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Stress verification and specimen design for ultrasonic fatigue testing
Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Enineering.
Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Enineering.
Karlstad University, Faculty of Technology and Science, Department of Mechanical and Materials Enineering.
2010 (English)In: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452Article in journal (Refereed) Submitted
Place, publisher, year, edition, pages
2010.
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:kau:diva-6245OAI: oai:DiVA.org:kau-6245DiVA: diva2:344188
Available from: 2010-08-18 Created: 2010-08-18 Last updated: 2011-10-27Bibliographically approved
In thesis
1. 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, JensEkengren, Jens

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