finspång.
    Influence of Interface Roughness on the Fatigue Life of Thermal Barrier Coatings2013Conference paper (Refereed)
  • 57.
    Eriksson, Robert
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Sjöström, Sören
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Brodin, Håkan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Östergren, Lars
    GKN Aerospace Engine Systems, Trollhättan, Sweden.
    Li, Xin-Hai
    Siemens Industrial Turbomachinery AB, Finspång, Sweden.
    TBC bond coat-top coat interface roughness: influence on fatigue life and modelling aspects2013In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 236, p. 230-238Article in journal (Refereed)
    Abstract [en]

    Thermal barrier coatings (TBCs), when used in gas turbines, may fail through thermal fatigue, causing the ceramic top coat to spall off the metallic bond coat. The life prediction of TBCs often involves finite element modelling of the stress field close to the bond coat/top coat interface and thus relies on accurate modelling of the interface. The present research studies the influence of bond coat/top coat interface roughness on the thermal fatigue life of plasma sprayed TBCs. By using different spraying parameters, specimens with varying interface roughness were obtained. During thermal cycling it was found that higher interface roughness promoted longer thermal fatigue life. The interfaces were characterised by roughness parameters, such as Ra, Rq and Rq, as well as by autocorrelation, material ratio curves, probability plots and slope distribution. The variation of spray parameters was found to affect amplitude parameters, such as Ra, but not spacing parameters, such as RSm. Three different interface geometries were tried for finite element crack growth simulation: cosine, ellipse and triangular shape. The cosine model was found to be an appropriate interface model and a procedure for obtaining the necessary parameters, amplitude and wavelength, was suggested. The positive effect of high roughness on life was suggested to be due to a shift from predominantly interface failure, for low roughness, to predominantly top coat failure, for high roughness.

  • 58.
    Eriksson, Robert
    et al.
    Linköping University, Department of Management and Engineering. Linköping University, Faculty of Science & Engineering.
    Yuan, Kang
    Linköping University, Department of Management and Engineering. Linköping University, Faculty of Science & Engineering.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    INTERSPLAT OXIDATION OF ATMOSPHERIC PLASMA SPRAYED MCRALY COATINGS2014In: PROCEEDINGS OF THE ASME TURBO EXPO: TURBINE TECHNICAL CONFERENCE AND EXPOSITION, 2014, VOL 6, AMER SOC MECHANICAL ENGINEERS , 2014, no V006T22A017Conference paper (Refereed)
    Abstract [en]

    MCrAlY coatings and thermal barrier coatings (TBC) are commonly used in gas turbines to prolong the life of structural parts. The atmospheric plasma spray (APS) process yields coatings with a typical splat-on-splat structure which oxidizes at intersplat boundaries during high-temperature exposure. A study was performed to establish the influence of intersplat oxidation on Al depletion. It was found that the P -depletion based life may be overestimated by a factor of 1.8-18 if intersplat oxidation is not considered. Two different mechanisms of intersplat oxidation were observed: At high temperature (1050 degrees C), a fraction of the intersplat boundaries remained in contact with the coating surface and oxidized with the same kinetics as the surface oxides. At lower temperature (900 degrees C), intersplat oxidation occurred by considerable slower growth rates than surface oxidation. The mechanisms behind intersplat oxide growth was further studied by O diffusion calculations.

  • 59.
    Eriksson, Robert
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Yuan, Kang
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Microstructure-based Life Prediction of Thermal Barrier Coatings2014Conference paper (Refereed)
    Abstract [en]

    The widespread use of thermal barrier coatings (TBC) in gas turbines stresses the importance of accurate life prediction models for TBCs. During service, the TBC may fail due to thermal fatigue or through the formation of thermally grown oxides (TGOs). The current paper presents a Thermo-Calc/Dictra-based approach to life prediction of isothermally oxidised atmospheric plasma sprayed (APS) TBCs. The β-phase depletion of the coating was predicted and compared to life prediction criteria based on TGO thickness and Al content in the coating. All tried life models underestimated the life of the coating where the β-depletion-based model was the most conservative.

  • 60.
    Eriksson, Robert
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Yuan, Kang
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Li, Xin-Hai
    Siemens Industrial Turbomachinery AB, Finspång.
    Life Prediction of High-Temperature MCr AIY Coatings Based on Microstructural Observations2014In: THERMEC 2013, Trans Tech Publications Inc., 2014, Vol. 922, p. 143-148Conference paper (Refereed)
    Abstract [en]

    Thermal barrier coatings are commonly used in gas turbines for protection against high tem-perature and oxidation. Life prediction of oxidation protective coatingsmay be done bymicrostructure-based techniques such as -depletion based life criteria. In this study, a thermal barrier coating sys-tem, with an overlay NiCoCrAlY coating as bond coat, was oxidised up to 10000 h at 900 C. Themicrostructure was studied and related to Al depletion. It was found that a -depletion based lifecriterion could not be used for the studied coating composition and temperature as it would be tooconservative. A 0-depletion based model was instead suggested and supported by interdiffusion sim-ulation.

  • 61.
    Gustafsson, David
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Hornqvist, Magnus
    Volvo Aero Corporation.
    Simonsson, Kjell
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Sjöström, Sören
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Sharifimajd, Babak
    Siemens Industrial Turbomachinery AB.
    Fatigue crack growth behaviour of Inconel 718 with high temperature hold times2010In: Procedia Engineering, ISSN 1877-7058, E-ISSN 1877-7058, Vol. 2, no 1, p. 1095-1104Article in journal (Refereed)
    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.

  • 62.
    Gustafsson, David
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Simonsson, Kjell
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Hornqvist, M
    Volvo Aero Corp.
    Mansson, T
    Volvo Aero Corp.
    Sjöström, Sören
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Influence of high temperature hold times on the fatigue crack propagation in Inconel 7182011In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 33, no 11, p. 1461-1469Article in journal (Refereed)
    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.

  • 63.
    Gustafsson, David
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Simonsson, Kjell
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Solid Mechanics.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Hörnqvist, Magnus
    Volvo Aero Corporation, Trollhättan.
    Månsson, Tomas
    Volvo Aero Corporation, Trollhättan.
    Sjöström, Sören
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Solid Mechanics.
    Fatigue Crack Growth behaviour of Inconel 718 - the Concept of a Damaged Zone Caused by High Temperature Hold Times2011In: Procedia Engineering, ISSN 1877-7058, E-ISSN 1877-7058, Vol. 10, p. 2821-2826Article in journal (Refereed)
    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.

  • 64.
    Hofslagare, Per
    et al.
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Johansson, Sten
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Delamination size dependence on fatigue crack growth in fiber metal laminatesManuscript (preprint) (Other academic)
    Abstract [en]

    A fatigue crack growth study have been carried out in order to reveal the dependence of the delamination shape and size on metal crack growth in fiber metal laminates (GLARE®). Fatigue crack growth tests with center crack tension specimen (CCT) with loading range shifts have been performed. Optical crack growth measurements for surface cracks combined with ultrasonic measurements, to determine the delamination size and shape, have been conducted. Experiment show that the shape of the delamination tip, in particular, but also the delamination size depends strongly on the loading range. The crack growth rate for a given loading range is dissimilar if the prior loading range was different. This dissirnilarity may remain with further crack growth, or disappear with further crack growth. A strong interaction between the development of the delamination tip and a loading shift exists. It is therefore believed that the crack tip shape is causing the dissimilar crack growth rate.

  • 65.
    Hofslagare, Per
    et al.
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Johansson, Sten
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Experimental observations and numerical analysis of fatigue crack development in fiber metal laminatesManuscript (preprint) (Other academic)
    Abstract [en]

    Experimental and numerical studies have been carried out in order to reveal and explain the crack growth behavior of glass fiber reinforced aluminum laminates (GLARE®). Fatigue crack growth tests with center crack tension specimen have been performed. Optical crack growth measurements for surface cracks combined with in situ ultrasonic measurements, to determine the delamination size and shape, have been conducted. Complimentary fatigue induced delamination growth tests have also been performed, and the results from the two experiments have been compared. A 3D linear elastic model has been developed. Comparison between model and experimental results are made, and suggestions for further development in modeling are given.

  • 66.
    Hofslagare, Per
    et al.
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Johansson, Sten
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Parametric study for som variabels, which affects the fatigue crack growth of fiber metal laminatesManuscript (preprint) (Other academic)
    Abstract [en]

    Research has been carried out to investigate the crack growth behavior of glass fiber reinforced aluminum laminates (GLARE®). In order to prove the validity of an effective stress intensity range model found in the literature, a parametric study of some of the key variables of the mode! has been performed. Crack growth tests have been performed to give crack growth data for the fiber-metal-laminates and for the metal sheet material, used in the fiber metal larninates. The idée is to compare fibermetal-laminates with metal sheet material with respect to the crack growth rate - stress intensity range relation. The experimental results show that the model seems to overestimate the stress intensity range for test conditions having a high mean stress in the aluminum layers. For the load range used, a high average stress in the aluminum layers also leads to larger delaminations. Any individual change of the key parameters investigated, cannot shift the calculated effective stress intensity range for the fiber-metal-laminates so that the experimental crack growth data fit the crack growth data of the non-reinforced aluminum.

    Even if the model overestimates the effective stress intensity range for some test conditions, the model succeeds to describe the overall crack growth behavior of fiber-metal-laminates.

  • 67.
    Hofslagare, Per
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Engineering Materials.
    Johansson, Sten
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Engineering Materials.
    The influence of bonding strength and residaul stresses on delamination growth in FML1999In: Fatigue 1999,1999, 1999Conference paper (Refereed)
  • 68.
    Hofslagare, Per
    et al.
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Johansson, Sten
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    The influence of delamination size on fibre reinforcement in fibre metal laminatesManuscript (preprint) (Other academic)
    Abstract [en]

    Research has been carried out to investigate the influence of delamination size for crack growth behaviour of glass fibre reinforced aluminium laminates (GLARE®). The aim of this work has been to investigate to what degree the restraining fibres in the wake of a metal fatigue crack carry load, and to what extent the size and shape of the delamination will affect the magnitude of the fibre-reinforcement. Tests for different delamination shapes by measuring the stiffness change when restraining fibres are removed has been performed and compared with finite element analysis. The investigation shows that the fibres can be assumed to have a constant stress through the metal crack length, and that a smaller delamination gives a higher restraining effect.

  • 69.
    Jia, N
    et al.
    Key Laboratory for Anisotrooy and Testure of Materials Northeastern university, Shenyang, China.
    Peng, Ru
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Engineering Materials .
    Chai, G C
    Sandvik Materials Technology SFM Sandviken.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials . Linköping University, The Institute of Technology.
    Wang, Y D
    Key Laboratory for Anisotropy and Texture of Materials Northeastern university, Shenyang, China.
    Direct experimental mapping of microscale deformation heterogeneity in duplex stainless steel2008In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 491, no 1-2, p. 425-433Article in journal (Refereed)
    Abstract [en]

    In situ tensile test has been performed with the electron back-scattering diffraction (EBSD) technique for characterizing the deformation heterogeneity at microscopic level of a duplex stainless steel consisting of austenite and ferrite. It was observed that, as deformation proceeded, the fraction of low-angle boundaries continuously increased and strain gradient developed at some grain boundaries and twin boundaries, as well as in the interior of some grains. The in situ experiments quantitatively captured the change of grain-orientation-dependent plastic behavior in respective phases and the strain partition between duplex phases as a function of applied strain. Using a visco-plastic self-consistent (VPSC) model incorporating the accommodation of micromechanical properties of grains with different orientations in two phases, the evolution of microstresses/microstrains at various length scales was simulated and discussed in detailed within the material undergoing plastic deformation. The experimental observations are well explained by the VPSC model. The present investigations provide the in-depth understanding of anisotropic micromechanical behaviors of the duplex steel. © 2008 Elsevier B.V. All rights reserved.

  • 70.
    Jia, N
    et al.
    Key Lab for Anisotropy and Texture of Materials Northeastern University, Shenyang, China.
    Peng, Ru
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Engineering Materials .
    Wang, Y D
    Dept of Materials Science and Engineering University of Tennessee, Knoxville, USA.
    Johansson, Sten
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Engineering Materials .
    Liaw, P K
    Dept of Materials Science and Engineering University of Tennessee, Knoxville, USA.
    Micromechanical behavior and texture evolution of duplex stainless steel studied by neutron diffraction and self-consistent modeling2008In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 56, no 4, p. 782-793Article in journal (Refereed)
    Abstract [en]

    Microscopic incompatibility-induced stresses in a duplex stainless steel undergoing plastic deformation are elucidated using a visco-plastic self-consistent model. The model considers not only the grain-orientation-dependent stresses and phase-to-phase interactions, but also texture evolution during deformation. The parameters used for describing the micromechanical behavior of the two-phase polycrystalline material are directly derived from the neutron diffraction data. A reliable prediction of the evolution of grain orientation distributions for both phases at small deformations is achieved after considering various micromechanical interactions of the studied material. © 2007 Acta Materialia Inc.

  • 71.
    Johansson, Sten
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Engineering Materials.
    Research in Engineering Materials at Linköping University2005In: China-Sweden Symposium on Materials Science,2005, 2005Conference paper (Other academic)
  • 72.
    Johansson, Sten
    et al.
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Andersson, Nils-Eric
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Zeng, Xiao-Hu
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    The variation of through thickness properties and structure of AA7010 thick plate1997In: International Conference on Thermomechanical Processing of Steel and Other Materials 1997: THERMEC '97 / [ed] T. Chandra and T. Sakai, 1997, p. 941-949Conference paper (Refereed)
    Abstract [en]

    The variation of through thickness structure and yield strength of AA7010-T7451 100 and 150 mm thick plate was investigated. Grain sizes at different depths were determined by using optical microscopy and EBSP maps. Texture measurements were carried out, using X-ray technique and EBSP, at the same depths as grain size studies and tensile property tests were performed. EBSP technique was used to compare degree of recovered and recrystallized grain structure at different depths. Tensile testing and hardness measurements reveal through thickness variations in yield strength and hardness. Variations in composition through the thickness are also possible. The influence of texture on yield strength was discussed.

  • 73.
    Johansson, Sten
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Engineering Materials.
    Chai, Guocai
    RD Centre Sandvik Materials Technology, Sandviken.
    Fatigue Crack Propagation of Super-Duplex Stainless Steel at Different Temperatures2006In: ECF16 16th European Conference of Fracture,2006, 2006Conference paper (Refereed)
  • 74.
    Johansson, Sten
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Engineering Materials .
    Fitzpatrick, ME
    Linkoping Univ, Dept Mech Engn, Div Engn Mat, S-58183 Linkoping, Sweden Open Univ, Dept Mat Engn, Milton Keynes MK7 6AA, Bucks, England.
    Errors in crack closure measurements caused by flexure test fixture support effects2001In: Experimental mechanics, ISSN 0014-4851, E-ISSN 1741-2765, Vol. 41, no 1, p. 47-51Article in journal (Refereed)
    Abstract [en]

    Flexural tests are sometimes used for the evaluation of fatigue and fracture properties, especially for thin cross sections such as plate material where compact tension specimens cannot be used, or where material thickness is limited in the direction required for data generation. The method is also useful for evaluation of crack closure provided the force transfer occurs correctly. This paper shows how the influence of incorrect test fixture supports, which are outside the standard testing arrangement for such test specimens, can affect the force-displacement curves as evidenced using the back-face strain method, The results show that incorrect test fixture supports may cause deviations in the force-displacement trace as an artifact of the testing conditions. This effect can severely influence crack closure measurements. The effect was also modeled with finite element analysis.

  • 75.
    Johansson, Sten
    et al.
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Hedbrant, Johan
    Linköping University, Department of Mechanical Engineering, Energy Systems. Linköping University, The Institute of Technology.
    Kursskal eller aktiv kurshemsida: Sammanfattning av några erfarenheter av kursskali teknologkurser2001Report (Other academic)
    Abstract [sv]

    Möjligheten att kommunicera med hjälp av datorer har funnits i mer än 20 år och ur denna möjlighet har ett antal idéer om hur en sådan kommunikation kan utnyttjas vid undervisning realiserats. Istället för att ersätta konventionella brev med elektroniska varianter blev det istället vanligt att skicka korta meddelanden eller att man tog i anspråk de datorstödda sk konferenssystem som utvecklades. Centrala funktioner i dessa system innebar att man inte bara kunde utbyta meddelanden med kort svarstid utan även kunde skapa möten eller aktiviteter, nyhetskontroll och organisation av lästa och olästa meddelanden i en struktur [1]. Dessa konferenssystem kan kompletteras med funktioner som formellt behövs för att kunna bedriva distansundervisning elektroniskt. Exempel på sådana funktioner är:

    • Elektroniska gruppdiskussioner
    • Databaser där elever kan söka, läsa och kopiera information och ävenladda ner undervisningsprogram
    • Datorstöd där läraren växelverkar med studenten
    • Datorstöd för distanstentamen
  • 76.
    Johansson, Sten
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Leidermark, Daniel
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Simonsson, Kjell
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Kanesund, Jan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Investigation of localized damage in single crystals subjected to thermalmechanical fatigue (TMF)2010In: Procedia Engineering, ISSN 1877-7058, Vol. 2, no 1, p. 657-666Article in journal (Refereed)
    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.

  • 77.
    Johansson, Sten
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Recent Applications of Scanning Electron Microscopy2013In: Practical Metallography, ISSN 0032-678X, Vol. 50, no 12, p. 810-820Article in journal (Refereed)
    Abstract [en]

    Scanning electron microscopy (SEM) has since it was commercially available in the sixties been used in the study of solid inorganic and organic materials at magnifications ranging from 10 to above 10000 times. Analysis tools are now including diffraction phenomena like EBSD for crystallographic studies The use of X-ray generated was early introduced and the performance of those EDS systems is enormous even if the basic principle of detection is almost the same. Even if the development of digital electronics is one important factor for todays performance of SEM, the most important factor for success is the generation of electron probe size with a small diameter to obtain as high resolving power as possible In addition to that the electron density plays a major role since the resolving power is dependent on peak to background ratio to get a sharp image, the development of bright guns is the most important factor.

  • 78.
    Johansson, Sten
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering, Engineering Materials.
    Ossbahr, Gilbert
    Linköping University, The Institute of Technology. Linköping University, Department of Mechanical Engineering.
    Harris, Tom
    Airbus Filton.
    Study of the Inluence of Drilling Method and Hole quality on Static Strength and Fatigue Life of Carbon Fiber Reinforced Plastic Aircraft Material2002Report (Other academic)
  • 79.
    Johansson, Sten
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Viskari, Leif
    Chalmers University of Technology and SKF Sweden.
    Stiller, Krystina
    Chalmers University of Technology Sweden.
    Hörnqvist, Magnus
    Chalmers University of Technology and GKN Aerospace Engine Systems Sweden.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Fracture Mechanisms During Intergranular Hold Time Fatigue Crack Growth in Inconel 718 Superalloy2013Conference paper (Refereed)
  • 80.
    Johansson, Sten
    et al.
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Zeng, Xiaohu
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Andersson, Nils-Eric
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Peng, Ru
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Measurement of average texture of cold-rolled aluminium sheet by electron back-scattering diffraction: a comparison with neutron diffraction2001In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 315, no 1-2, p. 129-135Article in journal (Refereed)
    Abstract [en]

         Measurements of the average texture on sheet of commercial pure aluminium have been performed using neutron diffraction and electron back-scattering diffraction (EBSD). Orientation distribution function maps have been calculated and compared. The results show a good correspondence provided that the data from the EBSD measurements are corrected according to a texture index versus inverted number of measurement procedure. Most errors are probably related to differences in investigated volume and calculation technique and to the fact that the microstructure was difficult for EBSD measurements.

  • 81.
    Kahl, Sören
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology. Gränges Technology, Gränges AB, Finspång, Sweden.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Calmunger, Mattias
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Olsson, Björn
    Sapa Technology, Sapa AB, Finspång, Sweden.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    In Situ EBSD During Tensile Test of Aluminum AA3003 Sheet2014In: Micron, ISSN 0968-4328, E-ISSN 1878-4291, ISSN 0968-4328, Vol. 58, p. 15-24Article in journal (Refereed)
    Abstract [en]

    Miniature tensile-test specimens of soft-annealed, weakly textured AA3003 aluminum sheet in 0.9 mm thickness were deformed until fracture inside a scanning electron microscope. Tensile strength measured by the miniature tensile test stage agreed well with the tensile strength by regular tensile testing. Strain over the microscope field of view was determined from changes in positions of constituent particles. Slip lines were visible in secondary electron images already at 0.3% strain; activity from secondary slip systems became apparent at 2% strain. Orientation rotation behavior of the tensile load axis with respect to the crystallographic axes agreed well with previously reported trends for other aluminum alloys. Start of the fracture and tensile crack propagation were documented in secondary electron images. The region of fracture nucleation included and was surrounded by many grains that possessed high Schmid factors at zero strain. Crystal lattice rotation angles in the grains surrounding the initial fracture zone were higher than average while rotations inside the initial fracture zone were lower than average for strains from zero to 31%. The orientation rotation behavior of the tensile load axes of the grains around the fracture zone deviated from the average behavior in this material.

  • 82.
    Kahl, Sören
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology. Gränges Technology, Gränges AB, Finspång.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Tensile Failure of Thin Aluminium Sheet Observed by In-Situ EBSD2015In: 17TH INTERNATIONAL CONFERENCE ON TEXTURES OF MATERIALS (ICOTOM 17), IOP Publishing , 2015, Vol. 82Conference paper (Refereed)
    Abstract [en]

    Tensile tests on two similar 75-μm-thick aluminium sheet materials were carried out inside a scanning electron microscope equipped with an electron backscatter detector. The materials were subjected to simulated brazing prior to the test because this type of material is used for fins in automotive heat exchangers. Grain sizes were large relative to sheet thickness and ND-rotated cube and P texture components dominated the recrystallization textures; their volume fractions differed strongly in the two different materials, though. Strains over the microscope image fields were determined from positions of constituent particles or from grain sizes; the two methods gave consistent results. Grains with high Schmid factors accumulated significantly more deformation than grains with low Schmid factors. Cracks nucleated in high-Schmid factor grains, or in groups of such grains, at the specimen edges. When only low-Schmid factor grains were present at the specimen edges, the crack nucleated inside the specimen. The subsequent crack growth was intragranular and occurred at approximately 90° relative to the load direction.

  • 83.
    Kanesund, Jan
    et al.
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Engineering Materials.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    A Study of the Influence of Plastic Pre Strain in Different Directions Before Ageing of Extruded and Hydro Formed Material on the Mechanical Properties of AA60632012Conference paper (Refereed)
  • 84.
    Kanesund, Jan
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Deformation and damage mechanisms in IN792 during thermomechanical fatigue2011In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 528, no 13-14, p. 4658-4668Article in journal (Refereed)
    Abstract [en]

    The deformation and damage mechanisms arising during thermomechanical fatigue (TMF) of the polycrystallinesuperalloy IN792 have been investigated. The TMF cycles used in this study are in-phase(IP) and out-of-phase (OP). The minimum temperature used in all TMF-tests is 100 ◦C while the maximumtemperature is 500 or 750 ◦C in the IP TMF-tests and 750, 850 or 950 ◦C in the OP TMF-tests. Themajority of the cracks are transcrystalline, except for the IP TMF-test at 750 ◦C, where some tendencyto intercrystalline crack growth can be seen. In all tests, the cracks were initiated and propagated inlocations where deformation structures such as deformation bands have formed in the material. In thetemperature interval 750–850 ◦C, twins were formed in both IP and OP TMF-tests and this behaviouris observed to be further enhanced close to a crack. Twins are to a significantly lesser extent observedfor tests with a lower (500 ◦C) and a higher (950 ◦C) maximum temperature. Recrystallization at grainboundaries, around particles and within the deformation structures have occurred in the OP TMF-testswith a maximum temperature of 850 and 950 ◦C and this is more apparent for the higher temperature.Void formation is frequently observed in the recrystallized areas even for the case of compressive stressesat high temperature.

  • 85.
    Kanesund, Jan
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    The Deformation and Damage Mechanisms During Thermomechanical Fatigue (TMF) in IN7922011In: Procedia Engineering, ISSN 1877-7058, E-ISSN 1877-7058, Vol. 10, p. 189-194Article in journal (Refereed)
    Abstract [en]

    The deformation and damage mechanisms arising during thermomechanical fatigue (TMF) of the polycrystalline superalloy IN792 have been investigated. The TMF cycles used in this study are in-phase (IP) and out-of-phase (OP). The minimum temperature used in all TMF-tests is 100 °C while the maximum temperature is 750 °C in the IP TMF-tests and 850° or 950 °C in the OP TMF-tests. Most cracks have propagated transgranularly through the material and this holds for all temperatures used in this study. In all tests, the cracks have initiated and propagated in locations where deformation structures such as deformation bands have formed in the material. In the temperature interval 750°-850 °C, twins are formed in both IP and OP TMF-tests and this behaviour is observed to be further enhanced close to a crack. Twins are to a significantly lesser extent observed for tests with a higher (950 °C) maximum temperature. Recrystallization at grain boundaries, around particles and within the deformation structures have occurred in the OP TMF-tests with a maximum temperature of 850° and 950 °C and this is more apparent for the higher temperature.

  • 86.
    Kaouache, Belkhiri
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials.
    Bäckström, Daniel
    Ahmad, Maqsood
    Vuoristo, Taina
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering.
    To Increase Fatigue Strength of Grey Iron By Shot Peening2015Conference paper (Refereed)
  • 87.
    Leidermark, Daniel
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Moverare, Johan J.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Simonsson, Kjell
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Sjöström, Sören
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Room temperature yield behaviour of a single-crystal nickel-base superalloy with tension/compression asymmetry2009In: Computational materials science, ISSN 0927-0256, E-ISSN 1879-0801, Vol. 47, no 2, p. 366-372Article in journal (Refereed)
    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.

  • 88.
    Leidermark, Daniel
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Simonsson, Kjell
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Sjöström, Sören
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Tension/Compression asymmetry of a single-crystal superalloy in virgin and degraded condition2010In: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 58, no 15, p. 4986-4997Article in journal (Refereed)
    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.

  • 89.
    Leidermark, Daniel
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Segersäll, Mikael
    Linköping University, The Institute of Technology. Linköping University, Department of Management and Engineering, Engineering Materials.
    Simonsson, Kjell
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Sjöström, Sören
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Evaluation of Fatigue Crack Initiation in a Notched Single-crystal Superalloy Component2011In: Procedia Engineering, ISSN 1877-7058, E-ISSN 1877-7058, Vol. 10, p. 619-624Article in journal (Refereed)
    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.

  • 90.
    Leidermark, Daniel
    et al.
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Moverare, Johan
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Simonsson, Kjell
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Sjöström, Sören
    Linköping University, Department of Management and Engineering, Solid Mechanics. Linköping University, The Institute of Technology.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Fatigue crack initiation in a notched single-crystal superalloy component2010In: Procedia Engineering, ISSN 1877-7058, E-ISSN 1877-7058, Vol. 2, no 1, p. 1067-1075Article in journal (Refereed)
    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.

  • 91.
    Liu, X. P.
    et al.
    Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education).
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Hofmann, M
    FRM-II, TU München, Garching, Germany .
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Wang, Y D
    Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education), Northeastern University, Shenyang, People’s Republic of China and School of Materials Science and Engineering, Beijing Institute of Technology, Beijing, People’s Republic of China.
    In-Situ Neutron Diffraction Studies of Micromechanical Behavior in a Friction Stir Welded AA7475-T7612011In: Metallurgical and Materials Transactions. A, ISSN 1073-5623, E-ISSN 1543-1940, Vol. 42A, no 1, p. 89-94Article in journal (Refereed)
    Abstract [en]

    An in-situ neutron diffraction technique was used to investigate the lattice strain distributions and micromechanical behavior in a friction stir welded (FSW) sheet of AA7475-T761. The neutron diffraction experiments were performed on the spectrometer for material research, STRESS-SPEC, at FRM II (Garching, Germany). The lattice strain profiles around the weld center were measured as a function of the applied strain during the tensile loading and unloading. The anisotropic elastic and plastic properties of the FSW aluminum alloy were simulated by elasto-plastic self-consistent (EPSC) model to predict the anisotropic deformation behaviors involving the grain-to-grain interactions. Material parameters used for describing the constitutive laws of each test position were determined from the measured lattice strain distributions for different diffraction hkl planes as well as the macroscopic stress-strain curve of the FSW aluminum alloy. A good agreement between experimental results and numerical simulations was obtained. The present investigations provided a reliable prediction of the anisotropic micromechanical behavior of the FSW aluminum alloy during tensile deformation.

  • 92.
    Lundberg, Mattias
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Ahmad, Maqsood
    Base Engine & Materials Technology, Volvo Powertrain, Göteborg.
    Bäckström, Daniel
    Testing Methods and Testing, Scania CV AB, Södertälje.
    Vuoristo, Taina
    Testing Methods and Testing, Scania CV AB, Södertälje.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Fatigue strength of Machined and Shot Peened Grey Cast Iron2014Conference paper (Refereed)
    Abstract [en]

    A common opinion is that cast iron, especially grey cast iron, is not as notch sensitive as steel therefore is not typically treated by shot peening to suppress crack initiation. For a heterogeneous material that also is brittle, just like grey cast iron, the shot peening parameters needed to induce beneficial surface residual stresses can be problematic to identify. Fatigue testing under uniaxial loading with an R value of -1, on mechanically polished and shot peened specimens, has been performed to determine the fatigue strength at 10(7) cycles as well as complete Wohler-curves. Two different types of specimen geometries were tested, one smooth and one notched specimen having k(t) equal to 1.05 and 1.33 respectively. With large shots and high peening intensity (heavy SP) the fatigue strength clearly decreased whereas small shots and low peening intensity (gentle SP) might have lowered the fatigue strength. A short annealing at 285 degrees after gentle SP increased the fatigue strength. The results are discussed and explained based on x-ray diffraction (XRD) measurements, i.e. residual stress and full width at half maximum profiles, as well as microstructural investigations using scanning electron microscope (SEM).

  • 93.
    Lundberg, Mattias
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Ahmad, Maqsood
    Base Engine & Materials Technology, Volvo Powertrain, Gothenburg, Sweden.
    Bäckström, Daniel
    Testing Methods and Testing, Scania CV AB, Södertälje, Sweden.
    Vuoristo, Taina
    Testing Methods and Testing, Scania CV AB, Södertälje, Sweden.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Fatigue Strength of Machined and Shot Peened Grey Cast Iron: Influence of Graphite Morphology2013Manuscript (preprint) (Other academic)
    Abstract [en]

    A common opinion is that cast iron, especially grey cast iron, is not as notch sensitive as steel and has therefore not been treated by shot peening to suppress crack initiation. For a heterogeneous material that also is brittle, just like grey cast iron, the shot peening parameters needed to induce beneficial surface residual stresses can be problematic to identify. Fatigue testing under uniaxial loading with an R value of -1, on mechanically polished and shot peened specimens, has been performed to determine the fatigue strength at 107 cycles as well as complete Wöhler-curves. Two different types of specimen geometries were tested, one smooth and one notched specimen having kt equal to 1.05 resp. 1.33. With large shots and high peening intensity (heavy shot peening) the fatigue strength clearly decreased whereas small shots and low peening intensity (gentle shot peening) might have lowered the fatigue strength. A short annealing at 285° after gentle shot peening increased the fatigue strength. The results are discussed and explained based on x-ray diffraction measurements, i.e. residual stress and full width at half maximum profiles, as well as microstructural investigations using scanning electron microscope (SEM).

  • 94.
    Lundberg, Mattias
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Ahmad, Maqsood
    Base Engine & Materials Technology, Volvo Powertrain, Göteborg.
    Bäckström, Daniel
    Testing Methods and Testing, Scania CV AB, Södertälje.
    Vuoristo, Taina
    Testing Methods and Testing, Scania CV AB, Södertälje.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Graphite Morphology's Influence on Shot Peening Results in Cast Irons2014Conference paper (Refereed)
    Abstract [en]

    The different shot peening responds of a grey cast iron (GI) with its flake graphite and a compacted cast iron (CGI) with its vermicular graphite was analyzed and compared in this paper. For peening using identical parameters, CGI showed a larger plastic deformation zone with higher subsurface compressive stresses than GI. Electron backscatter diffraction (EBSD) mapping and backscatter electron imaging revealed that plastic deformation of the matrix near graphite inclusions is affected by the size and geometry of the graphite. The different behaviors of graphite are explained by their capability to damp mechanical force but at the same time to cause stress concentration in the matrix. The better shot peening results for CGI may be attributed to a lower damping effect of its graphite inclusions and capability of the matrix for larger plastic deformation.

  • 95.
    Lundberg, Mattias
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Ahmad, Maqsood
    Base Engine & Materials Technology, Volvo Powertrain, Gothenburg, Sweden.
    Bäckström, Daniel
    Testing Methods and Testing, Scania CV AB, Södertälje, Sweden.
    Vuoristo, Taina
    Testing Methods and Testing, Scania CV AB, Södertälje, Sweden.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Shot Peening Induced Plastic Deformation in Cast Iron - Influence of Graphite Morphology2014In: HTM Journal of Heat Treatment and Material, ISSN 1867-2493, Vol. 69, no 2, p. 106-113Article in journal (Refereed)
    Abstract [en]

    Graphite morphology in cast iron strongly affects the mechanical properties such as: Young's modulus, tensile/compressive strength and cyclic mechanical behaviour. In this study, pearlitic compact graphite iron (CGI) and grey cast iron (GI) have been studied in a scanning electron microscope (SEM) before and after shot peening under different conditions. The plastic deformation behaviour of CGI and GI under different shot peening conditions has been analysed using electron backscattering diffraction (EBSD) and electron contrast channelling imaging (ECCI). EBSD and ECCI revealed that plastic deformation around graphite inclusions depends on the size and shape of the graphite. The different response of CGI and GI to shot peening is explained by the different damping properties of the graphite and the matrix capability for plastic deformation.

  • 96.
    Lundberg, Mattias
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Ahmad, Maqsood
    Base Engine & Materials Technology, Volvo Powertrain, Gothenburg, Sweden.
    Bäckström, Daniel
    Testing Methods and Testing, Scania CV AB, Södertälje, Sweden.
    Vuoristo, Taina
    Testing Methods and Testing, Scania CV AB, Södertälje, Sweden.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Shot Peening Induced Plastic Deformation in Cast Iron: Influence of Graphite Morphology2013Manuscript (preprint) (Other academic)
    Abstract [en]

    Graphite morphology in cast irons strongly affects their mechanical properties like the Young’s modulus, tensile/compressive strength and cyclic mechanical behaviour. In this paper, pearlitic compact graphite iron (CGI) and grey cast iron (GI) have been studied in a scanning electron microscope (SEM) before and after being shot peened under different conditions. The plastic deformation behaviour of CGI and GI under different shot peening conditions is analysed using electron backscattering diffraction (EBSD) and electron contrast channelling imaging (ECCI). EBSD and ECCI revealed that plastic deformation around graphite inclusions depends on the size and shape of the graphite. The different response of CGI and GI to shot peening is explained by the different damping properties of the graphite and the matrix capability for plastic deformation.

  • 97.
    Lundberg, Mattias
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Ahmad, Maqsood
    Base Engine & Materials Technology, Volvo Powertrain, Göteborg.
    Vuoristo, Taina
    Testing Methods and Testing, Scania CV AB, Södertälje.
    Bäckström, Daniel
    Testing Methods and Testing, Scania CV AB, Södertälje.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Influence of Shot Peening Parameters on Residual Stresses in Flake and Vermicular Cast Irons2014Conference paper (Refereed)
    Abstract [en]

    Test samples of grey and compacted graphite cast irons with pearlitic matrix were shot-peened to different surface conditions using twelve different combinations of shot size, peening intensity and peening coverage percentage. Relatively high surface compressive residual stresses varying between 245 to 565 MPa were observed and the compressive residual stresses reached a depth between 280 µm and 770 µm. Within the range of peening parameters used, the compacted graphite cast iron with its vermicular graphite showed a somewhat better response to the same shot-peening treatment than the grey cast iron containing flake graphite, giving a larger peening affected zone with higher compressive residual stresses. For both the cast irons, an increase in peening coverage percentage, shot size or peening intensity led often to a lower surface compressive stress. However, peening using a higher intensity greatly increased the degree and extent of plastic deformation and therefore increased the magnitude and penetration depth of the subsurface compressive residual stresses, while the effect of increasing shot size also depends on the peening intensity. On the other hand, measurements on the grey cast iron samples showed that the peening coverage has little effect on the depth profile of residual stress.

  • 98.
    Lundberg, Mattias
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Ahmad, Maqsood
    Base Engine & Materials Technology, Volvo Powertrain, Gothenburg, Sweden.
    Vuoristo, Taina
    Testing Methods and Testing, Scania CV AB, Södertälje, Sweden.
    Bäckström, Daniel
    Testing Methods and Testing, Scania CV AB, Södertälje, Sweden.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Residual Stresses in Shot Peened Grey and Compact Iron2013Manuscript (preprint) (Other academic)
    Abstract [en]

    In this paper grey and compact cast irons with a pearlitic matrix are investigated after shot peening with twelve unique combinations of parameters, namely shot size, intensity and coverage, followed by residual stress measurements and evaluations. Cylindrical test samples were cut out from real cylinder heads and polished on the top flat surface to decrease effects from cutting. Residual stresses and the affected depth from the different peening conditions varied between -245 to -565 MPa and from 280 μm to 770 μm in depth. By an increase in shot size or intensity or coverage resultant surface compressive stresses will decrease whereas the affected depth increases with increasing intensity. The increased affected depth is as a result from the increased extent and magnitude of plastic deformation. The compacted cast iron was more affected than the grey cast iron, meaning that the same shot peening parameters resulted in both higher compressive stresses and larger deformation depth.

  • 99.
    Lundberg, Mattias
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Peng, Ru
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Ahmad, Maqsood
    Volvo Powertrain, Gothenburg, Sweden.
    Vuoristo, Taina
    Scania CV AB, Södertälje, Sweden.
    Bäckström, Daniel
    Scania CV AB, Södertälje, Sweden.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    Residual Stresses in Shot Peened Grey and Compact Iron2014In: HTM Journal of Heat Treatment and Materials, ISSN 1867-2493, Vol. 69, no 1, p. 38-45Article in journal (Refereed)
    Abstract [en]

    Grey cast iron and compacted graphite iron with a pearlitic matrix are investigated in this study after shot peening using twelve unique combinations of parameters, namely shot size, peening intensity and coverage, followed by residual stress measurements and evaluations. Cylindrical test samples were cut out from heavy truck cylinder heads and polished on the top flat surface to decrease effects from cutting. Residual stresses and the affected depth from the different peening conditions varied between −245 MPa to −565 MPa and from 280 μm to 770 μm in depth. Resultant surface compressive stresses decrease with increasing shot size, peening intensity or coverage whereas the affected depth increases with increasing intensity. The increased affected depth is a result from the increased extent and magnitude of plastic deformation. The compacted graphite iron was more affected by shot peening than the grey cast iron, meaning that the same shot peening parameters resulted in both higher compressive stresses and larger deformation depth.

  • 100.
    Moverare, Johan
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials . Linköping University, The Institute of Technology.
    Johansson, Sten
    Linköping University, Department of Management and Engineering, Engineering Materials . Linköping University, The Institute of Technology.
    Damage mechanisms of a high-Cr single crystal superalloy during thermomechanical fatigue2010In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 527, no 3, p. 553-558Article in journal (Refereed)
    Abstract [en]

    The deformation and damage mechanisms arising during thermomechanical fatigue of a high-Cr single crystal superalloy have been investigated and a completely new failure mechanism involving recrystallization and oxidation has been discovered. The primary deformation mechanism is slip along the {1 1 1} planes. The deformation is highly localized to a number of bands, where recrystallization eventually occurs during the thermomechanical 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 γ′ depleted zone under the oxide layer.

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