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Local stresses and material damping in very high cycle fatigue
Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Engineering.
2010 (English)In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 32, 1669-1674 p.Article in journal (Other academic) Published
Place, publisher, year, edition, pages
2010. Vol. 32, 1669-1674 p.
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:kau:diva-3363DOI: 10.1016/j.ijfatigue.2010.03.007ISI: 000279622900014OAI: oai:DiVA.org:kau-3363DiVA: diva2:139557
Note

At the time of the licentiate thesis from Vitaliy Kazymyrovych, this article was unpublished, and had a status as a manuscript.

Available from: 2009-01-23 Created: 2009-01-23 Last updated: 2016-02-17Bibliographically approved
In thesis
1. Very high cycle fatigue of high performance steels
Open this publication in new window or tab >>Very high cycle fatigue of high performance steels
2008 (English)Licentiate 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.

 

 

Place, publisher, year, edition, pages
Karlstad: Karlstad University, 2008. 14 p.
Series
Karlstad University Studies, ISSN 1403-8099 ; 2008:56
Keyword
fatigue, tool steels, ultrasonic testing, fatigue life, crack growth rate, fatigue mechanisms
National Category
Materials Engineering
Research subject
Materials Engineering
Identifiers
urn:nbn:se:kau:diva-3066 (URN)978-91-7063-214-3 (ISBN)
Presentation
(English)
Available from: 2009-01-23 Created: 2008-11-24 Last updated: 2011-11-28Bibliographically approved
2. Very high cycle fatigue of tool steels
Open this publication in new window or tab >>Very high cycle fatigue of tool steels
2010 (English)Doctoral 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.

Place, publisher, year, edition, pages
Karlstad: Karlstad University, 2010. 45 p.
Series
Karlstad University Studies, ISSN 1403-8099 ; 2010:20
Keyword
fatigue, crack growth, ultrasonic testing, tool steels, inclusions
National Category
Materials Engineering
Research subject
Materials Engineering
Identifiers
urn:nbn:se:kau:diva-5877 (URN)978-91-7063-312-6 (ISBN)
Public defence
2010-09-10, 21A 244, Ljungberssalen, Karlstad University, 10:15 (English)
Opponent
Supervisors
Available from: 2010-08-20 Created: 2010-06-17 Last updated: 2011-10-27Bibliographically approved

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Kazymyrovych, VitaliyBergström, JensThuvander, Fredrik

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