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  • 1.
    Bergström, Jens
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Kazymyrovych, Vitaliy
    Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Burman, Christer
    Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Ekengren, Jens
    Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Test specimen geometry, stress calculation and mean stress in 20kHz testing in the very long fatigue life region2011In: VHCF5 5thInternational Conference on Very High Cycle Fatigue / [ed] Christina Berger, Hans-Jurgen Christ, Berlin: Deutcher Verband fur Materialforschung und prufung , 2011, p. 315-320Conference paper (Refereed)
  • 2.
    Ekengren, Jens
    et al.
    Karlstad University, Faculty of Technology and Science, Avdelningen för maskin- och materialteknik.
    Kazymyrovych, Vitaliy
    Karlstad University, Faculty of Technology and Science, Avdelningen för maskin- och materialteknik.
    Bergström, Jens
    Karlstad University, Faculty of Technology and Science, Avdelningen för maskin- och materialteknik.
    Assessment of strength and inclusions of Tool Steels in Very High Cycle Fatigue2009In: Proceedings of the 8th International Tooling Conference, Vol 1 / [ed] P. Beiss, C. Broeckmann, S. Franke, B. Keysselitz, Verlag Mainz, Wissenschaftsverlag , 2009Conference paper (Refereed)
    Abstract [en]

    Fatigue strength is an important material property for many tooling applications, particularly in high performance applications. The research in Very High Cycle Fatigue (VHCF) has demonstrated that the traditional fatigue limit may not be valid for many materials subjected to 107 or more load cycles. Presently, both materials data and mechanism knowledge is missing on VHCF applications, even though many components are run at these life lengths. The fatigue strength is commonly controlled by different defects initiating failure, as in well controlled laboratory experiments may be internal inclusions. In this paper VHCF experimental testing was accomplished by the use of ultrasonic fatigue testing run at 20 kHz allowing long life evaluation within reasonably short test time. Fatigue strength, failure mechanisms and inclusion content were accordingly assessed. Fatigue strength data on H13 tool steel are presented, as well as a statistical approach considering available defect distribution and load distribution in the critically stressed volume, important to both steel supplier and end-user.

  • 3.
    Ekengren, Jens
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Enineering.
    Kazymyrovych, Vitaliy
    Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Enineering.
    Burman, Christer
    Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Enineering.
    Bergström, Jens
    Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Enineering.
    Relating gigacycle fatigue to other methods in evaluating the inclusion distribution of a H13 tool steel2007In: Fourth International Conference on Very High Cycle Fatigue (VHCF-4) / [ed] John E. Allison, J. Wayne Jones, James M. Larsen & Robert O. Ritchie, TMS (The Minerals, Metals & Materials Society) , 2007, p. 45-50Conference paper (Refereed)
    Abstract [en]

    Inclusions play a crucial role for the fatigue properties of high strength steel, but to find the largest inclusions by microscopy measurements large areas have to be examined.In this study ultrasonic gigacycle staircase fatigue testing has been used to find large inclusions in an H13 tool steel. The inclusions have been examined in SEM and their size distribution modeled using methods from extreme value statistics. The inclusion distribution obtained from the fatigue crack surfaces is compared to distributions acquired by microscopy study of cross sections as well as ultrasound immersion tank measurements and to the corresponding staircase fatigue data via the Murakami √Area model.It is shown that the fatigue method more effectively finds large inclusions than the other methods. It is also shown that the correlation between predictions of inclusion sizes by the √Area model from stress levels and fatigue initiating inclusions is weak forthis material.

  • 4.
    Ekengren, Jens
    et al.
    Karlstad University, Faculty of Technology and Science, Materials Science. Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Kazymyrovych, Vitaliy
    Burman, Christer
    Karlstad University, Faculty of Technology and Science, Materials Science. Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Bergström, Jens
    Karlstad University, Faculty of Technology and Science, Materials Science. Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    RELATING GIGACYCLE FATIGUE TO OTHER METHODS IN EVALUATING THE INCLUSION DISTRIBUTION OF A H13 TOOL STEEL2007Conference paper (Refereed)
    Abstract [en]

    Inclusions play a crucial role for the fatigue properties of high strength steel, but to find the

    largest inclusions by microscopy measurements large areas have to be examined. In this study ultrasonic gigacycle staircase fatigue testing has been used to find large inclusions in an H13 tool steel. The inclusions have been examined in SEM and their size

    distribution modeled using methods from extreme value statistics. The inclusion distribution obtained from the fatigue crack surfaces is compared to distributions acquired by microscopy study of cross sections as well as ultrasound immersion tank measurements and to the corresponding staircase fatigue data via the Murakami \sqrt{Area} model. It is shown that the fatigue method more effectively finds large inclusions than the other methods. It is also shown that the correlation between predictions of inclusion sizes by the \sqrt{Area} model from stress levels and fatigue initiating inclusions is weak for this material

  • 5.
    Kazymyrovych, Vitaliy
    Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Enineering.
    Very high cycle fatigue of engineering materials: A literature review2009Report (Other (popular science, discussion, etc.))
    Abstract [en]

    Many engineering components reach a finite fatigue life well above 109 load cycles. Some examples of such components are found in airplanes, automobiles or high speed trains. For some materials the fatigue failures have lately been found to occur well after 107 load cycles, namely in the Very High Cycle Fatigue (VHCF) range. This finding contradicted the established concept of fatigue limit for these materials, which postulates that having sustained 107 load cycles the material is capable of enduring an infinite number of cycles provided that the service conditions are unchanged.

    With the development of modern ultrasonic fatigue testing equipment it became possible to experimentally establish VHCF behaviour of various materials. For most of them the existence of the fatigue limit at 107 load cycles has been proved wrong and their fatigue strength continues to decrease with increasing number of load cycles. This report describes very long life fatigue properties of most commonly used engineering materials including aluminium, titanium, nickel alloys and various types of steel.

  • 6. Kazymyrovych, Vitaliy
    Very high cycle fatigue of high performance steels2008Licentiate thesis, monograph (Other academic)
  • 7.
    Kazymyrovych, Vitaliy
    Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Enineering.
    Very high cycle fatigue of high performance steels2008Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Many engineering components reach a finite fatigue life well above 109 load cycles. Some examples of such components are found in airplanes, automobiles or high speed trains. For some materials the fatigue failures have lately been found to occur well after 107 load cycles, namely in the Very High Cycle Fatigue (VHCF) range. This finding contradicted the established concept of fatigue limit for these materials, which postulates that having sustained 107 load cycles the material is capable of enduring an infinite number of cycles provided that the service conditions are unchanged. With the development of modern ultrasonic fatigue testing equipment it became possible to experimentally establish VHCF behaviour of various materials. For most of them the existence of the fatigue limit at 107 load cycles has been proved wrong and their fatigue strength continues to decrease with increasing number of load cycles.

     

    One important group of materials used for the production of high performance components subjected to the VHCF is tool steels. This study explores the VHCF phenomenon using experimental data of ultrasonic fatigue testing of some tool steel grades. The causes and mechanisms of VHCF failures are investigated by means of high resolution scanning electron microscopy, and in relation to the existing theories of fatigue crack initiation and growth. The main type of VHCF origins in steels are slag inclusions.

    However, other microstructural defects may also initiate fatigue failure. A particular attention is paid to the fatigue crack initiation, as it has been shown that in the VHCF range crack formation consumes the majority of the total fatigue life. Understanding the driving forces for the fatigue crack initiation is a key to improve properties of components used for very long service lives. Finite element modelling of VHCF testing was added as an additional perspective to the study by enabling calculation of local stresses at the fatigue initiating defects.

     

     

  • 8.
    Kazymyrovych, Vitaliy
    Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Enineering.
    Very high cycle fatigue of tool steels2010Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    An increasing number of engineering components are expected to have fatigue life in the range of 107 - 1010 load cycles. Some examples of such components are found in airplanes, automobiles and high speed trains. For many materials fatigue failures have lately been reported to occur well after 107 load cycles, namely in the Very High Cycle Fatigue (VHCF) range. This finding contradicts the established concept of a fatigue limit, which postulates that having sustained around 107 load cycles the material is capable of enduring an infinite number of cycles provided that the service conditions are unchanged. With the development of modern ultrasonic fatigue testing equipment it became possible to experimentally establish VHCF behaviour of various materials. For many of them the existence of the fatigue limit at 107 load cycles has been proved wrong and their fatigue strength continues to decrease with increasing number of load cycles.

    High performance steels is an important group of materials used for the components subjected to VHCF. This study explores the VHCF phenomenon using experimental data generated by ultrasonic fatigue testing of selected tool steels. The overall aim is to gain knowledge of VHCF behaviour of some common tool steel grades, while establishing a fundamental understanding of mechanisms for crack development in the very long life regime. The study demonstrates that VHCF cracks in tested steels initiate from microstructural defects like slag inclusions, large carbides or voids. It is established that VHCF life is almost exclusively spent during crack formation at below threshold stress intensity values which results in a unique for VHCF morphology on the fracture surface.

    Significant attention is devoted in the thesis to the ultrasonic fatigue testing technique, i.e. the validity and applicability of its results. FEM is employed to give an additional perspective to the study. It was used to calculate local stresses at fatigue initiating defects; examine the effect of material damping on ultrasonic stresses; and to evaluate various specimen geometries with respect to resulting stress gradient and maximum stressed material volume.

  • 9.
    Kazymyrovych, Vitaliy
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Bergström, Jens
    Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Initial crack growth in very high cycle fatigue of a hot-work tool steel2010Manuscript (preprint) (Other academic)
  • 10.
    Kazymyrovych, Vitaliy
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Enineering.
    Bergström, Jens
    Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Enineering.
    Burman, Christer
    Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Enineering.
    The Significance of Crack Initiation Stage in Very High Cycle Fatigue of Steels2010In: Steel Research International, ISSN 1869-344X, Vol. 81, no 4, p. 308-314Article in journal (Refereed)
  • 11.
    Kazymyrovych, Vitaliy
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Bergström, Jens
    Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Ekengren, Jens
    Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Stress verification and specimen design for ultrasonic fatigue testing2010Manuscript (preprint) (Other academic)
  • 12.
    Kazymyrovych, Vitaliy
    et al.
    Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Bergström, Jens
    Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Thuvander, Fredrik
    Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Local stresses and material damping in very high cycle fatigue2010In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 32, p. 1669-1674Article in journal (Other academic)
  • 13. Kazymyrovych, Vitaliy
    et al.
    Ekengren, Jens
    Karlstad University, Faculty of Technology and Science, Materials Science. Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Bergström, Jens
    Karlstad University, Faculty of Technology and Science, Materials Science. Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Burman, Christer
    Karlstad University, Faculty of Technology and Science, Materials Science. Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
    Evaluation of the Giga-cycle fatigue strength crack initiation and growth in high strength H13 tool steel2007Conference paper (Refereed)
1 - 13 of 13
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