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Review of VHCF studies, short crack models and theory of vibrations
Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Physics. (Materials Engineering)
(English)Manuscript (preprint) (Other academic)
Abstract [en]

This literature review loosely connects different concepts of very high cycle fatigue which are of significance within the scope of this thesis work. The ultrasonic fatigue testing equipment and its basic principle of operation is discussed in detail. The phenomenon of damping in the light of theory of vibrations is outlined. The significance of the understanding of damping phenomenon in the ultrasonic fatigue testing is highlighted. On the other hand, SN fatigue data obtained by several researchers for different materials are reviewed. In addition, the fundamental mechanisms responsible for fatigue crack initiation are also summarized.

 

Considerable attention is focussed on the mathematical models developed for the prediction of growth behaviour of short fatigue cracks. The basic concepts, and models, which led to the development of the distributed dislocation dipole technique, have also been reviewed.

Keyword [en]
Very cycle high fatigue, crack initiation, short cracks, vibration, damping
National Category
Other Materials Engineering
Identifiers
URN: urn:nbn:se:kau:diva-34634OAI: oai:DiVA.org:kau-34634DiVA: diva2:765148
Projects
Very high cycle fatigue of stainless steels - an unknown life
Funder
Knowledge Foundation
Available from: 2014-11-21 Created: 2014-11-21 Last updated: 2014-12-10
In thesis
1. Very high cycle fatigue of duplex stainless steels and stress intensity calculations
Open this publication in new window or tab >>Very high cycle fatigue of duplex stainless steels and stress intensity calculations
2014 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Very high cycle fatigue (VHCF) is generally considered as the domain of fatigue lifetime beyond 10 million (107) load cycles. Few examples of structural components which are subjected to 107-109 load cycles during their service life are engine parts, turbine disks, railway axles and load-carrying parts of automobiles. Therefore, the safe and reliable operation of these components depends on the knowledge of their fatigue strength and the prevalent damage/failure mechanisms. Moreover, the fatigue life of materials in the VHCF regime is controlled by the fatigue crack initiation and early growth stage of short cracks.

This study was focussed on the evaluation of fatigue properties of duplex stainless steels in the VHCF regime using the ultrasonic fatigue testing equipment. The ultrasonic fatigue tests were conducted on the cold rolled duplex stainless strip steel and hot rolled duplex stainless steel grades. Two different geometries of ultrasonic fatigue test specimens were tested. Considerable attention was devoted to the evaluation of fatigue crack initiation and growth mechanisms using the high resolution scanning electron microscopy. The fatigue crack initiation was found to be surface initiated phenomena in all the tested grades, albeit different in each case.

The second part of this thesis work was the development of a distributed dislocation dipole technique for the analysis of multiple straight, kinked and branched cracks in an elastic half plane. Cracks with dimensions much smaller than the overall size of the domain were considered. The main goal of the development of this technique was the evaluation of stress intensity factor at each crack tip. The comparison of results from the stress intensity factor evaluation by the developed procedure and the well-established Finite Element Method software ABAQUS showed difference of less than 1% for Jacobi polynomial expansion of sixth order in the dipole density representation.

Place, publisher, year, edition, pages
Karlstad: Karlstads universitet, 2014. 30 p.
Series
Karlstad University Studies, ISSN 1403-8099 ; 2014:68
Keyword
Very high cycle fatigue, duplex stainless steel, ultrasonic fatigue testing, distributed dislocation dipole technique
National Category
Mechanical Engineering
Research subject
Materials Engineering
Identifiers
urn:nbn:se:kau:diva-34591 (URN)978-91-7063-610-3 (ISBN)
Presentation
2014-12-17, Karlstad, 10:15 (English)
Opponent
Supervisors
Projects
Very high cycle fatigue of stainless steels
Funder
Knowledge Foundation
Note

Article III was still in manuscript form at the time of the defense.

Available from: 2014-12-10 Created: 2014-11-13 Last updated: 2016-08-16Bibliographically approved

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Tofique, Muhammad Waqas
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